疲労 回転曲げ疲労破面のＸ線フラクトグラフィ （第２報） 疲労破面の残留主応力とき裂進展方向

Abstract

X-ray fractography is a technique for analyzing the cause of fractures through the information obtained by irradiating X-ray on the fractured surface. The residual stresses or full widths at half maximums are usually used as the information. This technique is a useful tool for fractrure analysis, since the quantitative loading condition etc. can be estimated. X-ray fractography is used in various countries alongside the electron-microscope fractography. In the previous paper, X-ray fractography has been applied to actual size four “Shinkansen (bullet train)” axles tested at the railway Technology Research Institute. The axles are about 200mm in diameters, induction hardened 0.38% carbon steel with semi-elliptical artificial flaw. X-ray stress measurements were carried out on the fractured surface along the line from the bottom of the artificial flaws to the axle center at intervals of 5mm. All the results showed that the residual stress on the fractured surface were tensile at the initial crack propagation region, increased to tensile maximums, decreased into compression reaching at the compressive maximums then went up toward zero stress near the final fractured surface.This paper describes the procedure estimating the crack propagation direction through rosette analyses of residual stresses. A CCT specimen, which was tested under similar stress condition as test axles, was analyzed and found out that crack propagation directions are coincide with the directions of residual principal stresses. This relationship was utilized in rosette analyses on fractured surface of a test axle, and crack propagation lines were estimated and also the crack closure behavior was discussed.