湿-热-交变载荷耦合作用下胶接结构强度退化预测模型研究

Adhesive bonding is widely used in aerospace, transportation and civil engineering due to the advantages in uniform stress distribution, keeping the material integrity and better corrosion and fatigue resistance, etc. Although adhesive bonding can overcome many disadvantages of the traditional connection methods, the strength degradation under hostile service condition remains a key factor that restricts its further application. In this project the strength degradation test is carried out on high-strength steel/aluminium adhesive joint under long-term “hygro-thermal-fluctuating load” coupled condition, to have a further investigation on the coupled environmental degradation behaviours, such as moisture diffusion, creep and thermal and hygroscopic expansion, etc. Then the joint multi-field coupled environmental degradation model is established based on the fully-coupled modelling technique. The strain-based Coffin-Manson fatigue model is improved by combining the FE secondary development and backface strain technique, to further investigate the effect of fluctuating load on the strength degradation of the adhesive joint. The Cohesive Zone Model of the adhesive layer is degraded based on the environmental accumulated degradation data and the fatigue damage factor, and then the effect of “hygro-thermal-fluctuating load” coupled condition on the damage and crack propagation in the adhesive layer is clarified. Thus the strength degradation and fatigue life of adhesive joint under complex service condition can be modelled and evaluated.

结构胶接技术具有应力分布均匀、保持基体材料完整性以及较好的抗腐蚀和抗疲劳特性等优点，广泛应用于航空航天、载运工具和土木工程领域。尽管胶接技术可以克服传统连接工艺的诸多不足，其复杂服役工况强度退化行为仍是阻碍其进一步应用的关键。本项目拟通过开展高强钢/铝合金胶接接头长期“湿-热-交变载荷”服役工况性能退化试验，深入探究吸湿、蠕变、热膨胀和吸湿膨胀等环境老化行为及其耦合影响机理，进而提出基于完全耦合建模方法、真实描述接头多场耦合工况环境老化行为力学模型；结合有限元二次开发和背面应变法，改进基于应变的Coffin-Manson疲劳模型，进一步探究交变载荷对胶接接头的强度退化效应，系统考察累积环境老化数据和疲劳损伤因子对胶层内聚力模型的退化机理，阐明“湿热环境-交变载荷”耦合工况对胶层损伤演变和裂纹扩展过程的影响规律，以期为胶接结构复杂工况下强度退化和疲劳寿命预测提供有效建模评估方法。

本项目按照计划针对高强钢/铝合金胶接接头长期“湿-热-交变载荷”服役工况性能退化开展研究，采用理论、实验和数值建模相结合的方法，研究吸湿、蠕变、热膨胀和吸湿膨胀等环境老化行为及其耦合作用下胶接接头影响机理。本项目按计划顺利执行。对经历极端环境后的试件开展了准静态拉伸力学性能测试，为预测模型提供了必要的模型参数和验证依据。采用扫描电子显微镜对接头破坏表面进行了形貌观测，分析接头破坏失效的微观机理。建立了胶接接头多场耦合工况环境退化行为模型，真实描述接头实际服役过程中的性能退化行为。将接头环境耐久性试验和模型预测结果进行对比，验证了所建立模型的有效性和准确性，实现对胶接接头耦合服役工况下残余强度和疲劳寿命的建模评估。项目相关研究成果得到了国有科研院所、新能源汽车企业和国外相关领域企业的关注，其中关键部件的制备、连接和建模预测技术则直接应用到了微电子、汽车等行业实际部件生产和服役寿命预测中。