Following our innovative experimental spontaneous fracture models for frictional fractures (compression and shear) and mixed-mode fractures (tension and shear) in identical materials, we designed a laboratory model to investigate the effects of material contrast on mixed-mode spontaneous fracture along a bimaterial interface. A series of interesting phenomena are observed, including asymmetry of crack propagation, with different speeds and levels of fracture parameters. Crack tips fracture

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... eters are observed to depend on crack speeds, on far-field loading, and on far-field mode-mixity. A strong dependence is also identified between mode-mixity and crack length. Most importantly, the fracture parameters are found to exhibit a strong dependence upon crack length and only a weak dependence on crack speed as is commonly thought. These observations are discussed in details in relation to material contrast. It is expected that these observations will have a profound influence on engineering practice involving the application of materials and structures with bimaterial interfaces.