Chapter 14 Flashcards
Define: PMC
A polymer matrix composite, consists of a polymer embedded with a reinforcing phase such as fibers or powders.
Define: FRP
Fiber Reinforced Polymers, Composites that can be designed with very high strength-to-weight and stiffness-to-weight rations.
Define: Roving
Similar to cloth, is a fabric consisting of untwisted filaments rather than yarns. Can be produced with unequal numbers of strands in the two directions so that they possess greater strength in one direction than the other.
Define: Cloth vs. Mat
Cloth: a fabric of woven yarns and most familiar form of continuous fiber
Mat: a felt consisting of randomly oriented short fibers held loosely together with a binder. Commercially available as blankets of various weights, thicknesses, and processes.
Define: SMC
Sheet Molded Compound; combination of Thermoset polymer resin, fillers, and other additives, and chopped glass fibers, all rolled into a sheet of typical thickness of 6.5mm. Most common resin is unsaturated polyester; Convenient for handling an cutting to proper size as molding charges.
Define: BMC
Bulk Molding Compound; consists of similar ingredients as those in SMC, but the compounded polymer is in billet form rather than sheet. Fibers in BMC are typically shorter
Define: Prepreg
Another prefabricated form of FRP shaping operations, consisting of fibers impregnated with partially cured thermosetting resins to facilitate shape processing. Available in the form of tapes or cross-plied sheets or fabrics.
Define: Contact Molding
Other names are “Open Mold Processes & Contact Lamination “f. Use of a single positive or negative mold surface to produce laminate FRP structures. Sometimes requires hand lay-up, spray-up, and automated tape-layering machines.
Define: Hand Lay-up
Oldest method of open mold shaping where:
1) Mold is cleaned and treated with a mold release agent
2) Thing gel coat is applied to become surface of molding
3) When gel coat sets, successive layers of resin and fiber added
4) The part is cured
5) Fully hardened part is removed from the mold.
Define: Wet. vs. Prepreg
Wet: where hand lay-up is done with a liquid resin that is applied and from there, the fiber mat or fabric is applied by hand rolling
Prepreg: Where impregnated layers of fiber reinforcement are first prepared outside the mold and then laid onto the mold surface, giving closer control over fiber-resin mixture.
Define: Spray-up
Form of open mold shaping in which liquid resin is sprayed onto an open mold. This spray gun has a chopper mechanism which cuts the filament rovings and adds them to the resin stream exiting the nozzle.
Define: Curing
Step required in all thermosetting resins usined in FRP laminated composites. Curign accomplishes cross-linking of the polymer, transforming it from its liquid condition into a hardened product. Either done at room temperature, in heated environment, or in an autoclave (giant oven).
Define: Autoclave
An enclosed chamber equipped to apply heat and/or pressure at control led levels. ex. Big oven for curing.
Define: Closed Mold Processes
Molding operation s performed in molds consisting of two sections that open and close during each modeling cycle. Advantages are good surface finish, higher production rates, closer control over tolerances, and more complex three-dimensional shapes.
Three classes: compression, transfer, and injection molding.
Define: RTM
Resin Transfer Molding; Refers to a closed mold process in which a preform mat is placed in the lower mold section, the mold is closed, and a thermosetting resin (polyester) is transferred into the cavity under moderate pressure to impregnate the preform. Sometimes called Resin Injection Molding.
