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Integration of lightweight and sustainable solutions in marine structures design is essential to achieve weight reduction goals and improve structural response. A key step to assess the reliability of innovative structural solutions is represented by large-scale experimental investigation. The current paper deals with the analysis of a lightweight ship balcony overhang, which includes an aluminium honeycomb sandwich structure and bimetallic welded joints. The design of the ship balcony overhang was previously performed, as an illustrative example, with the aim of suggesting the replacement of common marine structures with more green and lightweight alternatives. In order to validate the design procedure and to assess the feasibility of the suggested solution, an experimental investigation on a large-scale structure was performed. The ship balcony overhang was tested under bending with a configuration representative of severe loading conditions for ships balconies. The experimental analysis allowed the evaluation of the structure’s strength, stiffness and failure modes, which are useful data to improve the design methodology of such structures and to calibrate numerical models. Comparison with similar structures reported in literature were performed in order to assess the benefits and drawbacks of the suggested lightweight structure.

In the last years, the idea of implementing greener and sustainable solutions merged with the basic principles of life cycle assessment concept has turned to be of paramount importance for the boatbuilding industry. In this framework, construction technologies based on wood such as strip-planking represent possible solutions, as they allow the use of a natural-grown material for attaining refined and solid structures. However, since these techniques imply wood bonding through conventional epoxy adhesives, the global eco-friendliness of the final product is lowered. As a consequence, the adoption of innovative bio-based adhesives is a promising solution to investigate. It is known that, generally, bonded joints in wooden hulls are weak spots of the structure, so the performances of the used adhesives should be duly assessed in order to guarantee an effective bonding. In the present research activity, the assessment of the performances of bonded joints manufactured with bio-adhesives is carried out through a FEM-based methodology, starting from the data present in both technical datasheets and literature for the materials used. In such a way, the most promising products can be preliminarily identified in order to deeply investigate their mechanical characteristics through experimental tests, so limiting expensive and time-consuming activities. The proposed methodology was validated through the comparison between the results coming from the FE analysis and the ones stemming from experimental tests. Moreover, the proposed methodology could be profitably used to analyse more complex geometries, such as real and large structures of wooden hulls.

Structural S355 steel is widely applied in various sectors. Fatigue properties are of fundamental importance and extremely time consuming to be assessed. The aim of this research activity is to apply the Static Thermographic Method during tensile tests and correlate the temperature trend to the fatigue properties of the same steel. The Digital Image Correlation (DIC) and Infrared Thermography (IR) techniques have been used during all static tests. The Digital Image Correlation technique allowed the detection of displacements and strain, and so the evaluation of the mechanical properties of the material. Traditional fatigue tests were also performed in order to evaluate the stress-number of cycles to failure curve of the same steel. The value of the fatigue limit, obtained by the traditional procedure, was compared with the values predicted by means of the Static Thermographic Method (STM) obtained from tensile tests. The predicted values are in good agreement with the experimental values of fatigue life.

Welded joints are widely used in many sectors and represent the main joining technique also in the marine industry. The welded joints are sites of high stress concentrations and are subject to severe conditions for the marine environment. The design of marine welded joints has to consider the effects from wave loads, ship motions and loading/unloading operations and corrosion effects. The aim of this scientific work is to discuss about the state of the art of the standards and the approaches for predicting the fatigue life of welded joints used for the marine industry. Several approaches are examined in order to provide an overview and highlight the advantages and limitations of each method. Furthermore, recent advances in welding of dissimilar metals and autonomous welding are considered.

Industries have shown interest in the use of dissimilar metals to make corrosion-resistant materials combined with good mechanical properties in marine environments. Explosive welding can be considered a good method for joining dissimilar materials to prevent galvanic corrosion. The aim of the present study was to simulate the non-linear behaviour of a Ti6Al4V/Inconel 625 welded joint obtained by explosion welding from the values of the tensile ultimate strength and yielding strength of the parent materials. The present study compared the stress-strain curve from tensile loading obtained by the non-linear finite element analysis with the experimental stress-strain curve of a bimetallic joint. The applied method provides useful information for the development of models and the prediction of the structural behaviour of Ti6Al4V/Inconel 625 explosive welded joints.

Offshore and oil & gas industries have shown the interest toward the use of dissimilar metals, so there is the problem of their joining. The aim of this research activity was to analyze the fatigue behaviour of Ti6Al4V/Inconel 625 (Nickel alloy 625) welded joint, obtained by laser welding. The investigated joint was obtained including intermediate layers of Vanadium and AISI 304 stainless steel to enhance the mechanical properties. The experimental results in terms of fatigue strength demonstrated a good quality of the obtained joints. The temperature of the specimens during the fatigue tests was detected by means of an Infrared Camera for applying the Thermographic Method and assessing the fatigue strength. The value of the fatigue strength predicted by the Thermographic Method shows a good agreement with the value obtained from the traditional procedure.

