Craze width growth

The craze just behind the tip, however, is only a few nanometers wide, whereas crazes typically can attain widths of a few micrometers or so before fracture. Clearly, while the craze tip advance mechanism is responsible for initially generating very short lengths of fibrils, most of the fibril structure is generated by the mechanism of craze width growth. Even the stress conditions at the craze tip can be dramatically altered by the widening of the craze well behind the tip if the craze continues to widen without the craze tip advancing, the stress at the craze tip will rise until the craze tip... 

In all papers mentioned above the characterization of the craze growth has been performed by measuring the craze length. By application of the optical interference method the essential information on the growth of craze width is awiilable. Figure 22 shows the interference fringe patterns and measured craze zone sizes at a stationary crack tip in PMMA loaded in a creep test at a constant K,-value at loading times of 150 s and 2 1(F s... 

Fig. 23a and b. Growth of a primary craze at a stationary crack tip in PMMA in air, K, = 19 N/mm a craze length s as a function of loading time t b maximum craze width 2v as a function of loading time t... 

In order to obtain information on the craze growth and on the fibrillation process the maximum craze widths are plotted against craze lengths s for high molecular... 

Fig. 52. Influence of AK, on craze widths 2v at the crack tip in PVC during discontinuous crack growth...

It should be noted that this growth behavior differs from that reported previously which showed a linear increase in a log-log-plot. In that and a subsequent paper the increase in craze length was assumed to occur without a significant increase im maximum craze width and the latter remaining well below the critical displacement at fracture. In Fig. 3.6 also the measured time-dependent behavior of maximum craze width 2v is shown. Contrary to the above assumption, the maximum craze width exhibits a dramatic growth, in reaching three times its critical value at fracture after times under load approaching 10 s (cf. 3.2). 

Figure 3.22 shows the maximum craze width 2v and the corresponding craze length s as functions of crack speed a in HMW and LMW PMMA. The crack speeds for the HMW material cover the complete range of slow crack growth, while LMW PMMA has been investigated only up to speeds around 10 mm/s... 

Fig. 4.19. Craze growth as function of loading cycles N between successive crack jumps in PVC at AK, = 0.6 MPa /m (craze length s and craze widths at the crack tip at upper (2v) and lower (2vp) load)...

In order to gain an insight into the deformation behavior of the fibrils in the craze and the time-dependence of the fibrillation process it is useful to examine the growth in the width and the length of the craze. 

Using the interference optical method craze growth in both dimensions, length and width, can be investigated. Figure 3.5 shows the interference fringe patterns and the evaluated craze contours at a stationary crack tip in PMMA of high... 

---