Experimental and computational study of the impact deformation of titanium Taylor cylinder specimens

Deformation twinning during impact - numerical calculations using a constitutive theory based on multiple natural configurations

“…The new grain size is computed based on the number of twins per grain that is determined experimentally by examining the front section of the projectile after impact. The discrepancies observed in the ®rst model decreased when deformation twinning was taken into account in the second model (see also Holt et al 1994 in the regard). It can be concluded from the work of Zerilli and Armstrong (1988) that twinning plays a signi®cant role in the modeling of impact problems.…”

“…Deformation twinning is a process by which, when the material is subjected to suf®ciently high loads, a part of a crystal may be induced to suffer a ®nite amount of simple shear across particular lattice planes in speci®c directions, these planes and directions being determined by the fact that the lattice of the product is the same as that of the parent but reoriented (see Srinivasa et al, 1997;Holt et al, 1994).…”

“…Such high strain rates are reached, for example, when a projectile is ®red onto a rigid plate. This method of subjecting materials to high strain rates is known as the Taylor impact test or Taylor anvil test.Numerical modeling of the behavior of projectiles under these conditions has attracted the attention of many researchers (Taylor 1948;Johnson and Cook 1983, 1985;Zerilli and Armstrong 1988;Jones et al, 1989;Holt et al, 1994). Most of the models neglect twinning and assume that slip is the only mechanism of inelastic deformation.…”

“…Zener and Hollomon (1944) examined the effects of strain rate and temperature on the stress-strain relation for metals undergoing slip. Based on their investigations, it is now well accepted that, for this mode of inelasticity, i.e., slip, the effect of high strain rate on the response of the material is similar to that which occurs at low temperature and at low strain rate.It has been observed (e.g., Zerilli and Armstrong 1988;Holt et al, 1994) that some materials (especially those with bcc or hcp structures) such as titanium, tantalum, depleted uranium etc., are capable of an entirely different mode of inelasticity, especially under high strain rates ± namely deformation twinning. Deformation twinning is a process by which, when the material is subjected to suf®ciently high loads, a part of a crystal may be induced to suffer a ®nite amount of simple shear across particular lattice planes in speci®c directions, these planes and directions being determined by the fact that the lattice of the product is the same as that of the parent but reoriented (see Srinivasa et al, 1997;Holt et al, 1994).…”

Thermomechanics of twinning from a parent to a twin with mirror image symmetry

“…It has been observed, see Madhava and Armstrong [12], Zerilli and Armstrong [22], Holt et al [7], that some materials (titanium, tantalum, iron and so on) have the ability to develop the inelastic behaviour not only by the slip mechanism, but also by deformation twinning. In Lapczyk et al [10] the deformation twinning is characterized like a process by which, when the material is subjected to sufficiently high loads, a part of a crystal may be induced to suffer a finite amount of simple shear across particular lattice planes in specific directions, these planes and directions being determined by the fact that the lattice of the product is the same as that of the parent but reoriented.…”