Use of seawater to improve the static strength and fatigue life of bonded coated steel joints

La industria de la construcción naval exige soluciones adhesivas para unir componentes a sustratos pintados, ya que las tecnologías de soldadura tradicionales requieren operaciones de procesamiento costosas y que requieren mucho tiempo. Sin embargo, este tema rara vez se considera en la literatura. El objetivo del presente estudio es investigar la influencia de la exposición en disoluciones de cloruro de sodio en la resistencia estática y el rendimiento a la fatiga de juntas de acero pintadas unidas con adhesivo. Para ello, se utilizó un adhesivo epoxídico frágil de dos componentes para fabricar uniones a solape de aceros pintados unidos con adhesivo. Se realizaron ensayos estáticos y de fatiga tras envejecer las uniones mediante inmersión en soluciones cloradas durante diferentes periodos de tiempo. Las pruebas adicionales realizadas incluyeron pruebas FTIR, análisis de la temperatura de transición vítrea y pruebas de tracción de muestras de adhesivo envejecidas y sin envejecer, estudios experimentales y de simulación FEM de la absorción de agua, y análisis de la superficie de fractura de las juntas. Los resultados muestran, sorprendentemente, que tanto las propiedades mecánicas estáticas como las de fatiga de las juntas aumentan significativamente con el envejecimiento durante el primer mes de exposición. La difusión de agua que tuvo lugar durante el primer mes en las juntas a solape mejoró más del 30% tanto la resistencia estática como la resistencia a la fatiga de las juntas fabricadas con este adhesivo relativamente rígido. La tasa de absorción de agua del adhesivo también se calculó utilizando las relaciones de la ley de Fick. Los resultados se utilizaron para simular numéricamente el nivel de humedad absorbida por la capa de adhesivo de las uniones. La presente investigación demuestra que el fenómeno de absorción de humedad no conduce a resultados negativos para todas las uniones adhesivas. Para uniones adhesivas frágiles, como la analizada aquí, el contenido de agua reduce la concentración de tensiones en los extremos de unión, proporcionando una distribución de tensiones más uniforme a lo largo de la línea de unión. Este fenómeno permite que la unión sostenga niveles de carga más altos. Este comportamiento mecánico mejorado relacionado con la diferente distribución del contenido de agua puede considerarse una estrategia novedosa en el diseño de juntas, ya que puede reducir los costos del servicio y también puede reducir el peso total de la estructura adherida. Para aplicaciones navales, este estudio sugiere que la junta adhesiva considerada se puede utilizar en un entorno no sumergido. En este caso, la absorción de agua se desarrollará a un ritmo menor respecto a los resultados obtenidos, manteniendo su rendimiento durante un periodo mayor. Sin embargo, se deberían realizar más investigaciones para analizar este comportamiento. Esta contribución constituye la publicación más relevante de la Tesis Doctoral Industrial con mención internacional de Dª M. Ortega-Iguña, tesis dirigida por el solicitante (J.M Sánchez-Amaya), y defendida en 2023

A comprehensive review of the S-N fatigue behaviour of adhesive joints

The complex fatigue failure mechanisms render it challenging to arrive at definitive conclusions regarding the behaviour of adhesive joints under cyclic loading. The goal of this review paper is to compile the various research conducted in this field and offer insights into the S-N fatigue response of adhesive joints. This review delves into experimental studies that investigate different factors influencing the fatigue life of bonded structures, encompassing joint geometry, environmental conditions, and loading conditions. Subsequently, the various approaches to improve the fatigue performance and durability of bonded joints are explored. It also examines S-N based life prediction methods, analysing their merits and limitations in assessing the fatigue life of adhesive joints under different conditions. In addition, this review pays attention to studies that focus on real bonded joints. It highlights the importance of bridging the gap between simplified conditions and real-world performance to ensure the durability and safety of bonded joints under service conditions.The review demonstrates that factors such as adhesive/adherend thickness, fillet, and overlap shape (e.g., wavy pattern, step, scarf) do impact fatigue life. However, the critical role played by overlap length in the fatigue life of bonded joints stands out. Improving fatigue life through adjustments, such as adhesive/adherend thickness, depends on the specific case. Therefore, further investigations are warranted in this area. The review suggests that carbon family nanoparticles can enhance bonded joint fatigue strength. Hybrid reinforcement with carbon and organic nanoparticles, like silica, offers a cost-effective path to improve joint life. Regarding life prediction, there is currently no universal fatigue model that considers all parameters impacting the fatigue life of adhesive joints. Fatigue analysis methods considered for real adhesive joints vary between sectors. Initial designs frequently employ indirect fatigue life assessment methods, yet direct fatigue analysis through testing actual joints remains essential for ensuring reliability

A new technique to measure shear fracture toughness of adhesives using tensile load

