Loading Conditions and Effects

However, the exponent, m, in ceramics is considerably larger than reported for metals, i.e., in the 21-42 range (as opposed to 2-4 for metals) and having constant C scales inverse to the fracture toughness. AK is the stress-intensity range of the applied stress with a cyclic frequency varying between 1-50 Hz using a sinusoidal wave  

S is the stress and the subscript, op, stands for the crack-opening stress. Another factor to consider is that of stress-intensity, AK, which is given as  

AKth is the threshold-intensity factor, AKjp is the intrinsic or basic stress intensity required for the extension of a crack opening and AK p is an additional crackopening stress intensity required to resist crack closure and maintain a fully opened 

In the Mg-PSZ, the transformation from the metastable tetragonal phase to the monoclinic phase absorbs part of the energy required for crack propagation with consequent increase in fracture toughness, manifested as crack-tip shielding. 

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