Pressure-Shear Impact of 6061-T6 Aluminum

Experimental results are presented for impact of two parallel plates of 6061-T6 Aluminum, skewed at an angle of 26.6° from the axis of the projectile. A transverse displacement interferometer (TDI) [1] with a 200 lines/mm grating is used to monitor the transverse motion of the rear surface of the aluminum target plate. Two first-order diffracted laser beams are used for this TDI with a resulting sensitivity of 2.5 μm per fringe. In addition the normal motion of the rear surface is monitored simultaneously by means of a velocity interferometer [2] in which the zeroth-order diffracted beam is used as the beam reflected from a moving mirror. Comparison of the velocity-time profiles of the target rear surface with those predicted by the analysis given by Abou-Sayed and Clifton [17] indicates that the computed transverse velocity-time profiles have regions of steeper slope than observed in the experiments. This discrepancy appears to be mainly due to the inadequacy of the assumption of isotropic hardening and the Huber-Mises yield function in the analysis [17]. The sensitivity of the transverse velocity profiles to the plastic flow characteristics of the material suggests that the pressure-shear impact experiment, when used with a TDI, is a good technique for the study of material properties at very high strain rates (10⁴ ∼ 10⁵ sec⁻¹) and under postshock conditions.