Slow crack growth and fracture

Abstract

Fracture is usually identified as a ‘catastrophic’ event: under increasing load, an existing crack suddenly propagates rapidly and uncontrollably through the component (see Fracture Mechanics). However, in many polymers, and especially in thermoplastics, any cracking is usually seen after a long period of growth under constant or constantly-fluctuating stress (see Fatigue). The loading conditions which ultimately precipitate fracture may, therefore, be of much less practical importance than those during the preceding months or years of steady slow crack growth¹. Although slow crack growth also occurs in other classes of materials, the internal mobility of polymers makes them rather more susceptible, particularly in the presence of an active environment (see Environmental Effects).