Fracture in glassy polymers involving crazing

A prominent mechanism of crack advance in flexible-chain glassy polymers is associated with crazing, where it has been amply demonstrated that the fracture-process zone at the tip of advancing cracks is composed of one or more crazes 

The insight into the sequential processes of material separation at a craze border leading to eventual fracture permits a relatively simple estimate of the work of fracture /f in a glassy polymer as the total plastic work involved in the production of craze matter of average thickness S at the stage of initiation of the final crack-propagation process. This gives 

This gives a critical mode I stress-intensity factor ic of fracture instability as 

6 Molecular-scission-controlled fracture of oriented semi-crystalline poiymers 

A unique feature of the fracture behavior of such polymers is its thermally assisted character as shown in Fig. 12.21 that gives the stress dependenee of the fracture time at temperatures of 153 K, 198 K, and 293 K for Nylon-6. The dependence shown in Fig. 12.21 has the signature of a kinetic process having the form of 

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