Polymer Matrix Composite

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Polymer Matrix. Polymer reinforced composites can be classified to: Thermosetting or thermoplastic composites. Thermoplastic advantages: ▫ No cure.
Polymer Matrix Composite A polymer matrix composite (PMC) is a composite material consisting of a polymer imbedded with a reinforcing phase such as fibers or powders The importance of PMC processes derive deri e from the growing use of this class of material, especiall fiber-reinforced especially fib i f d polymers l (FRPs) – FRP composites can be designed with very high strength to weight and modulus-to-weight strength-to-weight modulus to weight ratios – These features make them attractive in aircraft, cars, trucks boats, trucks, boats and sports equipment

Categories of FRP Processes  Open mold processes - some of the original FRP manuall procedures d for f laying l i resins i andd fibers fib onto t forms  Closed mold processes - much the same as those used in plastic molding pp in  Filament windingg - continuous filaments are dipped liquid resin and wrapped around a rotating mandrel, producing a rigid, hollow, cylindrical shape  Pultrusion P lt i - similar i il to t extrusion t i only l adapted d t d to t include continuous fiber reinforcement

Classification of FRP Processes

Polymer Matrix Polymer reinforced composites can be classified to: Thermosetting or thermoplastic composites. Thermoplastic advantages:  No cure  Reprocessing possible  Fewer health risks due to chemicals during processing  Thermal shaping possible  Low moisture content  High toughness  High environmental tolerance Disadvantages: High viscosity, limitation in processing methods

Polymer Matrix  Thermosetting (TS) polymers are the most common matrix materials  Principal TS polymers are: Phenolics Ph li – usedd with ith particulate ti l t reinforcing i f i phases Polyesters P l t andd epoxies i - mostt closely l l associated i t d with FRPs  Thermoplastic molding compounds include fillers or reinforcing agents

Fibers as the Reinforcing Phase  Common fiber materials: glass, carbon, and Kevlar ( polymer) (a l )  In some fabrication processes, the filaments are continuous, i while hil in i others, h they h are chopped h d into i short lengths – In continuous form, individual filaments are usually available as rovings - collections of untwisted continuous i strands, d convenient i form f for f handling h dli – By contrast, a yarn is a twisted collection of filaments

Fibers as the Reinforcing Phase • The most familiar form of continuous fiber is a cloth - a fabric of woven yarns y • Similar to a cloth is a woven roving, a fabric consisting of untwisted filaments rather than yarns y – Woven rovings can be produced with unequal numbers of strands in the two directions so that they possess greater strength in one direction – Such unidirectional woven rovings are often preferred in laminated FRP composites

Mats and Preforms as Reinforcements Fibers can also be in a mat form - a felt consisting of randomly d l oriented i t d short h t fib fibers h held ld lloosely l together with a binder – Mats are commercially available as blankets of g , thicknesses,, and widths various weights, – Mats can be cut and shaped for use as preforms in some off th the closed l d mold ld processes

Prepregs Fibers impregnated with partially cured TS resins to facilitate shape processing  Available as tapes p or cross-plied p sheets or fabrics  Curing is completed during and/or after shaping  Advantage: prepregs are fabricated with continuous filaments rather than chopped random fibers, thus i increasing i strength t th andd modulus d l

Open Mold FRP Processes 1. Hand lay-up Spray-up y up 2.. Sp 3. Vacuum Bagging – uses hand-lay-up, uses atmospheric p ppressure to compact p laminate. 4. Automated tape-laying machines The differences are in the methods of applying the laminations to the mold,, alternative curingg techniques, and other differences

Hand lay-up Method Open mold shaping method in which successive layers of resin and reinforcement are manually applied to an open mold to build the laminated FRP composite structure  Oldest open mold method for FRP laminates, dating to th 1940s the 1940 when h it was first fi t usedd for f boat b t hulls h ll  Labor-intensive  Finished molding must usually be trimmed with a power saw to t size i outside t id edges d

Open Mold FRP Processes Hand lay-up

Hand lay-up (1) mold is treated with mold release agent; (2) thin gel coat resin) is applied, to the outside surface of molding; (3) when gel coat has partially set, layers of resin and fiber are applied applied, the fiber is in the form of mat or cloth; each layer is rolled to impregnate the fiber with resin and remove air; (4) part is cured; (5) fully hardened part is removed from mold.

Hand lay-up Generally large in size but low in production quantity not economical for high production Applications:  Boat hulls  Swimming pools g props p p  Movie and stage  Other formed sheets g molding g ever made was ship p hulls for the The largest British Royal Navy: 85 m (280 ft) long

Hand lay-up Generally large in size but low in production quantity not economical for high production

Spray-Up Method Liquid resin and chopped fibers are sprayed onto an open mold to build successive FRP laminations Attempt to mechanize application of resin resin-fiber fiber layers and reduce lay-up time Alternative for step (3) in the hand lay-up procedure

Spray-Up Method

P d t Made Products M d by b S Spray-Up U  Boat hulls, bathtubs, shower stalls, automobile and truck body parts, recreational p , furniture,, large g structural ppanels,, and containers. vehicle components,  Movie and stage props are sometimes made by this method

Bag Molding Bag Molding is conducted by laying up the laminae in the mold and cover them by flexible diaphragm and cured with heat and temperature. It is divided into three types:

Vacuum bag Pressure Bag Autoclave

Bag Molding

General Processes of bag molding

Bag g Moldingg

Vacuum Bagging gg g

 Use atmospheric pressure to suck air from under vacuum bag, to compact composite layers down and make a high quality laminate .  Layers from bottom include: mold, mold release, composite, peel-ply, breather cloth, vacuum bag, also need vacuum valve, sealing tape.

