Abstract
A paste comprising fine alumina particles was applied on surfaces of steel plate specimens and welded joint specimens, and the effects of the paste on restraint and visual detection of fatigue crack growth were experimentally investigated by performing fatigue tests with in situ observations by a CCD microscope and through various kinds of fractographic observations and elemental analyses using a SEM (Scanning Electron Microscope) and an EPMA (Electron Probe Microanalyser). As a result, the crack growth rate in the plate specimen was drastically retarded by the wedge effect of the alumina particles, and 344% increase in failure life was produced. Similar crack growth restraint effects were also observed on the welded joint specimens, producing 117-175% increase in failure life. In the fatigue tests of the specimens on which the alumina paste was applied, remarkable black color developed in the white alumina paste along the paths of crack propagation, exceedingly facilitating the visual detection of the cracks. An analysis using an X-ray diffractometer showed that the black matter in the paste consists of fine debris derived from the base metal and the alumina particles.
