抄録
A series of studies have been conducted on the effect of retightening (reloading) on stress relaxation behavior of high temperature bolts used in steam turbines.
The present paper describes the results of reloading stress relaxation tests made after relaxed to various specific values of residual stress for 19Cr-9Ni-1.4Mo-1.4W-Nb bolting steel at the test temperature of 650°C. Most of the repeated loadings on the specimens were brought up to rupture.
Logarithmic relations between the testing time at each cycle and the number of loading were analyzed numerically by taking the specific value of residual stress as a parameter. The results confirmed the previous empirical equation. As for rupture behavior, the following three terms, the number of loadings, the accumulated testing time, and the accumulated plastic strain, were expressed by power functions of the specific value of residual stress. From these equations obtained for reloading stress relaxation behavior and rupture, the design curves of retightening characteristics of bolts were presented.
