多轴载荷下缺口试件疲劳寿命预测研究

基于临界平面法,在分析光滑薄壁圆管试件疲劳寿命预测模型的基础上,借助有限元应力应变分析,进一步将模型推广应用到了缺口试件的多轴疲劳寿命预测中,并利用坐标变换原理,明确了临界平面及有效循环变量的确定方法.在存在平均应力的情况下,分析了平均应力对疲劳寿命的影响,并对所建模型进行了平均应力修正.     

A continuum damage model for the high-cycle fatigue life prediction of styrene-butadiene rubber under multiaxial loading

In the present contribution, the relationship between the fatigue life of styrene-butadiene rubber (SBR) and the stretch amplitude was established. Focusing on the multiaxial loading effect on the life duration of SBR, experimental tests were conducted using cylindrical specimens subjected to tension and torsion loadings under constant and variable amplitudes. Based upon the continuum damage mechanics approach, a three-dimensional model was derived and coupled with the cracking energy density criterion to predict the fatigue life of SBR. The capabilities of the model, which requires only three damage parameters to be identified, were analysed and a good agreement between predicted values and experimental data were clearly highlighted for tension and torsion loadings both in constant and variable amplitudes.     

基于临界平面法的多轴疲劳寿命估算模型研究

基于临界平面法,分析了WB模型的缺陷,发现：WB模型中的法向应变变程不能很好的反映材料非比例循环加载下的附加强化现象,且模型中的经验常数是一个与寿命相关的参数,该参数不能简单的利用拉伸和扭转疲劳极限来确定。为克服WB模型的缺陷,提出了一个新的多轴疲劳损伤参量,引入了一个新的应力相关因子,建立了新的寿命估算模型。新的损伤参量不含经验常数,应力相关因子能够反映材料非比例循环加载下的附加强化现象,所建模型能够精确估算材料的多轴疲劳寿命,便于工程应用。     

A simple multiaxial fatigue criterion for metals

A new simple multiaxial high-cycle fatigue endurance criterion, suitable for situations where the convex hull associated with the stress path approximates well an ellipsoid, is proposed. It considers, as measures of fatigue solicitation: (i) a new definition for the equivalent shear stress amplitude; and (ii) the maximum principal stress along the stress history. Assessment of the resulting criterion for a wide range of in-phase and out-phase cyclic loads shows that it compares very well with experimental data published in the literature. To cite this article: C.A. Gonçalves et al., C. R. Mecanique 332 (2004).

Résumé

On propose un critère simple d'endurance à la fatigue polycyclique, applicable à des situations pour lesquelles l'envelope convexe associé à l'histoire des contraintes s'approche bien d'une ellipse. Le critère considère, comme mesures de solicitation à la fatigue : (i) une nouvelle définition de l'amplitude de contrainte de cisaillement ; et (ii) la contrainte principale maximale au cours de l'histoire de chargement. Pour citer cet article : C.A. Gonçalves et al., C. R. Mecanique 332 (2004).     

Nonlinear energy-based relations and numerical procedure for multiaxial local analysis

In this paper, two sets of nonlinear energy-based approximate models are formulated and used to predict the local parameters in a two-phase composite system. A numerical procedure using Newton–Raphson method is developed to solve each system of nonlinear equations in small time steps. The procedure allows the estimation of the local parameters through various loading and unloading steps and therefore, is independent of a yield criterion. The local strain results obtained using the procedure are compared with experimental results obtained at the depth of circumferentially notched particulate metal matrix composite subjected to variable amplitude loads. The numerical results are in good agreement with corresponding experimental results for the geometry and load paths considered.     

A unified multiaxial fatigue damage parameter

According to the critical plane principle, a unified multiaxial fatigue damage parameter is presented based on the varying behaviour of the strains of the critical plane. Both the parameters of the maximum shear strain amplitude and normal strain excursion between adjacent turning points of the maximum shear strain on the critical plane are considered in the multiaxial fatigue damage parameter presented. An equivalent strain amplitude is made with both parameters of the maximum shear strain amplitude and normal strain excursion by means of von Mises criterion. Thus a new multiaxial fatigue damage parameter proposed in this paper may be used under either proportional or nonproportional loading, and may also be reduced to a uniaxial form. It is used to predict multiaxial fatigue life and good agreement is demonstrated by experimental data. The project is supported by the National Doctoral Foundation of China and National Natural Science Foundation of China.     

一种考虑拉伸保持效应的多轴疲劳寿命模型

通过定义考虑拉伸保载效应的CFI因子(creep-fatigue interaction factor),将拉伸蠕变损伤和疲劳损伤进行非线性耦合. 根据断裂实验的观察,针对拉伸主 导的裂纹萌生、扩展及破坏的多轴疲劳问题,给出了一个基于临界面方法的能量型高温多轴 疲劳寿命预测模型. 所给出的模型可对不同温度、不同载荷特点、不同保载时间的多轴疲劳 寿命进行预测,模型的材料参数不依赖于温度和载荷. 并且此方法可以很方便地推广到其它 因素主导破坏的高温多轴疲劳寿命预测. 通过拟合高温合金Udimet720Li单轴带保持时间的 低循环疲劳(low cycle fatigue, LCF)寿命试验数据,得到了材料常数. 结合黏 塑性有限元分析方法,对高温双轴带保载循环载荷下Cruciform试件的寿命进行了 预测,预测结果基本落在2倍分散带内,达到工程的要求,证明了该模型的有效性.     

