WELCOME TO COMPOSITE MATERIALS Introduction to Composite Materials Senior Elective in Mechanical Engineering Instructor: Autar Kaw

What are you going to learn? What are composite materials? How are they manufactured? What advantages and drawbacks do composites have over metals? Develop mathematical models to understand the mechanical response of composites to mechanical and hygrothermal loads? Use the above mathematical models to optimally design structures made of composites.

What is a composite? A composite is a structural material which consists of combining two or more constituents Examples: Flesh in your leg reinforced with bones Concrete reinforced with steel Epoxy reinforced with graphite fibers.

“You are no longer to supply the people with straw for making bricks; let them go and gather their own straw” - Exodus 5.7.

Shift in Paradigm About Materials “More important than any one new application is the new ‘materials’ concept itself ” Peter F. Drucker The Age of Discontinuity, 1969

What is this paradigm shift in materials? From substance to structures From artisan to science From workshop to mathematical modeling From what nature provides to what man can accomplish

Are Composites Important? Considered as one of the ten outstanding achievements of 1964-1989

From constituents to application

Chapter 1 Introduction to Composite Materials

Chapter 1: Objectives What is a composite? What are the advantages and drawbacks of composites over monolithic materials? What factors influence mechanical properties of a composite

Chapter Objectives (continued) How do we classify composites? What are the common types of fibers and matrices? How are composite materials manufactured? What are the mechanical properties of composite materials?

Chapter Objectives (continued) Give applications of composite materials. How are composites recycled? What terminology is used for studying mechanics of composites?

What is an advanced composite? Advanced composites are composite materials which were traditionally used in aerospace industries Examples include graphite/epoxy, Kevlar/epoxy and Boron/aluminum

Examples of Natural Composites Wood Cellulose Fibers Lignin Matrix Bones Collagen Fibers Mineral Matrix

Fibrous Composites Generally there are two phases Fiber as a reinforcement Matrix as a binder

Historical Perspective 4000 B.C. Fibrous composites were used in Egypt in making laminated writing materials 1300 BC: Reference to Book of Exodus 1700 AD: French Scientist, Reumer talked about potential of glass fibers

Historical Perspectives (continued) 1939: Glass fiber manufactured commercially for high temperature electrical applications 1950s: Boron and carbon fibers were produced to make ropes. 1960s: Matrix added to make polymeric matrix composites

Historical Perspectives (continued) 1970s: Cold war forces development of metal matrix composites for military aircrafts and missile guidance systems 1990s: High temperature ceramic matrix composites are being aggressively researched for use in next generation aircraft engines and power plant turbines

Shipments of Composites

World Market of Composites

Advantages of Composites Specific Strength and Stiffness Tailored Design Fatigue Life Dimensional Stability Corrosion Resistance Cost-Effective Fabrication

Drawbacks of Composites High cost of fabrication of composites Complex mechanical characterization Complicated repair of composite structures High combination of all required properties may not be available

Composites vs. Metals

Composites vs. Metals Comparison based on six primary material selection parameters

Why composites over metals? High Strength and High Stiffness Tailored Design Fatigue Life Dimensional Stability Corrosion Resistance

Why Composites over Metals? How is the mechanical advantage of composite measured?

Specific Strength vs. Year

Table 1.1. Specific modulus and strength of typical fibers, composites and bulk metals

Specific Strength vs Specific Modulus

Other Mechanical Parameters Are specific modulus and specific strength the only mechanical parameters used for measuring the relative advantage of composites over metals? NO!!

Tailored Design Engineered to meet specific demands as choices of making the material are many more as compared to metals. Examples of choices fiber volume fraction layer orientation type of layer layer stacking sequence

Fatigue Life Fatigue life is higher than metals such as aluminum. Important consideration in applications such as aircrafts bridges structures exposed to wind

Dimensional Stability Temperature changes can result in overheating of components (example engines) thermal fatigue due to cyclic temperature changes (space structures) render structures inoperable (space antennas)

Corrosion Resistance Polymers and ceramics matrix are corrosion resistant Examples include underground storage tanks doors window frames structural members of offshore drilling platforms

What is most limiting factor in the use of composites in structures? Lack of engineers with the knowledge and experience to design with these materials!!!!

