Dynamic Penetration and Bifurcation of a Crack at an Interface in a Transparent Bi-Layer: Effect of Impact Velocity

Abstract

Dynamic fracture behavior of layered PMMA sheets is studied using transmission-mode Digital Gradient Sensing (DGS) technique. DGS is a relatively new optical method that exploits elasto-optic effects exhibited by transparent solids allowing a direct quantification of two orthogonal in-plane stress gradients simultaneously and hence crack tip parameters when used to study fracture mechanics problems. The current work builds on authors’ previous two reports on this topic. Interfacial trapping, bifurcation and mixed-mode penetration into the second layer of a dynamically growing mode-I crack in the first layer encountering a normally oriented interface in a bi-layered configuration was reported in the first report [1]. In the second, the role of the location of a weak interface relative to the initial crack tip within the given geometry of the specimen was studied and interfacial penetration vs. bifurcation mechanisms was demonstrated and analyzed [2]. The current work focuses on the effect of impact velocity and the resulting loading rate on crack branching/penetration phenomenon when the mode-I crack encounters a normally oriented interface. In this ongoing work, a select location of interface relative to the initial crack tip is re-examined by varying the impact velocity. Using DGS for visualization and quantification, fracture mechanisms associated with crack growth are explained for the bi-layered system.