基于损伤力学的复杂航空构件疲劳寿命预估

为提高复杂航空构件疲劳寿命的分析精度,降低对试验的依赖程度,本文基于考虑局部应力状态的损伤力学理论,利用USDFLD子程序将损伤控制方程嵌入ABAQUS中,对航空挡块结构的疲劳寿命进行了预估仿真试验,实现了评估复杂构件裂纹萌生寿命的损伤力学-有限元分析方法,并与名义应力法的分析结果进行了对比。发现对于本次试验的预估,损伤力学法和名义应力法计算寿命与试验平均寿命的相对误差分别为6.9%和20%。因此,对于复杂结构形式,损伤力学法具有更高的精度,可以大大减少疲劳试验数量。     

基于损伤力学方法的铆接结构疲劳寿命预估

将损伤力学-有限元方法应用于飞机结构疲劳寿命预估中,对机翼蒙皮压窝形式的铆接结构进行了寿命计算和分析,得到了结构的疲劳寿命和疲劳损伤演化过程,并对铆接试验件进行了疲劳试验,将损伤力学方法的预测结果与试验结果进行了比较。分析结果反映出结构疲劳损伤累积初期较为缓慢、后期速率急剧上升的过程,符合损伤演化规律。在180MPa载荷水平下,计算寿命与试验平均寿命的相对误差为11.3%,满足工程精度要求。从而验证了损伤力学方法应用于实际工程结构寿命预测的可行性和可靠性。     

各向异性损伤力学在螺纹疲劳寿命预估中的应用

引用损伤力学方法研究金属构件疲劳问题。在微结构力学模型基础上建立轴对称的各向异性疲劳损伤本构关系,通过有限元-附加力解法编制考虑各向异性损伤的有限元程序。应用引入门槛条件的损伤演化方程,并以损伤划分步长预估了构件疲劳裂纹形成与扩展寿命。用这一方法预估30CrMnSiNi2Aφ5和φ8螺栓全寿命。结果表明,理论S-N曲线与试验S-N曲线吻合良好并且门槛条件对修正低应力下疲劳寿命有很好的效果。本方法所需机时较少,可用于工程实际构件的高周疲劳寿命预估及抗疲劳优化设计。     

随机载荷作用下结构疲劳损伤的累积

本文提出了一种计算在随机载荷作用下具有随机疲劳强度的结构的累积疲劳损伤与疲劳寿命的概率密度函数及可靠性函数的方法.对在平稳窄带高斯随机应力作用下的金属与钢筋混凝土构件,给出了上述函数的解析表达式.数例计算表明,理论结果与数字模拟结果颇为吻合.     

长期载人航天器舱内金属构件盐雾腐蚀疲劳寿命预估的损伤力学方法

根据热力学原理分别建立了预估单纯疲劳载荷作用下和单纯腐蚀环境下长期载人航天器舱内金属构件的损伤演化方程;并建立了疲劳载荷作用下和预腐蚀疲劳作用下光滑标准件的疲劳寿命预估方法;根据所建立方法和无腐蚀、预腐蚀条件下标准件的疲劳试验结果,建立了损伤演化方程中材质参数的识别方法;最后,建立了长期载人航天器舱内金属构件盐雾腐蚀疲劳寿命预估的损伤力学方法。计算结果与试验结果相比误差在5%以内,二者吻合较好。本文研究可为其他金属构件的预腐蚀和腐蚀疲劳寿命预估提供参考。     

含缺口构件高周疲劳寿命的损伤力学封闭解法

本文根据损伤力学建立含缺口板守恒积分、应力与应变集中系数公式以及疲劳裂纹形成寿命的封闭解法。对铝合金含缺口板寿命预估结果与实验结果基本一致。本方法节省机时并可代替大量实验,具有一定的工程实用性。     

沥青混合料疲劳过程的损伤力学分析

采用损伤力学方法研究沥青混合料的疲劳失效问题。针对悬壁梁弯曲疲劳试件,推导出疲劳过程中应力场、损伤场和疲劳裂纹形成寿命的工程封闭公式。根据沥青混合料特点,提出一种模拟疲劳裂纹扩展的特征单元失效模式,从而将疲劳裂纹形成与扩展两个阶段统一用损伤力学理论进行描述和分析。本文对沥青混合料试件的疲劳裂纹形成寿命与扩展寿命分段进行了预测,还对疲劳过程中刚度衰减及位移幅值的演化过程进行了数值模拟计算。理论预期与实验结果吻合良好。     

