复合材料修补金属裂损结构吸湿老化的试验与有限元分析

暴露在湿热环境中的复合材料修补金属裂损结构易吸湿老化,导致该结构性能下降,服役寿命缩短。为研究吸湿性对复合材料修补金属裂损结构修补效果和耐久性的影响,利用试验方法分析了吸湿性对复合材料胶补金属裂损结构及胶黏剂力学性能的影响;利用有限元方法评估了吸湿性对复合材料胶补金属裂损结构试验件修补效果和耐久性的影响。研究结果表明:吸湿后含穿透双边裂纹铝合金板玻璃纤维单面胶补试验件的疲劳裂纹扩展寿命和极限载荷的平均值分别下降为吸湿前的71%和90%;吸湿造成拉伸条件下复合材料胶补金属裂损结构胶层失效模式由内聚破坏为主转变为界面破坏为主;在"湿-热"老化30天后,E44/聚酰胺环氧树脂胶黏剂试验件吸水饱和,弹性模量下降为未老化前的40%,塑性应变超过了总应变的25%;有限元分析发现胶层损伤受吸湿影响明显,吸湿性加速了胶层损伤,且裂纹长度越长,加速作用越明显;同时吸湿使得裂纹尖端的J积分值急剧增大,导致修补结构的疲劳裂纹扩展寿命缩短,裂纹长度越长,吸湿性对于复合材料胶接修补效果的危害越严重。

Experimental study and finite element analysis on hygroscopic aging of adhesively bonded composite repaired metallic structures with cracks

Due to aeronautical facility serve under the environment of high temperature and high humidity, hygroscopic aging behaviors were commonly discovered in adhesively bonded composite repaired metallic aircraft structures, which resulting in the decrease in mechanical properties and server life. In order to investigate the effect of hygroscopic aging on adhesively bonded composite repaired structures, moisture absorption and aging test was performed on adhesively bonded composite repaired aluminum alloys plates containing double-sides cracks with single patch and E44/Polyamide epoxy resin, then the effect of hygroscopic aging on load carrying capability, crack propagation life, repaired effect and duration of fatigue load were analyzed by experimental method and finite element method ( including damage zone theory and J-integral ). The result show that hygroscopic aging decrease the load carrying capability and fatigue crack propagation life greatly, the average value of fatigue crack propagation life and ultimate load of repaired structure decreased by 29% and 10% after immersing in water for 40 days. After immersing in water for 30 days, the adhesive specimens became completely plastic, which decrease cohesive force between adhesive and aluminum plate, resulting in the fall off of composite patch from repaired region quickly. The effect of hygroscopic aging on the damage zone was obvious, which result in the fast damage of adhesive, and the longer the crack is, the faster the damage is. The hygroscopic aging of repaired structure also increase the value of J-integral around the crack tips, which decrease the crack propagation life of repaired structures.