Dynamic Crack Growth Normal to an Interface in Bi-Layered Materials: An Experimental Study Using Digital Gradient Sensing Technique

Abstract

The dynamic fracture behavior of layered architectures is experimentally studied. Specifically, crack penetration, trapping, and branching at an interface are examined. A newly introduced optical technique called Digital Gradient Sensing (DGS) that quantifies elasto-optic effects due to a non-uniform state of stress is extended to perform full-field measurements during the fracture event using ultrahigh-speed photography. By exploiting the richness of two simultaneously measured orthogonal stress gradient fields, a modified approach for extracting stress intensity factors (SIFs) is implemented for propagating crack-tips under mixed-mode conditions. The method is first calibrated using a quasi-static experiment complemented by finite element simulations before implementing it for studying dynamic mixed-mode fracture mechanics of layered configurations. The layered systems considered consist of two PMMA sheets bonded using an acrylic adhesive with the interface oriented normally to the initial crack propagation direction. Interfaces are characterized as 'strong' and 'weak' by their crack initiation toughness. The dynamic fracture of monolithic PMMA sheet is also studied in the same configuration for comparison. The crack growth and fracture parameter histories of propagating cracks are evaluated. The interface is shown to drastically perturb crack growth behavior resulting in higher dissipation of fracture energy by exciting crack trapping, branching, and mixed-mode growth mechanisms.

Plastic mismatch effect on plasticity induced crack closure: Fatigue crack propagation perpendicularly across a plastically mismatched interface

“…Suresh et al conducted a pioneering work of fatigue crack propagation experiments with bi‐material specimens: the crack propagation rate increases (or decreases) when the crack approaches the interface from the stronger (or weaker) side. Similar conclusions were further confirmed by other experiments . In the numerical field, Wang et al simulate the fatigue crack propagation towards plastically mismatched interface with cohesive zone model, where the degradation of cohesive strength is load history dependent.…”

Full‐field measurement of contact‐point and crack‐tip deformations in soda‐lime glass. Part‐I: Quasi‐static Loading

“…Glass being a very brittle, low toughness material, the resulting angular deflections due to applied load are generally very small (a few micro‐radians). Hence, Δ needs to be increased significantly to accommodate for this, different from the assumption of Δ≪ L made by the authors’ in earlier investigations on polymers, and necessitates accounting for the perspective effect during analysis.…”

“…Williams’ asymptotic stress fields for angular deflections near a statically loaded mode‐I crack‐tip become, …”

“…The mode‐I SIFs can also be evaluated from the load history obtained from the load‐cell and the sample geometry as, …”

“…The presence of stress singularity at an impact point or a crack‐tip makes DGS highly effective not only for mechanical field measurements but for locating the stress risers. Authors have previously reported various studies on transparent polymers demonstrating the efficacy of DGS. The current work is an attempt to extend it to study extremely brittle material such as soda‐lime glass.…”