考虑温度效应的复合材料紧固结构面外拉脱性能和失效机制

Out-of-plane pull-through performance and failure mechanisms of composite material fastening structures considering temperature effects

高低温交变是航空航天领域复合材料紧固件的典型服役环境,而紧固件的力学性能与服役环境温度密切相关。为了研究温度环境对不同紧固件拉脱力学性能的影响,设计了一种适用于高低温环境的新型拉脱试验夹具,并开展了碳纤维增强双马来酰亚胺树脂复合材料面外拉脱试验。通过声发射(AE)技术、光学显微镜、扫描电子显微镜(SEM)对拉脱失效机制进行多维度表征,揭示了服役温度对两种典型复合材料紧固件面外拉脱失效机制的影响规律。研究表明,随着温度升高,凸头紧固件的拉脱强度会逐步降低,而沉头紧固件的拉脱强度先升高后降低。温度会影响紧固件拉脱过程中的损伤模式,并在高温环境下观测到基体失效呈现“河流”模式,证实了高温环境中层间裂纹扩展过程存在基体塑性变形,这为沉头紧固件拉脱强度随温度上升的现象提供了合理的解释。

Alternating high and low temperatures represent a typical operational environment for fastening structures(e.g.,bolted structures)in the aerospace field,which have a pronounced/significant influence on the mechanical performance of bolted structures.In order to explore the impact of temperature variations on the pull-through mechanical performance of different bolts,an out-of-plane pull-through experiment was conducted on carbonfiber-reinforced bismaleimide resin composites.Additionally,a specialized pull-through experiment fixture was developed for high/low temperature conditions.Using acoustic emission(AE)techniques,optical microscopy,and scanning electron microscopy(SEM),a multidimensional characterization of pull-through failure mechanisms was conducted,revealing the influence of temperature environments and bolts on the pull-through experiment failure mechanisms of composite materials.The findings reveal a correlation between temperature variations and the pullthrough strength of differing bolts in composite materials.Specifically,as temperatures rise,the pull-through strength of protruding head fasteners demonstrates a gradual decline.However,the pull-through strength of countersink fasteners exhibits an initial increase followed by a subsequent decrease.The temperature exerts an influence on the damage patterns during the pull-through process of fastening structures.Observations in elevated temperature environments reveal a river pattern of matrix failure,confirming the existence of matrix plastic deformation in the process of interlaminar crack propagation at high temperatures.This provides a plausible explanation for the observed phenomenon of a decrease in pull-through strength of countersink structures with increasing temperature.