Definition of Composite Materials Fibers and Matrix Phases

Definition of Composite Materials Fibers and Matrix Phases Composite Composition and Properties Manufacturing Processes Applications INTRODUCTION TO COMPOSITE MATERIALS W. RANGSRI Intro. to Mechanics of Laminated Composite Materials Introduction to Composite Materials

Definition Composite material : a material made from two or more different materials with different physical or chemical properties Examples of natural composites Wood: Cellulose fibers bound by lignin matrix Bone: Stiff mineral “fibers” in a soft organic matrix permeated with holes filled with liquids Granite: Granular composite of quartz, feldspar, and mica Examples of man-made composites Concrete: Particulate composite of aggregates (limestone or granite), sand, cement and water Plywood: Several layers of wood veneer glued together Fiberglass: Plastic matrix reinforced by glass fibers Cemets: Ceramic and metal composites Fibrous composites: Variety of fibers (glass, kevlar, graphite, nylon, etc. ) bound together by a polymeric matrix

Definition • • • Some of the properties that can be improved by forming a composite material are strength stiffness weight wear resistance Attractiveness Naturally, not all of these properties are improved at the same time. Engineering composite materials are produced • • metals ceramics Polymers temp. -dependent behavior thermal conductivity thermal insulation acoustical insulation corrosion resistance

Definition • Many composite materials are composed of just two phases; o o • • matrix phase dispersed phase or reinforced phase. The properties of composites are a function of the properties of the constituent phases, their relative amountsthe geometry of the dispersed phase.

Classification and Characteristics

Particle-reinforced composites Large-particle � the matrix transfers some of the applied stress to the particles, which bear a fraction of the load. � the degree of reinforcement of mechanical behavior depends on strong bonding at the matrix–particle interface. Dispersion-strengthened � strengthening occur on the atomic or molecular level. the matrix bears the major portion of an applied load. � the small dispersed particles hinder or impede the motion of dislocations.

Fiber-reinforced composites

Particle-reinforced composites The dispersed phase is in the form of a fiber. Design goals is high strength and/or stiffness on a weight basis. � high specific strengths (high ratios of tensile strength to specific gravity) � high specific modulus of elasticity (high modulus of elasticity to specific gravity) Utilize low-density fiber and matrix materials. Subclassified by fiber length then orientation of fiber. Too short fiber can not produce a significant improvement in strength.

Structural composites Normally composed of both homogeneous and composite materials. Properties depend on � the constituent materials � the geometrical design of the various structural elements. The most common structural composites � laminar composites � sandwich panels

Structural composites Laminar composites Composed of two-dimensional sheets or panels having a preferred highstrength direction The layers are stacked and subsequently cemented together The orientation of the high-strength direction varies with each successive layer Laminations may be constructed using fabric material

Structural composites Sandwich panels Consist of faces and core Faces = two strong outer sheets • Typical material: • • • aluminum alloys fiber-reinforced plastics titanium steel Plywood

Structural composites Sandwich panels Core Separates the faces and resists deformations perpendicular to the face plane Lower stiffness, lower strength comparing with faces Provides a certain degree of shear rigidity along planes (perpendicular to the faces). Made of foamed polymers, synthetic rubbers, inorganic cements, balsa wood.

Structural composites Sandwich panels Core Separates the faces and resists deformations perpendicular to the face plane Lower stiffness, lower strength comparing with faces Provides a certain degree of shear rigidity along planes (perpendicular to the faces). Made of foamed polymers, synthetic rubbers, inorganic cements, balsa wood.

Fiber phase For most material �a critical surface flaw can lead to fracture � the presence of a critical surface flaw diminishes with decreasing specimen volume � a small diameter fiber is much stronger than the bulk material The above feature is used to advantage in the fiber-reinforced composites � The materials used for reinforcing fibers should high tensile strengths � Base on diameter and character, fibers are grouped into � whiskers fibers wires

Fiber phase Whiskers Very thin single crystals having extremely large length-to-diameter ratios � Single cristals � high degree of crystalline perfection � virtually flaw free, which accounts for their exceptionally high strengths � the strongest known materials. In spite of these high strengths � not utilized extensively as a reinforcement medium (extremely expensive). � Idifficult and often impractical to incorporate into a matrix.

