Fracture Behaviour of Two Creep-Resistant Materials Subjected to Cyclic Loading at Elevated Temperature

Abstract

An alloy steel and a nickel-chromium alloy are shown to exhibit similar fatigue behaviour over a wide range of temperatures. Endurances tended to be time-dependent at elevated temperatures, and repeated-tension cycles were found to be more damaging than push-pull but less damaging than static-tension (creep). The behaviour was reversed at room temperature where failures tended to be cycle-dependent (number of cycles to failure independent of applied frequency) and creep loading was least damaging. Rupture data for repeated-tension tests at approximately 10 c/min were analysed by a creep technique. For a wide range of temperature, the expressions fitted the experimental points encouragingly closely and the technique appears to be a useful method of describing this type of data. Tests at room temperature having more than 10⁴ cycles to failure were premature with respect to the analysed family of curves and this was attributed to failure occurring by a predominantly cycle-dependent mechanism. Fractures at higher stresses exhibited a ductile appearance attributed to a different fracture mechanism. Time-dependent behaviour was enhanced by increase in the peak tensile stress, tensile mean stress, and temperature, or by decrease in cyclic frequency.