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This work deals with the development of an improved numerical model, based on the explicit finite element method, aimed at investigating the energy absorption capabilities of a full-scale composite...

In this paper, a vertical drop test of a full composite fuselage section of a regional aircraft has been presented. This test was performed to investigate the structural response of a prototype of a composite fuselage section as well as the biomechanical response of the anthropomorphic dummies under a vertical crash loading condition. The research activity, carried out within the framework of Metodi di CERtificazione e Verifica Innovativi ed Avanzati (CERVIA) project, allowed collecting suitable amount of data for the assessment of the reliability of numerical models. The test article consists of a composite fuselage section with a diameter of 3445mmand a total length of 4750mm.It includes all main structural components, the passengers, and the cargo floor structure. Fuselage section has been also equipped with an aeronautical three-seat row. The accelerations, recorded in different locations, demonstrate that the structure is able to absorb a considerable impact energy amount, thus to mitigate the acceleration levels induced to the passengers.

It is well known that composite materials are founding increasing applications in the transport field thanks to their high strength to mass ratio. However, their use in primary structures is very challenging because of their high sensitivity to in-service damages and manufacturing defects. As a result, the current adopted damage tolerance approach leads to the oversizing of such structures. Structural health monitoring systems, aimed to the real time damage detection, can provide several benefits in terms of lightweight of the structures, maintenance operations and inspection costs. This paper deals with the use of the Probability Ellipse (PE) method, based on the propagation of ultrasonic guided waves on a composite winglet of a small aircraft. The PE method estimates the probability of the presence of the damage in the monitored area, starting from the knowledge of selected damage indexes for each sensors-path. The winglet, equipped with piezoelectric sensors, usable as both actuating and receiving devices, has been numerically and experimentally investigated under several configurations, varying the actuator location. Sensitivity analysis has been performed to assess the effectiveness of the PE method. The accuracy of the PE method in detecting both location and damaged area is herein discussed.

The contribution collects and illustrates "creative" methodological and design paths in the sectors of mobility and transport where design, biology, material technologies and bioengineering cooperate in a synergistic and proactive way for configurating new systems for fixing vehicles’ interior components. The aim has been to reduce the tolerance of human error during assembly by using innovative technological and material solutions and the conscious study of biological and biomechanical processes present in nature. In order to articulate the research activities, parameters have been identified and defined according to the requirements of the workers during the preparation and fixing of the components, according to the principles of safety, good design and material optimization. From the identification and literature survey of the patent documents and from the structural, material, feasibility and reliability assessments of the current installation procedures, critical issues related to stress, safety, times of installation and assembly and disassembly of the components have been carried out. Therefore, innovative biomimetic concept-solutions have been developed for the definition of architectures and fixing systems through an in-depth observation of the biological heritage, based on the organic integration of form, function, and processes. The path allowed the acquisition of specific knowledge and interdisciplinary skills to plan tangible results useful for optimizing, innovating and strengthening the design process from various industrial sectors such as engineering, aerospace, automotive, medical and pharmaceutical packaging.

The paper deals with numerical and experimental investigations aimed to develop a Finite Element (FE) model for predicting wave propagation in a blended composite winglet . Material anisotropy , inhomogeneity , multi-layered configuration and complex geometries tend to increase the complexity of the wave propagation phenomena and consequently the development of established FE models. Moreover, even if 2D finite elements seem to be not appropriate for modelling guided waves propagation , especially for complex anisotropic structural components, they are more attractive than 3D ones, because of the computational cost saving. For this reason, part of the presented research activity is addressed to investigate the efficiency of shell finite elements in modelling guided waves propagation in a such complex structure as a winglet. The development of an efficient model depends also on the numerical characterization of the medium within which guided waves propagate through. As a consequence, preliminary simple experimental bending and modal tests have been carried out to support the material properties modelling. Subsequently, guided wave propagation FE analyses were performed and the results compared with provided experimental data. A good agreement between numerical and experimental results of the different analyses has been achieved in terms of both signal time of flight and amplitudes.

