References : 1. Clark, Donald S. Engineering Materials and Processes. 3 rd Edition, USA: International Textbook Company, 1966. 2. Fink, Donald et al..

References : 1. Clark, Donald S. Engineering Materials and Processes. 3 rd Edition, USA: International Textbook Company, 1966. 2. Fink, Donald et al.. Standard Handbook for Electrical Engineers. 12 th Edition, USA: McGraw-Hill Book Company, 1987. 3. Schaffer, James et al.. The Science and Design of Engineering Materials. 2 nd Edition, USA: McGraw-Hill Book Company, 1999. 4. Moore, Herbert F. et al.. Materials of Engineering. 8 th Edition, Japan: McGraw-Hill Book Company, 1975.

Course Description: Engineering Materials and Processes is a course, which deals with the Fundamental Nature and Properties of Engineering Materials; Conductor Materials; Carbon and Graphite; Magnetic Materials; Insulating Materials and Wood Products. Course Objectives: At the end of the course, the students should be able to: 1. familiarize themselves with the materials of the trade. 2. learn the different processes involved in their manufacture. 3. make sound judgements as to the choice of materials to be used for a particular application.

Course Requirements: 1. Mid Term a. Quizzes b. Research/Reports c. Term Exam 2. Final Term a. Quizzes b. Research/Reports c. Term Exam Determination of Grades: Quizzes……………………………30% Research/Reports……………….35% Term Exams……………………..35% Total 100% Note: The final grade will be based on one-half of the mid-term grade and one-half of the final term grade.

Learning Units: 1. Fundamental Nature of Materials 1.1 Engineering Materials 1.2 Atomic Structure 1.3 Periodic Table of Elements 1.4 Atomic bonds 1.5 Crystal Structure 1.6 Crystallization 1.7 Allotropy 2. Properties of Engineering Materials 2.1 Chemical Properties 2.2 Physical Properties 2.3 Mechanical Properties 3. Alloy Systems 3.1 Alloy Formation 3.2 States of Matter 3.3 Compounds 3.4 Solid Solution

3.5 Factors Influencing Solubility 3.6 Structural Constituents 3.7 Solidification 3.8 Phase Equilibrium Diagrams 3.9 Cooling Curves 3.10 Phase Rule 3.11 Lever Arm Principle 3.12 Properties of Alloys 4. Conductor Materials 4.1 Definition of Conductor 4.2 General Properties 4.3 Metal Properties 4.4 Cooper 4.5 Aluminum 5. Conductors 5.1 Definition and Types of Electrical Conductors 5.2 Wire Sizes and Wire Gages

5.3 Stranded Conductors 6. Miscellaneous Metals and Alloys 6.1 Contact Metals 7. Carbon and Graphite 7.1 Forms of Carbon 7.2 Temperature Coefficient of Carbon and Graphite 7.3 Carbon Brush Applications 8. Magnetic Materials 8.1 Types of Magnetism 8.2 Commercial Magnetic Materials 8.3 Materials for Solid Cores 8.4 Materials for Laminated Cores 8.5 Magnetic Lamination Steels

9. Insulating Materials 9.1 Electrical Insulation and Dielectric Defined9.1 Electrical Insulation and Dielectric Defined 9.2 Dielectric strength 9.3 Application of Electrical Insulation 9.4 Insulating Gasses 9.5 Insulating Oils 9.6 Plastics 10. Wood Products 10.1 Definition of Wood 10.2 Classification of Wood 10.3 Properties of Wood 10.4 Decay and Prevention of Wood 10.5 Preservation and Treatment of Wood 10.6 Effects of Treatment on Resistivity 11.7 Wood Poles and Crossarms

12. Composite Materials 11.1 Strengthening by Fiber Reinforce 11.2 Critical Fiber Length 11.3 Reinforcement of fiber 11.4 Characteristic of fiber Materials 11.5 Typical Fiber 11.6 Surface Treatment 11.7 Characteristic of Matrix Materials 11.8 Pole of Interface 11.9 Region of Interface 11.10 Fiber Architecture 11.11 Wave Fiber 11.12 Laminated Composites 11.13 Metal-Matrix Composites 11.14 Polymer-Matrix Composites 11.15 Carbon-Carbon Composites 11.16 Ceramic Matrix Composites 11.17 Estimation of the Coefficient of Thermal Expansion11.17 Estimation of the Coefficient of Thermal Expansion 11.18 Fracture Behavior of Composites

12.19 Fatigue Behavior of Composites 12.20 Other Application of Composites 12.21 Estimation of Non Mechanical Properties of Composites 12.22 Composite Manufacturing Process 12.23 Liquid Infiltration Process

ENGINEERING MATERIALS AND PROCESSES LECTURE PRESENTATION

INTRODUCTION IN ENGINEERING MATERIALS AND PROCESSES

Our purpose in this computer-aided instruction is to examine the way in which impact society and to show how they are produced, processed, and used in all branches of engineering to advance the well-being of society. In doing this, we will emphasize the relationship between the structure of materials and its underlying properties, and we will develop general principles applicable to all materials. Our goal in following this approach is to enable students to develop a fundamental understanding of material behavior that will help prepare them for a rapidly changing, and sometimes bewildering, environment. Since engineering is essentially an applied activity, practical examples that build on and amplify the fundamentals will also be emphasized for all topics and materials that are considered.

The proton is the positively charged particle found in the nucleus. The electron is the negatively charge particle revolving about the nucleus. The neutron is the neutral particle found in the nucleus of an atom. Click to see figure.

Proton Electron BACK neutron

The properties of an atom are determined by many factors: 1) The atomic number (z) that corresponds to the number of electrons or protons in a neutral atom. (2) the mass of the atom (3) the spatial distribution of the electron in orbits around the nucleus, (4) the energy of the electron in the atom (5) the ease of adding or removing one or more electrons:

Wave mechanics is one form of quantum mechanics, this is more useful in a situation where the number of energy levels is infinite, as an electron in an atom. Schrödinger equation is the basis of the science of wave mechanics.  h mv Where:  wave length m = mass v = speed

The Quantum Theory. Light is emitted and absorbed by matter in protons or discrete amount of the light. Electrons are ejected when light quanta fall on certain metals, more electrons are expelled as the light intensity increases because the number of quanta increase but the electron velocities depend only on the light’s frequency. Click to see figure.Click to see figure.

Schrödinger Equation. Describe how a wave associated in an electron or other subatomic particle series on space and time as the particle moves under the influence of various forces.

The periodic table is a tabular arrangement of the chemical elements based on the atomic structure of elements arranged in horizontal rows by increasing atomic number. Listed above the symbol for each element the vertical groups represents the elements that have similar properties because they have the same number of valence electron. Click to see figure.

ATOMIC BONDS To be able to make a molecule you need to bond the atoms. Forces are exerted by atom in near proximity. In such case, force are attractive in nature an the atoms group together through the formation of bonds. These bonds have different characteristics depending on the atom or group of atom in question. The bond character determines the physical, chemical, and mechanical properties, including the state of matter as the structure.

Covalent bonds form in compounds compose of electronegative elements. Two atom combine in such a manner that no complete transfer of electrons take place instead, electrons have overlapping orbits of atom. This movement is called sharing of electron. Attractive force is produce as a result of shared electron called covalent bond and its process is called covalent bonding to understand this bonding deeper there are sets of example: Click to see figure.Click to see figure

Considering two Cl atoms with seven valence shell brought together acquiring full complement of eight electrons in valence shell and share a single pair of electron forming Cl 2 molecule. Click to see figure.Click to see figure. This shows that the electron of the two hydrogen atoms appear as electron clouds rather than a single point. The sharing process is involve of an overlapping clouds. Click to see figure.Click to see figure.

Electron cloud BACK

IONIC BONDING Type of bond in a compound containing both electronegative and electropositive element. It involves electron transfer from electropositive atom to the electronegative atom. If ions are brought almost into contact the force will be great to hold two ions.

Ex. 1 Two elements one negatively charge (0) and positively charge (Mg) held together forming MgO by ionic bond. Click to see figure.Click to see figure A single electron from the nearly empty valence bond of the Na atom is transferred to the nearly filled valence bond of Cl atom. Once transferred attractive force develop between the ions. Click to see figure.Click to see figure.

METALLIC BONDING The electropositive elements can obtain a stable electron configuration by “giving up” their valence electrons. Since there are no electronegative atom present to receive the ‘extra” electrons they are instead donated to the structure in general.

Mg atoms are combined to form a solid metal the valence electrons are delocalized from the nucleus and core electrons. This valence electron from a “cloud” or “sea” of electrons that surrounds the ion cores. The force holding the metal together is the attraction between the positively charge ion cores and the negatively charge electron cloud. Click to see figureClick to see figure

SECONDARY BOND TEMPORARY DIPOLEPERMANENT DIPOLE

Temporary dipole is formed when the electron switch constantly in motion are momentarily arranged so as to produce an symmetric charge distribution

Ex. 1 Isolated Ar atom (center of positive charge same as center of negative charge). Due to statistically the center of negative charge is spatially different than the center of positive charge. Temporary dipole at left can induce a dipole in the neighboring Ar atom result in Vander Waal’s bond between two Ar atoms. Click to see figure.Click to see figure.

