A re-interpretation of the BCR/VAMAS low cycle fatigue intercomparison programme using an energy criterion

Abstract

Data from a previous round robin low cycle fatigue exercise on 316L steel, 9Cr1Mo steel and IN718 alloy at 550°C and Nimonic 101 at 850°C are re-examined, emphasis being placed on material stress-strain response and associated energy expenditure rather than cycles to failure. It is shown that persistent inter-laboratory scatter in material 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 procedures. To some extent the data may be rationalised by assuming a constant energy expenditure at failure and choosing an earlier failure criterion than the often-used 25% load drop stage. In the best case, inter-laboratory scatter was reduced by a factor 5. As before, scatter within a laboratory (repeatability) was always less than that between laboratories (reproducibility).

Keywords:

• cyclic stress-strain
• hardening
• softening
• intrinsic and extrinsic scatter