ステンレス鋼のマルテンサイト変態を利用した接触応力測定法

Abstract

The stress distribution at the contact area of a machine element has a large effect on the total performance of the machine. It is one of the important factors that closely relate to the performance of the element as a gear pair, a set of bolt and nut and so on. Many theoretical studies for estimating the contact stress were published. However, their validity has not been proved by experiments, because the known measuring methods are insufficient in accuracy or resolving power. The measuring method using martensite transformation is offered in this paper. If the stress is applied to the test piece made of 18-8 stainless steel at a temperature of 198 K, the stressed part of the test piece changes its structure from austenite to martensite. The martensite structure has the nature of ferromagnetism. Therefore, the contact stress distribution in the test piece can be obtained by measuring the distribution of remaining magnetism. For confirming the practical use of the method some experiments have been done using the block type (10 mm in thickness) and the film type (5 μm in thickness) test pieces of stainless steel. It has been confirmed that at the more stressed part, the more martensite transformation is induced in the test pieces, and that the test pieces have sensitivity for the measurement of the stress distribution. A homogeneous structure in the test piece is needed for the purpose of measurement.