Analysis of high-strain-rate elastic-plastic crack growth

For crack-tip speeds which are even a modest fraction of the lowest elastic wave speed of a material, the strain rates that are induced at material points close to the crack tip are enormous. Experimental evidence is available which suggests that the flow stress is a fairly strong function of plastic strain rate at the rates anticipated. An approximate analysis of the high-strain-rate crack-growth process has been developed on the basis of this observation, which is interpreted as implying that the elastic strain rates dominate the plastic strain rates. The features of the approximate analysis are reviewed, and the results of more recent complete numerical analysis of the same crack-growth model are described. Using the growth of a macroscopic cleavage crack in mild steel as a vehicle for discussing the model, it is found that the approximate model appears to capture the essence of the process for those temperatures at which cleavage crack growth is supported. The numerical results indicate deficiencies in the approximate analysis for higher temperatures.