Experimental analysis and constitutive modeling of anisotropic creep damage in a wrought age-hardenable Al alloy. (January 2022) - Naumenko, Konstantin
Abstract: Many components of aerospace and automotive engineering manufactured from forged age-hardening aluminum alloys operate at high temperature in the range 0 . 3 T m – 0 . 5 T m, where T m is the melting temperature. Experimental data for uni-axial creep on specimens sampled from a forged AA2014 alloy component show that inelastic strain rates depend significantly on the orientation of loading with respect to the material flow direction during the manufacturing stage. Based on the recently developed constitutive model of anisotropic creep, hardening/recovery, softening and overageing processes, this paper addresses experimental analysis and modeling tertiary creep regime up to the final stage of creep rupture. The emphasis is placed on the damage evolution equation in order to account for different damage mechanisms depending on the loading mode and loading direction relative to grain axis: cavitation on elongated grain boundaries as well as decohesions and microcracks around and inside coarse grain particles. Experimental data of creep strain rates for longitudinal and transverse loading directions at 130, 150 and 170 °C have been used to calibrate the model. The validation of the model was carried out by comparing experimental and modeled creep curves in the case of a 30°angle between the loading and the material flow direction during forging. The results show that the assumed damage mechanisms and the developed damage evolution equation are able to reflect both the anisotropic accelerated creep and the time to creep rupture for different stress levels and loading directions. Highlights: Principal damage mechanisms for the forged, age hardening AA2014 in the creep regime are identified. Tertiary creep stage is found to be controlled by overageing of θ ′ phase as well as damage processes including cavities, decohesions and microcracks. The composite type constitutive model is developed to account for stress redistribution among different microstructural regions. The model describes creep rates over the entire creep process. Time to creep fracture for different angles between the loading and the grain axis directions including 0°, 30°, and 90°is predicted with satisfactory accuracy.