【作者】 段牧染；

【导师】 苏铁熊； 刘晓勇；

【作者基本信息】 中北大学 ， 动力机械及工程， 2012， 硕士

【摘要】 气缸盖作为柴油机的关键零件之一，在工作过程中承受着螺栓力、燃气压力和热负荷的周期性作用，其应力、应变和变形发生周期性的变化。随着强化程度的不断提高，多轴疲劳寿命问题逐渐成为研究热点。针对这一问题，本文以某V型柴油机为例，以气缸盖的一个整缸作为研究对象，在瞬态动力学问题及多轴疲劳寿命预测理论基础上，建立了气缸盖有限元模型、进行了气缸盖的瞬态动力学分析、开展了气缸盖的多轴疲劳寿命预测研究。在气缸盖的多轴疲劳寿命预测研究中对各种计算方法及影响因素进行了一定的探索，为更准确的预测气缸盖的多轴疲劳寿命提供了支撑。运用建模软件建立气缸盖、机体、缸套、缸垫、螺栓等零件的三维几何实体模型，然后将其导入专业的网格划分软件中对各个零件进行材料、属性的设置，在保证计算结果准确度的前提下，针对各个零件的结构特点，对结构进行一定的简化，并选择合理的单元类型和单元尺寸进行网格划分。分别在气缸盖与缸垫、气缸盖与螺栓、机体与缸垫等零件之间定义5对接触关系，模拟气缸盖的工作条件，施加约束、螺栓力和燃气压力。完成气缸盖组合结构的有限元模型的建立，为瞬态动力学分析提供了有限元模型。运用有限元分析软件，采用直接积分法中的完全积分法进行动态响应分析，得到各个节点位移和应力的时间历程，分析气缸盖上各个位置的位移和应力的时间历程，获得气缸盖不同位置的位移和应变时间历程的对比图线。为气缸盖的结构设计及改进提供理论依据，也为气缸盖的多轴疲劳寿命预测提供了数据。将瞬态动力学分析的计算结果导入疲劳寿命计算软件中，定义材料的属性，编制LDF文件，选择临界平面法中的Brown-Miller法作为多轴疲劳寿命计算方法，预测气缸盖的多轴疲劳寿命，获得气缸盖多轴疲劳寿命分布情况及安全系数图，引入威布尔寿命可靠度计算模型，对气缸盖在给定设计期望寿命值前提下的多轴疲劳寿命值进行可靠度研究。通过对气缸盖火力面、上部加工表面在不同粗糙度下的多轴疲劳寿命情况进行研究，发现提高气缸盖的表面加工质量是提高多轴疲劳寿命的一种有效措施，后续的分析模型中都考虑了粗糙度因素。研究气缸盖在三种多轴疲劳寿命计算模型下的疲劳寿命的区别，发现Brown-Miller法比正应变模型和剪应变模型更适合于气缸盖的多轴疲劳寿命计算。同时研究气缸盖在传统单轴计算模型下的疲劳寿命，与多轴疲劳寿命计算模型结果对比有待于进一步的试验验证。更多还原

【Abstract】 Cylinder cover as one of the key parts of the diesel engine, work in the process ofbearing force of the bolts, the gas pressure and the heat load of the periodic function, thestress、Strain and deformation of the occurrence of periodic change. Along with thestrengthening of diesel Engine, multi-axial fatigue life problem gradually becomes theresearch hot spot Aiming at this problem, this paper takes a V diesel engine as an example,one cylinder cover of a whole cylinder as the research object, on the basis of the dynamicproblem and multi-axial fatigue life prediction theory, established the finite element model ofcylinder cover, carried out the dynamic response analysis of cylinder cover and made themulti axial fatigue life prediction. To make some explorations on various calculation methodsand influencing factor in the research of the cylinder multi-axial fatigue life prediction, thiswill provide some support for more accurate prediction of cylinder head of the multi-axialfatigue life.Application of modeling software made the three-dimensional geometry entity model ofcylinder head, cylinder liner, cylinder pad, body, bolt and other parts, then import them intothe professional grid software and finish the material, attribute set on each part, Under thepremise of ensure the accuracy of the calculation results, make some certain simplification forvarious parts of the structure and choice reasonable unit type and unit size to grid. Defined the5 pairs of contacts between the cylinder head and cylinder gasket, cylinder head bolt, bodyand cylinder pad parts and so on, simulate the working conditions of the cylinder cover,loading the constraint, bolt force and gas pressure. Complete cylinder cover combinationstructure finite element model for transient dynamics. Using finite element analysis software, make the transient dynamics by direct integralmethod in the integral method, get and analysis each node displacement and stress timehistory on the cylinder cover, get the displacement and strain time history comparison chartbetween different position on the cylinder cover. This will not only provide the theory basisfor the cylinder cover design and improvement, but also provide data for the multi-axialfatigue life prediction.Let the transient dynamics results into the fatigue life calculation software. Definematerial properties, prepare the LDF file, choose the Brown-Miller method in critical planemethod for multi-axial fatigue life calculation, prediction of multi-axial fatigue life of thecylinder cover, get the multi-axial fatigue life distribution and safety coefficient map of thecylinder cover, introducing the Weibull function life reliability calculation model, make themulti-axial fatigue life reliability research in a given design life expectancy.Through the cylinder cover fire face, upper surface in different roughness undermulti-axial fatigue life was investigated, found improved cylinder head surface machiningquality is to improve the fatigue life of a measure, The follow-up analysis model taking intoaccount the roughness factor. Study on the cylinder head in three kinds of multi-axial fatiguelife calculation model of fatigue life of distinction, found the Brown-Miller method than thenormal strain model and shear strain model is more suitable for the cylinder cover ofmulti-axial fatigue life calculation. At the same time on the cylinder head in a conventionaluni-axial calculation model of fatigue life, contrasting results need further verification test.更多还原