Alliage d’aluminium à haute résistance 2024-T351. Comportement plastique et élastoplastique en bout de fissure

Abstract

Crack closure occurs as a consequence of crack tip plasticity. For a fattigue crack partially or entirely closed, ductile materials always result in a plastic strain at the crack tip even under small amplitude loading. Many theoretical and experimental studies have been carried out to evaluate the size and shape of the plastic zone in particular for large scale yielding. However in the case of confined plasticity, i.e. under small scale yielding conditions where the size of the affected zone is very small, the researchers are faced with some difficulties to evaluate the plastic and elastoplastic behavior near in the crack tip.In this study, it is shown that a correlation of the results obtained by two different measurment techniques can help one to determine the evaluation of strains in the strongly deformed regions in the viscinity of the crack tip. For distances greater than 500 µm from the crack tip micro strain gages have been used to measure the strain rate evaluation for a high strength aluminum alloy, 2024 T351, tested under constant ΔK loading conditions. For smaller distances, an interferometric method is used to determine the size of the deformed zones and the deformation rate evolution. Some of the obtained results are comparred with a finite element estimation by Anquez of the deformation profiles near the crack tip.