Abstract: Additive Manufacturing (AM) technologies are widely spreading into multiple engineering sectors thanks to their flexibility to create complex geometries with virtual no material waste. AM technologies capabilities can be fully exploited when working with periodic lattices, creating topology-optimized structures through different cell types with different dimensions and volume fractions. Several factors (i.e., process parameters, quality and type of raw materials) can modify the mechanical properties of printed components and can be exploited to selectively create functionally graded materials or conventional laminated hybrid materials structures. This paper analyses and compares the mechanical properties of different additively manufactured lattice BCC structures through experimental and numerical means. At first, the manufacturing procedure followed by experimental tests is presented. The retrieved mechanical properties are then used as a benchmark for the numerical Finite Element Analyses and compared with analytical models available in the literature. The numerical simulation campaign includes the comparison of a full 3D model and a 1D/2D beam/shell formulation model. The research findings demonstrate a good correlation between the experimental tests and the numerical simulation results, indicating the potential for the proposed methodologies to be broadly implemented within various domains of structures and materials.

Keywords: 3D lattice | Additive Manufacturing | Design for Manufacturing | FEM | Periodicity

Abstract: Additive manufacturing technologies spread widely in multiple scientific sectors thanks to their flexibility and property customisation. However, many aspects must be studied further since multiple factors such as their microstructure and internal defects can drastically change the overall mechanical behaviour of the final products. In this work, the stress-strain behaviour of a Selective Laser Melting AlSi10Mg alloy is retrieved through a homogenisation approach with FEM analyses using the Representative Volume Element approach. To this purpose, an in-house code has been developed to model a random spatial pore distribution inside the RVE according to literature references and to impose the periodicity boundary conditions. Results are presented at different overall porosities.

Abstract: Additive manufacturing (AM) technologies are gaining widespread adoption across multiple engineering sectors due to their ability to create customised components with tailored mechanical properties and reduced material waste. This work presents different innovative Finite Element Method (FEM) models to characterise the behaviour of AM structures. A numerical model is presented to characterise AM porosity defects using the Representative Volume Element (RVE) concept; additionally, different unit cell approaches to study the behaviour of lattice structures are presented. The procedures and methodologies presented offer a range of tools, each with different trade-offs between accuracy and computational cost

Keywords: Additive Manufacturing | FEM | Lattice

Abstract: In the present work, a finite element procedure, based on a modified beam approach, has been developed in order to simulate the elastic behavior of different periodic lattice unit cells. The standard numerical approach used to simulate lattice structure is to mesh the geometry with solid brick elements or with three-dimensional beams. In the first case, very precise results can be obtained from simulations but high computational efforts must be considered. In the second case, using commercial beam formulations, it is not possible to mimic the local stiffening effect of intersection joints between struts. In this work, it has been considered that each strut of the lattice cell is divided in three portions, one flexible in the mid part and two rigid at the ends. Numerical simulations have been performed to calibrate the correct length of the rigid portions in order to reproduce the elastic behavior predicted by solid models meshed with brick elements. It has been found that this length is a function of the strut diameter and of the cell topology. The good agreement with experimental results available in literature demonstrates the reliability of the proposed method.

Keywords: 3D lattice | BCC | Beam | FCC

Abstract: The design of a sailing yacht is mostly based on the traditional design techniques of trial-and-error which takes time and requires iterative corrections to reach the final result. Moreover, several design teams with different and complementary expertise are required. If the standpoint is the one of the designs of a pleasure yacht, most of the activities can be solved through the related standards. While, concerning regatta’s yacht, more deep investigations become mandatory and intensive application of digital design instruments is now a common practice in modern yacht design. In this paper, a parametric procedure has been set up aimed to design and numerically compare sailing hulls performances. The hull shape design follows the classical approach based on the definition of the main curves frame and the generation of a parametric surface. Preliminary information about the hull resistance can be quickly obtained with a dedicated module of the software. Once a satisfactory shape has been modeled, detailed investigations can be automatically executed with commercial fluid dynamics software. The procedure has been successfully applied to the design of a new boat belonging to a specific class-called 1001VELAcup R3- which is two people racing dinghy designed according to a box rule with limitations on materials, dimensions and total sail area. The availability of experimental data suggested the numerical investigation about the influence of the hull geometry on the sailing performances.

Keywords: CAD modeling | Numerical investigation | Yacht design

Abstract: In this work a modified beam approach to model the compressive behavior of additively manufactured BCC and reinforced BCC lattice structures is proposed. Three-dimensional beam models are of interest because of their reduced computational time, with respect to numerical models that involves solid mesh elements, but they are not able to capture the behavior of lattice structures in proximity of the unit cell nodes, that presents higher stiffness due to the struts intersection and consequent material overlapping. In order to overcome this drawback when using beam finite elements, a modified beam approach is used in this work considering each lattice cell strut subdivided in a central flexible portion and two rigid extremities. A numerical procedure is implemented to tune the rigid extremities length of the strut by means of numerical simulations that aims to reproduce accurately the compressive behavior of the lattice cell solid model. The experimental campaign conducted on different powder bed fusion manufactured lattice structures is presented and experimental results are provided along with a numerical-experimental correlation that proves the accuracy of the method.

