【作者】 汪昊；

【导师】 许伯强；

【作者基本信息】 江苏大学 ， 光学工程， 2010， 硕士

【摘要】 随着计算机科学、数值计算方法的快速发展,能够建立合适的数值模型,描述材料激光强化的物理过程。只要通过少量的实验验证理论模型及数值模拟计算的准确性,就可以利用计算机对大量的实际材料热处理过程进行准确的数值模拟。这样就实现了基于计算机数值模拟的虚拟材料激光表面强化过程。通过大量的计算机数值模拟计算,可以建立材料热处理工艺参数与材料热处理后性能的定量关系。这些数值模拟计算结果可以用于优化热处理工艺参数。基于多物理场耦合理论,采用有限元方法,建立了金属材料激光表面强化数值模型。数值模拟研究在激光作用下材料的温度场和流场分布,分析相变硬化区的宽度及深度与激光参数之间的定量关系;得到了激光产生熔池的温度场、熔池速度场及熔池的形状。数值模拟结果为激光加工的实际应用提供理论依据。论文主要包括以下内容:建立了激光辐照45CrMo钢的有限元分析模型,对激光相变硬化过程的温度场和激光相变硬化区的宽度及深度进行了数值模拟,详细讨论了激光功率和扫描速度变化分别对硬化层层深及层宽影响的敏感性。研究结果表明:激光功率变化对层深与层宽的影响明显大于扫描速度变化所产生的影响。基于多物理场耦合理论,数值模拟研究了激光与金属铝相互作用的温度场和流场,求解热传递与层流耦合的PDE方程。数值模拟中选取符合实际光束分布的激光参数,考虑了自然对流、表面张力梯度引起的Marangoni对流和热物理参数依赖于温度的实际情况.针对(?)γ/(?)T＜0、(?)γ/(?)T＞0、(?)γ/(?)T=0三种不同的表面张力梯度,计算得到了激光产生熔池的温度场、熔池速度场及熔池的形状.数值结果表明,熔池中Marangoni对流换热对熔池形貌影响较大,在激光加工过程中不可忽略.更多还原

【Abstract】 With the development computer science, finite element method and finite difference method, it is possible to set up a model to describe the physical processes of laser strengthening processes. If some experimental works were carried out to demonstrate the accuracy of modelling and simulation results, then,laser strengthening processes can been accurately simulated by computer; so the virtual laser strengthening processes can been realized based on computer simulation. The relationship between the properties of materials and the technical parameters heat treatment processes can been set up by a large amount of computer numerical simulation works. These numerical simulation results are useful to optimize the technical parameters Laser heat treatment.The theory of multi-physics coupling and finite element method are used to set up a model to describe the physical processes of laser strengthening processes. Then, the temperature field and stress field of these physical processes can been calculated accurately. The quantitative relationship between the laser parameters between laser parameters with the width and depth of harding area is Analyzed. The temperature distribution, the molten pool shapes and fluid flow have been computed,these numerical simulation results can provide the theoretical basis for the practical application of laser strengthening processing.The main work and results of this master dissertation are as follow:The finite element models used for modeling the distribution of temperature field in 45CrMo due to laser strengthening were created by using COMSOL software. The temperature field during laser transformation hardening process and the width and depth of laser transformation hardening zone were calculated. Discussed the sensitivity level of hardened layers effected by laser power and laser scanning speed. The results show that: Effects of changes in laser power on the layer depth is significantly greater than the changes in scanning speed.An axisymmetric numerical model of a laser-induced molten pool has been developed for a laser interaction with Al plate. Based on mixture continuity equations, the coupled PDE of a laminar fluid flow and heat transfer is solved by the finite element method, taking into account the coupled effects of buoyancy, Marangoni forces and the thermophysical characteristics with temperature variations. The temperature distribution, the molten pool shapes and fluid flow have been computed for three calculation cases: (?)γ/(?)T<0、(?)γ/(?)T>0、(?)γ/(?)T=0, corresponding to three different surface tension gradients. The numerical results showed that fluid flow has a significant effect on the shape of the molten pool and can not be ignored during laser processing.更多还原