Three permanent dipole molecules (a) H2O (b) H2S (c) NH3. The X’s represent valence electrons from the H atoms and the ‘s represent those from either O, S or N. The  + and  - symbols represent the spatial center of positive and negative charge for the molecule. The non bonding electron pairs, the local regions of negative charge and the isolated nucleus of an H atom, is a local region of positive. Click to see figure.

A lattice can be defined as an indefinitely extended arrangement of points, each of which is surrounded by an identical grouping of neighboring points. The smallest region that completely describe the pattern is known as the unit cell. Once the unit cell is established the entire extended pattern can be generated by translating the unit cell in lattice. Click to see figure.Click to see figure

The intercepts for a given plane are the distance from the origin of reference axes to the intersection of the axes with the plane. The intercepts are given in terms of the lattice parameters a, b, c. A simple cube lattice with x, y, z axes on which the unit lengths are designated by Greek symbols   . Use Grolier encyclopedia for more information.

Based on the law of rational indices this law states that the reciprocals of the intercepts of any plane are always rational fractions whose common denominator is a relatively small integer in a cubic unit cell. The direction of the applied force can be described as a projection from the bottom back left corner of the cube through the bottom right cube corner. Click to see figure.Click to see figure.

Is a common unit cell with cubic symmetry and one atom per position. This structure has an atom at each corner plus an additional atom at the center of each face. Each corner atom touches the atoms in the centers of the three adjacent faces, but corner atoms do not touch other corner atoms. Click to see figure.Click to see figure.

An atom lies at each corner of the cube and one in the center. Each corner atom touches the central atom, but the corner atoms do not touch each other. Other metals with the Body-Centered Lattice structure at room temperature include chromium, iron, molybdenum, and vanadium. Click to see figure.Click to see figure.

HEXAGONAL CLOSED-PACKED STRUCTURE The structure of a hexagonal system is most easily visualized by considering three unit cells arranged to form one large cell. There are six atoms at the corners of the top and bottom planes, each shared by six unit cell; one atom in the center of the upper and lower basal planes, each shared by two cells; and three atoms in the mid plane. Click to see figure.Click to see figure.

Unit cell is in the most common convention used to describe specific points, directions, and planes in the crystal-lattice system. The miller notation not only simplifies the description of direction, but also permits simple vector operation like the dot and cross product. For naming planes in a crystal lattice. The origin has been arbitrarily selected as the bottom left back corner of the upper unit cell in part (a) and the bottom left back corner of the part.

Most form a polycrystalline structure, the grains are small crystals that are typically on the order of 0.5 – 50  m. But they maybe up to a centimeter in diameter. The poly- crystal is composed of many grains separated by thin regions of disorder known as grain boundaries. Click to see figure. Click to see figure

Allotropies are the individual form of an elements that occur when more than one type of bonding between atom of the elements is possible. One of the allotropic element is carbon, it can exist in crystalline form as either diamond or graphite. The diamond structure has lattice tetrahedral network of covalent bond with C N =4. Thermodynamically favored from C at room temperature is graphite, which has a hexagonal two dimensional layered structure in which each C atom has only three nearest neighbor’s in the plane of the layer. Click to see figure.

Fig. Of allotropic material BACK

Chemical property pertain to the behavior of material during chemical reaction. Galvanic corrosion occur when two dissimilar metals are placed in electrical contact and immersed in an electrolyte pit and crevice corrosion are highly localized form’s of electro chemical attack involving oxygen concentration gradients. Click to see figure.Click to see figure.

Those properties which can be determine w/out causing a change in the identity of materials. A description of the physical behavior of a material would include characteristic such as specific heat, thermal conductivity, coefficient of expansion, color refraction index, density and electrical resistivity.

Mechanical property, materials used in load bearing application,when a force is applied in any form of body or a member of a structure or a machine and it changes it’s shape and dimension. Click to see figure.Click to see figure.

If a member is properly designed to withstand a force, a change in shape or dimension is very small, the change is not directly visible. If a force is too large and the structure is not properly designed, the deformation is visible and it will not return to it’s original shape. Click to see figure. Click to see figure.

A number of loop’s of wire with a high electrical resistance are placed on a paper then these loops are bonded to the location on the surface of the specimen part at which it is desired to measure a strain. Click to see figure.Click to see figure.

The internally distributed force which tend to resist deformation is defined as stress. Tension is a force that act directly in attempt to pull the material apart. While compression is force that act toward the bar, and in the shear there is an attempt to pull the one body with respect to the other. Click to see figure.Click to see figure.

Stress is defined quantitatively as the force per unit area. Stress can be determined by dividing the force with the cross sectional area of the bar.  W A Where: W = force  = stress A = area

If the area is carried to failure of a section is slightly decreased under tension and slightly increased under compression. S = PSPS A Where: P S = shearing force acting on one side of the section A = area of the section in square inches S = stress

The tensile stress normal to the oblique plane is less than it’s plane to it’s normal axis.The shearing stress is maximum for a plane at an angle of 45 0 with the axis and for this plane the shearing stress is given as Ss = P/2A. Click to see figure.

Material under low stress do not suffer any appreciable permanent change of form recovering their original shape after the removal of load under this condition. Click to see figure.

In inelastic action of a certain material will not give a serious problem to the structure unless it extend over a considerable volume in the member or exposed to low temperature. Click to see to figure.Click to see to figure.

Slip lines mark the places where sliding has occurred between plates of metals. Click to see figure.

The greatest stress which a material is capable of withstanding without a deviation from proportionality. Click to see figure. Click to see figure.

It is lowest stress at which marked increases in strain of the material occurs with out increase in load. Yield strength is the stress at which a material exhibits a specified limiting permanent set. Click to see figure.Click to see figure.

Hooke’s law simply means that the stress is proportional to the strain.   E Where:  deformation per unit length  total deformation E  modulus of elasticity

G = E 2( 1 +  ) Where: G = modulus of elasticity (shear) E = modulus of elasticity  Poisson’s ratio

Ev = E 3( 1 – 2 )) Where: Ev = Bulk modulus of elasticity E = modulus of elasticity  Poisson’s ratio

 Mc I Where: M = is the moment applied to the outer fiber c = distance from neutral axis I = is the moment of inertia

This permit the material to assume deformation under loads whose the strain when loads are removed.

It will be noted that above the line A/A the row of atom contains one more atom than in the row below and that there is general dislocation to accommodate this imperfection.This is called positive edge dislocation. Click to see figure.

Screw dislocation on the Burger’s vector is parallel to the dislocation line (b//t. A screw dislocation can also be envisioned as forming the axis of the helical ramp that runs through the crystal curved dislocation at position A has an edge of (b  t) and at position B it has a screw of (b//t)at intermediate point’s between A and B, the dislocation has a mixed character of edge or screw dislocation.The burger circuit at point A and B yield the same burgers vector. In fact the burger vector is an invariant for a dislocation, meaning that the variant is constant at any given dislocation.

Is the property of a material which enables it to absorbed load without being permanently deform.

Is the property by virtue of which that enable it to be drawn permanently through great change of shape with out rupture.

Is the property of a materials which enables it to absorb energy at high stress without fracture. Click to see figure.Click to see figure.

FRACTURE IN BRITTLE AND DUCTILE MATERIALS There is a small region in central portion of the specimen at which the fracture’s perpendicular to the direction of the primary cloud. This area is surrounded by a core having an angle of 45 0.

a.) The cylindrical form failed by buckling. b.) Show a rectangular piece of wood failed by buckling. c.) Shows how a piece of steel which has failed by shearing on a plane 45 0. Click to see figure.Click to see figure.

Brinell Hardness Test. This test is made by pressing a hardened steel ball against a smooth flat surface under certain standard condition. Click to see figure.Click to see figure Diamond Pyramid Hardness. The same as the Brinell Test, except that the penetrator is a diamond pyramid with an angle of 136 0 between the opposite faces. Click to see figure.Click to see figure. Rockwell test. Machine measures the depth of penetrator in the metal produced by a definite load on a small indenter. Click to see figure.Click to see figure. Scleroscope A small pointer hammer is allowed to fall from definite height into the material. Click to see figure.Click to see figure.

The test is use on thin sheets of metals since the standard hardness test can only perform test on this metals. Click to see figure.Click to see figure.

Fatigue is a limited stress below failure by progressive fracture can be determine after completion of a very large number. a.) original fracture flexure b.) specimen fracture by repeated cycles of reversed flexure c.) specimen bent by single load d.) original tension specimen e.) specimen fractured by repeated cycles of tension f.) specimen fracture by one slowly applied load. Click to see figure.Click to see figure.

a.) fracture at the circumference of a round shaft and spreading in toward the center. b.) fracture starting at one side and progressive toward the opposite side of a shaft. c.) fracture in railroad rail starting from crack caused by too-rapid cooling and spreading over the light colored area.

