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International audience; The assembly process in the aeronautical sector mostly uses mechani- cal fastening. It requires the drilling of hundreds of thousands of fastening holes. These holes are critical areas for the assembly fatigue life, thus he drilling oper- ation is a key point. The fatigue performance of a machined surface can be cor- related to the surface integrity, but this correlation seems very broad and com- plex, especially for the drilling of aluminum alloys (commonly used in the air- craft industry). Moreover, different drilling processes may be used, such as axial drilling or orbital drilling. Orbital drilling is particularly interesting for limiting burrs and improving chip evacuation. But the process can impact also the fatigue life of drilled parts. To study this impact, the hole surface integrity needs to be analyzed and its influence on fatigue strength must be investigated. The main challenge concerns the interactions between the surface integrity factors. More- over, the affected layer in drilled aluminum parts is particularly thin, and the ac- cess to the hole surface is geometrically restricted. The characterization of the surface integrity is thus a complex task. In this paper, the correlations between the hole surface integrity and fatigue life of drilled 2024-T351 aluminum alloy are addressed. The study considered both orbital and axial drilling processes. The generated surface integrity was characterized in terms of surface roughness, metallographic observations, hardness, and residual stress. Fatigue tests were performed and correlated to the surface integrity results.

International audience; The work presented here is an experimental and numerical study on a new technology called friction shims. Those are thin shim made of steel with a shape of washer. Their coating made of nickel and micro diamonds aim to increase the friction coefficient when located at the interface of two parts. The mechanical behaviour as well as the static and fatigue strengths of titanium bolted joints with this specific technology are presented in this study. Specimens are representative of hole-to-hole aeronautical joints, involving large clearance and misalignments. Specimen geometrical and material definition are presented as well as test set up. The experimental test results show limited impact on the static strength and a large increase in the fatigue strength. A numerical analysis based on the finite element method was developed and correlated with the experiments to provides complementary information and to understand the mechanical behaviour observed during the static tests and the gain in fatigue strength.

International audience; In today's business environment, the trend towards more product variety and customization is unbroken. Due to this development, the need of agile and reconfigurable production systems emerged to cope with various products and product families. To design and optimize production systems as well as to choose the optimal product matches, product analysis methods are needed. Indeed, most of the known methods aim to analyze a product or one product family on the physical level. Different product families, however, may differ largely in terms of the number and nature of components. This fact impedes an efficient comparison and choice of appropriate product family combinations for the production system. A new methodology is proposed to analyze existing products in view of their functional and physical architecture. The aim is to cluster these products in new assembly oriented product families for the optimization of existing assembly lines and the creation of future reconfigurable assembly systems. Based on Datum Flow Chain, the physical structure of the products is analyzed. Functional subassemblies are identified, and a functional analysis is performed. Moreover, a hybrid functional and physical architecture graph (HyFPAG) is the output which depicts the similarity between product families by providing design support to both, production system planners and product designers. An illustrative example of a nail-clipper is used to explain the proposed methodology. An industrial case study on two product families of steering columns of thyssenkrupp Presta France is then carried out to give a first industrial evaluation of the proposed approach.

International audience

Smart tightening development is part of the Industry 4.0 transformation with the introduction of smart tools, and preload in bolted assemblies is of major interest in today’s aircraft manufacturing process. So far, it has been difficult to estimate the importance of each parameter for tightening process quality, mainly because of the large number of combinations and configurations that exist.The present work aims at evaluating the effects and the interactions between different parameters that have to be taken in consideration in future torquing strategy. Many experimental tests have been conducted on an Automatica test bench using a Taguchi strategy and an analysis of the first main results is now presented, highlighting the complexity of the phenomena studied.All these points will help us to better understand tightening, so as to improve performance during installation, maintenance and repair.

Designed for aeronautical and automotive applications, the split sleeve cold expansion process is used to improve the fatigue life of bolted metallic parts. Although its application has been well tested on aluminum assemblies, hard metal applications are still being studied. This paper presents experimental results of double bolt joint assemblies under double shear fatigue tests after stacked split sleeve cold expansion. The behaviors of two sizes of assemblies with different degrees of expansion are investigated. S-N curves are the main indicators of this study but thermal aspects are also investigated to observe fretting in the specimens as bolts are preloaded. Bolt tension is a major parameter in assembly regarding fatigue life. Interference between those two phenomena is at the heart of this paper. The first results show that stacked cold expansion has a negative effect on mechanical performances, as it deteriorates the fatigue life of the assembly. However, an examination of these results provides a coherent explanation for the loss of performance that occurs.

