经编织物膜材偏轴中心撕裂行为及破坏机理

Off-axis central tearing behaviors and damage mechanisms of warp-knitted fabric membranes

为了探究双轴向经编织物膜材中心撕裂行为与破坏机理,本文以典型PVDF经编织物为研究对象,进行了7个偏轴角度下(0°、15°、30°、45°、60°、75°和90°)的单轴中心撕裂试验,系统分析了经编织物破坏形态及撕裂强度随偏轴角度的变化规律,并结合细观数值模型进一步挖掘了偏轴角度对撕裂强度的影响及纱线细观受力情况与变形机理。结果表明,经编织物膜材内部纱线的偏转可显著影响切缝的扩展方向和开口形状。临界撕裂应力和极限撕裂应力随偏轴角度的增加整体呈“W”形变化规律,断裂位移和失效位移随偏轴角度的增加整体呈倒“V”形变化规律。纱线的偏转可使承载纱线的应力集中范围和应力分布情况产生显著差异,45°偏轴角度因应力分布更加均匀,变形更加充分,达到最大撕裂强度,是经编织物膜材的最优承载机制。所得结论可为织物膜材局部裂纹止裂分析及建筑膜结构安全性评估提供有益参考。

In order to explore the central tearing behaviors and damage mechanisms of biaxial warp-knitted fabric membranes,series of uniaxial central tearing tests for seven off-axis angles,including 0°,15°,30°,45°,60°,75°,and 90°,and the development of microscopic numerical models were performed on a typical PVDF warp-knitted fabric.The variations of failure morphologies and tearing strengths of warp-knitted fabric membranes with the increase of off-axis angles were systematically analyzed.And combined with experimental and numerical results,the effects of off-axis angles on tearing strength and the micro-level load-carrying capacity and deformation mechanisms of yarns were further discussed.The results show that the yarn orientation of warp-knitted fabric has a significant effect on the direction of slit propagation and opening shape.As off-axis angles increase,a“W”shaped relationship between critical tearing strength,ultimate tearing strength and off-axis angle is presented,and an inverted“V”shaped relationship between ruptured displacement,failure displacement and off-axis angle is revealed.The yarn orientation of warp-knitted fabric also has a significant influence on the range of stress concentration and stress distribution.For 45°off-axis specimen,numerical simulation exhibits that the stress distribution is more uniform and the deformation is more sufficient than those of other off-axis angles.Therefore,45°off-axis angle shows the largest tearing strength and is considered as the optimal load-carrying scheme.The conclusion could offer useful reference for the analysis of local crack arrest and safety assessment of architectural membrane structures.