Keywords: BCC lattice cells | Lattice beam model | Lattice structures | SLM

Abstract: In this paper, the mechanical properties of a modified Body-Centred Cubic lattice cell with waved struts have been determined using FEM simulations with solid element mesh. The strut waviness introduces orthotropic properties in the cell and the correlation between geometrical cell parameters and resulting mechanical attitudes is calculated. For a complete determination of all the mechanical constants, uniaxial compression and in-plane shear have been simulated along different loading directions. Attention has been particularly paid to the definition of appropriate boundary constraints able to mimic the periodic condition that applies to a repetitive unit cell. At first, the numerical model has been validated with existing analytical and experimental results available in the literature, then parametric strut waviness has been introduced to this model. A systematic numerical study has been conducted on lattice cells with different density and different wave amplitude. Results have evidenced for the waved struts a considerable increase in the longitudinal uniaxial modulus and a negligible effect on the transverse moduli, while a slight reduction of the shear moduli is generally obtained in all the sliding planes. Poisson’s ratios are highly affected both by density and waviness. The obtained results can be useful for the optimized definition of a lattice cell, tailored to the specific mechanical requirements of an advanced component.

Keywords: 3D lattice | BCC | FEM | Orthotropy | Waviness

Abstract: Hybrid sandwich structures are often used in the aviation industry thanks to their high strength-to-weight ratio and resistance to bending and buckling. Today, through Additive Manufacturing technologies, it is possible to use different materials to create topology-optimized structures with complex shapes using lattice structures. In this work, a numerical approach is proposed to study the behaviour of a hybrid sandwich structure which can be used as a reinforcement for a control surface of a lightweight aircraft. A comparative analysis is conducted between a conventional honeycomb lattice core and lattice truss core structures.

Keywords: Additive Manufacturing | Design for Manufacturing | Hybrid Structures | Lattice Structures

Abstract: In this work the static analysis and the free-vibration analysis of Variable angle tow (VAT) multilayered panels have been investigated. The increasing demand for tailoring of advanced and complex structures lead to the development of advanced composite technologies to design structures with variable stiffness properties. The VAT structures are based on composites designed with curvilinear fibres. In the present work, the governing equations are obtained from the Principle of Virtual Displacements and higher-order models are considered to describe the unknown variables. The present formulation is assessed with 3D solutions obtained with commercial software. Some results are given for different loading and boundary conditions, different curvilinear paths, various lamination schemes.

Keywords: Composite | FEM | Numerical simulations | Plate | Variable angle tow

Abstract: In this paper, the effect of strut waviness on the mechanical properties of a BCC unit cell has been studied by means of numerical FEM simulations. Different waviness amplitudes have been introduced on variable relative density unit cell and resulting rigidity has been calculated. Two different loading configurations have been setup in order to simulate the uniaxial and the shear behavior. Periodic repetition of the unit cell in the three cartesian directions has been simulated with the proper definition of kinematic constraints on the boundaries. From the two loading configurations, the uniaxial modulus, the shear modulus and the Poisson ratio of the unit cell have been extracted and these entities have been compared with the corresponding of a straight strut BCC unit cell. Results have evidenced for the waved struts a considerable increase in the uniaxial modulus, a slight reduction of the shear modulus and a highly variable Poisson ratio, depending on the waviness amplitude.

Keywords: 3D lattice | BCC | FEM | Waviness

Abstract: Additive manufacturing represents a great candidate to boost smart materials expansion in the Industry 4.0 era through 4 D printing technologies. However, to fully exploit the benefits of these technologies, increasing knowledge is needed on how internal defects condition the overall behavior of the component. In this work, the Representative Volume Element approach is presented to investigate, through Finite Element Analyses, how micro-voids influence the stress-strain behavior of an AlSi10Mg additively manufactured through the Selective Laser Melting technique. An in-house code on the commercial software ANSYS Parametric Design Language APDL was developed to model a random pore distribution inside the RVE and to apply the boundary conditions necessary for the RVE periodicity; comparison with reference case studies from the literature are reported.

Keywords: additive manufacturing | FEM | Porosity | RVE

Abstract: In naval design it is common practice to define an internal regular web frame made of longitudinal elements and transversal sections with the purpose of giving stiffness to the whole structure and, at the same time, promoting lightness. In this work, FEM simulation and Topology Optimization (TO) tools are implemented to present a different approach in placing the reinforcements inside the hull of a sailing dinghy. The methodology proposed in this paper considers as a starting point the volume inside the hull and the deck completely filled with material and the result after the simulations is a free form shape of the sailboat reinforcements. The TO procedure is based on two different input FEM solutions: one is the result of a structural analysis on the boat loaded with real forces acting during navigation and the other one is the result of a modal analysis aimed to extract natural frequencies of the structure. The result must fulfil several requirements such as weight, stiffness and stress. TO models have been compared with a traditionally designed sailboat with the same total mass and relevant improvements have been obtained in terms of local stiffness and reduction of moments of inertia.

