基于有限元分析的柴油机.doc

摘 要
由于曲轴失效形式的复杂化和对曲轴修复后质量要求的日益提高，传统的修复技术已无法满足曲轴的修复要求。近年来，作为激光再制造技术的核心——激光熔覆技术迅速发展成为曲轴再制造的一种新型修复技术。本文主要研究船用柴油机废旧曲轴的再制造问题。
1. 从曲轴的磨损、烧蚀、弯扭变形以及裂纹和断裂四个方面具体分析了船用柴油机曲轴的失效原因，得出以下三点：
(1) 校核静强度安全系数，对曲轴的刚度、硬度和承受载荷能力进行可靠性评估。校核疲劳强度安全系数，评估船用柴油机曲轴再制造前后的疲劳寿命。
(2) 根据疲劳裂纹扩展规律和Paris公式，对曲轴的疲劳裂纹扩展寿命进行预测。
(3) 通过对曲轴材料性能的简单分析，利用传统的疲劳寿命预测方法、损伤力学和Miner疲劳损伤积累准则确定曲轴剩余疲劳寿命的预测方法，即先预测曲轴在最大载荷下的疲劳寿命，再减去最大载荷下的当量寿命，两者的差就是曲轴的剩余疲劳寿命。
2. 利用1/4点位移法和J积分法对曲轴圆角处裂纹应力强度因子的计算，判断其断裂失效的程度，并应用15节点三维1/4奇异元和20节点三维单元分析曲轴圆角处裂纹的应力场，求出应力强度因子。
3. 针对曲轴的再制造问题，本文研究了激光熔覆技术的原理和主要特点，为熔覆材料与曲轴基体材料的匹配性提供了判断依据；选择了镍基、钴基和铁基三种自熔性合金粉末作为熔覆材料；确定了修复工艺为同步式激光熔覆。对熔池状态的研究为下文中的热分析提供了理论依据，并为控制熔覆层的裂纹提供了解决的方法。
4. 根据温度场的有限元理论和ANSYS的热分析基础，通过对再制造曲轴进行有限元热应力分析，得到60秒后曲轴内部的温度场、位移、应力场的分布情况和三种熔覆材料的熔滴在100微秒时的温度场分布数据。根据熔覆层的应力状态理论分析三种熔覆层的残余应力场，通过比较得出铁基自熔性合金粉末Fe55与曲轴基材结合性较好，熔覆效果好。

关键词 激光再制造；激光熔覆；曲轴；有限元；残余应力



Abstract
The traditional repair techniques have been unable to meet the requirements of the crankshaft repair，as the crankshaft failure in the form of complex and the increasing quality requirements after the crankshaft has been repaired. In recent years, as the core of the laser remanufacturing technology — laser cladding technology has rapidly developed into a new crankshaft remanufacturing repair technology .The main content of this paper is about that the remanufacturing problem of the marine diesel engine waste crankshaft.
1. From the crankshaft wear, erosion, cracks and bending and torsion deformation and fracture in four areas, detailed analysis of the reasons for the failure of marine diesel engine crankshaft, draw the following three points:
(1) Checking static strength safety factor, assesses the reliability of the crankshaft stiffness, hardness and load bearing capacity. Checking the fatigue strength safety factor, assesses the fatigue life before and after remanufacturing of marine diesel engine crankshaft.
(2) According to the law of fatigue crack growth and Paris formula, predicts fatigue crack growth life of the crankshaft.
(3) Through a simple analysis of the crankshaft material properties, using traditional fatigue life prediction method, damage mechanics and miner fatigue damage accumulation criterion to determine the prediction method of the remaining fatigue life of the crankshaft, that is, first predicts the fatigue life of the crankshaft under maximum load, then minus the equivalent life under maximum load, the difference between the two is the remaining fatigue life of the crankshaft.
2. Using 1 / 4 point displacement method and the J-integral method to calculate the stress intensity factor of the crack at crankshaft fillet, judges it’s degree of fracture failure, while applies the 15-node three-dimensional 1 / 4 singular element and 20-node three-dimensional unit, analyses the stress field of the crack at crankshaft fillet and finds the stress intensity factor.
3. Against the problem of the crankshaft remanufacturing, the paper studies the principle and main characteristics of laser cladding, provides a theoretical basis for the matching of cladding material and the matrix material of crankshaft; chooses nickel , cobalt and iron base three kinds of self-fluxing alloy powder as cladding materials; determines the Repair process to be the synchronized laser cladding. The research on the pool State provides a theoretical basis for the thermal analysis below, and provides a solution for the control of cracks in the cladding layer.
4. According to the finite element theory of temperature field and the basis of thermal analysis of ANSYS, get the distribution of the temperature field, displacement, and the stress field inside the crankshaft after 60 seconds through the finite element thermal stress analysis of the remanufactured crankshaft and the temperature distribution data of three kinds of cladding material’s droplet at 100 microseconds. According to the stress state theory of the cladding layer, analyzed the residual stress fields of the three cladding layer, obtains that the combination of Fe-based self-fluxing alloy powder Fe55 and the crankshaft substrate is better and it’s cladding effect is well by comparison.

Keywords laser remanufa..