Abstract: Osseointegrated implant is a promising solution for limb amputations, but its widespread use is limited by risks such as bone resorption, infections, and strict patient requirements. Typically, the bone and prosthesis are coupled using a press-fit condition, providing short-term stability, or primary stability (PS), which leads to bone in-growth and long-term stability, or secondary stability (SS). However, the greater stiffness of the implant compared to the bone is a concern for SS. Currently, osseointegrated implants are commercially available only in fixed configurations, with a limited use of customization. This study aims to compare the contact effectiveness of three press-fitted intramedullary stems for femoral amputations, developed using three designs (straight, standard curvature, and patient-specific curvature). Moreover, a novel implant design methodology is reported, such is an easy way to develop a patient-specific design. The von Mises stress distribution at the bone-implant interface was analyzed. The study uses CAD models of a femur acquired through CT scans. A FEA was conducted to evaluate the elastic behavior of the bone when the implant is press-fitted with an interference of 0.1 mm. The outcomes show how the patient-specific implant result in a more physiological distribution of the load in the bone. This study could be used as a starting point for further studies on primary and secondary stabilities.

Keywords: 3D Modelling | Finite Element Model | Osseointegration | Patient-Specific Design | Transfemoral Implant

Abstract: In a digital world where technological development allows the implementation of computer-based methods that can objectively support human activities, it is no more conceivable that activities such as the analysis, classification, and reconstruction of archaeological ceramics are made manually. This determines that expert operators are involved in time-consuming, tedious, poorly repeatable, and reproducible activities whose results depend on his/her experience. This problem concerns the need for robust and reliable automatic methods supporting the operator in these activities. To address these problems, in the last years, the University of L'Aquila research group published robust and reliable methods based on the codification of archaeologists’ knowledge in recognizing the most significant geometric and morphological features of sherds. With such tools now available, producing more objective knowledge referring to a huge amount of sherds, the need arises to develop computer-based systems capable of sharing this knowledge. For this purpose, in this paper, a dedicated database is proposed. Particular efforts were made to implement an intuitive and interactive web interface with commands that co-determine the essential interaction of the archaeologist with the fragments in the traditional method.

Keywords: Automatic features recognition | Computer methods in archaeology | Innovative representation scheme | Semantic annotations | Web-based application

Abstract: As is widely recognized, advancements in new design and rapid prototyping techniques such as CAD modeling and 3D printing are pioneering individualized medicine, facilitating the implementation of new methodologies for creating customized orthoses. The aim of this paper is to develop a new automatic technique for producing personalized orthoses in a straightforward manner, eliminating the necessity for doctors to collaborate directly with technicians. A novel design method for creating customized wrist orthoses has been implemented, notably featuring a generative algorithm for the parametric modeling of the orthosis. To assess the efficacy of the developed algorithm, a case study was conducted involving the design and rapid prototyping of a wrist orthosis using Fused Deposition Modeling (FDM) technology. Subsequently, the developed algorithm was tested by clinicians and patients. The results obtained indicate that the implemented algorithm is user-friendly and could potentially enable non-expert users to design customized orthoses. These results introduce innovative elements of originality within the CAD modeling, offering promising solutions to the challenges associated with the design and production of customized orthoses. Future developments could consist of a better investigation regarding the parameters that influence the accuracy of the scanning and of the printing processes.

Keywords: additive manufacturing | CAD | generative design | reverse engineering | wrist orthosis

Abstract: Composite sandwich panels with honeycomb, corrugated, tetrahedral, trapezoidal, 3D periodic and hybrid lattice cores have long been studied for their use in various industrial fields. In this study, several numerical analyses were conducted in ANSYS APDL environment in order to analyze the effect of a novel bi-directional corrugated core configuration on the flexural performance of a CFRP sandwich panel. In particular, the sandwich core is obtained by repeating a regular unit cell in two different directions to form a three-dimensional lattice structure. In order to determine the optimal values of the geometrical parameters of the core unit cell and to evaluate how the layout of the composite laminate could affect the mechanical performances of the structure, a numerical study was conducted by using the Group Search Optimizer (GSO) algorithm, a metaheuristic animal-inspired optimization algorithm used to solve various real-world problems. The obtained results show that the GSO algorithm is very effective to optimize the main geometrical parameters of the composite sandwich panel with the novel bi-directional corrugated core. More generally, the implemented procedure provides an open framework to solve complex optimization problems that are very difficult to solve using exact methods, making the GSO algorithm particularly attractive for many industrial applications.

Keywords: ANSYS | Finite element analysis | Group search optimizer | Numerical optimization

Abstract: In this work a Reverse Engineering based approach has been implemented aiming to reconstruct the 3D shape of a strongly damaged and no longer usable impeller of a submersible centrifugal pump. After obtaining the 3D model, new designs of the impeller were investigated in terms of structural stability and corrosion resistance by changing the geometry and the material. Obtained results show the used approach can be very useful both to reproduce, by Additive Manufacturing, no longer available spare parts, so allowing to extend the useful life of old machineries and to reduce costs resulting from plant shutdowns, but also to improve the performances of old designs, making use of different materials and new manufacturing processes.

Keywords: CAD | Centrifugal pump | Impeller | Modal analysis | Reverse Engineering

Abstract: Editorial for the Special Issue “Advanced Design and Manufacturing in Industry 4.0”

Abstract: The peak stress method (PSM) allows a rapid application of the notch stress intensity factor (NSIF) approach to the fatigue life assessment of welded structures, by employing the linear elastic peak stresses evaluated by FE analyses with coarse meshes. Because of the widespread adoption of 3D modeling of large and complex structures in the industry, the PSM has recently been boosted by including four-node and ten-node tetrahedral elements of Ansys FE software, which allows to discretize complex geometries. In this paper, a Round Robin among eleven Italian Universities has been performed to calibrate the PSM with seven different commercial FE software packages. Several 3D mode I, II and III problems have been considered to investigate the influence of (i) FE code, (ii) element type, (iii) mesh pattern, and (iv) procedure to extrapolate stresses at FE nodes. The majority of the adopted FE software packages present similar values of the PSM parameters, the main source of discrepancy being the stress extrapolation method at FE nodes.