Keywords: FEM | Reinforcement | Topology optimization | Yacht design

Abstract: Additive Manufacturing technologies have been extensively used in different industry sectors thanks to the optimisation of material waste, reduction of the high production costs and the ability to create components with complex geometric shapes and highly customisable mechanical performance. However, to fully exploit the benefits of these technologies, in-depth knowledge is needed on how internal defects condition the overall behaviour of the component. In this work, a Representative Volume Element like approach is presented to study, through different numerical analyses, the effect of size, number and spatial distribution of micro-voids on the stress-strain behaviour of Selective Laser Melting additive manufactured AlSi10Mg. An in-house code on the commercial software ANSYS Parametric Design Language APDL is used to model a random pore distribution inside the RVE in compliance with statistical distribution retrieved from the literature; comparison with reference case studies are reported.

Keywords: AdditiveManufacturing | FEM | Porosity | RVE

Abstract: The process of designing a sail can be a challenging task because of the difficulties in predicting the real aerodynamic performance. This is especially true in the case of downwind sails, where the evaluation of the real shapes and aerodynamic forces can be very complex because of turbulent and detached flows and the high-deformable behavior of structures. Of course, numerical methods are very useful and reliable tools to investigate sail performances, and their use, also as a result of the exponential growth of computational resources at a very low cost, is spreading more and more, even in not highly competitive fields. This paper presents a new methodology to support sail designers in evaluating and optimizing downwind sail performance and manufacturing. A new weakly coupled fluid–structure interaction (FSI) procedure has been developed to study downwind sails. The proposed method is parametric and automated and allows for investigating multiple kinds of sails under different sailing conditions. The study of a gennaker of a small sailing yacht is presented as a case study. Based on the numerical results obtained, an analytical formulation for calculating the sail corner loads has been also proposed. The novel proposed methodology could represent a promising approach to allow for the widespread and effective use of numerical methods in the design and manufacturing of yacht sails.

Keywords: Computational fluid dynamics | Finite element method | FSI | Gennaker | Sail design | Sail loads

Abstract: In this paper, a tool able to support the sailing yacht designer during the early stage of the design process has been developed. Cubic Rational Bézier curves have been selected to describe the main curves defining the hull of a sailing yacht. The adopted approach is based upon the definition of a set of parameters, say the length of waterline, the beam of the waterline, canoe body draft and some dimensionless coefficients according to the traditional way of the yacht designer. Some geometrical constraints imposed on the curves (e.g., continuity, endpoint angles, curvature) have been conceived aimed to avoid unreasonable shapes. These curves can be imported into any commercial Computer Aided Design (CAD) software and used as a frame to fit with a surface. The resistance of the hull can be calculated and plotted in order to have a real time estimation of the performances. The algorithm and the related Graphical User Interface (GUI) have been written in Visual Basic for Excel. To test the usability and the precision of the tool, two existing sailboats with different characteristics have been successfully replicated and a new design, taking advantages of both the hulls, has been developed. The new design shows good performances in terms of resistance values in a wide range of Froude numbers with respect to the original hulls.

Keywords: CAD | Excel | Rational Bézier curves | Sailing yacht design | VBA | VPP

Abstract: In this paper, a novel approach has been followed based on FEM simulation and Topology Optimization tools to locate and model the reinforcements inside the hull of a sailing dinghy. This process assumes that the inner volume included between the hull and the deck is, at the beginning of the simulation, filled with material; then a portion of this inner volume is eroded until a final free form shape of the reinforcements is obtained. A key point of this procedure is the definition of the optimization constrains because the final shape of the reinforcements must fulfill several requirements such as weight, stiffness and stress. At the end of the optimization procedure, the final shape of internal reinforcements consists of a truss-like web frame with a final weight equal to the 18% of the initial full body.

Keywords: Reinforcement | Topology optimization | Yacht design

Abstract: In this paper, a tool able to support the sailing yacht designer during the early stage of the design process has been developed. Quadratic and cubic Rational Bézier curves have been selected to describe the main curves defining the hull of a sailing yacht. The adopted approach is based upon the definition of a set of parameters, say the length of water line, the beam of the waterline, canoe body draft and some dimensionless coefficients according to the traditional way of the yacht designer. Some geometrical constraints imposed on the curves (e.g. continuity, endpoint angles) have been conceived aimed to avoid unreasonable shapes. These curves can be imported in any commercial CAD software and used as a frame to fit with a surface. The algorithm and the related Graphical User Interface (GUI) have been written in Visual Basic for Excel. To test the usability and the precision of the tool, two sailboats with different characteristics have been replicated. The rebuilt version of the hulls is very close to the original ones both in terms of shape and dimensionless coefficients.

Keywords: CAD | Rational Bézier curves | Sailing yacht design

Abstract: In this paper a multi-method approach is used to setup and validate a monitoring system applied to a small sailing boat during real sailing conditions. This monitoring system is able to transform the data coming from some typical devices installed on board into information about the deformed state of the boat. GPS, Wind Data Logger and cameras have been installed on the boat to measure its route and speed, the apparent wind velocity and direction and the positions of the crew members. These data are processed to determine the equilibrium of the boat and estimate the loads applied on it. Then, a CAD/FEM model calculates the effects of these loads on the boat shape. The resulting deformed model is compared with measurements of local strains obtained with Electrical Resistance strain gauges applied on the hull and on reinforcements of the boat. Onboard measuring devices are real-time monitored with a home-made software while the numerical prediction of the global boat deformation is obtained a posteriori once FEM computation is achieved. A test at sea has been performed to check the efficiency of the system: data computed with the proposed procedure have been compared with those coming from the field test.

