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The fibre-reinforced epoxy composite materials, thanks to their high specific strength, have found many applications in the last decades, especially in the transportation field. However, even though this great advantage allows having a lightweight and strong structure, their application is limited by many critical aspects. Some of these depend on the fact that the composite materials are prone to a large range of defects and damages if subjected to some types of loads. Such defects and damages can be very critical for composites structures, because they may be invisible and cause a significant decrease of the residual strength. In these circumstances, if a structure is not designed under a damage tolerance philosophy it might fail under an unexpected load value, also because the presence of defects can promote the arising of unexpected instability phenomena, as for example buckling under compressive loads. For this reason, one of the most critical aspects to consider during a design process is the structural behaviour of a component under compression load. In fact, fibre and matrix failures and delaminations could reduce the residual strength of a structural component and decrease the buckling load limit. So, defects and damages which could be due either to a critical phenomenon that has previously affected the structure, such as a Low Velocity Impact (LVI), or due to voids and defects caused by manufacturing and production processes, have to be taken into account during the design process. In particular, among different defects and damages, which can affect a composite material, both delamination and fibre failures are the most dangerous. In order to assess the residual strength of damaged composite structures, compression tests are usually performed on such structures. For example, compressive tests are experimentally carried out on damaged structural components, which have been affected to an LVI in a previous phase. With the aim of studying and better understanding the structural behaviour of composites panel under compressive loads, some experimental tests and the respective numerical simulations, based on finite elements theory, have been performed and presented in the paper. The compressive test is numerically reproduced by using the finite element code Abaqus®, which, thanks to its implemented algorithms, has allowed considering different failure modes. Moreover, the progressive damage of fibre reinforced composites has been modelled by using Hashin's criteria which allowed considering two different laws for damage initiation and propagation. In particular, the paper deals with structural behaviour of both undamaged and damaged aircraft panels, with omega stiffeners, made of fibre-reinforced composite materials subjected to static compression tests. A comparison between the structural behaviours of both types of panels has been performed and presented in the paper. Moreover, with numerical model validation purpose, also a correlation between numerical and experimental results has been performed and shown in the paper.

The paper deals with structural behaviour of laminated composite plates under low velocity impact loading conditions. The aim of the work is to develop numerical finite element models and simulation techniques to be implemented in a numerical procedure, which is aimed to improve designer forecasting capabilities of damaging resistance in composite structures. On the base of advanced material models and of selected failure criteria, the proposed numerical techniques can describe the damage initiation and propagation of impact damages in composite structures. A global/local finite element modeling approach has been proposed, in order to be able to develop explicit finite element analysis of the impact event, including damage initiation and propagation of both interlaminar and intralaminar damages. The same model has been analysed under quasi static compression conditions by taking into account, in a single explicit finite element analysis, both the impact and the after impact damages. For validation purpose, numerical results have been compared with data from two sessions of experimental impact tests, followed by compression after impact tests; the considered impact energy values are 50 J and 100 J respectively.

Fiber-reinforced composite materials have found increasing industrial applications in the last decades, especially in the aerospace and ground transport fields, due to their high specific strength. However, even though this property allows having a lightweight and strong structure, some critical aspects still limit their use. Most of these depend on several types of undetectable defects and damages, which could affect the residual strength of the composite structures. The paper deals with failure mechanisms involving composite materials under several critic loading conditions, with the aim to assess the limits of currently used failure criteria for composite materials and to show the actual request of developing new failure criteria in order to increase the effectiveness of current design practices. Nowadays, such design practice is based on a damage tolerance philosophy, which allows a structure to tolerate the presence of damages during its in service life, only if the residual strength is kept higher than specific threshold values depending on the damage severity. Hence, the main goal of such paper is to assess the failure criteria’s capability to predict the life of composite components under several quasi-static and dynamic loading conditions. Intra-laminar and inter-laminar failure criteria have been investigated and considerations have been provided about the possibility to model the post-failure phase and to implement them within numerical predictive tools, based on finite element method.

