1. ME 429 Introduction to Composite Materials
Dr. Ahmet Erkliğ
Fall Semester
www1.gantep.edu.tr/~erklig/me429/introduction.ppt, 13 Dec 2010

2. Composite materials – Introduction
Definition: any combination of two or more different materials at the macroscopic level. OR
Two inherently different materials that when combined together produce a material with properties that exceed the constituent materials.
Reinforcement phase (e.g., Fibers)
Binder phase (e.g., compliant matrix)
Advantages
High strength and stiffness
Low weight ratio
Material can be designed in addition to the structure

3. Applications Straw in clay construction by Egyptians
Aerospace industry
Sporting goods
Automotive
Construction

4. Types of Composites MMC’s CMC’s PMC’s Matrix phase/Reinforcement Phase
Metal
Ceramic
Polymer
Powder metallurgy parts – combining immiscible metals
Cermets (ceramic-metal composite)
Brake pads
Cermets, TiC, TiCN
Cemented carbides – used in tools
Fiber-reinforced metals
SiC reinforced Al2O3
Tool materials
Fiberglass
Kevlar fibers in an epoxy matrix
Elemental (Carbon, Boron, etc.)
Fiber reinforced metals
Auto parts
aerospace
Rubber with carbon (tires)
Boron, Carbon reinforced plastics
MMC’s CMC’s PMC’s
Metal Matrix Composites Ceramic Matrix Comp’s Polymer Matrix Comp’s

5. Costs of composite manufacture
Material costs -- higher for composites
Constituent materials (e.g., fibers and resin)
Processing costs -- embedding fibers in matrix
not required for metals Carbon fibers order of magnitude higher than aluminum
Design costs -- lower for composites
Can reduce the number of parts in a complex assembly by designing the material in combination with the structure
Increased performance must justify higher material costs

6. Types of Composite Materials
There are five basic types of composite materials: Fiber, particle, flake, laminar or layered and filled composites.

7. A. Fiber Composites
In fiber composites, the fibers reinforce along the line of their length. Reinforcement may be mainly 1-D, 2-D or 3-D. Figure shows the three basic types of fiber orientation.
1-D gives maximum strength in one direction.
2-D gives strength in two directions.
Isotropic gives strength equally in all directions.

8. Composite strength depends on following factors:
Inherent fiber strength, Fiber length, Number of flaws
Fiber shape
The bonding of the fiber (equally stress distribution)
Voids
Moisture (coupling agents)

9. B. Particle Composites
Particles usually reinforce a composite equally in all directions (called isotropic). Plastics, cermets and metals are examples of particles.
Particles used to strengthen a matrix do not do so in the same way as fibers. For one thing, particles are not directional like fibers. Spread at random through out a matrix, particles tend to reinforce in all directions equally.
Cermets
(1) Oxide–Based cermets
(e.g. Combination of Al2O3 with Cr)
(2) Carbide–Based Cermets
(e.g. Tungsten–carbide, titanium–carbide)
Metal–plastic particle composites
(e.g. Aluminum, iron & steel, copper particles)
Metal–in–metal Particle Composites and Dispersion Hardened Alloys
(e.g. Ceramic–oxide particles)

10. C. Flake Composites - 1
Flakes, because of their shape, usually reinforce in 2-D. Two common flake materials are glass and mica. (Also aluminum is used as metal flakes)

11. C. Flake Composites -2
A flake composite consists of thin, flat flakes held together by a binder or placed in a matrix. Almost all flake composite matrixes are plastic resins. The most important flake materials are:
Aluminum
Mica
Glass

12. C. Flake Composites -3 Basically, flakes will provide:
Uniform mechanical properties in the plane of the flakes
Higher strength
Higher flexural modulus
Higher dielectric strength and heat resistance
Better resistance to penetration by liquids and vapor
Lower cost

13. D. Laminar Composites - 1
Laminar composites involve two or more layers of the same or different materials. The layers can be arranged in different directions to give strength where needed. Speedboat hulls are among the very many products of this kind.

14. D. Laminar Composites - 2
Like all composites laminar composites aim at combining constituents to produce properties that neither constituent alone would have.
In laminar composites outer metal is not called a matrix but a face. The inner metal, even if stronger, is not called a reinforcement. It is called a base.

