【作者】 石海燕；

【导师】 王延遐；

【作者基本信息】 山东理工大学 ， 固体力学， 2008， 硕士

【摘要】 本文应用断裂力学的理论,结合试验,在数值模拟的基础上,对硅铝合金活塞机械疲劳可靠性问题展开了研究。1.活塞销孔疲劳试验。利用活塞销孔机械疲劳试验机装置进行的试验表明,活塞顶部及内腔承受的交变液压,在销孔内侧上端处产生很大的棱缘负荷,导致销孔开裂,2.活塞有限元分析。计算了活塞在热应力场、机械应力场以及热-力耦合应力场中的应力应变值。研究表明:在活塞销孔内侧上端出现了应力集中,裂纹开启于此处。分析结果与试验相吻合。通过对活塞实体模型加载交变的机械载荷,采用隐式算法(Newmark法)进行了活塞的瞬态动力学分析,得到了活塞销孔危险部位的循环应力幅值。3.形状几何因子表达式。本文采用“自上而下”的子结构模型法施加裂纹体,计算了裂纹尖端的应力强度因子,计算值与应力强度因子手册中给出的理论值非常吻合,最大误差不超过6%。分析可知,热载荷对裂纹尖端的应力场起很小的作用,而起决定作用的是机械载荷。因此,忽略热载荷的影响,利用最小二乘法,拟合出了活塞在机械应力场中的形状几何因子的表达式。4.基于线弹性断裂理论,分析出活塞裂纹属于Ⅰ型裂纹,开启于销孔内侧上端应力集中处,属于孔边角裂纹;经过交变载荷长时间的加载,裂纹会继续扩展到内腔处,成为表面裂纹,最后断裂失效;在Paris疲劳寿命经验公式的基础上,给出了修正的疲劳寿命估算公式。估算结果表明,活塞疲劳寿命与试验值吻合。更多还原

【Abstract】 This work employs the theory of fracture mechanics, combines the experiment, on the basis of numerical simulation, have launched research to the fatigue reliability and safety problem of silicon aluminium alloy piston.1. The mechanical fatigue experiment. Utilizing piston of machinery fatigue testing machine, this work executes fatigue test. The result indicates that the great tensile stress generates at the upper end of the piston pin seat.2. The finite element analysis of piston. This work calculates piston’s thermal stress field, mechanical stress field and coupling stress field. The calculation results indicate that the great tensile stress generates at the upper end of the piston pin seat. Via analyzing the dynamics under the transient loading, the circulatory stress of the crack tip is computed, and the critical crack length is calculated.3. The expression of the piston shape geometry factor. Using the sub-structure model method, this work exerts the crack body to compute the stress intensity factor for different crack depths. The calculation results are extremely tallied with the academic values offered by the handbook; the limiting error is less than 6%. Thereby the expression of the shape geometry factor is obtained by curve fitting.4. Based on the theory of rupture, the crack is considered to be type I, and the crack location and expansion direction also have been confirmed. The special crack is separated into two sections, one is the horny crack at the aperture and the other is the surface crack at the lumen. In order to calculate the exact data, a modificatory Paris formula is available to prognosticate the fatigue life-span of the piston.更多还原