Keywords: coarse mesh | FE analysis | notch stress intensity factor (NSIF) | peak stress method (PSM) | tetrahedral element

Abstract: In the mid-1980s, several metaheuristic methods began to be developed for solving a very large class of computational problems with the aim of obtaining more robust and efficient procedures. Among them, many metaheuristic methods use bio-inspired intelligent algorithms. In recent years, these methods are becoming increasingly important and they can be used in various subject areas for solving complex problems. Firefly Algorithm is a nature-inspired optimization algorithm proposed by Yang to solve multimodal optimization problems. In particular, the method is inspired by the nature of fireflies to emit a light signal to attract other individuals of this species. In this work, a numerical study for solving a structural problem using the Firefly Algorithm as optimization method is conducted. In particular, the implementation of the Firefly Algorithm in several input files realized in the ANSYS Parametric Design Language has allowed the definition of the optimal stacking sequence and the laminate thickness of a composite gear housing used to enclose the components of a mechanical reducer.

Keywords: ANSYS | Finite element analysis | Firefly Algorithm | Structural optimization

Abstract: The standard method of design and manufacturing customised orthoses is still very time-consuming due to their often very complex shape. Different authors have tried to solve this problem but, unfortunately, the proposed approaches cannot be easily used in clinical practice because they require substantial interaction among medical staff and engineers or technicians. The aim of this work is to present the framework of a new design approach that could allow clinicians to easily model a customised orthosis, without a skilled technician develops the entire procedure. In particular, an automatic process based on Generative Design has been implemented. The obtained results have demonstrated that the implemented algorithm is simple to use and could allow also not-skilled users to design customised orthoses.

Keywords: CAD | Customised orthosis | Generative design | Reverse engineering

Abstract: Although the best configuration of the joints used to connect a common GFRP sandwich panel with the main structures is the adhesively bonded one, that permit high static and fatigue performances as well as to avoid stress concentrations, mechanical or hybrid joints are still widely used in the industrial field. After a preliminary theoretical design, the optimal configuration of an end adhesively bonded double-lap joint constituted by a simple insert as internal adherent and the same face sheets as external adherent, has been researched. In detail, several experimental tests and successive numerical simulations under tensile and bending loading, performed by varying the main influence parameters as the overlap length and the material of the internal insert (aluminum, steel, CFRP), have been carried out. In brief, the experimental and numerical analyses have shown that, due to the limited effects of the stiffness unbalancing of the joints, as well as to the appreciable peel stress values associated with tensile and especially bending loading, the optimal joint configuration is obtained in practice by using an insert made by CFRP with an overlap length equal to about a double the theoretical overlap value. Also, due to the different damage tolerance of the epoxy adhesive to the shear and peel stresses, the accurate strength prediction of such joints has to be performed by assess the failure processes that occur at the two attach points of the double lap joint. In detail, the delamination growth that can occurs at the attach point of the face sheets, can be predicted by using a delamination criterion along with a point stress approach, whereas the unstable delamination growth that can occur at the opposite point of attach of the insert, can be evaluated by using a simple delamination criterion with the classical approach of the maximum stress.

Keywords: Composite sandwich panels | double-lap joint | experimental tests | finite element analysis | strength criteria

Abstract: Thanks to good mechanical performances, high availability, low cost and low weight, the agave sisalana fiber allows to obtain biocomposites characterised by high specific properties, potentially very attractive for the replacement of synthetic materials in various industrial fields. Unfortunately, due to the low strength versus transversal damage processes mainly related to the matrix brittleness and/or to the low fiber/matrix adhesion, the tensile performance of random short fiber biocomposites are quite low, and to date most of the fiber treatments proposed in literature to improve the fiber-matrix adhesion, have not led to very satisfactory results. In order to overcome such a drawback, this work in turn proposes the proper introduction of low fractions carbon nanotubes to activate advantageous improvements in matrix toughness as well as fiber-matrix bridging effects, that can both lead to appreciable increments of the tensile strength. Systematic experimental static and fatigue tests performed on high quality biocomposites obtained by an optimized compression molding process, have shown that the introduction of 1% of carbon nanotubes is sufficient to gives significant improvement in both stiffness and static tensile strength, respectively by approximately 28% and 30%. Furthermore, toughening the biocomposite with 1% of nanotubes results in an appreciable enhancement in lifetime of at least 3 orders of magnitude. Biocomposites with 2% of CNTs show instead more limited improvement of 13% in stiffness, 6% in strength and 150% in lifetime. Also, a thorough analysis of the damage processes by SEM micrographs, as well as of the main fatigue data, has allowed to determine the model that can be used to predict the fatigue performance of such biocomposites.

Keywords: Biocomposite | Carbon nanotube | Fatigue | Polymer composites | Sisal

Abstract: The paradigm of Industry 4.0 allows to increase the efficiency and effectiveness of the production. Companies that will implement advanced solutions in production systems will increase their level of competitiveness and will be able reach high market shares. The present paper is focused on the development of advanced digital solutions to be implemented on a close power loop test bench designed to test high power transmissions for naval unit. In particular, the test configuration consists of a back-to-back connection between two identical mechanical reducers. Since the efficiency of these systems are very high, it is not necessary to use large electric motors, thus managing to contain the operating costs of the testing phase. The particular test bench allows to size the electric motor simply based on the dissipated power by the kinematic mechanisms. By means of suitable sensors installed on the test bench it is possible to extrapolate countless technical data. The implementation of Industry 4.0 enabling technologies allows to evaluate the increase in efficiency compared to traditional systems in terms of reduction of noise and vibrations, efficiency of lubrication, reduction of consumption, installation and maintenance cost of the entire system.

Keywords: Cad modeling | digital transformation | Experimental tests | Industry 4.0 | Internet of things | Shipyard 4.0 | Sustainability | Test bench

Abstract: Industry 4.0 promises to increase the efficiency of production plants and the quality of the final product. Consequently, companies that implement advanced solutions in production systems will have a competitive advantage in the future. The principles of Industry 4.0 can also be applied to shipyards to transform them into “smart shipyards” (Shipyard 4.0). The aim of this research is to implement an interactive approach by Internet of Things on a closed power-loop test bench equipped with sophisticated sensors that is specifically designed to test high-power thrusters before they are installed on high-speed crafts, which are used in passenger transport. The preliminary results of the proposed Internet of Things-platform demonstrates the efficacy of the decision-making support tool in improving the design of propulsion systems and increasing their efficiency compared to traditional systems.

