27
1
7. Strands of glass and carbon fibers are called roving and tow,
respectively.
8. Composite materials are porous and have breathability.
9. It is impossible to produce composite free of voids or
defects.
10. Most polymers are susceptible to UV degradation.
11. Polyester matrix-based composites are the most UV
resistant.
12. Failure in composites initiates from microcrazing or
microcracking of the matrix.
Exercises
1. What is processability? What do you understand about the processability of composites?
2. Why is the dimensional stability of a twill or satin weave less
than a plain weave?
3. Why are satin weave fabrics having a harness more than 8 not
commercialized in composite industries?
4. What are the weaves or pattern of reinforcement to be selected
for fabrication of (a) composite boat hull, (b) composite nose
cone of aircraft, (c) composite water storage tank, and (d) composite pole/mast? Give reasons for your selections.
5. Calculate the weight percentage of the reinforcement and
matrix for (a) glass fibre-reinforced epoxy composite and (b)
carbon fibre-reinforced epoxy composites. Densities of glass
fibre, carbon fibre, epoxy resin, and polyester resin are 2.54 g/
cm 3 , 1.8 g/cm 3 , 1.2 g/cm 3 , and 1.5 g/cm 3 , respectively.
6. What should be the critical length of carbon fibre in a short carbon fibre-reinforced bismaleimide composite? The diameter of
carbon fibre is 7 μm.
7. What is the failure mechanism in polymeric composites? What
are the common defects in composites?
8. Calculate the processability factors for a sisal fibre-reinforced
rosin gum natural composite made using a hand layup process.
The processable constant of the composite is 0.5. The entropy
of this natural composite is 0.1 joules.
9. Calculate the processability constant of an injection moulded
E-glass-reinforced nylon composite part. The processability factors, C f and P f , are 1.0 each. The value of entropy is 0.2 joules.
10. What is the effect of water on composites? Explain the effect of
water on a glass fibre-reinforced polyester composite.
11. What are the frequencies of light that affect composites? What
chemical changes occur in composites when exposed to UV
radiation?
12. What is the role of anisotropy of a composite in its thermal
behaviour? How do you use anisotropy in design to take the
advantage of thermal response of the composite?
13. What is the role of a matrix in a composite? How do you select a
matrix for a composite?
1.7 · Properties of Polymeric Composites
1
7. Strands of glass and carbon fibers are called roving and tow,
respectively.
8. Composite materials are porous and have breathability.
9. It is impossible to produce composite free of voids or
defects.
10. Most polymers are susceptible to UV degradation.
11. Polyester matrix-based composites are the most UV
resistant.
12. Failure in composites initiates from microcrazing or
microcracking of the matrix.
Exercises
1. What is processability? What do you understand about the processability of composites?
2. Why is the dimensional stability of a twill or satin weave less
than a plain weave?
3. Why are satin weave fabrics having a harness more than 8 not
commercialized in composite industries?
4. What are the weaves or pattern of reinforcement to be selected
for fabrication of (a) composite boat hull, (b) composite nose
cone of aircraft, (c) composite water storage tank, and (d) composite pole/mast? Give reasons for your selections.
5. Calculate the weight percentage of the reinforcement and
matrix for (a) glass fibre-reinforced epoxy composite and (b)
carbon fibre-reinforced epoxy composites. Densities of glass
fibre, carbon fibre, epoxy resin, and polyester resin are 2.54 g/
cm 3 , 1.8 g/cm 3 , 1.2 g/cm 3 , and 1.5 g/cm 3 , respectively.
6. What should be the critical length of carbon fibre in a short carbon fibre-reinforced bismaleimide composite? The diameter of
carbon fibre is 7 μm.
7. What is the failure mechanism in polymeric composites? What
are the common defects in composites?
8. Calculate the processability factors for a sisal fibre-reinforced
rosin gum natural composite made using a hand layup process.
The processable constant of the composite is 0.5. The entropy
of this natural composite is 0.1 joules.
9. Calculate the processability constant of an injection moulded
E-glass-reinforced nylon composite part. The processability factors, C f and P f , are 1.0 each. The value of entropy is 0.2 joules.
10. What is the effect of water on composites? Explain the effect of
water on a glass fibre-reinforced polyester composite.
11. What are the frequencies of light that affect composites? What
chemical changes occur in composites when exposed to UV
radiation?
12. What is the role of anisotropy of a composite in its thermal
behaviour? How do you use anisotropy in design to take the
advantage of thermal response of the composite?
13. What is the role of a matrix in a composite? How do you select a
matrix for a composite?
1.7 · Properties of Polymeric Composites