15. D. Laminar Composites - 3
We can divide laminar composites into three basic types:
Unreinforced–layer composites
(1) All–Metal
(a) Plated and coated metals (electrogalvanized steel – steel plated with zinc)
(b) Clad metals (aluminum–clad, copper–clad)
(c) Multilayer metal laminates (tungsten, beryllium)
(2) Metal–Nonmetal (metal with plastic, rubber, etc.)
(3) Nonmetal (glass–plastic laminates, etc.)
Reinforced–layer composites (laminae and laminates)
Combined composites (reinforced–plastic laminates well bonded with steel, aluminum, copper, rubber, gold, etc.)

16. D. Laminar Composites - 4
A lamina (laminae) is any arrangement of unidirectional or woven fibers in a matrix. Usually this arrangement is flat, although it may be curved, as in a shell.
A laminate is a stack of lamina arranged with their main reinforcement in at least two different directions.

17. E. Filled Composites
There are two types of filled composites. In one, filler materials are added to a normal composite result in strengthening the composite and reducing weight. The second type of filled composite consists of a skeletal 3-D matrix holding a second material. The most widely used composites of this kind are sandwich structures and honeycombs.

18. F. Combined Composites
It is possible to combine several different materials into a single composite. It is also possible to combine several different composites into a single product. A good example is a modern ski. (combination of wood as natural fiber, and layers as laminar composites)

19. Forms of Reinforcement Phase
Fibers
cross-section can be circular, square or hexagonal
Diameters --> ” “
Lengths --> L/D ratio
for chopped fiber
much longer for continuous fiber
Particulate
small particles that impede dislocation movement (in metal composites) and strengthens the matrix
For sizes > 1 mm, strength of particle is involves in load sharing with matrix
Flakes
flat platelet form

20. Fiber Reinforcement
The typical composite consists of a matrix holding reinforcing materials. The reinforcing materials, the most important is the fibers, supply the basic strength of the composite. However, reinforcing materials can contribute much more than strength. They can conduct heat or resist chemical corrosion. They can resist or conduct electricity. They may be chosen for their stiffness (modulus of elasticity) or for many other properties.

21. Types of Fibers The fibers are divided into two main groups:
Glass fibers: There are many different kinds of glass, ranging from ordinary bottle glass to high purity quartz glass. All of these glasses can be made into fibers. Each offers its own set of properties.
Advanced fibers: These materials offer high strength and high stiffness at low weight. Boron, silicon, carbide and graphite fibers are in this category. So are the aramids, a group of plastic fibers of the polyamide (nylon) family.

22. Fibers - Glass
Fiberglass properties vary somewhat according to the type of glass used. However, glass in general has several well–known properties that contribute to its great usefulness as a reinforcing agent:
Tensile strength
Chemical resistance
Moisture resistance
Thermal properties
Electrical properties
There are four main types of glass used in fiberglass:
A–glass
C–glass
E–glass
S–glass

23. Fibers - Glass Most widely used fiber
Uses: piping, tanks, boats, sporting goods
Advantages
Low cost
Corrosion resistance
Low cost relative to other composites:
Disadvantages
Relatively low strength
High elongation
Moderate strength and weight
Types:
E-Glass - electrical, cheaper
S-Glass - high strength

24. Fibers - Aramid (kevlar, Twaron)
Uses:
high performance replacement for glass fiber
Examples
Armor, protective clothing, industrial, sporting goods
Advantages:
higher strength and lighter than glass
More ductile than carbon

25. Fibers - Carbon 2nd most widely used fiber Examples Advantages
aerospace, sporting goods
Advantages
high stiffness and strength
Low density
Intermediate cost
Properties:
Standard modulus: Gpa
Intermediate modulus: GPa
High modulus: GPa
Diameter: 5-8 microns, smaller than human hair
Fibers grouped into tows or yarns of 2-12k fibers

26. Fibers -- Carbon (2) Types of carbon fiber Intermediate modulus
vary in strength with processing
Trade-off between strength and modulus
Intermediate modulus
PAN (Polyacrylonitrile)
fiber precursor heated and stretched to align structure and remove non-carbon material
High modulus
made from petroleum pitch precursor at lower cost
much lower strength

27. Fibers - Others Boron Polyethylene - trade name: Spectra fiber
High stiffness, very high cost
Large diameter microns
Good compressive strength
Polyethylene - trade name: Spectra fiber
Textile industry
High strength
Extremely light weight
Low range of temperature usage

28. Fibers -- Others (2) Ceramic Fibers (and matrices)
Very high temperature applications (e.g. engine components)
Silicon carbide fiber - in whisker form.
Ceramic matrix so temperature resistance is not compromised
Infrequent use

29. Fiber Material Properties
Steel: density (Fe) = 7.87 g/cc; TS=0.380 GPa; Modulus=207 GPa
Al: density=2.71 g/cc; TS=0.035 GPa; Modulus=69 GPa