Fiber phase Whiskers Typical material: � graphite � silicon carbide silicon nitride aluminum oxide

Fiber phase Fibers Small diameters In Polycrystalline or amorphous phase Polymers or ceramics polymer aramids glass carbon boron aluminum oxide silicon carbide

Fiber phase Fibers

Fiber phase Fibers Glass Fibers � ASTM C 162 classification according to the end use and chemical compositions E (Electrical) Low electrical conductivity S (Strenth) High stregth C (Chemical) High chemical durability M (Modulus) High stiffness A (Alkali) High alkali or soda lime glass D (Dielectric) Low directric constant � Glass is a good impact resistant fiber but weighs more than carbon or aramid � Glass fibers have excellent mechanical characteristics � The lower modulus requires special design treatment where stiffness is

Fiber phase Fibers Carbon Fibers � Made from organic precursors, including PAN (polyacrylonitrile), rayon, and pitches � Offers the highest strength and stiffness of all the � reinforcement fibers � Can cause galvanic corrosion when used next to metals � High temperature performance � Graphite technically refers to fibers that are greater than 99 percent carbon composition � Carbon fiber composites are more brittle than glass or aramid.

Fiber phase Fibers Aramid Fibers (Polyaramids): � Offer good mechanical properties at a low density toughness damage/impact � Are resistance. insulators of both electricity and heat � Are resistant to organic solvents, fuels and lubricants � Aramid composites are not as good in compressive strength as glass or carbon composites. � Dry aramid fibers are tough and have been used as cables or ropes � Kevlar® is the registered trademark for a para-aramid � Synthetic fiber

Fiber phase Fibers reinforcement forms Multi-End Single-End Prepreg Milled

Fiber phase Fibers reinforcement forms Unidirection al Mats Veils & Woven, stitched Braided & 3 -D

Fiber phase Wires � � � relatively large diameters comparing with fibers steel, molybdenum, tungsten Application automobile tires filament-wound rocket casings wire-wound high-pressure hoses

Matrix phase Matrix material : metal, polymer, or ceramic � � Metals and polymers have suitable ductility Ceramic-matrix: improve fracture toughness of composite We will focus on polymer and metal matrices Roles of matrix phase fiber-reinforced composites � binds the fibers together � protects the individual fibers from surface damage mechanical abrasion or chemical reactions with the environtment � transmit and distribute externally applied stress to the fibers very small load proportion is sustained by the matrix phase matrix material should be ductile elastic modulus of the fiber should be much higher than that of the matrix surface flaws -> forming cracks -> failure at low tensile stress levels separates the fibers and prevents the propagation of brittle cracks from fiber to fiber

Matrix phase About failure � Total composite fracture will not occur until large numbers of adjacent fibers form a cluster of critical size � Adhesive bonding forces between fiber and matrix must be high to minimize fiber pull-out � Bonding strength is an important consideration in the choice � of the matrix–fiber combination � Adequate bonding is essential to maximize the stress transmittance from the weak matrix to the strong fibers

Polymer-matrix composites (PMCs) = polymer resin (matrix) + fibers as the reinforcement medium. Used in the greatest diversity of composite applications, as well as in the largest quantities � good properties in room-temperature properties ease of fabrication � low cost. Cassifications of PMCs according to reinforcement type � glass fiber-reinforced polymer (GFRP) � composites carbon fiber-reinforced polymer (CFRP) � composites aramid fiber-reinforced polymer

Polymer-matrix composites Polymer-matrix There are two major groups of polymer-matrix � thermosets � thermos plastics. Polymers � large molecules made up of long chains of smaller molecules or monomers Thermoset polymers � Used to make most composites � Converted from a liquid to a solid through a process called polymerization, or cross-linking. � Thermosets cross link during the curing process to form an irreversible bond.

