微尺度压痕实验的数值模拟及相关问题研究

IMECH-IR > 力学所知识产出(1956-2008)

	微尺度压痕实验的数值模拟及相关问题研究
	李敏
导师	洪友士
	2002
学位授予单位	中国科学院力学研究所
学位授予地点	北京
学位类别	博士后
学位专业	固体力学
关键词	纳米压痕技术显微硬度有限元模拟力学性能表层材料 Nanoindentation Technique Microhardness Finite Element Simulation Mechanical Capabilities Surface Layer On Material
英文摘要	目前国际上占主导地位的纳米压痕技术是由Oliver与Pharr提出并发展,目前的纳米压痕可以给出整个加、卸载过程的载荷—位移曲线以及硬度与弹性模量随压痕深度变化的曲线,从而提供了丰富的、比较精确的信息,为利用它探索材料比较完整的力学特性提供了可能.为达到该目的,就必须对压痕实验的加、卸过程进行较为深入的研究.作为主要的研究工具,有限元方法模拟微压痕过程在探讨通过实验数据得到更多、更准确的材料表层力学性能参数以及解释实验现象等方面发挥着重要作用.基于计算机速度与容量的原因,较早进行微压痕过程有限元模拟的BhattacharyaandNix、LaursenandSino都使用圆锥压头模拟维氏显微硬度标准正四棱锥Vicker压头与纳米压痕仪标准正三棱锥Berkovich压头,因为圆锥压头具有旋转对称性,可用二维旋转对称单元(二维实体单元)进行计算从而降低计算规模.即便如此,以当时大型计算机的水平,对规模为400~2000个四节点矩形单元的有限元模型进行一次完整的加、卸载过程也需要1~2天.到目前为止,微尺度压痕实验的数值模拟沿用二维模型.事实上,由于加工工艺的限制,微尺度压痕仪的压头如Berkovich与Vicker压头均不个旋转对称性;就微观尺度而言,实际的表层材料都是非均匀的.这些特征均不能由二维模拟体现,所以该文首先建立三维有限元模型,模拟带滑动接触的微尺度压痕加、卸载过程.在此基础上重点讨论了压头几何效应的问题,如二维模拟与三维模拟的关系、显微硬度与纳米的压痕硬度的关系、不同压头下材料的应力应变场、压痕间距与压痕边界的效应等,最后针对微尺度压痕实验中出现的压痕硬度随压痕深度减小而升高的现象,讨论了影响不同压痕深度硬度值的因素.; The material destructive patterns include oxidative corrosion, wear, and fatigue break down. The oxidative corrosion and wear depend directly on the surface layer of material, and fatigue breakdown usually begins on it. In recent years it was emphasis and hotspot in material research that how to improve or modify the properties on the surface layer of material. These techniques included sputtering, vapor deposition, ion implantation, laser glazing and etc. All the techniques introduced an important problem: how to appraise the characteristics of modified surface layer on material? The material with surface modification has two main characteristics: The first one is that the thickness of surface layer is very thin, just from several nanometers to several hundreds micron; and the second is that the material properties vary gradually along the depth direction. Because the thickness of surface layer is thin and adhesion on matrix material, the mechanical capabilities could not obtain by material tensile test. Up to now, the characteristics of surface layer could be hold only by hardness test. The hardness test was a simple and effective method for evaluating the mechanical properties of material. For nearly one hundred years it was used widely in industry. Recent years have seen significant improvements in indentation equipment and a growing need for measuring the mechanical properties of materials on small scales. Nanoindentation technique has been presented and developed by Oliver. It could provide load-displacement data of entire loading and unloading process. Compared with microhardness only providing hardness data, the nanoindentation technique gives plenty and precise information that could be used to look for entire material properties. As a main method, finite element method simulating micro-scale indentation process played important role in discussing how to get more and exact mechanical properties of material layer and better understanding experiment phenomenon. As the limitations of computer in speed and capability, Bhattacharya, who firstly used finite element method simulating micro-scale indentation process of homogeneous material, used the 2D axisymmetric cone model simulating Vicker indenter and Berkovich indenter. Up to now, almost all people used 2D model. In fact, the micro-scale indenters are not axisymmetric, and all material is uneven in micro-scale. These properties could not be presented in 2D cone model. In this paper the 3D model was used to simulate loading and unloading process with glide contact. Based on it, the geometric effect was discussed, including the relationships between 2D and 3D simulation, the relationships between microhardness and nanoindentation hardness, the strain field(or stress field) with different indenters, the distance between different indentations, the distance between indentation and boundary. At last, point at the phenomenon that the material hardness increases with indentation depth decreasing, several factors which influence nanoindentation test results on small impression depth were discussed.
索取号	30005
语种	中文
文献类型	学位论文
条目标识符	http://dspace.imech.ac.cn/handle/311007/23320
专题	力学所知识产出(1956-2008)
推荐引用方式 GB/T 7714	李敏. 微尺度压痕实验的数值模拟及相关问题研究[D]. 北京. 中国科学院力学研究所,2002.

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