Although anaerobic adhesives are extensively used in addition to mechanical tightening in flanged couplings, interference fits, and threaded connections, their constitutive behaviour still needs to...

The AA 5083 aluminium alloy is widely used in high speed marine vehicles. The aim of this scientific work was to develop and validate a procedure, starting only from hardness measurements, to predict the elastic-plastic behavior of AA 5083 welded joints under static loading using non-linear FEA analyses. The hardness measurements allowed identifying the different zones and to assess their different mechanical properties, which were considered in the finite element model. Finally, the finite element model results were validated experimentally, comparing the results with the measurements obtained by means of a full-field technique such as the Digital Image Correlation technique.

The aim of this research was the development and application of the following structural strain approaches for predicting the low-cycle fatigue life of AA 5083 welded joints: Finite Element equivalent structural strain approach and Digital Image Correlation equivalent structural strain approach. The first one was already applied for the low-cycle fatigue life prediction of welded joints, while the second approach is here proposed for the first time. Low-cycle fatigue tests were conducted at displacement ratios equal to minus one and zero. The Digital Image Correlation technique was used to analyze the local behaviour in proximity of the welded fillet and to obtain a notch equivalent strain range–number of cycles curve. Furthermore, a complete indipendent experimental procedure to evaluate the equivalent structural strain range, using the Digital Image Correlation technique, was proposed. A Finite Element analysis, with the advantage of being mesh insensitive and requiring only the elastic parameters, was performed in order to apply the Finite Element equivalent structural strain approach. The two structural strain approaches were used to predict the fatigue life, obtainining good agreement with the ASME mean curve representing over 1000 experimental data.

The aim of the present investigation was to assess the behaviour of strip-planked parts by comparing wooden specimens glued using two different bio-based adhesives with wooden specimens glued using a conventional epoxy resin generally used in boatbuilding. Experimental tests in accordance with UNI EN standards were performed in order to evaluate mechanical properties such as tensile strength, shear strength, elastic modulus and shear modulus. In addition, compression shear tests were performed in order to assess the shear modulus of the adhesives. The obtained results demonstrate that the mechanical properties of the investigated bio-based adhesives are comparable to, and sometimes better than, the conventional epoxy resin. Moreover, the experimental results give useful information for the design of wooden boats when the strip-planking process is used. Furthermore, a new procedure to assess the shear modulus of elasticity and shear strength, using the application of compression loadings, was proposed. The results were compared to standard lap-joint tests and showed even lower dispersion. Consequently, the testing procedure proposed by the authors is valid to assess shear properties under compression loading, and it can be applied in most laboratories since it involves the use of common testing devices.

The peak stress method (PSM) is an engineering, finite element (FE)-oriented method to rapidly estimate the notch stress intensity factors by using the singular linear elastic peak stresses calculated from coarse FE analyses. The average element size adopted to generate the mesh pattern can be chosen arbitrarily within a given range. Originally, the PSM has been calibrated under pure mode I and pure mode II loadings by means of Ansys FE software. In the present contribution, a round robin between 10 Italian universities has been carried out to calibrate the PSM with 7 different commercial FE codes. To this aim, several two-dimensional mode I and mode II problems have been analysed independently by the participants. The obtained results have been used to calibrate the PSM for given stress analysis conditions in (i) FE software, (ii) element type and element formulation, (iii) mesh pattern, and (iv) criteria for stress extrapolation and principal stress analysis at FE nodes.

A procedure to simulate the non-linear behavior of explosion welded joints used for shipbuilding applications, starting only from hardness measurements, was developed. The explosion welded joints consist of three different materials: ASTM A516 structural steel, AA5086 aluminum alloy and an intermediate layer of pure aluminum. Three point bending tests were carried out on explosion welded joints with and without an initial notch. The Digital Image Correlation, which is a non-contact full-field technique, was applied in order to measure the displacement and strain patterns of the different metals during the bending tests. Non - linear finite element analyses were performed. The stress-strain curves of the materials, applied in the finite element model, were obtained using Ramberg Osgood type equations and considering the results of the micro-hardness measurements, which were correlated to the mechanical properties of the different materials. The finite element model was validated experimentally, comparing the results with the measurements obtained using the Digital Image Correlation technique. Furthermore, the procedure was extended to a specimen with an initial notch, for which the FE results were compared to the experimental tests.

