Papers by Keyword: Multiaxial Fatigue

Abstract: Wear of materials in rail/wheel industry is closely related to the cyclic creep. This contribution presents main results of experimental testing on R7T wheel steel. The cyclic creep is investigated under non-proportional loading conditions simulating a line rolling contact case. McDowell extrapolation was successfully applied to the calculation of twist. Cyclic material model MAKOC and MAKOC with memory surface were used for cyclic creep prediction. The plasticity model is based on AbdelKarim-Ohno kinematic hardening and Calloch isotropic hardening rules. Second material model was extended with Jiang-Sehitoglu memory surface, which is introduced in stress space. Material models were successfully used for predicting accumulation of shear strain.

Abstract: In this work the biaxial behavior of 316 stainless steel is studied under the lens of critical plane approach. A series of ten experiments were developed on dog bone shape hollow cylindrical specimens made of type 316 stainless steel. Five different loading conditions were assessed, with (i) only axial stress, (ii) only hoop stress, (iii) proportional combination of axial and hoop stresses, (iv) non-proportional combination of axial and hoop stresses with square shape and (v) non-proportional combination of axial and hoop stresses with L-shape. The fatigue analysis is performed following four different critical plane theories, namely Wang-Brown, Fatemi-Socie, Liu I and Liu II. The efficiency of all four theories is studied in terms of the accuracy of their life predictions.

Abstract: The present work assesses the fatigue life prediction capability of a recently proposed critical plane model. For this study, multiaxial fatigue data of S355-J2G3 steel were used; in-phase and 90o out-of-phase sinusoidal axial-torsional straining from 103 to 106 cycles, so it was possible to evaluate the model at low and high cycle fatigue, as well as the hardening effect. The damage parameters considered in this paper include the effect of hardening, mean shear stress effect and the effect due to interaction of shear and normal stress on the critical plane. A comparative evaluation of well accepted models (Wang-Brown, Fatemi-Socie and Liu 1 and 2) with the new recently proposed model (Suman-Kallmeyer) is done. The ability of the different models to predict the fatigue life for large and diverse load data set are discussed.

Abstract: The critical plane method is widely discussed because of its effectiveness for predicting the multiaxial fatigue life prediction of metallic materials under the non-proportional loading conditions. The aim of the present paper is to give a comparison of the applicability of the critical plane methods on multiaxial fatigue life prediction. A total of 205 multiaxial fatigue test data of nine kinds of metallic materials under various strain paths are adopted for the experimental verification. Results shows that the von Mises effective strain parameter and KBM critical plane parameter can give well predicted fatigue lives for multiaxial proportional loading conditions, but give poor prediction lives evaluation for multiaxial non-proportional loading conditions. However, FS parameter shows better accuracy than the KBM parameter for multiaxial fatigue prediction for both proportional and non-proportional loading conditions.

Abstract: High–cycle multiaxial fatigue tests under proportional and non-proportional loading conditions with various combinations of superimposed static mean stresses was carried out on Cu-ETP copper. The results show differences in fatigue life between various ratios of mean stresses. These results are similar to others described in the literature.

Abstract: Stress invariants approach to the multiaxial fatigue life estimation is generally based on the root mean square value of second invariant of the deviatoric stress amplitude and the value of hydrostatic stress. Such an approach omits a significant part of the information about multiaxial load history. It is particularly noticeable in case of non-proportional loadings, which lead to a reduction of fatigue life (i.e. [1–3]). In this work a new method based on the mean value of modified second invariant of the deviatoric stress has been presented.

Abstract: Fatigue strength prediction methods of blades of a high pressure steam turbine are the main topic of this article. Experimental approaches, as well as use of the experimental results for the verification of the finite element method (FEM) and fatigue models, were performed on two basic levels. First, verification by the fatigue tests of smooth and notched cylindrical specimens under room and service conditions was performed. Second, verification of the real blade fatigue limit prediction was conducted. These tests were carried out using special test stand under the typical combined blades loading. Appropriate uniaxial and multiaxial fatigue criteria were applied. Achieved results were finally used in the process of the fatigue strength prediction of rotor blades.

Abstract: The lack of clarities in estimating the residual stress threat to the structural integrity has led to conservative assumptions in the current design of welds. The complexities become more in the case of multiaxial loading of welded structure, considering fracture or fatigue. To what extent the residual stresses influence the performance of a welded structure, depends on how stable they are under service loads. Finite element analyses are used here to describe the development of welding residual stresses in tubular joints and their relaxation under multiaxial loading. It is observed that the effect of the torsion load is more significant than the effect of tension load in releasing of the residual stresses. For pure tensile loading, the relaxation of the residual stresses are negligible as long as the applied load is lower than 50% of the yield strength of the material. For a combined tension-torsion loading of 75% of the yield strength, the residual stresses are almost completely released, and in the weld zone they become compressive.

Abstract: Fretting fatigue denotes the detrimental effect on a material arising from the cyclic sliding of two contacting surfaces with small relative displacements between them. One or both of the components in contact may be subject to bulk stresses caused by cyclic loads. The assessment of the fretting fatigue strength and life of any component is a complicated issue due to the many parameters affecting it, the complexity of the stress fields cyclic variation during fretting and the uncertainties associated to the contact conditions. This paper describes some singular aspects of fretting fatigue related to strength analysis and testing, presents a procedure developed by the authors during the last years to estimate the fretting fatigue strength and life and compares the assessment outcomes with the results of tests carried out by different authors.

Abstract: A special situation arises when multiaxial fatigue loadings are present, given not only the time-dependency of extreme principal stress values, but also the fact that principal plane positions change during one load cycle (non-proportional loading). Thus, the analysis of principal stress and principal direction variation becomes a very important step, necessary to be carried out before starting any multiaxial fatigue testing. Based on the above, the authors present a generalized method for computing principal stresses and determining principal plane positions, applicable for cyclic tension-torsion loadings with zero mean stresses but with different phase shifts and amplitude ratios. Based on original experimental data and data collected from the literature, the authors point out in the final part of the paper that the maximum principal shear stress can be considered as the main parameter for plotting Wöhler curves.