International audience; This research deals with the development of a new semi-analytical model for composite-metal eccentric tensile bolted joints of casing structures. The model is based on a direct stiffness method considering structural elements, where flanges are modeled with axisymmetric shell elements, the bolt with a beam element and contact behavior with a specific number of compressive linear springs, identified by means of convergence tests. A hybrid element is added in order to set the link between flange and bolt. Since the model is intended for the preliminary design of bolted joints including composite materials, we propose an extension of the stiffness matrix formulation of isotropic axisymmetric shell elements to orthotropic ones. This formulation is validated with respect to a 2D FE axisymmetric model. Then, a semi-analytical model is established for a casing assembly approximately corresponding to a real casing of an aircraft engine. Design criteria such as normal stress on the bolt, bending moment and axial load at a specific section of the composite flange, given by the semi-analytical model are compared to a 3D FE computation. Results are in very good agreement and the semi-analytical model offers considerable time saving where the computation time was 120 times faster than the 3D FE model. Moreover, relative error does not exceed 2% for normal stress of the bolt and 9% for the flange bending moment which is satisfactory in a preliminary design approach. However, due to the formulation of hybrid element, less accurate results were observed for axial displacement of the composite flange and it would be advisable to consider a new formulation. This will be detailed in future work. Finally, a parametric study showed the ability of the semi-analytical model to predict the physical behavior of joints and proved its usability for running optimization studies and its reliability as a preliminary design tool.

The main aim of the present work is to study the effect of axial preload on the durability of aerospace fastened joints. For that purpose, experimental and numerical approaches are adopted to demonstrate the beneficial effect of axial preload on the fatigue life of representative aerospace fastened joints. In the experimental approach, an innovative tightening technique, based on iterative tightening, is used to reduce the scatter habitually induced on preload when the conventional torque tightening technique is employed. The main benefit, besides the use of this alternative tightening technique, is to allow an accurate preload to be introduced without geometry or stiffness modification, thus enabling the preload effect to be determined precisely. The results show the effect of preload on the static resistance, fatigue life and failure mode of fastened joints. In the numerical approach, a 3D finite element model is developed and the analysis of its behavior confirms and explains experimental observations. Analysis of longitudinal stresses through critical paths shows that the effect of high preload is beneficial because it reduces hydrostatic pressure and shear stress amplitude, thus leading to longer fatigue lives. The correlation between experimental observations and the numerical results is studied using SWT and Crossland multiaxial fatigue criteria.

International audience; This article is devoted to the development of a calculation macro-model for the sizing of aircraft wheel fasteners. By their design, airliners tires are too rigid to be mounted on the wheel like car or motorcycle tires. Therefore, it is necessary to design a wheel in two separate parts so as to plug the tire on a first half-wheel and then “close” the assembly with the second. Therefore, the two half-wheels must be held together. Inmost cases, a bolted joint plays this essential role. The aim of this work is to develop a methodology related to the generation of semi-analytical model representative of the assembly. The tool is designed with a local approach that models an angular wheel sector including the most solicited bolt. It makes possible to evaluate tensile and bending stresses in the bolt, taking into account the roundness effect of the wheel. The objective is to obtain results close to finite element 3D modeling but with a very limited computation time. To achieve this goal, the principle of this model is to represent all parts of the wheel by 1D axisymmetric elements such as plate and shell elements, beam, tube, and spring elements (to model the contact) ensuring a description close to the actual wheel. Contact between the two half-wheels is also taken into account in order to detect the location of any unsticking after application of external loads. Different cases will be simulated (inflation case, straight line, and cornering case). The mechanical strength of the most solicited bolt will be analyzed for these different configurations. The results in tensile and bending stresses will be observed at the screwlevel.Acomparison of the results from the proposed digital macro-model and the 3D digital simulations will be analyzed. The developed tool will be used in the early design phase which allows the design engineer to define the mechanical and geometric properties of the wheel and bolts to find the optimal assembly.

