引入应力梯度及磨损影响的圆弧型榫连结构微动疲劳寿命预测

Fretting fatigue (FF) has become recognized as a major failure mode in aero-engine when service time continues beyond 4000 h. With the development of technology, circular arc dovetails have been used in current advanced high bypass ratio turbofan engine, which FF behavior should be pay more attention. We try to find the key factors how to affect the FF life, analyze the failure mechanism, and establish a life model to improve the precision of life prediction for circular arc dovetail. Several key questions should be concerned and solved that are as following: how to find the numerical solution of 3D contact stresses with high gradient, how to describe the evolution law of these stresses under cyclic loading, how to catch the features of stress gradient and give the stress gradient factor in life model, how to simulate the wear process and give the wear factor in life model, and at last how to establish the life model based on the multi-axial fatigue theory. It is well known that experiments are the basis for studying the FF life of materials and structures, and three types of experiments are essential, such as notch fatigue test, 3D dovetail fatigue test and simulation structure test. The first two would use to determine the parameters in the life model, and the third would play a role in verifying and correctting the model. A combined experimental-numerical approach is used in the study. Firstly, according to the calculated fretting stresses at positions with high stress gradients, life model based on theory of multi-axial fatigue is established. Secondly, the stress gradient and the wear should be introduced in the life model as correction factor, which would promote the usability and prediction precision. At last, the model should be verified by test for its engineering application. The research idea shows innovation that is modeling, correction, and verification based on the role of different components of 3D contact stress. At the same time, stress gradient and wear fit together well in the model. Test technology has also been developed. All these would provide a theoretical basis for the design of a new type of dovetail attachment.

针对高涵道比涡轮风扇发动机圆弧型榫连结构的微动疲劳问题，探索关键影响因素（应力梯度、磨损）在工作载荷下对结构微动疲劳寿命的影响，分析失效机理，建立工程适用的、满足精度需求的寿命预测方法。 采用数值模拟结合试验验证解决如下关键问题：高梯度接触应力三维条件下的数值求解及演化规律分析；应力梯度描述方法及寿命应力梯度影响因子的建立；磨损过程模拟方法及寿命磨损因子的建立；基于多轴疲劳理论的寿命方程的建立。 研究过程:在获得接触应力精确计算结果的基础上,依据缺口疲劳试验及榫连结构疲劳试验结果确定应力梯度及磨损影响因子,进而建立寿命方程的表达式,最后开展榫连结构模拟件试验用以验证/改进寿命预测方法。 创新点在于：根据三维接触应力分量的不同作用效果，建立的寿命方程可同时考虑应力梯度及磨损对微动疲劳寿命的影响；另一方面，设计试验方案、搭建试验平台，发展微动疲劳试验技术,为研制新型榫连结构提供理论依据。

项目以航空发动机中结构特征明显的圆弧型榫连结构作为研究对象，重点考虑在循环载荷作用下的微动疲劳和微动磨损问题。主要研究内容包括如下三个方面：1）圆弧型榫连结构接触应力分析（突出循环载荷特征和几何特征）；2）微动疲劳寿命预测（突出多轴应力状态、应力梯度和磨损影响）；3）缺口疲劳及微动疲劳试验（提供数据和验证模型）。在研究、解决上述问题的基础上，探索微动疲劳失效机理及模式，寻求改善、解决微动疲劳问题的工程方法，提高工程结构的抗微动能力，并准确评估结构的微动疲劳寿命。.研究开展过程中，准确模拟了高梯度应力下的接触状态，形成了微动疲劳寿命分析方法及实现流程，形成了缺口疲劳寿命的分析方法及实现流程，并探索了如何采用数值方法模拟磨损过程，积累了微动疲劳、缺口疲劳的大量基础数据，也验证了所发展方法的准确性及工程适用性。特别是在微动疲劳寿命评估方法中，建立了总寿命方法，并考虑了裂纹闭合效应的影响，拓宽了微动疲劳分析的思路，提高了计算精度。.项目得到的结论/结果对提高榫连结构的安全性、可靠性及设计新型榫连结构具有工程指导意义，形成的计算方法/分析流程，已经在叶片、轮盘、圆弧型榫连结构的工程分析中获得了应用。随着整体叶盘结构的出现，风扇/压气机榫连结构的微动问题将获得本质上的解决，但从技术成熟度的角度出发，风扇/压气机榫连结构、热端涡轮叶片/轮盘榫连结构将在未来很长一段时间内继续采用，微动问题仍值得深入研究。