In the recent years, the study of the behaviour of damaged structures has been focused on cracked components in presence of an extensive material yielding at the crack tip; under this condition, linear elastic fracture mechanics theory (LEFM) is not able to describe the real plastic zone shape and size. Within this work, an extensive numerical analysis, based on elastic plastic fracture mechanics theory (EPFM), of the plastic zone size at the tip of a Mode I pre-crack at the notch edge in a plate is presented.

In order to study the onset and the evolution of low velocity impact damages in Carbon–Epoxy plates, a numerical investigation has been led. A detailed finite element model has been created by using the finite element code Abaqus® which, thanks to the different implemented algorithms, allowed considering both intra-laminar and inter-laminar failure criteria. In particular, the numerical modelling technique of such failure criteria allowed predicting delamination growth, by using special purpose-elements (cohesive elements) and fiber and matrix failure, by using Hashin criteria. Moreover, with the aim to reduce the required CPU time, a global/local finite element modelling approach has been proposed. For validation purpose, numerical results have been compared with data from two sessions of experimental impact tests. The considered impact energy values are 6 J, 10 J and 13 J respectively.

The aim of the proposed research activity is to investigate on the structural behaviour of laminated composite plates under low velocity impacts. Analytical closed-form methods are generally unable to describe simultaneously different composite failure modes, as well as experimental tests are unable to be applied to complex boundary conditions or component geometries. Within this work it is shown that numerical simulation appears a reliable tool to describe and forecast the damage onset and growth in composite components. A numerical procedure, based on explicit finite element methods, has been proposed and applied to the simulation of drop mass impacts on composite plates, by taking in account both intra-lamina and inter-laminates damages onset and propagation up to component failure. A global/local modelling approach has been employed to create the model and its validation has been performed by considering results from different sessions of experimental tests.

This paper presents two modelling strategies for the simulation of low velocity impact induced damage onset and evolution in composite plates. Both the strategies use a global–local technique to refine the mesh in the impact zone in order to increase the accuracy in predicting the impact phenomena without affecting the computational cost. Cohesive elements are used to simulate the inter-lamina damage behaviour (delaminations) and Hashin’s failure criteria are adopted to predict the intra-lamina failure mechanisms. The two modelling strategies differ in terms of input parameters for the inter-lamina and intra-lamina damage evolution laws and in terms of modelling solutions in the impacted area. Comparisons between numerical and experimental results on composite plates subjected to different impact energies, according to the ASTM D7136 requirements, have been used to assess the peculiarities and the fields of application for the two proposed modelling strategies. Both the strategies have been tested by adopting the finite element code ABAQUS®. The different approaches to set the parameters of cohesive elements’ constitutive laws and Hashin’s criteria and the different choices made in quantifying the dependence of failure criteria on the finite elements’ average size have been taken into account.

A fatigue test on a full scale panel with complex loading condition and geometry configuration has been carried out using a triaxial test machine. The demonstrator is made up of two skins which are linked by a transversal butt-joint, parallel to the stringer direction. A fatigue load was applied in the direction normal to the longitudinal joint, while a constant load was applied in the longitudinal joint direction. The test panel was instrumented with strain gages and previously quasi-static tests were conducted to ensure a proper load transferring to the panel. In order to support the tests, geometric nonlinear shell finite element analyses were conducted to predict strain and stress distributions. The demonstrator broke up after about 177000 cycles. Subsequently, a finite element analysis (FEA) was carried out in order to correlate failure events; due to the biaxial nature of the fatigue loads, Sines criterion was used. The analysis was performed taking into account the different materials by which the panel is composed. The numerical results show a good correlation with experimental data, successfully predicting failure locations on the panel.

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.