Keywords: CAD modelling | Experimental tests | Industry 4.0 | Internet of Things (IoT) | Test bench

Abstract: The use of light but strong materials is largely studied in various area of the shipbuilding, this because the need of reducing the weight, and especially the weight of all the structures above the main deck assume primary importance for the stability. Traditionally in fast boats like fast ferries, hydrofoils, patrol boats, the typical materials are Aluminum alloy or composites, both those materials have advantages and disadvantages, but the new development of technologies made possible to combine them, in order to have a new material, combining the advantages of both, in terms of fatigue resistance, firefighting characteristics. In this paper, predominant mode II fatigue delamination tests of fiber metal laminates made of alternating layers of 2024-T3 aluminum alloy sheets and unidirectional E-Glass/epoxy laminates are presented. Several experimental tests are carried out employing the End Notched Flexure fixture and a progressive damage model is used to simulate the damage accumulation in the aluminum-composite interface, in the localized area in front of the crack tip, where micro-cracking or void formation reduce the delamination strength during fatigue tests. In particular, the numerical model is based on the cohesive zone approach and on the analytical definition of a damage parameter, directly related to the fatigue crack growth rate da/dN. The numerical model, implemented in ANSYS environment, uses a fracture mechanics-based criterion in order to determine the damage propagation. In particular, the study has allowed to determine the damage model constants that are used for numerical verification of the experimental results.

Keywords: End notched flexure | FE analysis | Fibre metal laminates

Abstract: The hydrofoil is a craft where the weight is entirely supported by the lift generated by the submerged part of wings. The particular structure of the craft requires a thorough study of the architecture of the hull, whose structure differs from others high speed vessels since the lift on wing surfaces are transmitted to the hull in limited areas (wing attacks). The authors have developed a research to optimize geometry of hull and wing system on a hydrofoil capable to carry 250 passengers at a speed of 35 knots, operating among Sicilian island. The principal goals of the new hydrofoil concern both the fuel reduction that the improvement of the comfort in terms of seakeeping and levels of acoustic vibrations. In order to reduce the power engines and the acoustic vibrations and to increase the seakeeping during the cruising route and the takeoff, a thorough study of the bow sections (whose profile contributes during this step to exert a thrust which, added to that provided by the wing surfaces, drastically reduces takeoff times) is conducted. Several experimental tests, performed at the towing tank, have allowed to better define the shapes of the hydrofoil and the profile of the wings. An economic assessment was carried out in order to demonstrate that the innovation effort contributes to reducing both construction that operating costs.

Keywords: Economic assessment | Experimental analysis | Hydrofoil | Towing tank

Abstract: Total elbow arthroplasty (TEA) is an effective and frequently used treatment for patients with debilitating elbow pathology. Total elbow prostheses have lagged behind those of the knee, hip and shoulder for different reasons, such as the high failure rate of the early designs. Concern remains regarding the longevity of TEA implants, especially in younger patients. The main cause of revision of the implant is usually related to the phenomenon of aseptic loosening mainly due to the cement-bone interface failure. Aim of this work is the biomechanical analysis of a new elbow prosthesis to investigate the mechanical behaviour at the cement-bone interface. For this reason, a musculoskeletal model has been developed by modelling the forces of the muscles and after FEM analyses have been performed. Obtained results confirm the validity of the implemented model and can provide guidelines for surgeons regarding the implant configurations with the aim to reduce the aseptic loosening.

Keywords: CAD | FEM | Reverse engineering | Total elbow arthroplasty

Abstract: Mechanical fastening is a popular choice in joining composites because of the ability to transfer high loads and the ease of assembly and disassembly. In this study, the failure behavior of composite–aluminum single-lap bolted joint is investigated. In particular, the effects of varying the preload on the bolt are examined. In order to accurately measure the preload, a specialized sensor that uses a fiber Bragg grating sensor embedded in the bolt is proposed and created. This sensor is realized for the current tests but can be expanded to other applications. An experimental study of bolted single-lap joints varying the tightening torque value has been carried out and, in order to validate the experimental tests, several finite element analyses conducted in ANSYS environment with explicit solver are performed. Comparison between numerical results and experimental tests allows us to determine the effect of bolting parameters on the strength of joint and to verify the effectiveness of the use of the specialized preload sensor.

Keywords: Composite materials | Fiber Bragg sensor | Finite element analysis | Mechanical fastening | Preload sensor

Abstract: The aim of the research is to develop an azimuthing contra-rotating propeller for commercial applications with a power of 2000 kW. The thruster system is designed especially to be installed on high speed crafts (HSCs) for passenger transport with a cruising speed of about 35-40 knots. The topic is very useful because the azimuth thruster solutions currently do not find commercial applications in naval units for passenger transport. The latter are heavy, not very efficient from a hydrodynamic point of view and suitable for maximum cruising speed of about 18-20 knots. The study is interesting because among the advantages that these solutions provide are the possibility of transmitting very high torques and to guarantee a much longer life cycle. In more detail, the propulsion is realized by using a C-drive configuration, with a first mechanical transmission realized by using bevel gears mounted in a frame inside the hull, and a second transmission realized by bevel gears housed in a profiled hull at the lower end of a support structure. In the profiled hull will be installed the shafts of the propellers, in a contra-rotating configuration. In order to optimize the system before its industrial use, a close power loop test bench has been studied and designed to test high power transmissions. The test configuration allows to implement a back-to-back connection between two identical azimuthing contra-rotating propellers. Moreover, the particular test bench allows to size the electric motor simply based on the dissipated power by the kinematic mechanisms. Since the efficiency of these systems are very high, it is not necessary to use large electric motors, thus managing to contain the operating costs of the testing phase. The most significant disadvantage is the need to have two identical transmissions with consequent increase in installation costs. Through the back-to-back test bench it was possible to study the increase in efficiency compared to traditional systems.

Keywords: azimuthing contra-rotating propeller | CAD modeling | experimental test | finite element analysis | POD | Thruster

Abstract: Finding the locations of departments or machines in a workspace is classified as a Facility Layout Problem. Good placement of departments has a relevant influence on manufacturing costs, work in process, lead times and production efficiency. This paper analyses the problem of allocating departments with restrictions in terms of unequal area and rectangular shape within a facility, in order to minimize the sum of material handling costs taking into account the satisfaction of the aspect ratio requested. In particular, we propose for the first time a Firefly Algorithm based on the slicing structure encoding. The proposed method was tested comparing the results obtained from other authors on the same literature instance. The results confirm the effectiveness of the Firefly Algorithm in solving the Facility Layout Problem by generating the best solutions with respect to those provided by previous researches.

