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**Materials Chapter 2 Friday, April 14, 2017**

Dr. Mohammad Suliman Abuhaiba, PE

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**Chapter Outline Material Strength and Stiffness**

Statistical Significance of Material Properties Strength and Cold Work Hardness Impact Properties Temperature Effects Numbering Systems Hot-Working Processes Cold-Working Processes Alloy Steels Corrosion-Resistant Steels Casting Materials Nonferrous Metals Plastics Composite Materials Materials Selection Friday, April 14, 2017 Dr. Mohammad Suliman Abuhaiba, PE

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Standard Tensile Test Used to obtain material characteristics and strengths Loaded in tension with slowly increasing P Load and deflection are recorded Friday, April 14, 2017 Dr. Mohammad Suliman Abuhaiba, PE

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**Stress-Strain Diagram**

Linear relation until proportional limit, pl No permanent deformation until elastic limit, el Yield strength, Sy Ultimate strength, Su Ductile material Brittle material Friday, April 14, 2017 Dr. Mohammad Suliman Abuhaiba, PE

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**Elastic Relationship of Stress and Strain**

E = modulus of elasticity E is relatively constant for a given type of material (steel, copper) Table A-5: typical values Usually independent of heat treatment, carbon content, or alloying Friday, April 14, 2017 Dr. Mohammad Suliman Abuhaiba, PE

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**True Stress-Strain Diagram**

Engineering stress-strain diagram. True stress-strain diagram Engineering stress-strain True Stress-strain Friday, April 14, 2017 Dr. Mohammad Suliman Abuhaiba, PE

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**For ductile materials, Suc ≈ Sut For brittle materials, Suc > Sut**

Compression Strength For ductile materials, Suc ≈ Sut For brittle materials, Suc > Sut Friday, April 14, 2017 Dr. Mohammad Suliman Abuhaiba, PE

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Torsional Strengths Torsional strengths are found by twisting solid circular bars. Max shear stress is related to angle of twist by q = angle of twist (radians) r = radius of bar l0 = gauge length G = shear modulus or modulus of rigidity. Friday, April 14, 2017 Dr. Mohammad Suliman Abuhaiba, PE

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**Torsional Strengths Max shear stress is related to applied torque**

J = polar second moment of area of cross section Torsional yield strength, Ssy = max shear stress at the point where torque-twist diagram becomes significantly non-linear Modulus of rupture, Ssu = max point on torque-twist diagram Friday, April 14, 2017 Dr. Mohammad Suliman Abuhaiba, PE

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Resilience Resilience – Capacity of a material to absorb energy within its elastic range Modulus of resilience, uR Energy absorbed per unit volume without permanent deformation Equals to area under stress-strain curve up to elastic limit Elastic limit often approximated by yield point Friday, April 14, 2017 Dr. Mohammad Suliman Abuhaiba, PE

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**Resilience Area under curve to yield point gives approximation**

If elastic region is linear, For two materials with the same yield strength, the less stiff material (lower E) has greater resilience Friday, April 14, 2017 Dr. Mohammad Suliman Abuhaiba, PE

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Toughness Toughness – capacity of a material to absorb energy without fracture Modulus of toughness, uT Energy absorbed per unit volume without fracture Equals area under stress-strain curve up to fracture point Friday, April 14, 2017 Dr. Mohammad Suliman Abuhaiba, PE

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**Toughness Area under curve up to fracture point**

Approximated by using average of yield & ultimate strengths and strain at fracture Friday, April 14, 2017 Dr. Mohammad Suliman Abuhaiba, PE

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**Statistical Significance of Material Properties**

Strength values are obtained from testing many nominally identical specimens Strength, a material property, is distributional and thus statistical in nature Friday, April 14, 2017 Dr. Mohammad Suliman Abuhaiba, PE

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**Example for Statistical Material Property**

Histographic report for max stress of tensile tests on 1020 steel Probability density: # of occurrences divided by total sample number Friday, April 14, 2017 Dr. Mohammad Suliman Abuhaiba, PE

