Growth fracturing

A void nucleation and growth fracture model embedded in a general viscoelastic-plastic material model is representative of approaches to ductile dynamic fracture (Davison et al., 1977 Kipp and Stevens, 1976). Other approaches include employing the plastic strain as a damage variable (Johnson and Cook, 1985) so that both spall and large strain-to-failure can be treated. 

Plastics are susceptible to brittle crack-growth fractures as a result of cyclic stresses in much the same way as metals. In addition, because of their high damping and low thermal conductivity, plastics are prone to thermal softening if the cyclic stress or cyclic rate is high. Examples of the TPs with the best fatigue resistance include PP and ethylene-propylene copolymers. 

Wei, R. P., The Effect of Temperature and Environment on Subcritical Crack Growth, Fracture Prevention and Control, ASM Materials/Metalworking Technology Series No. 3 (1974), 73. 

S. R. Choi, D. Zhu, R.A. Miller, High temperature slow crack growth, fracture toughness and room temperature deformation behaviour of plasma sprayed Zr02 8wt%Y203, Ceram. Eng. Sci. Proc., Vol. 19, 1998, 293 301... 

An additional issue in fiber strength is that of fatigue (22), which can produce delayed failure of a fiber. Fatigue is thought to be caused by a surface reaction of fiber and OH causing the growth of subcritical flaws to the point where fracture occurs. 

An attempt has been made to define a single critical value, like for brittle fracture, from these curves (5). However, the amount of crack growth which is used to define this critical value is inevitably rather arbitrary. A more recent approach (6) is to fit a power law curve of the form... 

The use of fatigue data and crack length measurements to predict the remaining service life of a stmcture under cyclic loading is possibly the most common application of fracture mechanics for performance prediction. In complex stmctures the growth of cracks is routinely monitored at intervals, and from data about crack growth rates and the applied loadings at that point in the stmcture, a decision is made about whether the stmcmre can continue to operate safely until the next scheduled inspection. 

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