Keywords: Firefly algorithm | Problem | Slicing structure | Unequal area-facility layout

Abstract: In a sustainable management of logistics, transportation plays a crucial role. Traditionally, the main purpose was to solve the Vehicle Routing Problem minimizing the cost associated with the travelled distances. Nowadays, the economic profit cannot be the only driver for achieving sustainability and environmental issues have to be also considered. In this paper, to satisfy the intricate limits involved in real vehicle routing problem, the study has been structured considering different types of vehicles in terms of maximum capacity, velocity and emissions, asymmetric paths, vehicle-client constraints and delivery time windows. The firefly algorithm has been implemented to solve the vehicle routing problem and the TOPSIS technique has been applied to integrate economic and environmental factors. Finally, to prove the effectiveness of the proposed approach, a numerical example has been proposed using data provided by a logistic company located in Sicily.

Keywords: Decision making | Firefly algorithm | Sustainability | TOPSIS | Vehicle routing problem

Abstract: At present time the project of a naval vehicle, where with the word project we refer to all the process of design and manufacturing, especially when the vehicle offers special formal and performance characteristics, involves a number of operators that has been increasing considerably in recent decades, and this increased complexity can be correlated with dimensional and typological growth of many categories of ships. Simultaneously we are witnessing a complete new project approach, where the possibility given by the computer contribution to represent processes and results becomes crucial. The paper aims to investigate the consequences of this progress in the organization of the project and focuses on the innovative methodologies, bringing as an emblematic case the evolution of the hull study and the role of "planning matrix" that it also constitutes even on the graphic plane. The studio cases examined, which the reflections presented here refer to, are related to ships where the combination of performances and shapes takes on a particularly significant value: therefore, references are made to yachts and fast vehicles such as hydrofoils or catamarans. Finally, with special regards to Hydrofoils, the study will report a comparison made about the seakeeping and resistance of 2 different types of wings for hydrofoils, the comparison has been done at first step by using CFD calculations and then validated trough tank tests to show the validity of the results.

Abstract: Solar and wind energy are the two most available renewable energy resources in the world. In this paper, a high-resolution analysis that allows sizing a hybrid photovoltaic-wind turbine-battery banks has been carried out. The analysis aims to minimize the annualized cost of the systems satisfying two reliability constraints. The solution has been obtained numerically by means of an iterative technique. The decision variables are the photovoltaic area, wind turbine radius, and battery capacity. A high-resolution model, based on fuzzy logic inference system, has been developed to evaluate the number of active occupants and the domestic electricity consumption. In order to allow a more accurate sizing of the system, a new reliability parameter named seasonal loss of load probability ratio that takes into account the seasonality of data has been defined. Seasonal loss of load probability ratio has been used in the iterative process in addition to the most common loss of load probability. Compared with traditional processes, the obtained results demonstrate that the introduction of the new parameter to iterative process causes a meaningful improvement of the system's reliability and a slight increase of its cost on the other hand. The simulation, conducted in MATLAB® environment, has been carried out to supply power for a domestic dwelling located in three different locations of Sicily. Compared to reliability values arising from the traditional procedure, the obtained results show that a reliability improvement of 75% is reached by using the new sizing procedure. Therefore, the proposed methodology gives an important advancement on the current state of the art since it allows at designing renewable plants in a more efficient way.

Keywords: Economic optimization | Fuzzy inference system | Hybrid PV-Wind energy system | LLP | Matlab

Abstract: Although several works have been published in literature on agave fibers and their biocomposites, accurate information about the choice of both the fibers and the manufacturing processes that allow the user to optimize the biocomposites properties in terms of strength and stiffness are not yet available; also, no theoretical models that can be used for an accurate evaluation of the mechanical properties of these biocomposites, are reported. To this aim, the present work intends to give a contribution by considering green epoxy biocomposites reinforced by both short and discontinuous sisal agave fibers arranged in proper MAT-type fabrics. In particular, an optimized manufacturing process that allows to obtain good quality biocomposites, is proposed. A detailed analysis of the experimental results, obtained through preliminary pull-out and tensile tests carried out, along with an accurate analysis of the damage process performed by SEM micrographs, have allowed to develop reliable theoretical models that permit the mechanical properties evaluation of the analyzed biocomposites. Finally, the comparison with the most performing short/discontinuous fiber biocomposites reported in literature has shown how the implemented biocomposites exhibit comparable tensile strength and significantly higher stiffness, also respect to biocomposites reinforced by more stiff and more expensive fibers (flax, hemp, etc.).

Keywords: Biocomposites | Eco-friendly matrix | Natural fibers | Sisal fibers

Abstract: The increasing interest about eco-sustainable materials in the industrial production (automotive, civil construction, packaging), has led to the increase of the research works dealing with biocomposites. However, until now the most attention has been devoted to the development of short fiber biocomposites for non-structural applications, whereas only a few works have considered high performance biocomposites for structural applications. Consequently, the development of structural biocomposites from robust natural fibers, as sisal fibers, is a result expected from the scientific community, but not yet achieved. In order to give a contribution to the implementation of high performance biocomposites constituted by a green matrix reinforced by sisal fibers, the present work proposes a manufacturing process that allows to obtain good quality unidirectional biocomposites with fiber volume fraction up to 70%. In detail, it uses unidirectional “stitched” fabrics, properly obtained in laboratory from optimized fibers, and a curing under a proper pressure cycle. The comparison with independent data reported in literature, has evidenced how the proposed biocomposites exhibit mechanical properties higher than most of biocomposites described in literature, so that they can advantageously substitute not only materials as steel, aluminum and glass fiber reinforced plastics, but also other biocomposites reinforced by more expensive fibers.

Keywords: Biocomposites | Ecofriendly matrixes | Natural fibers | Sisal fibers

Abstract: Hybrid bolted/bonded joints are used to assemble structural components, commonly made by carbon fiber reinforced plastics (CFRP), with aluminum frames. Hence, they have become common solutions in a number of modern structural applications in the industrial fields, as well as civil constructions. Unfortunately, due to the lack of understanding of the relationships between the multiple parameters of influence that characterize their mechanical performance, only limited improvement have been achieved so far over classical bonding approaches, in terms of static and fatigue strength. As a result, further studies are needed in order to better exploit the potential of hybrid bolted/bonded joints and identify optimum joint configurations. This paper describes an optimization procedure of the joints, achieved through a systematic experimental analysis of hybrid single lap aluminum–CFRP structural joints. This, analyzing the effect of overlap length, stiffness imbalance, adhesive curing as well as of size, positioning and preload of the bolt, results in a significant rise of the strength, especially in presence of high cycles fatigue loading. Also, micrographic analysis and related numerical simulations have allowed to gain a better insight into the damage mechanisms occurring during the in-service tensile loading, corroborating the highest mechanical performance of the angle-ply lay-up proposed for the CFRP adherent.