International audience; This paper proposes the use of 1D basic models to build a design assistance tool capable of evaluating the heat transfer between a third-level electronic packaging and its support, considering a conventional configuration where a thermal interface material is placed between these two parts. Using this kind of tool early in the design process may facilitate choices concerning geometry and material. The packaging is modelled by a stepped beam (the equipment) and the interface layer by a nonlinear elastic foundation (the thermal interface material). Considering that the electronic equipment bends under the effect of the forces exerted by the fasteners, the tool makes it possible to determine the contact zone remaining operative after deformation, and the pressure distribution at the interface. Mechanical results are then used to calculate the steady-state heat transfer between the equipment and its support, taking into account the diffusion within the equipment and the thermal interface material, and also the thermal contact resistances, the latter being dependent on the contact pressure. A detailed case study is used to illustrate the utility of the approach. The 1D models are exploited to illustrate the interest of the design assistance tool. The influence of different parameters on the thermal performance is studied and a new innovative proposal is analyzed, which could lead to a significant increase in thermal performance.

International audience; The self-loosening of a joint through unscrewing of the bolt is a phenomenon mainly occurring when the assembly is solicited by transverse repeated loads. Previous works highlighted that the transversal sliding of the bearing surfaces, either in the threads or underneath the bearing surfaces of bolts and/or nuts, is its root cause and that this phenomenon begins during the first loading cycles. In order to study the early stage of this self-loosening, a simplified numerical model has been developed. The latter factors the bearing surfaces of the bolt, the preload, the friction coefficient, the amplitude of the shear-load and the fastener's material. Through measurements and interpretation of the results, the shearing of the fastener has been identified as the main deformation leading to the self-loosening of the assembly, while the bending of the fastener shank limits the self-loosening. Moreover, according to the values of preload and shear-load, the behaviors were identified, and an interpretation has been proposed.

International audience; This paper presents the experimental and numerical work achieved in the aim of evaluating the heat transfer at the interfaces of threaded spacecraft assemblies, where Thermal Interface Materials (TIMs) are placed between two surfaces to improve the thermal performance. Developing a model to predict thermal resistance for such an assembly is a serious challenge, which has to take various influencing parameters into account. First, mechanical and thermal experiments used to characterise TIMs are summarised. Second, a numerical model capable of representing the behaviour of these materials is built. To verify the mechanical model, the preload of a single fastener assembly is measured and compared with a simulation. The thermo-mechanical model is verified by an assembly heated by a power resistor to evaluate the thermal aspects. The proposed material model is able to predict the loss of preload caused by creep/relaxation of the TIM and the temperature distribution of the assembly. This work is part of a broader study that seeks to develop a multi-physics approach to evaluate the heat transfer at interfaces of space application assemblies.

International audience; The self-loosening of bolted assembly is a phenomenon that has been studied several times in the past. Among the existing solicitations, it has been showed that transverse loading might cause the most severe loosening. Thus, different explanations have been proposed. In spite of their similarity, as they all consider sliding as the root cause, the sliding surface distinguish them one from another. This paper will aim at giving another point of view of the problematic in order to advantage a Zadoks' theory, which highlights the transverse sliding of components. To do so, firstly a double-shear assembly will be modeled. Its specificities are the preload application by screwing the nut, and the use of a self-locking nut. Secondly, some tests will be done in order to valid the built model. Those experiments will also factor the thickness of the assembly in the self-loosening. Thirdly, the analysis of the numerical results and of the experiments, especially the interface surfaces will give us a clue in order to validate the sliding phenomena, which is according to Zadoks, the movement implying the self-loosening of the assembly.

International audience; In this paper, the mechanisms of damage of an oxide/oxide ceramic matrix composite bearing are studied with a new experimental setup, the balanced quarter hole device (BQH). This test was designed to allow direct observation of the damage development on a material subjected to bearing failure. In a standard bearing experiment, real time monitoring is extremely difficult to set up, and post mortem observations of the bearing plane can be biased by the cutting operation. High speed cameras were used to take pictures of the bearing plane so that the damage development could be studied and a damage chronology established. The validity of the setup was verified by comparing the results obtained with those of a standard bearing test. Two different stacking sequences were studied, and the influence of the material microstructure and composite machining was investigated. It was shown that the first critical damage, matrix cracks, appeared before the load drop, and then led to delamination and kink bands, causing the final failure of the material.

