基于细观力学的大开孔层合板缝合补强力学性能计算的新方法基于细观力学的大开孔层合板缝合补强力学性能计算的新方法

从细观力学的角度出发，考虑了面内纤维弯曲及富树脂缺陷，建立了大开孔层合板缝合补强孔边针脚损伤的单胞模型。建立了纤维弯曲函数，推导了纤维弯曲区域的纤维体积分数及纤维弯曲角度。基于复合材料力学分析方法，计算得出了单胞的材料弹性常数。研究表明:缝合导致单胞面内纤维最大弯曲角不超过20°，单层板纵向杨氏模量减小，横向杨氏模量、剪切模量及泊松比均增大，变化幅度均在-8%~20%之间；且对于大开孔层合板缝合补强而言，针距变化引起的材料性能变化相对边距大许多。由上述计算结果，建立了一种缝合补强大开孔层合板力学性能计算的新方法，同时引入针孔模拟针脚处的应力集中现象，结果表明:缝合会造成层合板面内力学性能降低，并且对面内的压缩性能影响大于对面内拉伸性能的影响。 

A new method for calculating of stitching reinforcement for composite laminates containing a large circular hole based on micromechanics

From the perspective of micromechanics, taking into account the in-plane fiber bending and resin-rich defect, an unit cell model was established for stitch damage of the stitching reinforcement for composite laminates containing a large circular hole. The fiber bending function was established and the fiber volume content and fiber bending angle of the fiber bending region were deduced. By applying the method of mechanical analysis of composite materials, the elastic constant of the unit cell was calculated. The study shows that the maximum bending angle of the fibers in the cell surface is never over 20°, the longitudinal Young's modulus decreases while the transverse Young's modulus, shear modulus, and Poisson's ratio increase by not more than -8%-20%; as for composite laminates containing a large circular hole, the variation in material properties caused by changes in needle span is much greater, compared with the edge distance. Based on the calculation results above, a new method for calculating the mechanical properties of the stitching reinforcement for the composite laminates containing a large hole was established. Simultaneously, stitch holes were used to simulate the stress concentration at the stitching. The study results reveal that the stitching may lead to the decrease of the laminates' in-plane mechanical properties, and there is a much stronger influence on the in-plane compress performance than the one of in-plane tensile properties.