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Multiaxial Fatigue Analysis under Complex Non-proportional Loading Conditions

Sharifimehr, Shahriar
http://rave.ohiolink.edu/etdc/view?acc_num=toledo1544787705876488

Abstract Details

2018, Doctor of Philosophy, University of Toledo, Engineering.
The analysis of the fatigue behavior of metallic materials and components under variable amplitude multiaxial cyclic loading conditions is of great interest to many industries. These loading conditions represent the loading histories to which many parts are subjected throughout their service lives. This type of analysis requires some key steps. These key steps include understanding the deformation behavior of the material including the cyclic behavior under proportional and non-proportional loading conditions, modeling the fatigue behavior of the material under constant amplitude cyclic loading, cycle counting procedures, damage parameters which can represent the damage mechanisms of the material under multiaxial loading conditions, and damage accumulation methods. In this study a methodology for the analysis of fatigue behavior under multiaxial variable amplitude loading conditions is employed which accounts for the aforementioned issues. This methodology consists of several steps of analysis, each of which is developed to address some of the challenges. At its core, the applied methodology uses critical plane analysis based on the failure behavior of each material to assess the fatigue damage under cyclic loading conditions. In order to evaluate the performance of the analysis method,axial, torsional, and combined axial-torsional variable amplitude tests were performed on one ductile and one brittle behaving steel and the experimental results were compared with those estimated from the analysis. The applied methodology resulted in close estimation of fatigue life for both ductile and brittle behaving steels. Furthermore, interactions between different components of stress such as normal and shear stresses play an important role in multiaxial fatigue damage. The main aim of this study was to investigate this interactions effect on fatigue behavior of shear failure mode materials under multiaxial loading conditions. In order to model the influence of normal stress on fatigue damage, the present study introduces a method based on the idea that the normal stress acting on the critical plane orientation causes two types of influence, first by affecting roughness induced closure, and second, by a fluctuating normal stress affecting the growth of small cracks in mode II. The summation of these terms could then be used in shear-based critical plane damage models, for example FS damage model, which use normal stress as a secondary input. In order to investigate the effect of the modification, constant amplitude load paths with different levels of interaction between the normal and shear stresses, as well as variable amplitude tests with histories both taken from service loading conditions, and generated using random numbers were designed for an experimental program. The proposed modification was observed to result in improved fatigue life estimations where significant interactions between normal and shear stresses exist. In addition, since shear fatigue properties are key properties in the analysis of fatigue behavior of ductile metallic materials, this study evaluated the accuracy of different methods in estimating shear fatigue behavior of steels and titanium alloys from properties which are easier to obtain such as monotonic properties and hardness. In order to achieve this goal, test results of 23 types of carbon steel, Inconel 718, and three types of titanium alloys commonly used in industry were found in the literature. In addition, two types of steel and a Ti-6Al-4V titanium alloy were subjected to axial monotonic and fatigue tests as well as torsion fatigue tests. The results of these tests were used along with the data from literature. A reasonable correlation between uniaxial fatigue properties and shear fatigue properties of ductile and brittle behaving materials were found using von Mises and maximum principal strain criteria, respectively. Estimations from the experimentally obtained uniaxial fatigue properties were compared to those from uniaxial fatigue properties which were calculated from the Roessle-Fatemi hardness estimation method. It was observed from the comparison that for steels and Inconel 718 obtaining shear fatigue properties from uniaxial fatigue properties, which were in turn calculated from Roessle-Fatemi hardness estimation method, resulted in reasonable estimations. The performance of shear fatigue properties estimated from the Roessle-Fatemi hardness method was also used for the analysis of variable amplitude axial-torsion fatigue tests performed on three types of ductile steel. Reasonable predictions of fatigue life were observed for the analyzed variable amplitude tests, as most of the predictions fell within a factor of 3 of the experimental data. Furthermore, in order to use the Roessle-Fatemi hardness method for estimating the shear fatigue behavior of titanium alloys, this method was modified based on the uniaxial fatigue properties of titanium alloys.
Ali Fatemi (Committee Chair)
Mohamed Samir Hefzy (Committee Member)
Hongyan Zhang (Committee Member)
Syed Reza Rizvi (Committee Member)
Nicholas R Gates (Committee Member)
169 p.
Automotive Materials; Engineering; Mechanical Engineering; Mechanics
multiaxial fatigue; variable amplitude; service loading; non-proportional; critical plane; fatigue life estimation; ductile behaving steel; brittle behaving steel; normal and shear stress interactions; estimation of shear fatigue properties

Recommended Citations

Citations

  • Sharifimehr, S. (2018). Multiaxial Fatigue Analysis under Complex Non-proportional Loading Conditions [Doctoral dissertation, University of Toledo]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=toledo1544787705876488

    APA Style (7th edition)

  • Sharifimehr, Shahriar. Multiaxial Fatigue Analysis under Complex Non-proportional Loading Conditions. 2018. University of Toledo, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=toledo1544787705876488.

    MLA Style (8th edition)

  • Sharifimehr, Shahriar. "Multiaxial Fatigue Analysis under Complex Non-proportional Loading Conditions." Doctoral dissertation, University of Toledo, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=toledo1544787705876488

    Chicago Manual of Style (17th edition)

toledo1544787705876488
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This open access ETD is published by University of Toledo and OhioLINK.