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Fracture Mechanisms in Nonmetals 269
FIGURE 6.11 Fracture surface of craze-crack growth in polypropylene. Photograph provided by Mr. Sun Yongqi.
The addition of rubbery second-phase particles to a polymer matrix significantly increases
toughness by making craze initiation easier [16]. The low-modulus particles provide sites for void
nucleation, thereby lowering the stress required for craze formation. The detrimental effect of the
dust particles is largely negated because the stress in the fibrils tends to be well below that required
for fracture. Figure 6.12 is an SEM fractograph that shows crack growth in a rubber-toughened
polymer. Note the high concentration of voids, compared to the fracture surface in Figure 6.11.
FIGURE 6.12 Fracture surface of a rubber-toughened polyvinyl chloride (PVC). Note the high concentration
of microvoids. Photograph provided by Mr. Sun Yongqi.
