1、PDF外文：http:/ 中文 7853 字， 4400 单词 出处： Lee K S, Assanis D N, Lee J, et al. Measurements and Predictions of Steady-State and Transient Stress Distributions in a Diesel Engine Cylinder HeadJ. Sae Technical Papers, 1999. 本科毕业论文 外文文献及译文 &nb
2、sp; 文献、资料题目 ： Measurements and Predictions of Steady-State and Transient Stress Distributions in a Diesel Engine Cylinder Head 文献、资料来源： SAE &
3、nbsp; 文献、资料发表日期： 1999.4 院 （部）： 机电工程学院 专 业： 班 级： 姓 名： 学 号： 指导教师： 完
4、成日期： 1 外文文献 ： Measurements and Predictions of Steady-State and Transient Stress Distributions in a Diesel Engine Cylinder Head ABSTRACT A combined experimental and analytical approach was followed in this work to study stress distributions and causes of failure in diesel cylinder
5、 heads under steady-state and transient operation. Experimental studies were conducted first to measure temperatures, heat fluxes and stresses under a series of steady-state operating conditions. Furthermore, by placing high temperature strain gages within the thermal penetration depth of the cylind
6、er head, the effect of thermal shock loading under rapid transients was studied. A comparison of our steady-state and transient measurements suggests that the steady-state temperature gradients and the level of temperatures are the primary causes of thermal fatigue in cast-iron cylinder heads. Subse
7、quently, a finite element analysis was conducted to predict the detailed steady-state temperature and stress distributions within the cylinder head. A comparison of the predicted steady-state temperatures and stresses compared well with our measurements. Furthermore, the predicted location of the cr
8、ack initiation point correlated well with experimental observations. This suggests that a validated steady-state FEM stress analysis can play a very effective role in the rapid prototyping of cast-iron cylinder heads. INTRODUCTION Heavy-duty diesel engine cylinder heads experience severe therm
9、al and mechanical loading, under both steady-state and transient engine operation. Consequently, cylinder head design is very sophisticated as it needs to house complex cooling passages for ensuring compliance with thermal stresses, while providing sufficient mechanical strength to withstand combust
10、ion pressures, and yet accommodating intake and exhaust valves and ports, and the fuel injector. As a result of design, weight and manufacturing compromises, cylinder heads often fail in operation due to cracks that are initiated due to thermal fatigue in regions where cooling is limited, such as in
11、 the narrow bridge between valves, or around the exhaust valve seat. A number of studies have so far been conducted to develop analytical methodologies 2 suitable for rapid design and virtual prototyping of cylinder heads. The finite element method has been the foundation of many of the
12、 analyses that predict the thermal and stress fields within the cylinder head. However, the accuracy of such analyses critically depends on our understanding of the problem, and the accuracy of the boundary conditions used in the formulation. Thermal stresses are induced by any of the following caus
13、es： Temperature gradients under steady-state operation, including the effects of cyclic temperature changes in the combustion chamber wall An increase in the mean temperature of a component, which affects the expansion and distortion characteristics, thus inducing stresses Thermal
14、 shock loading resulting from a sudden change in speed or load during transients, which change the rate of heat flux from the gas to the cylinder head. Due to the inherent difficulties in measuring stress fields near the critical regions on the firedeck surface, especially under transient conditions
15、, limited sets of measurements that can shed light on the problem have been reported .A numerical study of thermal shock calculations by Keribar and Morel has shown that thermal waves propagate into components during engine transients, with the steepness of the front depending on material thermal pr
16、operties. While for a ceramic component severe shock loads can cause surface compressive stresses to overshoot final steady-state values, the effect was not pronounced in higher conductivity materials. In order to validate this analytical finding, and attribute appropriately causes of failure in cas
17、t-iron cylinder heads, a combined experimental and analytical approach is followed here to study stress distributions under steady-state and transient operation. Experimental studies are conducted first to measure temperatures, heat fluxes and stresses under a series of steady-state and transi
18、ent operating conditions. Both biaxial and uni-axial high temperature strain gages have been inserted within the thermal penetration depth of a diesel engine cylinder head. The strain gage insertion beneath the surface of the firedeck ensures the durability and reliability of the sensor. At the same time, the placement within the thermal penetration depth allows for studying the effect of thermal shock loading under rapid transients, and for contrasting those measurements with corresponding steady-state magnitudes. Subsequently, a finite element analysis is
