Algorithm for three-dimensional analysis of cleavage facet and its application for brittle fracture surface of steels.

Abstract

Computer image processing technology has been applied to cleavage fracture surface analysis and the algorithm for the estimation of 3-dimensional cleavage facet boundaries and 3-dimensional facet areas has been developed. An angle αi, j between relative normal vectors of one mesh Pi, j and adjacent mesh plane Pi+1, j was calculated and the αi, j was compared to the threshold one αth. If αi, j is larger than αth and the αi+1, j calculated between the mesh planes Pi+1, j and Pi+2, j along X axis is smaller than αth, the Pi+1, j mesh plane was decided to be the facet boundary. The same calculation was continued along both X- and Y-axes and facet numbers being contained in the analyzed area were obtained. After the estimation of facet boundaries, 3-dimensional facet areas were calculated dividing by the 2-dimensional facet areas by cos βk which is the angle between average normal vector of facet and vertical vector. By this algorithm, the cleavage fracture surfaces were analyzed of JIS SS41 and HT80 steels and the effect of the threshold angles αth was discussed on the facet numbers estimated, the distribution of the values of α and the 3-dimensional facet areas. The method developed is very useful to analyze the cleavage facet size and to discuss the relationship between the cleavage fracture and microstructures of steels, such as ferritic grain size and prior austenitic grain.