Keywords: Computer aided engineering | On board monitoring system | Sailing yacht

Abstract: In this paper, a topological optimization procedure has been applied on a real component of the deck of a sailing multi-hull in order to find the internal shape that best save the material used in the manufacturing process without a relevant loss of structural rigidity. The multi-hull boat is a 16 feet length catamaran equipped with an asymmetric foil on both centerboards and with a symmetric foil on both rudders. The task of the analyzed object is to act as a cylindrical support for the screw that drives the rotation of the centerboard. The process adopted to manufacture this object is the Fused Deposition Modeling (FDM) technique, because of its high versatility and its relative low-cost impact. The aim of this work is to verify the applicability of FDM to structural naval component subjected to demanding loads during navigation and, at the same time, to investigate on the robustness of a topology optimization strategy in creating new shapes that recent additive manufacturing are able to create.

Keywords: CAD modeling | Fused deposition modeling | Topology optimization

Abstract: The use of finite element method (FEM) tools is proposed to investigate the structural response of an eco-sustainable sailing yacht to different loading conditions, typical of those acting during regattas. The boat is, in particular, a 4.60 m dinghy with the hull and the deck made of an hybrid flax–cork sandwich and internal reinforcements made of marine plywood. A preliminary activity has consisted in the refitting of an existing model in order to reduce the hull weight and to improve performances during manoeuvrings. These tasks have been interactively simulated in the virtual environment of the boat CAD model, where longitudinal and transversal reinforcements were enlightened and the maximum beam reduced. At the same time, results of FEM simulations on the modified model were analysed in order to verify the structural integrity. Shape modifications have been applied to the real model in laboratory and the resulting hull has been instrumented with strain gauges and tested under rigging conditions to validate the numerical procedure. Finally, the FEM model was used to predict the response of the boat to loading systems typical of sailing conditions.

Keywords: FEM | Refitting | Sailing yacht

Abstract: In this paper, most significant steps involved during the whole process of designing a sailing yacht are outlined. In particular, a novel simultaneous approach has been proposed to optimize the design process of a sailing yacht. Analytical resistance prediction models are simultaneously used with CAD systems and computational fluid dynamics tools to find, in the more effective way, the best solution for the chosen design conditions. As a general rule, in fact, once the target point has been decided, task of the designer is the definition of those systems of aerodynamic and hydrodynamic forces that are in equilibrium when the boat sails at its target. Unfortunately, a multi-purpose yacht does not exist. If the target point is in upwind sailing then, performances will be better for such a condition and worse for others. The effectiveness of the proposed procedure has been tested by means of a case study related to the design of hull, appendages and sails of a 15” yacht subject to box-rules, designed and manufactured at the University of Palermo.

Keywords: Computational fluid dynamics | Conceptual design | Numerical methods | Optimization | Sailing yacht

Abstract: A 4.60 m sailing yacht, made with a flax fiber composite and wood, has been refitted with the aim of hull weight reduction and performance improvement during regattas. The first objective was obtained with a lightening of internal hull reinforcements while the second one with a reduction of the maximum beam, in order to minimize the longitudinal moment of inertia. The refitting was first simulated via CAD-FEM interaction to establish the feasibility of the procedure and to verify the structural integrity. The resulting hull was then instrumented with strain gauges and tested under typical rigging and sailing conditions. Results obtained by the numerical modeling and measured from experiments were compared.

Keywords: Parametric design | Refitting | Sailing yacht

Abstract: Purpose: The purpose of this study was to characterize the biomechanical effect of two grasping suture techniques used during ligament reconstruction: the modified rolling-hitch (MRH) and the modified finger-trap (MFT). Methods: Flexor profundus tendons were harvested from fresh pig hind-leg trotters. Each specimen was mounted on an electro-mechanic universal testing machine (Instron 3367). In half of all tendons (15 specimens), the suture was passed around the tendon following the MRH knot (Group 1). In the remaining half of all tendons (15 specimens), the suture was passed over a distance of 30 mm according to the MFT suture technique (Group 2). As per standard intra-operative technique, a 1 cm residual tendon stub was left free from suture in all samples. All specimens were preconditioned to a load of 50 N for 10 min, followed by three cycles loading between 50 and 120 N. At this point, each sample was cyclically tensioned between 35 and 240 N, at 1 Hz for 200 cycles. Load-to-failure test was then carried out at a rate of 200 mm/min. Results: Rupture of the suture material at the knot was the mode of failure in all specimens during the loaded to failure test. Significant difference was found between Group 1 vs Group 2 for the elongation between the 0th cycle and 10th cycle, the elongation between the 10th cycle and 200th cycle, the mean stiffness at the 10th cycle, and the mean stiffness at the 190th cycle. No significant differences were noted between Group 1 and Group 2 concerning the ultimate load-to-failure. Conclusion: This study showed that both suture methods appear to be biomechanically effective in a porcine tendon model. However, the single-knot grasping technique (MRH) provided superior biomechanical properties compared with the MFT technique.

