基于仿真加速试验和数理统计的活塞可靠性研究

发布时间：2017-12-27 22:10

本文关键词：基于仿真加速试验和数理统计的活塞可靠性研究　出处：《山东大学》2017年硕士论文　论文类型：学位论文

【摘要】：随着对产品性能要求的提高和国家低碳经济发展的需要,内燃机作为当今社会的主要动力装置之一,其功率密度有着显著提高,这就带来了高热负荷和高爆发压力的挑战。而活塞作为内燃机的核心部分之一,顶面直接承受燃烧室内高温高压工质影响,其可靠性备受相关人员的关注。本文针对该领域尚未解决的问题,利用三维仿真对缸内燃烧进行分析,运用有限元得到活塞应力分布,并结合加速试验理论通过不同加速工况的仿真结果估算活塞额定工况的寿命,对活塞的可靠性进行评估。具体的,首先针对国内主要利用经验公式获取活塞顶面边界条件的现状,本文运用三维CFD软件对一个周期内燃烧室中的情况进行仿真,不仅能够对缸内流动、传热、燃烧状况进行评估,还能从中获得活塞顶面温度与换热系数分布规律,且相较于经验公式法,更能充分地体现空间特性。之后利用一维仿真的结果进行标定,以保证仿真模型基本准确的前提下,将仿真结果作为活塞顶面的边界条件。其次,利用三维仿真获得的顶面边界条件,结合试验数据、经验设置以及其他仿真结果,对活塞温度场和应力场的计算进行相关设置,从而在Abaqus软件中获得活塞温度场,以及活塞在热负荷、机械负荷和热机耦合负荷影响下的应力与应变分布规律。仿真结果显示,由于缸内湍流和进气冷却等原因,排气侧温度普遍高于进气侧,从而热应力较大,且在第二环内缘面上达到最大值。机械应力则由于存在与活塞销的接触,从而在活塞销座内侧上部出现了最大值。对于热机耦合状态下,活塞最大应力值出现在第二环内缘面,这是两种负荷产生的应力叠加的结果。活塞销座处由于刚销柔座的材料设定,两种应力有所抵消,从而应力相对变小。最后,利用仿真获得的结果计算出活塞的疲劳寿命,结合加速试验相关理论,选取合适的加速模型,通过不同加速工况的仿真疲劳寿命在Matlab中进行拟合。通过对比仿真值与拟合值可以看出拟合效果良好,从而通过拟合曲线估算活塞在额定工况下的疲劳寿命。与仿真值进行比较,在热负荷、机械负荷和耦合负荷下,相对误差分别为4.11%,2.66%,7.91%,均相对较小,基本符合工程使用的要求,从而证明阿伦尼斯模型、逆幂律模型和广义艾林模型分别作为这三种负荷下加速模型的可行性。之后还讨论了当有实际故障数据时,需先分析其分布模型,从而获得对应的特征寿命,接着便可根据情况利用合适加速模型估计额定工况的寿命。综上,本文提出的利用三维CFD获取活塞顶面边界条件,结合加速试验理论预测活塞疲劳寿命的方式有着较高的准确度,可以在工程上运用于活塞可靠性的评估。
[Abstract]:With the improvement of product performance requirements and the development of national low carbon economy, the power density of internal combustion engine as a major power device in today's society has been significantly improved, which brings the challenge of high heat load and high explosive pressure. As one of the core parts of the internal combustion engine, the piston is directly affected by the high temperature and high pressure working quality in the combustion chamber. The reliability of the piston has attracted much attention from the relevant personnel. According to the field of unsolved problems of cylinder combustion were analyzed by using the finite element simulation, get the stress distribution, combined with the accelerated test theory through the simulation results of different acceleration estimation of piston rated life, to assess the reliability of the piston. Specifically, first at home mainly by empirical formula to get the status quo of the piston top surface boundary conditions, this paper uses 3D CFD software to simulate the combustion chamber in a cycle, not only can the in cylinder flow, heat transfer, combustion condition assessment, but also get the piston top surface temperature and heat transfer coefficient distribution from, and compared with the empirical formula, can fully reflect the spatial characteristics. Then the results of one dimensional simulation are calibrated to ensure the accuracy of the simulation model, and the simulation results are used as the boundary conditions of the piston top surface. Secondly, the top surface of the boundary conditions obtained by 3D simulation, combined with the test data and the experience of setting up and other simulation results of the temperature field and stress field calculation related settings, so as to obtain the temperature field in Abaqus software, and the piston in the thermal load, mechanical load and thermal mechanical coupling loads under the influence of the the stress and strain distribution. The simulation results show that the in cylinder turbulence and inlet air cooling and other reasons, the exhaust side temperature is generally higher than the intake side, thus the thermal stress is larger, and the maximum in the second ring inner surface. Mechanical stress is due to the existence of contact with the piston pin, and the maximum value appears in the upper part of the piston pin seat. For the thermo mechanical coupling condition, the maximum stress in the piston of the second inner face, this is the two kind of load stress produced by superposition of the results. Because of the material setting of the rigid pin flexible seat, the two kinds of stress are offset, and the stress is relatively small. Finally, the fatigue life of the piston is calculated by the results obtained by simulation. Combined with the accelerated test theory, a suitable acceleration model is selected, and the simulation fatigue life of different acceleration conditions is fitted in Matlab. By comparing the simulation value and the fitting value, it can be seen that the fitting effect is good, thus the fatigue life of the piston is estimated under the rated condition through the fitting curve. Compared with the simulation results, the thermal load, mechanical load and coupled load, the relative errors were 4.11%, 2.66%, 7.91%, are relatively small, basically meet the engineering requirements, thus proving Allen nice model, inverse power law model and generalized Eyring model respectively as the feasibility of these three kinds of acceleration model under load. After that, it is discussed that when the actual fault data is available, the distribution model should be analyzed first, so that the corresponding characteristic life can be obtained. Then the suitable acceleration model can be used to estimate the service life of the rated condition according to the situation. In conclusion, the three-dimensional boundary condition of piston top surface obtained by 3D CFD and the accelerated test theory are of high accuracy for predicting piston fatigue life. It can be applied to piston reliability evaluation in engineering.
【学位授予单位】：山东大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TK401;O21

【相似文献】