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Multiaxial fatigue and deformation including non-proportional hardening and variable amplitude loading effects.

机译：多轴疲劳和变形，包括非比例硬化和可变振幅载荷效应。

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摘要

This study investigates fatigue damage and deformation behavior under multiaxial loading conditions, with the aim of evaluating reliable predictive models for life predictions. Life prediction for multiaxial variable amplitude loading involves a variety of issues to be considered. These include cyclic plasticity modeling, material properties and variations with hardness and microstructure, fatigue damage evolution, fatigue damage quantification parameters, cycle counting procedure, damage accumulation rule, and effects of multiaxial load non-proportionality on deformation and fatigue behaviors.;To evaluate the effect of hardness and microstructure on additional non-proportional hardening and fatigue behaviors, 1050 steel in normalized, quenched and tempered, and induction hardened conditions as well as 304L stainless steel were utilized. Constant amplitude in-phase and 90º out-of-phase strain-controlled axial-torsional cyclic tests were conducted. Reductions in the non-proportional cyclic hardening were observed as the microstructure of 1050 steel changed from pearlitic-ferritic with lower hardness to tempered martensite with higher hardness. Significant non-proportional cyclic hardening was also observed for 304L stainless steel with austenitic microstructure. Multiaxial data generated in this study as well as multiaxial deformation data of several materials from literature suggest non-proportional cyclic hardening can be related to uniaxial cyclic hardening. Non-proportional hardening coefficients predicted from a proposed equation based on this observation were found to be in very good agreement with the experimental values in this study and from literature. Similar fatigue life variation as a function of hardness of steels was found for in-phase and out-of-phase loadings, with higher ductility beneficial in low cycle fatigue (LCF) and higher strength beneficial in high cycle fatigue (HCF).;Multiaxial fatigue data were satisfactorily correlated for all hardness levels with the Fatemi-Socie parameter. Furthermore, in order to predict multiaxial fatigue life of steels in the absence of any fatigue data, the Roessle-Fatemi hardness method was used. The applicability of the prediction method based on hardness was examined for several steels under a wide range of loading conditions. The great majority of the observed fatigue lives were found to be in good agreement with predicted lives.;Some discriminating multiaxial cyclic strain paths with incremental and random sequences were used to investigate fatigue and cyclic deformation behaviors of materials with low and high sensitivity to non-proportional loadings. Tubular specimens made of 1050 quenched and tempered (QT) steel with no non-proportional hardening and 304L stainless steel with significant non-proportional hardening were utilized. The 1050 QT steel was found to exhibit very similar stress responses under various multiaxial loading paths, whereas significant effects of loading sequence were observed on stress responses of 304L stainless steel. In-phase cycles with a random sequence of axial-torsional cycles on an equivalent strain circle were found to cause cyclic hardening levels similar to 90° out-of-phase loading of 304L stainless steel. In contrast, straining with a small increment of axial-torsional on an equivalent strain circle resulted in higher stress than for in-phase loading of 304L stainless steel, but the level of hardening was much lower than for 90° out-of-phase loading. Tanaka's non-proportionality parameter coupled with a Fredrick-Armstrong incremental plasticity model, and Kanazawa et al.'s empirical formulation as a representative of such empirical models were used to predict the stabilized stress response of the two materials under variable amplitude axial-torsional strain paths. While Kanazawa et al.'s empirical formulation could not distinguish between strain paths with random and incremental sequences of straining, resulting in