Damage after impact often involves aeronautic structures. The aircraft can be involved in impacts during the assembly stage and operative life. Typical impacts can be related to falling tools, hailstones, debris on the take-off strip thrown against the aircraft by the rolling tyres, maintenance operations. There are two categories of damage impact: Low and High Velocity Impact (LVI, HVI). Damages coming from low velocity impacts are difficult to identify because they are often within the composite structure and the use of non-destructive testing, e.g. ultrasonic test, is not convenient. In order to prevent catastrophic events the designers must increase the safety margin and thereby the weight of the aircraft. The present study shows two different numerical procedures based on finite elements method to investigate on some damage mechanisms of a carbon fibre reinforced plastic (CFRP) structures (e.g. interface debonding, fibre or matrix cracking) and the residual strength of such structures under live loads.

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.

Coupling techniques for components of different materials is spreading in mechanical industry; the test case studied in this work deals with the connection of an aluminium alloy component with a carbon fibre composite one. In particular, the first component is made of an aluminium-zinc alloy and exhibits an isotropic behaviour, while the second is made of a carbon fibre reinforced polymer (CFRP) and shows a strongly anisotropic behaviour; both materials are widely used in engineering applications. A titanium bolt connects the parts. This work is focused on the influence of the geometrical parameters which characterize the coupling between the components. In particular, a study has been carried out on the influence of the shank-hole clearance, the bolt head size, the bolt preload and the shape of the bolt head. A numerical model has been built and statically tested; the results have been compared with the experimental ones from literature. Once validated, the same numerical model has been used to evaluate the performance of the joint in presence of a change of the above mentioned characteristic parameters. The required numerical analyses have been performed using Abaqus/Standard® numerical code.

Laminated composite structures are increasingly finding more applications in various fields thanks to their lower weight if compared with other materials of the same strength. Nevertheless, composites thin plates show a critical behavior in terms of damage propagation mechanisms when subjected to (low velocity) impact. Indeed they tend to produce delaminations which can be hardly detected by optical inspections and can affect the global load carrying capability, leading to a premature structural collapse. The aim of this paper is to assess the capabilities of the Davies-Zhang approach (introduced in 1994 and aimed to the estimation of both the delamination initiation impact load and the size of the impact induced delaminations) by using a multiscale FE model based on the mesh superposition technique. Indeed the impact area has been modeled layer-wise with an element per layer while the rest of the structure has been modeled at laminate level by layered elements by means of a homogenization approach for the determination of the equivalent laminate material properties. The impact induced delamination area has been determined by adopting stress-based criteria. The results (in terms of delamination initiation impact force and delamination size) have been compared to the ones obtained by adopting the Davies-Zhang approach.

The energy absorption capability of an exposed crashworthy element or system is largely affected by material properties and structural design: prismatic sandwich structures, made of foam or honeycomb core between two metallic or laminated composite face plates, are good candidates. This work deals with a numerical investigation on the energy absorbing capability of such a structural component. There are several difficulties associated with the numerical simulation of a composite impact-absorber, such as high geometrical non-linearities, boundary contact conditions, failure criteria, material behaviour; that is because the main objectives of any numerical investigation are the calibration of the model with experimental results and the evaluation of the sensitivity of the variables with respect to the geometrical and physical parameters which influence the study at hand. The latter is a very relevant aspect for designers if the application of the model to real cases has to be a robust one from both a physical and a numerical point of view. In this paper a preliminary calibration of a numerical model for a composite impact absorber is presented, on the basis of experimental data found in literature; then a sensitivity analysis of the same model to the variation of the main geometrical and material parameters, developed by using the explicit finite element algorithms implemented in the Ls-Dyna code, is illustrated. © (2010) Trans Tech Publications, Switzerland.

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.

In this work, a parametric numerical investigation on the plastic zone size and shape at the crack front of a through crack in a plate is presented. The thickness of the plate, the size of the crack and the applied remote load values are considered as parameters. The obtained results allow assessing the limits of the linear elastic fracture mechanics in presence of an extensive material yielding at the crack front and the relationship between the plastic zone size and other parameters of the elastic-plastic fracture mechanics theory is highlighted.