TYPES OF FATIGUE TESTING MACHINES

CANTILEVER ROTATING BEAM TESTING MACHINES This is a machine in which the bending moment is on the specimen. The moment and consequently the stress is varied by using different weight for the rotating beam machines. Click to see figure.Click to see figure.

VIBRATORY TYPE OF FATIGUE TESTING MACHINE Figure of a vibratory machine. This is a machine in which the bending force is measured either by the deflection of the specimen, or vibration of a flat steel bolted to the end. Click to see figure.Click to see figure. Tension-Compression fatigue testing machine. The function of this machine is to measure the tensile and compressive force applied to the specimen and the deflection is measured by the micrometer. Click to see figure.Click to see figure. Fatigue testing machine for Bending test. This can be equipped for torsion test or for light loads in tension and compression. Click to see figure.Click to see figure.

Fig. Of vibratory machine BACK

Recrystallization. Recovery process occurs at temperature roughly equal to one half the absolute melting temperature. Click to see figure.Click to see figure.

When a structure is subjected to stress in a temperature and deformation continue, the most marked effect caused a slow flow or “Creep”.

At ordinary temperature metals do not show any sign of fracture under creep, actually the condition in the development of eff. heat engines is the lack of known metals.

SLIP Structure damage by distortion. The motion distortion under stress diminished after a short time. Ultimate strength in slip in the crystalline flakes soon come to rest. CREEP Under ultimate strength and motion distortion continues as long as the stress is applied or until the natural is fracture.

As an element that possesses certain properties which are referred to as the metallic properties. The particularly distinguishing feature about the metallic materials is the type of bond between atoms. The metals posses metallic luster, more or less ductility, and considerable ability to conduct heat and electricity. In electrolysis, metallic compounds are decomposed without the action of a reducing elements. Some of the elements, such as carbon, boron, and silicon, occupy an intermediate position and are called metalloids. Elements may be combined in various ways to produce a substance that also possesses metallic properties. These substances cannot in themselves be called metals, since they are not single elements. A combination of elements which possesses metallic properties is referred to as an alloy. At least one of the elements forming the alloy is a mete\all. The other elements in the alloy may or may not be metallic.

STATE OF MATER One familiar with the formation of liquid solution, such as the combining of the liquids which dissolve in each other in all proportions to form a homogeneous substance in some combination the components are not completely soluble. Therefore two liquids of distinctly differing characteristics are observed the mechanical mixture, phase and system. Metals in the liquid state may act in a manner when metals are cast from the liquid state it is usually desirable to have the components completely.

SOLID ALLOY CLASSIFICATION ELEMENTS PURE METALMETALLOIDS CHEMICAL COMPOUNDS COMBINATION OF PURE METAL COMBINATION OF METAL AND METALLIODS COMBINATION OF METALS AND NON METALS SOLID SOLUTION

Elements may combine in definite proportions to form substances that have characteristics which is typical of chemical compounds. The compounds are characterized by extreme hardness and brittleness and many of the usual metallic properties.

SOLID SOLUTION An alloy prepared from two metals, such as gold and silver or copper and nickel, will be found to be homogeneous. When solid solution is formed, the crystal structure of the combination is that in atom of the solvent component and the atoms at the solute are incorporated in the structure, this is called the substitution solid solution.

The complete solubility of two metals in the solid state will occur only if the crystal structure s of these two metals are essentially the same. In general, solubility tends to be favored when the crystal structure of the two metals is of the same type. However, there are other factors which must be considered in determining the probable solubility of metals. These factors are: (1). The relative atomic diameters of solvent and solute atoms. (2). The relative electronegative valence of solvent and solute atom. (3) The relative valence of solvent and solute atoms.

When solidification occurs in alloys of the type in which the components are not completely in the solid state, the phases may be arranged in a unique manner to form the structure. The unique units or aggregations of the phases are referred to as structural constituents. In other words, a structural constituents. In other words, a structure constituents is a unique arrangement of phases forming the structure of the alloy. A eutectic is defined as an intimate mechanical mixture of two or more phases having a definite freezing or melting point.

The change of energy of the system is plotted as a function of the radius of the nucleus. If a nucleus forms, there is an increase in energy and if the nucleus is larger than that indicated by the maximum of each curve the nucleus continues to grow.

An equilibrium may be defined as plot of the composition of phase as function of temperature in any alloy system under equilibrium condition.In phase diagram of a one component system the curves denote the conditions of temperature and pressure where two phases are in equilibrium, they meet at the triple point, the unique set of condition where all phases are in equilibrium. (see Grolier encyclopedia )

1.Components completely soluble in the liquid state. a.) completely soluble in the solid state. b.) partly soluble in the solid state. c.) insoluble in the solid state 2. Components completely insoluble in the liquid state. a.) completely insoluble in the solid state. 3. Components partially soluble in the liquid state

Cooling curve is the plot of the temperature at which phase changes occur in a system as a function of time during the very slow cooling of different alloys in the system.

[ p ( c – 1 ) + v ] – [ c ( p – 1 ) ] = F p – c = v - F If constant: p – c = 1 – F Where: p = the number of phase in equilibrium e = the number of components in the system v = the variables of temperature and pressure F = the number of degrees of freedom

Phase rule is the relation between the number of coexisting phases the number of components, and the number of variables, based on thermodynamic consideration.

X S – X L X O – X L X S –X O Lever Pivot pt. Where: X L = composition of liquid X s = composition of solid Xo = composition of alloy M l = mass of liquid M s = mass of solid

The equilibrium diagram indicates the composition of the phases that will be in equilibrium at any particular temperature. The diagram also makes it possible to determine the proportion of coexisting phases at any given temperature. This Lever-arm principle can be applied anywhere in the equilibrium diagram, where the phases co-exist, one only need to move to right and to the left of the composition of the entire alloy to determine the composition of those phase.

The properties of alloy depend upon two factors: 1.The properties of the phase or phase of which it is composed. 2.The manner in which the several phase are associated to form the aggregate.

A conductor is a body so constructed from a conducting material, that it may be used as a carrier of electrical current. In ordinary engineering usage a conductor is a material of relatively high conductivity.

Capacitance and Leakage conductance depend in part up on the external dimension of the conductors and their distance. Inductance is a function of the magnetic field established by the current in a conductor.Resistance is the property of an electric circuit tending to prevent the flow of current and the same time causing electric energy to be converted to heat energy. CAPACITANCE INDUCTANCE RESISTANCE

Specific gravity is the ratio of mass of any material to that of the same volume of water @ 40 0 C Density is the unit weigh of material expressed as lb/in 3. It has an internal density of 8.89 @ 20 0 C with weigh of 0.32117 lb/in 3.

MATERIALS DENSITY AND WEIGH DENSITY AND WEIGH TEMPERATURE Copper alloys 8.899 /cm 3 20 0 C Copper clad alloys 8.15 / cm 3 Aluminum wire (hard drawn) 2.698 / cm 3 20 0 C Aluminum wire (comm. Hard drawn) 2.709 / cm 3 20 0 C Aluminum clad wire 6.59 / cm 3 20 0 C Aluminum alloy 2.703 / cm 3 Pure iron 7.90 / cm 3 20 0 C Galvanized steel wire (CLASS A) 7.83 / cm 3 20 0 C Galvanized steel wire (CLASS B) 7.80 / cm 3 20 0 C Galvanize steel wire (CLASS C) 7.78 / cm 3 20 0 C METAL PROPERTIES

ELECTRICAL RESISTIVITY Is measured by the resistance of a unit quantity of a given material. It may be expressed in terms of mass or volume.

 RA L Where:  volume resistivity R = resistance A = cross-sectional area L = length

 Rm L2L2 Where:  mass resistivity R = resistance m = mass L 2 = length in square

R R 2 a b R 1 c a 1 C 1 b 1 t1t1 t2t2 T T RR O RORO R1R1 R2R2 t1t1 t2t2 O R ACTUAL CURVE By Similar Triangle abc and a’b’c’  R = R 2- R 1  T T 2- T 1 Over a limited range of temperature the resistance of the metallic conductor is a linear function of temperature.

Within the temperature ranges of ordinary service there is no appreciable change in the properties of conductor materials, except in electrical resistance and physical dimension.

