Comparison of the failure conditions for creep, stress relaxation, and constant strain rate measurements to predict pipe burst for two ABS materials using the universal viscoelastic model

摘要

The universal viscoelastic model was further validated in this study using two acrylonitrile-butadiene-styrene (ABS) viscoelastic materials to better elucidate the direct relationship between the failure criterion characteristics involving creep, constant strain rate, stress relaxation, and pipe burst. Using the yield strain as the failure criterion for constant strain rate and stress relaxation measurements and the strain at critical creep, the failure condition for creep, it was found that the universal viscoelastic model allowed these failure criteria to yield remarkably good agreement on a projected time scale. The relationship of the failure criteria between these three different techniques for characterizing a viscoelastic material was successfully used to identify several complementary approaches to predict long-term pipe burst for two different ABS materials. The pipe burst data for ABS-A appeared to fit the Tresca failure criterion better than the von Mises failure criterion, as predicted from failure criteria using constant strain rate, creep, and stress relaxation measurements. For ABS-A the extrapolated creep and the constant strain rate failure criterion appeared to best predict the Tresca failure criterion pipe burst data. However, the hoop burst stress for ABS-N, adjusted with the von Mises failure criterion modification, was found to give the best agreement with the yield stress equivalent failure criterion for constant strain rate, creep, and stress relaxation. For ABS-N, the extrapolated creep failure criteria appeared to best predict the von Mises pipe burst failure criterion. In this study, the relationships between the failure criteria for the three different experimental techniques of constant strain rate, creep, and stress relaxation were shown to be reasonably interchangeable relative to a three-dimensional failure configuration such as pipe burst. Because this interchangeability approach was found to work so well in the laboratory, there is no reason to believe that this same technique, using the universal viscoelastic model, would not also work as well to predict failure criteria for design applications using finite-element analysis. (C) 2004 Wiley Periodicals, Inc.