Keywords: Adhesive joints | delamination | fatigue | finite element analysis (FEA) | structural composites

Abstract: 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.

Keywords: coarse mesh | finite element (FE) analysis | notch stress intensity factor (NSIF) | peak stress method (PSM)

Abstract: Although several works have recently been published in literature about biocomposites, i.e. about composites with polymeric matrix reinforced by natural fibers, only a few articles have been devoted to the implementation of high performance biocomposites for structural and semi-structural applications. The present study aims to give a contribution by considering biocomposites obtained by using an eco-friendly partially bio-based epoxy (green epoxy) and sisal (agave sisalana fibers) obtained by a proper optimization process. Through a systematic experimental analysis, three different types of biocomposites obtained with a suitable manufacturing process, such as random short fiber biocomposites, random discontinuous fibers biocomposite obtained through the preliminary manufacture of MAT fabrics, and unidirectional long fibers biocomposites obtained through the preliminary manufacture of unidirectional "stitched" fabrics, have been studied.

Keywords: agave fibers | biocomposites | eco-friendly matrices | natural fibers

Abstract: In the present paper, the complex mechanical behaviour of the surfaces joining two different bodies is analysed by a cohesive-frictional interface constitutive model. The kinematical behaviour is characterized by the presence of discontinuous displacement fields, that take place at the internal connecting surfaces, both in the fully cohesive phase and in the delamination one. Generally, in order to catch discontinuous displacement fields, internal connecting surfaces (adhesive layers) are modelled by means of interface elements, which connect, node by node, the meshes of the joined bodies, requiring the mesh to be conforming to the geometry of the single bodies and to the relevant connecting surface. In the present paper, the Extended Finite Element Method (XFEM) is employed to model, both from the geometrical and from the kinematical point of view, the whole domain, including the connected bodies and the joining surface. The joining surface is not discretized by specific finite elements, but it is defined as an internal discontinuity surface, whose spatial position inside the mesh is analytically defined. The proposed approach is developed for two-dimensional composite domains, formed by two or more material portions joined together by means of a zero thickness adhesive layer. The numerical results obtained with the proposed approach are compared with the results of the classical interface finite element approach. Some examples of delamination and frictional contact are proposed with linear, circular and curvilinear adhesive layer.

Keywords: Cohesive-frictional | Delamination | Interface | Joined solids | XFEM

Abstract: In this paper, an analytic study of the subject of mechanical power transmission in HAWT wind turbine has been carried out. For the most part, the study analyzes the use of continuously variable transmission (CVT) in order to allow the turbine and the electric generator to couple, allowing in turn, an unremitting transmission ratio adjustment. In low-wind sites, the design criteria suggest an oversizing of the wind turbine in order to generate adequate electrical power even at low wind speed. The proposed solution enhances the space of operating points since it allows the electric generator to release the rotational speed from the turbine one (limited due to structural integrity). Employing a CVT transmission, the modulation system of the input power to the turbine starts operating at higher wind speeds when compared to a conventional direct-drive case: this corresponds with the possibility to fully exploit the wind power at a higher speed range, therefore maximizing the wind turbine's energy production. The analysis has showed that, in the case of CVT configuration, the annual energy yield increases of about 50% compared to direct-drive solution.

Keywords: CVT | Direct-drive turbine | Renewable energy | Wind turbine

Abstract: In this paper, the main causes of technical malfunction of a hydrofoil was analyzed. In particular, a preliminary analysis evaluates the economic impact for the navigation company of the periodical maintenance related to the keeping of the vessel in dry dock. The study demonstrated that the main critical points are focused on the fragility of the stabilization control system. The increasing of operating costs has motivated the realization of a study aimed at redesigning the stabilization system. The continuing failure of the stabilization system (usually in waterimmersed) severely limits the use of the high-speed craft. The proposed design solution considers the positioning of the control actuators of the flaps inside the hull. Therefore, a kinematic system constituted by a slider-crank mechanism that is driven by a double-acting hydraulic cylinder positioned above the waterline was studied and developed. In order to design the mechanical system, it was necessary to take into account of the critical factors related to the transmission of high torque loads with limited space available for the placement of the system components. In fact, in order to reduce the motion resistance and to optimize the hydrodynamic flows in the connection area of the wings to the central strut, it was necessary to design a double cardan joint of reduced radial dimension. Several numerical analyses conducted in ANSYS environment allowed to validate the proposed solution. Fatigue tests on an experimental prototype of the stabilization system allowed to ensure the integrity of the solution during the navigation.

Keywords: Fatigue tests | FE analysis | High-speed craft | Hydrofoil | Stabilization control system

Abstract: In the paper, a numerical and experimental study was carried out to highlight the effect of the distance d between the weld seam and the reinforcement on the residual stress distribution in Friction Stir Welded AA6082-T6 structures. An L-shaped profile was welded to a sheet metal with varying tool rotation and distance d from the weld seam. The Cut Compliance method was used to determine the resulting longitudinal residual stress. A dedicated FE model for FSW was set up, validated and utilized to predict the longitudinal residual stress in the assembled part. The analysis allowed the identification of a few design guidelines in order to reduce the detrimental effects of the residual stresses.

Keywords: Cut compliance | FE analysis | Friction Stir Welding | Residual stress | Skin and stringer

Abstract: The generation of permanent compressive stresses around the holes is recognized as a valuable mean to delay the onset and propagation of the defects and to extend the fatigue life of the mechanical components. In the work, a bilateral indentation process, performed on each side of the component, is widely used in order to create a residual circumferential stress field around the area to be drilled and that persists after the drilling operation. In order to evaluate the process parameters and to identify optimal geometric solutions, several static and fatigue tests are conducted on AW 6082-T6 aluminum alloy specimen where two holes are created. In particular, experimental tests on only drilled specimens (OD) and specimens subjected to Indentation process (IP) varying the indentation depth and the center-tocenter distance of the holes are performed. Several numerical analyses, conducted in ANSYS APDL environment with explicit solver, allow to determine the influence of the distance between two adjacent holes and the effect of the indentation depth on the residual stress distribution.