Nowadays explosion weld is widely used in marine structures, thanks to its reliability. AL/FE explosive welded joints, used in shipbuilding applications, were investigated in this research activity. Static and fatigue bending tests were carried out on rectangular specimens made of ASTM A516 low carbon steel, clad by explosion welding with A5086 aluminum alloy and provided with an intermediate layer of pure aluminum. Two full-field techniques were applied during the bending tests: Digital Image Correlation and Infrared Thermography. The digital image correlation technique allowed determining the displacement and strain fields showing that the aluminium side has a higher strain with respect to the steel side, and Infrared Thermography was used to detect the superficial temperature of the specimen allowing the determination of the fatigue limit. The fatigue limit values, predicted using the Thermographic Method during static and fatigue tests, are in good agreement with the experimental values of the fatigue limit.

The aim of this research activity was to study the fatigue behavior of laser welded joints of titanium alloy, in which the welding was performed using a laser source and in the absence of filler material, by means of unconventional full field techniques: Digital Image Correlation (DIC), and Infrared Thermography (IRT). The DIC technique allowed evaluating the strain gradients around the welded zone. The IRT technique allowed analyzing the thermal evolution of the welded surface during all the fatigue tests. The fatigue limit estimated using the Thermographic Method corresponds with good approximation to the value obtained from the experimental fatigue tests. The obtained results provided useful information for the development of methods and models to predict the fatigue behavior of welded T-joints in titanium alloy. © 2018, Gruppo Italiano Frattura. All rights reserved.

This paper reports the experimental tests, which have been carried out to assess the mechanical properties of Iroko wood laminates used for the construction of a large wooden sailing ship. Three-point bending tests have been carried out on different types of specimens: laminates with 3 layers @ 0° and without scarf joints, laminates with 3 layers @ 0° having the outer layers with scarf joints, and laminates with 4 layers @ 0°/±45°/0° and no scarf joints. The tests have been performed in compliance with the current EN Standards. The analyses of the experimental data allowed the assessment of the mechanical properties of the laminated Iroko wood as well as the influence of scarf joints. The experimental results demonstrated that the presence of scarf joints only affect the strength of the glued laminate, while the stiffness properties in terms of Young modulus in bending and shear modulus, obtained applying the “method of variable support span”, remain essentially the same. The investigated laminates have been also analysed using a 3D computed tomography and an ultrasonic phased array equipment in order to assess the dimensions of possible defects or voids in the adhesive and the dynamic modulus of elasticity. The tomographic measurements of the glue thickness explained the reason of the reduced strength of the scarf joints, due to the inhomogeneity of the glue bond-line. The value of the dynamic modulus of elasticity, obtained by the ultrasonic technique, is slightly higher than the value of the modulus of elasticity obtained by the bending tests. Finally, the experimental findings have been compared with those drawn from both Classical Lamination Theory and Dietz approach, obtaining a good agreement and confirming that the Dietz approach is a fast and easy way to assess the elastic properties of a laminated structure.

The traditional methods of fatigue assessment of metallic and composite materials are extremely time consuming. The thermographic measurements during static tests can be used to predict the fatigue limit. This procedure has been already applied to composite materials. The aim of this study is the application of this procedure for the fatigue assessment of steel welded joints. Static tensile and fatigue tests were carried out on butt welded specimens, made of S355 steel. Two full-field techniques were applied during the tests: digital image correlation and infrared thermography techniques. Fatigue tests at increasing loads were performed by a stepwise succession in order to apply the Thermographic Method. The value of the fatigue limit, obtained by the traditional procedure, was compared with the values predicted by means of the Thermographic Method during stepwise succession fatigue tests and by means of the infrared thermography technique during static tensile tests. The predicted values are in good agreement with the experimental values of fatigue life.

The paper deals with investigations about mechanical properties of Iroko, a hardwood species used for structures in shipbuilding as glued laminated timber. Experimental tests have been carried out to assess strength, stiffness and density of Iroko in accordance with current EN Standards. All the results obtained by tensile and three-point bending tests, along with the statistical analyses performed to define the characteristics values of some mechanical properties, are reported in the paper. These values allowed to assign the strength class, reported in EN 338 Standard, to the investigated Iroko wood population. The experiments have taken into account both solid timber strips and scarf-jointed strips, in order to evaluate the influence of such a type of joint, which is widely used in wooden shipbuilding on strength and stiffness. Eventually, peculiar investigations have been carried out to analyse the failure mode of some test pieces through special experimental techniques: three-dimensional computed tomography and infrared thermography.