Temperature Resistance Coefficients for Aluminum and Copper Copper Clad Steel Wire 0.00098/ 0 c 20 0 c Aluminum Alloy (5005H1g) 0.00353/ 0 C 6201- T 81 0.00347/ 0 C 20 0 C Aluminum Clad wire 0.0036/ 0 C 20 0 C

The change of resistivity of copper per degree Celsius is a constant independent of the temperature of the reference and of the sample of copper this “ RESISTIVITY- TEMPERATURE CONSTANT ” may be taken for general purposes. R T2 R T1 T 1` T2T2

Lt 1 Lt 2 = 1 + [            Then; Lt 2 = Lt 1 [ 1 +        Where: T 2 = final temperature T 1 = initial temperature L = length  degrees  degrees

Pure metals over a range of several hundred degrees is not a linear function of the temperature but is well expressed by a quadratic equation., for the temperature expansion of coefficients for conductors can be seen in Table 6, ( Fink and Beaty Electrical Handbook, Chapter 4 ).

The Wiedemann-Franz- Lorenz Law, states that the ratio of the thermal and electrical conductivities at a given temperature is independent of the nature of the conductor, holds closely for copper. ( Thermal Conductivity of some Copper Alloys can be seen in Table 7, of Standard Handbook for Electrical Engineers by Fink and Beaty, Chapter 4). Ratio = k  Where: k = Thermal conductivity  Electrical conductivity T = absolute temperature

It is a metallic element of great technological and historical importance. It is the one of the most important non-ferrous metal.

ALLOYS OF COPPER Copper mixes well with many elements and more than 1000 different alloys have been formed several of which are technologically significant. ORE COLORCHEM.FORMULA ChalcopyriteBrass yellowC u F e S 2 BorniteRed brownF e S. 2 C u2 S.C u S EnargiteGray black3 C u 2 S.A S 2 S 5 TetrahedriteGray black4 C u2 S. Sb 2 S 3 CupriteRed C u 2 O MalachiteGreenC u Co 3 Cu (OH) 2 AzuriteBlue2Cu CO 3.C(OH) 2 Native copperredCu

Copper ores taken from open pits are usually moistures of iron and copper sulfides. The process of copper refining consists of crushing the ore (1), then pulverizing it and mixing it with water (2). Frothing agents and air are added (3) and a froth of sulfides is removed from the surface of the mixture.A thickening tank (4) and a rotating suction filter (5) extract the water. The solids are heated (6),then mixed with fluxing agents and smelted (7).Iron oxide slag's is removed (8).Air blown into a converter furnace (9)removes sulfur dioxide, and residual iron oxides are poured off (10), The copper melt is refined in a reverbatory furnace (11), and cast in slabs (12)which are used as anode plates in an electrolytic unit (13),Almost pure copper that is deposited on the cathodes periodically removed and cast in bars.

Aluminum is the most abundant metal found in the crust of the earth, because its chemical account. Aluminum always occurs combined with the other elements chiefly as clay. Its specific gravity is 2.703. Pure aluminum melts at 660 0 C (1220 0 F). Aluminum has relatively high thermal and electrical conductivities. The metal is always covered with a thin, invisible film oxide which is impermeable and protective in character. Aluminum, therefore, shows stability and long life under ordinary atmospheric exposure.

Aluminum is found naturally as an oxide in bauxite (a mixture of sand, aluminum, iron, and titanum oxides). The illustration traces the many stages required in the processing of bauxite ore to produce pure aluminum. Numbers indicate bauxite mine (1)transport of the ore (2); storage (3); rod mill, to grind the ore (4) ; lime and water added in a slurry mixer(5); soda ash added to form caustic soda with lime (6); steam-heated slurry in which the alumina dissolves in caustic soda (7); settling tanks, where impurities (sand, iron) are removed (8) in a coffee-colored mud (9); filter (10); aluminum seed crystals (11), which, after being pumped into large precipitators, precipitate as aluminum hydroxide; cooling and thickening, followed by settling (12) and filtering to wash out lye (10); kiln heating, which converts aluminum hydroxide to alumina (driving off moisture) 9130 cooling box 914); separation of oxygen from alumina by an electric current in a cryolite - filled reduction cell (15) yielding 99.8% pure aluminum (16) for casting and alloying; (17) final refining.

CONDUCTORS. A wire or combination of wires not insulated from one another, suitable for carrying an electric current. STRANDED CONDUCTOR. It is composed of group of wires, usually combination of twisted wires. WIRE. Is a slender rod or filament of drawn metal. STRAND. One of the wires. STRANDED WIRE. A group of small wires used as a single wire. CORD. A small cable, very flexible and substantially insulated to withstand wear.

CONCENTRIC STRAND. A strand composed of a central core surrounded by one or more layers of helically laid wires or groups of wires. CONCENTRIC-LAY CONDUCTOR. Conductor constructed with a central core surrounded by one or more layers of helically laid wires. ROPE-LAY CONDUCTOR. Conductor constructed of a bunch- stranded or a concentric stranded member or members. N-CONDUCTOR CABLE. A combination of N-Conductors insulated from one another. N-CONDUCTOR CONCENTRIC CABLE. A cable composed of an insulated central conducting core with N-1 tabulator – stranded conductors laid over it concentrically and separated by layers of insulation.

Mil is a term universally employed in this century to measure wire diameters and is a unit of length equal to one thousandth of an inch. Circular Mil is a term universally used to define cross sectional areas, being a unit of area equal to the area of a circle 1 mil in diameter has a cross-sectional area of 100 cmills or 78.54 mils. Circular Mil Foot this uses English System where resistance is in circular mil foot, this unit is the resistance of a wire having a cross-sectional of 1 cir mil and a length of 1 feet.

American Wire Gage also known as BROWN and Shape Gage, it is usually written as AWG, its number is retrogressive a larger number denoting a smaller wire, corresponding to the operations of drawing. These gage numbers are not arbitrarily chosen, as in many gages, but follow the mathematical law upon which the gage is founded and it is the most commonly used gage in U.S. Steel Wire Gage originally as the Wash Burn and Moen and later as the American Steel and Wire Co’s gage, this gage with a number of its sizes rounded off the thousandths of an inch, is also employed in wire mils.

Birmingham Wire Gage. also known as Stubs Wire Gage and Stubs Iron Wire Gage was used to designate the stubs soft- wire sizes and should not be confused with stub’s steel – wire gage, this gage is generally in commercial use in the U.S for iron and steel wires. Standard Wire Gage. should be properly designated as British Standard Wire Gage. It is also known as the New British Standard Gage and the Imperial Wire Gage. It was constructed by modifying the Birmingham Gages that the differences between consecutive sizes become more regular.

Old English Wire Gage. also known as the London Wire Gage, differs very little from the Birmingham Gage. It formerly used to some extent for brass and copper wire but is now nearly obsolete. Millimeter Wire Gage. also known as the Metric Gage is based on giving progressive sizes, calling 0.1 mm in diameter “No.1,2” etc. German Wire Gage. in which the diameter or thickness is expressed in millimeters, progressive and contains 25 sizes.

Used generally because of their increased flexibility and consequent ease in handling. The greater the number of wires in any given cross section the greater will be the flexibility of the finished conductor

Number of wires in stranded conductors, each successive layer in a concentrically stranded conductor contains six more wires than the preceding one. For 1 – wire construction (1,7,19,etc) N=3n(n+1)+1. For 3- wire core construction (3,12,etc) N= 3n (n+2) +3.

D = d ( 2n + k) Where: d = diameter of individual wire n = number of layers over core which is not counted as ` a layer k = one for construction having one wire core ( 1, 7, 19, etc.) k = 2.155 for construction having 3 wire core (3, 12, etc.)

Diameter of stranded conductors (circumscribing circle) For stranded concentric – lay stranded conductors, multiply the diameter of the solid wire of the same cross sectional area by the appropriate factor found in standard handbook for electrical engineer’s.

A = Nd 2 cmils =1/4  Nd 2 x10 -6 in 2 where: N = total number of wire D = individual diameter in mils

Concentric – lay stranded conductor, the diameter can be obtained by multiplying the diameter of the solid wire of the cross – sectional area by the appropriate factor as follows; Num. Of wires Factor 3 1.244 61 1.152 7 1.143 91 1.153 12 1.199 127 1.154 19 1.147 69 1.154 37 1.151 217 1.154

Standard concentric – lay stranded conductors, the ff rule gives a simple method of determining the outside diameter of a stranded conductor from the known diameter of a solid wire of the same cross – sectional area.

C mils = in 2 x 1,273,200 = mm 2 x 1973.5 Conductor conversion size using this method.

W =  l d2d2 4 where:  = density d = diameter l = length

Lay or pitch, the axial length of one computed turn or helix of a wire in a stranded conductor also expressed as the pitch ratio. Click to see figure.Click to see figure.

. where: ac = axis of the stranded conductor L = axial length of any individual wire L+ΔL = one complete turn bc = circumference of circle bac,  = pitch ratio BACK

The increase in weight of the spiral members in a cable is proportional to the increase in length L +  L L = sec  = 1 + tan 2  =1 +   = 1 2 1 8 _ +      approximation of this ratio equals 1 + 0.5 (   /   ) and a pitch of 15.7 produces a ratio of 1.02. This correction factor should be computed separately for each layer if the pitch  varies from layer to layer.