Keywords: Biomechanics grasping suture | FiberWire suture | Grasping suture | Modified finger-trap | Rolling-hitch | Suture ligament

Abstract: This paper presents a method to evaluate the accuracy of a manufactured object with respect to its original CAD model. Different errors caused by the manufacturing process are assumed to come from global axis deformation and transverse sections rotation of the object with respect to its ideal CAD. Object and CAD shapes are given in form of point clouds, the former derived from a laser-scanning measurement, the latter from sampling the ideal surface by a dense and uniform point grid. Point clouds are sectioned in a finite number of thin blocks. This method has been applied to the analysis of a helical Darrieus blade prototype, parametrically designed and modelled with McNeel Rhinoceros and Grasshopper software, manufactured with a three-axes Computer Numerical Control machine. This procedure is able to check the conformity of the manufactured airfoil to the theoretical one and to establish the efficiency of the final prototype of the blade turbine.

Keywords: Point cloud | reverse engineering | shape accuracy

Abstract: This paper presents an applicative method for evaluating the global axis deformation of a sweep object caused by the manufacturing process with respect to its ideal CAD model. Object and CAD shapes are given in form of point clouds, the former derived from a laser-scanning measurement, the latter from sampling the original surface by a dense and uniform point grid. After an initial rigid registration, approximated centroidal axes of both shapes are extracted, compared and processed in order to evaluate macroscopical translation errors occurring in any scanned object's section. This method has been applied and tested to the analysis of a helical Darrieus blade prototype, parametrically designed and modelled with McNeel Rhinoceros and Grasshopper software, manufactured with a three-axes CNC machine and reinforced by a carbon fibre composite laminate. The point cloud obtained from the subsequent laser scanning has been processed and compared to the original NURBS model in order to build the global contour map of the mutual difference. The application of this procedure is able to check the conformity of the manufactured airfoil to the theoretical one and, therefore, to establish the efficiency of the final prototype of the blade turbine.

Keywords: axis deformation | error estimation | Point Cloud

Abstract: The present work describes the experimental mechanical characterisation of a natural flax fibre reinforced epoxy polymer composite. A commercial plain woven quasi-unidirectional flax fabric with spun-twisted yarns is employed in particular, as well as unidirectional composite panels manufactured with three techniques: hand-lay-up, vacuum bagging and resin infusion. The stiffness and strength behaviours are investigated under both monotonic and low-cycle fatigue loadings. The analysed material has, in particular, shown a typical bilinear behaviour under pure traction, with a knee yield point occurring at a rather low stress value, after which the material tensile stiffness is significantly reduced. In the present work, such a mechanism is investigated by a phenomenological approach, performing periodical loading/unloading cycles, and repeating tensile tests on previously "yielded" samples to assess the evolution of stiffness behaviour. Infrared thermography is also employed to measure the temperature of specimens during monotonic and cyclic loading. In the first case, the thermal signal is monitored to correlate departures from the thermoelastic behaviour with the onset of energy loss mechanisms. In the case of cyclic loading, the thermoelastic signal and the second harmonic component are both determined in order to investigate the extent of elastic behaviour of the material.

Keywords: Crimped unidirectional textiles | Damage | Flax fibre composite | IR thermography | Tensile properties | Thermoelastic stress analysis

Abstract: This work investigates the flexural behavior of a composite sandwich made of flax fibers reinforced skin facings and an agglomerated cork core, to be employed as an eco-friendly solution for the making of structural components of small sailing boats. An experimental mechanical characterization of the strength and stiffness flexural behavior of the proposed sandwich is carried out, providing a comparison of performances from three implemented assembling techniques: hand-lay-up, vacuum bagging and resin infusion. Sandwich beams have been tested under three point bending (TPB) at various span lengths. A procedure is also proposed and implemented to consider the potential influence of the local elastic indentation in the experimental evaluation of the flexural stiffness. This procedure is based on the analytical solution of an indented beam resting on a fully backed Winkler foundation.

Keywords: Agglomerated Cork Core | Composite Sandwich | Flexural Behaviour | Indentation | Long Flax Fibres | Winkler foundation

Abstract: To analyze the complex and unsteady aerodynamic flow associated with wind turbine functioning, computational fluid dynamics (CFD) is an attractive and powerful method. In this work, the influence of different numerical aspects on the accuracy of simulating a rotating wind turbine is studied. In particular, the effects of mesh size and structure, time step and rotational velocity have been taken into account for simulation of different wind turbine geometries. The applicative goal of this study is the comparison of the performance between a straight blade vertical axis wind turbine and a helical blade one. Analyses are carried out through the use of computational fluid dynamic ANSYS® Fluent® software, solving the Reynolds averaged Navier-Stokes (RANS) equations. At first, two-dimensional simulations are used in a preliminary setup of the numerical procedure and to compute approximated performance parameters, namely the torque, power, lift and drag coefficients. Then, three-dimensional simulations are carried out with the aim of an accurate determination of the differences in the complex aerodynamic flow associated with the straight and the helical blade turbines. Static and dynamic results are then reported for different values of rotational speed.

