Damage in gamma titanium aluminides due to small particle impacts

Initiation of cracking due to small particle impacts on low ductility inter metallics is investigated experimentally and theoretically. The gamma titan ium aluminide alloys of interest which are being considered for elevated te mperature structural applications in aircraft engines exhibit tensile ducti lities on the order of 1-2%. Cracking due to any source, including small pa rticle impacts, is of concern given the rapid growth of cracks in fatigue. This investigation focuses on a model geometry which reproduces the rear fa ce cracking that is induced by a small particle impinging on an air foil le ading edge. Small steer spheres are projected onto thin plates at velocitie s ranging from 76 to 305 m/s; cracking is thereby induced on the rear surfa ce of the plates. Through finite element analyses of the dynamic impact eve nt and some analytical estimates, we examine the hypothesis that crack init iation due to small particle impacts can be correlated with material ductil ity and with the severity and spatial extent of the straining during the im pact event. In addition, with the use of static indentation tests in which similar strain distributions are present, some insight is gained into the d ifference in ductility between high and low strain rates. (C) 1998 Elsevier Science Ltd: All rights reserved.