Abstract
Internal cracks in polymethyl methacrylate (PMMA) specimens were generated by pulsed laser light. The interactions of coplanar cracks, parallel cracks, and cracks in T and H configurations were investigated. The tensile strength of specimens with a single internal crack decreased with increasing crack size, and the strength correlated well with the initial crack and unstable crack size in the Griffith relationship. For specimens with coplanar and parallel cracks, the strength increased and decreased with the crack distance, respectively. For the T and H crack configurations, the presence of delamination cracks decreased the strength, and the reduction in strength became more significant when the crack distance was small. All fracture surfaces showed similar fracture morphology in the sequence of laser-generated crack, smooth fracture mirror, mist with hyperbolic markings, and rough hackle region with rib markings. Examination of the fracture surfaces revealed crack arrest by the delamination cracks in both T and H configurations, and crack bowing between delamination cracks in the H configuration. The propagating crack was eventually able to circumvent the delamination cracks. The experimental results are compared with the available theoretical analyses, and the relevance of the present study to the toughening of brittle materials is discussed.
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