Keywords: Computational fluid dynamics (CFD) | Helical blade | Straight blade | Vertical axis wind turbines (VAWT)

Abstract: In the field of topology optimization problems, the Evolutionary Structural Optimization (ESO) method is one of the most popular and easy to use. When dealing with problems of reasonable difficulty, the ESO method is able to give very good results in reduced times and with a limited request of computational resources. Generally, main applications of this method are addressed to the definition of the optimal topology of a component subjected to a single load condition.

Keywords: Evolutionary structural optimization | FEM | Numerical methods | Topology optimization

Abstract: In this work a commercial reverse shoulder prosthesis has been redesigned to improve performances in terms of range of movements of the implant and stability to dislocation. A kinematic and mechanic study has been performed using a realistic solid model of the prothesised shoulder: in particular, all the components of the prosthesis have been acquired via a 3D laser scanner and inserted in a virtual humerus-glenoid system by reproducing the common surgical procedure. The final model has been used to measure the maximum angles of abduction and rotation of the arm and the shear forces that cause dislocation. Modifications proposed to the commercial prosthesis are: a different orientation of the cutting plane of the glenoid component and the interposition of a spacer to move the center of rotation of the arm.

Keywords: CAD modelling | Digital shape acquisition | Reverse shoulder prosthesis

Abstract: In this work the mechanical behaviour of a core reinforced composite sandwich structure is studied. The sandwich employs a Glass Reinforced Polymer (GRP) orthotropic material for both the two external skins and the inner core web. In particular, the core is designed in order to cooperate with the GRP skins in membrane and flexural properties by means of the addition of a corrugated laminate into the foam core. An analytical model has been developed to replace a unit cell of this structure with an orthotropic equivalent thick plate that reproduces the in plane and out of plane behaviour of the original geometry. Different validation procedures have been implemented to verify the quality of the proposed method. At first a comparison has been performed between the analytical model and the original unit cell modelled with a Finite Element mesh. Elementary loading conditions are reproduced and results are compared. Once the reliability of the analytical model was assessed, this homogenised model was implemented within the formulation of a shell finite element. The goal of this step is to simplify the FE analysis of complex structures made of corrugated core sandwiches; in fact, by using the homogenised element, the global response of a real structure can be investigated only with the discretization of its mid-surface. Advantages are mainly in terms of time to solution saving and CAD modelling simplification. Last step is then the comparison between this FE model and experiments made on sandwich beams and panels whose skins and corrugated cores are made of orthotropic cross-ply GRP laminates. Good agreement between experimental and numerical results confirms the validity of the proposed model.

Keywords: Corrugated Core | Finite Element | Homogenisation | Sandwich Structures

Abstract: Aim of this paper is to setup a novel procedure able to analyze performances of a reverse shoulder prosthesis when different geometrical configurations are assumed. Nowadays, such a prosthesis is widely used but, because of its novelty, data in literature give poor information about performances and limits to its applicability. The activity has been divided into the following steps. At the beginning the shape of the prosthesis has been digitally acquired via a 3D scanner. Then, CAD models of all prosthetic components have been geometrically optimized in a way to obtain final entities suitable for numerical simulations. After that, CAD assemblies have been created between prosthetic components and bones (humerus and scapula) involved in the shoulder joint. Following step has been the setup of numerical finite element method models to simulate use conditions. To this scope, analyses have been performed in accordance with experimental conditions found in literature. Stability conditions have been verified under the action of horizontal and vertical instability loads with different version angles between humerus and the humeral implant. In particular, the stability ratios of the prosthesis have been calculated for the analysed loading conditions. Obtained results show how the positioning has a great influence on the shoulder stability and allow the definition of guidelines for the application of this prosthesis. © 2014 Springer-Verlag France.

Keywords: 3D scanner acquisition | Non linear FEM analyses | Reversed shoulder prosthesis | Shoulder stability ratio

Abstract: The work describes the preparation and physical-mechanical characterization of unidirectional CFRP panels manufactured by an electron beam curing technique. Delamination fracture toughness in Mode I and II is investigated in order to evaluate the influence of fiber-matrix adhesion strength, matrix toughness and matrix crosslinking density as determined by the radiation curing process. A matrix system comprising a DGEBA epoxy monomer and an initiator of cationic polymerization have been used, with one batch of resin mixed with a PES monomer in order to enhance matrix toughness. Curing was achieved with a pulsed 10 MeV Electron Beam accelerator. Thermally cured composite systems have also been manufactured and tested for comparison. Results from double cantilever beam and end notched flexure delamination tests have been analyzed and correlated with results from short beam shear, dynamic mechanical thermal analysis tests and SEM micrographs of delaminated surfaces. POLYM. COMPOS., 35:1529-1542, 2014. © 2013 Society of Plastics Engineers.

