The use of carbon fibre reinforced polymer (CFRP) materials is increasing in many different industries, such as those operating in the aviation, marine, and automotive sectors. In these applications, composite parts are often joined with other composite or metallic parts, where adhesive bonding plays a key role. Unlike conventional joining methods, adhesive bonding does not add weight or require the drilling of holes, both of which are major sources of stress concentration. The performance of a composite joint is dependent on multiple factors and can be improved by modifying the adhesive layer or the composite layup of the adherend. Moreover, joint geometry, surface preparation, and the manufacturing methods used for production are also important factors. The present work reviews recent developments on the design and manufacture of adhesively bonded joints with composite substrates, with particular interest in adherend modification techniques. The effects of stacking sequence, use of thin-plies, composite metal laminates and its specific surface preparations, and the use of toughened surface layers in the composite adherends are described for adhesively bonded CFRP structures.

The adhesion of pressure-sensitive adhesives (PSAs) is a complex phenomenon that can be understood through the characterization of different properties, including viscoelastic, mechanical, and fracture properties. The aim of the present paper is to determine the viscoelastic behaviour of an acrylic PSA and place it in the viscoelastic window, as well as to determine the tensile strength of the material. Additionally, different numbers of stacked adhesive layers and two crosshead speeds were applied to characterize the tensile strength of the adhesive in the different conditions. Adding a new interface between layers showed a negative influence in the tensile strength, while a higher crosshead speed implied a considerable increase in the same value. Finally, double cantilever beam (DCB) fracture tests were performed, and the J-integral approach was used to evaluate the fracture energy throughout the tests. The substrate roughness, the number of stacked layers, and the thickness of the PSA proved to decrease the performance of the PSA in fracture tests. While tensile bulk tests in viscoelastic materials are not easily found in the literature, as well as DCB tests, for fracture characterization, the obtained results allowed for the characterization of those properties in an acrylic PSA.

The presence of residual stresses in composite materials can significantly affect material performance, especially when integrated in bonded joints. These stresses, often generated during the cure process, can cause cracking and distortion of the material, and are caused by differences in the coefficients of thermal expansion or cure shrinkage. In the current research, multimaterial adherends combining carbon-fibre-reinforced polymer (CFRP) and aluminium in a single-lap joint (SLJ) configuration are analysed, allowing us to understand the effect of the thermal residual stresses, developed during the curing process, in the overall performance of the joints. A numerical model resorting to a finite element analysis (FEA) is developed to assess and predict the behaviour of the joints. The use of FML (fibre metal laminates) was found to significantly improve the strength of the joints, as well as the failure mode. The proposed geometry performed similarly to the comparable FML geometry, in addition to a decrease in the joint weight.

In the present paper, an exploratory study on the creep behavior of a pressure sensitive adhesive (PSA) is performed. After the determination of the quasi-static behavior of the adhesive for bulk specimens and single lap joints (SLJ), SLJs were subjected to creep tests at 80%, 60%, and 30% of their respective failure load. It was verified that the durability of the joints increases under static creep conditions as the load level decreases, with the second phase of the creep curve becoming more pronounced, where the strain rate is close to zero. In addition, cyclic creep tests were performed for the 30% load level at a frequency of 0.04 Hz. Finally, an analytical model was applied to the experimental results in order to reproduce the values obtained for both static and cyclic tests. The model was found to be effective, reproducing the three phases of the curves which allowed for the characterization of the full creep curve, something not commonly found in the literature, especially for PSAs.

In response to heightened environmental awareness, various industries, including the civil and automotive sector, are contemplating a shift towards the utilization of more sustainable materials. For adhesive bonding, this necessitates the exploration of materials derived from renewable sources, commonly denoted as bio-adhesives. This study focuses on a bio-adhesive L-joint, which is a commonly employed configuration in the automotive sector for creating bonded structural components with significant bending stiffness. In this investigation, the behavior of joints composed of pine wood and bio-based adhesives was studied. Two distinct configurations were studied, differing solely in the fiber orientation of the wood. The research combined experimental testing and finite element modeling to analyze the strength of the joints and determine their failure mode when subjected to tensile loading conditions. The findings indicate that the configuration of the joint plays a crucial role in its overall performance, with one of the solutions demonstrating higher strength. Additionally, a good degree of agreement was observed between the experimental and numerical analyses for one of the configurations, while the consideration of the maximum principal stress failure predictor (MPSFP) proved to accurately predict the location for crack propagation in both configurations.

Understanding the creep behaviour of materials is crucial in structural design, since assessing their durability and long-term performance is essential for ensuring the safety of the structures. Experimental testing allows to gather data on the creep behaviour of materials, as well as observe the damage mechanisms and dependence on environmental effects, such as stress and temperature. In this paper, the development of a cyclic creep testing station is presented. An innovative compact device is designed for testing single-lap joints using pressure-sensitive adhesives (PSAs) at different stress and temperature levels. The design is based on a mechanism that periodically supports a hanging weight resulting in an alternating load applied to the bonded joint. The assembled testing setup is validated by comparing the results of the developed machine with cyclic creep experimental data obtained with a servo-hydraulic testing machine adapted for cyclic creep. After validation, preliminary tests with one PSA at 55 °C are presented to evaluate its performance at higher temperatures. The results indicate that the developed cyclic creep machine can be used to characterise the creep behaviour of PSAs under cyclic loading.