Crack tip stress-induced phase transformation mechanisms in nickel–titanium alloys (NiTi), subjected to fatigue mechanical loads, have been analyzed by full field measurement techniques. In particular, Infrared thermography (IR) and Digital Image Correlation (DIC), have been applied to analyze the cyclic temperature and displacement evolutions in the crack tip region of a commercial pseudoelastic alloy, together with the associated thermal and mechanical hysteresis, by using Single Edge Crack (SEC) specimens. IR investigations revealed a global temperature variation of the specimen due to crack formation and propagation mechanisms, which is similar to common engineering metals, i.e. surface temperature rises quickly in an initial phase, then it reaches an almost constant value, and finally it increases rapidly as a consequence of the fatigue crack growth. In addition, cyclic thermal variation in the crack tip region and related hysteresis (temperature vs load) has been measured, which can been directly related to the thermal effects of the reversible stress-induced phase transformations. Furthermore, a proper experimental setup has been made, based on a reflection microscope, for direct measurements of the crack tip displacement field by the DIC technique. Furthermore, a fitting procedure has been developed to calculate the mode I Stress Intensity Factor (SIF), starting from the displacement field, and the related mechanical hysteresis (SIF vs load).

The aim of this scientific work was to investigate the behaviour of cruciform welded joints under static loading using a full-field technique: Digital Image Correlation. The material curves, relative to different zones (base material, heat affected zone, weld), were obtained by hardness measurements, which were done by means of a fully automated hardness scanner with high resolution. This innovative technique, based on the UCI method, allowed to identify the different zones and to assess their different mechanical properties, which were considered in the finite element model. Finally the finite element model was validated experimentally, comparing the results with the measurements obtained using the Digital Image Correlation technique.

The present paper focuses on the effect of a thermo-oxidative environment (150 °C under atmospheric air) on the deformation behaviour of multistable IM7-977-2 [0/90] unsymmetric carbon–epoxy composite plates. Sample curvatures are measured at high temperature as a function of the ageing time by an optical method, by following the displacement of marker points situated on the external side of the plate and by fitting them with an interpolation algorithm. The predictions of a composite plate model taking into account thermo-oxidative affected mechanical properties of the elementary ply and the residual strains produced by thermo-oxidation allow interpreting and understanding the experimental results.

The welded structures used in the naval field are generally subjected to fluctuating stress over time. In some structural welded details, due to changing loading conditions, significant elastic-plastic deformation can arise, which may lead to the failure of the structure after a relatively low number of cycles. The aim of this scientific work was to investigate the behavior of welded T-joints under low-cycle fatigue using full-field techniques: digital image correlation and infrared thermography. Low-cycle fatigue tests were carried out on welded “small-scale” specimens with the aim of obtaining loading and boundary conditions similar to those that occur in “large-scale” components in their real operating conditions. A nonlinear finite element analysis was also performed. The material curves, relative to different zones (base material, heat-affected zone, weld), were obtained by hardness measurements, which were done by means of a fully automated hardness scanner with high resolution. This innovative technique, based on the ultrasonic contact impedance method, allowed to identify the different zones (base material, heat-affected zone, weld metal) and to assess their cyclic curves, which were considered in the finite element model. Finally, the finite element model was validated experimentally comparing the results with the measurements obtained using the digital image correlation technique. The applied procedure allows providing useful information to the development of models for the prediction of fracture and fatigue behavior of the welded joints under the low-cycle fatigue loading.

There are many studies in literature on the thermal response of composites during static tests for a prediction of the fatigue limit, but only few studies about the thermal response of steels during static tests, and, as far as the authors are aware, this study is the first one about the application of the Thermographic Method during static tensile tests for the fatigue assessment of steel welded joints. Tensile tests were carried out on base material and welded specimens, made of S690QL steel. The Digital Image Correlation and thermographic techniques have been used during all tests. Moreover fatigue tests at increasing loads were carried out on steel base material and welded specimens by a stepwise succession (applied to the same specimen) for applying the Thermographic Method. The predictions of the fatigue limit, obtained by the analysis of the temperature evolution during the static tests, were compared with the predictions obtained applying the Thermographic Method during fatigue tests.

Two full-field techniques were applied for the study of the base material and welded specimens, made of S690QL steel: digital image correlation and thermographic techniques. Static and fatigue tests were carried out. The thermographic measurements can be used to predict the fatigue, with a great saving in time and effort. Fatigue tests at increasing loads were carried out by a stepwise succession, applied to the same specimen, for applying an energy-based approach. The predictions of the fatigue life, obtained by means of the Energy Approach, were compared with the values obtained by the traditional procedure.