Matrix Materials

Abstract

A brief description of the various matrix materials, polymers, metals, and ceramics, is given in this chapter. We emphasize the characteristics that are relevant to composites. The reader should consult the references listed under Further Reading for greater details regarding any particular aspect of these materials.

Problems

• 3.1. Ductility, the ability to deform plastically in response to stresses, is more of a characteristic of metals than it is of ceramics or polymers. Why?

• 3.2. Ceramic materials generally have some residual porosity. How does the presence of porosity affect the elastic constants of ceramic materials? How does it affect the fracture energy of ceramics?

• 3.3. Explain why it is difficult to compare the stress–strain behavior of polymers (particularly thermoplastics) with that of metals.

• 3.4. The mechanical behavior of a polymer can be represented by an elastic spring and a dashpot in parallel (Voigt model). For such a model we can write for stress

  $$ \sigma = {\sigma_{\rm{el}}} + {\sigma_{\rm{visc}}} = {E_{\varepsilon }} + \eta \,{\hbox{d}}\varepsilon /{\hbox{d}}t, $$

  where E is the Young’s modulus, ε is the strain, η is the viscosity, and t is the time. Show that

  $$ \varepsilon = \sigma /E\left[ {1 - \exp ( - E/\eta )t} \right]. $$

• 3.5. What is the effect of the degree of crystallinity on fatigue resistance of polymers?

• 3.6. Discuss the importance of thermal effects (hysteretic heating) on fatigue of polymers.

• 3.7. Glass-ceramics combine the generally superior mechanical properties of crystalline ceramics with the processing ease of glasses. Give a typical thermal cycle involving the various stages for producing a glass-ceramic.

• 3.8. Silica-based glasses and many polymers have amorphous structure. An amorphous structure is characterized by a glass transition temperature. Explain why silica-based glasses have a much higher glass transition temperature than polymers.