Abstract: Epoxy/carbon fibre reinforced composites were produced by means of e-beam irradiation through a pulsed 10MeV electron beam accelerator. The matrix consisted of a difunctional epoxy monomer (DGEBA) and an initiator of cationic polymerisation, while the reinforcement was a unidirectional high modulus carbon fibre fabric. Dynamic mechanical thermal analysis was carried out in order to determine the cross-linking degree. The analysis pointed out a nonuniformity in the cross-linking degree of the e-beam cured panels, with the formation of clusters at low Tg (glass transition temperature) and clusters at high Tg. An out-of-mould post irradiation thermal treatment on e-beam cured samples provides a higher uniformity in the network although some slight degradation effects. Mode I delamination fracture toughness and Interlaminar Shear Strength (ISS) were also investigated by means of Double Cantilever Beam (DCB) and Short Beam Shear tests, respectively. Results from this mechanical characterisation allowed to correlate fracture toughness of the bulk matrix resin, cross-linking density and fibre/matrix interaction to the delamination fracture behaviour of the fibre reinforced material. © 2013 Elsevier Ltd.

Keywords: Carbon fibre reinforced epoxy resin | Delamination fracture toughness | Dynamic mechanical thermal analysis | Radiation curing

Abstract: Aim of this work is to compare two different total knee prostheses that differ mainly in the shape of the polyethylene (PE) component inserted between the femoral and tibial plates. The best solution between them has been originally reshaped in order to reduce stress peaks. The study procedure has been divided into the following steps. First step is the digitalisation of the shape of the prostheses by means of a 3D laser scanner. The morphology of two prototypes of the prostheses has been acquired by elaborating multiple Moirè fringe patterns projected on their surfaces. Second step consisted on the manipulation of these data in a CAD module, that is the interpolation of raw data into NURBS surfaces, reducing singularities due to the typical scattering of the acquiring system. Third step has been the setting up of FEM simulations to evaluate the prostheses behaviour under benchmark loading conditions given in literature. The CAD model of the prostheses has been meshed into solid finite elements. Different flexion angles configurations have been analysed, the load being applied along the femoral axis. FEM analyses have returned stress fields in the PE insert and, in particular, in the stabilizing cam which function is to avoid dislocation. Last step has been the integrated use of CAD and FEM to modify the shape of the stabilizing cam of the best prosthesis, in order to reduce the stress peaks in the original prosthesis without affecting kinematics of the joint. Good results have been obtained both in terms of stress and contact pressure peaks reduction. © 2012 Springer-Verlag.

Keywords: Contact analysis | FEM simulation | Total knee replacement

Abstract: In this paper a structural Finite Element analysis of a 50 ft pleasure vessel is presented. The study is performed under different loads conditions: modal analyses have been done in order to find the natural frequencies of the vessel, structural analyses to verify the strength of the vessel to design loads. The design loads for the vessel considered are computed according to RINA rules for the construction and classification of pleasure vessels [1]. Two different composites are used for the lamination: one is a monolithic sequence of short fibre and balanced glass lamina, used for the bottom of the vessel and for structural reinforcements, the other is a sandwich made of glass fibre composite skins and a PVC core, used for the main deck and sides of the vessel. All the analyses are performed by using Patran/Nastran™ finite element commercial software in order to identify critical areas where possible reinforcement or redesign needs to be considered. © (2012) Trans Tech Publications, Switzerland.

Keywords: Composite sandwich | Finite element method | Modal analysis

Abstract: In this work the Mode I fracture toughness behavior of unidirectional CFRP laminates is investigated by means of Double Cantilever Beam (DCB) tests. The composite samples were manufactured by thermal curing after impregnation of a Carbon fabric with a DGEBA epoxy and anhydride HHPA curing agent. One resin batch was also mixed with a PES thermoplastic monomer to enhance the matrix toughness. Two lots of samples, toughened and untoughened, were then left to soak in hot water to achieve various degrees of aging. The influence of matrix toughening and hydrothermal aging on the delamination behavior of the composite have then been assessed and correlated with characterization data from Dynamic Mechanical Thermal Analysis (DMTA) and Scanning Electron Microscopy (SEM). © 2012 American Institute of Physics.

Keywords: CFRP | Delamination Fracture Toughness | Epoxy Resins | Hydrothermal Aging

Abstract: In this work Mode I fracture toughness behavior of Electron Beam cured unidirectional CFRP laminates is investigated by means of standardized Double Cantilever Beam (DCB) tests. A matrix system, comprising a DGEBA epoxy monomer and a typical initiator of cationic polymerization, was used and panel samples assembled by hand lay-up. Curing was achieved by 20 to 40 minutes irradiation on a pulsed 10 MeV Electron Beam accelerator. One batch of resin was also mixed with 10 phr of a PES thermoplastic monomer in order to enhance the matrix toughness. The influence of fibre-matrix adhesion, matrix toughening and matrix crosslinking density on the mode I delamination behavior have been investigated by correlating the results of DCB and Dynamic Mechanical Thermal Analysis (DMTA) tests.

Keywords: CFRP | Delamination fracture toughness | Dynamic mechanical thermal analysis | Radiation curing

Abstract: The aim of this work is the analysis of the contact area in a knee prosthesis using two different approaches. In particular, the interface between the femoral component and the polyethylene insert has been studied both numerically and experimentally. The interest in studying the contact area is related to the fact that the wear of the polyethylene insert, due to the high contact pressures, represents one of the major causes of failure of the total knee prosthesis. The possibility to evaluate the contact area at different loads and mutual position between femur and tibia is, therefore, of fundamental importance to study the service life of a prosthesis and to improve its performance. The finite element numerical approach has required the acquisition, through reverse engineering, and CAD modelling of the prosthetic components. Then the FEM simulations have been developed considering two different load conditions. In order to compare the calculated data, the same load configurations have been used for experimental tests based on ultrasonic method. In this case, some preliminary tests were required to calibrate the system depending on the particular characteristics of materials, geometries and surface finish of the prosthesis. The results show a good correlation between the data obtained with the two different approaches and, consequently, a good level of reliability of the procedures developed for the numerical and experimental evaluation of the contact area. The numerical procedure can be used to determine the area for different angles and loads, but especially in the design phase. The ultrasonic technique can be used to validate the numerical data.

