金属材料弹塑性参数的球形压入一体化测试技术

In the present project, great efforts will be made to develop an integrated testing technique for determining the elastic-plastic parameters of metals by instrumented spherical indentation, which is an in-situ, micro-region and surficial testing technique widely used in the academic and engineering community for characterizing the mechanical properties of small volumes of material such as thin films deposited on substrate and evaluating safety performance of small structures such as MEMS. The research contents of this project mainly include: (1) Mechanical analysis. Firstly, based on the contact theory of a rigid spherical indenter indenting a linear elastic-power law plastic or a linear elastic-linear plastic half-space, relating the elastic-plastic parameters to the indentation data, and then establish the integrated methods for determination of the elastic-plastic parameters. Their accuracy and sensitivity will also be carefully discussed. Secondly, develop a method to predict the constitutive of the specimen with the aid of finite element analysis. (2) Mechanical measurement. Discussing the potential factors such as indenter tip defect, the initial contact point and the frame compliance of the equipment that may influence the measurement accuracy, and then develop corresponding methods to minimize the influence of such factors. (3) Experimental verification. Considering the elastic modulus determined by ultrasonic tests and the yield strain and hardening factor determined by tension tests as the nominal reference results, the corresponding elastic-plastic parameters determined by indentation tests were compared with these reference values to verify the reliability of the proposed method. (4) Testing methodology. According to the commercial nano-indentation and micro-indentation equipment, develop a standard testing procedure. Integrating the constitutive-prediction method, the elastic-plastic-parameter-determination method and the testing procedure, leads to a reliable micro/nano-mechanical testing technique. With the successful accomplishment of this proposed project, we will have a deep insight into the theory of indention deformation. Besides, the instrumented indentation will be multi-functional, which is helpful for the development and application of this technique in the in-situ and nondestructive examination field. In summary, the proposed project is a frontier basic investigation with a vast application prospect.

本申请项目拟基于现有仪器化压入测量技术，发展金属材料弹塑性参数识别的球形压入一体化测试技术，满足科学研究和工程应用对表面、微区、原位力学测试的需要，用于材料测试表征和结构安全评估。研究内容主要包括：在力学分析方面，选用可精确测量参量作为分析参量，研究球形压入变形模型，发展一体化识别弹塑性参数的分析方法，确认其敏感性和准确性，并建立材料本构关系识别的预判方法。在力学测量方面，研究测量影响因素，发展压头缺陷修正和接触零点确定等方法。在试验验证方面，对比典型材料的超声试验(测定弹性模量)和拉伸试验(测定屈服应变和硬化参数)结果，确认压入测试的可靠性。在测试方法方面，针对商业纳米压入仪和微米压入仪，编制程序化的测试步骤，形成一种理论合理、技术可行、结果可靠的微/纳米力学测试技术。本研究可以深化压入变形的理论研究，丰富仪器化压入技术的测试功能。因此，本申请项目是一项应用领域广泛的前沿基础问题研究。

本项目基于现有仪器化压入测量技术，发展金属材料弹塑性参数识别的球形压入一体化测试技术，满足科学研究和工程应用对表面、微区、原位和无损力学测试的需要，用于材料测试表征和结构安全评估。.研究内容及其重要结果：(1)在理论模型方面，对于球形压入加载阶段，针对理想塑性、线弹-幂硬化和线弹-线硬化等三种典型材料本构关系，分别得到相应本构关系下的压入总功解析式；对于压入卸载阶段，假设变形为弹性，得到卸载功解析式。(2)在分析方法方面，选用压入总功、卸载功和Meyer系数作为分析参量，采用有限元软件ABAQUS模拟压入过程，修正压入总功和卸载功的解析式，并拟合线弹-线硬化本构和线弹-幂硬化本构下Meyer系数与塑性参量的关系式。联立压入总功、卸载功和Meyer系数关系式，建立三种本构下一体化识别弹塑性参数的分析方法，并数值验证分析方法的准确性和稳定性。(3)在识别本构方面，甄选半压深能量累积率和Meyer系数作为分析参量，模拟结果表明不同本构关系之间存在明显的分界线，拟合分界线，引入本构预判参量，实现本构关系预判。(4)在力学测量方面，采用激光共聚焦显微镜或原子力显微镜等手段测量压头的形貌，通过体积等效法确定球形压头半径；提出一种拟合-反向搜索的方法，自动确定载荷-深度测量过程中压头与试样表面接触的零点。(5)在试验验证方面，选取四种常用金属材料，对比典型材料的超声试验(测定弹性模量)和拉伸试验(测定屈服应变和硬化参数)结果，证实本方法能够预测材料的本构关系，提高识别弹塑性参数的准确度。基于识别的弹塑性参数预测应力-应变曲线能够较好地吻合单轴拉伸试验结果，确认压入测试的可靠性。(6)在测试方法方面，针对商业纳米压入仪和微米压入仪，编制程序化的测试步骤，形成一种理论合理、技术可行、结果可靠的微/纳米力学测试技术。.本结题项目深化接触变形的理论研究，丰富仪器化压入技术的测试功能，是一项应用领域广泛的前沿基础问题研究。