Abstract
The authors have reported in the previous paper that the brittle coatings may break when the maximum principal strain exceeds a critical value and the cracks may spread perpendicularly to the principal strain.
The elastic constant and Poisson's ratio of coating are different from those of the base material; therefore, the stresses in the coating and those of the surface of specimen are different even when subjected to the same deformation. Standing on such a point of view, the law governing the fracture of coating is necessary to be strictly investigated. The relations of the stress and strain of coating to those of the base material are considered. Utilizing this relation, it has been explained by the experiments of the specimens with a uniaxial and a biaxial stress distribution whether of a few general laws of fracture should be applied.
By this experiment, the authors have found that the law of fracture based on the maximum principal strain can be applied with enough accuracy.
