Transverse fracture in multilayers from tension and line-wedge indentation

Crack propagation across laminated brittle solids from uniaxial tension or line-wedge loading is studied in real time using a model glass/epoxy architecture. The fracture progresses from one layer to the next via reinitiation from pre-existing flaws on the glass surfaces ahead of the primary crack in a process accompanied by some penetration through the interlayer but generally little or no delamination or deflection along the glass/epoxy interface. Depending on the system parameters, the material behind the crack front may be fully or intermittently severed. A 2D brittle fracture analysis is developed with the aid of the FEM technique taking into consideration stress gradients over flaws and flexure from contact loading. The analysis identified the flaw size and misfit in modulus, toughness and thickness between the layer and interlayer as the prime system variables. The results generally collaborate well with the experiments. Thick and compliant interlayers are generally advantageous except for contact loading, where they may promote crack reinitiation from the back surface of a layer. The explicit relations for crack penetration and reinitiation presented in this work facilitate convenient means for optimal design.