significant over-prediction of stress for 304L stainless steel, consistent results between experimental observations and predictions were obtained by employing the plasticity model.;Contrary to common expectations, fatigue lives for 1050 QT steel with no non-proportional hardening were found to be more sensitive to non-proportionality of loadings as compared to 304L stainless steel with significant non-proportional hardening. In-phase cycles with random sequences of axial-torsional within an equivalent strain circle, while resulting in higher stress response for 304L stainless steel, did not significantly affect fatigue life for either material. Experimentally observed failure planes for all strain paths in this study were in very good agreements with predicted failure planes based on the Fatemi-Socie critical plane parameter. Bannantine-Socie and Wang-Brown cycle counting methods were utilized to identify loading cycles for variable amplitude strain paths in this study. Fatigue damage for each counted cycle was evaluated using Fatemi-Socie damage parameter taking into consideration constitutive behavior effects and reflective of the material damage mechanisms. Linear cumulative fatigue damage was then employed to account for accumulation of damage. Fatigue lives for both materials under these strain paths were predicted satisfactorily employing this approach and either Bannantine-Socie or Wang-Brown cycle counting methods.;Finally, cracking behavior was analyzed for different materials investigated and under various loading conditions. Micro-cracks were observed to be around the maximum shear plane for in-phase and 90° out-of-phase loadings. It was also observed that the ratio of crack initiation life to total fatigue life as well as the crack growth rate depend on variety of factors including strain amplitude level, load non-proportionality, material ductility, and specimen geometry. It was also observed that cracks nucleate and grow on a wide range of planes around the critical plane depending on the load non-proportionality and strain level. Crack growth rates for in-phase and 90º out-of-phase loading were correlated well by Reddy-Fatemi effective strain-based intensity factor.
机译：这项研究调查了多轴载荷条件下的疲劳损伤和变形行为，目的是评估可靠的寿命预测模型。多轴可变振幅载荷的寿命预测涉及许多要考虑的问题。其中包括循环塑性建模，材料特性以及硬度和微观结构的变化，疲劳损伤演变，疲劳损伤量化参数，循环计数程序，损伤累积规则以及多轴载荷非比例对变形和疲劳行为的影响。硬度和显微组织对附加的非比例硬化和疲劳行为的影响，利用了1050钢在正火，调质和感应淬火条件下以及304L不锈钢。进行了恒定振幅同相和90º异相应变控制的轴向扭转循环试验。随着1050钢的显微组织从较低硬度的珠光体-铁素体转变为较高硬度的回火马氏体，观察到非比例循环淬火的减少。还观察到具有奥氏体微观结构的304L不锈钢有明显的非比例循环硬化。这项研究中产生的多轴数据以及文献中几种材料的多轴变形数据表明，非比例循环硬化可能与单轴循环硬化有关。根据该观察结果，从提议的方程式预测的非比例硬化系数与本研究和文献中的实验值非常吻合。对于同相和异相载荷，发现了类似的疲劳寿命变化随钢的硬度变化的关系，具有较高的延展性有利于低周疲劳（LCF），具有较高的强度有利于高周疲劳（HCF）。疲劳数据与所有硬度水平均与Fatemi-Socie参数令人满意地相关。此外，为了在没有任何疲劳数据的情况下预测钢的多轴疲劳寿命，使用了Roessle-Fatemi硬度法。在多种载荷条件下，对几种钢进行了基于硬度的预测方法的适用性检验。发现大多数观察到的疲劳寿命与预测寿命非常吻合。;使用一些区分增量和随机序列的多轴循环应变路径来研究对非敏感性低和高的材料的疲劳和循环变形行为比例载荷。使用由1050淬火和回火（QT）钢制成的，无非比例硬化的管状试样和具有显着非比例硬化的304L不锈钢制成的管状试样。发现1050 QT钢在各种多轴加载路径下均表现出非常相似的应力响应，而加载顺序对304L不锈钢的应力响应却产生了显着影响。已发现在同一个应变圆上具有随机的轴向扭转循环序列的同相循环会导致循环硬化水平，类似于304L不锈钢的90°异相加载。相比之下，在等效应变圆上以较小的轴向扭转增量进行应变所产生的应力要高于304L不锈钢的同相加载，但硬化水平远低于90°异相加载的情况。 。田中的非比例性参数与Fredrick-Armstrong增量塑性模型以及Kanazawa等人的经验公式（作为此类经验模型的代表）一起用于预测两种材料在变幅轴向扭转应变下的稳定应力响应。路径。尽管Kanazawa等人的经验公式无法区分具有随机应变序列和增量应变序列的应变路径，从而导致304L不锈钢的应力过高预测，但通过使用可塑性模型，实验观察结果和预测结果之间具有一致的结果与通常的期望相反，发现没有非比例硬化的1050 QT钢的疲劳寿命与具有显着非比例硬化的304L不锈钢相比，对载荷的非比例性更敏感。在同一个应变圈内具有随机的轴向扭转序列的同相循环，同时导致304L不锈钢具有更高的应力响应，对两种材料的疲劳寿命均无明显影响。在这项研究中，实验观察到的所有应变路径的破坏平面与基于Fatemi-Socie临界平面参数的预测破坏平面非常吻合。在这项研究中，利用Bannantine-Socie和Wang-Brown循环计数方法来确定可变振幅应变路径的加载循环。使用Fatemi-Socie损伤参数评估每个计数周期的疲劳损伤，考虑到本构行为效应并反映出材料损伤机理。然后采用线性累积疲劳损伤来说明损伤的累积。使用这种方法以及Bannantine-Socie或Wang-Brown循环计数方法可以令人满意地预测这两种材料在这些应变路径下的疲劳寿命。最后，分析了在不同载荷条件下研究的不同材料的开裂行为。对于同相和90°异相载荷，观察到微裂纹在最大剪切平面附近。还观察到，裂纹萌生寿命与总疲劳寿命之比以及裂纹扩展速率取决于多种因素，包括应变幅度水平，载荷非比例性，材料延性和试样几何形状。还观察到，取决于载荷的非比例性和应变水平，裂纹在临界面周围的宽范围内成核并扩展。 Reddy-Fatemi基于应变的有效强度因子将同相和90º异相加载的裂纹扩展速率很好地关联在一起。

著录项

  • 作者

    Shamsaei, Nima.;

  • 作者单位

    The University of Toledo.;

  • 授予单位 The University of Toledo.;
  • 学科 Engineering Mechanical.
  • 学位 Ph.D.
  • 年度 2010
  • 页码 328 p.
  • 总页数 328
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类
  • 关键词

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