Abstract
Combined axial-torsional testings were conducted using tubular specimens of stainless steel (SUS304), on which alumina was coated by the detonation method. In this investigation, two kinds of specimens with different thickness of ceramic coating were prepared, and the loading modes tested were three types of tension, torsion and combined loading. The fracture behaviors were observed by a plastic replication or a direct photography. In each case, the failure of ceramic coating was found to progress through three stages, which were identified as the initiation of small cracks almost vertical to the maximum principal stress direction, the extention of cracking with debonding around the cracking, and the falling-off.
The stress states in the ceramic-coated specimens under three loading conditions were analyzed by an elastic-plastic finite element method. The failure modes of ceramic coating were correlated with the maximum principal stress and the equivalent stress of the Mises type, which were calculated using the analytical results in the ceramic coating. The results indicated that the start or transition of each failure mode was explained by using the equivalent stress rather than the principal stress.