Right Hand Lay, follows the rule of the Right Hand Screw Thread, the direction of lay is the lateral direction in which the individual wires of a cable run over the top of the cable as they recede from an observer in clockwise rotation.

Left-Hand Lay, is the opposite of the Right-Hand Lay. The outer layer of a cable is ordinarily applied with Left-Hand Lay, although the opposite lay can be use if desired.

Skin Effect, is a phenomenon which occurs in conductors carrying currents whose intensity varies rapidly from instant to instant but does not occur with continuous current. It arises from the fact that elements or filaments of variable current at different points in the cross section of a conductor do not encounter equal components of inductance, but the central or axial filament meets the maximum inductance, and in general the inductance offered to other filaments of current decreases as the distance of the filament from the axis increases, becoming a minimum at the surface of the conductor.

With R’ as an effective resistance, of linear cylindrical conductor to sinusoidal AC and R as the true resistance, continuous current, then R’=Kk where k is Constant, and can find from in Table 4.6 designated as x ( in Electrical Handbook by Fink and Beaty page 4-28.) x = 2  a ff  or  ff R Where: a = radius of conductor in centimeter f = frequency in cycles/second  magnetic permeability of conductor  resistivity in abohm-cm (abohm=10 -9 W) R = dc resistance at operating temperature in  mile.

With L’ as effective inductance, AC sinusoidal L’ = L 1 + k’L 2 Where: L 1 = external portion of inductance L 2 = internal portion due to magnetic field within conductor k’ = is from table 4.6 of Electrical Handbook by Fink and Beaty interms of x. For Total Effective Inductance L’ = 2ln d a +k’  2 abhenry/cm Where: a = radius of conductor d = the separation of conductor and return conductor

Armored cable, the type AC is a fabricated assembly of insulated conductors enclosed in flexible metal sheath. Armored cable is used both in exposed and concealed work. Metal clad cable, type MC is a factory assembled cable of one or more conductors, each individually insulated and enclosed in a metallic sheath of interlocking tape, or a smooth or corrugated tube. This type is used specially for service feeders of branch circuits, either exposed or concealed and for indoor or outdoor work.

Mineral insulated cable, type MI is a factory assembly of one or more conductors insulated with a highly compressed refractory mineral insulation and enclosed in a liquid tight and gas tight continuous copper sheath. The type MI is used in dry, wet or continuously moist location as service, feeders or branch circuit. Non – metallic sheathed cable, types NM and NMC are factory assembled of two or more insulated conductors having a moisture resistance, flame retardant and non-metallic material outer sheath.

Shielded Nonmetallic Sheathed Cable, The SNM type, is a factory assembled of two or more insulated conductors in an extruded core within an overlapping spiral metal type. This type is used in hazardous locations and in cable trays or in raceways. Service Entrance Cable, Is a single conductor or multi – conductor assembly provided with or without over all covering primarily used for services and of types SE and USE. Underground Feeder and Branch Circuit Cable, The type UF, is a moisture resistant cable used for underground, including direct burial in the ground, as feeder or branch circuit.

Power and Control Tray Cable, Type TC cable is a factory assembled two or more insulated conductors with or without associated bare or covered grounding under a metallic sheath. This is used for installation in cable trays,raceways or where supported by a messenger wire. Flat Conductor Cable, Type FCC constant of three or more flat copper conductor placed edge separated and enclosed within an insulating assembly. This type of cable is used for general purpose,appliance branch circuit and for individual branch circuits specially in hard, smooth, continuous floor surfaces.

Is an assembly of parallel conductors formed integrally with an insulating material web designed specially for field installation in metal surface raceway.Cables of this types are the types FC

Contact metals are usually where operation are continuous or very frequent and current has nominal value of 5 to 10 ampere. HARD METAL NON- CORRODING METAL HIGHLY CONDUCTIVE METALS CONTACT METAL

Tungsten ( W ), is a hard, dense, slow wearing metal and good thermal and electrical conductor characterized by its high melting resistance and freedom from sticking or welding. Molybdenum (Mo), has contact characteristic about midway between tungsten and fine silver. It often replaces greater wear resistance than that of lower contact surface resistance. Silver (Ag), has the highest thermal and electrical conductivity of any metal. It has low contact, surface resistance since it’s oxide decomposes at a approximately 300 0 F

Fine silver, is used extensively under low contact pressure where sensitivity and low contact-surface resistance are essential or where the circuit is operated infrequently. Sterling and coin silver, are harder than fine silver and resist transfer at low voltage (6 to 8v). This need a higher contact closing force. Silver alloys of copper (Cu), nickel (Ni), cadmium (Cd), iron (Fe), carbon (C) etc. other are used to improve hardness, resistance to wear and arc erosion.

Platinum, is one of the most stable of all metals under the combined action of corrosion and electrical erosion. It has a high melting point and does not corrode, and surfaces remain clean and low in resistance under most adverse atmospheric and electrical conditions. Palladium (Pd), it has many properties of platinum and frequently use d as an alternate for platinum and it’s alloy. Gold (Au), is similar to platinum in corrosion resistance but has a much lower melting point. And can easily formed into a variety of shapes.

Carbons are in different forms, some are amorphous. This are forms of carbon that has no definite shape, other are in crystalline structure. CARBON AMORPHOUSCRYSTALLINE charcoal, coke, coal, carbon black diamond, graphite

Carbon is use to designate all types of sliding electrical contacts that contain any appreciable percentage of carbon or graphite in their composition. Carbon brush has the characteristic of good conductivity, low coefficient of friction and high durability.

FUNCTION OF CARBON BRUSHES AC MACHINES SLIP RINGS DC MACHINES COMMUTATOR SPAN OF LIFE ARMATURE COILS

Slip ring, in machine, provide a suitable sliding electrical connection between the line and the rotor with reasonable life Armature coils, part’s of current in the armature coils reverses during the time they are short circuited. To be able to do this with out sparking or arcing there must be appreciable resistance in the contact between brush and commutator. Commutator brushes, carry the current to and out of commutator Span of life, brush carbon should have a reasonable life for economic use

For many years the word magnets means a horseshoe – shape piece of metal that has the ability to attract small object over a limited distance. This ability to attract object is a primary concern of engineers now a days. Magnets are used in many applications like motors, power generators etc.Strong magnets are used in transportation systems in which the vehicles are levitated above a track. There are different types of magnets, namely; antiferromagnetism, ferrimagnetism, diamagnetism, paramagnetism.

Atomic dipoles can interact to form an order array of magnetic dipoles. If the orientation relationships between neighboring dipoles, align their selves in an anti-parallel configuration with alternating dipoles that has an equal strength it said to be antiferromagnetic.

If all dipoles are pointing in the same direction. Ferrimagnetism occurs when more than one type of metal atom is in structure. If the two metal atoms have unequal dipole strength, then even if their dipoles are aligned, there will be no net magnetic dipole. Materials under this have magnetic susceptibilities between those of anti-ferromagnetic and ferromagnetic materials.

Diamagnetism and paramagnetism are both weak forms of interaction between solid and external magnetic fields. In diamagnetic solids the internal magnetic fields is anti parallel to the external fields. While in paramagnetic solids the internal and external fields point in same direction. The orbital motion of electron around it’s nucleus always results in a contribution to the diametric response of material.

Ferromagnetism, solids display magnetic susceptibility values much greater than 1. The primary difference between paramagnetic and ferromagnetic materials is in the strength of the interaction between adjacent atomic magnetic dipoles.At low temperature this dipoles are strong enough to overcome the thermal fluctuations.

MAGNETICALLY “SOFT” MATERIALS MAGNETICALLY “HARD” MATERIALS MATERIALS W/ SOLID CORES MATERIALS W/ LAMINATED CORES MATERIALS FOR SPECIAL FOR PURPOSES PERMANENT MAGNET

MAGNETICALLY “SOFT” MATERIALS. are permeable, they reemployed as core materials in the magnetic circuit of electromagnetic equipment. Click to see figure.Click to see figure.

WROUGHT IRONCAST IRONCARBON STEEL COMPOSITIONCOMPOSITION PROPERTIESPROPERTIES USESUSES USESUSES COMPOSITIONCOMPOSITION PROPERTIESPROPERTIES TYPESTYPES TYPESTYPES

WROUGHT IRON is a ferrous material from a solidifying mass of pasty particle of highly refined metallic iron, into which is incorporated w/o subsequent fusion, this is also known as Swedish iron, used mainly in relays.

A. Wrought iron contains less than 0.2% carbon. B. It contains traces of silicon sulfur and phosphorus. C. Wrought iron is the purest form of iron. D. Slag, which is not an impurity but an important ingredient of wrought iron, giving its quality of toughness.

PROPERTIES SOFTDUCTILE FIBROUS STRUCTURE MALLEABLECAN BE WELDED AND FORGED

a. It is used to make bolts, chains, machine parts, wires, rails and other hardware. b. Used in anchors and boiler pipes because it does not rust as readily as the more impure cast iron. c. Electromagnetics are made of wrought iron because it loses as magnetism.