Cost Considerations Composites may be more expensive per pound than conventional materials. Then why do we use composite materials?

Factors in Cost Estimate For Composite Materials Fewer pounds are required Fabrication cost may be lower Transportation costs are generally lower Less maintenance than conventional materials is required

Fiber Factors What fiber factors contribute to the mechanical performance of a composite? Length Orientation Shape Material

Fiber Factor - Length Long Fibers Short Fibers Easy to orient Easy to process Higher impact resistance Dimensional stability Short Fibers Low Cost Fast cycle time

Fiber Factor - Orientation One direction orientation High stiffness and strength in that direction Low stiffness and strength in other directions Multi-direction orientation Less stiffness but more direction independent

Fiber Factor - Shape Most common shape is circular Hexagon and square shapes give high packing factors

Fiber Factor - Material Graphite and aramids have high strength and stiffness Glass has low stiffness but cost less

Matrix Factors What are the matrix factors which contribute to the mechanical performance of composites? Binds fibers together Protects fibers from environment Shielding from damage due to handling Distributing the load to fibers.

Factors Other Than Fiber and Matrix Fiber-matrix interface Chemical bonding Mechanical bonding

Fiber Types Glass Fiber (first synthetic fiber) Boron (first advanced fiber) Carbon Silicon Carbide

Types of Matrices Polymers Metals Ceramics

Polymer Matrix Thermosets Thermoplastics polyester epoxy polymide polypropylene polyvinyl chloride nylon

Metal Matrix Aluminum Titanium Copper

Ceramic Matrix Carbon Silicon Carbide Calcium AluminoSilicate Lithium AluminoSilicate

Why do fibers have thin diameter? Less flaws More toughness and ductility Higher flexibility Thin Fiber Thick Fiber

Less Flaws

More Toughness and Ductility Fiber-matrix interface area is inversely proportional to the diameter of the fibers Higher surface area of fiber-matrix interface results in higher ductility and toughness, and better transfer of loads.

More Flexibility Flexibility is proportional to inverse of Young’s modulus Fourth power of diameter Thinner fibers hence have a higher flexibility and are easy to handle in manufacturing.

Classification CONCRETE: Gravel, sand and cement PAINT: Paint and aluminum flakes GRAPHITE/EPOXYGraphite fibers in epoxy matrix

Polymer Matrix Composites What are the most common advanced composites? Graphite/Epoxy Kevlar/Epoxy Boron/Epoxy

Polymer Matrix Composites What are the drawbacks of polymer matrix composites? Low operating temperatures High CTE and CMEs Low elastic properties in certian directions

Are Carbon and Graphite the Same? No Carbon fibers have 93%-95% carbon content and graphite has >99% carbon content Carbon fibers are produced at 2400o F and graphite fibers are produced at 3400o F

Table 1.4. Typical mechanical properties of polymer matrix composites and monolithic materials

Comparative Stiffness of PMCs and Metals

How to make a PMC

Schematic of Prepreg Manufacturing

Prepreg Boron/Epoxy

Autoclave Lamination

Filament Winding

Resin Transfer Molding

Common PMC Fibers & Matrices Graphite Glass Kevlar Matrices Epoxy Phenolic Polyester

Table 1.5 Typical mechanical properties of fibers used in polymer matrix composites

Cost Comparison of PMC fibers Type of fiber Cost ($ per pound) A-glass .65 - .90 C-glass .75 - 1.00 E-glass .75 - 1.00 S-2 Glass 6.00 - 8.00 Heavy Tow 9.00 - 12.00 Medium Tow 15.00 -20.00 Low Tow 40.00 -70.00+ Kev29 12.00 -14.00 Kev149 25.00 -30.00

Manufacturing of Glass Fibers

Glass Fiber Types E-glass (fiberglass) - electrical applications S-glass - strength applications C-glass - Corrosion resistant D-glass - Low dielectric applications A-glass - Appearance applications AR-glass - Alkali resistant

