Structures In Marine Applications Research Articles

Curved Polymeric Sandwich Composites Subjected to Air Shock: An Experimental Investigation

BackgroundThe vulnerability of polymeric composite sandwich structures in marine applications to air explosions highlights a significant gap in our understanding of the dynamic behavior of the curved sandwich structures, which is essential for design improvements.ObjectiveThis study aims to explore the dynamic response and failure mechanisms of curved sandwich composite panels subjected to air-blast loading, providing insights into their structural integrity under such conditions.MethodsExperiments were performed using laboratory-simulated air shocks generated by a shock tube, employing high-speed photography and digital image correlation to measure deflections on the back surface of the panels. The panels, made with PVC closed-cell foam cores of two densities (H45 and H130), were tested across three curved geometries (radii of 112 mm, 305 mm, and infinity) under various boundary conditions.ResultsFindings indicate an increase in deformation with a decreased radius of curvature under simple support conditions, a trend that reverses under arrested displacement conditions. Moreover, a reduced radius significantly enhances panel strength and resistance to interfacial damage, with the primary failure mode transitioning from core shear cracking to interfacial debonding as core density increases.ConclusionsThe study reveals that the radius of curvature, boundary conditions, and core density significantly affect curved sandwich panels’ dynamic response and performance. Panels with smaller radii and higher core densities exhibit increased strength, though boundary conditions introduce variable effects on deformation behavior.

Changes in Corrosion Behaviour of Zinc and Aluminium Coatings with Increasing Seawater Acidification.

The increase in greenhouse gas emissions has led to seawater acidification, increasing the corrosion rate of metal structures in marine applications. This paper indicates that the spraying of four types of coatings, namely Zn, Al, Zn-Al, and Al-Mg, using the arc-spraying technique on steel substrate S235JR, creates effective protective coatings that interact differently with various pH solutions exposed to varying levels of seawater acidification. The study analyses the structural properties of the coating materials using SEM and XRD techniques. Electrochemical parameters are evaluated in solutions with different pH and salinity levels. The results demonstrate that alloy metallic coatings provide excellent resistance to corrosion in low-pH solutions.

Design against Fatigue of Super Duplex Stainless Steel Structures Fabricated by Wire Arc Additive Manufacturing Process

Additive manufacturing (AM) is increasingly used to make complex components for a wide spectrum of applications in engineering, medicine and dentistry. Wire arc additive manufacturing (WAAM), as one of AM processes, utilises electric arc and metal wire to fabricate fully dense and heavy metal parts at relatively low costs and high-energy efficiencies. WAAM was successfully applied in the production of several welding-based metal structures. Recently, there was a growing interest in WAAM processing of super duplex stainless steels (SDSS) due to their high strength and excellent corrosion resistance, which make them the prime choice for load-bearing structures in marine applications. Although a number of studies investigated the microstructural and mechanical properties of WAAM-processed SDSS components, little is known regarding their fatigue performance, which is critical in engineering design. This study reports on the outcomes of fatigue tests and fracture surface fractography of WAAM-processed SDSS. The results obtained indicate a significant anisotropy of fatigue properties and fatigue crack initiations resulting from internal defects rather than surface flaws. Based on these experimental results, we suggest an effective design methodology to improve the fatigue life of the WAAM-fabricated SDSS components. We also indicate that post-manufacturing surface treatments should not be underlined for the enhanced fatigue resistance of WAAM-processed SDSS structures.

Shearography non-destructive testing of thick GFRP laminates: Numerical and experimental study on defect detection with thermal loading

Thick composite materials are commonly used as load-bearing structures in marine applications. Developing a suitable and sophisticated non-destructive testing (NDT) method for thick composites is an urgent challenge to improve the safety, reliability and maintenance of these structures. Digital shearography has become an important NDT technique for detecting defects in thin composite materials because of the advantages of high sensitivity to deformation change, and whole-field measurement. So far, the efficacy of shearography for thick composite inspection (e.g. thickness as more than50 mm) has not been fully characterised. This paper combines finite element methods (FEM) and experimental tests to investigate the defect detection capabilities of shearography for inspecting thick glass fiber-reinforced polymer laminates. A thermal–mechanical model was established by computing equivalent thermal and mechanical properties and was evaluated by experimental shearography testing. In order to reliably simulate major defects in thick composite, flat bottom holes were manufactured in the specimen. Both simulations and experiments show that shearography is a promising technique to inspect thick composites. The thresholds for defect-induced phase change and the corresponding defect-induced deformation are determined for shearography testing of thick composites in this paper. Afterwards, the effect of mechanical boundary conditions on defect-induced deformation is studied by FEM.

Wire arc additive manufacturing for repairing aluminium structures in marine applications

A new approach is proposed wherein WAAM can be utilized to repair corroded surfaces in AA5052 structures. Being a marine suitable Al grade when exposed to seawater regularly, its corrosion-resistant properties decline over time. To restore the corroded surfaces, Aluminium filler material ER4043 is deposited on AA5052 using Cold metal transfer (CMT) process-based Wire arc additive manufacturing (WAAM) technology. The microstructural evolution of WAAM processed plates via CMT, and CMT + Pulse (CMT + P) modes are investigated. The microstructure of CMT + P mode revealed fine equiaxed dendrites in comparison to CMT mode. Energy Dispersive X-Ray Spectroscopy (EDS) elemental maps and line scan revealed the presence of Al-Si eutectic phase. The corrosion rate of WAAM processed samples (0.18–0.20 mm/year) was comparable with the wrought counterparts (0.19–0.21 mm/year). The industrial impact of the study is the feasibility of employing WAAM technology for repairing aluminium structures in marine environments.

