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Adhesive bonding is widely used in modern industry. It has many advantages—the main one being the reduction in production costs. It also has certain limitations. One of the limitations of adhesive bonds is the relatively long bonding time of the joints. The main objective of this research was to determine the possibility of studying the kinetics of adhesive bond formation using a non-destructive ultrasonic method. A research experiment was planned and carried out. Adhesive specimens were prepared, and their quality changes over time were evaluated. In addition, the change in ultrasonic measures during the testing of these bonds was evaluated, as well as the hardness of the adhesive. In this study, the choice of test apparatus was made, in particular ultrasonic probes for the adhesive used and the materials to be bonded. The choice of adhesive was also made, for one in which bonding phenomena occur uniformly throughout the volume. This work examined the changes in the mechanical strength and hardness with time. The tests showed that the greatest changes in mechanical strength occur within the first 24 h after the bond was made. With the mechanical strength reaching 12.6 Mpa after 216 h, the strength in the first 24 h was 10.36 (for bonded steel sheets). For bonded steel discs, the maximum tensile strength was 26.99 Mpa (after 216 h), with a hardness of 22.93 Mpa during the first 24 h. Also, significant changes were observed in the adhesive hardness during the first 24 h. The hardness of the adhesive after 216 h was 70.4 Shore’a on the D scale, while after 24 h it was 69.4 Shore’a on the D scale. Changes in the ultrasonic parameters of the adhesive bond quality were found to occur along with changes in the bond quality.

An overview of recent development of cohesive modelling is given. Cohesive models are discussed in general and specifically for the modelling of adhesive layers. It is argued that most cohesive models model a material volume and not a surface. Detailed microscopic and mesomechanical studies of the fracture process of an engineering epoxy are discussed. These studies show how plasticity on the mesomechanical length scale contributes to the fracture energy in shear dominated load cases. Methods to measure cohesive laws are presented in a general setting. Conclusions and conjectures based on experimental and mesomechanical studies are presented. The influence of temperature and strain rate on the peak stress and fracture energy of cohesive laws indicates fundamentally different mechanisms responsible for these properties. Experiments and mesomechanical studies show that in-plane straining of an adhesive layer can give large contributions to the registered fracture energy. Finite element formulations including a method to incorporate this influence are discussed.

Purpose This paper aims to present a new approach to the fast determination of the effective, dynamic, mechanical properties of an adhesive for linear and nonlinear regions of the adhesive response, for both healthy and damaged states of the bond. Design/methodology/approach The proposed approach is based on the measurement of the linear and nonlinear frequency response function (FRF) of adhesive-bonded structure and using artificial neural network identification technique. For this purpose, linear and nonlinear FRFs are measured for several single-lap joint specimens that are fabricated in healthy and damaged configurations of the bond. The measured FRFs of healthy and damaged specimens are then used to identify the natural frequencies of the specimens. The experimental natural frequencies, in turn, would be used to train artificial neural network (ANN) which would be able to predict the effective Young’s and shear moduli and damping of adhesive in healthy and damaged specimens, for any given excitation level and frequency, within the training domain. Findings Simultaneous identification of the effective mechanical properties of adhesive for linear and nonlinear response regions, as well as healthy and damages states of the adhesive bond. Practical implications The introduced method is effective to model the assembled structures with the viscoelastic adhesive joints, for linear and nonlinear regions. Originality/value A fast methodology, using ANN, for identification the effective mechanical properties of adhesives, compared to other methods for both linear and nonlinear regions.

One of the most relevant geometrical factors defining an adhesive joint is the thickness of the adhesive layer. The influence of the adhesive layer thickness on the joint strength has not been precisely understood so far. This article presents simplified analytical formulas for adhesive joint strength and adhesive joint coefficient for different joint loading, assuming, inter alia: linear-elastic strain of adhesive layer, elastic strain of adherends and only one kind of stress in adhesive. On the basis of the presented adhesive joint coefficient, the butt joint was selected for the tests of the influence of adhesive thickness on the adhesive failure stress. The tests showed clearly that with an increase in the thickness of the tested adhesive layers (up to about 0.17 mm), the value of their failure stress decreased quasi linearly. Furthermore, some adhesive joints (inter alia subjected to shearing) may display the optimum value of the thickness of the adhesive layer in terms of the strength of the joint. Thus, the aim of this work was to explain the phenomenon of optimal adhesive layer thickness in some types of adhesive joints. The verifying test was conducted with use of single simple lap joints. Finally, with the use of the FE method, the authors were able to obtain stresses in the adhesive layers of lap joints for loads that destroyed that joints in the experiment, and the FEM-calculated failure stresses for lap joints were compared with the adhesive failure stresses determined experimentally using the butt specimens. Numerical calculations were conducted with the use of the continuum mechanics approach (stress-based), and the non-linear behavior of the adhesive and plastic strain of the adherends was taken into account.

This work aims to compare quantitatively different nondestructive testing (NDT) techniques and data fusion features for the evaluation of adhesive bonding quality. Adhesively bonded composite-epoxy single-lap joints have been investigated with advanced ultrasonic nondestructive testing and induction thermography. Bonded structures with artificial debonding defects in three different case studies have been investigated: debonding with release film inclusion, debonding with brass film-large, debonding with brass film-small. After completing preprocessing of the data for data fusion, the feature matrices, depending on the interface reflection peak-to-peak amplitude and the principal component analysis, have been extracted from ultrasonic and thermography inspection results, respectively. The obtained feature matrices have been used as the source in basic (average, difference, weighted average, Hadamard product) and statistical (Dempster–Shafer rule of combination) data fusion algorithms. The defect detection performances of advanced nondestructive testing techniques, in addition to data fusion algorithms have been evaluated quantitatively by receiver operating characteristics. In conclusion, it is shown that data fusion can increase the detectability of artificial debonding in single-lap joints.

