Abstract
Surface coatings have come into a wider use to increase an ability of machine elements such as a paper machine roll. These surface-coated rolls have been designed empirically, because no evaluation method of strength for coating films has been developed.
In this study, fatigue tests of chromium plated rolls were carried out under a contact loading condition and a fracture mode was investigated in detail to establish the evaluation method for coating film strength.
As a result, we found out that a coating film began to break in the axial direction, then number of cracks initiated, and after that, the surface film became to be in flakes. Also, we confirmed that a number of stress cycles to flake off depended on a thickness of the coating film, but a number of stress cycles to initiate a crack did not depend on it.
Then, to evaluate the dependence of the crack initiation on the coating film thickness, a stress analysis by FEM was performed. As a result, a tangential stress that must cause the cracking did not change remarkably when the coating film thickness was changed.
From the above mentioned facts, we considered that the cracking was caused by the fatigue of the compressive tangential stress.