According to the international literature postures, exerted forces, manual handling and repetitive actions with upper limbs must be considered in order to estimate the workers’ exposure to biomechanical overload risk, but also a preventive ergonomic approach in the design phase is possible. Within the Industry 4.0, the digitalisation of manufacturing processes generate benefits in terms of production costs and time. Regarding the ergonomics, it is possible to set up a predictive model for the evaluation of biomechanical overload risk. This paper proposes an appraisal of a workplace design and ergonomics validation procedure based on simulation: data from assembly tasks simulation of Digital Human Models (DHM) can be used to assess the ergonomic indexes (OWAS, NIOSH, OCRA, EAWS, etc.). So, it is possible to preventively solve ergonomic risks during the design phase. A test case, regarding a real workplace of an assembly line of an important automotive Company, is also presented.

In the present work two different crash scenarios have been numerically investigated in order to evaluate the structural behaviour of a full-scale composite made fuselage section of a regional aircraft under dynamic load conditions. The developed Finite Element model has been validated with respect to the experimental results obtained during a test campaign performed at Italian Aerospace Research Centre (CIRA). The reference experimental test consisted in a 4.26 m vertical drop with an impact velocity equal to 9.14 m/s. Starting from the FE model validated respect to the pure vertical drop test condition, in this work, a new impact scenario onto a rigid surface has been simulated applying both horizontal and vertical velocity components, resulting in an overall impact speed of 22 m/s. The FE explicit solver LS-DYNA® has been used to perform the simulation. The results, in terms of global deformations, failures and local accelerations, have been compared with the numeric pure vertical drop test ones in order to evaluate how more complex impact conditions could influence the structural behaviour of the fuselage section with a focus of improved crashworthy components in Certification by Analysis (CbA) point of view.

Since the early development for health purposes in 1950s, motion tracking systems have been strongly developed for several applications. Nowadays, using Micro Electro-Mechanics Systems (MEMS) technologies, these systems have become compact and light, being popular for several applications. Looking at the manufacturing industry, such as the automotive one, ergonomic postural analyses are a key step in the workplaces design and motion tracking systems represent fundamental tools to provide data about postures of workers while carrying out working tasks, in order to assess the critical issues according to ISO 11226 standard. The aim of this work is to present an experimental wearable inertial motion tracking system, developed at the Dept. of Engineering of the University of Campania “Luigi Vanvitelli” in collaboration with Linup S.r.l., composed by several low-cost inertial measurement units (IMU). The system allows to estimate the orientation of selected human body segments and to analyze the postures assumed during the working tasks. To increase the flexibility of use, the system is highly modular: it’s composed by 4 independent modules in full-body configuration, each one made of 3 or 4 inertial units. In this paper, the overall system is presented, supported by several test cases, carried out in Fiat Chrysler Automobile (FCA) assembly lines, to test the system reliability in industrial environments. Furthermore, an automatic posture analysis code is presented to evaluate the postural critical issue of the workplaces.

In the era of Industry 4.0, several advantages for industries come by the implementation of new technologies that play a key role for improving production processes, focusing on working times, product quality, accuracy of operations and other important parameters of the production systems. In order to evaluate these parameters, simulation may be used as a tool to verify (i) the improvement adopted on existing production lines or (ii) the design solutions adopted for a new line, optimizing the processes. The aim of this paper is to investigate the possibility to assess the before said parameters in a specific case study by implementing a Discrete Event Simulation (DES). The study concerns two consecutive workplaces of an automotive assembly line in which three workers are involved in assembly activities. The results demonstrated that the Digital Manufacturing (DM) approach and simulation may be used for verifying the performances of the line, thanks to the evaluation of important parameters, such as the Overall Equipment Effectiveness (OEE).

This paper deals with the development of an established hybrid finite element multibody (FE-MB) model for the simulation of an experimental sled test of a single row of a double passenger seat placed in front of a fuselage bulkhead, by considering a single anthropomorphic Hybrid II 50th dummy arranged on one of the seat places. The numerical investigation has been carried out by focusing on the passenger passive safety. Specifically, the occupant injury assessment has been quantitatively monitored by means of the head injury criterion (HIC), which, based on the average value of the dummy head acceleration during a crash event, should not exceed, according to the standards, the value of 1000. Numerical results provided by the hybrid model have been compared with the experimental ones provided by the Geven S.p.A. company and with the results carried out by a full FE model. The hybrid model simulates with a good level of accuracy the experimental test and allows reducing significantly the computing time with respect to the full FE one.

