摘要：
To investigate the dynamic mechanical property of a 50％ short-glass-fiber reinforced polyamide,the quasi-static hydraulic testing machine and split Hopkinson pressure/tension bar are used to apply loading on specimens with diameters from 6 mm to 10 mm,and the average strain rate is between 0.000 5 s-1 and 1 600 s-1.The stress-strain curves and failure modes of specimens are obtained and investigated.Micro-mechanics of failure process at different strain rates are analyzed.It can be seen from the stress-strain curves that the strength of material under dynamic loading are obviously higher than that under quasi-static loading (the compression strengths are increased by 31％,25％ and 29％ at the strain rates of 400 s-1,900 s-1 and 1 600 s-1,respectively;and the tensile strengths are increased by 46％,47％ and 28％ at the strain rates of 400 s-1,800 s-1 and 1 200 s-1,respectively),and the failure strain decreases significantly.The failure processes at different strain rates are also investigated.Under compression loading,the specimens experience the compaction of existing defect,elastic deformation and failure;under tensile loading,the specimens experience only elastic deformation and failure.The growth processes of micro-cracks are obviously different under static loading and quasi-static loading:under quasi-static loading,the micro-cracks assembly into macro-cracks.On the contrary,micro-cracks separately grow into macro-cracks.Optical observation and scanning electron microscope (SEM) are adopted to investigate the fracture surface.Results show that the fiber pull-out and fiber fracture are generated under dynamic compression,the fracture surface are smoother under quasi-static compression.And under tensile loading,dynamic surface shows fiber fracture,and quasi-static surface shows fiber pull-out.%为研究纤维含量50％短玻璃纤维增强聚酰胺复合材料PA-GF50的动态力学性能及其应变率效应,利用准静态液压试验机及分离式Hopkinson压杆、Hopkinson拉杆对标距段尺寸为6～10 mm的试样,进行了应变率范围0.000 5 ～1 600 s-1的准静态压缩、准静态拉伸、动态压缩和动态拉伸试验.对试样的应力-应变曲线和最终破坏形态,材料在不同应变率下失效破坏过程的微结构力学机理进行了分析.研究结果表明:动态载荷下,材料强度明显高于准静态载荷(压缩载荷下材料在400 s-1、900 s-1和1600 s-1应变率下分别较准静态载荷下增强31％、25％和29％;拉伸载荷下材料在400 s-1、800 s-1和1200 s-1应变率下分别较准静态载荷下增强46％、47％和28％),且失效应变有所降低;试样变形和最终破坏形态为压缩载荷下试样经历缺陷压实过程再进入弹性变形最终达到强度后失效,拉伸载荷下试样经历弹性变形达到强度后失效断裂;材料在不同应变率下的微结构机理为准静态载荷下微观裂纹扩展组合成为宏观裂纹,动态载荷下微裂纹分别扩展成为宏观裂纹;试样的宏观断口和扫描电子显微镜结果证实,材料在准静态压缩加载条件下断口较为平整,动态压缩载荷形成纤维拔出、纤维断裂等特征,准静态拉伸载荷下纤维拔出明显,而动态拉伸载荷下主要表现为纤维断裂.
