激光直接金属沉积石墨—铜功能梯度复合材料应力场数值模拟

发布时间：2018-06-15 22:37

本文选题：激光直接金属沉积 + 功能梯度复合材料　；参考：《华东交通大学》2015年硕士论文

【摘要】：石墨-铜功能梯度复合材料具有优异的导热、导电和自润滑性能，在轨道交通、电力传输等领域具有广阔的应用前景。本文采用ANSYS软件对激光直接金属沉积石墨-铜功能梯度复合材料过程的温度场和应力场进行了研究。借助于APDL语言的二次开发以及生死单元技术对多层单道的激光直接金属沉积过程进行了仿真计算，并且采用间接耦合的方式对温度场进行了热应力耦合，建立了激光沉积均质复合材料和功能梯度复合材料的应力场；获得了激光功率、扫描速率和扫描方式等工艺参数与梯度分布指数、层数和层厚等结构参数对石墨铜功能梯度复合材料开裂的作用机制，得出以下结论：（1）均质复合材料的等效残余应力比功能梯度复合材料大，且大应力遍布于整个材料；梯度复合材料的等效残余应力由底层到顶层依次变小，即梯度结构对残余应力起到了缓和作用。（2）激光功率在3600W-4200W范围内，，随着功率的递增，残余应力平均值先增大后减小，并且功率4200W时平均残余应力最小；扫描速率在200mm/min-400mm/min范围内，平行于X轴路径的X向残余应力平均值先增小后增大，扫描速率为300mm/min时平均残余应力最小；结合层与层之间的粘结强度分析，功率的最佳范围为4000W-4200W,扫描速率最佳范围为300mm/min-400mm/min。（3）往复式扫描比单向式扫描的各向残余应力更小，且残余应力分布均匀。（4）梯度分布指数0.25-4范围内，P=1时材料残余应力整体较小；在层厚0.4mm-0.8mm以及层数6-10层范围内，得知随着层厚的加厚以及层数的增多，制件沿各个路径的残余应力都逐渐递增；综合分析得出梯度分布指数P=1、层厚0.6mm、8层为最优结构参数。（5）功能梯度复合材料中平行于X轴路径的X向残余应力的极大值出现在左侧3mm处或右侧31mm处，这两处区域的应力值较大,是产生沿Y向裂纹的高发区；平行于Y轴路径的Y向残余应力曲线呈“W”型，即在路径的中间部位以及两端的应力较大；平行于Z轴路径的Z向残余应力由沉积件底部至顶部逐渐减小，即基板与沉积件之间容易开裂。
[Abstract]:Graphite-copper functionally gradient composites have excellent thermal conductivity, electrical conductivity and self-lubricating properties, and have a broad application prospect in rail transit, electric power transmission and other fields. In this paper, the temperature field and stress field of graphite-copper functionally gradient composites deposited by laser direct metal are studied by ANSYS software. With the help of the secondary development of APDL language and the birth and death element technique, the laser direct metal deposition process with multi-layer and single channel is simulated, and the thermal stress coupling of temperature field is carried out by indirect coupling method. The stress field of homogeneous composites and functionally graded composites deposited by laser was established, and the laser power, scanning rate and scanning mode were obtained, and the gradient distribution index was obtained. The mechanism of crack cracking of graphite-copper functionally gradient composites with structural parameters such as number of layers and thickness of layers is discussed. The conclusions are as follows: (1) the equivalent residual stress of homogeneous composites is larger than that of functionally graded composites. The equivalent residual stress of gradient composites decreases from the bottom layer to the top layer, that is, the gradient structure plays a moderating role on the residual stress, and the laser power increases with the increase of the power in the range of 3600W-4200W. The average value of residual stress increased first and then decreased, and the average residual stress at power of 4200W was the smallest, and the scanning rate was in the range of 200mm/min-400mm/min, and the average value of X-ray residual stress parallel to the X axis path increased first and then increased. When the scanning rate is 300mm/min, the average residual stress is the smallest, and the optimum power range is 4000W-4200W for bond strength analysis between layers, and the optimal scanning rate is 300mm / min-400mm / min.n.) the reciprocating scanning is smaller than the unidirectional scanning. And the residual stress distribution is uniform. The gradient distribution index is 0.25-4. The residual stress of the material is smaller in the range of 0.25-4, and in the range of 0.4mm-0.8mm and 6-10 layers, it is found that with the thickening of the layer thickness and the increase of the number of layers, the residual stress of the material is relatively small in the range of 0.25-4. The residual stress along each path increases gradually. Comprehensive analysis shows that the gradient distribution index Pu 1 and the layer thickness 0.6 mm / L are the optimal structural parameters. The maximum value of the X direction residual stress parallel to the X axis path in the functional gradient composite appears at the left 3mm or the right side 31mm in the functional gradient composite, and the maximum value of the X direction residual stress in the functional gradient composite is found at the left side or the right side of the composite. The stress values of these two regions are larger, and the Y direction residual stress curves parallel to Y axis path are "W" type, that is, the stresses in the middle part and both ends of the path are larger than those in the Y axis path, and the Y direction residual stress curves parallel to the Y axis path are of "W" type. The Z direction residual stress parallel to the Z axis path decreases gradually from the bottom to the top of the deposited part, that is, it is easy to crack between the substrate and the deposited part.
【学位授予单位】：华东交通大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TB333

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