Crack front pinning

Fig. 13. Optical micrograph of fra-ture surface of glass-filled epoxy polymers showing the crack front pinned between glass particles 22) (Arrow indicates direction of crack growth)...

Figure 8.44. Crack front propagation slowed down by a pinning mechanism. [Adapted, by permission, from Azimi H R, Pearson R A, Hertzberg R W, J. Appl. Polym. Sci., 58, No.2, 1995,449-63.]...

Fig. 8.52 Breakaway position of crack front from 2 pairs of pinning positions, each separated by distance d. Distance between 2 arms of crack front anterior to each pinning position (indicated by 2 arrows) is hypothesized to control breakaway position because of overlapping stress field. Large arrow is direction of crack propagation [36], With kind permission of John Wiley and Sons...

It is interesting to observe that the crack front bores out between the domains, whilst still remaining pinned at all positions when it has encountered the particles (see Fig. 39). 

FIGURE 2.4 Schematic representation of the crack pinning-toughening mechanism. The propagating crack front bows out and pins at the particle sites. 

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