Papers by Keyword: Mean Stress

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Authors: Phani C.R. Sree, Daniel Kujawski
Abstract: The Smith-Watson-Topper (SWT) parameter was originally suggested and is still widely used to account for mean stress effects in fatigue life analysis. It is well recognized however, that the SWT parameter might be non-conservative for cyclic loads that involve relatively large compressive mean stresses. Such large compressive mean stresses can develop in notches after overloads. An energy interpretation of the SWT parameter is presented first. Based on analogy with the Neuber’s rule a new deviatoric formulation of the SWTD parameter is proposed. It is found that for positive mean stresses and moderate negative mean stresses the original SWT parameter and the proposed deviatoric SWTD parameter yield similar results. At large compressive mean stresses and non-proportional biaxial fatigue, the deviatoric SWTD parameter demonstrates a fairly good correlation to test data while the original SWT parameter results in wide scatter.
Authors: Peng Yue, Qiang Lei, Cheng Lin Zhang, Shun Peng Zhu, Hong Zhong Huang
Abstract: To evaluate the fatigue damage accumulation and predict the residual life of components at different stress levels, this paper proposed a modified cumulative damage model based on the strain energy density parameter. Noting that mean stress and load interaction under uniaxial fatigue loading exhibit significant effects on fatigue damage accumulation and life prediction. According to this, a new model based on damaged stress model which considers the effects of mean stress and load interaction was presented in this paper. The proposed model was verified by using four experimental data sets of aluminium alloys and steels. The experimental results are compared with those of the Miner’s rule, damaged stress model (DSM) and damaged energy model (DEM). Results show that the proposed model agrees better with the experimental observations than others.
Authors: Isao Ishimoto, Masahiro Endo
Abstract: A unified method is presented for the prediction of the fatigue strength of steel components containing small holes and being subjected to combined loading. Materials investigated were an annealed 0.37% carbon steel and a quenched and tempered Cr-Mo steel. Combined axial and torsional fatigue loading tests were carried out using specimens containing a small hole, which was introduced into the surface by drilling. The diameter of holes equaled the depth and was either 100µm or 500µm. The non-propagating cracks emanating in the radial direction from the holes were observed at the fatigue limit. When the loading condition is the same, they were on a plane that inclined at the same angle with respect to the specimen axis, regardless of the size of holes. This result suggested that the fatigue strength would be controlled by the Mode I threshold condition for propagation of a crack initiated on a critical plane. A criterion connecting uniaxial fatigue strength with multiaxial fatigue strength was proposed based upon the assumption that at the threshold level, the variation of the stress intensity factor of a Mode I crack initiated under combined loading equaled that under uniaxial loading. The predictive method proposed based upon this criterion is practical in that no fatigue test is necessary in making predictions. For the various conditions of in-phase and out-of-phase fatigue loadings with an imposed mean or static load, experimental results agreed well with predictions.
Authors: Y.H. Seo, Byoung Kee Kim, H.D. Son
Abstract: Wire cutting(EDM) or blanking is used to made workpieces from sheet metal. Wire EDM provides a relatively simple method for making holes of any desired cross section in material. But EDM requires a lot of working time and the high unit cost of production. In conventional blanking, for the production of precision devices or assemblies, it is always necessary that at least two, but generally more, secondary operations are required per piece part. Using the fine blanking process, a precise finished part with inner and outer forms clearly sheared over the whole material thickness are produced in one single operation. In this study an attempt is made to manufacture a sprocket with fine blanking process. The sprocket is parts for the tape feeder of surface mount system in electronic parts. First, a change of the existing design is made in a sprocket. The materials selected are three kinds of stainless steel, SUS304, SUS316 and SUS430. And the mechanical properties are investigated through the tensile test. After fine blanking, hardness and precision are examined with hardness test and 3-dimensional coordinate measuring for samples. The results of investigations of fine-blanking process with the help of FEM code, DEFORM 2D, are presented. For the simulation, SUS304 and SUS316 are used as materials. The damage model of Cockroft and Latham is used to calculate damage. Die-roll height, die-roll width, burnish zone and fracture zone from the fine blanking simulation are investigated in comparison with them of samples. And the applied force at each part of fine-blanking die is estimated with load-stroke diagram.
