CFRP-钢层状复合结构的表面划痕损伤容限

Scratch damage tolerance at the surface of CFRP-steel laminated composite structure

碳纤维增强树脂复合材料(CFRP)-钢层状结构在实际运营过程中,脆性碳纤维层容易出现划痕等表面损伤,因此为了保障损伤后复合结构的安全运行,需要对其进行损伤容限研究。基于边界效应理论模型(Boundary effect model,BEM),建立了表面划痕损伤后的CFRP-钢层状结构三点弯曲断裂强度解析模型,并在CFRP表面分别预制了0.2 mm和0.4 mm深度的表面初始划痕缺陷,通过三点弯曲梁的成组试验验证了理论模型的可行性。研究结果表明:(1)利用金相显微镜观测了CFRP-钢层状结构三点弯曲极限荷载时的断裂特征,确定了表面划痕损伤后CFRP的结构特征参数C_(ch),代入解析模型获得了CFRP层的拉伸强度,并与CFRP直接拉伸试验测试的拉伸强度对比,两者偏差小于10%;(2)该解析模型为“断裂荷载=拉伸强度×等效面积”的线性方程形式,“等效面积”仅与CFRP-钢层状结构和表面裂纹的几何参数有关,因此,通过CFRP的直接拉伸强度可以预测表面损伤后CFRP-钢层状结构的断裂强度,实现损伤容限设计。

In the actual operation process, the surface of brittle carbon fiber layer of carbon fiber reinforced polymer(CFRP)-steel layered structure suffered from scratch and other damage. Therefore, it is necessary to study the damage tolerance to ensure the safe operation of the damaged composite structure. An analytical model of fracture strength at the three-point bending(3-p-b) test for CFRP-steel laminated structure with surface scratch damage was established based on the boundary effect model(BEM). And the initial scratch defects of 0.2 mm and 0.4 mm depth were prefabricated on the surface of CFRP, respectively. The feasibility of this theoretical model was verified at the 3-p-b tests. The results indicate that:(1) The fracture characteristics of CFRP-steel laminated structure at the 3-p-b tests were observed by metallographic microscope, and the structural characteristic parameter C_(ch) of CFRP after scratch damage was determined. The tensile strength of CFRP layer was carried out according to this analytical model, and the deviation is less than 10% compared with the tensile strength measured by CFRP direct tensile test.(2) The analytical model is a linear equation of “fracture load = tensile strength × equivalent area”. The “equivalent area” is only related to CFRP-steel laminated structure and the geometric parameters of surface crack. Therefore, the fracture strength of CFRP-steel laminated structure with surface damage can be predicted by the direct tensile strength of CFRP, and the damage tolerance design can be realized.