Measurements of strain fields around crack tips under proportional and non-proportional mixed-mode fatigue loading

For various configurations examined in a series of fatigue experiments on thin-walled tubes under tension and torsion, the experimental results – crack path, crack growth life, near crack tip deformations, and crack closure – are measured. Optical inspections and digital image correlation technique were used in the experimental investigation. Crack opening and closure loads were determined. The mechanical material behavior has been assumed as linear elastic in a first approach for calculating stress intensity factors. The non-linear nature of the cyclic deformation has been determined experimentally for future use in a cyclic plasticity model.