Mesoscopic modeling of crack arrestor delamination in Al-Li: primary crack shielding and -stress effect

摘要

This work explores the effects of grain orientation and T-stress on crack-front shielding and delamination cracking in modern aluminum-lithium alloys. In the crack-arrestor configuration of interest here, a primary crack extends through the grain thickness while triggering delaminations over susceptible grain boundaries that lie normal to the plane of the primary crack. A three-dimensional, small-scale-yielding framework that employs a gradient-enhanced, crystal plasticity material model reveals key features of the strain/stress fields in a simulation of pancake-shaped grains with alternating orientation near a primary crack front. The alternating grain configurations exhibit a soft/stiff behavior and alternating out-of-plane, L-T shear stress-effects observed in recently-published experiments completed by the authors and others on various Al-Li alloys. Both texture effects contribute to highly localized driving forces for delamination cracking while concurrently shielding the primary crack. Moreover, texture does not act to shield the arrestor delamination planes, thereby favoring arrestor delamination development over primary crack growth. A compressive T-stress further enhances shielding of the primary crack-a result which aids in understanding marked differences in observed fracture behavior of tested M(T) and C(T) specimens of Al-Li alloys.