Adhesive bonds are subject to multiple environmental conditions that can affect their mechanical performance during service. Therefore, it is important to evaluate the influence of temperature on ...adhesive strength, as it can impact joint safety and should be considered during the design phase. This study presents an analysis of the effect of high temperatures on the mechanical behaviour of joints made with highly elastic adhesives, specifically a polyurethane and a silicon-modified polymer. Shear and tensile tests were conducted at temperatures of 23, 50, and 80 °C using dumbbell specimens for tensile tests and single lap specimens (SLJ) for shear tests. The tests were performed with two different substrates, aluminium (Al) and glass fibre reinforced polyester panel (GRP), and with varying adhesive thicknesses. These tests aim to assess the impact of temperature conditions on the mechanical properties of the adhesive and the behaviour of the joints. The analysis of the experimental results reveals that the adhesive degrades when exposed to high temperatures, resulting in reduced strength and stiffness, and less linear behaviour.
Furthermore, this work involves the determination of a model able to reproduce the mechanical behaviour of hyperelastic adhesive at high temperatures, considering diverse constitutive modelling approaches. To achieve this, a testing protocol was conducted on basic uniaxial and planar specimens. The results indicate that the Ogden N=2 model is the most suitable for representing the non-linear behaviour of the hyperelastic adhesive at high temperatures. In contrast, the Mooney Rivlin model is more suitable to represent the material behaviour under ambient conditions. To conclude this work, the law has been satisfactorily validated by comparing the results of tests carried out on SLJ specimens with different adhesive thicknesses.
This work presents the results of an experimental and numerical investigation on the flexural behaviour of reinforced concrete (RC) slabs strengthened by carbon fibre reinforced polymers (CFRP) ...laminates applied according to the near surface mounted (NSM) technique, using stiff and flexible adhesives. Two study variables were analysed: i) the adhesive type and ii) the existence or not of pre-cracking on the slabs. The results show a clear dependence of slab's flexural performance on the adhesive type: the use of flexible adhesive yields to 80% of the maximum load achieved with stiff adhesives. The existence of pre-damage did not affect the structural behaviour of the slabs. CFRP rupture was observed with the use of stiff adhesives while CFRP debonding has occurred with the flexible one. Finally, a higher ductility was observed when using flexible adhesive.
A numerical model was worked out and calibrated to simulate the flexural behaviour of the tested slabs. The numerical simulations showed a very good agreement with the experiments. Besides the very good predictive performance in terms of load-displacement behaviour, the numerical model also correctly reproduced the failure modes obtained in the experiments and the differences in the bonding mechanisms of slabs strengthened with the stiff and flexible adhesives. It was demonstrated that the proposed numerical model can be used in engineering practice for the analysis and design of NSM CFPR strengthening systems for existing RC structures.
This work focuses on the mechanical characterisation of adhesives with hyperelastic behaviour and on the determination of the behavioural laws that best represent it, in order to introduce them in ...simulation models. First, a test plan is carried out on simple specimens: uniaxial and planar configuration. These are designed to measure the non-linear behaviour of adhesives in both tensile and pure shear. Unlike the uniaxial specimen, which is governed by a test standard (UNE-ISO 37) that defines its geometry, the planar specimen does not have a standard that defines its dimensions. Therefore, in this research it is proposed to carry out tests with specimens of different width-length sizes to evaluate how these dimensions affect the stress-strain curves.For mechanical characterisation, finite element programs provide the tool to evaluate the predicted behaviour of a hyperelastic material from the experimental results, displaying in the same graph the degree of approximation obtained for the results of each test (Dumbbell and planar) with different hyperelastic models, allowing us to select the hyperelastic model that best fits the experimental data.The Mooney-Rivlin model was found to be the best fitting model and therefore the most appropriate to describe the behaviour of hyperelastic adhesives used in this study. To conclude this study, the obtained law was validated by comparing the results of tests carried out on single lap joint (SLJ) specimens of different thickness.
This paper discusses the issue of a lap joint in the form of a thin film attached to a rigid base with the use of a layer of flexible adhesive exhibiting a non-linear constitutive relation between ...shear stress and distortional strain, which is approximated by the second-order power law. Similarity theory is used to perform a qualitative analysis of the influence of magnitude of non-linearity on the performance of the system. The introduced similarity numbers are proposed to be used in formulation of simple design tools. The analysis is performed by solving the derived governing equations for characteristic cases in a numerical way combining the fourth-order Runge-Kutta algorithm and iterative shooting ruled by a steepest descent method. The results are compared with the results of the plane stress finite element analysis. It can be observed that within considered models the influence of the material non-linearity is of minor importance and in some cases it may be almost entirely surpassed by local effects resulting from boundary conditions. For relatively small load intensity it becomes negligibly small.
Flexible adhesive joints, with adhesives of very low elastic modulus and very large failure deformation, are of special interest in industrial applications. Nevertheless, there is a lack of effective ...models for predicting their behaviour for structural applications. Existing methods developed for stiff compressible adhesives are not able to accurately capture the nonlinearities present on a thick flexible bondline. This paper presents a new analytical model for the simulation of a flexible adhesive bonded joint in a double cantilever beam (DCB) setup. Using the concepts of elastic foundation beam theory and developing them for a more general non-linear hyperelastic foundation case, a semi-analytical model is proposed. The effectiveness of the model, with respect to other approaches shown in the literature, is compared against experimental results for Krafft’s flexible adhesive SILKRON POLYMER H-100. The hyperelastic foundation model accurately predicts the load-displacement response of the adhesive.
