微观尺度下的摩擦机理与测试方法研究

发布时间：2018-12-18 02:00

【摘要】：近年来随着微型零件产品的需求日益增大，微塑性成形工艺作为微观领域中重要的加工方法，得到迅速的发展。但是在微观尺度下，由于材料变形行为尺寸效应和摩擦尺寸效应现象的出现，使得传统的宏观塑性成形工艺理论和技术难以直接应用于微成形工艺中。因此，，进行微观领域中的尺寸效应研究具有重要的理论意义和使用价值。本文通过实验，观察研究微观尺度下材料变形行为尺寸效应现象，建立表面过渡层模型以模拟微型圆环镦粗过程，结合实验研究分析摩擦尺寸效应现象，并根据微成形中镦挤复合变形方式提出一种新型摩擦测试方法。首先通过室温下纯铜材料的微型圆柱压缩实验，研究分析了试样尺寸和晶粒尺寸对变形试样表面形貌和材料流动应力的影响。实验结果显示，晶粒尺寸增大、圆柱试样尺寸减小时，试样圆柱面的变形非均匀性增大；流动应力随着晶粒尺寸的增大、圆柱试样尺寸的减小而呈现出降低的趋势。依据微塑性成形特点，考虑晶粒变形之间的相互作用，通过考虑过渡层晶粒状态，在表面层模型的基础上建立了表面过渡层模型。对微型圆柱压缩得到的流动应力曲线进行了计算，得到三种晶粒对应的流动应力曲线，发现内层晶粒的流动应力比表面晶粒要高，而过渡层晶粒的流动应力则介乎两者之间。采用表面过渡层模型对微型圆环镦粗过程进行了模拟，结合实验结果，测量了不同摩擦情况下的摩擦因子。测量结果发现，在液体润滑情况下出现了明显的摩擦尺寸效应现象，摩擦因子随着平均晶粒尺寸的增大、试样尺寸的减小而增大；而在无润滑干摩擦情况下，则没有体现出明显的摩擦尺寸效应现象。针对微成形中的镦挤复合的变形模式，提出了T形筋板镦挤实验方法，通过模拟发现成形过程中的筋高与腹板宽度均对摩擦敏感，将筋高与腹板宽度的比值作为衡量摩擦因子大小的表征量，并对T形变形过程进行摩擦分析与参数优化研究。
[Abstract]:In recent years, with the increasing demand for micro-parts, micro-plastic forming technology, as an important processing method in the micro field, has been developed rapidly. However, at the micro scale, due to the appearance of material deformation behavior size effect and friction size effect, it is difficult to apply the traditional macroscopic plastic forming technology theory and technology to microforming process directly. Therefore, it is of great theoretical significance and practical value to study the size effect in the micro field. In this paper, we observe and study the dimensional effect of material deformation behavior on the micro scale, establish a surface transition layer model to simulate the upsetting process of micro ring, and analyze the friction size effect in combination with the experiment. A new friction testing method is proposed according to the composite deformation of upsetting and extrusion in micro forming. Firstly, the effects of sample size and grain size on the surface morphology and flow stress of the deformed samples were studied by the micro cylindrical compression experiments of pure copper materials at room temperature. The experimental results show that the deformation inhomogeneity of the cylindrical surface increases with the increase of grain size and the decrease of cylindrical specimen size, and the flow stress decreases with the increase of grain size. According to the characteristics of microplastic forming and considering the interaction between grain deformation, the surface transition layer model was established on the basis of the surface layer model by considering the grain state of the transition layer. The flow stress curves obtained by compression of micro cylinders are calculated and the flow stress curves corresponding to three kinds of grains are obtained. It is found that the flow stress of inner grain is higher than that of surface grain, while the flow stress of transition layer grain is between them. The surface transition layer model was used to simulate the upsetting process of the micro ring. The friction factors under different friction conditions were measured by combining the experimental results. The results show that the friction size effect is obvious in the case of liquid lubrication, and the friction factor increases with the increase of average grain size and the decrease of sample size. However, in the case of dry friction without lubrication, there is no obvious effect of friction size. Aiming at the composite deformation mode of upsetting and extruding in micro-forming, an experimental method of upsetting extrusion of T-shaped stiffener is proposed. It is found by simulation that both the height of rib and the width of web are sensitive to friction. The ratio of rib height to web width is taken as the representation of friction factor, and the friction analysis and parameter optimization of T-shape deformation process are carried out.
【学位授予单位】：华中科技大学
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：TH117

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