钛合金多轴疲劳寿命预测方法研究

发布时间：2018-04-13 05:17

本文选题：多轴疲劳 + 比例与非比例加载　；参考：《南京航空航天大学》2014年博士论文

【摘要】：工程实际中的许多结构和构件,如航空发动机叶片、机匣以及主轴等常常处于多轴应力状态,一方面是由于这些结构本身的几何形状比较复杂,其结构上往往具有小孔、凸台、沟槽、焊缝等,即使仅承受单一疲劳载荷作用,结构局部应力应变分布实际为多轴应力状态;另一方面这些结构在工作时往往承受多种载荷的循环作用,各载荷之间可能为比例加载,也可能为非比例加载,甚至是随机加载。因此,发展相应于多轴的疲劳理论和疲劳试验方法对于更好地解决实际问题有着十分重要的意义。本文选取航空发动机结构典型材料TC4钛合金,对其开展多轴疲劳试验与理论研究,论文的主要内容包括以下四个方面:针对航空发动机结构典型材料TC4钛合金开展了单轴、多轴疲劳试验研究,试验包括准静态拉伸、单向拉压疲劳、纯扭转疲劳、比例与非比例常幅多轴、变幅多轴、缺口常幅多轴及缺口变幅多轴疲劳试验。试验研究表明,TC4钛合金在循环载荷作用下呈现循环软化现象。采用位移控制模式对光滑薄壁圆筒进行常幅多轴疲劳试验的结果表明,45o和90o非比例载荷下,TC4钛合金非比例硬化现象明显,在低寿命区,非比例载荷路径下的疲劳损伤更大,疲劳寿命降低。采用载荷控制模式对两种类型的缺口件进行缺口多轴疲劳试验的结果表明,45o和90o非比例载荷下的疲劳损伤比比例载荷下的小,疲劳寿命较长。验证和评估了几种常用的多轴疲劳寿命模型对TC4钛合金多轴常幅疲劳寿命的预测能力,并在此基础上基于临界平面理论,提出了一种新的多轴疲劳寿命预测模型,该模型以最大剪应变幅平面为临界平面,考虑了临界平面上的正应力和正应变对疲劳损伤的贡献,可以同时适用于比例和非比例加载下的多轴疲劳问题,能够描述平均应力对材料多轴疲劳寿命的影响。采用TC4钛合金及其他5种金属材料的多轴常幅疲劳试验数据对该模型的寿命预测能力进行验证和评估,结果表明提出的多轴疲劳寿命模型具有较高的预测精度。基于本文提出的多轴疲劳寿命模型,针对变幅多轴载荷下的疲劳寿命问题,提出了一种变幅多轴载荷下的疲劳寿命预测方法。采用TC4钛合金及其他三种金属材料的多轴变幅疲劳试验数据对该方法的寿命预测能力进行了验证和评估,对几种材料的多轴变幅疲劳寿命预测结果均在试验结果的2倍分散带内。提出了缺口件在多轴载荷下疲劳危险点的确定方法。将临界距离理论应用于缺口件多轴疲劳寿命预测中,给出了多轴载荷作用下缺口件缺口根部损伤梯度修正的点法和线法的临界距离的计算方法。采用TC4钛合金缺口件的多轴疲劳试验数据对点法和线法的疲劳损伤梯度修正能力进行了评估,结果表明这两种方法具有良好的损伤梯度修正能力,并且修正能力相当。
[Abstract]:In engineering practice, many structures and components, such as aeroengine blades, casing and spindle, are often in a multi-axial stress state.Even if the groove, weld, etc., are subjected to single fatigue load, the local stress and strain distribution of the structure is actually a multiaxial stress state; on the other hand, these structures are often subjected to the cyclic action of many kinds of loads.The load may be proportional, non-proportional, or even random.Therefore, it is very important to develop fatigue theory and fatigue test method corresponding to multi-axis for solving practical problems better.In this paper, the typical material of aero-engine structure, TC4 titanium alloy, is selected to carry out multiaxial fatigue test and theoretical research. The main contents of this paper include the following four aspects: single axis is developed for TC4 titanium alloy, a typical material of aero-engine structure.The multiaxial fatigue tests include quasi-static tension, uniaxial tension and compression fatigue, pure torsional fatigue, proportional and non-proportional constant amplitude multiaxial, variable amplitude multiaxial, notched constant multiaxial and notch variable multiaxial fatigue test.The experimental results show that TC4 alloy shows cyclic softening under cyclic loading.The results of constant amplitude multiaxial fatigue test on smooth thin-walled cylinder by displacement control mode show that the non-proportional hardening phenomenon of TC4 titanium alloy is obvious under non-proportional load of 45o and 90o, and the fatigue damage of TC4 titanium alloy under non-proportional load path is more serious in low life region.The fatigue life is reduced.The results of multiaxial fatigue tests on two types of notched parts by load control mode show that the fatigue damage under non-proportional load is smaller and the fatigue life is longer than that under proportional load.The ability of several commonly used multiaxial fatigue life models to predict the multiaxial fatigue life of TC4 titanium alloy is verified and evaluated. Based on the critical plane theory, a new multiaxial fatigue life prediction model is proposed.The model takes the maximum shear strain amplitude plane as the critical plane and considers the contribution of normal stress and normal strain on the critical plane to fatigue damage. It can be applied to the multiaxial fatigue problem under both proportional and non-proportional loading.The effect of average stress on multiaxial fatigue life of materials can be described.The multiaxial constant amplitude fatigue test data of TC4 titanium alloy and other five kinds of metal materials are used to verify and evaluate the prediction ability of the model. The results show that the proposed multiaxial fatigue life model has higher prediction accuracy.Based on the multiaxial fatigue life model proposed in this paper, a prediction method for fatigue life under variable amplitude multiaxial loading is proposed.The life prediction ability of TC4 titanium alloy and other three kinds of metal materials is verified and evaluated by using the multiaxial variable amplitude fatigue test data.The prediction results of multiaxial variable amplitude fatigue life of several kinds of materials are in the dispersion band of 2 times of the experimental results.A method for determining fatigue hazard point of notched parts under multi-axial load is presented.The critical distance theory is applied to the prediction of multiaxial fatigue life of notched parts. The point method and the critical distance calculation method of notch root damage gradient correction under multiaxial loading are given.The multiaxial fatigue test data of TC4 titanium alloy notches are used to evaluate the fatigue damage gradient correction ability of point method and line method. The results show that the two methods have good damage gradient correction ability and the correction ability is equivalent.
【学位授予单位】：南京航空航天大学
【学位级别】：博士
【学位授予年份】：2014
【分类号】：TH133.2

【参考文献】