工程结构的振动疲劳问题

阐明了结构振动疲劳问题的概念和定义,并指出它的特点以及它与常规结构疲劳问题的区别,文中建议将疲劳问题分为结构静态疲劳和动态疲劳两类,对这两类问题统一按照静态疲劳方法进行处理,不但不符合实际问题本身的规律性,还可能造成分析和试验的较大误差。     

基于损伤力学方法的中周疲劳双尺度损伤模型

通常对于发生在高低周疲劳之间,损伤兼具弹塑性损伤特性的疲劳行为称为中周疲劳。本文将损伤力学方法与细观力学模型相结合,对双尺度代表性体积单元(RVE)的本构关系进行了合理假设,并分别研究了两个尺度的损伤演化规律。根据细观力学方法,考虑两相损伤的分别演化和互相作用,最终得到RVE的损伤演化模型。然后根据ABAQUS软件的接口与UMAT对接实现二次开发,建立了材料疲劳寿命预估的损伤力学——有限元解法。对铝合金LC4CS缺口件进行疲劳寿命预估以及损伤分析计算,预估结果均处于试验结果的两倍误差带内,验证了所提出双尺度模型的有效性。     

非对称循环载荷下材料低周疲劳寿命分析与计算

提出了一个用于计算非对称循环载荷下材料低周疲劳寿命的累积损伤模型和方法,该方法利用全应变幅及损伤积累来控制和计算疲劳寿命,并给出了裂纹的开裂尺寸和开裂方向,这为我们进行各种疲劳寿命计算以及结构优化设计提供了一个新的思路和方法。     

Revised damage evolution equation for high cycle fatigue life prediction of aluminum alloy LC4 under uniaxial loading

The fatigue life prediction for components is a difficult task since many factors can affect the final fatigue life. Based on the damage evolution equation of Lemaitre and Desmorat, a revised two-scale damage evolution equation for high cycle fatigue is presented according to the experimental data, in which factors such as the stress amplitude and mean stress are taken into account. Then, a method is proposed to obtain the material parameters of the revised equation from the present fatigue experimental data. Finally, with the utilization of the ANSYS parametric design language (APDL) on the ANSYS platform, the coupling effect between the fatigue damage of materials and the stress distribution in structures is taken into account, and the fatigue life of specimens is predicted. The outcome shows that the numerical prediction is in accord with the experimental results, indicating that the revised two-scale damage evolution model can be well applied for the high cycle fatigue life prediction under uniaxial loading.     

New approach based on continuum damage mechanics with simple parameter identification to fretting fatigue life prediction

A new continuum damage mechanics model for fretting fatigue life prediction is established. In this model, the damage evolution rate is described by two kinds of quantities. One is associated with the cyclic stress characteristics obtained by the finite element(FE) analysis, and the other is associated with the material fatigue property identified from the fatigue test data of standard specimens. The wear is modeled by the energy wear law to simulate the contact geometry evolution. A two-dimensional(2D) plane strain FE implementation of the damage mechanics model and the energy wear model is presented in the platform of ABAQUS to simulate the evolutions of the fatigue damage and the wear scar. The effect of the specimen thickness is also investigated. The predicted results of the crack initiation site and the fretting fatigue life agree well with available experimental data. Comparisons are made with the critical plane SmithWatson-Topper(SWT) method.     

利用间隙元的方法计算和分析疲劳寿命

提出了一个利用结构有限元方法中间隙元的原理来计算和分析疲劳寿命的新的累积损伤模型和方法。该方法利用间隙来模拟裂纹的形成和扩展 ,并提出新的累积损伤理论。不仅可以得到构件的疲劳总寿命 ,而且还可以用于计算裂纹的生成寿命、扩展寿命。同时又描述了裂纹的开裂过程 ,即裂纹的开裂尺寸和开裂方向。这为进行各种疲劳强度设计提供了一个新的思路和方法     

一种新型的宽带随机谱下疲劳寿命计算模型的建立与分析

通过严密的数学推导和具体的数值分析，建立了一种新型的宽带随机载荷谱下疲劳寿命计算模型，数值计算表明，本模型较国际上已有的几种有代表性的近似计算模型有更大的适应范围和更高的精度。     