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**Example for Statistical Material Property**

Probability density function (See Ex. 20-4) Friday, April 14, 2017 Dr. Mohammad Suliman Abuhaiba, PE

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Statistical Quantity Statistical quantity described by mean, standard deviation, and distribution type From 1020 steel example: Mean stress = kpsi Standard deviation = kpsi Distribution is normal Friday, April 14, 2017 Dr. Mohammad Suliman Abuhaiba, PE

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Strengths from Tables Property tables often only report a single value for a strength term Important to check if it is mean, minimum, or some percentile Common to use 99% min strength, indicating 99% of samples exceed the reported value Friday, April 14, 2017 Dr. Mohammad Suliman Abuhaiba, PE

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Cold Work Cold work: Process of plastic straining below recrystallization temperature in the plastic region of stress-strain diagram Loading to point i beyond yield point, then unloading, causes permanent plastic deformation, ϵp Reloading to point i behaves elastically all the way to i, with additional elastic strain ϵe Friday, April 14, 2017 Dr. Mohammad Suliman Abuhaiba, PE

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**Cold Work Yield point is effectively increased to point i**

Material is said to have been cold worked, or strain hardened Material is less ductile (more brittle) since the plastic zone between yield strength & ultimate strength is reduced Repeated strain hardening can lead to brittle failure Friday, April 14, 2017 Dr. Mohammad Suliman Abuhaiba, PE

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**Reduction in Area R is a measure of ductility**

Ductility represents the ability of a material to absorb overloads and to be cold-worked Friday, April 14, 2017 Dr. Mohammad Suliman Abuhaiba, PE

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Cold-work Factor Cold-work factor W: A measure of the quantity of cold work Friday, April 14, 2017 Dr. Mohammad Suliman Abuhaiba, PE

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**Equations for Cold-worked Strengths**

Dr. Mohammad Suliman Abuhaiba, PE

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Example 2-1 Dr. Mohammad Suliman Abuhaiba, PE

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Example 2-1 (Continued) Dr. Mohammad Suliman Abuhaiba, PE

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Hardness Hardness –resistance of a material to penetration by a pointed tool Most common hardness-measuring systems Rockwell Brinell Vickers Friday, April 14, 2017 Dr. Mohammad Suliman Abuhaiba, PE

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**Strength and Hardness For steels For cast iron Friday, April 14, 2017**

Dr. Mohammad Suliman Abuhaiba, PE

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Example 2-2 Dr. Mohammad Suliman Abuhaiba, PE

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Impact Properties Charpy notched-bar test used to determine brittleness and impact strength Specimen struck by pendulum Energy absorbed, called impact value, is computed from height of swing after fracture Friday, April 14, 2017 Dr. Mohammad Suliman Abuhaiba, PE

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**Effect of Temperature on Impact**

Friday, April 14, 2017 Dr. Mohammad Suliman Abuhaiba, PE

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**Effect of Strain Rate on Impact**

Average strain rate for stress-strain diagram is in/(in·s) Increasing strain rate increases strengths Friday, April 14, 2017 Dr. Mohammad Suliman Abuhaiba, PE

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**Temperature Effects on Strengths**

Strength vs. temperature for carbon & alloy steels As temperature increases above RT: Sut increase slightly, then decreases significantly Sy decreases continuously Friday, April 14, 2017 Dr. Mohammad Suliman Abuhaiba, PE

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Creep Creep: continuous deformation under load for long periods of time at elevated temperatures Friday, April 14, 2017 Dr. Mohammad Suliman Abuhaiba, PE

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Creep Three stages 1st stage: elastic & plastic deformation; decreasing creep rate due to strain hardening 2nd stage: constant min creep rate caused by annealing effect 3rd stage: considerable reduction in area; increased true stress; higher creep rate leading to fracture Friday, April 14, 2017 Dr. Mohammad Suliman Abuhaiba, PE