Abstract: This paper deals with the experimental analysis of the delamination phenomena in composite materials under different loading conditions. Quasi-static and fatigue tests are performed on specimens made of glass-fibre (GFRP) and carbon-fibre (CFRP) reinforced plastic. In particular, experiments have been carried out under single fracture modes I and II (using standard DCB and ENF test configurations) and mixed modes I+II (using the MMB test configuration) with several mode mixtures. Results obtained for the two materials have been compared paying attention on the relationship between the parameters that describe the fatigue behaviour and the mode mixture acting during the crack propagation. © 2011 Published by Elsevier Ltd.

Keywords: Delamination | Fatigue crack growth | Fibre reinforced materials

Abstract: A numerical model, obtained by implementing a cyclic damage model in the framework of an interface element, is here proposed to reproduce the crack growth in laminated composites subjected to cyclically repeated loads. This model, which differs from the few studies in the literature on the topic, applies not only to single fracture modes but also to mixed modes, and to constant or variable crack growth rates. The applied load (in terms of force or displacement) is assumed to oscillate between a minimum and a maximum constant value. The Paris curve can be reproduced with accuracy once some parameters in the numerical model are tuned with experiments. These parameters are preliminarily found by simulating fatigue delamination in mode I (DCB test), in mode II (ELS or ENF test) and with a fixed mode mixture φ = GII/G (MMB test). A non-monotonic curve is then used to interpolate these preliminary results. Furthermore, tests where the mode mixture changes with crack length could also be reproduced. With this model it is possible to predict the crack growth rate with cycle of a generic structure without knowing a priori how the mode mixture φ changes during the crack propagation. This novel procedure gives a new opportunity in the design of composite structures subjected to repeatedly applied loads. © SAGE Publications 2007.

Keywords: Damage | Delamination | Fatigue | Finite element analysis (FEA) | Interface element

Abstract: The behaviour of thin composite laminates (unidirectional, cross-ply and angle-ply) under compressive loads has been examined in cases where multiple delaminations are present. The problem is solved using the Finite Element Method (FEM) both with linear analyses, based on the eigenvalues research problem, and with nonlinear analyses, based on incremental-iterative procedures. In particular, the role of the delamination length, of the angle of the plies and of the stacking sequence on the critical load is investigated. Results are compared with those found in literature derived from experimental or numerical 2D analyses. © Freund Publishing House Ltd.

Keywords: Buckling | Composite laminates | Delaminations | FEM analysis

Abstract: Experimental investigations and numerical simulations are performed in order to numerically predict the buckling behaviour of thin composite laminated specimens. Experiments are aimed at two objectives: the first is to completely characterize the carbon/epoxy material under simple loading configurations, the second is to test this material in buckling and post-buckling situations. The data collected with the first campaign of experiments are used to obtain the strength parameters required to define a damage model based on the failure theory by Tsai-Wu. This model is implemented in a Finite Element (FE) code and numerical simulations of buckling are executed for unidirectional and cross-ply laminates; results are in good agreement with experiments both in terms of determination of the critical loads and prediction of failure during post-buckling. © BME-PT and GTE.

Keywords: Mechanical properties | Modelling and simulation | Polymer composites

Abstract: In this paper the buckling and post-buckling behaviour of unidirectional and cross-ply composite laminated plates with multiple delaminations has been studied. Finite elements analyses have been performed, using a linear buckling model, based on the solution of the eigenvalues problem, and a non-linear one, based on an incremental-iterative method. With non-linear method large displacements have been taken into account and also contact constraints between sublaminates have been added to avoid their interpenetration. It has been found that both delamination length and position and stacking sequence of the plies influence the critical load of the plate; furthermore, linear and non-linear buckling models are not always in perfect agreement. © 2005 Elsevier Ltd. All rights reserved.

Keywords: Buckling | Composite laminated plates | Composite materials | Delamination | Numerical analysis

Abstract: This paper presents a computational technique for the prediction of fatigue-driven delamination growth in composite materials. The interface element, which has been extensively applied to predict delamination growth due to static loading, has been modified to incorporate the effects of cyclic loading. Using a damage mechanics formulation, the constitutive law for the interface element has been extended by incorporating a modified version of a continuum fatigue damage model. The paper presents details of the fatigue degradation strategy and examples of the predicted fatigue delamination growth in mode I, mode II and mixed mode I/II are presented to demonstrate that the numerical model mimics the Paris law behaviour usually observed in experimental testing. Copyright © 2005 John Wiley & Sons, Ltd.

Keywords: Composite materials | Delamination | Fatigue | Interface elements