Automatic restraint and visual detection of fatigue crack growth by applying an alumina paste
A paste comprising fine alumina particles was applied on surfaces of steel plate specimens and a welded joint specimen, 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 charge coupled device (CCD) microscope and through various kinds of fractographic observations and elemental analyses using an scanning electron microscope (SEM) and an electron probe microanalyser (EPMA). As a result, the crack growth rate in the plate specimen was drastically retarded by the wedge effect of the alumina particles, and a 311% increase in failure life was produced on an average. The restraint of crack opening displacement (COD) value by the wedge materials was estimated by elastic finite element (FE) analyses, and the results were compared with the experimental data. Similar crack growth restraint effects were also observed on the welded joint specimen, producing a 117% increase in failure life. In the fatigue tests of the specimens on which the alumina paste was applied, a remarkable black colour developed in the white alumina paste along the paths of crack propagation, 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.
Keywords: alumina paste; crack closure; crack opening displacement; fatigue crack growth; fine particles; fractography; retardation; stress intensity factor; visual detection; wedge effect; welded joint
Document Type: Research Article
Affiliations: National Maritime Research Institute, 6-38-1 Shinkawa, Mitaka, Tokyo 181-0004, Japan
Publication date: 2007-09-01