双轴向经编类膜材PVDF8028偏轴强度及刚度特征

Mechanical Characteristics of Off-axis Tensile Strength and Stiffness of Biaxial Warp-knitted Fabric PVDF8028

双轴向经编类膜材具有多层次的复合结构,为深入揭示其强度及刚度特征,以高性能膜材Seaman PVDF8028为研究对象,进行了7个偏轴角度(梯度15°)的拉伸力学性能试验,获得了各角度下应力-应变关系、强度及变形数据,推导了相应弹模-应变关系并对其衍变规律进行了深入研究.研究表明:双轴向经编类膜材PVDF8028为典型的非线性、各向异性材料;各角度下的变形刚度特征差异明显,且表现出规律性的衍变特征;应变全域内的应力及弹模关系曲线呈现出特征鲜明的3阶段:起始线弹性段、应变强化段及应力强化段;此外,膜材的强度随角度变化表现出典型的“W”形规律,异于Tsai-Hill等强度准则的“U”形规律.所得研究结论可为双轴向经编类膜材变形强度预测及相应膜结构的设计分析提供有益参考.

To reveal detailedly the strength and stiffness characteristics of biaxial warp-knitted fabrics,which contain multi-layered composite structures,high performance biaxial warp-knitted fabric Seaman PVDF8028 was taken as the research object,and seven tensile tests of off-axis angles with a gradient of 15° were performed. Based on the obtained stress-strain relationship,strength and deformation data of different angles,the relationship between elastic modulus and strain was deduced,and its evolution was analyzed minutely. The results show that biaxal warp-knitted fabric PVDF8028 is a typical nonlinear and anisotropic material. Stiffness characteristics of different angles present obvious differences and evolve regularly. In the whole tested strain range,the stress-strain relationship and elastic modulus-strain relationship exhibit three distinct sections,including the initial linear elastic section,strain hardening section,and stress hardening section. Additionally,there is a “W” shaped relationship between tensile strength and off-axis angles,which is different from the “U” shaped relationship of Tsai-Hill strength criterion. The results can provide some useful references for strength prediction and deformation analysis of biaxial warp-knitted fabrics,as well as the design and analysis of membrane structures.