The improvement of the current design practice, especially for conventional materials, has allowed the production of structures able to better tolerate the presence of cracks and, in general, damages under the in-service loading conditions. As a result, especially in the aerospace field, nowadays, the damage tolerance philosophy is the core of the current design practice. However, conversely to the conventional materials, composite materials still cannot count on established prediction models supporting the damage tolerance approach. Among the critical damages which could affect composite materials, BVIDs (Barely Visible Impact Damages) due to accidental Low Velocity Impact (LVI) phenomena play a critical role. Since they cannot be easily detectable during the inspection intervals, in order to fulfil the damage tolerance targets, large safety factors are applied during the design current practice, resulting in the oversizing of the structure. For these reasons, Structural Health Monitoring (SHM) techniques are being widely used for the improvement of the current design practice, allowing the damage detection. Thanks to the possibility to assess the structural health during the in-service loading conditions, Lamb waves, among the several non-destructive testing (NDT), appear to be the best candidate for damage detection. Studies on this topic are never enough and the literature cannot still count on a Finite Element (FE) procedure able to simulate Lamb wave propagation on LVI damaged plates. This work deals with a FE procedure, developed by using the FE code Abaqus v.6.14®, for the simulation of the interaction between ultrasonic guided waves and LVI damages in composite laminates, whose damages have been modelled by means of Hashin criteria in a previous impact simulation.

In the Industry 4.0 and digital revolution era, the world of manufacturing industry is experiencing an innovative reconfiguration of design tools and methodologies, with a different approach to the production processes organization. The design philosophy is changing, integrating to engineering contribution interpretative aspects (design thinking), executive practices (design doing) and cognitive aspects (design cultures). The design becomes human–centered. The new Virtual Reality technologies allow to validate performances of designed products and production processes by means of virtual prototypes in a virtual simulated environment. This approach generates several benefits to the companies, in terms of costs and time, and allows optimizing the assembly line design and related workplaces, by improving workers’ benefits too. This paper proposes an innovative method to validate the design of workplaces on automotive assembly lines in a virtual environment, based on ergonomic approach, according to ERGO – Uas system, applied by FCA (Fiat Chrysler Automobiles) groups, that integrates UAS method for measurement and EAWS method for biomechanical effort evaluation. Creating 3D virtual scenarios allows to carry on assembly tasks by virtual manikins in order to be evaluated from different points of view. In particular, data coming from the simulation can be used to assess several ergonomic indexes, improving safety, quality and design. The analysis is supported by the use of a motion capture system, developed by the University of Campania and composed of wearable inertial sensors, that estimates the attitude of fundamental human segments, using sensor fusion algorithms based on Kalman filtering. In this way, it is possible to make a further design validation, assessing the EAWS index basing on posture angles trends evaluated. This method can represent an innovation for human-centered design of workplace in developing new products, reducing costs and improving job quality.

The paper deals with dynamic tensile tests on Carbon Fibre Reinforced Polymer – CFRP laminates. As a result of their viscoelastic nature, plastics exhibit rate dependence in their stress-strain response. The need to develop failure criteria to determine the dynamic failure stress for composite material under dynamic loading conditions is a current challenge for the research community. The main goal of such paper is to assess the efficiency of the analytical models provided by literature to predict the strain-rate effects on composite coupons tensile strength. Moreover, experimental tests have been performed in order to evaluate the mechanical behaviour of different stacking sequences at different strain rate.

