FRACTURE-BEHAVIOR OF CVD SIC-COATED GRAPHITE .2. CONDITIONS FOR THE ONSET OF MULTIPLE CRACKING

Crack arrest and multiple cracking can be observed during the fracture of coated substrates even in the absence of coating delamination. Cle arly, it would be useful to understand the mechanics and material para meters that control this process. The conditions for the arrest of the initial crack were modeled using an approximate stress intensity fact or approach, and it was determined there is a critical coating thickne ss, below which the multiple cracking occurs. The critical thickness w as determined to depend on the coating strength, substrate toughness, and the relative Young's moduli of the coating and the substrate. The effects of these parameters and residual stresses on the fracture beha vior are discussed. The results of the model are compared to the exper imental data on a SiC-coated graphite (sandwich composite).