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[en] The effects of temperature (-75⁰C to 760⁰C) and cyclic strain rate (2 x 10^-4sec^-1 to 4 x 10^-1sec^-1) on the fracture mechanism were investigated using OFHC copper and Type 304 stainless steel under strain control. It was found that time dependent fracture predominates at high temperatures and low strain rates. However, at high strain rates the life was insensitive to temperature. The role of grain boundary migration on the fracture process was investigated. Grain boundary migration was found to be dependent on the strain rate for copper whereas for Type 304 stainless steel, grain boundary migration was inhibited at high temperature (760⁰C) due to the presence of precipitates at the grain boundaries. During strain cycling of OFHC copper and Type 304 stainless steel, creep damage cannot be summed to the fatigue damage to give a total damage of unity for failure, if only a single deformation and fracture mechanism is operating. The sense of the damage accumulation does not affect these findings. In general, the amount of previous damage has no influence on the damage accumulation which follows, if it is not of the same kind. (author)

[en] This paper describes a study performed at the University of Waterloo which combined data from nine investigations of fatigue of mild steels at room temperature under fully-reversed, biaxial, stress or strain controlled, conditions. This assemblage of some 260 data points covers the fatigue life range from 10 to 10⁷ cycles. Biaxial stress ratios, from equibiaxial (+1) to torsional (-1) are represented. By combining data a broad view of the effect of biaxiality on fatigue is obtained. Areas where data are scant or show inconsistencies become apparent and conclusions drawn have more general applicability than those based on a single investigation. The data analyzed are published as amplitude or range of stress, total strain, plastic strain or equivalent plastic strain. A variety of testing techniques and interpretations of specimen failure were used. The chemical composition and heat treatment of the steels used also varied. The paper shows how some standard and other less usual strain based criteria describe the data. Two-part criteria were investigated in which the equivalent elastic and plastic strain components are based on either octahedral - or maximum -shear strain with the equivalent plastic strain modified to include a hydrostatic stress effect. The collected data were also compared to the ASME Pressure Vessel Code curves for design against fatigue. The safety factors included are shown to be less than the desired 2 on stress or 20 on life particularly at short fatigue lives. Some modifications to the design practice to restore these safety factors are suggested

No abstract available

[en] Design of pressure vessels, including components of nuclear reactors, where loading varies periodically during service, requires an estimate of fatigue life for conditions of biaxial stress. The ASME pressure vessel code, does this by the use of the maximum shear criterion, modified to include the strain dependence of fatigue behaviour. However, since the ASME code was developed a number of authors have reported biaxial fatigue data which are more accurately described by various other criteria. This study attempts to generate a relationship that describes a broad range of published biaxial fatigue data and to review the accuracy of the ASME code fatigue criterion. This paper describes a study of performed at the University of Waterloo which combined data from nine investigations of fatigue of mild steels at room temperature under fully-reversed, biaxial, stress or strain controlled, conditions. This assemblage of some 260 data points covers the fatigue life range from 10 to 10⁷ cycles. Biaxial stress ratios, from equibiaxial (+1) to torsional (-1) are represented. By combining data a broad view of the effect of biaxiality on fatigue is obtained. Areas where data are scant or show inconsistencies become apparent and conclusions drawn have more general applicability than those based on a single investigation. (Auth.)