PREDICTING THE EFFECTS OF CRACK TIP CONSTRAINT ON MATERIAL RESISTANCE CURVES USING DUCTILE DAMAGE THEORY

— In recent years much interest has been focused on the geometry dependence of the resistance to stable ductile crack growth of engineering materials, and in particular, in explaining this in terms of “constraint” effects. This paper describes the results of work using the Rousselier ductile damage model in finite element studies to simulate the growth and coalescence of voids, and hence the mechanics of ductile crack growth, to predict the effect of constraint on resistance to fracture. Using the modified boundary layer solution, where constraint is controlled by the application of remote displacements, it was possible to simulate resistance curves for different constraint conditions. This has produced a “net” of resistance curves, within which the curve for any specimen geometry can be found from a knowledge of the crack tip constraint for that specimen. This has been tested by comparing the results with those obtained from two specimens for which the constraint conditions are known. Good agreement has been achieved. The results show that, although constraint has very little effect on conditions at the crack tip at initiation of crack growth, beyond that constraint plays an important part in defining the resistance curve. For low constraint geometries there is a very large loss in crack tip constraint which results in a large increase in the slope of the resistance curve. On the other hand, high constraint geometries exhibit very little dependence on crack tip constraint.