Evaluation of Strain Controlled Fatigue and Crack Growth Behaviour of Al–3.4Mg Alloy

Abstract

Present study focuses on fatigue performance of Al–3.4Mg (AA5754) aluminium alloy. Fatigue crack growth (FCG) and strain controlled low cycle fatigue (LCF) tests are performed for as received and precipitation strengthened AA5754 alloy. Precipitation strengthening heat treatment (PSHT) process significantly alters the mechanical and fatigue strength of Al–3.4Mg alloy. Fatigue crack growth (FCG) test is performed at load ratio (R-ratio = Pmax/Pmin) of 0.1 and 0.5 using compact tension (CT) specimens. Strain controlled low cycle fatigue (LCF) tests are performed at 1.2 and 1.0% strain ranges. FCG test results depict that PSHT alloys offer higher resistance against crack growth and improvement in fatigue life. LCF test reveals the cyclic hardening behaviour for both as received and PSHT AA5754 alloys. Improvement in fatigue life at both strain ranges is observed for PSHT alloys. Numerical simulations for crack growth analysis are performed by using eXtended Finite Element Method (XFEM). Chaboche kinematic hardening model coupled with finite element method (FEM) is used to simulate the experimental hysteresis loops and fatigue life obtained during strain controlled LCF tests. The present study concludes that lower crack growth rate by FCG test and higher fatigue strength during LCF test is obtained for precipitation strengthened AA5754 alloy as compared with as received alloy. The crack growth simulations by XFEM have good convergence with experimental results. The simulations performed by kinematic hardening model have good agreement with experimental results.