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.     

A damage function used for prediction of low cyclic fatigue life

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Definition of a new predictor for multiaxial fatigue crack nucleation in rubber

From an engineering point of view, prediction of fatigue crack nucleation in automotive rubber parts is an essential prerequisite for the design of new components. We have derived a new predictor for fatigue crack nucleation in rubber. It is motivated by microscopic mechanisms induced by fatigue and developed in the framework of Configurational Mechanics. As the occurrence of macroscopic fatigue cracks is the consequence of the growth of pre-existing microscopic defects, the energy release rate of these flaws need to be quantified. It is shown that this microstructural evolution is governed by the smallest eigenvalue of the configurational (Eshelby) stress tensor. Indeed, this quantity appears to be a relevant multiaxial fatigue predictor under proportional loading conditions. Then, its generalization to non-proportional multiaxial fatigue problems is derived. Results show that the present predictor, which is related to the previously published predictors, is capable to unify multiaxial fatigue data.     

Correction to: Mean stress effect in multiaxial fatigue limit criteria

Archive of Applied Mechanics - The calculation of the parameter was written without last operations (addition of 1, squaring the product, subtraction of 1).     

Models of multiaxial fatigue fracture and service life estimation of structural elements

We study criteria and models of multiaxial fracture under the conditions of low-cycle fatigue (LCF). The model parameters are determined by using the data of uniaxial fatigue tests for different coefficients of the cycle asymmetry. A procedure for calculating the stress state of the compressor disk in a gas turbine engine (GTE) in the flight cycle of loading is outlined. The calculated stress state and models of multiaxial fatigue fracture are used to estimate the service life of the compressor disk. The results are compared with the observational data collected during the operation.     

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     

A micro-mechanically based continuum damage model for fatigue life prediction of filled rubbers

This paper presents a continuum damage model based on two mechanisms: decohesion between fillers and matrix at a micro-scale followed by a crack nucleation at a macro-scale. That scenario was developed considering SEM observations and an original experimental procedure based on simple shear and tension specimens. Damage accumulation is related to fatigue life using the continuum damage mechanics (CDM). The material behavior is investigated using the statistical framework introduced by Martinez et al. (2011). A Finite Element implementation is proposed and some numerical examples are provided.     

Fatigue limit under multiaxial loadings: on the definition of the equivalent shear stress

The goal of the present paper is to propose a criterion to predict the fatigue strength of hard metals under conditions of multiaxial, non-proportional loadings. It is very simple to compute, but still provides very good results for a wide range of in-phase and out-of-phase cycling loads.     

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。     

Bi-variable damage model for fatigue life prediction of metal components

Based on the theory of continuum damage mechanics,a bi-variable damage mechanics model is developed,which,according to thermodynamics,is accessible to derivation of damage driving force,damage evolution equation and damage evolution criteria. Furthermore,damage evolution equations of time rate are established by the generalized Drucker’s postulate. The damage evolution equation of cycle rate is obtained by integrating the time damage evolution equations,and the fatigue life prediction method for smooth specimens under repeated loading with constant strain amplitude is constructed. Likewise,for notched specimens under the repeated loading with constant strain amplitude,the fatigue life prediction method is obtained on the ground of the theory of conservative integral in damage mechanics. Thus,the material parameters in the damage evolution equation can be obtained by reference to the fatigue test results of standard specimens with stress concentration factor equal to 1,2 and 3.     

A fatigue life prediction methodology for cylindrical shell with an inclined crack under torsion

Considered is the fatigue life prediction of a cylindrical shell with an inclined crack under torsion. The effects of the initial angles of inclination and shell curvatures on fatigue crack growth rate are investigated. The mixed mode fracture parameters are extended to describe the fatigue crack growth behavior. A methodology for fatigue life prediction is suggested.     

A general cyclic plasticity model taking into account yield surface distortion for multiaxial ratchetting

Most of the theoretical studies devoted to multiaxial ratchetting are focused on the location of the macroscopic yield domain in order to predict the correct direction of plastic strain rate, since normality of the plastic strain rate to the yield surface is usually assumed. To the authors' knowledge, the shape of subsequent yield surfaces was always kept constant in these models for simplicity reasons but unlike experimental observations. In a previous paper [J. Eng. Mater. Technol. 124(4) (2002) 402], the authors have explained the need to take into account yield surface distortion in macroscopic modeling and have therefore proposed such a constitutive model but only for biaxial loadings. In the present paper, the generalization of this distortional model is proposed for any loading paths. The model is then identified and validated on a large data base obtained firstly with an efficient polycrystalline model that can predict multiaxial ratchetting as well as yield surface distortion, and secondly with the experimental results of complex tests realized on a type 316L stainless steel.