Continuum Damage Mechanics and the Life-Fraction Rule

[+] Author and Article Information
U. Stigh

Division of Mechanical Engineering,  University of Skövde, P. O. Box 408, SE-541 28, Skövde, Sweden

J. Appl. Mech 73(4), 702-704 (Oct 24, 2005) (3 pages) doi:10.1115/1.2150502 History: Received January 12, 2005; Revised October 24, 2005

This paper gives a short review of two different methods for life prediction at high temperature; namely continuum damage mechanics (CDM) and the linear life-fraction rule (LFR). It is well known that the class of CDM theories with a separable evolution law gives a life prediction in accordance with the LFR. However, it appears to be an open question if this is a necessary condition. It is here shown that in order for a CDM theory to comply with the LFR it must have a separable evolution law. That is, if we can assume that a material follows the LFR, it is necessary to chose a separable evolution law for this material. The reverse is also true, to get a life-fraction different from unity, we must chose a nonseparable evolution law.

Copyright © 2006 by American Society of Mechanical Engineers
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Grahic Jump Location
Figure 2

Two-step load history. During the time 0<t<T, σ=σ1. From t=T, σ=σ2 which is held constant until rupture at t=t*.

Grahic Jump Location
Figure 1

Left panel: Step-up and step-down experiments. Right panel: Life-fraction at rupture during step-up and step-down experiments performed with an austenitic stainless steel at 700°C. The ordinate shows the life-fraction at rupture and the abscissa shows the number n of experiments yielding a life-fraction less than the value on the ordinate. Experimental results from Ref. 4.



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