The industrial application of adhesively bonded joints has increased significantly in the last few years, driven by benefits such as the increased design flexibility, high vibration damping, the capability of joining dissimilar materials and the possibility of being used in combination with other joining techniques. However, the presence of stress concentrations at the overlap ends, especially in single lap joints, is one of the major issues associated with this technique, reducing joint strength. To solve this drawback, several techniques have been proposed, such as the use of adhesive spew, adhesive and adherend shaping, mixed adhesive joints and functionally graded adhesive joints. Functionally graded adhesive joints use an adhesive layer where the properties gradually change along the bondline, which results in the reduction of stress concentration peaks at the ends of the overlap, leading to a more uniform stress distribution. Multiple techniques for the creation of a functionally graded bondline have been presented in the literature, such as the inclusion of particles and nanoparticles and the use of functionally graded curing. However, the experimental works available in the literature only report results for quasi-static loading conditions, with the impact behaviour of these joints being an unstudied topic. The main objective of the present work is to fill this gap and study the mechanical behaviour of functionally graded adhesive joints loaded under impact conditions, using both experimental testing and numerical modelling. The results obtained show that, unlike what is found for quasi-static loads, graded joints do not offer significant strength improvement under impact loads. In contrast, energy absorption is significantly increased. This behaviour is explained by the completely different stress distribution on the adhesive layer for quasi-static and impact conditions, leading to the lower effectiveness of functionally graded adhesive joints under impact loads.

在过去的几年中，由于诸如提高设计灵活性，高减振性，连接异种材料的能力以及与其他连接技术结合使用等优点的推动，胶粘接头的工业应用已显着增加。但是，重叠端（特别是在单膝关节中）应力集中的存在是与该技术相关的主要问题之一，从而降低了接头强度。为了解决该缺点，已经提出了几种技术，例如使用胶粘剂喷头，胶粘剂和被粘物成形，混合胶粘剂接头和功能梯度胶粘剂接头。功能分级的粘合接头使用粘合层，其性能沿粘合线逐渐变化，这会导致重叠末端的应力集中峰减少，从而导致应力分布更加均匀。文献中已经介绍了多种创建功能梯度粘合线的技术，例如包含颗粒和纳米粒子以及使用功能梯度固化。但是，文献中提供的实验工作仅报告了准静态载荷条件下的结果，而这些接头的冲击行为却是尚未研究的话题。本工作的主要目的是填补这一空白，并通过实验测试和数值模拟研究在冲击条件下加载的功能梯度胶接接头的机械性能。获得的结果表明，与准静态负载不同，梯度接头在冲击载荷下不能显着提高强度。相反，能量吸收显着增加。在准静态和冲击条件下，粘合剂层上的应力分布完全不同，从而解释了此行为，从而导致功能分级的粘合剂接头在冲击载荷下的有效性较低。