CAST IRON contain carbon in excess of the amount which can be maintained in solid solution in austenite as the eutetic temperature.This is used in yokes of DC dynamos in early days of machines.

a.Cast iron contains 3% to 5% carbon and about 7% manganese both of which are desirable impurities. b.Contains smaller quantities of silicon, sulfur and phosphorous which are undesirable impurities. c.Cast iron is the most impure form of iron.

a.Cast iron is used where massiveness and little tensile strength are required. b.It maybe used where brittleness can be tolerated. c.Cast iron is used in the manufacture of stoves, radiators frames and machine support.

PROPERTIES OF CAST IRON VARIES IN COLOR MELTS READILY EASILY CAST HARD BUT BRITTLE NOT STOCK AND VIBRATION RESISTANCE CORODE EASILY CANT BE WELD OR FORGE

a.Gray cast iron, graphite is present in the form of flakes, poor in magnetic properties and also not ductile, and has inferior mechanical properties. It does lend itself to be cast in complex shapes and is readily machinable. b. Malleable cast iron is present in temper carbon nodules magnetically better than the first type. c. Ductile cast iron, graphite is present in spheroidal shape and magnetically better than gray cast iron. This has a good castability and machinability of gray cast iron together with much greater strength, ductility, and shock resistance.

CARBON STEELS contains less than 0.1% carbon to more than 1%, magnetic properties are dependent on the carbon content and distribution of carbon.

WROUGHT CARBON STEELS are widely used as solid core materials, the low carbon types are preferred in most application. CAST CARBON STEELS are used as yoke in DC machine way back but, it was been replaced by wrought iron.

MATERIALS FOR LAMINATED CORE ELECTRICAL STEELS GRADING TIME ORIENTED MATERIALS GRAIN ORIENTED MATERIALS ASTMAISI FULLY PROCESS SEMI PROCESS

MATERIALS FOR LAMINATED CORE,are widely employed in wound or stacked cores in electromagnetic devices operated at the commercial power frequencies are the electrical steel and the specially processed carbon steels designated as magnetic lamination steel.The primary requirement for low core loss, high permeability and high saturation ELECTRICAL STEELS, this are flat rolled low- carbon silicon-iron alloys.The core losses of electrical steels are normally guaranteed by the producers. GRADING, electrical steels are usually graded by high induction core loss. It uses two system, ASTM and AISI.

FULLY PROCESSED NONORIENTED MATERIALS, stresses introduced into these materials during fabrication of magnetic cores must be relieved by annealing to achieved optimum magnetic properties in the core. This materials contain up to 3.5% silicon and a small amount (less than 0.5%) of aluminum. SEMI-PROCESSED NONORIENTED MATERIALS, these materials are used primarily in high volume production of small laminations and cores which would require stress-relief annealing if made from fully processed material. These material contain up to 3% silicon and a small amount (less than 0.5%) of aluminum is usually present.

This application of soft or non retentive material, special alloy and other materials have been develop which after poorer fabrication and heat – treatment have superior properties. NICKEL IRON ALLOYS, nickel alloyed with iron in various proportion produces a series of alloys with a wide range of magnetic properties, with 30% nickel, the alloy is practically non magnetic and has a resistivity of 86  / cm. PERMAALLOY is compose of 78.5% nickel – iron alloys, the important properties of which are high permeability and low hysteresis loss in relatively low magnetizing field.

ELECTRICAL INSULATION, is a medium or a material which, when placed between conductors at different potentials, permits only a small or negligible current in phase with the applied voltage to flow through it. The term dielectric is almost the same with electric insulation but differ in a way that there is no co- induction current and only capacitive charging current between conductors.

EXAMPE: If 24000 volts is impressed across 30 mils, of insulation. Find the voltage gradient. GRADIENT=voltage/ mils = 24000/30 =800 volts per mils This is the ability of substance to resist dielectric breakdown.This is impressed in volts per unit thickness when the substance is place between the flat electrodes having rounded edges.The volts per unit thickness is impressed across a dielectric voltage gradient.

C = k o A/ t = 0.0884x10 -12 A/t farads where: ko = dielectric constant of vacuum = 0.225x10 -12 A/t ;if A/t is in inch per unit A = area in cm 2 t = spacing of the plates in cm

C = k k o A/t farads where: C= capacitance k= relative dielectric constant k o= dielectric constant in vacuum A= area in cm 2 t= spacing of plates in cm

(a) two parallel metallic plates separated by a distance d, when a potential difference E is applied to the plates, a positive charge + q1 is found on the upper plate and a negative charge - q1 is found on the lower plate. (If the slab of glass, hard rubber or some other good dielectric be inserted between the plates so as to fill completely the intervening force.) (b) the charges +q1 and –q1 will be found to have increased to +q2 and –q2 with the same value of E, applied potential difference.The increase in charge must be due to the presence of he glass, rubber,or other dielectric which may be inserted.

This is necessary to consider not only the electrical requirement but also the mechanical and environmental conditions of the applications. Mechanical fracture often leads to electrical failure and mechanical failure is frequently the primary cause of an aged insulation.

Gas is a highly compressible dielectric medium usually of low conductivity and with dielectric constant only a little greater than unity except at high pressures. In high electric fields the gas may become conducting as a result of impact ionization of the gas molecules by electrons accelerated by the field sand by the secondary process, which produce partial breakdown or complete breakdown.

Mineral insulating oils are hydrocarbons refined from crude petroleum deposits from the ground. They consist partly of aliphatic compounds with the general formula C n H 2n+2 and C n H 2n+6 comprising a mixture of straight and branched chain and cyclic or partially cyclic compounds. Solubility is proportional to the partial pressure of the gas above the oil.

Askarel Liquids, these liquids have been primarily used for fire resistant transformer and capacitors.They are biphenyl with 2 to 6 chlorinated atom attach to the rings.They are used alone or mixed with tri- or -tetrachlorobenzen. The liquids used have viscosities similar to transformer. Fluorocarbon Liquids, a variety of nonpolar nonflammable perfluorinated aliphatic compounds, in which the hydrogen has been completely replace by fluorine, is available with different ranges of viscosity and boiling point from below room temperature to more than 200 0 C.These compounds have low permittivities (near 2.0) and very low conductivity.

Ester Fluids, mostly for capacitors, where organic ester compounds are used. These liquids have a somewhat higher permittivity, in the range of about 4 to 7, depending on the ratio of the ester groups to hydrocarbon chain length. Their conductivities are generally somewhat higher than those of the other insulating liquids. The compounds are easily subject to hydrolysis with water to form acids and alcohols. Their thermal stability is poor. Silicon Fluids, these fluids, chemically formed from Si – O chains with organic side groups, have a high thermal stability, low temperature coefficient of viscosity, low dielectric losses, and high dielectric strength. They can be obtained with various levels of viscosity and correlated vapor pressures. Rated service temperature extend from -65 to 200 0 C. Some having short time capability up to 300 0 C.

Thermoplastics, this compounds are capable of repeatedly softened or melted by increasing temperature, there are different forms of thermoplastics.

POLYPROPYLENE, these polymer are often reacted with ethylene to form copolymers.They have high tensile strength and low density. POLYSTYENE, a transparent polymer, polystyrene has a good electrical properties but low impact resistance. POLYVINYL CHLORIDE, PVC polymer number in the hundreds, they can be made either rigid or flexible and are chemically resistant with good impact resistance. POLYETHYLENE, the ethylene are a large family divided into three groups by density,the groups are low density from 0.910 to 0.940, medium density from 0.941to 0.955 and high density above 0.960.

Polyester. are a very large family of thermoset materials. They can be cast like epoxies but are often used as molding compounds.They are available as bulk molding compounds (BMC)and sheet molding compounds (SMC). Silicone. are high – temperature materials wherein certain of carbon atoms in the polymer chain are replace with silicon. Allyl. is the most common of these polymers are diallyl phthalate and diallyl isophthalate. They are dimensionally stable with low water absorption and excellent electrical properties. They are often selected for electronic insulation.

Epoxy. most often used in the cast form, epoxies are also found in molding compounds, where they have high modulus and impact strength. Melamine. these polymers are the reaction products of melamine and formaldehyde.They are hard and though with a good surface appearance. Phenolic. these polymers are the reaction product of phenol and formaldehyde. Urea. These polymers are obtained by reacting urea and formaldehyde. As molding compounds they are filled with cellulose. They are resistant to chemicals and perform well electrically, but have limited dimensional and thermal stability.

Wood is the hard, fibrous substance beneath the bark of trees and shrubs. Compose of specially hardened cells whose two main functions are transporting water and dissolve minerals from the roots to leave to support body parts.

