高压扭转试样不均匀塑变过程仿真及其实验验证

发布时间：2018-04-26 03:20

本文选题：高压扭转 + 有限元分析　；参考：《山东农业大学》2017年硕士论文

【摘要】：高压扭转(High pressure torsion,HPT)是众多大塑性变形(Severe plastic deformation,SPD)工艺中行之有效的工艺之一,能够有效制备出亚微米或纳米块体超细晶(Ultrafine grained, UFG)材料。块体超细晶材料由于其表面结构和晶粒结构发生特殊变形,使其具备优异的力学性能和加工性能,备受世界各国研究学者关注,成为目前金属纳米材料研究领域的热点。虽然通过试验研究工艺参数对材料高压扭转过程塑性变形的影响非常直观有效,但在高压扭转过程中,试样应力应变场的测试较为困难,并且试样的不均匀塑性变形一直没有得到足够的重视,这成为块体超细晶材料高压扭转制备原理分析及工艺优化的难题之一。基于此,本文采用ANSYS和DEFORM-3D有限元数值模拟与物理实验相结合的方式对不同材料高压扭转过程中的不均匀塑性变形特征及影响因素进行了研究。本文的主要研究结果如下所示: ~(1)在压力对压缩阶段试样不均匀塑性变形的影响、扭转圈数对高压扭转试样塑性变形的影响的研究中发现,随着压力和扭转圈数的增加,试样等效应变、硬度及显微组织结构的不均匀分程度加大,且三者不均匀分布规律相一致,自心部到边缘位置应变、硬度增加,晶粒细化:心部等效应变低、晶粒粗大、晶界明显、硬度低;中间区域应变、硬度较高,分布较为均匀;边缘位置等效应变、硬度高,呈等轴细晶组织。并且,发现心部的硬度峰、凹槽处的变形死区以及径向中心线边缘处的软区三个与整体变形规律不相符的特征区域。此外,高压扭转扭转阶段,相对压缩阶段产生剧烈变形,晶格畸变严重,晶粒细化更明显。(2)在模具参数(凹槽深度d、凹槽倾角Φ)对试样塑性变形影响的研究中发现,随着凹槽深度的增加,纯铜试样压缩阶段的不均匀塑性变形程度增加,自心部到边缘,试样整体上变形越来越剧烈。并且,变形死区的范围越来越大,软区径向宽度越来越大,并且试样径向塑性流动距离增加。随着凹槽倾角的增加,试样整体塑性变形减小,其不均匀分布程度降低,变形逐渐趋于平稳,而硬度峰区域的应变峰值、软区径向范围以及变形死区范围均随之降低。(3)摩擦对高压扭转两个阶段塑性变形的影响以及高压扭转后试样上下表层变形滞后的研究结果表明:在摩擦对高压扭转两个阶段塑性变形影响的研究中发现,无论是在压缩阶段还是扭转阶段,随着摩擦系数的增加,试样整体塑性变形增加,其不均匀分布程度加深,并且,与整体变形规律不符的特征区域(硬度峰、软区、变形死区)将随着摩擦系数的变化,产生相应的改变。在高压扭转后试样的组织观察中发现,由于上下模之间不同的运动形式及模具与试样间摩擦的存在,导致试样上下表面的塑性变形程度出现差异,上表面的变形滞后于下表面,并且,随着扭转圈数的增加,变形滞后性范围将向边缘位置靠近。
[Abstract]:High pressure torsion pressure is one of the most effective processes for large plastic deformation plastic deformation.Submicron or nanocrystalline ultrafine grained (UFG) materials can be prepared effectively. Due to the special deformation of the surface structure and grain structure of bulk ultrafine crystalline materials, they have excellent mechanical properties and processing properties, which have attracted the attention of researchers all over the world, and have become a hot spot in the field of metal nanomaterials. Although the effect of process parameters on the plastic deformation during high pressure torsion is very direct and effective, it is difficult to measure the stress and strain field in the process of high pressure torsion. And the inhomogeneous plastic deformation of the sample has not been paid enough attention to, which has become one of the difficult problems in the preparation principle analysis and process optimization of bulk ultrafine grain material under high pressure torsion. Based on this, the inhomogeneous plastic deformation characteristics and influencing factors of different materials during high pressure torsion are studied by means of ANSYS and DEFORM-3D finite element numerical simulation and physical experiments. The main results of this paper are as follows: (1) in the study of the effect of pressure on the uneven plastic deformation of specimens in compression stage, and the effect of torsion circle number on plastic deformation of high-pressure torsional specimens, it is found that, with the increase of pressure and torsional cycles, The equivalent strain, hardness and the inhomogeneity of the microstructure of the sample are increased, and the distribution of the three inhomogeneity is consistent. The hardness increases from the center to the edge, and the grain size is fine: the equivalent strain in the core is low, the grain is coarse, The grain boundary is obvious, the hardness is low, the strain in the middle region is higher, the hardness is higher, the distribution is more uniform, the edge position is equivalent strain, the hardness is high, and the structure is equiaxed fine crystal. In addition, the hardness peak of the center, the deformational dead zone at the groove and the soft zone at the edge of the radial center line are found to be three characteristic regions which do not accord with the law of global deformation. In addition, in the high pressure torsion stage, the relative compression stage produces severe deformation, the lattice distortion is serious, and the grain refinement is more obvious. It is found in the study of the influence of die parameters (groove depth d, groove dip angle 桅) on the plastic deformation of the specimen. With the increase of groove depth, the degree of inhomogeneous plastic deformation of pure copper specimen increases during compression, and the deformation of the sample is more and more intense from the center to the edge. Moreover, the range of dead zone of deformation is increasing, the radial width of soft zone is increasing, and the radial plastic flow distance of specimen is increasing. With the increase of groove inclination angle, the whole plastic deformation of the specimen decreases, the degree of uneven distribution decreases, the deformation gradually tends to be stable, and the strain peak in the hardness peak region, The influence of friction on the plastic deformation in the two stages of high pressure torsion and the study on the lag of the upper and lower surface deformation of the specimen after high pressure torsion show that the friction has a negative effect on the high pressure torsion. In the study of the effect of plastic deformation in two stages, it is found that, Whether in compression or torsion stage, with the increase of friction coefficient, the plastic deformation of the whole specimen increases, and the uneven distribution of the specimen increases, and the characteristic region (hardness peak, soft zone) that does not conform to the law of integral deformation, The deformed dead zone) will change with the change of friction coefficient. In the observation of the microstructure of the specimen after high pressure torsion, it is found that due to the different motion forms between the upper and lower die and the existence of friction between the mould and the specimen, the plastic deformation degree of the upper and lower surface of the specimen is different, and the deformation of the upper surface lags behind that of the lower surface. Moreover, with the increase of the number of torsion cycles, the lag range of deformation will be near to the edge.
【学位授予单位】：山东农业大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TB30

【参考文献】