【作者】 刘宇杰；

【导师】 高庆； 康国政；

【作者基本信息】 西南交通大学 ， 固体力学， 2008， 博士

【摘要】 材料和构件的疲劳破坏问题一直是国内外学者和工程界研究和关心的热点课题。航空航天、核工业、化工以及铁路机车车辆中许多金属构件在复杂加载条件下服役的,要对这些结构构件的可靠性、安全性和疲劳寿命进行合理的评估,必须要得到能够精确描述复杂加载条件下材料变形行为的本构方程与描述材料衰坏过程的损伤演化方程以及相应的失效准则。复杂加载条件下材料的本构行为描述和疲劳失效准则的研究一直是固体力学界的研究重点、难点与热点之一。近二十年来,国内外学者对材料的循环变形行为进行了大量的研究,并已建立了一些循环塑性和粘塑性本构模型,但对于非对称应力控制循环中产生的棘轮行为(塑性应变的循环累积)的本构描述尚不尽完善。对于材料的低周疲劳行为,目前绝大多数的研究都是针对应变控制循环加载工况,对于应力控制循环加载下的低周疲劳研究较少。特别是在有平均应力的应力循环下,材料将产生逐渐增长的棘轮变形,这种情况下,估算材料的疲劳寿命,必须同时考虑棘轮行为和疲劳损伤及它们之间的相互作用。因此,有必要对应力控制循环下的棘轮-疲劳交互作用做更加深入的研究,并发展非比例多轴应力复杂加载条件下的考虑棘轮效应的疲劳失效模型。这对于固体力学学科及其相关学科具有重要的理论意义,对工程构件更可靠的设计和使用也具有重要的应用价值。为了对金属材料的非比例多轴棘轮-疲劳交互作用行为进行深入系统的实验和理论研究,本论文开展了如下工作:1.在室温下,对三类材料(循环硬化材料304不锈钢;循环软化材料调质42CrMo钢;循环稳定的退火42CrMo钢)室温单轴和非比例多轴应力循环加载条件下的棘轮变形、疲劳失效行为及损伤演化规律进行系统的实验研究。通过研究,得到了材料棘轮-疲劳交互作用行为的基本特性,为耦合损伤循环本构模型以及考虑棘轮效应的低周疲劳失效模型的理论研究奠定了基础。2.在连续介质损伤力学和统一粘塑性循环本构的框架下,提出了一个新的耦合损伤的粘塑性本构模型,对调质42CrMo钢的全寿命棘轮行为进行了描述,并结合所选用的失效判据,对材料在应力循环下的疲劳寿命进行了预测。该模型在粘塑性本构模型中引入了疲劳损伤,将损伤分为宏观弹性损伤和塑性损伤两部分,并采用不同的损伤演化方程来描述这两类损伤。针对材料不同的失效模式,分别采用损伤变量门槛值和最大应变作为失效判据。模型的模拟结果表明,发展的耦合损伤本构模型合理地描述了调质42CrMo钢单轴和多轴全寿命棘轮行为,并较准确地预测了相应的疲劳寿命。3.根据材料不同的特性,以系统的实验研究为基础,建立了考虑棘轮效应的简化疲劳失效模型。这些模型以应力作为基本参量,反映了棘轮效应对疲劳寿命的影响,能方便地估算各种非对称应力循环加载工况下的疲劳寿命。更多还原

【Abstract】 The fatigue of material and structure components is always concerned by scholars and engineers. In the area of aerospace, nuclear industry, chemical industry and railway, many metal components are subjected to a complex loading condition. In order to evaluate the reliability, security and fatigue life of such componetnts reasonablely, it is necessary to obtain an accurate constitutive model to describe the material deformation behavior of materials under the complex loading conditions, and a damage evolution quation to describe the performance deterioration of materials during the loading, as well as a fatigue failure criterion to predict the failure life of materials. At present, the constituitve modelling for materials subjected to complex loading conditions and the construction of relative fatigue failure model are one of the key issues for solid mechanics. In the last two decades, many experimental and theoretical studies on the cyclic deformation of metal have been achieved. The cyclic plastic and visco-plastic constitutive models have advanced significantly. However, the constitutive modelling to the ratchetting of the metals has not been perfectely solved yet, and much further effort is necessary. For the low cycle fatigue of materials, most of referable literatures concern the cases under the strain-controlled loading, while few literatures discusss the low cycle faituge under the stress-controlled loading. Ratchetting, a cyclic accumulation of inelastic deformation, will occur under asymmetrical cyclic stressing. It is extremely necessary to consider the ratchetting, fatigue and their interaction simultaneously in order to simulate the cyclic deformation and fatigue failure of the materials subjected to the stress cyclic loading. Therefore, it is very significant to discusss the ratchetting -fatigue interaction experimentally and theoretically.In order to realize the ratchetting-fatigue interaction of metal materials and develop a damage-coupled constitutive model and fatigue failure model, this thesis has carried out the studies as follows:1. An experimental study was performed to the uniaxial and non-proportionally multiaxial ratchetting deformation, fatigue failure and damage evolution of the materials (i.e., SS304 stainlesss steel, annealed 42CrMo steel and tempered 42CrMo steel) under asymmetrical stress cyclic loading and at room temperature. Some significant results of ratchetting-fatigue interaciton are obtained by analyzing the experimental data, which are very useful to construct corresponding constitutive model and fatigue failure model.2. Based on the framework of unified visco-plasticity and continuum damage mechanics, a damage-coupled visco-plastic cyclic constitutive model is proposed to simulate the whole-life ratchetting. Combined with the corresponding fatigue criterion, the model can predict the fatigue failure life too. In the proposed model, the damage is introduced, and the damage is divided into two parts, i.e., macroscopic elastic damage and plastic damage, which were described by different evolution equations, respectively. The threshold value of damage and maximum strain are adopted as failure criterion to reflect fatigue failure and ductile failure respectively. It is shown that the model simulates the whole-life ratchetting behavior and fatigue life of tempered 42CrMo steel reasonably.3. Based on the systemic experimental study, a stress-based simplified fatigue failure models were proposed to predict the fatigue life of the materials by addressing the ratchetting-fatigue interaction. In the model, the stress paramters are adopted as basic parameter, and the effects of ratchetting deformation and multiaxial loading path on the fatigue life are also included. The fatigue lives of the materials under various cyclic stressing cases can be predicted directly by the simplified failure model.更多还原