30. Fiber Strength

31. Matrix Materials Functions of the matrix Demands on matrix
Transmit force between fibers
arrest cracks from spreading between fibers
do not carry most of the load
hold fibers in proper orientation
protect fibers from environment
mechanical forces can cause cracks that allow environment to affect fibers
Demands on matrix
Interlaminar shear strength
Toughness
Moisture/environmental resistance
Temperature properties
Cost

32. Matrices - Polymeric Thermosets cure by chemical reaction Irreversible
Examples
Polyester, vinylester
Most common, lower cost, solvent resistance
Epoxy resins
Superior performance, relatively costly

33. Matrices - Thermosets Polyester
Polyesters have good mechanical properties, electrical properties and chemical resistance. Polyesters are amenable to multiple fabrication techniques and are low cost.
Vinyl Esters
Vinyl Esters are similar to polyester in performance. Vinyl esters have increased resistance to corrosive environments as well as a high degree of moisture resistance.

34. Matrices - Thermosets Epoxy
Epoxies have improved strength and stiffness properties over polyesters. Epoxies offer excellent corrosion resistance and resistance to solvents and alkalis. Cure cycles are usually longer than polyesters, however no by-products are produced.
Flexibility and improved performance is also achieved by the utilization of additives and fillers.

35. Matrices - Thermoplastics
Formed by heating to elevated temperature at which softening occurs
Reversible reaction
Can be reformed and/or repaired - not common
Limited in temperature range to 150C
Examples
Polypropylene
with nylon or glass
can be injected-- inexpensive
Soften layers of combined fiber and resin and place in a mold -- higher costs

36. Matrices - Others Metal Matrix Composites - higher temperature
e.g., Aluminum with boron or carbon fibers
Ceramic matrix materials - very high temperature
Fiber is used to add toughness, not necessarily higher in strength and stiffness

37. Important Note
Composite properties are less than that of the fiber because of dilution by the matrix and the need to orient fibers in different directions.

38. MANUFACTURING PROCESSES OF COMPOSITES
Composite materials have succeeded remarkably in their relatively short history. But for continued growth, especially in structural uses, certain obstacles must be overcome. A major one is the tendency of designers to rely on traditional materials such as steel and aluminum unless composites can be produced at lower cost.
Cost concerns have led to several changes in the composites industry. There is a general movement toward the use of less expensive fibers. For example, graphite and aramid fibers have largely supplanted the more costly boron in advanced–fiber composites. As important as savings on materials may be, the real key to cutting composite costs lies in the area of processing.

39. The processing of fiber reinforced laminates can be divided into two main steps:
Lay–up
Curing
Curing is the drying and hardening (or polymerization) of the resin matrix of a finished composite. This may be done unaided or by applying heat and/or pressure.
Lay–up basically is the process of arranging fiber–reinforced layers (laminae) in a laminate and shaping the laminate to make the part desired. (The term lay–up is also used to refer to the laminate itself before curing.) Unless prepregs are used, lay–up includes the actual creation of laminae by applying resins to fiber reinforcements.

40. Laminate lay–up operations fall into three main groups:
Winding and laying operations
Molding operations
Continuous lamination
Continuous lamination is relatively unimportant compared with quality parameters as not good as wrt other two processes. In this process, layers of fabric or mat are passed through a resin dip and brought together between cellophane covering sheets. Laminate thickness and resin content are controlled by squeegee rolls. The lay–up is passed through a heat zone to cure the resin.

41. A. Winding Operation
The most important operation in this category is filament winding. Fibers are passed through liquid resin, and then wound onto a mandrel. After lay–up is completed, the composite is cured on the mandrel. The mandrel is then removed by melting, dissolving, breaking–out or some other method.

42. B. Molding Operations
Molding operations are used in making a large number of common composite products. There are two types of processes:
Open–mold
(1) Hand lay–up
(2) Spray–up
(3) Vacuum–bag molding
(4) Pressure–bag molding
(5) Thermal expansion molding
(6) Autoclave molding
(7) Centrifugal casting
(8) Continuous pultrusion and pulforming.

43. 1. Hand Lay-up
Hand lay–up, or contact molding, is the oldest and simplest way of making fiberglass–resin composites. Applications are standard wind turbine blades, boats, etc.)

44. 2. Spray-up
In Spray–up process, chopped fibers and resins are sprayed simultaneously into or onto the mold. Applications are lightly loaded structural panels, e.g. caravan bodies, truck fairings, bathtubes, small boats, etc.