Purpose – The purpose of this paper is to investigate on the behaviour of a delaminated stiffened panel; the delamination growth is simulated via fracture elements implemented in B2000++® code based on the Modified Virtual Crack Closure Technique (MVCCT), matrix cracking and fibre failure have been also taken into account. Design/methodology/approach – In order to correctly apply the MVCCT on the delamination front a very fine three-dimensional (3D) mesh is required very close to the delaminated area, while a 2D-shell model has been employed for the areas of minor interest. In order to couple the shell domain to the solid one, shell-to-solid coupling elements based on kinematic constraints have been used. Findings – Results obtained with the global/local approach are in good correlation with those obtained with experimental results. Originality/value – The global/local approach based on kinematic coupling elements in conjunction with fracture elements allows to investigate and predict the behaviour of a stiffened delaminated composite panel in an efficient and effective way.

This paper concerns the numerical characterization of the static strength of a flat stiffened panel, designed as a fiber metal laminates (FML) and made of Aluminium alloy and Fiber Glass FRP. The panel is full scale and was tested under static loads, applied by means of an in house designed and built multi-axial fatigue machine. The static test is simulated by the Finite Element Method (FEM) in a three-dimensional approach. The strain gauge outcomes are compared with corresponding numerical results, getting a satisfactory correlation.

The extension of the plastic zone which takes place at the tip of a crack strictly depends on many variables, such as the yield stress of the material, the loading conditions, the crack size and the thickness of the cracked component; an exact analytical solution, such as to evaluate the plastic zone size (PZS) while taking into account all those parameters, is not yet available, mainly because of the difficulties in computing the stress–strain field ahead of the tip of a growing crack. In the present paper, by using a parametric 3D finite element model, the authors show the results obtained from extensive numerical analyses which have been developed first of all with the aim to assess the limits of linear elastic fracture mechanics (LEFM) parameters, when used to describe the stress state at the crack tip of both physically short cracks and long cracks in presence of high loads. Subsequently, the combined influence of the loading conditions, the yield stress of the material, the crack size and the thickness of the component on PZS at the crack tip has been investigated. At the end, an analytical relationship, which links, in a closed form, PZS to all these parameters and which is able to determine the PZS at crack tip of both physically short cracks and long cracks has been proposed.

Delamination and other damage mechanisms, such as matrix cracks, fibre-matrix debonding and fiber failure can appear as a consequence of impact events with foreign objects under in service conditions and maintenance operations. These phenomena are seldom analyzed together without discussing how the interferences between the different damage mechanisms can influence their evolution under different loading conditions. The present work is focused on the development of a specific numerical procedure, able to take into account the failure modes interaction in composite laminated structures subject to a low velocity impact. As a matter of fact, a very fine mesh refinement is required to correctly evaluate the stress state where the impact induced damage onsets. Hence, in order to reduce the computational cost without compromising the accuracy of results, a global/local approach, characterized by a very refined mesh in the critical impact region interacting with a coarser mesh in the rest of the geometrical domain, has been implemented in the FE model. In the present work, Multi-Point-Constraints (MPC) has been used to link the refined local domain to the coarse global domain without using transition meshes. The implementation and the analyses have been performed in the ABAQUSA (R) FE environment.

This work deals with the application of the micromechanical Gurson-Tvergaard (GT) model to the determination of the residual strength of analuminumflat stiffened panel (2024 T3) with a central through crack, by means of finite element simulations. The load condition is represented by a monotonic traction along the direction orthogonal to the crack plane. The used Finite Element code is WARP 3D®, which allows simulating ductile damage propagation by considering the GT model. Numerical results have been compared with experimental ones available in literature. In the second part of the work, a home madeprocedurefounded on the SDI (Stochastic Design Improvement) technique is presented and applied to the improvement of the residual strength properties of the considered panel.

