胶层厚度对碳纤维/双马来酰亚胺树脂复合材料平-折-平混合连接接头力学性能的影响

以碳纤维/双马来酰亚胺(BMI)树脂复合材料平-折-平(FJF)连接接头为对象，通过试验对比分析了特定胶层厚度下碳纤维/BMI树脂复合材料FJF连接接头的静强度和疲劳性能，并探究了胶层厚度对碳纤维/BMI树脂复合材料FJF混合接头力学性能的影响。利用背面应变技术对碳纤维/BMI树脂复合材料FJF混合接头搭接区端部胶层开裂进行监测。利用有限元软件ABAQUS对不同胶层厚度下碳纤维/BMI树脂复合材料FJF混合接头搭接区胶层应力分布进行了分析。结果表明，碳纤维/BMI树脂复合材料FJF混合接头的平均拉伸极限载荷、搭接区端部胶层开裂平均循环次数和平均疲劳寿命均随着胶层厚度在0.1~0.3 mm范围内增加而增大。不同胶层厚度的碳纤维/BMI树脂复合材料FJF混合接头均经历相同的失效阶段，即搭接区胶层端部开裂，胶层沿搭接区断裂扩展，最终靠近加载端孔边拉伸断裂，呈±45°断口。随着胶层厚度在0.1~0.3 mm范围的增加，搭接区端部胶层剥离应力、剪切应力及孔边胶层压缩应力均减小。在胶层厚度为0.1~0.3 mm范围内，剪应力是胶层破坏的控制因素。 

Effect of adhesive thickness on mechanical properties of carbon fiber/bismaleimide resin composite flat-joggle-flat hybrid (bonded-bolted) joint

Experiments were carried out to compare the static strengths and fatigue behaviors of the carbon fiber/bismaleimide (BMI) resin composite flat-joggle-flat (FJF) joints under a certain adhesive thickness. Meanwhile, effects of the adhesive thickness on the mechanical properties of the carbon fiber/BMI resin composite FJF hybrid joints were explored. Backface strain technology was used to detect the adhesive cracking at the end of the overlap zone. Adhesive stress distributions in the overlap zone of the carbon fiber/BMI resin composite FJF hybrid joints were analyzed based on the ABAQUS software. The results show that the average tensile ultimate load, the average adhesive cracking cycles at the end of the overlap zone and the average fatigue life of the carbon fiber/BMI resin composite FJF hybrid joints all rise with the increasing adhesive thickness in a certain range of 0.1 mm to 0.3 mm. The carbon fiber/BMI resin composite FJF hybrid joints with different adhesive thicknesses all go through the same failure stages: Firstly the adhesive cracking happens at the end of the overlap zone, then the adhesive crack extends along the overlap zone, finally a net-tension failure occurs at the hole near the loading end, presenting the fracture appearance of ±45°. As the adhesive thickness increases within the range of 0.1 mm to 0.3 mm, adhesive peel and shear stress at the end of the overlap zone and the compressive stresses around the bolt hole all decrease. Shear stress is the main factor that accounts for the adhesive failure.