Lifetime Analysis-Modelling # 1995 Edinburgh
This paper presents results and experiences obtained at Studsvik Material AB from the use of the Standard Extrapolation Method (SEM) according to I S O n R 9080. Results obtained from SEM calculations are demonstrated in creep rupture curves for pipe materials of PE, PP and PEX. Attention is also given to problems experienced with the method itself and to unclear formulations in ISO/TR 9080. Our investigation of the SEM was initiated in 1988. At the, end of 1990, the computer programme LTHS was available at Studsvik to support the SEM calculations. Our latest version of LTHS allows automatic optimisation of the location of knee points by the incorporation of iterative routines, which minimise the total residual sum of squares, in addition to the SEM according to ISORR 9080. Results obtained from analyses in which these routines have been used are also shown and discussed in the paper.