The optimization of production processes has always been one of the cornerstones for manufacturing companies, aimed to increase their productivity, minimizing the related costs. In the Industry 4.0 era, some innovative technologies, perceived as far away until a few years ago, have become reachable by everyone. The massive introduction of these technologies directly in the factories allows interconnecting the resources (machines and humans) and the entire production chain to be kept under control, thanks to the collection and the analyses of real production data, supporting the decision making process. This article aims to propose a methodological framework that, thanks to the use of Industrial Internet of Things&mdash, IoT devices, in particular the wearable sensors, and simulation tools, supports the analyses of production line performance parameters, by considering both experimental and numerical data, allowing a continuous monitoring of the line balancing and performance at varying of the production demand. A case study, regarding a manual task of a real manufacturing production line, is presented to demonstrate the applicability and the effectiveness of the proposed procedure.

This paper deals with the redesign of an aircraft passenger seat, placed at the first seat row, which was not compliant with Federal Aviation Regulations FAR 25.562 “Emergency landing dynamic conditions” regulation (due to a high value for the Head Injury Criterion (HIC)) and related guidelines. Starting from an accurate analysis of some results obtained via an experimental seat sled test, a numerical procedure was developed in order to improve the passenger safety with respect to head injury. Specifically, the proposed numerical procedure, using the advantages of a Finite Element (FE) model and a Design of Experiment (DoE) approach for simulation modeling, was aimed at identifying a new design solution to avoid the impact between the passenger’s head and the bulkhead. The redesign of the passenger seat was validated against an experimental test carried out at Geven S.p.A. Company by demonstrating, consequently, the compliance of the modified seat-belt system with the regulations.

This study used the Finite Element (FE) method to numerically analyze the thermo-mechanical behavior and residual stresses in dissimilar welded T-joints. Residual stresses induced by the fusion arc-welding of steel joints in power generation plants are a concern to the industry. The structural integrity assessment of welded structures requires the consideration of weld-induced residual stresses for the safe operations in power plants, which may be compromised by their presence. Details on the used thermo-mechanical FE model and the results analysis are herein presented.

The certification of aircraft seats involves the investigation of the structural performance of their components under emergency landing conditions. . The paper reports the activities related to an experimental sled-test of a single row of two seats placed in front of a stiff fuselage bulkhead, by considering a single anthropomorphic dummy arranged on one of the seats. Tests have been developed at the facility equipped with a sled decelerator testing system compliant with certification requirements from FAR25 for TSO C127a regulations. Four different numerical models have been developed in order to simulate the experimental test: a full-FE modelby LSTC-LsDyna® code, a full-MB modeland a hybrid FE/MB developed using by TNO-Madymo® code and a Coupled FE/MB model. Numerical results achieved by these models have been compared with experimental ones, in order to assess their use for CBA (certification by analysis) purposeto be applied since the preliminary design phase of the seat.

Laminated composite plates are widely used in the aerospace field, the prediction of their residual life is a interesting challenge for research communities. Their structural behaviour could be affected by several rupture mechanisms due to exercise loading conditions. One of the most critical is the low velocities impacts with different impact energies. This paper deals with an experimental test program performed in order to validate a numerical model developed by using finite element method. All experimental tests were carried out under international standard ASTM D7136 while all numerical tests were carried out by use of a worldwide numerical code Abaqus®. Inter-laminar and intra-laminar rupture mechanisms were taken into account and special-purpose elements were used. Rupture criteria were implemented in the numerical models thanks to their functional ease; results of numerical-experimental comparison were presented and discussed.

Purpose This paper aims to investigate the role of Smart Technologies and Big Data as relevant dimensions in affecting the emerging social and economic dynamics of society with the aim to trace possible guidelines and pathways for decision makers and researchers interested in the governance of the Smart City’s ecosystem. The increasing attention to the domain of technologies and the amazing scenario that is emerging as a consequence of the influence of Smart Technology and Big Data in everyday life require reflection upon the ways in which the world is changing. Design/methodology/approach The paper adopts the interpretative lens provided by the systems thinking to investigate the challenging domain of the Smart City. A qualitative and interpretative approach is adopted to reflect upon the role of technologies in everyday life. Findings The Smart City ecosystem is defined as a multilevel construct useful for understanding how technical and technological dimensions of the Smart City can be managed not only as supportive instruments but also as key pillars to support, facilitate and ensure an effective cognitive alignment among all the involved actors. Originality/value This paper provides a tangible evidence of the systems thinking contribution in analysing, understanding and managing dimensions and paths of social dynamics. A contribution to previous studies is provided with reference to systems thinking, Big Data and Smart City.

