THE INFLUENCE OF LOAD MISALIGNMENT DURING UNIAXIAL LOW‐CYCLE FATIGUE TESTING—I: MODELLING

Abstract

Abstract— A quantitative model has been proposed which predicts the extent of lifetime scatter in low‐cycle fatigue due to the influence of bending caused by load misalignment. The main components of the model are the mechanism of bending, the type of extensometer used to control strain and the fatigue characteristics of the material being assessed. Three mechanisms of bending have been studied and it is argued that the most damaging one is a consequence of a lateral offset in the centre‐lines of the load‐train with respect to either a machine's frame or ram. Scatter in lifetime is a maximum when strain is controlled by a single extensometer (which is generally the case) and when fatigue behaviour is dictated by crack initiation at the largest surface defect. Two types of scatter have been examined, (i) repeatability scatter due to testing practice within a single laboratory, and (ii) reproducibility scatter between laboratories. An example of the magnitude of reproducibility scatter due to bending has been given by using an equation based on the universal slopes method due to Manson.