V Vacuum b bagging i d details il

Although, thermoplastic prereg requires only contact pressure for consolidation, many times higher consolidation pressures than for thermosets are specified. This is to ensure that the higher viscosities associated with thermoplastics do not prevent complete consolidation.

Vacuum Bagging Advantages of vacuum bag: It needs simple p equipment. q p Suitable for large parts and complex shape.

Problems: It depends on the worker skill in laying up and bagging. Bag leaks. Leaks occur at sealant bag film interface or the result of film failure due to improper handling.

Filament Winding Resin-impregnated continuous fibers are wrapped around a rotating mandrel that has the internal shape of the desired FRP product; the resin is then cured and the mandrel removed .  The fiber rovings are pulled through a resin bath immediately before being wound in a helical pattern onto the mandrel .  The operation is repeated to form additional layers, each having a criss-cross pattern with the previous, until the desired part thickness has been obtained.

Filament Winding

The mandrel design and materials have a great importance. The mandrel construction can be simple or sophisticated depending on weight, shape, finish and production vol. finish, vol Bad design leads to fiber damage and excessive residual stresses. stresses The mandrel material can be wood, cardboard tubes, blow molded thermoplastic, Al, steel..

Filament Winding

Schematic representations of helical, circumferential, i f ti l andd polar l filament fil t winding techniques

Filament Winding

Schematic representations polar filament winding techniques

Filament Winding

A large multi spindle filament winding i di machine. hi

Tabletop filament winding machine.

Filament Winding Process for Producing Metal Matrix Composite (MMC) Pressure Vessels

A high-strength, impact-resistant composite Left: Metal Matrix Composite Cylinders Produced Using Filament Winding Process. Right: Metal Matrix Composite Cylinder with Integrally Wound Domes.

storage tank material is needed that overcomes leakage problems without resorting to a liner. This process can be used to produce storage tanks that are affordable, impermeable, tough, p and maintain. and easyy to repair Potential applications include the containment of corrosive fluids, and solid rocket motor cases.

Pultrusion Continuous fiber rovings are dipped into a resin bath and pulled through a shaping die where the impregnated resin cures

 The sections produced are reinforced by continuous fibers  Like extrusion, the pieces have a constant cross section (e.g. I- section, pipe, round, plate…) whose profile is determined by the shape of the die opening  The cured product is cut into long straight sections

Pultrusion

Schematic of pultrusion equipment that uses die forming and microwave curing

Prepregs Fibers impregnated with partially cured TS resins to facilitate shape processing – Available as tapes or cross-plied sheets or fabrics – Curing is completed during and/or after shaping

Advantage: prepregs are fabricated with continuous filaments rather than chopped random fibers, thus i increasing i strengthh andd modulus d l

Prepregs

Schematic diagram illustrating the production of prepreg tape using a thermoset polymer. polymer

Pulforming Pultrusion with additional steps to form the length into a semicircular contour and alter the cross section at one or more locations along the length  Pultrusion is limited to straight sections of constant cross section  There is also a need for long parts with continuous fiber reinforcement that are curved rather than straight and whose cross sections may vary throughout length  Pulforming is suited to these less regular shapes

Pulforming

Pulforming process (not shown in the sketch is the cut cut-off off of the pulformed part).

Closed Mold Processes Performed in molds consisting of two sections that open and close each molding cycle. cycle Tooling cost is more than twice the cost of a comparable open mold due to the more complex equipment required i d in i these th processes Advantages of a closed mold are:  Good finish on all part surfaces. surfaces  Higher production rates.  Closer control over tolerances  More complex three-dimensional shapes are possible

Injection Molding

Injection molding is noted for low cost production of plastic parts t in i large l quantities titi . • Although most closely associated with thermoplastics, the process can also be adapted to thermosets. • It is the most widely used process for discontinuous reinforcement (particles, whisker, and chopped fibers) of thermoplastic. thermoplastic

The mixed pellets of matrix and reinforcement are softened by h ti andd mixed heating i d in i an extrusion t i type t screw. The mixture is forced under high injection pressure from a screw into a cooled and pressure clamped mold where it solidify to the desired shape. The finished part is ejected from the mold. The runner and sprues are cut and remolded. remolded

The reciprocating-screw injection system

Injection Molding Limitation: 1. The reinforcement size is limited by the gate dimensions and must not be larger than the gate diameter. 2. The amount of the reinforcement is also limited to 30-40 wt %, because the presence of the reinforcement i f t causes flow fl restrictions. t i ti

Extrusion  This process is used for high volume production of uniform if cross section ti parts. t  It is similar to injection molding but with larger equipment.  The main differences are the extrusion pprocess is continuous so no check valve is required and the product forced through p g the die and cut to the required length rather than into a mold.