CONICET | Buscador de Institutos y Recursos Humanos

When a crack is submitted to cyclic shear-mode loading, crack faces interference reduces the effective KII and often leads to deceleration and bifurcation. The nominal KII is thus not representative of the real displacement, stress and strain fields at the crack tip and the effective crack driving force has to be determined. The limitations of the method generally used in the literature to derive the effective stress intensity factor in mode II, allowance made for friction effects, from measured crack faces displacement are discussed, based on accurate measurements performed in a SEM during in situ Mode II fatigue crack growth tests on maraging steel, ferritic-pearlitic steel and TA6V. When crack tip plasticity is moderate (high yield stress, low KII), crack tip shielding by friction can be evaluated from the comparison of measured displacements with those predicted by LEFM, but when plasticity is important, it tends to make displacements larger than predicted by LEFM and to hide friction effects. To evaluate friction effects, measured displacements have to be compared with those obtained by elastic-plastic finite element simulations. Simulations combining friction and plasticity are performed to separate both effects. Elastic-plastic finite element simulations of mode II crack growth through periodic node release were also performed to check if friction-induced decrease in effective KII is the only reason for the deceleration of cracks or if stress/strain redistributions as the crack propagates through its plastic zone also play a role.

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