Cracking in γ-TiAl due to high speed particle impact

Cracking due to small particle impacts on prospective γ-TiAl blades in jet turbine engines has been studied experimentally and theoretically. Flat rectangular specimens of two γ-TiAl alloys, with edges chamfered to resemble the taper of blades, were subjected to small particle impacts. The forms of damage observed resembled those revealed by earlier studies using specimens that were cast closely to the shape of blade leading edges. Numerical simulations of the impact events were carried out using finite element analysis, using uniaxial stress-strain behavior that was obtained in compression at high strain rates. A criterion for cracking is proposed that requires critical levels of plastic strain and tensile stress. Predictions of crack extent that were based on such a combined criterion were found to be in the range of observations. The predictive methodology, together with information on the fatigue strength of various damage states, potentially offers designers the opportunity to examine the risk associated with small particle damage on contemplated blades.