An observation on the roughening of the surfaces of rapidly growing cracks in brittle materials
Ben Freund (University of Illinois at U-C)
Eringen Medal Symposium in honor of G. Ravichandran
Mon 9:00 - 10:30
Salomon 001
The theory of dynamic fracture mechanics has been reasonably successful as a framework for characterization and quantitative analysis of rapid crack growth phenomena in both relatively brittle engineering materials and geological materials. The focus of the theory is on the phenomenon of growth of a single dominant crack through a nominally elastic material undergoing relatively small amplitude deformation. Nonetheless, the literature is replete with reports that the theory ``fails’’ for growth conditions involving very fast crack growth and/or extreme loading conditions. In fact, the reported deviations from the theory are most commonly the result of the system exhibiting behavior that departs from the range of behaviors over which that theory can be expected to be valid. Perhaps the most common examples of such behavior are multiple crack formation, non-planar growth, and large deformation. Over the years since dynamic elastic fracture mechanics has come into common usage, little progress has been made toward a mechanistic understanding of the reasons underlying these departures from the prevailing theory. Here, we seek a possible explanation for one of these deviations, namely, the transition from fracture advance as a dominant crack with a flat crack surface to growth with roughened, nonplanar crack surfaces on a small size scale. This is pursued on the basis of recent advances in understanding the influence of loading rate on the resistance of molecular/atomic bonds to forced separation. Examination of the statistics of the behaviour of many bonds being forcibly separated simultaneously leads to a constitutive description of forced separation of surfaces which may provide clues to the reasons underlying the onset of crack surface roughening during dynamic crack growth in a brittle material.