The research reported in this paper was aimed mainly to investigate the different NDE techniques on specimens made by a new process labeled as "pulsed infusion", very crucial for voids content under critical loading conditions. The impact load, in fact, is critical for composite laminates due to their anisotropy, in particular in extreme temperature conditions due to their brittleness. An additional and very relevant aim was to collect a large number of experimental results to supply useful information for the numerical models needed to simulate the dynamic behavior of composite laminates. At the aim to investigate the response under dynamic loads of laminates fabricated by a new vacuum assisted technology labeled as "pulsed infusion", rectangular carbon fiber composite specimens were subjected to low velocity impact tests. Experimental tests up to complete penetration and at different energy levels, were carried out by a modular falling weight tower. All the parameters related to the phenomenon, like penetration energy, maximum force and indentation depths, were used to validate existing semi-empirical and numerical models. The largely used ultra sound technique (US) was adopted to investigate the delamination together with the thermo graphic technique. The results of the measurements were compared with data obtained on the same specimens by holographic analysis (ESPI). One of the scope was to investigate the crucial internal impact damage and assess the ability of an unconventional ND system (ESPI) in giving right information about non-visual damage generated inside composite laminates subjected to dynamic loads. Moreover, some of the specimens were cut to allow the fractographic analysis. The efficiency of the above mentioned new fabrication technology was studied also comparing the results with measurements from literature on impacted autoclave cured laminates. By the comparison between the results, good agreements were found denoting the efficiency and the applicability of the new fabrication and the used NDE methods. © 2015 Elsevier Ltd. All rights reserved.

Among Non-Destructive Testing, guided ultrasonic Lamb waves are particularly suitable for Structural Health Monitoring (SHM) applications for composite structures because of their sensitivity to damage. This paper presents a numerical simulation technique for guided waves propagation in damaged composite laminates by using the finite element code Abaqus®. The damage modeling has been achieved by lowering the elastic material properties of the area affected by damages. Lamb waves propagation have been performed on both undamaged and damaged laminate, in order to investigate the detection criteria. In particular, the influence of different parameters such as the shape, size and extend of damage on the damage reflected wave has been studied.

The Electron Beam Melting (EBM) is an Additive Layer Manufacturing (ALM) technique used to directly manufacture 3D functional parts from metal powder, selectively melted, layer by layer, by an electron beam according to a geometry defined by a CAD model. The EBM technology allows benefitting from countless advantages: material waste reduction, easy manufacturing of complex shapes, lead time reduction, etc; on the other hand the EBM process is typically associated with lower resolutions and higher surface roughness (Ra = 25–30 μm) compared to similar laser based powder bed metal processes. Therefore the surface morphology may be a critical issue for the structural integrity of components made in EBM and used in-service in their “as built” condition, i.e. with the characteristic surface released by the process. This study evaluates surface morphology and tensile properties of Ti6Al4V specimens of varying nominal thickness (1–5.0 mm), made by using EBM process with a layer thickness of 50 μm. The aim is therefore to investigate how the surface morphology and the tensile properties are affected by the nominal thickness of the component.

In the era of Industry 4.0, automation plays a key role in improving manufacturing production processes in terms of working times, accuracy of operations, products’ quality, and so on. With focus on the working tasks on composite components, drilling and riveting operations require particular attention due to the possibility of damage to the final product, especially when they are executed manually. To reduce these kinds of risks, the introduction of a robot in the working area could represent an improvement to speed up the processes and to ensure a better quality result. It is worth noting that human intervention remains necessary for carrying out a part of the sub-tasks, especially in the case of composite assembly procedures. This paper aims at presenting a case study about the drilling and riveting operations on a composite aircraft fuselage whose working cell is characterized by the coexistence of a human and a robot. Moreover, the implementation of a numerical simulation allows validating the working cycle and the adopted solutions in terms of ergonomic performance.

