Characterising statistical strain-life fatigue parameters

In today's industry environment, the need to accelerate product development schedules requires that engineers actively engage simulation models to eliminate iterations from the design and test process. Much time is spent on the design for and evaluation of component reliability and durability. If accurate descriptions of the fatigue behaviour of materials are available, then simulation software can be used to simulate component durability and thus provide insight to design flaws more quickly than can the design and test cycle. A method is presented that facilitates the development of accurate statistical strain-life curves given experimental data from strain controlled uni-axial fatigue tests. The method establishes a series of selection criteria that ensure that the data used in the statistical analysis is significant and representative of the materials true behaviour. The method goes on to establish a procedure for the statistical analysis that ensures that each domain of the materials behaviour is accurately represented. The result is an R50 strain-life curve that is then scaled to an R90C90 strain-life curve by incorporating a technique presented by Shen and Wirsching. This R90C90 curve represents a strain-life curve that encapsulates the behaviour of 90% of samples of a material and in which 90% confidence exits. This R90C90 curve is then suitable for use in industrial simulation software.