Quantitative Fracture Surface Analysis of Spheroidal Graphite Cast Iron by Run Length Statistics
Masahiro TAKANASHI, Kenta YAMAGIWA, Satoshi IZUMI and Shinsuke SAKAI
Abstract:Fractography is the most popular method for failure analysis. This method, however, has been mainly applied to structural steels, and has not been always effective to cast irons. Since many factors like graphite, matrix, cast defects, and so on affect fracture of cast iron, they made it difficult to estimate failure causes from the fracture surfaces. In this study, therefore, quantitative fracture surface analysis was carried out on spheloidal graphite cast iron to improve accuracy of the estimation. When fracture surface analysis is conducted on images obtained with scanning electron microscopes(SEM) that are commonly used in the failure analysis fields, the characteristic values extracted from the images can possibly depend upon the contrast of the images. To minimize the contrast influence, we proposed the fracture surface analysis method that edges are extracted from the SEM images by differentiating them and fracture surface analysis is conducted on the texture images. The proposed method was applied to the fracture surfaces formed by a fracture toughness test. By computing run length statistics which are parameters widely used in texture analysis, we could divide the fatigue fracture surface produced in introducing a pre-fatigue crack from the rapid fracture surface produced during the fracture toughness test. Key Words:Key words: Spheroidal graphite cast iron, Fractography, Fracture toughness, Texture analysis, Run length statistics