Combined macroscopic and microscopic approach to the fracture of metals. Annual progress report, 1983-1984

A finite element study of the strain hardening of a simple composite model was conducted which shows that the work hardening behavior can be understood by the effects of geometric and material properties on the development of slip regions. The fracture of dual-phase steels is now being treated theoretically by examining models for the description of the limits of ductilities in uniform elongation and post-uniform elongation. Detailed studies continue on the effects of tempering on aluminum and titanium-killed steels. A new correlation is shown between measured K/sub IC/ values and those calculated using our model based on a criteria of critical strains achieved over a critical distance, the former being identified with the measured plane strain ductility, the latter with the average particle spacing. Work on the role of hydrogen in the fracture of steels has been carried out on initially smooth and circumferentially notched specimens of a 1015 steel modified with Mn. Finite element studies of notched bend specimens have been carried out which exhibit the large strains and localized shearing modes in the highly deformed notch tip region often observed in high strength steels. In the case of fully plastic crack problems, we have given a concise derivationmore » of a volume integral expression for the local energy release rate that can be applied to three-dimensional as well as two-dimensional cracked bodies. Numerical results have been obtained that illustrate the computational advantage of this approach. We have obtained solutions in short crack and deep crack limits, which are of interest since the design life of a structure is generally estimated from short crack solutions while the fracture resistance (or creep crack growth rate) is typically determined from deep cracked specimens. Also, comparison of these solutions with known limiting solutions permits the accuracy as well as consistency of the numerical results to be assessed.« less