Keywords: Cold working | Fatigue | FE analysis | Indentation process | Residual stress

Abstract: A new interface constitutive model based on damage mechanics and frictional plasticity is presented. The model is thermodynamically consistent, it is able to accurately reproduce arbitrary mixed mode debonding conditions and it is proved that the separation work is always bounded between the fracture energy in mode I and the fracture energy in mode II. Analytical results are given for proportional loading paths and for two non-proportional loading paths, confirming the correct behavior of the model for complex loading histories. Numerical and analytical solutions are compared for three classical delamination tests and frictional effects on 4ENF are also considered.

Keywords: Cohesive-frictional interface | Mixed-mode delamination | Thermodynamics

Abstract: Design and manufacture of mechanical elements are strongly influenced by the evaluation of the residual stresses due to their effects on the material strength. This paper presents numerical and experimental results performed on AW 6082-T6 aluminum alloy drilled specimens when the hole is created after a bilateral indentation process. The plastic deformation induced by the indenters creates a compressive residual stress field around the hole, which persists after the drilling operation. Several numerical analysis have been carried out in ANSYS APDL explicit solver for different indentation depths and hole diameters in order to evaluate the compressive circumferential stresses, optimal process parameters and relevant geometric features. Fatigue tests are performed in order to determine the cycles to failure and the corresponding Wöhler diagram.

Keywords: Cold working | Fatigue | FE analysis | Indentation process | Residual stress

Abstract: The increasing interest of the industry (especially automotive, aviation and marine) in the fastener joints (riveted, bolted, etc.) between metallic materials, has re-opened the study on the possibility to improve the performance of the drilled structure using plastic deformation processes. Indentation process, performed before the drilling operation, creates circumferential compression stresses around the hole which increase significantly the mechanical performance of the drilled structures. In this paper, static and the fatigue performances of aluminum-aluminum (AW 6082-T6) single-lap bolted joints are studied. In particular, the study compares the mechanical strength of only drilled single-lap bolted joints (OD specimens) and single-lap bolted joints subject to an indentation process (IP specimens). In order to determine the cycles to failure and the corresponding Wöhler diagram, several fatigue tests are performed. The analyses allow to determine the mechanical performance and the failure mode of the analyzed joints. Several numerical analysis, conducted in ANSYS environment on three-dimensional models of the single-lap joint, are focused on the evaluation of the residual stress on the indented plate and, in particular, to compare the stress distribution on both type of analyzed joints.

Keywords: Fatigue | Finite element analysis | Indentation process | Residual stress | Single-lap joint

Abstract: Abstract The article deals with the fatigue life of plates with hole made of aluminum alloy. Specifically, the combined effect of cold working expansion and ring indentation on improved fatigue life performance was investigated. Multiple fatigue tests were performed to determine the cycles to failure and the corresponding Wöhler diagram. Experimental results were compared with those of nontreated specimens. The conclusion was that cold working expansion and indentation create a delay on crack formation and fatigue failure.

Keywords: Cold Expansion of Holes | Cold Working | Fatigue | Ring Indentation | Wöhler Diagram

Abstract: Progressive delamination in composite materials under static or fatigue loading condition are, in many structures, one of the predominant cause of failure. In the paper, an accurate study of quasi-static delamination growth under mode II loading condition is conducted. Several experimental tests are performed on composite laminates consisting of unidirectional carbon/epoxy layers. Four-point end-notched flexure (4ENF) test is employed in order to characterize the mode II interlaminar fracture toughness. The R-curve is obtained by means of optical and numerical determination of crack tip position. The energy release rate and the crack length are calculated through experimental determination of the compliance until unstable advance occurs. In order to confirm the experimental results, a cohesive-frictional model, implemented in the finite element program FEAP, allows to evaluate the influence of frictional phenomena in the Mode II delamination, when the compression of the two interfaces increases the energy dissipation due to the friction.

Keywords: 4ENF | CFRP | Cohesive Zone Model | Composite materials | Delamination | Mode II

Abstract: In the present paper a new thermodynamically consistent cohesive interface model is proposed; it based on a predefined Helmhotz free energy with a single scalar damage variable and produces two independent fracture energies, in pure mode I and pure mode II debonding conditions. The proposed model can also take in to account the frictional effects with a smooth transition of the mechanical behaviour, from the initial cohesive one of the sound material, to the frictional one of the fully debonded interface. The cohesive-frictional behaviour is based on the mesoscale geometric interpretation of the scalar damage variable, which distinguish sound and debonded fractions of a representative surface element of the interface. The proposed formulation is defined by a damage activation function, which depends on the separation displacement. Traction components, damage evolution and the relevant constitutive equations are derived by following the classical Noll and Coleman procedure, and the model implicitly verify the second thermodynamic law by proving that dissipation is non-negative for any loading path. The numerical simulations of mixed mode delamination tests are performed and compared to the experimental results, for different mixed mode ratio.

Keywords: Delamination | Fracture | Friction | Interface | Mode II

Abstract: Due to their reliability and ease of assembly, both the adhesively bonded and the mechanical joints are commonly used in different fields of modern industrial design and manufacturing, to joint composite materials or composites with metals. As it is well known, adhesively bonded joints are characterized by high stiffness and good fatigue life, although delamination phenomena localized near the free edges may limit their use, especially for applications where corrosive environments and/or moisture can lead to premature failure of the bonding. In these cases, a possible alternative is given by the well-known mechanical joints. On the contrary, these last joints (bolted, riveted) require a preliminary drilling of the elements to be joined, that may cause localized material damage and stress concentration, especially for anisotropic laminates characterized by high stress concentration factors and easy drilling damaging, with significant decrease of the load-carrying capacity of the joined elements. In order to exploit the advantages of the bonded joints and those of the mechanical joints, both industrial manufacturing and research activity have been focused recently on the so called hybrid joints, obtained by the superposition of a mechanical joint to a simple adhesively bonded joint. In order to give a contribution to the knowledge of the mechanical behavior of hybrid bonded/riveted joints, in the present work a numerical-experimental study of bonded/riveted double-lap joints between aluminum and carbon fiber reinforced polymer (CFRP) laminates, has been carried out. It has permitted to highlight both the static and the fatigue performance of such joints obtained by using aluminum and steel rivets, as well as to known the particular damage mechanisms related also to the premature localized delamination of the CFRP laminate due to the riveting process.