""\\"Carbon fibre reinforced polymers (CFRP) composite materials are widely used in mechanics. The joints between one metal plate with composite one are widely used in the same way and in many cases are the critical point of the whole structure as a result of the physical discontinuity between the parts, the stress concentrations developing around the joint area, and surface manufacturing of the parts. This work is focussed on the influence of both manufacturing and numerical modelling parameters on the structural behaviour of a hybrid mechanical coupling. Numerical models have been built and tested; the results have been compared with experimental ones. Afterwards numerical analyses have been performed to evaluate the influence of such above mentioned parameters on the structural behaviour of hybrid joints. Numerical analyses have been performed using Abaqus\\\\\\\/Standard® numerical code.. \\"""

In this work the Boundary Element Method (BEM) and the Finite Element Method (FEM) have been used for an elastic-static analysis of both a Branemark dental implant and a generic conic threaded implant, modelled either in the complete mandible or in a mandibular segment, under axial and lateral loading conditions. Two different hypotheses are considered with reference to degree of osteo-integration between the implant and the mandibular bone: perfect and partial osteointegration. The BEM analysis takes advantage of the submodelling technique, applied on the region surrounding the implant. Such region is extracted from the overall mandible and the boundary conditions for such submodel are obtained from the stress analysis realised on the complete mandible. The obtained results provide the localisation of the most stressed areas at the bone-implant interface and at the mandibular canal (containing the alveolar nerve) which represent the most critical areas during mastication. This methodology, enriched with the tools necessary for the numerical mandible reconstruction, is useful to realise sensitivity analysis of the stress field against a variation of the localisation, inclination and typology of the considered implant, in order to assess the optimal implant conditions for each patient under treatment. Due to the high flexibility in the pre- and post-processing phase and accuracy in reproducing superficial stress gradients, BEM is more efficient than FEM in facing this kind of problem, especially when a linear elastic constitutive material law is adopted.

PurposeThe purpose of this paper is to investigate and to assess the capabilities of the most common finite element (FE)‐based tools to deal with global‐local analysis. Two kinds of coupling were investigated: shell to shell and shell to solid.Design/methodology/approachThe issue of connecting non‐matching FE global and local models, characterized by different mesh refinements and/or different element types, was addressed by introducing appropriate kinematic constraints on the nodes at the interfaces. The coupling techniques available in the three FE‐based codes (ABAQUS®, NASTRAN® and ANSYS®), were assessed by applying them on a common numerical test case (non‐linear buckling analysis of a square plate). Results of the global‐local simulations were compared to the results obtained for relevant reference solutions.FindingsThe 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 were used as parameters to test the quality of the results. It was observed that the tools implemented in the different codes provide different results. The results characterized by a higher quality were found by using the Multi Point Constraint available in ABAQUS®.Originality/valueWhen dealing with complex structures, multi‐scale (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”. In this paper an overview of the coupling tools available in the main commercial FE code is given.

In this work, results from a study on bolted joints made of unidirectional, quasi isotropic Carbon Fiber Reinforced Polymer (CFRP) composites, subjected to tensile loads, are reported. CFRP composite materials are widely used in the mechanical industry, such as that of aerospace, where requirements of weight reduction and structural high performances are very compelling. Composite materials generally present a high resistance to fatigue and corrosion; however, the presence of joints produces the major problems and a poor design of joints leads to a drastic reduction of the reliability of structures made of these materials. A hybrid bolted joint involving a metal plate, made of aluminum alloy, and a CFRP composite plate has been considered; the plates are held together by a titanium bolt. Experimental results from literature are compared with those obtained through a numerical analysis developed with Abaqus code. Once the CFRP composite has been analyzed and the numerical model validated through numerical-experimental correlations, other possible configurations have been numerically analyzed in order to ensure the highest strength of the examined hybrid joint. Afterwards the effects of bolt-hole clearance on the stiffness and strength of the same joint have been investigated. © (2012) Trans Tech Publications.

