玻璃态高聚物屈服参数的纳米压入测试技术

The yield strength of glassy polymers may be sensitive to the hydrostatic pressure and also be influenced by the strain rate. To evaluate the yield strength under the given hydrostatic pressure and strain rate, three yield parameters (the yield strength under the pure shear deformation, Yo; the coefficient of internal friction, k, which reflects the effect of hydrostatic pressure on the yield strength; and the strain-rate sensitivity factor, B, which reflects the effect of strain rate on the yield strength) must be determined a priori. However, the conventional tensile test for the determination of the yield parameters cannot be readily used for very small structures such as polymeric MEMS and polymeric thin films deposited on substrates. As the nanoindetation tests are conducted on a micro-region of the actual components with little specimen preparing, nanoindetation is a promising technique for determining the yield parameters of such products. The proposed project is aimed to establish an analysis method for extracting all yield parameters (Yo, k and B) from the indentation load-depth curve. Primary coverage of this proposed project include: (1) Using theoretical analysis and with the help of finite element simulations, the correlation between the indentation strain rate and the effective strain rate will be established to estimate the effective strain rate under a conical indenter. (2) Based on the correlation between the yield strength and the effective strain rate which could be obtained by dimensional analysis and finite element analysis, the method for determining the strain-rate sensitivity factor, B, will be established. (3) The method for determining B will be combined with the existing method for determining Yo and k to obtain an integrated method which could determine Yo, k and B simultaneously. (4) The uniqueness, sensitivity and reliability of this integrated method will be validated using finite element simulations and experiments in order to ensure the accuracy of the testing results. When this proposed project is successfully accomplished, an efficient and convenient local testing technique for determining the yield parameters of glassy polymers will be obtained. And this new technique will expand the working range of the conventional testing techniques.

为评估玻璃态高聚物对静水压力和应变率敏感的屈服强度，需事先测定三个屈服参数(无静水压力下的屈服强度Yo，内摩擦系数k和率敏感因子B)。对于高聚物MEMS和薄膜等特征尺寸微小的结构，其屈服参数的测定成为挑战。纳米压入技术因测试尺度小、制样简单，有望发展成为解决上述难题的工具。关键在于：研究锥形压入中的基础规律和关系，建立识别屈服参数的分析方法。主要内容包括：通过解析推导和数值模拟建立压入应变率与等效应变率的关系，以确定接触非均匀应变场的等效应变率；通过量纲分析和数值模拟确定等效应变率对屈服强度的影响规律，以建立识别B的分析方法；通过与本人前期提出识别Yo和k的分析方法相集成，以建立一体化识别三参数的分析方法；通过数值验证和实验比对检验分析方法的唯一性、敏感性和可靠性，以确保其技术可行、结果可靠。本申请项目的完成，将发展一种高效便捷的屈服参数微区测试新技术，拓宽传统技术的测试尺度范围。

玻璃态高聚物的屈服强度对服役条件(静水压力和应变率)敏感，是与服役条件相关的函数，为预测其在服役条件下的屈服强度，就必须测定出三个本征的屈服参数(无静水压力下的屈服强度Yo，内摩擦系数k和率敏感因子B)。对于高聚物MEMS和薄膜等特征尺寸微小的结构，其屈服参数的测定成为挑战。纳米压入技术因测试尺度小、制样简单，有望发展成为解决上述难题的工具。其关键是：研究锥形压入中的基础规律和关系，建立识别屈服参数的分析方法。主要内容包括：通过解析推导和数值模拟建立压入应变率与等效应变率的关系，以确定接触非均匀应变场的等效应变率；通过量纲分析和数值模拟确定等效应变率对屈服强度的影响规律，以建立识别B的分析方法；通过与本人前期提出识别Yo和k的分析方法相集成，以建立一体化识别三参数的分析方法；通过数值模拟和实验比对检验分析方法的唯一性、敏感性和可靠性，以确保其技术可行、结果可靠。.通过上述工作的开展，确定出压入应变率等于7.4倍的等效应变率，该等效关系适用于线黏弹-塑性材料(如高聚物等)和幂律蠕变材料(如非晶合金等)；结合该应变率等效关系和不同压入应变率下的屈服强度测定方法，建立起率敏感因子B的压入分析方法；并形成三个本征的屈服参数(Yo，k和B)的一体化压入分析方法；通过三种典型高聚物材料UPVC、PC和PP的实验验证，表明该一体化方法能够较为准确地(相对误差在±15%以内)预测高聚物在不同工况下的屈服强度。该一体化方法作为一种屈服参数的微区测试新技术，可以拓宽传统技术的测试尺度范围。