Effects of Stress Triaxiality and Lode Parameter on Ductile Fracture in Aluminum Alloy

Many theoretical and experimental studies showed that stress triaxiality has an important influence on ductile fracture. However, recent studies showed that Lode parameter, which can be linked to normalized third stress invariant, is also an essential factor. In the present study, round notched bar and flat grooved plate specimens made of 7075 aluminum alloy were used to assess the effect of stress triaxiality and Lode parameter on ductile fracture and on the corresponding microscopic mechanism. Quasi-static tensile tests and parallel numerical simulations were conducted to obtain stress triaxiality, Lode parameter and failure locus. A fractographic analysis was performed to determine the rules of void evolution under different stress states. The results show that stress triaxiality and Lode parameter have an important influence on failure strain. The effect of Lode parameter decreases with the increase in stress triaxiality. The fractographs show that the size of the void decreases with the increase of stress triaxiality, and the morphologies of the voids of different Lode parameters are obviously different. The nucleation rate and growth degree of secondary voids are also affected by Lode parameter. Copyright © 2019, Northwest Institute for Nonferrous Metal Research. Published by Elsevier BV. All rights reserved.