Axial Stress Fatigue, Creep, and Rupture Properties of Unnotched and Notched Specimens of Heat Resistant Alloys

Abstract

Fatigue, rupture, and creep data at various temperatures obtained under various combinations of mean and alternating stress are presented for the alloys Stellite 31, 6.3 per cent molybdenum-Waspalloy, Inconel X-550, 16-25-6 Timken, Lapelloy, and stainless steel type 403. Tests were performed under axial stress on unnotched specimens and specimens having theoretical stress concentration factors of 2.4 and 3.4. The data are presented as stress range diagrams to show the effect on the fatigue and creep properties of specimen notch, temperature, ratio of alternating-to-mean stress, and stress magnitude. The role of both creep and fatigue as design factors and the relation of notch sensitivity to loading conditions are discussed with particular reference to temperature and ratio of alternating-to-mean stress.

Experimental and Numerical Study on Temperature Evolution for Rapid Evaluation of Fatigue Limit

“…where is the area of current stress-strain hysteresis loop used to calculate A ' p T ' , 1 H and 2 H are the minimum and maximum strain of the hysteresis loop, l V and u V are the stresses in the loading and unloading part of the hysteresis loop, respectively.…”

“…The determination of fatigue limit by traditional Wöhler method is properly a time consuming task. Therefore, various techniques for rapidly evaluating fatigue limit have been considered for more than 100 years [1]: for example, techniques based on change of temperature, change in modulus of elasticity, change of electrical resistance, change of radiation with respect to progressive increase of loading amplitude. Although many attempts have been made, these techniques are not widely applied to practical engineering problems for lack of reliability compared to traditional Wöhler method.…”

Discussion: “Effect of Relaxation on the Behavior of Materials Under Combined Alternating and Static Stress” (Vitovec, F. H., 1960, ASME J. Basic Eng., 82, pp. 441–445)

“…At high mean-to-alternating stress ratios, however, net flow occurs and strain-rate effects must be considered. The writer 4 has postulated the rate of loading from the minimum to maximum stress (alternating-stress range) and the maximum stress governs the incremental flow which adds to the creep strain resulting from the minimum stress. The effective stress for flow and rupture, therefore, lies between the minimum and mean stress; this results in a higher apparent creep-rupture strength at high mean-to-alternating stress ratios.…”