Abstract The Colombian aeronautical industry has stimulated research into the mechanical behaviours of materials under the different loading conditions that aircrafts are generally exposed during their operation. Calima T-90, the first military aircraft that was built in Colombia, is used for the primary flights training of Colombian Air Force pilots, and is thus often exposed to adverse operating situations, such as hard landings, which cause impact loads and can subsequently produce impact fatigue. The Calima T-90's structure is mainly comprised of composites materials, generating assemblies and subassemblies of different components of it. The main method of bonding these components is by using adhesive joints with different thicknesses. This study aimed to characterise these adhesive joints as they were placed under typical loads. For this purpose, an evaluation of the effects of adhesive thickness on the mechanical performances of such joints was accomplished and conducted using quasi-static loading conditions and impact fatigue, employing single lap-joint (SLJ) specimens. Cyclic impacts were induced using a drop weight impact testing machine, in order to obtain the characteristic impact-fatigue life diagrams. The evolution of dynamic parameters was then analysed such as residual strength, impact contact time and stiffness degradation; this was done for all the adhesive thicknesses tested. A modified phenomenological prediction model for strength degradation and a cycle to failure prediction model in terms of the adhesive thickness of the joint, mass and the impact strain rate were proposed. It was found that the impact fatigue life of the joints decreased as adhesive thicknesses increased under the same linear momentum, however, this did not occur when the specimens were subjected to similar impact energy values. Subsequently, an analysis of the fracture surfaces of the specimens was conducted that, considered the mechanical interactions between the substrate and the adhesive, fiber tearing and debonding from the composite matrix was found as well as delamination, resulting in a beneficial adhesion mechanism.

中文翻译：

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玻璃纤维复合材料军用飞机胶粘单搭接接头在循环冲击载荷下的动态响应分析

摘要 哥伦比亚航空工业促进了对飞机在运行过程中通常暴露在不同载荷条件下的材料力学行为的研究。Calima T-90 是哥伦比亚制造的第一架军用飞机，用于哥伦比亚空军飞行员的初级飞行训练，因此经常暴露在不利的操作环境中，例如硬着陆，这会产生冲击载荷，随后产生冲击疲劳。Calima T-90 的结构主要由复合材料、生成组件和其不同组件的子组件组成。粘接这些部件的主要方法是使用不同厚度的粘接接头。本研究旨在表征这些粘合接头在典型负载下的特性。为此，使用单搭接接头 (SLJ) 试样，使用准静态加载条件和冲击疲劳完成并进行了粘合剂厚度对此类接头机械性能影响的评估。使用落锤冲击试验机引起循环冲击，以获得特征冲击疲劳寿命图。然后分析了动态参数的演变，例如残余强度、冲击接触时间和刚度退化；这是对所有测试的粘合剂厚度进行的。提出了一种改进的强度退化现象学预测模型和一个关于接头粘合剂厚度、质量和冲击应变率的失效周期预测模型。结果表明，在相同的线性动量下，随着粘合剂厚度的增加，接头的冲击疲劳寿命降低，但是，当试样受到相似的冲击能量值时，这种情况不会发生。随后，对试样的断裂面进行了分析，考虑到基材和粘合剂之间的机械相互作用，发现纤维从复合基质中撕裂和脱粘以及分层，从而产生了有益的粘合机制。