The end notched flexure (ENF) test is the most common method for measuring the mode II fracture energy of adhesives which provides reliable results but has some inherent problems. The shear fracture energy calculated using ENF for brittle adhesives is often based on a single data point (corresponding to the fracture load) obtained from the test where the crack grows catastrophically and the results are significantly sensitive to pre-crack tip conditions. The aim of the current study is to introduce a new pure mode II fracture test suitable for measuring the shear fracture energy of adhesives. A new technique for measuring the mode II critical strain energy release rate (SERR) of brittle adhesives is proposed based on the central cut ply (CCP) configuration. Fracture tests were carried out on adhesively bonded steel CCP specimens. It is shown that the crack growth in CCP joints is more stable, and the failure develops in multiple steps that generates more experimental data point during the crack propagation. The mode II fracture energy of a brittle epoxy-based adhesive is extracted using CCP method and is compared with the shear fracture energy obtained from the ENF tests. The effect of adhesive thickness on the obtained fracture energies is also analyzed. The CCP technique can be used to find both the crack initiation and crack propagation toughness values whereas the ENF method only provides the crack initiation fracture energy

Fracture energy assessment of adhesives Part II: Is GIIc an adhesive material property? (A neural network analysis)

Different joint configurations were considered to analyze the fracture toughness of adhesives. However, based on the literature, fracture toughness depends on various factors including geometrical parameters, material properties, and testing conditions. In Part I of this study, the tensile fracture toughness (GIc) of adhesives was assessed. The present Part II of this research deals with the influencing factors in shear fracture energy of adhesive materials. The main goal of this study is to find the role of the effective parameters on mode II fracture toughness (GIIc) of adhesives. The rational connection between these parameters and the shear fracture energy is also obtained. The interaction between the effective variables is also investigated. To attain this goal, the artificial neural network (ANN) technique was conducted on over 45 values of GIIc already obtained and reported by different authors using different joint geometries and adhesive materials. The influence of the variables was obtained, and the least important variables were detected and omitted from the model. The effect of different parameters and their interaction on the obtained GIIc were also analyzed. The results indicated that GIIc is remarkably sensitive to the alteration of the adherend Young's modulus and its thickness, the loading rate, and the crack length. It was found that GIIc is less influenced by the adhesive stiffness. In addition, the interaction results indicated that the loading rate has the highest interaction with the other studied variables. This study enables to estimate the mode II fracture toughness of adhesive joints and also to advise a configuration to improve the shear fracture energy of a specific adhesive. Designing a test procedure to minimize the effects of substrate parameters on the obtained GIIc is also possible using the obtained results

Decoupling fracture modes in non-standard test specimens: state of the art

We call here as non-standard an interfacial fracture specimen that features an asymmetry w.r.t. the crack plane (e.g., bimaterial joint). Such specimens generally undergo mixed-mode (I/II) fracture even if they are loaded in pure mode (I or II). Aiming, however, to characterize the pure-mode fracture of them, several attempts have been made to decouple mode I and mode II. Ouyang et al. [1] focused on the bimaterial case. They stated that mode decoupling is achieved when the differential equation of the mode I (mode II) fracture is only governed by the interfacial normal (shear) stress and relative transverse (axial) displacement. A similar statement was recently made by Bennati et al. [2], who provided a more general decoupling condition covering the case where both adherents feature bending-extension coupling. The same topic was also investigated by Maimí et al. [3], who provided a different decoupling condition from that by Bennati et al. Wang et al.’s [4] “strain-based” decoupling condition is the same with that by Ouyang et al. based on an assumption (i.e., matching the axial strains of the two adherents) simpler than solving the mathematical problem. In parallel, individual authors sometimes adopt different decoupling criteria (e.g., matching the bending rigidities of the two adherents), usually without justifying their choice, though. The present work brings together and reviews the scattered—and sometimes overlapping—contributions, aiming to elucidate the confusion observed

A comprehensive review on structural joining techniques in the marine industries_July 2021 (AB 2021)

Since many modules of a ship cannot be practically reduced to a single structure, joining technologies are employed to join various substructures and transfer loads between the different components. These joining methods include welding, mechanical fastening, adhesive bonding, overlamination, and hybrid joining. In the current study, a comprehensive review has been conducted on the mechanical performance of the common joining techniques in the marine industry. This project has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 101006860 (FIBRE4YARDS project)

A comprehensive review on structural joining techniques in the marine industries_July 2021 (IAMaC 2021)

Since many modules of a ship cannot be practically reduced to a single structure, joining technologies are employed to join various substructures and transfer loads between the different components. These joining methods include welding, mechanical fastening, adhesive bonding, overlamination, and hybrid joining. In the current study, a comprehensive review has been conducted on the mechanical performance of the common joining techniques in the marine industry. This project has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 101006860 (FIBRE4YARDS project)