In the present paper the authors refer about a series of experimental tests, where an aluminium alloy square tube, filled with an aluminium foam, was crushed by a longitudinal load at a speed of 10 m/s. The test apparatus consisted of a sled installed on a very stiff frame moving on appropriate guides, as the specimen was set on a home-made fixture. Two arrangements of square tubes were considered as specimens: a “standard” one and an “optimized” one. Both crushing behaviours and energy absorption capabilities were analyzed experimentally and numerically simulated by means of the explicit FE code LS-DYNA®; the complete numerical model consisted of the striker, the assemblage of square tubes and the base. A high-speed video recording system was used to capture the images from the physical test. The results from the numerical analyses were compared to those obtained from the experiments: those results showed that the force–deflection response had been overestimated by the numerical model. The authors attempted to justify this inconsistency by considering the influence of the strain rate parameters of the considered Cowper-Symonds analytical model on the results. It was shown that the “optimized” energy absorber exhibited a more desirable force–deflection response than the standard one due to some easy design changes, which involved the insertion of aluminium foam dampers.

For a railway vehicle, the structural integrity of the seat frame and of its connection to that of the coach is a very important aspect of the design phase addressed to the improvement of the passive safety performances, at most because the analysis of the accidents occurred in recent years shows that secondary impacts against vehicle interiors remain one of the main causes of injury. All regulations which apply to this task start from the assumption that whatever happens to the vehicle the seat must remain connected to the vehicle frame, as well as the different parts to each other. Numerical evaluations are obviously necessary to match with this design requirement; it would be desirable to apply multi-body (MB) codes to this task, as they are really fast, but unfortunately they can’t provide detailed results for what concerns the structural behaviour of the involved seat and vehicle components. For this reason, in the present work a full finite element model of a sled-test, including a FE dummy, has been developed, analysed and validated by comparison with the available experimental results; it has been also showed how this kind of numerical simulation is suited and necessary to evaluate the structural behaviour of the structural components of the seat frame. In the context of the presented study the MADYMO® code has been adopted to perform the preliminary MB analyses necessary to calibrate and evaluate the relevant parameters of dummy-seat contact surfaces and of seat-belt stiffness, while LS DYNA® code has been used for the structural dynamic FE analyses.Copyright © 2011 by ASME

Plastic zone size at the tip of a crack strictly depends upon many variables, such as yield stress of material, load conditions, crack size and component thickness, but an exact analytical solution for PZS such as to consider all these parameters is not yet available, mainly because of the difficulties in computing the stress-strain field ahead of the tip of a growing crack, in particular if the crack can be classified as a short one, for which case the PZS can be very large respect to the crack dimensions. By using a parametric 3D finite element model, numerical analyses have been developed under Ansys® and Warp3D® FE codes with the aim to derive an analytical relationship between the PZS and the aforesaid parameters.

There are several difficulties associated with the numerical simulation of the stretch bending process of extruded components; the main ones are non-linear material behavior, geometrical non-linearities, modeling of boundary conditions, contact between die and specimen, springback during the unloading phase. Another very complex aspect is the calibration of the numerical model, as rather few experimental results are generally available. This paper deals with a numerical simulation of a complete stretch bending process with the aim to select the most suitable numerical procedure oriented to the evaluation of the process-induced distortions and residual stresses; to validate the proposed procedure, numerical–experimental comparisons have been performed. The activities reported have been developed in collaboration with ALENIA Finmeccanica s.p.a. within the VI FP’s research project called COMPACT.

In this work the structural behaviour of a mandible considering a unilateral occlusion is numerically analysed by means of the Finite Element Method (FEM). The mandible, considered as completely edentolous, is modelled together with its articular disks, whose material behaviour is assumed as elastic or hyper-elastic. The mandible model is obtained by computer tomography scans. The anisotropic and non homogeneous bone material behaviour is considered and the loads applied to the mandible are those related to the active muscle groups during unilateral occlusion. The results of FEM analysis are presented mainly in terms of stress distribution on the mandible. Because of uncertainty on the determination of the adopted parameters, a sensitivity analysis is provided, showing the way in which the variation of articular disc stiffness and temporomandibular joint friction coefficient has an impact on the mandible stress peak and occlusal force. © Armentani et al.; Licensee Bentham Open.

