Interpretation of Craze Propagation and Breakdown

The foregoing discussion on the phenomenology of craze initiation has also given a molecular interpretation of the propagation of an individual craze. Taking into consideration the formation of many crazes either simultaneously, or in sequence, a particular craze grows through  

There are three aspects of craze propagation which will be discussed at this point the kinetics of craze growth, the stress at the craze-matrix interface (region C in Fig. 9.13), and the craze breakdown. 

Another method, Knight s analysis of stress distribution along a craze, has been used in a number of investigations (cf. [76, 77]). Verheulpen-Heymans [157] quite recently pointed out, however, that the — mostly unknown — rheological behavior of craze material and of the craze tip zone has such a strong effect on the calculated stress field that at the present time the results of this method cannot be interpreted unambigously. 

Using holographic interferometry Peterson et al. [148] determined the distribution of the incremental stresses caused by a strain increment applied to a craze in PC. At low prestrains (1.3—1.7%) they observed that the craze material near the tip of the craze actually supported a stress increment AcTy well in excess of the average stress increment Auy (Aoy/Aoy equal to 1.2 to 1.45). The peaks in the stress increments occurred at a distance of 0.2 to 0.4 of the craze length behind the craze tip. 

In their photoelastic studies of PMMA and PC crack tips Narisawa et al. [127] noted high stress concentrations just before the initiation of a craze and very modest stresses 60 min later. No noticeable new stress concentration appeared at the craze tip. 

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