LIFETIME, TOUGHNESS AND RELIABILITY OF ENGINEERING THERMOPLASTICS
Chudnovsky, D. Baron, Y. Shulkin, K. Sehanobish* and C. P. Bosnyak* Dept. of Civil & Materials Engineering University of Illinois at Chicago, 842 W. Taylor, Chicago IL 60607 *The Dow Chemical Company, Freeport, TX 77566
The existing empirical methods of lifetime prediction for polyethylenes (PEs), based on extrapolations of experimental data obtained under high temperatures and stresses to significantly lower application temperature and stresses, are reconsidered. A new method is proposed as a combination of mathematical modeling of slow crack growth in PEs and experimental determination of material parameters for the model from short-term experiments. The description of the crack behavior and prediction of lifetime resulting from this approach are in good agreement with observations from various PEs. For a particular material, specimen geometry, applied stress level and temperature, the method establishes the dependence of lifetime on initial crack size. This size is randomly distributed quantity. Its probability density is evaluated in a quality control test. Then a standard statistical treatment produces the probability density for lifetime. This makes it possible to calculate the reliability function of the structural component. For example, the method allows the manufacturer of gas piping grade PE structures to recommend a replacement interval (dependable lifetime) for any level of desired reliability.
Publication Source: Trends in NDE Science & Technology; Proceedings of the 14th World Conference on Non-Destructive Testing, New Delhi, 8-13 December 1996.full paper not received Publisher:Ashgate Publishing Company
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