The paper deals with the development of a Finite Element (FE) model aimed to simulate the propagation mechanisms of guided waves in a complex composite structure, such as a blended Glass Fibre Reinforced Polymers (GFRP) winglet, for real-time damage detection and monitoring purposes. The reliability of the herein presented FE model has been assessed against an experimental tests campaign, involving the winglet under both reference/pristine configuration and impacted/damaged configuration, also changing the actuator location. Because of the good level of accuracy shown by the numerical-experimental comparisons, the FE model has been used also for numerically investigating new actuators and damage position configurations, not experimentally analysed. Damage Indexes (DI’s) have been calculated to quantify the variations of the signals’ amplitude caused by the induced damage. Moreover, the Probability Ellipse (PE) method, which estimates the probability of the presence of the damage in the monitored area starting from the knowledge of selected DI’s for each sensors-path, has been used in both older and newer damage position. The accuracy of the PE method in detecting the damage location is herein discussed.

In this paper, a multibody calculation methodology has been applied to the vibration analysis of a 4-cylinder, 4-stroke, turbocharged diesel engine, with a simulation driven study of the angular speed variation of a crankshaft under consideration of different modeling assumptions. Moreover, time dependent simulation results, evaluated at the engine supports, are condensed to a vibration index and compared with experimental results, obtaining satisfactory outcomes. The modal analysis also considers the damping aspects and has been conducted using a multibody model created with the software AVL/EXCITE. The influence of crankshaft torsional frequencies on the rotational speed behavior has been evaluated in order to reduce the vibration phenomena. The focus of this work is related to industrial aspects since, for an existing and commercialized engine, a numerical and experimental complex study has been performed to enable design improvements aimed at reducing noise and vibrations. Existing procedures and algorithms are combined here to reach the abovementioned objectives in the most efficient way.

Lamb waves based Structural Health Monitoring (SHM) systems, thanks to their high sensitivity to damage detection and the ability to travel over a long distance with low power consumption, are founding increasing industrial applications, especially in the aerospace field, where airworthiness authorities require that composite materials in primary structures must remain undamaged during the in-service life. In order to tolerate damage and monitor its severity and, consequently, to repair the structure only when strictly needed, the use of SHM systems appears to be an efficient solution providing benefits for the current design practice. The continuous assessment of the structural integrity, which can be accomplished by SHM systems, can play a key-role to achieve a less-conservative design as well as to facilitate maintenance operations. This paper deals with a sensitivity analysis, based on the Finite Element (FE) theory, aimed to investigate numerically the influence of the damage orientation on the damage detection capability of a Lamb waves based SHM system arranged on a damaged Glass Fiber Reinforced Polymer composite winglet. Damage detection sensitivity has been measured by analyzing the interaction between the modelled damages and guided waves under a specific central frequency. Signals recorded at different locations by piezoelectric sensors have been compared with the baseline signals achieved under a pristine configuration of the winglet by means of a damage index. A specific trend of the considered damage index has been found out as function of the damage orientation.

In the aircraft industry, the use of fiber reinforced materials for primary structural components over metallic parts has increased up to more than 50% in the recent years, because of their high strength and high modulus to weight ratios, high fatigue and corrosion resistance. Currently, the need of lowering weight and fuel consumption is pushing the world’s largest aircraft manufacturers in the design and building of structures entirely made of composites. Fuselage structure plays an important role in absorbing the kinetic energy during a crash. Through the deformation, crushing and damage of fuselage sub-floor structure, a survivable space inside the cabin area should be preserved during and after a crash impact in order to minimize the risk of passengers’ injuries. In this work, a Finite Element (FE) model of a full-scale 95% composites made fuselage section of a regional aircraft under vertical drop test is presented. The experiment, conducted by the Italian Aerospace Research Centre (CIRA) with an actual impact velocity of 9.14 m/s in according to the FAR/CS 25, has been numerically simulated. Two ATDs (Anthropomorphic Test Dummies), both 50th percentile, seats and belts have been modelled to reproduce the experimental setup. The results of the simulation, performed by using LS-DYNA® explicit FE code, have been validated by correlation with the experimental ones. Such comparisons highlight that a good agreement has been achieved. The presented FE model allows verifying the structural behavior under a dynamic load condition and also estimating the passive safety capabilities of the designed structure. Since the experiment is expensive and non-repeatable, a FE model can be used for Certification by Analysis purposes since, if established, it is able to virtually demonstrate the compliance to the airworthiness rules.

