A REINTERPRETATION OF THE BCR VAMAS LOW-CYCLE FATIGUE INTERCOMPARISONPROGRAM USING AN ENERGY CRITERION/

Data from a previous round robin low cycle fatigue exercise on 316L st eel, 9Cr1Mo steel and IN718 alloy at 550 degrees C and Nimonic 101 at 850 degrees C are re-examined, emphasis being placed on material stres s-strain response and associated energy expenditure rather than cycles to failure. It is shown that persistent inter-laboratory scatter in m aterial response remains even at the very early stages of testing and that this may be due, during this period, to intrinsic microstructural behaviour as well as to imprecision in test system calibration proced ures. To some extent the data may be rationalised by assuming a consta nt energy expenditure at failure and choosing an earlier failure crite rion than the often-used 25% load drop stage. In the best case, inter- laboratory scatter was reduced by a factor 5. As before, scatter withi n a laboratory (repeatability) was always less than that between labor atories (reproducibility).