International audience; The paper examines the static behavior of the inverted planetary roller screw (PRS) through numerical and experimental studies. The numerical analysis of the inverted PRS is first presented to capture the global and local deformations in different configurations. Using a three-dimensional finite element (3D FE) method, a sectorial model of the mechanism is built involving an entire roller. The model describes the static behavior of the system under a heavy load and shows the state of the contacts and the in-depth stress zones. The current work also investigates the axial stiffness (AS) and the load distribution (LD) under both compressive and tensile loadings. It is shown that the LDs are not the same at each contact interface of the roller and that they depend on the configuration of the system. Also, the nut is less stressed than the screw shaft because of their contact curvatures. In parallel, complementary experiments are carried out to measure the axial deflection of the screw shaft and the rollers in five cases with different numbers of rollers. In each situation, the mechanism is under the same equivalent axial and static load. The tests reveal that rollers do not have the same behavior, the difference certainly being due to manufacturing and positioning errors that directly affect the number of effective contacts in the device. This stresses the fact that the external load is unequally shared over rollers and contacting threads. By introducing the notion of an equivalent roller, the results are used to validate the previous numerical model of an inverted PRS. As they provide a better understanding of the inverted PRS, these investigations are useful to improve the existing analytical models of the device.

International audience; A high‐pressure device, reaching an axial pressure of 1000 MPa, intended to the extraction of the pore solution of rigid and slightly porous materials, has been developed to improve the efficiency of extraction. This paper gives an application of fluid extraction from mortars made with Portland cement. It includes an experimental study of the performance of the apparatus, and an analysis of the results in terms of efficiency of extraction, repeatability of measurement, and effect of the squeezing pressure on the pore solution composition. Results shows that: (1) the squeezing efficiency using our apparatus is higher than those found in the literature; (2) the measurement uncertainty ranges between 1.5% and 14%; (3) no significant effect of pressure (up to 1000 MPa) is observed for concentrations of Ca, Na, K, and Si. This paper suggests conducting extraction at 1000 MPa, especially on old concrete or concrete made with low W/C ratios.

PurposeThis paper seeks to deal with a new modelization method which aims at fatigue sizing of preloaded bolted joints. Industrial design offices indeed need new models which, on the one hand, take bending of the bolts and geometrical non‐linearity into account and, on the other hand, run fast enough to be used for preliminary design stages. Usual sizing procedures derive from VDI recommendations, which makes them inaccurate. On the contrary, classical finite element methods are revealed to be very costly.Design/methodology/approachThe first task lies in reducing the physical problem down and model the structure using axisymmetrical elements. Then, the core of the method lies in modifying the stiffness matrix of a tube element, in order to modify the axial compression stiffness to the one used by preloaded assembly classical computations. Eventually, a 2D finite element model is programmed which takes advantage of the modified element. A mounting was built to reproduce the typical loading of a slewing bearing. Experimental tests were carried out in order to help analyse the problem and to check finite element simulation results.FindingsSample experimental results are presented which confirm the need for new models and validate the 2D model that was developed.Research limitations/implicationsThe new finite element, as well as the set of hypotheses that are used, appear to be usable for other bolted joints.Practical implicationsA software was produced for the industrial partners, which is usable by non FE‐specialists.Originality/valueThis work may serve as a basis for building fast and accurate finite element models of other types of bolted joints.

International audience; The cold expansion process is a technology that is widely used to enhance the fatigue resistance of aircraft metallic parts. The issue analysed in this paper concerns the case when the expansion is carried out through an assembly composed of several sheets. The numerical work conducted was intended to understand the phenomenology of the process within a stiff assembly. In particular, it aimed to analyse the deformation of the sheets and the residual stress fields generated by the process. For this purpose, an axisymmetric finite element model of the split sleeve process was developed, simulating a single expansion performed through a stack of two titanium holes (Ti-6Al-4V). The sheets to be expanded were positioned between two steel plates to simulate the assembly. The model could predict the shape and intensities of the fields within the expanded sections and their global outer shapes. We particularly focused on the phenomena prevailing between sheets. The simulation showed that deformations at the interface were greatly reduced when the stack was stiffened axially. Moreover, high circumferential and axial residual stresses were generated in the sheets. Results were compared with a single hole expanded without axial stiffening.

Research in interactive Design – Vol. 4 presents the most recent successful developments in mechanics, design engineering and advanced manufacturing for innovation in product, process and production engineering. The readers are invited to discover new techniques, methods, models and tools based on integrated and interactive design approaches. In a context of worldwide competition, there is an unquestionable need for such approaches to improve the reactivity, flexibility and capacity for innovation of engineers faced with particular challenges in enhancing the development of transport systems, the production of energy, the manufacture of consumer goods, the building engineering or the product design. But these approaches are also of great interest to academics, to improve the content of their curriculum and education programmes and to define novel research roadmaps in the field of mechanics, design engineering and advanced manufacturing.