A shape memory polymer (SMP) adhesive forms a conformal and hermetic contact with a target surface at the soft, rubbery state and provides a high-strength dry adhesion at the rigid, glassy state. In ...particular, recent SMP adhesive studies show SMP’s ability to adhere to various rough and even underwater yet rigid surfaces. However, achieving and retaining the strong adhesion on flexible target surfaces such as common fabrics has not been reported since a flexible target surface would easily be peeled off from an SMP adhesive, which is too rigid to accommodate the target surface flexing. Here, we introduce the dual adaptation of an SMP adhesive composed of a thin SMP layer and a backing fabric, which involves the shape adaptation to make a strong adhesive contact and the flexure adaptation to tolerate a target surface flexing. To discover the criteria for optimizing both shape and flexure adaptations, we present the theoretical rationale as well as the computational and experimental studies in this work. Based on the findings here, we design a thin SMP adhesive and demonstrate its dry and underwater adhesive performances on common clothes to highlight its potential applications.
The influence of the adhesive type on bond behaviour between concrete and Carbon Fibre Reinforced Polymers (CFRP) laminate strips, in the context of Near Surface Mounted (NSM) strengthening ...technique, is considered as crucial for an efficient design. Thus, direct pullout tests were carried out to assess the influence of i) type of adhesive ii)CFRP cross-section and (iii) bond length on behaviour of NSM-CFRP system. Two types of stiff adhesives and one type of flexible adhesive were studied. For similar bond lengths, significantly higher maximum pullout force and bond stiffness were observed in the case of stiff adhesives, while noticeably higher slip at maximum force was achieved with the flexible adhesive. Analytical and numerical investigations were carried out in order to determine the local bond stress-slip relationships for both stiff and flexible adhesives. After demonstrating its good predictive performance, the analytical approach was used to design curves of the required anchorage lengths of NSM-CFRP system at ultimate limit state conditions. For the analytically calibrated mechanical parameters of NSM bond-slip law a two-dimensional numerical model of the direct pullout tests was worked out.
•Stiff and flexible adhesives yield to different CFRP-glass composite bond responses.•Flexible adhesives smooth the stress concentration near the loaded end section.•DIC method is extremely relevant ...in documenting the damage propagation mechanisms.•Analytical and numerical tools accurately simulate bond responses.•The local bond-slip laws are useful for modelling structural composite systems.
Within the context of glass structures, reinforcement strategies have been recently developed to prevent catastrophic failures by promoting the composite action between components. In this regard, the behaviour of adhesively bonded connections between glass and the reinforcement plays a crucial role. This paper presents an experimental, analytical and numerical study focussing on the bond behaviour of CFRP-to-glass adhesively bonded joints, comprising annealed glass sheets and CFRP laminates bonded with two stiff adhesives and one flexible adhesive. The experimental programme included (i) mechanical characterization tests and (i) tensile tests on CFRP-to-glass double-lap joints, evaluating the influence of the type of adhesive and the overlap length. Digital image correlation (DIC) method, analytical investigations and numerical modelling were performed to determine the local bond stress-slip laws for each adhesive, aiming at providing the required information to subsequently support the design of glass structural elements. Compared to the flexible adhesive, the stiff adhesives seem to promote more favourable interaction between the adherends; however, the former is better at promoting stress redistribution mechanisms, therefore, mobilizing longer bond lengths to transfer the tensile force between adherends. Adhesives with an extremely stiff response induce high stress concentrations in small areas and, consequently, the bonding system may fail prematurely at the glass adherend governed by localized phenomena, such as the low quality of glass processing methods, the high density of surfaces flaws and localized damage during handling.
One of the most important performance indicators of flexible adhesives is the peeling force from the rigid substrate. The most common method for determining this parameter is the method of uneven ...peeling of flexible material from a rigid plate at an angle of 90о. Devices used today to determine this parameter do not provide high accuracy of measuring the peeling force due to design features. In this paper, a method for determining the exfoliation force of flexible material from a rigid plate with self-regulating maintenance of the exfoliation angle equal to 90о is theoretically justified and experimentally confirmed. As a result of experimental studies using a medical patch, it was found that the developed device allows clearly recording and measuring with high accuracy the exfoliation force of flexible material from a rigid plate with self-regulating maintenance of the exfoliation angle equal to 90±3о. Одним из важнейших эксплуатационных показателей гибких клеящих материалов является усилие отслаивания от жесткой подложки. Наиболее распространенным методом определения этого параметра является метод неравномерного отслаивания гибкого материала от жесткой пластины под углом 90о. Применяемые на сегодня устройства для определения этого параметра в силу конструктивных особенностей не обеспечивают высокую точность измерения усилия отслаивания. В данной работе теоретически обоснован и экспериментально подтвержден способ определения усилия отслаивания гибкого материала от жесткой пластины с саморегулируемым поддержанием угла отслаивания, равным 90о. В результате проведенных экспериментальных исследований с использованием медицинского пластыря установлено, что разработанное устройство позволяет четко фиксировать и измерять с высокой точностью усилие отслаивания гибкого материала от жесткой пластины с саморегулирующим поддержанием угла отслаивания, равным 90±3о.
Creep behavior of Cross-Laminated-Timber (CLT) beams with a finite-thickness layer of flexible adhesives is investigated. Creep tests were carried out for all component materials as well as for the ...composite structure itself. Three-point bending creep tests were performed for spruce planks and for CLT beams, and uniaxial compression creep tests were performed for two flexible polyurethane adhesives: Sika
PS and Sika
PMM. All materials are characterized with the use of the three-element Generalized Maxwell Model. The results of creep tests for component materials were used in elaboration of the Finite Element (FE) model. The problem of linear theory of viscoelasticity was solved numerically with the use of the Abaqus software. Obtained results of Finite Element Analysis (FEA) are compared with experimental results.
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