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It has been established that contrast in the elastic properties can lead to enhancement of fracture toughness in heterogeneous materials. Focussing on layered materials as a model system, we show that this enhancement is a result of two distinct phenomena – first, fluctuations in stress leading to regions where the stress intensity at the crack is considerably smaller than that of the macroscopically applied value; and second, the lack of stress intensity when a crack is at a compliant to stiff interface thereby requiring renucleation. Using theoretical, computational and experimental methods, we study two geometries – a layered material and a layered material with a narrow channel – to separate the two phenomena. The stress fluctuation is present in both, but renucleation is present only in the layered medium. We provide quantitative estimates for the enhanced toughness.

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Journal of the Mechanics and Physics of Solids

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