Combined macroscopic and microscopic approach to the fracture of metals. Annual progress report, 1980-1981

Recent progress was achieved in refining and generalizing the methods previously developed for treating the stable crack growth problem, with particular attention to the approximate asymptotic solution of Rice, Drugan and Sham for stress and deformation fields near the tip of a growing crack. The microstructural aspects of ductile fracture were studied in dual-phase steels and high-strength 4340 steels. Very interesting results were obtained in the work on hydrogen effects in steels. In medium strength steels, the ductility-reducing effect of hydrogen is tentatively attributed to the accumulation of hydrogen at internal interfaces with a resulting loss in the resistance to interfacial separation. Extension of Needleman and Rice's work on the growth of cavities at elevated temperatures to the investigation of the effects of triaxial stressing relates the rate of void growth by grain boundary diffusion and dislocation creep to the triaxiality. It provides a good model to analyze the growth of macro-cracks in polycrystals by the mechanisms of growth and coalescence of micro-voids.