Hardwood is comprise of broad – leafed trees, such as elm and oak. It is also term as “Porus”, this refers to vessels that conduct sap, ash, beech, teak, walnut, mahogany, and rosewood are other example of hardwoods. Softwood or in other term coniferns is referred to trees with scale like leaves. The term nonporus is also use, this means that vessels are absent,the structure of the wood is relatively homogeneous.this are cedar, fir, and pine.

The popularity of wood is understood when examining its properties. Wood is a poor conductor of heat therefore, it is usually used as insulator. Different woods have different use because the properties of wood differ from species to species. Density, the weight per unit volume, is usually compared to water to yield the specific gravity. Most woods have a specific gravity less than 1.0 coz it is lighter than H 2 O. The range of specific gravity is from 0.04 to 1.40. Specific gravity less than 0.05 is a light wood, 0.05 to 0.70.

The moisture content of wood is expressed as a percentage of the oven dry weight of wood. It can be measured by weighing a wood sample before and after drying to constant weight @ 210 0 F. Wood is a hygroscopic materials. Moisture in wood occurs in three form: a. water vapor in air spaces in the cell cavities. b. capillary water in the cell cavities. c. water molecules bound to the hydroxyl groups of the cellulose in the cell wall.

Decay. Durability is the ability of wood to resist decay, insect infestation, chemicals, fungi, and marine organisms. High temperature to ground progress decay on wood near ground line down at several feet below, catalpa, cedar, chestnut, black locust, and osage orange trees are resistant to decay. Aspen, cottonwood, fir and willow are prone to decay. Prevention. Proper seasoning, together with the protection against the entrance of moisture and impregnating with fungus-inhibiting compounds that prevent fungi.

This fall in two main classes: (1) Oil-borne Preservatives this is used extensively for products that are exposed to ground contact whereby resistance to leaching is an important requirement of the preservative. (2) Water- borne metallic salts is used mainly for treating a lumber. Wood fall to this type is clear, paintable and odorless.

Creosote is a distillate of coal far formed during the cooking of coal. On the basis of the quantity of wood treated, it is the most important preservatives. Much of the treated wood is used in ground contact: appreciable to amount are also used in costal waters infested with marine organism that bore into and destroy untreated wood. Pentachlorophenol this is in a liquid solution of petroleum gas which is subject to practically complete removal by evaporation, leaving the treated wood very clean and readily paintable. Other standard oil preservation are copper 8-quinolinolate and tributyltin oxide.

Paint, varnishes, and stains are used for decorative effects, but they also afford surface protection by retarding moisture changes and thus decreasing checking, warping and weathering. Such protection is only superficial, however the internal decay maybe expected unless the wood is kept dry. Fire Retardant Chemical are used as ammonium phosphate and sulfate and salts of zinc and boron are used to decrease the flammability of wood and prevention to decay.

These can be divided into three classes: Pressure. This methods are by far the most effective for protecting wood. In pressure methods the wood is enclosed in a vessel, and the liquid preservative is forced into the wood under considerable hydrostatic pressure. Non Pressure. This methods do not utilize artificial pressure, the preservative being applied by dipping, soaking, brushing or spraying. Thermal Method. This method is consist of heating the wood to expel air then allowing the wood to cool in the liquid, whereby a partial vacuum forms in the internal spaces.Although the movement of the liquid into the wood is due to atmospheric pressure, the process is not classed among pressure process.

When wood has been treated with salts for preservatives or fire retardant purposes its electrical resistivity may reduced the effect of such salt treatment is small when the wood moisture is below about 8% but increases rapidly as the moisture content exceeds about 10%. Treatment with creosote or pentachlorophenol has practically no effect on the resistivity of wood.

Western red cedar and south yellow pine are two common species use in the U.S. for poles to support electric supply and communication equipment. In northeast part of U.S., chestnut and northern white pine are use but this are not for purchase as this time. In the western state, douglas fir, lodge pole pine, western larch are used considerably. Other species used but not considered so desirably are eastern hemlock, eastern larch, jack pine, northern white pine, ponderosa pine, red pine, spruce, sugar pine, and white fir.

A composite is a combination of a reinforcing phase in the form of particles, whiskers or fibers in a matrix that holds the discrete reinforcement pieces together and provides then with the lateral support. The particles is enbeded in the other material known as matrix phase. The reinforcing phase can be metal,ceramic or polymer. Reinforcing phase are usually strong with low densities while matrix phase is usually ductile or tough material. If rienforcement strength and toughness of matrix is combined together with good fabrication a desirable properties not present in a single material is achieve.

The idealized structure of concrete containing large gravel stones and small sand particles in a matrix of cement. The wide particle size distribution aids in achieving a higher volume fraction of the reinforcing phase. Composite parts in the main structure of the BOEING757-200 aircraft aerospace industry is weigh conscious so they required material with high specific strength and stiffness. Composite save weight, increase maneuverability and may provide the capability to avoid radar detection.

Fiber do not run continuously from one end of the component to the other. It’s length is significantly less than the component dimensions known as discontinuous fiber reinforced composite. When the discontinuous fiber with high elastic modulus is combined with a low modulus material and the resulting composite is loaded in the fiber direction, the fiber carry a high load than does the matrix.

Critical fiber length requires effective strengthening it’s function of several variables. The relationship among three variables is found by using force balance, carried by fibers equal to the normal stress in fiber multiplied by their cross sectional area. This force is transferred to the fibers via shear stress acting on the fiber surface.

Critical aspect ratio,this ranges from 20 to150 for most fiber and matrix material. A typical fiber diameter is between 10 and 30  m, critical fiber lengths are on the order of 0.2-4.5. The fiber length is much larger than critical fiber length. lc d  fu 2  my =

Isolated fiber embedded in a matrix in the unloaded state. If the normal stress is applied to the composite. The distribution of shear and normal stress vary along the length of the fiber.The tensile stress in the fiber increases from zero at the ends to a maximum value in the central region.

The commonly use geometrical shape the reinforcing phase in a high performance structure is a fiber.For some reasons like it’s strength of a brittle material is inversely related to the square root of it’s maximum flow size and the chance of having a large flow in a given length,of fiber decreases as the cross sectional decreases a small diameter is an advantage 3..5 3.0 2.5 2.0 6810121416 d(  m) ff

Elastic modulus of carbon fibers can be increased significantly by orienting the graphite –like planes to the coincide with the fiber axis since graphitic like planes do not lie along the fiber axis variability in fiber properties depends on the degree of orientation.

Boron fibers are used for stiffening aluminum matrices. Since boron is inherently brittle, it is chemically deposited on a tungsten (w) wire or a carbon – coated glass the fibers containing the tungsten filament are expensive, but have superior properties compared to glass filament, fiber often result a surface defects,the surface of boron fiber is usually polished to remove defects, with thin layer of SiC coating to produce compressive surface.

The surface treatments considerably enhance the fracture strength of boron fiber.(a) the fiber is a composite consisting of a series of concentric layer.(b) the residual stress pattern across a section of the boron fiber. The view of inter metallic layer and SiC jacket are not shown.The transverse direction or the direction perpendicular to the fiber axis. Click to see figure.Click to see figure.

Carbon is also use as matrix materials with carbon fibers in a class of composites known as carbon-carbon composites. The primary purpose of the matrix materials are to provide lateral support to the fibers and transfer load. Majority of fiber material are brittle, cracks, that have propagated through brittle fiber are stoped with relatively tougher matrix materials.

Interfaces play an important role in determining the properties of composites. The large interfacial area can significantly affect the properties of composites in particular the crucial properties of toughness and ductility. If the matrix and fiber have different thermal coefficient, then cooling from a high fabrication temperature causes thermal contraction between the fiber and the matrix that results to thermal stresses at the interfaces. This problem can be minimized by matching the expansion coefficient to fibers and matrix.

Various regions of such an interface in a metal-matrix composite, since the bonds are primary and result of extensive chemical interactions between fiber and matrix, the interfacial strength is much greater than with wettability bonds alone. Coating and coupling agent are frequently used to promote chemical reaction. Click to see figure.Click to see figure.

One additional factor in determining composite properties is the fiber arrangement also known as fiber architecture. This arrangement are known as square, hexagonal or rectangular. Hexagonal fiber array has the nearest neighbor distance between the fiber centers along three directions in the transverse plane. These composites behave roughly like isotropic materials in the transverse plane and are termed transversely isotropic.

Other type of fiber arrangement is known as fiber wave architecture. a. Plane wave b. Five harness satin wave.

This can be designed to have different fiber arrangement directions. This sheets of uniundirectional composites stacked in an arrangement so that bi-fibers are oriented along 0 0 to 90 0 and  45 0 direction. The sheets are called laminae, this can be stacked together to form laminated composite.

Fiber oriented at 0 0 and 90 0 is strength high along the said direction but poor in shear resistance. To obtain a good shear resistance laminae should be oriented at  45 0. Laminae are strong in all directions with in the plane containing the fiber but are weak in the direction normal to the fiber planes.