Polymer-matrix composites Polymer-matrix Cured by the use of a catalyst, heat or a combination of the two �Once cured, solid thermoset cannot be converted back to their original liquid form. �Common thermosets are polyester vinyl ester epoxy polyurethane.

Polymer-matrix composites Polymer-matrix Thermoplastic polymers are not cross-linked § can be melted, formed, re-melted and re-formed. § characterized by materials such as § ABS § polyethylene § Polystyrene

Metal-matrix composites Metal-matrix composites (MMCs) The matrix is a ductile metal. alloys of aluminum alloys of magnesium The reinforcement may improve specific stiffness specific strength abrasion resistance polymermatrix composites higher operating temperatures nonflammability greater resistance to degradation by organic fluids alloys of titanium alloys of copper creep resistance thermal conductivity dimensional stability

Metal-matrix composites MMCs are much more expensive than PMCs The reinforcement may be in the form of � particulates � continuous fibers � discontinuous fibers � whiskers Automobile engine components � aluminum-alloy matrix reinforced with alumina and carbon fibers light in weight resists wear and thermal distortions

Ceramic-matrix composites Ceramic-matrix composites (CMCs) Ceramic materials are inherently resilient to oxidation and deterioration at elevated temperatures; Use in hightemperature and severe-stress applications � automobile engines � aircraft gas turbine engines. Fracture toughness values for ceramic materials are low. Ceramic-matrix composite materials have extended fracture toughnesses � by embedding fibers or whiskers of one ceramic material into a matrix of another ceramic

Hybrid Composites Hybrid obtained by using two or more different kinds of fibers in a single matrix Hybrids have a better all-around combination of properties than composites containing only a single fiber type. Most common system, both carbon and glass fibers are incorporated into a polymeric resin. The carbon fibers � strong � relatively stiff � provide a low-density reinforcement expensive

Hybrid Composites Glass fibers � inexpensive � lack the stiffness of carbon. The glass–carbon hybrid � stronger � tougher � higher impact resistance � produced at a lower cost than either of comparable all-carbon reinforced plastics comparable all-glass reinforced plastics

Manufacturing processes Manufacturing process types Open molding lay-up � spray-up � filament Winding � reinforced molding � hand Closed molding � vacuum bag molding � vacuum infusion processing � compression molding � pultrusion Prepreg reaction injection

Hand lay-up suitable for making a wide variety of composites production volume per mold is low simplest composites molding method, low cost tooling minimum investment in equipment Process • • • apply gel-coat with brush or soft roller for easy removal apply matrix resin with brush or roller cut the fit reinforcement layer lay-up the reinforcement consolidate with ribbed roller repeat 2. 3. 4. 5. until required thickness achieved cure the composite in an oven then cool to room temp.

Spray-up spray-up or chopping is similar to hand lay-up Process � the mould is waxed using gel-coat and polished for easy removal � the mixture of catalyst, resin and fiber is sprayed � a roller is used for compaction after each layer has been applied � the composite part is then cured in an oven and left to cool to room

Filament winding continuous fibers are positioned to form a hollow shape fibers (strands or tows) are fed through a resin bath continuously wound onto a mandrel is removed

Filament winding curing is carried out in an oven or at room temperature various winding patterns are possible to give the desired mechanical characteristics common filament-wound structures rocket motor casings

Vacuum bag molding General information improves the mechanical properties of open-mold laminates pressure inside the vacuum bag is reduced ->external atmospheric pressure exerts force on the bag � removes entrapped air � removes excess resin � compacts the laminate

Vacuum bag molding Process place vacuum bagging, a flexible film (PVA, nylon, mylar, orpolyethylene) over the wet lay up seal the edge of the bag over the mold in which lay up composite placed draw the air from the caity between the wet lay up and the bag eliminate voids force excess resin from the laminate

Vacuum infusion processing General information variation of vacuum bagging � resin is introduced into the mold after the vacuum has pulled the bag down � when the resin is pulled into the mold the laminate is already compacted no room for excess resin uniform degree of consolidation, producing high strength, lightweight structures

