NUMERICAL MODELING OF DUCTILE CRACK-GROWTH IN 3-D USING COMPUTATIONALCELL ELEMENTS

This study describes a 3-D computational framework to model stable ext ension of a macroscopic crack under mode I conditions in ductile metal s. The Gurson-Tvergaard dilatant plasticity model for voided materials describes the degradation of material stress capacity. Fixed-size, co mputational cell elements defined over a thin layer at the crack plane provide an explicit length scale for the continuum damage process. Ou tside this layer, the material remains undamaged by void growth, consi stent with metallurgical observations. An element vanish procedure rem oves highly voided cells from further consideration in the analysis, t hereby creating new traction-free surfaces which extend the macroscopi c crack. The key micro-mechanics parameters are D, the thickness of th e computational cell layer, and f(0), the initial cell porosity. Calib ration of these parameters proceeds through analyses of ductile tearin g to match R-curves obtained from testing of deep-notch, through-crack bend specimens. The resulting computational model, coupled with refin ed 3-D meshes, enables the detailed study of non-uniform growth along the crack front and predictions of specimen size, geometry and loading mode effects on tearing resistance. here described by J-Delta a curve s. Computational and experimental studies are described for shallow an d deep-notch SE(B) specimens having side grooves and for a conventiona l C(T) specimen without side grooves. The computational models prove c apable of predicting the measured R-curves, post-test measured crack p rofiles, and measured load-displacement records.