Keywords: A. Polymer-matrix composites (PMCs) | B. Mechanical properties | C. Finite element analysis (FEA) | E. Joints/joining

Abstract: Purpose: A suture passed along the part of the graft that will be inserted into the femoral tunnel is widely used by surgeons, because it could prevent the graft sliding on the femoral fixation device during pulling from the tibial side. The aim of this study was to evaluate the biomechanical effects of suturing the intratunnel femoral part of the graft during an anterior cruciate ligament (ACL) reconstruction. Methods: Bovine digital extensor tendons and tibias were harvested from 20 fresh-frozen mature bovine knees ranging in age from 18 to 24 months. Quadruple-strand bovine tendons were passed through the tibial tunnel and secured distally with a bioabsorbable interference screw. In one half of all grafts (N = 10), the looped-over part of the graft was sutured in a whipstitch technique over a distance of 30 mm (Group 1). In one half of all grafts (N = 10), the looped-over part was left free from any suture (Group 2). The grafts were preconditioned at 50 N for 10 min, followed by cyclic loading at 1 Hz between 50 N and 250 N for 1,000 cycles. Load-to-failure test was then carried out at a rate of 1 mm/s. Results: There was no statistically significant difference between mean stiffness at pullout and yield load between the two groups. In all specimens on Group 1, failure occurred following to partial breaking and then slipping of the tendons between the screw and the tunnel. Concerning Group 2, in six cases failure occurred as described for Group 1 specimens. In the remaining four cases, failure occurred entirely through the ligament mid-substance. Conclusions: Suturing in a whipstitch fashion the femoral portion of the graft doesn't affect the mechanical proprieties of the ACL graft. When suspension fixation device is used, suturing the looped-over part of the graft could be helpful in order to provide equal tension in all of the strands of the graft at time of tibial fixation. © 2013 Springer-Verlag Berlin Heidelberg.

Keywords: ACL graft | ACL reconstruction | Anterior cruciate ligament | Biomechanics | Graft properties

Abstract: Bonded joints are highly sensitive to the presence of defects and to the degradation phenomena, and this aspect represents the primary obstacle to their use in different structural engineering applications. Delamination in a bonded joint represents, in fact, one of the primary, most common and insidious causes of damage. In this paper, a numerical-experimental study on the crack propagation along the adhesive layer of a bonded joint specimen is carried out. Experimental study is focused on the evaluation of the damage modalities of a bonded joint when the specimens are subject to fatigue load. Experimental tests are compared with the results of several numerical analysis performed in ANSYS environment. A crack growth model is implemented in the finite element method solver and allows the simulation of the progressive delamination process. Comparison between numerical results and experimental tests allows to identify the descriptive numerical parameters of fatigue crack propagation, which may be used in the structures design. © 2013 Wiley Publishing Ltd.

Keywords: bonded joint | damage models | fatigue crack propagation | FEM analysis | mixed-mode crack growth | VCCT

Abstract: The present paper proposes an experimental and a numerical analysis of the frictional effect on the mode II delamination. Frictional stresses between the crack edges can absorb and dissipate significant energy contributions in the delamination zones, especially under cyclic loading conditions. The experimental tests are performed for a set of unidirectional End-Notched Flexure (ENF) composite specimens, which are subjected to fatigue loading law with increasing mean value. The numerical analyses are performed considering a cohesive-frictional constitutive model, which is able to reproduce the transition of the interface behavior from the sound elastic condition to the fully cracked one, with only frictional strength. Finally, the numerical results are compared with the experimental ones in order to evaluate the frictional constitutive parameters. © 2013 Elsevier Ltd.

Keywords: Delamination | Fracture | Friction | Interface model | Mode II

Abstract: A drilled plate of ferromagnetic material suitably coupled by coils of enameled copper wire fed by a DC power supply to 30 V is considered in this paper. It is analyzed with finite element and later experiments are performed to validate the obtained results. After polishing the plate, two strain gauges for measuring the deformation along the x axis and along the z axis are installed. The values of strain are 5 μm/m in z direction and -2 μm/m in x direction. The experimental-numerical comparison shows that the laboratory results are lower than numerical, while signs and orders of magnitude are the same. It is concluded that the results of the FEM analysis can be considered acceptable because the orthogonality of the plane of the coils relative to the plane of the plate and because of the packing coefficient of copper. The position of the two coils is changed in order to found the optimal configuration which allows the maximum compressive stresses in the area around the hole; it is obtained using two coils joined (positioned above the hole) or using a single coil. Moreover numerical simulations are executed to verify the improvement of the fatigue life calculating the stress at the crack tip. © 2013 Elsevier Ltd. All rights reserved.

Keywords: Drilled plates | Induced strain | Induced stress | Magnetic induction | Magnetoelastic behavior

Abstract: In offshore applications and moreover in transports from ship-to-ship, the needs of highly sophisticated motion compensation solution are increasing. They consist of sensors, actuators and control units. To design the best mechatronic solution, it is necessary modeling the mechanical system in order to identify the transfer function and the dynamic behavior of the system. Currently Active Heave Compensation Systems are widely used in order to compensate for heave vessel motion, between a vessel moving under sea state and a fixed base or vice versa. Several research projects are ongoing in order to develop solutions able to compensate undesired movements also in ship to ship offloading operations especially in defense and military area in ship to ship operations. In this work we present an application of multibody modeling in Matlab/Simulink platform to simulate the dynamic behavior of Mother-Feeder ships during thansfer made by a marine crane, installed on Mother ship. In particular it will be payed attention on the dynamic quantities like position, velocity and acceleration needed to compensate for heave load movement.

Abstract: Currently, directional and stability control systems (rudders and flaps) of high speed craft (HSC) are made by heavy steel box-shaped elements. This is mainly caused by the high hydrodynamic stresses applied on these elements due to the high cruising speed of HSC. In order to reduce the weight of these elements and to increase the resistance to external corrosive action, innovative manufacturing technologies and new materials are studied. In this paper, innovative hybrid steel-composite rudder are presented to use in high speed craft.

