聚氨酯(PU)在力学性能测试中的摩擦效应与变形均匀性研究

作为防弹玻璃夹层材料,PU的动态力学性能一直受到学者们的关注。为准确表征其动态力学性能,本文采用ABAQUS有限元软件对不同摩擦系数下的单轴压缩试验进行数值仿真,分析试样加载端面的摩擦效应和几何尺寸对单轴压缩试验结果的影响;结合高速摄影技术(HSP)与数字图像相关技术(DIC)观测到试样在拉伸试验中的动态变形场和应变场,探讨标距段的应力均衡性;同时对PU材料在不同应变率下的单轴压缩、拉伸力学性能进行测试。结果表明:压缩试样的端面摩擦效应限制横向变形,影响了试样内部的受力分布,使得测量得到的应力值偏大;试样长径比越小,端面摩擦效应的影响越大;在单轴动态拉伸试验中,板状拉伸试样的标距段选取应当考虑两端倒角尺寸。通过测试PU的拉、压力学性能,发现材料具有显著的应变率敏感性。

On the Friction Effect and Deformation Uniformity of PU in Mechanical Property Measurement

As a bullet-proof glass sandwich material, dynamic mechanical property of PU has been the concern of scholars. In this paper, in order to accurately characterize its dynamic mechanical properties, finite element software ABAQUS was employed to numerically simulate the uniaxial compression experiment under condition of different friction coefficients. The influence of loading end surface friction effect and end surface geometry on experimental results of uniaxial compression was analyzed. Combining high-speed photography (HSP) and Digital image correlation (DIC) technique, dynamic deformation and relevant strain field of samples in tensile experiment were observed, based on which, stress equilibrium in gauge length range can be discussed. Moreover, mechanical properties of PU material were measured under both uniaxial compression and tensile conditions with different strain rates. Results show that firstly, the loading end surface friction effect can limit the lateral deformation of compressed sample and then can change internal stress distribution resulting in the measured stress values larger than that from engineering stress-strain curve; secondly, along with the decrease of slenderness ratio, the end surface friction effect increases; thirdly, in dynamic uniaxial tension experiment, the chamfer size should be considered during the option of gauge length for laminar samples. Finally, according to tensile and compression measurement results, PU mateial is obviously sensitive to strain rate.