刀一屑摩擦对残余应力分布影响的模拟分析

【作者】 汪小芳；

【导师】 郭乙木；

【作者基本信息】 浙江大学 ， 工程力学， 2004， 硕士

【摘要】 残余应力是在无外力的作用时，以平衡状态存在于物体内部的应力。在各种机械加工和机器构件的制造过程中，零件内部都将产生残余应力。残余应力的存在对零件的各种机械性能尤其是疲劳寿命有着显著的影响，它也是产生变形和开裂等工艺缺陷的重要原因。 金属切削是一个伴随着高温的塑性大变形过程，在加工表面往往产生高达几百兆帕的残余应力。在关于切削中残余应力现象的研究工作的回顾中，我们很明显地可以看到，这种残余应力的大小和分布会因切削条件和工件材料的不同，而表现出很大的变化。随着生产实践要求的提高，往往要对各种情况下的加工后零件内的残余应力进行预测。如果采用传统的实验研究方法，这将是相当费时费力又耗成本的。 在文献综述中，已有大量的专家和学者运用有限元方法成功地模拟了整个切削加工过程，并对加工表面残余应力的大小和分布进行了预测，得到了和切削实验比较吻合的结果。然而，在研究中也发现，前刀面与切屑之间的摩擦会对残余应力的分布产生较大的影响。 由于刀一屑之间接触关系的复杂性，使得要正确地反应其间的摩擦规律变得很困难。在通常的模拟计算中，一般都采用比较简单的平均摩擦系数法即Coulomb摩擦规律处理刀—屑之间的应力关系。在本文的切削实例模拟中，发现相同的切削条件下，当采用不同的摩擦系数时，会对加工表面的残余应力产生较大的影响。 为了更逼真地反应刀—屑之间的摩擦规律，本文在具体的前刀面应力分布实验数据的基础上，建立了多项式摩擦模型，并对照常规的Coulomb摩擦进行了对比模拟分析，发现两者之间存在着较大的差值。 本文的研究结论表明，有效地模拟刀—屑之间的摩擦，将是成功预测工件表面残余应力分布的关键。更多还原

【Abstract】 Residual stresses are those that are remained inside body but balanced themselves after all the external loads are removed. When a component is under manufacturing process, it’s easy to bring residual stresses. The quality of a mechanical component such as its geometrical stability and fatigue life are significantly affected by the residual stresses.Metal cutting generally involves a large amount of plastic deformation and is coupled thermomechanical process. It always comes with several hundred MPa of residual stresses on the machined surface. From the literature review on the study of residual stresses induced by machining process, it is clear that the residual stresses vary largely with cutting conditions and workpiece material. Recently, with the improvement that production practices require, it’s necessary to predict the residual stresses remained inside the part. Currently, the determination of residual stress heavily depends on experimentation. However, experimental approach has many limitations such as time consuming, high costs etc.In the past, a large number of expert and scholar have used the finite element method to simulate the whole machine process, and has predicted the distribution of the residual stresses under the surface. It is proved that the simulation results are consistent well with the experimentation. Still, residual stresses are found to depend strongly on the tool-chip friction.Taking into account that the complexity of the contact between tool and chip, it’s some more difficult to express accurately the friction. In most common simulation, researchers used to take the Coulomb friction to gain the relationship of shear stress and normal stress at the tool-chip interface. In this thesis, we’ll find that the coefficient of friction has significant influence on the distribution of residual stresses.Taking the average coefficient of friction in conventional approach obviously simplified the complex contact between tool rake face and chip. Then, we suggest a polynomial model of friction. By comparing the results with those from the conventional approach, the analysis of the influence of different friction model upon the residual stresses is performed.更多还原