Durability and protection of timber structures in marine environments in Europe: An overview

Timber structures in marine applications are often exposed to severe degradation conditions caused by mechanical loads and wood-degrading organisms. This paper presents the use of timber in marine environments in Europe from a wood protection perspective. It discusses the use of wood in coastline protection and archeological marine wood, reviews the marine borer taxa in European waters, and gives an overview of potential solutions for protection of timber in marine environments. Information was compiled from the most relevant literature sources with an emphasis on new wood protection methods; the need for research and potential solutions are discussed. Traditionally, timber has been extensively utilized in a variety of marine applications. Although there is a strong need for developing new protection systems for timber in marine applications, the research in this field has been scarce for many years. New attempts to protect timber used in marine environments in Europe have mainly focused on wood modification and the use of mechanical barriers to prevent colonization of marine wood borers. The importance of understanding the mechanisms of settlement, migration, boring, and digestion of the degrading organisms is key for developing effective systems for protecting timber in marine environments.

Durability and protection of timber structures in marine environments in Europe: An overview

Timber structures in marine applications are often exposed to severe degradation conditions caused by mechanical loads and wood-degrading organisms. This paper presents the use of timber in marine environments in Europe from a wood protection perspective. It discusses the use of wood in coastline protection and archeological marine wood, reviews the marine borer taxa in European waters, and gives an overview of potential solutions for protection of timber in marine environments. Information was compiled from the most relevant literature sources with an emphasis on new wood protection methods; the need for research and potential solutions are discussed. Traditionally, timber has been extensively utilized in a variety of marine applications. Although there is a strong need for developing new protection systems for timber in marine applications, the research in this field has been scarce for many years. New attempts to protect timber used in marine environments in Europe have mainly focused on wood modification and the use of mechanical barriers to prevent colonization of marine wood borers. The importance of understanding the mechanisms of settlement, migration, boring, and digestion of the degrading organisms is key for developing effective systems for protecting timber in marine environments.

Experimental Study of Blast Resistance on BFRP Bar‐Reinforced Cellular Concrete Slabs Fabricated with Millimeter‐Sized Saturated SAP

An innovative cellular concrete procured with sat‐SAP (superabsorbent polymer) is introduced. Combined with BFRP bars, this concrete may play a role as protective structures in marine applications. Eight BFRP‐reinforced cellular concrete slabs (BSs) and three steel‐reinforced normal concrete slabs (SPs) are exposed to simulated blast loadings in a shock tube device. Low‐modulus cellular concrete and BFRP bars cause BSs to exhibit distinctive behaviours compared to those of SPs. BSs, which are more flexible at the same reinforcement ratio, have more intensive vibrations and larger deformations compared to SPs under various blast loadings. In addition to the porous structure of cellular concrete, BSs demonstrate better wave‐attenuating and energy‐absorbing abilities. More severe damage such as cracks, deflections, and breaches is observed for BSs. In the current research, a comprehensively superior blast resistance can be achieved through improving reinforcement ratio to promote serviceability.

Fatigue Behaviour of Acrylic Matrix Composites: Influence of Seawater

The recent introduction of liquid acrylic thermoplastic matrix resins which can impregnate fibre reinforcements using traditional infusion moulding offers significant potential for future composite structures in marine applications, such as marine energy devices. However, to date very few results are available to evaluate the long term durability of these composites in a marine environment. This paper describes results from a series of cyclic loading tests on glass and carbon fibre reinforced acrylic composites under both tension and four point flexural loading. Tests were performed before and after aging in natural seawater. The results were compared to results for a glass/epoxy used today in marine structures, and show a lower loss of both static and cyclic properties for glass/acrylic composites after seawater saturation. A carbon fibre reinforced acrylic composite was also tested. This showed excellent properties in tension, but poor out-of-plane properties due to manufacturing defects.

Modelo de difusión de cloruros en las estructuras de hormigón armado expuestas en la Península de Yucatán (México)

Corrosion of reinforcing steel can seriously limit the service life of concrete structures in marine applications. Chloride diffusion is one of the two major problems causing this phenomenon, increasing when the concrete is exposed to a marine environment in coastal areas. The service life of a structure may be divided into two general phases: an initiation period, in which the reinforcing steel surface is still passive as a result of the contact with a high pH medium, in which the aggressive ions penetrate the concrete toward the reinforcing bar, and a propagation period that starts when the chloride ion contamination on the steel surface exceeds the critical threshold level for the passivity breakdown. The aim of this work is to examine the chloride diffusion at the initial period on a marine environment by considering the variability of the diffusion coefficients with inherent parameters of the concrete, exposed during a period of two years in Yucatan, Mexico. A model based on the second Fick's law is proposed; the non-linearity of the problem is taken into account and a numerical procedure based on the finite difference method is developed to solve the set of equations. Comparisons with experimental data are also carried out in order to show the reliability and the effectiveness of the proposed numerical model.