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In the manufacturing industry, the process of applying adhesive to join two substrates can be challenging. It requires precise placement of adhesive so that it is distributed in the desired pattern, ensuring a strong bond between the substrates. Overfilling is a common practice to ensure that the bond is not underfilled after the substrates are pressed together. However, this approach leads to unnecessary adhesive waste and can result in additional cleaning work. To address these issues, an optimization algorithm has been developed that can compute an initial adhesive pattern to flow into any desired geometry. The algorithm is based on a transient squeeze flow simulation, which iteratively removes fluid material as it flows out of the target bond domain. For example, to obtain a square bond geometry after a parallel squeezing process, the adhesive needs to be initially applied in a star shape. However, the algorithm is highly adaptable and can be used for many desired bond geometries as shown in this paper. The results are independent of the mesh resolution and fluid flow law, thus eliminating the need for complex rheological fluid characterization. The algorithm requires only two input parameters, namely the target bond geometry and the degree of compression. This highly simplifies the adaption of the proposed optimization method for manufacturers, and their design requirements can be considered with ease. The results are reliable and consistent despite the simulation's complexity. Overall, this new optimization methodology represents a significant advance in adhesive application technology, eliminating the need of overfilling and thus making the manufacturing process more efficient, sustainable and cost-effective. [ABSTRACT FROM AUTHOR]

Dimensioning adhesively bonded joints remains a challenging task. Their diversity in geometry and material (including combinations thereof), characteristic stress peaks, scatter and brittleness are aspects few practitioners are prepared to handle for dimensioning purposes. As developed in the first part of this two-part paper, direct stress based methods, despite diverse fudging techniques, proved to be unsuitable. This left the field open for fracture mechanics, which, however, departed very much from the engineering reality leading to only lukewarm acceptance from practitioners. Almost unnoticed, probabilistic methods, much closer to classical mechanics, may offer an alternative. Based upon the presentation, in the first part of this series, of the concepts, the authors suggested an implementation in terms of design procedure. The second part of this two-part paper, is dedicated to the presentation of several examples, from available literature, of adhesively bonded joints involving a large variety of typologies (single and double-lap, tubular, and hybrid joints) and materials (fibre-reinforced polymers, steel, wood). The focus therein is set on practitioner oriented aspects, in particular on techniques for implementation. [ABSTRACT FROM AUTHOR]

Recent adhesive research starts to consider more process oriented problems, in addition to the classical static stress and strength related topics, thus shifting towards a more global view on adhesive bonding. This includes the consideration of adhesive flow during application and joining of the substrates with all the information about initial application pattern and the resulting adhesive distribution contained after joining. Since the surface condition plays a major role and various different pretreatments are commonly used to improve the strength and durability of bonded joints while modifying their surface structure, the question of whether this influences the dynamics of the squeeze flow – or not – is addressed in this paper. In particular the materials glass and steel in combination with two designated surface pretreatments (blasting and flame-treatment) as well as their respective untreated reference surface are considered. For validation purposes the surfaces were characterized by means of roughness R a and contact angle θ measurements, performed before and after the pretreatment, which resulted in a range of surface parameters for R a from almost 0 to 3.3 μ m and for θ from approximately 0 to 35°. However based on the measured force–displacement behaviour during the squeeze process no statistically significant difference regarding the dynamics of the adhesive flow could be observed between the untreated and pretreated surfaces for all investigated materials. [ABSTRACT FROM AUTHOR]

The highly automated world of manufacturing industry offers new possibilities for the application of adhesives which are not fully utilized yet. In addition to the classical static stress and strength related topics, a more global view on adhesive bonding is needed. This includes the consideration of adhesive flow during application and joining of the substrates with all the information about initial application pattern and the resulting adhesive distribution contained after joining, and thus benefit from the modern manufacturing possibilities. To do so, research which addresses this issue is needed in the first place to elaborate innovative approaches on how to design and develop adhesive application pattern which minimize adhesive spillage and waste while achieving a bond without any air enclosures or other imperfections. This paper systematically investigates different phenomena which can occur during the joining process, such as the formation of air pockets and how they behave once formed. Furthermore, optimized application pattern and the merging behaviour of different flow fronts are considered. In total, four different adhesive application patterns were investigated experimentally and analysed using Particle Image Velocimetry. The investigations were complemented by a numerical simulation of the corresponding squeeze flow experiments — which achieved a high level of agreement. It was found that during the joining process, existing air pockets can reform due to the phenomenon of viscous fingering and subsequently cure into flat cavities, which are more critical in terms of bonding strength than spherical ones. [ABSTRACT FROM AUTHOR]