Authors: Ping Zhao, Hong Wen Yan
Abstract: The influence of mean stress on fatigue has to be considered by means of Haigh diagram, the actual stress range is modified to damage-equivalent range. There are three main methods for creating Haigh diagram, such as experiment and empirical relationships and six points, which has the different application field. The creating and application of Haigh diagram in GL certification for wind turbines is studied, and the solving method for the mean stress sensitivity is given.
Authors: Jaroslav Polák, Martin Petrenec, Jiří Man, Tomáš Kruml
Abstract: Smooth specimens made from austenitic-ferritic duplex steel were subjected to constant stress amplitude loading with positive mean stresses. Hysteresis loops were recorded during the fatigue life and plastic strain amplitude and cyclic creep rate were determined. Fatigue hardening/softening curves, cyclic creep curves and cyclic stress-strain curves for different positive mean stresses were evaluated. Typical dislocation structures developed in both phases of the duplex steel were identified using TEM, compared with the saturated plastic strain amplitude and correlated with the decrease of the cyclic creep rate during cycling and the slope of the cyclic stress-strain curve.
Authors: Sai Jiao, Marcin Zielinski, Jean François Michaud, Thierry Chassagne, Marc Portail, Daniel Alquier
Abstract: A detailed experimental study of the mean and gradient stress, existing in the as-grown cubic silicon carbide epilayers, is presented in this paper. (100) and (111) oriented epiwafers with considerable film thickness variation have been elaborated using a horizontal low pressure chemical vapor deposition reactor. The mean and gradient stress within the 3C-SiC film were estimated from the static mechanical deformation of micromachined clamped-free beams. For both studied orientations, we observe a stress gradient inversion phenomenon that can be explained in terms of creep occurring in 3C-SiC film.
Authors: Adam Niesłony, Michał Böhm
Abstract: The paper deals with a comparison of fatigue life calculations, obtained on the basis of classical Basquin diagrams and approximated diagrams acquired with the use of the section method, which allows us to fit the diagrams shape to real material properties. While comparing the calculation results, literature data concerning fatigue tests of welded cruciform specimens from high performance low-alloy steel HSLA-80 presented by Kihl and Sarkani as well as of smooth specimens out of the aluminum alloy 75S-T6 by Grover et al. has been used. It has been noticed that the calculations performed with the use of fatigue diagrams approximated using the section method reflect the true behavior of the material. The models by Niesłony-Böhm and Smith-Watson-Topper compensating the influence of the mean stress gave similar results.
Authors: Tian Qing Liu, Xin Hong Shi, Jian Yu Zhang
Abstract: Fatigue tests have been carried out to investigate the effects of mean-stress and phase-difference on the tension-torsion fatigue failure of 2A12-T4 aluminum alloy. The results show that for fully reversed tension-torsion loading, the fatigue life increases with the increase of phase angle, but the fatigue life decreases with the increase of phase angle, when mean-stress exists, both for shear mean-stress and normal mean-stress. Fracture appearance shows that the crack initiation is on the direction of maximum shear stress amplitude plane. Critical plane criteria based on the linear combination of the maximum shear stress amplitude and maximum normal stress are studied and further discussion on the drawbacks of this kind of criteria are performed.
Authors: K. Morishige, Hiroshi Noguchi
Abstract: Effect of mean stress on fatigue strength at N=107 of non-combustible magnesium alloy AMX602B(X=Ca) was investigated. Rotating bending fatigue test and tension-compression fatigue test were carried out on specimens with a small hole or crack. It was clarified that the fatigue strength at N=107 of the specimen with the small hole was about 30-150% higher than that of the specimen with the small crack within the range of σm=0~100MPa. This is the reason why the fatigue strength at N=107 of the specimen with the small hole can be not threshold condition for crack propagation but crack initiation. The fatigue strength at N=107 of the specimens with the small hole decreased within the range of σm=100~195MPa due to a static small crack initiating from the small hole at first loading. The effect of mean stress on fatigue strength at N=107 both oh the specimens with the small hole and crack could be estimated using modified Goodman diagram.
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