激光烧蚀损伤对复合材料结构的弯曲失效模式和承载能力的影响

Effect of laser ablation damage on the flexural failure mode and load-bearing capacity of composite structures

  • 摘要: 碳纤维增强聚合物(CFRP)以其轻量、高强度等优点,已成为航空航天领域不可缺少的关键材料。本文采用试验与数值模拟相结合的方法,研究了激光烧蚀损伤对碳纤维/环氧树脂基复合材料的弯曲失效模式和承载能力的影响。在试验方面,对激光烧蚀(热流密度为4000 kW/m2;热源半径为20 mm;加热时长为7 s)后的试样进行了四点弯曲试验,实验结果表明,失效过程大致分成三个阶段:Ⅰ阶段为热解区域的纤维失效后出现的Ⅰ型分层损伤;Ⅱ阶段为纤维断裂和分层失效沿着厚度方向的持续扩展;Ⅲ阶段为上表面由压缩载荷所导致的屈曲诱发的分层损伤。烧蚀后复合材料的承载能力显著下降,其弯曲强度较烧蚀前下降45.04%。数值模拟方面,结合传热方程、阿伦尼乌斯方程、连续性方程、刚度矩阵、Hashin失效准则和刚度退化准则,提出了受烧蚀因素影响的Hashin失效准则和刚度退化准则,通过对UMAT、UMATHT和DFLUX用户子程序进行二次开发,建立了碳纤维/环氧树脂基复合材料的热-化-力耦合模型,分析了试样的烧蚀过程及其在四点弯曲情况下的失效行为,得到了含激光烧蚀损伤试样在失效第一阶段对应的载荷位移曲线,模拟结果与实验结果吻合较好。本研究可为含有热损伤材料在机械加载下的失效形式及其剩余强度的评估提供参考。

     

    Abstract: Carbon fiber reinforced polymer (CFRP) has become an indispensable key material in the aerospace field due to its light weight and high strength. In this paper, the effects of laser ablation damage on the bending failure mode and bearing capacity of carbon fiber/epoxy matrix composites were studied by combining experimental and numerical simulations. In terms of testing, a four-point bending test was carried out on the sample after laser ablation (the heat flux density was 4 000 kW/m2; the radius of the heat source was 20 mm; the heating time was 7 s), and the experimental results show that the failure process was be roughly divided into three stages: stage I is the type I delamination damage that occurs after the fiber failure in the pyrolysis region; stage II is the continuous expansion of fiber fracture and delamination failure along the thickness direction; stage III is the delamination damage induced by buckling due to compressive loading on the upper surface. The bearing capacity of the composites decreased significantly after ablation, and the flexural strength decreased by 45.04% compared with that before ablation. In terms of numerical simulation, combined with the heat transfer equation, Arrhenius equation, continuity equation, stiffness matrix, Hashin failure criterion and stiffness degradation criterion, the Hashin failure criterion and stiffness degradation criterion affected by ablation factors were proposed. The load displacement curves corresponding to the first stage of failure of the samples with laser ablation damage are obtained, and the simulation results are in good agreement with the experimental results. This study can provide a reference for the evaluation of the failure mode and residual strength of materials containing thermal damage under mechanical loading.

     

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