This paper deals with a numerical investigation, based on the Finite Element (FE) theory, of a Structural Health Monitoring (SHM) system for a large radio-telescope, aimed to damage detection and location. The investigated SHM system is based on the comparison of the Frequency Response Functions (FRFs) achieved under both pristine and damaged configurations, respectively. A preliminary study has been carried out in order to achieve information on the optimal sensors locations. As a result, the structural response of the radio-telescope under the in-service loading conditions has been numerically investigated. All FE analyses have been carried out by means of MD Nastran® code.

The structural behaviour of a single-lap hybrid (bonded/bolted) composite joint subjected to a tensile external load was evaluated by means of the Finite Element Method (FEM). In particular, the distribution of stresses acting in its adhesive layer was compared with that relative to the case of a simply adhesive bonded joint. Furthermore, the load transferred by the bolt was determined at different characteristics of the adhesive and of the applied external tensile load, corresponding to both single and double bolt configuration. The obtained values were in turn compared with experimental data found in literature, so validating the produced numerical simulations.

Usually during the design of landing gear, simplified Finite Element (FE) models, based on one-dimensional finite elements (stick model), are used to investigate the in-service reaction forces involving each subcomponent. After that, the design of such subcomponent is carried out through detailed Global/Local FE analyses where, once at time, each component, modelled with three-dimensional finite elements, is assembled into a one-dimensional finite elements based FE model, representing the whole landing gear under the investigated loading conditions. Moreover, the landing gears are usually investigated also under a kinematic point of view, through the multibody (MB) methods, which allow achieving the reaction forces involving each subcomponent in a very short time. However, simplified stick (FE) and MB models introduce several approximations, providing results far from the real behaviour of the landing gear. Therefore, the first goal of this paper consists of assessing the effectiveness of such approaches against a 3D full-FE model. Three numerical models of the main landing gear of a regional airliner have been developed, according to MB, “stick,” and 3D full-FE methods, respectively. The former has been developed by means of ADAMS® software, the other two by means of NASTRAN® software. Once this assessment phase has been carried out, also the Global/Local technique has verified with regard to the results achieved by the 3D full-FE model. Finally, the dynamic behaviour of the landing gear has been investigated both numerically and experimentally. In particular, Magnaghi Aeronautica S.p.A. Company performed the experimental test, consisting of a drop test according to EASA CS 25 regulations. Concerning the 3D full-FE investigation, the analysis has been simulated by means of Ls-Dyna® software. A good level of accuracy has been achieved by all the developed numerical methods.

Among the most promising models introduced in recent years, with which it is possible to obtain very useful results for a better understanding of the physical phenomena involved in the macroscopic mechanism of crack propagation, the one proposed by Gurson and Tvergaard links the propagation of a crack to the nucleation, growth and coalescence of micro-voids, which is likely to connect the micromechanical characteristics of the component under examination to crack initiation and propagation up to a macroscopic scale. It must be pointed out that, even if the statistical character of some of the many physical parameters involved in the said model has been put in evidence, no serious attempt has been made insofar to link the corresponding statistic to the experimental and macroscopic results, as for example crack initiation time, material toughness, residual strength of the cracked component (R-Curve), and so on. In this work, such an analysis was carried out in a twofold way: the former concerned the study of the influence exerted by each of the physical parameters on the material toughness, and the latter concerned the use of the Stochastic Design Improvement (SDI) technique to perform a “robust” numerical calibration of the model evaluating the nominal values of the physical and correction parameters, which fit a particular experimental result even in the presence of their “natural” variability.

