Cycle symmetrization, asymmetrical behaviour and ratchetting during low cycle fatigue of high temperature alloys

Strain-controlled (low-cycle fatigue type) experiments were performed on 12 different high temperature alloys (ferritic, austenitic, superalloys, single-crystal material, a directionally solidified alloy and two titanium alloys) in the range 550–950°C. Symmetrical cycling conditions were suddenly changed to offset strain cycling at the same strain range, but in the tension or compression direction. Up to 50 cycles were allowed to determine the subsequent approach to symmetrical stress limits for each material (elastoplastic shakedown). Comparison is made with limited reported tests and related load-control tests involving strain ratchetting . Shakedown behaviour is shown to depend both on the path of approach, defined by stress–strain properties, but overall trends of stress versus cycle plots are best made by assuming an effective strain range which is less than the imposed experimental strain range.