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**Material Numbering Systems**

Common numbering systems Society of Automotive Engineers (SAE) American Iron and Steel Institute (AISI) Unified Numbering System (UNS) American Society for Testing and Materials (ASTM) for cast irons Friday, April 14, 2017 Dr. Mohammad Suliman Abuhaiba, PE

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**UNS Numbering System Established by SAE in 1975**

Letter prefix followed by 5 digit number Letter prefix designates material class G – carbon and alloy steel A – Aluminum alloy C – Copper-based alloy S – Stainless or corrosion-resistant steel Friday, April 14, 2017 Dr. Mohammad Suliman Abuhaiba, PE

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UNS for Steels, G First two numbers indicate composition, excluding carbon content Second pair of numbers indicates carbon content in hundredths of a percent by weight Fifth number is used for special situations Example: G52986 is chromium alloy with 0.98% carbon Friday, April 14, 2017 Dr. Mohammad Suliman Abuhaiba, PE

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**Alloy Steels Chromium Nickel Manganese Silicon Molybdenum Vanadium**

Tungsten Friday, April 14, 2017 Dr. Mohammad Suliman Abuhaiba, PE

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**Corrosion-Resistant Steels**

Stainless steels Iron-base alloys with at least 12 % chromium Resists many corrosive conditions Four types of stainless steels Ferritic chromium Austenitic chromium-nickel Martensitic Precipitation-hardenable Friday, April 14, 2017 Dr. Mohammad Suliman Abuhaiba, PE

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**Casting Materials Gray Cast Iron Ductile and Nodular Cast Iron**

White Cast Iron Malleable Cast Iron Alloy Cast Iron Cast Steel Friday, April 14, 2017 Dr. Mohammad Suliman Abuhaiba, PE

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**Nonferrous Metals Aluminum Magnesium Titanium Friday, April 14, 2017**

Dr. Mohammad Suliman Abuhaiba, PE

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**Nonferrous Metals Copper-based alloys Brass with 5 to 15 % zinc**

Gilding brass, commercial bronze, red brass Brass with 20 to 36 % zinc Low brass, cartridge brass, yellow brass Low-leaded brass, high-leaded brass (engraver’s brass), free-cutting brass Admiralty metal Aluminum brass Brass with 36 to 40 % zinc Muntz metal, naval brass Bronze Silcon bronze, phosphor bronze, aluminum bronze, beryllium bronze Friday, April 14, 2017 Dr. Mohammad Suliman Abuhaiba, PE

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Plastics Thermoplastic – any plastic that flows or is moldable when heat is applied Thermoset – a plastic for which the polymerization process is finished in a hot molding press where the plastic is liquefied under pressure Friday, April 14, 2017 Dr. Mohammad Suliman Abuhaiba, PE

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**Table 2-2: Thermoplastic Properties**

Dr. Mohammad Suliman Abuhaiba, PE

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**Table 2-3: Thermoset Properties**

Dr. Mohammad Suliman Abuhaiba, PE

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Composite Materials Formed from two or more dissimilar materials, each of which contributes to the final properties Materials remain distinct from each other at the macroscopic level Usually amorphous & non-isotropic Often consists of laminates of filler to provide stiffness and strength and a matrix to hold the material together Friday, April 14, 2017 Dr. Mohammad Suliman Abuhaiba, PE

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**Composite Materials Common filler types: Friday, April 14, 2017**

Dr. Mohammad Suliman Abuhaiba, PE

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**Table 2-4: Material Families and Classes**

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**Table 2-4: Material Families and Classes**

Friday, April 14, 2017 Dr. Mohammad Suliman Abuhaiba, PE

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**Table 2-4: Material Families and Classes**

Friday, April 14, 2017 Dr. Mohammad Suliman Abuhaiba, PE

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**Table 2-4: Material Families and Classes**

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**Young’s Modulus for Various Materials**

Dr. Mohammad Suliman Abuhaiba, PE

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