Free-running fracture

As it is known [1, 2], the dilation concept of solid bodies fracture process assumes negative fluctuation density formation - dilaton, length of which is defined by phonons free run length A. In this case the overloading coefficient K on breaking bonds can be expressed as follows [3] ... 

It is by no means certain that the mechanism of fracture-induced decomposition reaction will be the same as that described for slow decomposition. For example, when the crack is running at its maximum velocity, chemical bonds are broken on a time scale comparable to that required for a bond to make one vibration. It can be imagined, therefore, that those bonds which are near their maximum amplitude of vibration when the crack approaches wiU be most likely to break, probably leaving the surface in a highly active state and producing free radicals in the gas phase. Such a process was envisaged by Taylor and Weale... 

After a run of nearly two years accident-free, a company employee slipped on a step and was unlucky enough to fracture a small bone in his foot. He was unable to work for several weeks and an LTI was recorded with a subsequent loss of safety awards to staff. At about the same time a container was dropped during an off-shore lifting operation. This latter incident had tremendous potential for injury but as luck would have it no-one was hurt. There is no doubt that the lifting incident was much more serious. 

In this case, cracks run along the interface between two materials due to interactions between the stress field in the adhesive layer and spatial variations in fracture properties. The cracks are not generally free to evolve as mode I cracks, as was the case for cohesive cracks, and mixed-mode fracture concepts (combinations of tension and shear) have to be considered. Mode II or shear components are induced, even in what appear to be nominally mode I loadings, due to differences in moduli about the interface. Again, if the presence of the adhesive layer is being ignored and the adherends are dissimilar, then a crack appears to be adhesive (i.e. an adhesion failure) on the macroscopic scale. 

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