The aim of this paper is to understand the effects of the damage criteria modelling on the training phase (performed by means of Finite Element simulations) of an artificial neural network (ANN) enabled to locate impacts onto a CFRP laminate. The developed FE models have been also used to investigate the intra-laminar damage mode, which, among different ones, has the most effects on the residual strength of the panel.

The investigation of the mechanical response of fibre-reinforced composite laminates under impact loads can be very difficult due to the occurrence of simultaneous failure phenomena. Indeed, as a consequence of low velocity impacts, intra-laminar damages, like fibre and matrix cracking, and inter-laminar damages, such as delaminations, can take place simultaneously. These damage mechanisms can lead to significant reductions in strength and stability of the composite structure. In this paper a joint numerical-experimental study is proposed which, by means of non-destructive testing techniques (Ultra-sound and thermography) and non-linear explicit FEM analyses, aims to completely characterise the impact induced damage in composite laminates under low velocity impacts. Indeed the proposed numerical tool has been used to improve the understanding of the experimental data obtained by Non-Destructive Techniques. Applications on samples tested according to the AECMA (European Association of Aerospace Manufacturers) prEn6038 standard at three different impact energies are presented. The interaction between numerical and experimental investigation allowed to obtain an exhaustive insight on the different phases of the impact event considering the inter-laminar damage formation and evolution.

The mechanical response of reinforced composite structures under impact loads is particularly challenging owing to the rising of multiple and simultaneous failure phenomena. Indeed, low velocity impacts may produce intra-laminar damages, like fibre breakage and matrix cracking, and inter-laminar damages, such as delaminations and skin-stringer debonding. As already remarked, these failure phenomena often take place simultaneously, leading to a significant reduction in strength and stability of the composite components. In this paper, the behaviour of stiffened composite panels, with omega shaped stringers, under low velocity impacts is numerically investigated by means of non-linear explicit FEM analyses. Different impact energy levels are considered and correlation with experimental data is provided, in terms of impact force, displacement and energy. A sensitivity analysis has been performed to investigate the influence of numerical models’ approximations on the accuracy of the obtained numerical results. Models with an increasing level of damage simulation details have been adopted to study the effects of combined and separated intra-laminar and inter-laminar failures providing an interesting insight on the modelling requirements for an accurate simulation of the investigated phenomena.

This qualitative paper aims to point out the incidence of small world characteristics in the World Wide Web. To this end, some theoretical implications of small world theory (SWT) are verified using information from focus groups and in-depth interviews administered to experts and users of the World Wide Web. The purpose of this study is to investigate whether it is possible to apply small world properties to online social networks while pointing out the key variables of website centrality in that context. Building on this, the paper traces possible contributions for better management of the World Wide Web in terms of the professional use of social media to facilitate information or product and service sharing. The results of the proposed investigation highlight some pivotal aspects of small world properties on the web, as well as on website centrality. The findings are relevant for the application of social media marketing (SMM) and search engine optimisation (SEO).

When simulating, by FE analyses, the mechanical behavior of complex structures, different degrees of mesh refinement or different element formulations may be needed throughout the structure. Indeed, depending on the geometrical configuration of the structure and on its response in terms of stress distributions to the applied loading conditions, some regions may need to be represented by an increased number of elements, or by elements of higher order to guarantee the desired accuracy in results. When dealing with such complex structures, multiscale (global-local) approaches are commonly adopted to optimize the computational cost by increasing mesh refinements and /or introducing elements with different formulations in specific region of the structures identified as “local model” and connected to the rest of the structure identified as “global model”.This paper addresses the issue of connecting non matching FE global and local modelsby introducing appropriate kinematic constraints at the interfaces. A sensitivity analysis on simple specimen is presented here. The aim is to investigate and to discuss the capability of the most common FE based tools to deal with global-local Analysis. The continuity of displacements and stresses across the interface between global and local models and the influence of the presence of the local model on the global model solution are used as parameters to test the quality of results. The work presented in this paper has been funded by the European Community's Seventh Framework Programme (FP7/2007-2013) under the grant agreement n° 234147. © 2011 Published by Elsevier Ltd. Selection and peer-review under responsibility of ICM11