蜂窝夹芯挖补修理结构弯曲性能研究

从试验及有限元2个方面对复合材料蜂窝夹芯挖补修理结构的弯曲性能进行研究。通过3点弯曲试验对无损及修理件弯曲性能进行测试，试验结果表明，蜂窝夹芯结构破坏模式为典型的蜂窝剪切破坏，修理件相比于无损件弯曲强度恢复率为110%，修理后结构弯曲刚度也略高于无损件；基于试验结果建立三维有限元模型对蜂窝夹芯修理结构的弯曲性能进行研究，通过用户自定义子程序VUSDFLD编写Hashin失效准则、基于应力的Besant失效准则，实现复合材料面板及蜂窝芯子2种材料的损伤起始及演化。数值模型得到的破坏模式、破坏载荷及弯曲刚度均与试验结果吻合得较好；改变有限元模型参数，研究损伤直径及补片厚度对修理后弯曲性能影响，结果表明，随着损伤直径从30~70 mm逐渐增加，修理件强度先增加后减小，并在损伤直径为50 mm时取得最大值，此外，补片厚度为1~2.5 mm时弯曲强度恢复率高于100%；本文为复合材料蜂窝夹芯结构的修理设计提供了可靠的数值模拟方法。 

Flexural performance of scarf repaired honeycomb sandwich structures

The flexural behavior of scarf repaired honeycomb sandwich structures was investigated via experiments and finite element analysis. A three-point bending test was carried out on both undamaged and repaired specimens. Test results demonstrate that the failure mode is core shearing, and that the flexural strength recovery ratio of the repaired to the undamaged panels is 110%. The flexural rigidity of the repaired panel is slightly higher than that of the undamaged panel. Based on these results, a 3D finite element model was proposed to investigate the flexural behavior of the repaired specimens. Using VUSDFLD, we developed Hashin fabric and Besant failure criteria to achieve the damage initiation and evolution of composite and honeycomb materials. The failure pattern, the ultimate load and the calculated stiffness are in good agreement with the test results. Then the effect of the damage diameter and the thickness of the patch on the repaired panels was analyzed by changing the parameters of the FEM, and the results show that with the increase of the damage diameter from 30 mm to 70 mm, the ultimate loads of repaired specimens increase, then decrease, and finally reach the maximal value at the diameter of 50 mm; besides, the strength recovery ratio is larger than 100% while the thickness of the patch ranges from 1 mm to 2.5 mm. This study indicates that the numerical model developed provides an efficient method for repair design of composite honeycomb sandwich panels.