微纳尺寸单晶金属的应变强化与应变突变现象研究

This Research Proposal considers the single crystals fcc metals Al and Au with feature sizes ranging from micro- to nano-meters. Uniaxial compression and tension tests will be performed firstly on them, in order to observe their stress-strain curves, plastic flow, initial yielding, strain hardening and strain burst. Within the framework of single crystal continuum theory of plasticity, the applicability of different strain hardening models will be investigated. For the peculiar strain burst phenomenon, new constitutive model needs to be developed based on their deformation mechanism at mesoscale, in order to describe the regularly-observed intermittency associated with plastic deformation. Then, finite element simulations will be used to obtain the uniaxial responses of these single crystal metals, and to compare with experimental results. By combining these aspects, single crystal theory of plasticity and the necessary ingredients of constitutive relations are expected to construct for single crystal metals ranging from micro- to nano-meters in size, which should describe reasonably and precisely the size-dependent strain hardening and fluctuation phenomenon of strain activity associated with plastic deformation. These issues are rather fundamental in describing the plastic behavior of metals at micrometer and nanometer scales. And the research outputs will have their scientific significance as well as practical importance in designing, fabrication and application of micro- and nano-devices.

本项目研究对象为特征尺寸处于数十纳米至数微米的单晶金属Al和Au，首先将开展两类单晶金属的单轴压缩和拉伸特性的实验测试，观察和分析其应力－应变特性曲线、塑性流动特征、初始屈服、应变强化和应变突变特性等；然后，在单晶塑性连续理论的框架下，研究已有的塑性本构模型对微纳米尺寸金属的适用性，重点考察各类应变强化模型的合理性；再针对微纳米单晶金属表现出的十分特殊的应变突变现象，基于变形机理，尝试在细观尺度构建能够描述塑性间歇性流动的应变突变模型。进而，采用有限元模拟方法，对上述单晶金属的单轴响应进行数值模拟和对比分析。在上述研究基础上，建立单晶金属连续力学模型和相应的塑性本构关系，力求合理、准确地描述微纳米金属塑性响应中的尺寸效应、锯齿状塑性流动等特异变形行为。这些问题是微纳米尺寸金属的塑性行为研究方面十分基础性的工作，研究结果对微纳器件的设计、制备与使用有着重要的科学意义和支撑作用。

本项目主要针对微纳尺寸单晶金属的应变强化与应变突变现象，希望建立合理、准确的微纳尺寸金属塑性特异变形行为的力学模型。研究过程中，侧重分析了微米尺度FCC类单晶金属的应变强化与应变突变现象，特别是重点探讨了应变突变行为。获得的主要成果也集中在这两个方面，包括：建立了描述微米尺度单晶金属应变突变的理论模型——间歇性流动连续模型，提出了判定应变突变发生的二阶功准则；提出了描述微米尺度单晶金属应变强化的新理论模型——随机单臂源SSAS模型。在这些理论成果基础上，完善了描述单晶金属间歇性塑性变形的塑性本构理论，扩展编写了相应的有限元数值模拟程序。本项目研究实现了计划的各项研究内容和工作，达到了预期的研究目标，取得了研究成果也符合最初项目计划书的要求。这些研究所得对有助于合理、准确地描述微纳米金属塑性响应中的尺寸效应、锯齿状塑性流动等特异变形行为，属于微尺度金属塑性行为研究方面的基础性的工作；也有助于支撑单晶金属类微器件系统的设计、制备与使用，可为微纳器件的制造和应用提供分析方法和计算依据。