SHAPING PROCESSES FOR POLYMER MATRIX COMPOSITES AND RUBBER Flashcards
What are the principal polymers used in fiber-reinforced polymers?
Principal polymer matrices in FRPs are unsaturated polyesters and epoxies.
What is the difference between a roving and a yarn?
A roving consists of untwisted filaments, while a yarn consists of twisted fibers.
In the context of fiber reinforcement, what is a mat?
A mat is a felt consisting of randomly oriented fibers held loosely together in a binder.
Why are particles and flakes members of the same basic class of reinforcing material?
Flakes are simply particles that possess very low width-to-thickness ratios.
What is sheet molding compound (SMC)?
SMC consists of TS polymer resin, fillers, and chopped glass fibers, all rolled into a sheet of typical thickness = 6.5 mm (0.250 in).
How is a prepreg different from a molding compound?
Prepregs have continuous fibers rather than chopped fibers as in molding compounds.
Why are laminated FRP products made by the spray-up method not as strong as similar products made by hand lay-up?
Because in hand lay-up, orientation of the fibers is controlled; whereas in spray-up, the fibers in each layer are randomly oriented.
What is the difference between the wet lay-up approach and the prepreg approach in hand lay-up?
In wet lay-up, the layer of fiber reinforcement is placed into the mold dry, and the uncured resin is then applied to it to form the composite laminate. In the prepreg approach, layers of fiber preimpregnated with resin are laid into the mold.
What is an autoclave?
An autoclave is an enclosed chamber which can supply heat and/or pressure at controlled levels.
What are some of the advantages of the closed mold processes for PMCs relative to open mold processes?
The advantages of a closed mold are (1) good finish on all part surfaces, (2) higher production rates, (3) closer control over tolerances, and (4) more complex three-dimensional shapes are possible.
Identify some of the different forms of polymer matrix composite molding compounds.
PMC molding compounds include sheet molding compounds, thick molding compounds (a.k.a. dough molding compounds), and bulk molding compounds.
What is preform molding?
Preform molding is a compression molding process in which a precut mat is placed into the
lower half of a mold together with a charge of thermosetting resin; the materials are then pressed
between heated molds to cure the resin and produce a fiber-reinforced molding.
Describe reinforced reaction injection molding (RRIM).
RRIM involves the injection of resins that cure by chemical reaction together with
reinforcing fibers into a closed mold. The resulting part is a fiber-reinforced (usually glass fiber)
plastic molding.
What is filament winding?
Filament winding is a process in which resin-impregnated continuous fibers are wrapped
around a rotating mandrel with the internal shape of the FRP product; the resin is cured and the
mandrel is removed.
Describe the pultrusion process.
Pultrusion is a process in which continuous fibers are dipped into a resin and pulled
through a shaping die (somewhat like an extrusion die) where the resin cures. The resulting sections
are similar to extruded parts except that they are reinforced with continuous fibers.
