COMPOSITES
Definition A composite is a combination of two or more simple materials to get another material with better properties
Examples Wood (a natural composite - comprising cellulose fibers in a lignin and hemicellulose matrix ) Cemented carbides (WC with Co binder) Plastic molding compounds containing fillers Rubber mixed with carbon black
Components in a Composite Material All composite materials consist of two phases: 1. Primary phase called the matrix 2. Secondary phase (or) imbedded phase also called a reinforcing agent.
Functions of Matrix Material (Primary Phase) Provides the bulk form of the composite material Holds the imbedded phase in place, usually enclosing and often concealing it When a load is applied, the matrix shares the load with the secondary phase, in some cases deforming so that the stress is essentially born by the reinforcing agent
Functions of Particle Material (Secondary Phase) It reinforces the primary phase It takes the form of an infiltrated phase in a skeletal or porous matrix Example: a powder metallurgy part infiltrated with polymer
Possible physical shapes of imbedded (secondary) phases (a) fiber, (b) particle & (c) flake
The matrix phase is continuous, soft, ductile, almost clay-like and surrounds the fiber phase. The fiber (or particle) phase is typically much stronger than the matrix. Together, the two phases can give a material that has better properties.
Why Composites are Important Composites are very strong stiff very light in weight ( so ratios of strength-to-weight and stiffness-to-weight are several times greater than steel or aluminum ) Better Fatigue Greater Toughness They do not corrode Possible to achieve combinations of properties which cannot be obtained with metals, ceramics, or polymers alone
Classification Based on Source Based on Primary Phase Based on Secondary Phase Based on Orientation of Fibre
Source Traditional Synthetic
Source 1. Traditional composites composite materials that occur in nature or have been used by civilizations for many years Examples: wood, concrete, asphalt 2.Synthetic composites modern material systems normally associated with the manufacturing industries, in which the components are first produced separately and then combined in a controlled way to achieve the desired structure, properties, and part geometry Examples : FRP
Primary Phase Matrix Metal (MMC) Plastic (PMC) Ceramics (CMC)
Based On Primary Phase 1. Metal Matrix Composites (MMCs) - mixtures of ceramics and metals, CERMETS example cemented carbides 2. Polymer Matrix Composites (PMCs) - thermosetting resins are widely used in PMCs Examples: epoxy and polyester with fiber reinforcement, and phenolic with powders 3. Ceramic Matrix Composites (CMC s) Examples : Al 2 O 3 and SiC imbedded with fibers to improve properties and find use in high temperature applications (It is the least common composite matrix)
Secondary Phase Particulate Composite Layered Composite Fibre Reinforced Composite
Based on Secondary Phase 1.Particulate Composites Example : W ThO 2, Cermets, Concrete 2. Layered Composites Example : Plywood, Copper Clad Stainless steel vessels 3. Fibre Reinforced Composites: Example : Glass Reinforced Plastics, Aluminium Boron Composites
Fiber Orientation One Dimension Two dimension (Planar) Three Dimension (Random)
Based on Orientation of Fibre One-dimensional reinforcement, in which maximum strength and stiffness are obtained in the direction of the fiber Two Dimensional, in some cases in the form of a planar woven fabric Three-dimensional ( Random) in which the composite material tends to possess isotropic properties
a) One (b) Two ( c ) Three
One Dimension Two Dimension
Polymer Matrix Composites Primary Phase is Polymer Secondary Phase may be Fibre / Particle / flakes Commercially PMCs are more important than MMCs or CMCs Examples: most plastic molding compounds rubber reinforced with carbon black Fibre-Reinforced Polymers (FRPs)
Fibre Reinforced Plastics (FRP) FRPs are most closely identified with the term composite Primary Phase : Polymer Usually a thermosetting (TS) plastic such as unsaturated polyester or epoxy Can also be thermoplastic (TP), such as nylons (polyamides), polycarbonate, polystyrene, and polyvinylchloride
Secondary Phase : Fibre Principal fiber materials in FRPs are glass, carbon, and Kevlar 49 Less common fibers include boron, SiC, and Al 2 O 3, and steel Glass (in particular E-glass) is the most common fiber material; its use to reinforce plastics dates from around 1920 Fibre can be discontinuous (chopped), continuous
Common FRP Structure Most widely used form of FRP is a laminar structure, made by stacking and bonding thin layers of fiber and polymer By varying fiber orientation among layers, a specified level of anisotropy (elasticity) in properties can be achieved in the laminate
Properties of FRP Excellent strength-to-weight and modulus-to-weight ratios Low specific gravity (FRP weighs only about 1/5 as much as steel) Good fatigue strength Good corrosion resistance Low thermal expansion - for many FRPs, leading to good dimensional stability
Applications Aerospace the structural weight of airplanes and helicopters consist of FRPs Automotive body panels for cars and truck cabs FRP is used for boat hulls since the 1940s Sports and recreation fishing rods, tennis rackets, golf club shafts, helmets, skis, bows and arrows.
Some Important Fibre Reinforced Polymer Composites
Glass FRP Primary Phase :Nylon, Polyester etc., Secondary Phase : Long and Short Glass Fibres Properties: Low density, High Tensile Strength,High Impact Resistance, Excellent Resistance to corrosion and chemicals, low stiffness and low rigidity Limitations: Cannot be used for a wide range of temperature and as structural material Applications: Automobile parts, Storage tanks, Flooring,Pipes
Carbon FRP / High Performance composites / Advanced Polymer Matrix Composites Primary Phase :Epoxy resin Secondary Phase :Graphite fibre Properties: Excellent Corrosion resistance, Very light Thermal stability Limitation: Very Expensive Applications: Structural component of air borne automobiles, Fishing rods, Golf club etc.,
Aramid FRP Primary Phase : Polymer Secondary Phase ; PPTA Poly para phenyl tere phthalamide (Kevlar) Properties: High Toughness, high Strength and ultra high modulus, Good thermal and wear properties. Limitations: Low resistance for axial compression, Hygroscopic Applications ; automobile break and clutches, Structural material for aircraft, fire proof dress
Other Important Composites Alumina Reinforced Metal Composite (type 1) Primary Phase : Al alloy Secondary phase : Alumina fibre Properties : Low Density, Good wear resistance and good dimensional stabiliity Applications : Components of automobile engine
. Alumina composite ( type 2) Primary Phase : Ni and Co based alloys Secondary Phase : Alumina Properties: Excellent impact resistance, Good creep and rupture resistance, Good thermal stability Applications: Components of turbine engine.
Nano FRP Composites Nano composites are a New Class of Materials Adding nano particulates to a polymer matrix can enhance its performance This strategy is particularly effective in yielding high performance composites
Polymer nanocomposites are plastic materials with small amounts of clay added to them. Specifically, a few molecules of clay are sandwiched between miniscule layers of plastics (polymers), resulting in a 'super material' with numerous enhanced properties such as greater strength, higher resistance to permeability and higher heat stability
Used in food packaging, automobile parts and medical devices
.Nano composites Superthermites are nano composite made of silica and other metal oxides matrix with Al as reinforcing agent They are used as power tool housings, mower hoods and covers for portable electronic equipment such as mobile phones, pagers etc