Adhesive bonding is increasingly being considered by engineers for load-bearing joints to complement, or supplement, traditional mechanical fasteners for a large variety of structural materials, including fibre-reinforced polymers, timber, and steel. However, practitioners are still largely applying analysis and design methods, including codes and standards, that rely heavily on fudge factors. This is not due to the relative novelty of the joining technique, and the complexity of the associated mechanics. This paper guides the reader through some of the most important aspects of adhesively bonded joints, and the reasons why classical mechanics can only be applied in conjunction with fudge factors. Subsequently, the principles of fracture mechanics (FM) are presented; it is shown that, despite its conceptual strengths, FM is rather difficult to implement, as it introduces mechanical concepts practitioners are not familiar with. Then probabilistic methods (PM) are introduced; it is shown that PM can be considered as an extension of classical mechanics, as they can be easily implemented as a post-processing routine of the latter. Additionally, it is shown that PM, unlike FM, neither require specific test procedures for characterisation, nor complicated numerical analyses. Lastly, the paper offers a step-by-step guide for the implementation of PM for the dimensioning of adhesively bonded joints. The second part of this paper illustrates the latter analysis and design of adhesively bonded joints on a series of examples involving FRP, timber, and steel. [ABSTRACT FROM AUTHOR]

Current studies show great, but unutilized potential for mechanical optimization of adhesively bonded joints. There are different approaches, e. g. mixed adhesive joints; tapered adherends or joints with spew fillets, all of which try to redistribute the stress peaks, occurring at the ends of adhesive layer overlap, in favor to the load capacity. However, these investigations fail to take a general approach to find optimal geometric solutions to the problem of joining two materials by means of adhesive bonding. Instead the geometry is changed by predefined parameters such as tapering angles, spew fillet radii or the number of adhesives in mixed adhesive joints. To allow a non-parametric optimization, this paper proposes and investigates an extended bi-directional evolutionary structural optimization methodology based on a failure criterion to account for othotropic materials, which are often used in the context of bonding. The optimized joint geometry, generated by the proposed algorithm, resulted in a fairly constant distribution of elemental failure probability compared to the non-optimized state, thus eliminating underutilized spots of material and increasing the efficiency of the connection. Furthermore the influence of different parameters such as the overlap-length to adherend thickness ratio; the stiffness between adherend and adhesive as well as the adherend degree of orthotropy were investigated for optimal joint geometry. [ABSTRACT FROM AUTHOR]

This study examines grouted joints for offshore wind turbine systems, where gaps between steel pipes are filled with grout, relying on adhesion, friction and compression struts formed by shear keys. Concerns about the limited load carrying capacity of large diameter grouted joints in offshore structures have prompted investigation. Whilst adhesive bonds are recognized for load transfer in structural steel, the complete replacement of grouting with bonding alone is proving impractical for large gaps in offshore structures, posing challenges in terms of cost and handling. To address these challenges, the study presents an innovative hybrid grouted joint for steel structures that combines grout and adhesive layers. This novel approach replaces traditional large shear keys with distributed micro-shear keys — small granules embedded in the grout material. Under axial loading, the hybrid joint demonstrates robust performance, with a maximum nominal shear stress on the inner pipe of 30.1 MPa and consistent load capacity across tests. Average shear strength is in line with, and occasionally exceeds, expectations. Notably, the hybrid joint shows resilience in different configurations and maintains a low coefficient of variation of 5.5%, indicating consistent performance. When the influence of the adhesive material on the hybrid joint is examined, the effect on the joint stiffness is minimal, despite variations in adhesive stiffness. Sikadur 370, which has a higher modulus of elasticity than DuploTEC, shows similar deformation curves in the elastic region, emphasizing the robustness of the joint. Differences in the maximum loads are attributed to the thickness of the adhesive layer and the lower modulus of DuploTEC, resulting in different shear strengths. The proposed hybrid joint offers a promising solution to improve the performance of conventional grouts and adhesives in offshore structures. The study also formulates a failure criterion, performs numerical stress analysis, and models the effect of geometric dimensions, eccentricity, and misalignment on load capacity. The methodology's accuracy in predicting load capacity, supported by numerical analysis and large-scale joint simulations, contributes to a comprehensive understanding of hybrid joint performance in engineering applications. [ABSTRACT FROM AUTHOR]

The installation of offshore wind turbines has achieved rapid and substantial progress worldwide and further increase is predicted by enhanced technologies that will reduce costs and increase service time. Secondary structures applied to the primary structure, as the transition piece of a monopole, can be e.g. cable support, boat landing or anode systems. These structures are often welded, which leads to problematic notch effects and hydrogen embrittlement, especially for underwater applications. Also the handling of technical equipment as power current or artificial housings for scuba divers for underwater welding is challenging. Adhesive bonding will lead to cost reduction as the mentioned negative aspects can be avoided. The corrosion protection coating and the primary structure will no longer be damaged and therefore do not need a subsequent coating. This article focuses on the area which is permanently exposed to water. A critical point is how the capability to form adhesion and cohesion, will be influenced by the application process under water. Therefore, stud bonding fasteners are designed that enable the injection of adhesive to the bonding area under water. The load capacities for different adhesives, surface pre-treatments and the degradation by exposure to artificial sea water were investigated. Adhesion was achieved with two different adhesives, which were able to cure and realize reasonable strength under water. Furthermore, two selected coating systems were able to improve the performance of the adhesive bond. [ABSTRACT FROM AUTHOR]