Vacuum infusion processing Process (1) coat the mold by gel-coat after the gel coat cures, place the reinforcement in the mold layer by layer place a perforated release film over the dry reinforcement position a flow media consisting of a coarse mesh or a “crinkle” position the perforated tubing as a manifold to distribute resin

Vacuum infusion processing Process (2) the vacuum bag is then positioned and sealed at the mold perimeter connect a tube between the vacuum bag and the resin container apply a vacuum to consolidate the laminate

Resin transfer molding General information resin transfer molding (RTM) resin is injected under pressure into a mold cavity producing parts with two finished surfaces part thickness is determined by the tool cavity

Resin transfer molding Process the mold is gel coated the reinforcement is positioned in the mold and the mold is closed and clamped the resin is injected under pressure the part is cured in the mold

Compression molding General information enables part design flexibility and features good surface finishes lower part finishing cost minimization of subsequent trimming and machining operations

Compression molding Process the mold set is mounted in a hydraulic or mechanical molding press a weighed charge of molding material is placed in the open mold

Pultrusion General information used for the manufacture of components having � continuous lengths � constant cross-sectional shape continuous and easily automated production rates are relatively high, making it very cost effective. wide variety of shapes are possible matrix materials include polyesters, vinyl esters, and epoxy

Pultrusion Process continuous fiber rovings, or tows impregnated with a thermosetting resin then pulled through a steel die (preforms to the desired shape and establishes the resin/fiber ratio) the stock then passes through a curing die (cure and impart the final shape) a pulling device draws the stock through the dies

Reinforced reaction injection molding reinforced reaction injection molding (RRIM) is an extension of reaction injection molding (RIM) in RIM two liquid components are pumped at high speed and pressures into a mixing head and then into a mold where the two components react to polymerize rapidly

Reinforced reaction injection molding advantages very fast cycle time polymerization shrinkage and thermal expansion are reduced droop and sag of the composite at elevated temperatures is minimized

Prepreg Concept continuous fiber reinforcement preimpregnated with a polymer resin being partially cured delivered in tape form to the manufacturer directly molds and fully cures the product without having to add

Prepreg production process collimating a series of spool-wound continuous fiber tows calendering process � tows are sandwiched and pressed between sheets of release and carrier paper using heated rollers the release paper sheet has been coated with a thin film of heated resin solution a “doctor blade” spreads the resin into a film of uniform thickness and width

Prepreg production process the final prepreg product � � thin tape consisting of continuous and aligned fibers embedded in a partially cured resin prepared for packaging by winding onto a cardboard core

Prepreg matrix and reinforcement at room temperature thermoset matrix undergoes curing reactions the prepreg is stored at 0 C (32 F)or lower the time in use at room temperature must be minimized

Prepreg matrix and reinforcement If properly handled, thermoset prepregs have a lifetime of at least six months and usually longer both thermoplastic and thermosetting resins are utilized carbon, glass, and aramid fibers are the common reinforcements

Prepreg composite fabrication lay-up the prepreg tape onto a tooled surface the lay-up arrangement may be unidirectional, cross-ply or angleply laminate final curing is accomplished by the simultaneous application of heat and pressure the lay-up procedure may be carried out by hand or by automated lay-up

Applications Aerospace Architecture Automotive Energy Marine Sport

Applications Aerospace

Applications Architecture Composites create a curved building under tight construction deadlines Information & shopping pavilion 475 -square-foot, curved building Process: Hand Lay-up Year: 2012 Washington, D. C. compositeslab. com

Applications Automotive

Applications Automotive

Applications Automotive

Applications Energy Wind turbines Composite wind turbines provide electricity that helps power monument 17 x 10. 5 -foot GFRP turbines Year: 2015 Process: Vacuum assisted resin transfer molding compositeslab. com

Applications Marine 53 -foot catamaran Sleek, lightweight catamaran is ready to travel the world Scope: CRFP hull Year: 2015 Volume: One custommade vessel Process: Vacuum infusion processing

Applications Sport Motorcycle racing helmet Thin, lightweight helmet reduces neck fatigue for riders Scope: CFRP helmet shell reinforced with carbon fiber fabric Year: 2015 Process: Bladder molding compositeslab. com