交变载荷下缺口根部应力—应变近似计算方法研究

发布时间：2018-11-04 11:39

【摘要】：机械零构件的疲劳破坏是目前机械故障诊断领域最引人关注的问题之一,目前的理论认为对疲劳寿命预测关键的在于获得缺口根部的应力-应变响应。在众多缺口根部应力-应变分析方法中,近似计算方法由于容易实现、计算速度快,在工程应用中有很高的实用价值。本文针对受到单轴或多轴比例与非比例加载的交变载荷下缺口根部的应力-应变近似计算方法进行研究。经过对三种最典型的建立外加名义应力-应变和缺口根部实际应力-应变关系的方法:Neuber法、ESED方法和热力学方法,从能量角度进行分析比较,发现三种方法的内在联系。通过引入一个类似于振动阻尼系数的参量C_q,建立了一个描述外加名义应力-应变和缺口根部实际应力-应变关系的统一表达式,(?)表示塑性变形过程中的热力学耗散系数,当它取不同值时分别对应Neuber法、ESED方法和热力学方法。一个统一表达式推广的增量表达形式方程被提出,该方程结合Jiang-Sehitoglu材料本构关系模型得到一个关于缺口根部应力-应变和应力-应变增量的方程组。利用得到的方程组可以实现非比例加载情况下对缺口根部的应力-应变响应路径进行计算。用FORTRAN编写了一个用于该方程组数值求解的计算机程序。有限元分析方法被用于确定缺口根部应力集中的位置和缺口几何参数:真实应力集中系数、真实应变集中系数和理论应力集中系数??。在四种多轴加载路径下,用本文提出的统一表达式计算得到的Neuber法、ESED方法和热力学方法对应的缺口根部应变响应,分别与实验数值比较,结果显示:Neuber法通常高估缺口根部的应变;ESED法通常低估缺口根部的应变;热力学方法得到的数值最接近实验数值。该结果与大量已有的实验和有限元分析结论相吻合。
[Abstract]:The fatigue failure of mechanical components is one of the most interesting problems in the field of mechanical fault diagnosis. The current theory holds that the key to predicting fatigue life is to obtain the stress-strain response at the root of the notch. Among many stress strain analysis methods at the root of notches, the approximate calculation method is easy to be realized, and has high practical value in engineering application. In this paper, the approximate calculation method of stress-strain of notch root under uniaxial or multiaxial proportional and non-proportional loading is studied. Through the analysis and comparison of three most typical methods to establish the relationship between nominal stress and strain and actual stress-strain at the notch root: Neuber method, ESED method and thermodynamic method, the internal relations of the three methods are found from the point of view of energy. By introducing a parameter, CQ, similar to the damping coefficient of vibration, a unified expression describing the relationship between nominal stress-strain and actual stress-strain at the notch root is established. The thermodynamic dissipation coefficient in plastic deformation process is expressed. When different values are taken, it corresponds to Neuber method, ESED method and thermodynamic method respectively. A generalized incremental expression equation is proposed, which combines with the constitutive model of Jiang-Sehitoglu materials to obtain a set of equations for stress-strain and stress-strain increment at the notch root. The equations can be used to calculate the stress-strain response paths of the notched roots under non-proportional loading. A computer program for the numerical solution of the equations is written in FORTRAN. The finite element method is used to determine the location and geometric parameters of notch stress concentration at the root: true stress concentration factor, real strain concentration factor and theoretical stress concentration factor. Under four multiaxial loading paths, the Neuber method, ESED method and thermodynamic method are used to calculate the notched root strain response corresponding to the proposed unified expression, respectively, compared with the experimental values. The results show that Neuber method usually overestimates the strain at the root of the notch. The ESED method usually underestimates the strain at the root of the notch, and the thermodynamic method is the closest to the experimental value. The results are in agreement with a large number of experimental and finite element analysis results.
【学位授予单位】：上海交通大学
【学位级别】：硕士
【学位授予年份】：2011
【分类号】：TH165.3

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