弯曲载荷下复合材料夹芯“L”型接头强度和疲劳试验研究（英文）

Experimental Study on Strength and Fatigue of Sandwich Composite L-joint under Bending

文章研究了复合材料夹芯"L"型接头在弯曲载荷下的静强度和疲劳问题。通过静加载试验,得到该接头的极限承载能力和破坏模式。在此基础上,对不同载荷水平下的试件进行疲劳试验。基于试验数据建立S-N曲线,比较了半对数线性拟合和"S"型函数拟合结果。结果表明,"S"型曲线的预测结果好于半对数线性拟合。同时,分析了疲劳载荷下的接头破坏模式,包括夹芯和面板之间脱粘、面板分层和纤维断裂。根据试验现象划分了表明裂纹扩展的3个阶段。建立了刚度退化模型表现不同载荷水平下刚度退化规律。

Sandwich composite L-joints, comprising E-glass plain woven skins and PVC foam core,are designed and tested under both static and cyclic loading. Three specimens were tested statically to failure to obtain the maximum load-carrying capacity of the L-joint. Nine specimens were tested under cyclic load at three load levels. Load-life(S-N) curves are established by sigmoid and linear fitting, respectively. The study shows that the sigmoid function has higher accuracy and is recommended for life prediction. The maximum service load based on the sigmoid function is determined to be 9.30 kN. Failure mode analysis of the L-joint failed in fatigue test is made, including debonding between skins and foam core, delamination and fiber breakage. Propagation process of crack is divided into three stages: small crack initiates where ‘stress whitening' exists; crack propagates along the thickness direction of the arc bracket; crack covers the section of arc bracket indicating the failure of the joint. Degradation of the stiffness in fatigue is represented by a power function. The rate of stiffness degradation grows with the load level.