MMCs are fabricated by plasma spray of the matrix material over properly laid fiber, liquid in filtration methods, physical vapor deposition, not pressing, squeeze casting and other methods. This has a good high-temperature capability, good transverse properties and reasonably high compressive and shear strength, because of the combination of good strength and toughness of the metal-matrix and good interface bonding.

Polymer matrix composite (PMCs) are the workhorse of the composite industry. It has an excellent room – temperature properties at a comparatively low cost. The matrix consist of various thermosetting resins and more recently thermoplastic polymers reinforced by glass carbon, boron,or organic fibers.This is usually use in secondary load – bearing aerospace in structure;I- beams, automotive parts, steel belted tires and sports goods.

In this class of fiber reinforce composites both the matrix and the fiber are fabricated fro carbon.These materials offer a unique combination of properties including the ability to withstand extremely high service temperature (>3000 0 c) high specific strength, excellent resistance to wear, good resistance to thermal shock, and reasonable machinability.The maximum use temperature for these composites is limited by oxidation problems.Typical application include brake compounds, heat shields and rocket nozzles, not your household composites because of high costs. Carbon – carbon composites can be fabricated using CVD methods, this is done by impregnating graphite fibers with a carbon based polymer that is then pyrolyzed to” burn off’ the non carbon atoms in the polymer, or combination of two atoms.

Ceramic matrix composites (CMCs) is used to reinforce concrete for a long time.It has a low tensile strength, it is used to a limited structure subjected to compressive loading ceramic as known for it’s elevated temperature oxidation and creep resistance. So if the brittle behavior of ceramic is controlled this can be a good material or aircraft gas turbine hot section components such as blades, rotor etc.Also could be a good material for automobile. Flexural strength of brittle material is determined by using a four point bend test instead of tensile specimens used for ductile materials to prevent failure from occurring in the grips.It represent an estimation of the tensile strength of material

The interface in these materials consist of mechanical bonding with some strength derive from inter diffusion between the fiber and matrix.Cracking begins in the brittle material often the matrix.When a crack tip encounter the fiber two things may happened. If the fiber – matrix bond is strong the crack will not continue. In these case having fibers offers no apparent advantage. When the load is raise further the matrix on the other side of the fiber begins to crack but the fiber is still capable of transferring load across the crack. In the section containing a random flaw the matrix crack advances further some load still carried by the fiber.

Across the crack plane because of continued fiber bringing subsequent loading the fiber is pulled out of the matrix near the short end.It requires energy to overcome the functional forces between the fiber the matrix and rises the toughness level of Cmcs.

The coefficient of thermal expansion is an important design parameter for all structural materials subjected to even modest variations in temperature during service. The most common composites,  m>  f, so in a uniaxial composite the fibers constrain the expansion of the matrix in the longitudinal direction. This causes the composites to expand less in the longitudinal direction and more in the transverse direction than predicted.  m = Vm  m + Vf  f Where:  m = expansion coefficient of matrix  f = expansion coefficient of fiber  c = expansion coefficient of composites Vm = volume of matrix Vf = volume of fiber

Fracture in composites usually begins with cracking of the most brittle phase. In metal matrix polymer-matrix composites, this usually means that cracking begins in the brittle fibers; in ceramic-matrix composites usually means cracking begins in matrix. Interfaces play a major role in stabilizing fractures.

If delamination occurs at the interface, effective blunting of the crack occurs and the fracture is stabilized. The fracture mode is preferable because substantial energy is absorbed both during plastic deformation of the matrix and during delamination, the process contribute to overall toughness of the composites; The interfaces are so strong that no delamination is possible and the matrix is not ductile enough to effectively blunt the fiber cracks, then the progression of damage remains localized and a low- energy fracture results.

 d( )  my = ( )  fu lc 2 d2d2 4 where: lc = critical fiber length d = diameter of fiber  fu = ultimate tensile strength  my = matrix shear yield strength

Fatigue failure usually occur in the surface because of microplastisity, which leads to crack formation. These cracks propagate and become larger, causing final fracture. The different stages of fatigue of laminates consist of ply cracking, the density increases rapidly at first and then reaches a constant value. Delamination does not occur initially but occurs rapidly after saturation of ply cracking. Delamination saturates when the last stage of composite fatigue, fiber fatigue begins. Fiber Fatigue, when there is enough fibers that has fracture because of fatigue, the composite fails. In a laminated with fibers in 0 0 and 90 0, the number of applied fatigue cycles is divided by the number of cycles of failure to derive a cycle ratio.

Normalized elastic modulus (E/E o ) as a function of fatigue cycles in a glass fiber-polymer matrix composite, the elastic modulus of the composite decreases continuously as fatigue damage accumulates and is frequently used as an indicator of the progression of fatigue damage. The relationship between ratio of the applied maximum stress during a fatigue cycle to the ultimate strength and the number of fatigue cycles to failure. The loss of stiffness in many composite structural applications constitutes fractional failure. Repeated heating and cooling are part of component’s service duty cycle, thermal fatigue may occur.

Magnetic resonance imaging (MRI) is commonly use in medical field for noninvasive of internal organs, uses superconducting solenoids to produce high intensity magnetic fields. The solenoid is made up of niobium- titanium filament in a matrix of high-purity cooper. Several small-diameter superconducting filaments are embedded in a cooper matrix when the resistance of filament change, current can be conducted by the surrounding copper which also effectively removes the heat. Superconducting cable surrounded by a cooper matrix.

Superconducting material containing copper, yttrium, barium and oxygen have been developed with critical temperatures greater than 100K. This will allow superconducting behavior at liquid nitrogen temperatures. The wires made from these materials will also be composites. A low voltage field emitter array cathode for potential use in microwave amplifiers. It is made from a directionally solidified oxide-metal eutectic composite consisting of parallel array of continuous fibers of refractory metal such as W and Mo in an oxide matrix.

P = VP ( ii nn c i ) where; Pc = estimate property of composites Pi = properties of components Vi = volume fractions n = a value of –1 or +1 depending on directions

This equation can be used to estimate several other properties of composites, including density and under certain conditions, the electrical and thermal conductivities of the material. In the case of density, the value of n is +1 regardless of the spatial distribution of the components of the composite. For both thermal and electrical conductivities, the equation is only useful if the second face is in the form of fibers or sheets. For such composites, n has a value of –1 in a direction perpendicular to the fiber and +1 in the direction parallel to the fibers.

Composite can be classified as polymer-matrix, metal- matrix and ceramic-matrix composites. The manufacturing process are different for each class of materials and are also also quite different from those used for the monolithic materials.

Hand layup is the simplest technique for making PMCs materials. Continuous fiber are laid in a mold, and the resin precursor is either brushed or sprayed on. If chopped fibers are need, a mixture of resin and fibers is sprayed into the mold. The composite is then cured or crosslinked at the appropriate temperature. This technique is most commonly used for composite materials utilizing glass fibers in thermosetting resins, also need for making laminated composite. Filament winding. This technique is used for cylindrical objects. Continuous tow or roving is passed through a resin bath, which impregnates the fiber with the resin. The fibers are then wound on a mandrel with successive layers applied at specific angles until the desired material thickness is attained.

Pultrusion is an effective way of making continuous fiber composites with constant cross section, like I- beam. The preimpregnated fibers of oxide glass or carbon are pulled slowly through a heated die to make the composite. Resins used include polyester and some epoxies.

The most common matrix materials used for making MMCs are aluminum and titanium alloys. Fibers used in MMCs include boron, carbon and SiC in continuous as well as whisker and particulate forms. Boron and carbon fibers require surface treatment to avoid reactions, at the fiber-matrix interfaces during processing and to promote good wetting at the interfaces. In the solid- state-fabrication, alternate layers of properly spaced boron fibers and aluminum foil are stacked. Resin- based binders are used to keep the fibers in place. In liquid-state fabrication technique, long fibers are first properly aligned and arranged. Subsequently, liquid matrix material is infiltrated under inert gas, air or vacuum conditions. Liquid infiltration occurs by capillary action, by gravity, or by applied pressure.

One advance technique in liquid infiltration is the pressureless molten metal infiltration process the contact angle of the liquid metal approaches zero, so that spontaneous spreading and, hence, spontaneous infiltration occurs. In aluminum alloys, the wetting can be enhanced by adding magnesium or lithium, which can also provide solid solution strengthening in aluminum. In the figure, shows the making of a near-net-shape electronic package casing composed of SiC particulate in an aluminum matrix.

References : 1. Clark, Donald S. Engineering Materials and Processes. 3 rd Edition, USA: International Textbook Company, 1966. 2. Fink, Donald et al..

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References : 1. Clark, Donald S. Engineering Materials and Processes. 3 rd Edition, USA: International Textbook Company, 1966. 2. Fink, Donald et al..

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Presentation on theme: "References : 1. Clark, Donald S. Engineering Materials and Processes. 3 rd Edition, USA: International Textbook Company, 1966. 2. Fink, Donald et al.."— Presentation transcript:

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