45. 3. Vacuum-Bag Molding
The vacuum–bag process was developed for making a variety of components, including relatively large parts with complex shapes. Applications are large cruising boats, racecar components, etc.

46. 4. Pressure-Bag Molding
Pressure–bag process is virtually a mirror image of vacuum–bag molding. Applications are sonar domes, antenna housings, aircraft fairings, etc.

47. 5. Thermal Expansion Molding
In Thermal Expansion Molding process, prepreg layers are wrapped around rubber blocks, and then placed in a metal mold. As the entire assembly is heated, the rubber expands more than the metal, putting pressure on the laminate. Complex shapes can be made reducing the need for later joining and fastening operations.

48. 6. Autoclave Molding
Autoclave molding is similar to both vacuum–bag and pressure–bag molding. Applications are lighter, faster and more agile fighter aircraft, motor sport vehicles.

49. 7. Centrifugal Casting
Centrifugal Casting is used to form round objects such as pipes Continuous Pultrusion and Pulforming
Continuous pultrusion is the composite counterpart of metal extrusion. Complex parts can be made.

50. Pulforming is similar to pultrusion in many ways
Pulforming is similar to pultrusion in many ways. However, pultrusion is capable only of making straight products that have the same volume all along their lengths. Pulformed products, on the other hand, can be either straight or curved, with changing shapes and volumes. A typical pulformed product is a curved reinforced plastic car spring. (shown in figure.)

51. B. Closed–mold
(1) Matched–die molding: As the name suggests, a matched–die mold consists of closely matched male and female dies (shown in figure). Applications are spacecraft parts, toys, etc.
(2) Injection molding: The injection process begins with a thermosetting (or sometimes thermoplastic) material outside the mold. The plastic may contain reinforcements or not. It is first softened by heating and/or mechanical working with an extrusion–type screw. It is then forced, under high pressure from a ram or screw, into the cool mold. Applications are auto parts, vanes, engine cowling defrosters and aircraft radomes.

52. Material Forms and Manufacturing
Objectives of material production
assemble fibers
impregnate resin
shape product
cure resin

53. Sheet Molding Compound (SMC)
Chopped glass fiber added to polyester resin mixture
Question: Is SMC isotropic or anisotropic?

54. Manufacturing - Filament Winding
Highly automated
low manufacturing costs if high throughput
e.g., Glass fiber pipe, sailboard masts

55. Prepregs Prepreg and prepreg layup
“prepreg” - partially cured mixture of fiber and resin
Unidirectional prepreg tape with paper backing
wound on spools
Cut and stacked
Curing conditions
Typical temperature and pressure in autoclave is C, 100 psi

56. Manufacturing - Layups
compression
molding
vacuum bagging

57. Material Forms Textile forms Braiding or weaving Tubular braided form
can be flattened and cut for non-tubular products

58. Fabric Structures
Woven: Series of Interlaced yarns at 90° to each other
Knit: Series of Interlooped Yarns
Braided: Series of Intertwined, Spiral Yarns
Nonwoven: Oriented fibers either mechanically, chemically, or thermally bonded

59. Woven Fabrics
Basic woven fabrics consists of two systems of yarns interlaced at right angles to create a single layer with isotropic or biaxial properties.

60. Physical Properties Construction (ends & picks) Weight Thickness
Weave Type

61. Components of a Woven Fabric

62. Basic Weave Types
Plain Weave

63. Basic Weave Types
Satin 5HS

64. Basic Weave Types
2 x 2 Twill

65. Basic Weave Types
Non-Crimp

66. Braiding
A braid consists of two sets of yarns, which are helically intertwined.
The resulting structure is oriented to the longitudinal axis of the braid.
This structure is imparted with a high level of conformability, relative low cost and ease of manufacture.

67. Braid Structure

68. Types of Braids

69. Triaxial Yarns
A system of longitudinal yarns can be introduced which are held in place by the braiding yarns
These yarns will add dimensional stability, improve tensile properties, stiffness and compressive strength.
Yarns can also be added to the core of the braid to form a solid braid.

70. Fabric effects on material properties

71. Resin transfer molding (RTM)
Dry-fiber preform placed in a closed mold, resin injected into mold, then cured

72. Material Forms Pultrusion
Fiber and matrix are pulled through a die, like extrusion of metals -- assembles fibers, impregnates the resin, shapes the product, and cures the resin in one step.
Example. Fishing rods

73. Pultrusion

74. Manufacturing Tube rolling - tubular products Examples
fishing rods
golf clubs
oars
Prepreg tape typically used wrapped in 2 directions or spiral wrapped