Modelling and simulation of dynamic fracture of a polycrystalline TiAl alloy under high velocity particle impact

Multi-phase polycrystalline TiAl alloys show complex fracture behaviour under high velocity particle impact (HVPI). The front-side damage and back-side crack networks are found to be microstructure sensitive, which implies that the local microstructure variations of this alloy may lead to unwanted blade failure during operation. Therefore, it is important to know how these microstructures influence crack initiation and crack propagation. To this aim in the present work a numerical modelling approach has been proposed that takes into account the microstructural statistics via polycrystal modelling, and a combined damage and fracture ansatz for impact fracture behaviour. The polycrystal models were generated using Voronoi cells considering grain aspect ratio and texture. The grain boundaries were modelled applying thin cohesive layers between grains. Two types of microstructures have been studied; one with globular grains and the other with elongated grains. The material data were obtained from detail experimental work [1]. The proposed approach allows a quantitative prediction of crack networks as observed by the experiments for different TiAl microstructures. Under dynamic impact, cracks mainly propagate through grain boundaries, which have been captured using cohesive damage model. It was found that for globular grains star-shaped crack network was formed and for the elongated grains the crack extends longitudinally. The length of the crack branches can be studied for varying damage parameters at the grain boundaries. This information is useful for further analysis of fatigue life and durability of the TiAl alloy