Page 64 - Mechanical Behavior of Materials

64 Chapter 2 Structure and Deformation in Materials

affected by this; and if so, should it increase or decrease, and why? Also, answer the same
question for the elastic modulus.
2.10 In metals, grain size d is observed to be related to yield strength by

σ o = A + Bd −1/2

where A and B are constants for a given material. Does this trend make physical sense? Can
you explain qualitatively why this equation is reasonable? What physical interpretation can
you make of the constant A?
2.11 An important group of polymers called thermosetting plastics forms a network structure
by means of covalent bonds between the chain molecules. How would you expect these to
differ from other polymers as to the value of the elastic modulus and the resistance to creep
deformation, and why?
2.12 Consider creep by diffusion of vacancies in a polycrystalline metal or ceramic, as illustrated
in Fig. 2.26. Would you expect the resulting creep strain to vary with the crystal grain size of
the material? Do larger grains result in more rapid accumulation of creep strain, or in slower
accumulation of creep strain? Why?