随机不确定性下Kriging辅助的谐波减速器柔轮疲劳寿命预测

柔轮作为谐波减速器核心传动件,在循环交变载荷作用下容易发生疲劳失效,其疲劳寿命直接影响谐波减速器的工作寿命。为揭示随机不确定性因素对谐波减速器柔轮疲劳寿命的影响规律,本文考虑材料属性和载荷等不确定因素对谐波减速器柔轮开展疲劳寿命预测研究,以期实现更客观地评估柔轮疲劳寿命。首先,建立柔轮的三维模型和有限元模型,通过有限元分析及寿命计算获得确定性条件下的柔轮寿命。然后,将材料属性及载荷考虑为随机变量,采用拉丁超立方抽样方法对柔轮进行试验设计。最后,基于主动学习Kriging模型和柔轮材料P-S-N曲线,通过逐一加点的方式对柔轮进行疲劳寿命分析,获得疲劳寿命统计结果,并与确定性条件下的柔轮疲劳寿命结果进行对比。结果表明,随机不确定因素影响下柔轮疲劳寿命预测结果与确定性条件下相比有所降低,对柔轮抗疲劳设计具有一定指导意义。     

A criterion for high-cycle fatigue life and fatigue limit prediction in biaxial loading conditions

This paper presents a criterion for high-cycle fatigue life and fatigue strength estimation under periodic proportional and non-proportional cyclic loading. The criterion is based on the mean and maximum values of the second invariant of the stress deviator. Important elements of the criterion are: function of the non-proportionality of fatigue loading and the materials parameter that expresses the materials sensitivity to non-proportional loading. The methods for the materials parameters determination uses three S–N curves: tension–compression, torsion, and any non-proportional loading proposed. The criterion has been verified using experimental data, and the results are included in the paper. These results should be considered as promising. The paper also includes a proposal for multiaxial fatigue models classification due to the approach for the nonproportionality of loading.     

Damage precursor detection for structures subjected to rotational base vibration

This paper presents a nonlinear dynamic methodology for monitoring precursors of fatigue damage in metallic structures under variable rotational base excitation. The methodology accounts for important nonlinearities due to the complex loading generated by variable rotation and structural degradation. The sources of the nonlinearities include: structural stiffening due to gyroscopic motion and high-response amplitude at the fundamental mode, softening due to inertial forces and gyroscopic loads, and localized microscopic material damage and micro-plasticity. The loading intensity and number of vibration cycles increase the influence of these effects. The change in the dynamic response due to fatigue damage accumulation is experimentally investigated by exciting a cantilever beam at variable rotational base motions. The observed fatigue evolution in the material microstructure at regions of large stresses (and the resulting progressive structural softening) is tracked by quantifying the growth in the tip response, the change in the fundamental natural frequency of the beam and the skewedness of the stepped-sine response curve. Previous understanding of the structural dynamic behavior is necessary to ascertain the damage precursor location and evolution. Nanoindentation studies near the beam clamped boundary are conducted to confirm the gradual progression in the local mechanical properties as a function of loading cycles, and microstructural studies are conducted to obtain qualitative preliminary insights into the microstructure evolution. This study demonstrates that careful monitoring of the nonlinearities in the structural dynamic response can be a sensitive parameter for detection of damage precursors.     

A damage function used for prediction of low cyclic fatigue life

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阵风谱载下疲劳寿命可靠性预测

基于维概率ＭＩＮＥＲ准则,建立了在阵风谱载下对结构构件疲劳寿命进行可靠性预测的方法。根据一组ＬＹ１２－ＣＺ铝合金中心孔试件的疲劳试验数据对上述方法进行了较为成功的验证,验证结果表明本方法的预测值与试验值吻合良好,具有较好的工程实用价值     

吊车荷载作用下钢结构吊车梁的疲劳可靠寿命评估

从Miner累积损伤的定义出发,视累积损伤为随机过程,临界损伤为随机变量,基于疲劳动态可靠性理论,提出了在役钢结构吊车梁疲劳剩余寿命的可靠寿命评估法。之后与现行《钢结构检测评定与加固技术规程》(YB9257-96)中安全期限寿命评估法进行了分析比较,说明了安全寿命评估方法的概率意义。算例分析结果表明,本文提出的可靠寿命评估方法更加合理。