An experimental study has been made of the manner in which microfractures initiate and grow along adiabatic shear bands formed in the titanium alloy Ti–6AI–4V by the normal impact of hard steel spheres at velocities up to 340 m s−1. It is suggested that a critical shear strain must be exceeded along the shear bands for microvoids to nucleate, or to cause significant local thermal softening in the bands, leading to the formation of single voids or arrays of voids and smooth-sided cracks when the stress state became predominantly tensile. The final shape of the micro fractures within the shear bands and the morphology of the resultant fracture surfaces are explained in terms of the density of void nucleation sites and the tensile-stress state across the shear bands.
MST/179
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