An engineering component or structure is often designed with a specified reliability. This ensures the component to perform its intended function throughout the design life. The deterministic design approach employs nominal or mean quantities when comparing the calculated stresses against the strength of the material, with an appropriate factor of safety. However, the continuous pursuit towards design optimization calls for improved performance with lighter structures and known reliability. In this respect, the knowledge of the response of the materials to the operating load and environment is indispensable for safe operation of the structures. The mechanical response of the material consists of two aspects, namely the mechanics of deformation and the mechanism of the failure. While the mechanics of the deformation have been considered in the classical design methods, the mechanism of the failure should also be accounted for in view of the desired optimized design.