In this paper, an experimental study on the effect of surface roughness of different adherend material on adhesive bond strength was carried out. The adherend material used was aluminium AA6061 and wood in the form of sheet, and the adhesive was an epoxy resin. Different surface roughness obtained by mechanical abrasion using an emery paper and sand paper for aluminium and wood adherend samples respectively. Single strap joints were tested at room temperature. Results showed that there is clear dependency observed in between the adhesive bond strength and surface roughness of both wood and aluminium adherend joints. Optimum surface roughness values were obtained in the range of R a  = 1.68 ± 0.14 µm and R a  = 1.64 ± 0.2 µm for the aluminium and wood adherend joints respectively. Surface roughness along with the adhered material parameters should be considered during design stage of adhesively bonded joints.

The adoption of lightweight materials in engineering applications has become more popular over recent years, with adhesives replacing traditional joining methods such as bolts and rivets. Adhesion science and related technologies are arising as cleaner options for sustainable production in modern industry, with adhesive-bonded joints increasingly being used as design solutions in complex products and assemblies. However, the use of structural adhesives has several significant drawbacks, most of which are related to environmental impact, linked to the nature of the adhesive substance, as well as product disassembly/disposal deriving from the fact that adhesive joints are usually irreversible. Within this context, the goal of this paper is to study adhesive joints in mechanical assemblies from a life cycle perspective, offering more comprehensive analysis tools and assembly solutions suitable for industries such as automotive, aerospace, and assembly/packaging machinery. A methodological framework for the comprehensive characterization of bonded joints using effective surface activation techniques has been created and tested. The first phase encompasses the production of samples for mechanical testing under static and fatigue loading conditions. The second includes the characterization of inputs/outputs (life cycle inventory—LCI) for life cycle assessment (LCA) of mechanical assemblies employing adhesive joints and innovative surface activation techniques. The final phase provides a set of eco-design actions based on a critical analysis of the obtained results. The outcomes demonstrate how it is possible to achieve optimal adhesive-bonded joint properties under specific working conditions (e.g., static or fatigue loading) while maintaining a low environmental load using novel surface pre-treatments such as laser and plasma technologies. These outcomes are supported by a case-study in which adhesive joints are applied to the mechanical assembly of a bottle gripper for a food packaging machine. The adoption of eco-design rules in adhesive joint applications will help designers in the development of suitable solutions for lightweight applications from a complete life cycle perspective.

The aim of this work is to achieve reliable nondestructive evaluation (NDE) of adhesively bonded aerospace components by developing novel multidimensional data fusion techniques, which would combine the information obtained by ultrasonic and X-ray NDE methods. Separately, both NDE techniques have their advantages and limitations. The integration of data obtained from pulse echo immersion ultrasound testing and radiography holds immense potential to help improve the reliability of non-destructive evaluation. In this study, distinctive features obtained from single techniques, traditional ultrasonic pulse echo testing, and radiography, as well as fused images, were investigated and the suitability of these distinctive features and fusion techniques for improving the probability of defect detection was evaluated. For this purpose, aluminum single lap joints with brass inclusions were analyzed using ultrasound pulse echo and radiography techniques. The distinctive features were extracted from the data obtained, and images of features obtained by both techniques were fused together. Different combinations of features and fusion algorithms were investigated, considering the desire to automate data evaluation in the future.

It is known that bond strength is affected by the application conditions and methods of adhesive connections. Knowing which method can increase the joint strength more and choosing those methods is important in terms of preventing time loss and financial losses. This study aims to experimentally examine the effects of aluminum alloy and carbon fiber reinforced polymer (CFRP) composite panels on the mechanical properties of adhesive thickness, different temperatures, pressure and filler in adhesive joints and model data. Experiments were carried out by using AA7075-T6/CFRP panels with single lap joint bonding joints, unfilled, 1% and 2% by weight carbon fiber filled, at 19, 50 and 100 °C and also by pressing under 2 MPa pressure without applying pressure. It is understood from the results that the parameters that affect the bond strength the most are the adhesive thickness and the amount of pressing applied on it. The effect of the experiments carried out under these conditions on the tensile failure load values was examined, and also artificial neural network (ANN) and gene expression programming (GEP) models were presented for failure load estimation. The R 2 values of the ANN model are 0.9456. The R 2 values of the GEP model are 0.9029–0.9572 for training and validation, respectively. High accuracy rates were obtained with both models. It is seen that there is a good agreement between the observed and predicted values in the errors of the training and validation sets. As a result, it was concluded that ANN and GEP models can be used to select the optimum value in similar applications.

Wood, a potentially good construction material in terms of sustainability, has less structural use now in India. Due to easy availability, low cost and good working quality there is a scope for the value addition of rubber wood in the Country. Finger jointing technology benefits high economic advantage by upgrading rubber wood. There is a dearth of information for the influence of adhesive on the mechanical properties of jointed rubber wood in India. This study was conducted to evaluate the effects of adhesive type on the end jointing and face gluing of rubber wood. The end jointing adopted for the study was the most common finger joint configuration of the wood industry in Kerala, the largest producer of rubber wood in the Country. The adhesives were polyvinyl acetate (PVAc) and phenol resorcinol formaldehyde (PRF). The face gluing evaluation was done based on the adhesive bond strength and percentage wood failure. The integrity of glue types to delamination was also tested .The results of the study have indicated glue type has no statistically significant effect on modulus of rupture, modulus of elasticity of finger joints and the shear strength of adhesive bond in the dry stage with the same wood failure percentage. The joint efficiency of PRF adhesive was superior to PVAc in tension and compression of finger joints. The PRF adhesive exhibited excellent performance in the exterior exposure condition durability test.