Extrapolation for Creep-Rupture Strength by Nonlinear Programming.

Up to now, various TTP (time-temperature parameter) methods have been proposed to deter. mine creep-rupture strength by extrapolation. The TTP methods based on regression analysis, however, reflect such a general tendency of the regression curve that the estimation accuracy of rupture time is low at the lowest and highest stresses in the test stress range. For the purposes of improving the extrapolation accuracy and formulating the master rupture curve, the we authors have developed two estimation procedures employing nonlinear programming : one is an extrapolation prediction method for the creep-rupture curve under constant temperature conditions ; another is an interpolating prediction method for the master creep-rupture curve. According to the examples of extrapolation to the range of 6∼8 times as long as the test duration by the presently developed methods, these prediction methods are also applicable to cases where the deterioration of creep-rupture strength occurs under conditions of high temperature and/or long duration.