FINITE ELEMENT CALCULATION AND MEASUREMENT OF THERMAL STRESSES IN HIGH STRENGTH ALUMINIUM ALLOYS

Abstract

Thick parts of high strength aluminium alloys usually undergo a drastic quench which gives rise to thermal stresses and may cause distortion of products. The control of complex phenomena involved during quenching is achieved by determining the temperature distribution, thermal strains and residual stresses using the MARC finite element program. In this approach, the thermo-mechanical problem is assumed to be uncoupled, i.e. the thermal and mechanical calculations are solved consecutively. First a non-linear heat transfer analysis is performed taking into account the temperature dependence of the thermo-physical properties and transient conditions of convection at the surface of the plate. This is followed by a thermo-elasto-plastic stress analysis using the predicted temperature distributions, assuming an isotropic behaviour of the material and taking into account the temperature dependence of its mechanical properties. The calculation of thermal stresses occurring during cold and hot water quenching of a 70 mm thick plate of 7075 alloy using this method shows a good agreement between theoretical predictions and experimental values of residual stresses, as measured by a layer-removal method.