Table 1.6 Comparison of properties of E-glass and S-glass

Table 1.7 Chemical Composition of E-Glass and S-glass Fibers

Fig 1.10 Forms of Fibers

Fig 1.11 Manufacturing Graphite Fibers

Resin Systems Polyester Phenolics Epoxy Silicone Polymide

Properties of epoxy

Curing Stages of Epoxy

Comparison of Resins

Difference between thermosets and thermoplastics

Pre-Preg Graphite/Epoxy

Application of Polymer Matrix Composites A strong, ultralight leg prosthesis of graphite/epoxy helps an athelete compete in world-class bicycle race.

Space Shuttle

Lear Fan

Fighter Jets

Corvette Leaf Springs

Snow Skis

Space Shuttle

I-beam

Pressure vessels

Metal Matrix Composites What are metal-matrix composites? Metal matrix composites have a metal matrix. Examples include silicon carbide fibers in aluminum, graphite fibers in aluminum.

Advantages of MMCs Higher specific strength and modulus over metals. Lower coefficients of thermal expansion than metals by reinforcing with graphite. Maintenance of high strength properties at high temperatures.

Degrading properties in MMCs (Fig 1.3) Are there any properties which degrade when metals are reinforced with fibers? Yes, they may have reduced ductility and fracture toughness.

Typical mechanical properties of metal matrix composites

Boron Fiber

Step 0: Cutting the shape

Step 1: Apply Aluminum File

Step 3: Lay Up Desired Plies

Step 4:Vacuum the specimen

Step5: Heat to Fabrication Temperature

Step 6: Apply Pressure and Hold for Consolidation Cycle

Step 7: Cool, Remove and Clean Part

Schematic of Diffusion Bonding

Silicon Carbide/ Aluminum Composite

Application of MMCs

Application of MMCs

Application of MMCs

Ceramic Matrix Composites What are ceramic matrix composites? Ceramic matrix composites have matrices of alumina, calcium alumino silicate (CAS), lithium alumino silicate (LAS). Examples include Silicon Carbide/CAS and Carbon/LAS.

Owens Corning Webster about CMS Advantages of CMCs High strength, hardness and high service temperatures Chemical inertness Low Density Owens Corning Webster about CMS

Table 1.12 Typical fracture toughness of monolithic materials and ceramic matrix composites

Table 1.13 Typical mechanical properties of some ceramic matrix composites

Manufacturing of Ceramic Matrix Composites - Slurry Infiltration

Application of CMCs

Carbon-Carbon Compoistes What are carbon-carbon composites? Carbon - Carbon composites have carbon fibers in carbon matrix.

Advantages of Carbon-Carbon Composites Gradual failure Withstand high temperatures Low creep at high temperatures Low density High thermal conductivity Low and tailorable Coefficient of Thermal Expansion

Advantages of Carbon-Carbon Composites Great strength to weight ratio High modulus, thermal conductivity, and electrical conductivity Good thermal shock resistance, abrasion resistance, and fracture toughness Excellent high temperature durability in inert or vacuum environment Good corrosion resistance

Table 1.14 Typical mechanical properties of carbon-carbon matrix composites

Carbon-Carbon Manufacturing (Fig 1.34)

Applications of C-C Composites Space Shuttle Nose Cones Re-entry temperature of 3092 K Aircraft Brakes Saves 450 kgs of mass Two-four times durability vs. steel 2.5 times specific heat of steel

Applications of Carbon-Carbon Composites

Recycling of Composites What types of process are used for recycling of composites? Why is recycling of composites complex? What can one do if one cannot separate different types of composites?

Recycling Continued What are the various steps in mechanical recycling of short fiber-reinforced composites? Where are mechanically recycled short fiber composites used?

Chemical Recycling Why is chemical recycling not as popular as mechanical recycling? Which chemical process shows the most promise?

Definitions Isotropic body Homogeneous body Anisotropic body Nonhomogeneous body Lamina Laminate

Schematic of Analysis of Laminated Composites

An Artist’s Rendition of a Composite Material