高低温环境下复合材料-铝合金双钉双搭接胶螺混合结构拉伸失效行为

Tensile failure behaviors of composite-aluminum alloy double-bolt double-lap bolted-bonded hybrid structures under high and low temperature environments

  • 摘要: 飞行器在服役期间难免会经历高温、低温等恶劣环境,高低温环境可能会对其连接结构力学性能与承载能力造成影响,从而威胁结构安全性、完整性及使用寿命。因此,本文以GFRP-铝合金双钉双搭接胶螺混合结构为研究对象,通过试验和数值仿真研究高低温环境对胶螺混合连接接头拉伸强度和失效行为的影响。结合Micro-CT和SEM等损伤表征手段,观察和分析连接结构复合材料层合板孔周区域的损伤模式,同时采用基于3维Hashin准则的复合材料渐进损伤失效模型和内聚力单元分析方法来对连接结构失效过程进行模拟分析。结果表明,胶螺混合连接接头在80℃、25℃和−40℃环境下的极限载荷相较于纯螺栓连接接头分别提高了5.1%、27.5%和17.2%;相比较于室温环境,80℃高温环境会使胶螺混合连接接头的极限载荷下降24.6%,而−40℃低温环境会使胶螺混合连接接头的极限载荷提高3.5%。由于树脂的强度通常随着温度的升高而下降,高温环境使树脂软化降低复合材料的承载力,低温环境下树脂变得坚硬且表现出脆性。因此,随着温度升高,胶螺混合连接接头的承载能力在不断下降。这三种温度环境下复合材料损伤扩展趋势和最终失效模式基本一致,失效模式均为孔边出现扇形拉伸断裂失效,孔周出现局部挤压失效。本研究成果可为高低温环境下飞行器复合材料-金属连接结构设计提供理论指导与参考。

     

    Abstract: During service, aircrafts will inevitably experience harsh environments such as high temperature and low temperature. The high and low temperature environments may have an impact on the mechanical properties and load-bearing capacity of the connection structure of aircraft, which will threaten the safety, stability and service life of the structure. Therefore, this paper took the composite-aluminum alloy double-bolt double-lap bolted-bonded hybrid structure as the research object, and studied the influences of high and low temperature environment on the tensile strengths and failure behaviors of the bolted-bonded hybrid connection joints through experiments and numerical simulations. The Micro-CT and SEM damage characterization techniques were used to observe and analyze damage modes of composite laminates at the surrounding area of bolt holes. Meanwhile, a progressive damage failure model of composite material based on the 3D Hashin criterion and cohesive element analysis method was used to simulate and analyze the failure process of connection structures. The results show that the ultimate loads of the bolted-bonded hybrid joints at 80℃, 25℃ and −40℃ environments increase by 5.1%, 27.5% and 17.2% respectively, compared with the pure bolted joints. Moreover, compared to the room temperature environment, the ultimate load of the bolted-bonded hybrid joint at the 80℃ environment decreases by 24.6%, while the ultimate load of the bolted-bonded hybrid joint at −40℃ environment increases by 3.5%. As the strength of the resin usually decreases with the increase of the environment temperature, the high temperature will soften the resin and reduce the bearing capacity of the composite material, while the low temperature environment will make the resin hard and brittle. Therefore, with the increase of environment temperature, the bearing capacity of the bolted-bonded hybrid joint will decrease. The damage propagation trends and final failure modes of the composites under these three temperature environments are basically consistent. The failure modes are fan-shaped tensile fracture failure at the edge of the hole and local compression failure around the hole. The research results can provide theoretical guidance and reference for the design of composite-metal connected structures of aircraft at high and low temperature environment.

     

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