Abstract: Composite materials have increasingly become more common in ground transportation. As this occured thicker panels, as compared to composite panels used in aviation, become necessary in order to withstand high impact loads and day to day degradation. The effectiveness of these panels was often limited by the strength of the joint in which the panel was attached to the frame of the vehicle. Investigating methods of reducing strain concentrations within these joints would increase the effectiveness in using composite materials in ground transportation applications by increasing the load necessary for joint failure to occur. In this study, fiber optic strain gages were embedded in a composite panel along the bearing plane of a thick, single-lap, bolted joint. The gages allow for the strain profile above the hole to be determined experimentally. Several clearance values were then implemented in the bolt to determine their effect on the strain concentrations. Strain increased at every gage, by nearly the same proportion, when clearance was increased from zero to three percent. When clearance was further increased to five percent strain only continued to increase at gages three and four, with one and two remaining similar in value to what was seen at three percent clearance. Ultimately, like in thin composite panels, the zero percent clearance condition was the stiftest. ©2010 Society for Experimental Mechanics Inc.

Abstract: Composite materials have increasingly become more common in ground transportation. As this occured thicker panels, as compared to composite panels used in aviation, become necessary in order to withstand high impact loads and day to day degradation. The effectiveness of these panels was often limited by the strength of the joint in which the panel was attached to the frame of the vehicle. Investigating methods of reducing strain concentrations within these joints would increase the effectiveness in using composite materials in ground transportation applications by increasing the load necessary for joint failure to occur. In this study, fiber optic strain gages were embedded in a composite panel along the bearing plane of a thick, single-lap, bolted joint. The gages allow for the strain profile above the hole to be determined experimentally. Several clearance values were then implemented in the bolt to determine their effect on the strain concentrations. Strain increased at every gage, by nearly the same proportion, when clearance was increased from zero to three percent. When clearance was further increased to five percent strain only continued to increase at gages three and four, with one and two remaining similar in value to what was seen at three percent clearance. Ultimately, like in thin composite panels, the zero percent clearance condition was the stiffest. © 2010 Society for Experimental Mechanics Inc.

Abstract: Bolted joints involving composite plates used to be almost entirely dedicated to aerospace applications. As the need for energy conservation has increased, the field of composite bolted joints has found new applications in ground armoured vehicles. Thick panels able to withstand large in-plane and impact loads are critical. The present investigation evaluates the interior strain field, through the thickness, of a composite plate connected to an aluminium panel with a single-lap bolted joint. The area of interest is the bearing plane region close to the hole because of the presence of stress concentrations that heavily modify the stress field. Experimental data for the bolted joint were recorded by fibre-optic strain gauges that were embedded in the bearing plane of the composite plate. Numerical analyses were performed using ANSYS as a pre-processor and LS-DYNA as a solver. The overall goal was to evaluate the magnitude of contact strains around the hole and through the thickness of the composite. These values were analysed and compared with the finite-element method results: the finite-element analysis correlated reasonably well with the experiments. An investigation of error causes was also carried out, in particular to evaluate the influence of incorrect gauge positioning and the effect of friction coefficients. General design considerations were finally provided, based on the complete three-dimensional finite-element analysis.

Keywords: ANSYS | bolted joint | composite materials | FEM | fibre-optic strain gauge (FOSG) | LS-DYNA

Abstract: This paper presents the results of an extended method of measurement on a tyre for an off-road vehicle 175/82 R16, inserting Prescale paper at the contact with the ground. The experimental analysis of the pressures is carried out, in a cross-sectional direction, in five zones corresponding to the middle of the single dowels that constitute the tread. The results are analysed by means of suitable software so as to refer easily to the value of the pressure. The obtained results are critically analysed and the results are compared with those obtained by the formulae of Rowland and MacLaurin, and by the nominal pressure at the ground, concluding that the expression of MMP for vehicles on wheels is simply to consider a pointer of the performances, in comparison with other vehicles or wheels, rather than a real prediction of the pressure on the ground. Furthermore, a good agreement is found between the tyre deflection calculated and measured experimentally. © IMechE 2009.

Keywords: Behaviour of the tyre | MMP | NGP | Prescale paper

Abstract: The propagation of an interface crack subjected to mixed mode I/II was investigated for two 2024-T351 aluminum thin layers joined by means of DP760 epoxy adhesive produced by 3M©. On the basis of beam theory, an analytical expression for computing the energy release rate is presented for the mixed-mode end loaded split (MMELS) test. The analytical strain energy release rate was compared by finite element (FE) analysis using the virtual crack closure technique (VCCT). Several fatigue crack growth tests were carried out in a plane bending machine to compare the experimental energy release rates to those of the analytical and FE solutions. Experimental results showed the relationship between the delamination modality and initial crack length rather than the applied load. The crack growth behavior showed stable crack growth followed by rapid propagation at the interface with the adhesive layer. © 2008 Elsevier Ltd. All rights reserved.

Keywords: Adhesive joint | Crack growth | Interface crack | MMELS specimen | Virtual crack closure technique

Abstract: The purpose of the work is the realization of a composite material with long glass fibers having better characteristic than a fiber random composite, to permit the reduction of weight and costs to shipyards for pleasure craft. Structural optimization is performed by ANSYS for the choice of the layers disposition to obtain the maximum stiffness with minimum material employment, saving weight. The study is centered on the research of the better configurations of plies packing in relation of pure shear stress for four different plies. Unidirectional plies, both symmetric orthotropic and symmetric non-orthotropic ones, are realized successively by the vacuum bag technique. Experimental tests of traction, bending, inter laminar shear and pure shear are executed to characterize the three different type of material. Experimental results are compared to ones obtained numerically to validate the procedures; the comparison with the analytical results permitted to attribute an adequate value to shape factor of the fibers. In all the cases the optimization permitted the construction of much more resistant plies than random ones, with a lower thickness. © 2008 Springer Science+Business Media B.V.

Keywords: Composite material test | Random composite | Structural optimization

Abstract: The onset and propagation of interlaminar defects is one of the main damage mechanisms in composite materials. This is even more the case when considering layered materials comprising metallic laminae (typically Aluminium) and FRP laminae. Propagation of delamination mainly depends on the initial crack extension and its loading mode. This work presents some results of a combined analytical-numerical-experimental study on the onset and propagation mechanisms regarding interlaminar defects. Two cases have been analysed in particular, the first consisting of a glass-fibre reinforced epoxy resin laminate, and the second consisting of a hybrid laminate where a lamina of aluminium is layered between FRP laminae. © 2006 Elsevier Ltd. All rights reserved.

Keywords: Composite materials | Dissimilar mixed mode bending specimen | Fracture toughness