This set of Composite Materials Multiple Choice Questions & Answers (MCQs) focuses on “Incorporation of Fibers into Matrix”.
1. In ____________, the fibers and matrix are directly processed into the finished product.
a) compression molding
b) autoclave molding
c) pultrusion
d) bag molding process
View Answer
Explanation: In pultrusion, the fibers and matrix are directly processed into the final structure. While in all other processes, fibers are incorporated into the matrix to prepare ready to make sheets that can be stored and later processed to form laminated structures.
2. __________ are the thin sheets of fibers impregnated into a determined quantity of uniformly distributed polymer matrix.
a) Prepregs
b) Resins
c) Sheet molding compounds
d) Fillers
View Answer
Explanation: Prepregs can also be defined as the composite material in which fibers are reinforced to the thermoset or thermoplastic resin in a certain proportion. These prepregs are ready to make sheets which are stored and processed to form finished composite materials by different processes.
3. Prepreg sheets wider than 457 mm is called as ____________
a) broadgoods
b) widegoods
c) shortgoods
d) long-goods
View Answer
Explanation: Broadgoods are the fibre woven from fabric sheets which are wider than 457 mm and up to 1270 mm wide. It is usually furnished in rolls of 25 to 140 kg and may or may not be impregnated with resin and may or may not be impregnated with resin.
4. The SMC-R contains randomly oriented continuous fibers.
a) True
b) False
View Answer
Explanation: SMC-R sheets are manufactured on a sheet-molding compound machine. SMC-R, containing randomly oriented discontinuous fibers. The fiber content by weight per cent is usually represented by two-digit numbers after the letter R. For example, the fiber content in SMC-R30 is 30 weight per cent.
5. Resin content in commercially available prepregs is between _______ by weight.
a) 30% to 45%
b) 20% to 30%
c) 5% to 10%
d) 10% to 20%
View Answer
Explanation: Resin content in commercially available prepregs is between 30% and 45% by weight. A certain ratio between resin and reinforcement has to maintain since prepregs are to be stored for a long period and processed.
6. What is the normal shelf life for epoxy prepregs at room temperature?
a) 5 days – 10 days
b) 1 week – 2 weeks
c) 3 weeks – 8 weeks
d) 5 hours – 20 hours
View Answer
Explanation: Shelf length is the time duration that the epoxy prepregs can be stored without becoming unfit for the use or purpose. At 23°C, the normal shelf life of epoxy prepregs is 3 weeks to 8 weeks which can be prolonged up to 6 months if the temperature is set to -18°C.
7. ___________ are thin sheets of fibers compounded with a thermoset resin which are used primarily in the compression molding process.
a) Sheet molding compounds
b) Prepregs
c) Dough molding compounds
d) Plastic molding compounds
View Answer
Explanation: Sheet-molding compounds (SMC) are thin sheets of fibers compounded with a thermoset resin used primarily in the compression molding process. Polyesters and vinyl esters are the common thermoset resins for SMC sheets. The different types of sheet molding compounds are SMC-R, SMC-CR, XMC etc.
8. Which type of sheet molding compounds contains a layer of unidirectional continuous fibers on top of randomly oriented discontinuous fibers?
a) SMC-R
b) SMC-CR
c) XMC
d) SMC
View Answer
Explanation: SMC-CR contains a layer of randomly oriented discontinuous fibers and a layer of unidirectional continuous fibers on its top. The fiber contents are usually represented by two-digit numbers after the letters C and R. For example, the fiber contents in SMC-C40R30 are 40% by weight of unidirectional continuous fibers and 30% by weight of randomly oriented discontinuous fibers.
9. XMC contains continuous fibers arranged in an X pattern.
a) True
b) False
View Answer
Explanation: XMC is a trademark of PPG Industries, containing continuous fibers arranged in an X pattern, where the angle between the interlaced fibers is between 5° and 7°. It may also contain randomly oriented discontinuous fibers interspersed with continuous fibers.
10. What is the function of an additive in the formulation of sheet molding compounds?
a) To initiate the polymerization reaction
b) To prevent premature curing of the resin
c) To act as an internal lubricant
d) To reduce polymerization shrinkage
View Answer
Explanation: In the formulation of sheet molding compounds, the unsaturated polyester and styrene are polymerized together to form the polyester matrix. The low shrink additive, which is a thermoplastic polymer powder, serves to reduce the polymerization shrinkage.
11. The ___________ increases the viscosity of the compound without permanently curing the resin and thereby makes it easier to handle an SMC sheet before molding.
a) thickener
b) filler
c) mold release agent
d) catalyst
View Answer
Explanation: The thickener is a very important component in SMC formulation. By the thickening reaction, the compound becomes dry, nontacky, and easy to cut and shape. Another method of thickening is known as the interpenetrating thickening process (ITP), in which a proprietary polyurethane rubber is used to form a temporary three-dimensional network structure with the polyester or vinyl ester resin.
12. Which of the following compounds is not used as a thickener in SMC formulation?
a) MgO
b) Mg(OH)2
c) CaO
d) NaCl
View Answer
Explanation: The oxides and hydroxides of magnesium and calcium, such as MgO, Mg(OH)2, CaO, and Ca(OH)2 are the common thickeners used in SMC formulation.
13. Which of the following process is used for manufacturing XMC sheets?
a) Autoclave molding
b) Compression molding
c) Filament winding process
d) Pultrusion
View Answer
Explanation: XMC sheets are manufactured by the filament winding process. The continuous strand rovings are pulled through a tank of resin paste and are wound under tension around a rotating cylindrical drum. During the time of winding, chopped fibers which are usually 25.4 mm long, are deposited on the continuous fiber layer. After the desired thickness is obtained, the XMC sheet is formed by cutting the built-up material by a knife along a longitudinal slit on the drum.
14. Which of the following process is used to impregnate LARC-TPI?
a) Solution impregnation
b) Liquid impregnation
c) Hot-melt impregnation
d) Film stacking
View Answer
Explanation: Liquid impregnation uses low-molecular-weight monomers or precursors to coat the fibers. This process is commonly used for LARC-TPI and a few other thermoplastic polyimides.
15. Fiber mixing is possible only if the thermoplastic polymer is available in the filamentary form.
a) True
b) False
View Answer
Explanation: In case for PEEK and PPS, they are made into monofilaments with diameters in the range of 16–18 mm. Polypropylene (PP) and polyethene terephthalate (PET) fibers are also used in making commingled rovings and fabrics.
Sanfoundry Global Education & Learning Series – Composite Materials.
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