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Based on the existed experimental results of 304 stainless steel, the evolution of fatigue damage during the stress-controlled cyclic loading was discussed first. Then, a damage-coupled visco-plastic cyclic constitutive model was proposed in the framework of unified visco-plasticity and continuum damage mechanics to simulate the whole-life ratcheting and predict the fatigue failure life of the material presented during the uniaxial stress-controlled cyclic loading with non-zero mean stress. In the proposed model, the whole life ratcheting was described by employing a non-linear kinematic hardening rule, i.e., the Armstrong-Frederick model combined with the Ohno-Wang model I, and considering the effect of fatigue damage. The damage threshold was employed to determine the failure life of the material. The simulated whole-life ratcheting and predicted failure lives are in a fairly good agreement with the experimental ones of 304 stainless steel.

The crack propagation properties for ultrafine-grained Zn-22wt%Al alloy during low cycle fatigue (LCF) in the superplastic region and the non-superplastic region were investigated and compared with the corresponding results for several other materials. With the Zn- 22wt%Al alloy, it was possible to conduct LCF tests even at high strain amplitudes of more than ±5%, and the alloy appeared to exhibit a longer LCF lifetime than the other materials examined. The fatigue life is higher in the superplastic region than in the non-superplastic region. The rate of fatigue crack propagation in the superplastic region is lower than that in the other materials in the high J-integral range. In addition, the formation of cavities and crack branching were observed around a crack tip in the supereplastic region. We therefore conclude that the formation of cavities and secondary cracks as a result of the relaxation of stress concentration around the crack tip results in a reduction in the rate of fatigue crack propagation and results in a longer fatigue lifetime.

Total strain controlled low cycle fatigue tests were conducted at 1173K for DD32 and SRR99 alloys. With the increase of total strain range, the stress amplitude of DD32 alloy improved more fleetly than that of SRR99 alloy. At total strain ranges less than or equal to 1.0%, the low cycle fatigue life of DD32 alloy was greater than that of SRR99 alloy. It was shown that the higher content of refractory elements in DD32 alloy resulted in a remarkable improvement of LCF properties compared to SRR99 alloy. The crack propagation perpendicular to the stress axis occurred in transgranular mode in both alloys. DD32 alloy presented more ductile character than SRR99 alloy.

Member failure due to low cycle fatigue may occur for steel structures under strong earthquakes. In this paper, the seismic response of single-layer latticed domes composed of welded round pipes is analyzed by the software Open System for Earthquake Engineering Simulation (OpenSees) incorporating low cyclic fatigue, in which the equations of initial camber for members are obtained from the buckling coefficient curve of compression members in Chinese codes. Single-layer latticed domes composed of welded round pipes with different parameters are modeled, and the seismic responses of the domes with and without material fatigue are compared by the incremental dynamic analysis. The results show that under strong earthquakes, the seismic responses including the maximum displacements and plastic development of the domes with fatigue are larger than those of the domes without fatigue. The collapsed PGAs decrease by 10–25% if low cycle fatigue is incorporated. Therefore, the low cycle fatigue of material should be taken into account in the seismic analyses of single-layer latticed domes under strong earthquakes.

Combining the application of the shakedown theory and a multiscale approach to analysis of fatigue allows interpreting all types of fatigue problems in an efficient manner. The description of the stabilized mechanical state after shakedown at the engineering macroscopic scale and at the mesoscopic scale of grains gives access to the engineering values which will drive the fatigue damage of the structure. The evolution of stress and strain tensors thus obtained for a cycle of fatigue allows predicting the fatigue strength of structures. At high cycle fatigue (HCF), when elastic shakedown takes place, the fatigue strength can be described by a simple combination of mesoscopic shear amplitude and hydrostatic tension at any point of the calculated structure, irrespective of the complexity of the structure and the loading. Two new developments incorporating spectral or modal approaches allow analyzing the fatigue resistance of structures undergoing vibrations in a very efficient manner. At low cycle fatigue (LCF), from the stabilized state of stress and strain, the fatigue strength is derived from a combination of the inelastic strain energy and the hydrostatic pressure. Numerous examples of fatigue analysis are presented.

This paper presents a proposed methodology to account for cyclic plastic response of the thin shell ANDES and line-spring finite elements. A through thickness integration scheme is employed for the shell element and stress resultant plasticity is used for the line-spring element. A simplified contact formulation to account for crack closure in the line-spring element is also presented. Numerical comparisons between the proposed models and detailed 3D analyses (pipes) are carried out and presented herein. A comparison between the present implementation and large scale experiment of a surface cracked pipe subjected to large cyclic plastic strains is also presented. The purpose of the presented implementation is to account for cyclic loading in pipeline technology where significant amount of plasticity in the loading cycles occurs.

Co-base superalloys have been applied in the stationary components of gas turbine owing to their excellent high temperature properties. Low cycle fatigue data on ECY-768 reported in a companion paper were used to evaluate fatigue life prediction models. In this study, low cycle fatigue tests are performed as the variables of total strain range and temperatures. The relations between plastic and total strain energy densities and number of cycles to failure are examined in order to predict the low cycle fatigue life of Cobalt-based super alloy at different temperatures. The fatigue lives is evaluated using predicted by Coffin-Manson method and strain energy methods is compared with the measured fatigue lives at different temperatures. The microstructure observing was performed for how affect able to low-cycle fatigue life by increasing the temperature.

Based on the existed experimental results of 304 stainless steel, the evolution of fatigue damage during the stress-controlled cyclic loading was discussed first. Then, a damage-coupled visco-plastic cyclic constitutive model was proposed in the framework of unified visco-plasticity and continuum damage mechanics to simulate the whole-life ratcheting and predict the fatigue failure life of the material presented during the uniaxial stress-controlled cyclic loading with non-zero mean stress. In the proposed model, the whole life ratcheting was described by employing a non-linear kinematic hardening rule, i.e., the Armstrong-Frederick model combined with the Ohno-Wang model I, and considering the effect of fatigue damage. The damage threshold was employed to determine the failure life of the material. The simulated whole-life ratcheting and predicted failure lives are in a fairly good agreement with the experimental ones of 304 stainless steel.

The crack propagation properties for ultrafine-grained Zn–22wt%Al alloy during low cycle fatigue (LCF) in the superplastic region and the non-superplastic region were investigated and compared with the corresponding results for several other materials. With the Zn–22wt%Al alloy, it was possible to conduct LCF tests even at high strain amplitudes of more than ±5%, and the alloy appeared to exhibit a longer LCF lifetime than the other materials examined. The fatigue life is higher in the superplastic region than in the non-superplastic region. The rate of fatigue crack propagation in the superplastic region is lower than that in the other materials in the high J-integral range. In addition, the formation of cavities and crack branching were observed around a crack tip in the supereplastic region. We therefore conclude that the formation of cavities and secondary cracks as a result of the relaxation of stress concentration around the crack tip results in a reduction in the rate of fatigue crack propagation and results in a longer fatigue lifetime.