In the present work numerical‐experimental analysis for the characterization of a structural adhesive has been performed. The numerical analysis has been carried out through the finite element method by using, for the phases pre / post processing were used commercial programs while for the phase of numerical solution the Abaqus code was used. The experimental analyses were carried out at laboratories of C.R.F. S.C.p.A. by using of a standard quasi static testing machine. Later numerical analysis was performed comparing the torsional stiffness of a vehicle in which the welded connection between the pavilion and the flank has been substituted by bonded one. This comparison has allowed to demonstrate the ability of the bonded joint discussed to provide mechanical performances comparable with those of a welded joint widely used in the automotive industry.

This work deals with a numerical investigation on the energy absorbing capability of structural composite components. There are several difficulties associated with the numerical simulation of a composite impact‐absorber, such as high geometrical non‐linearities, boundary contact conditions, failure criteria, material behaviour; all those aspects make the calibration of numerical models and the evaluation of their sensitivity to the governing geometrical, physical and numerical parameters one of the main objectives of whatever numerical investigation. The last aspect is a very important one for designers in order to make the application of the model to real cases robust from both a physical and a numerical point of view.At first, on the basis of experimental data from literature, a preliminary calibration of the numerical model of a composite impact absorber and then a sensitivity analysis to the variation of the main geometrical and material parameters have been developed, by using explicit finite elemen...

A very large number of variables affect the response of bolted or riveted joints typically used in aerospace applications: geometry of the joint, characteristics of the sheets, friction between sheets, geometry of head and kind of fastener, amplitude of clearance before assembly, mounting axial load, pressure effects after manufacture. It must be also recalled that these parameters influence the many failure modes existing for such joints, among which a relevant importance is attributed to bearing. The present paper deals with the study of the influence of assembly parameters on the joint operational behaviour and in particular with the analysis, performed through numerical simulations, of the influence of the residual stress-strain state coming from the riveting operation on the bearing resistance of an aluminium alloy joint. This work has been developed within the FP6 research project called MUSCA (Non linear static multiscale analysis of large aero-structures).

A new interest has been increasingly directed in recent years to study the behaviour of joints provided with various kinds of fasteners and the mechanism of load transfer; profiting of the present capabilities of computing systems and analysis codes, which appear such as to deal with models built with more than one million elements, thanks to new numerical techniques which can solve huge systems of equations. However, the main interest has been limited to the case of bolted joints, for which several models are now available, while a few results are known for the case of riveted joints, where more complex mechanisms are involved. In the present paper a full set of analyses has been reported, with reference to both normal and blind rivets, where the manufacturing operation has been simulated through Ls-Dyna to evaluate the stress and strain states induced into the jointed sheets, varying the dimensional and riveting load characteristics of the joint. A subsequent investigation is presented, which aims to evaluate the effects of the compressed zone over the behaviour of an approaching crack.

The objective of robust design is to optimize the mean of a given target variable and to minimize the variability that results from uncertainty represented by “noise” factors. A recent strategy for robust design is based on stochastic processes, which has resulted in a new design technique called “stochastic design improvement” (SDI). In this work a home-made procedure is presented, which is based on the SDI technique and which is illustrated with reference to a case study which aims to increase the residual strength of a cracked stiffened aluminum panel.

This paper deals with numerical investigation on a stiffened composite panel under longitudinal compression load, in presence of artificial delamination defects between skin/stringer interface layers. At first, both the experimental and numerical non-linear equilibrium paths were determined, until the failure load value of the structure was reached. Then local evaluation of the energy release rate parameter was performed at defect front, by means of a hybrid (FEM/analytical) procedure based on a particularized virtual crack closure technique. The same FE shell model was used to perform both global and local calculations by means of a single analysis.

This work is focussed on the numerical prediction of the fracture resistance of a flat fullscale aluminium alloy 2024 T3 stiffened panel under monotonic traction loading condition. The numerical simulations are based on the micromechanical Gurson-Tvergaard (GT) model for ductile damage. The applicability of the GT model to this kind of structural problem has been studied and assessed by comparing numerical results, obtained by using the WARP 3D finite element code, with experimental data provided from literature.