Impact-induced deformation mechanisms in unstrengthened and chemically strengthened glass bars

• Impact damage modes of unstrengthened and strengthened glass bars were examined.
• An overall energy balance was performed to identify key energy dissipation modes.
• Bar dilation, ejecta, frictional contact and elastic waves were major energy modes.
• Self-sustained fracture energy matched the computed residual tensile strain energy.
• Uniform dilation of the entire glass bar matched the residual compressive energy.

Ball impact experiments were performed on unstrengthened and chemically strengthened glass bars at impact velocities of 52–345 m/s. The damage characteristics were captured by high-speed imaging (up to 500,000 frames per second). It was found that the damage front propagation velocity, ejecta velocity, and radial bar dilation depth and velocity increased with increasing impact velocity (i.e., energy). Impact damage in the unstrengthened glass was constrained within a short distance from the impact-end, but the reflected tensile wave caused additional damage at the rear-end of the bar. In contrast, self-sustained damage propagation occurred along the entire length of the strengthened glass bar, which has been attributed to the stored tensile strain energy. Both glasses exhibited similar radial dilation over a finite length from the impact-end; however, an additional mode of uniform dilation over the entire bar length was observed in the strengthened glass. This behavior has been associated with stored energy release from the near-surface regions containing high residual compression. The increased fragmentation and uniform dilation in the strengthened glass bar is proposed to contribute to increased ejecta velocities and greater frictional contact between the ball (impactor) and the glass (target). It was determined that bar dilation, ejecta, frictional contact, and elastic wave propagation encompassed greater than 95% of the total energy dissipated.