Bolted joints are one of the most common elements in aerostructures. Currently, the preload applied to join the parts together is achieved by applying torque to the bolt head or to the nut. In the case of shear joints, an emerging opportunity to optimise structural joints is to apply the preload more accurately. Up to now, the preload effect is most often neglected due to the large scatter on its value due to torque tightening. The aim of this article is to describe the effect of preload on shear joints, for this reason, a numerical and experimental approach has been adopted to demonstrate its influence. In the experimental approach, iterative tightening was used to reduce the scatter on preload. The benefits of preload on high load transfer double lap shear joints will be discussed. In the numerical section, an approach of predicting fatigue life of shear joints is presented. The effect of preload/friction of coefficient is also studied. Finally, practical aspects like alternative tightening techniques and a focus on an industrial application case are also presented.

International audience; The cold expansion process is a technology that is widely used to enhance the fatigue resistance of aircraft metallic parts. The issue analysed in this paper concerns the case when the expansion is carried out through an assembly composed of several sheets. The numerical work conducted was intended to understand the phenomenology of the process within a stiff assembly. In particular, it aimed to analyse the deformation of the sheets and the residual stress fields generated by the process. For this purpose, an axisymmetric finite element model of the split sleeve process was developed, simulating a single expansion performed through a stack of two titanium holes (Ti-6Al-4V). The sheets to be expanded were positioned between two steel plates to simulate the assembly. The model could predict the shape and intensities of the fields within the expanded sections and their global outer shapes. We particularly focused on the phenomena prevailing between sheets. The simulation showed that deformations at the interface were greatly reduced when the stack was stiffened axially. Moreover, high circumferential and axial residual stresses were generated in the sheets. Results were compared with a single hole expanded without axial stiffening.

International audience; In this paper, an original approach is proposed to calculate the static load distribution and the axial stiffness of a planetary roller screw (PRS) mechanism. Assuming that the external loading is shared equally over an arbitrary number of rollers, only a sector of the system is represented to save on computing time. The approach consists in using a structure of bars, beams, and nonlinear springs to model the different components of the mechanism and their interactions. This nonlinear model describes the details of the mechanism and captures the shape of the nut as well as the bending deformation of the roller. All materials are assumed to operate in the elastic range. The load distribution and the axial stiffness are determined in three specific configurations of the system for both compressive and tensile loads. Further, the influence of the shape of the nut is studied in the case of the inverted PRS. The results obtained from this approach are also compared to those computed with a three-dimensional finite-element (3D FE) model. Finally, since the calculations appear to be very accurate, a parametric study is conducted to show the impact of the bending of the roller on the load distribution.

International audience; The fatigue behaviour of bolts under axial load has always been considered from the component point of view for which fatigue limit is usually taken equal to 50 MPa, and few results are available to designers for limited lifetimes. Here, we take up this problem from a material point of view using a local approach. For each case of fatigue testing, using finite‐element (FE) model of the bolt, we determine the stabilized local stress at the root of the first thread in contact with the nut. To characterize bolt behaviour with these numerical results, we use Dang Van multiaxial fatigue criterion for which we extend application to the medium fatigue life. These results can be correlated with the experimental numbers of cycles to failure to determine material parameters of the generalized criterion. Using statistical Gauss method, we can make lifetime predictions for any level of risk of failure. In addition, we propose an analytical model to rapidly determine the local stress condition from nominal loading data (mean stress and alternating stress). This model dispenses us from a new modelling if the bolt is stressed in the same manner as the bolts used for behaviour characterization. Using this model and the generalized criterion, it is extremely easy to make lifetime predictions whatever the risk considered.

International audience; Bolted joints are essential elements of mechanical structures and metal constructions. Although their static behaviour is fairly well known, their dynamic behaviour due to shocks and vibrations has been less studied, because of the large size of the finite element models needed for a detailed simulation. This work presents four different simplified models suitable for studying the dynamic behaviour of an elementary bolted joint. Three of them include contact elements to allow sliding of the screw head and the nut on the assembled parts, and the last one allows rotation between screw and nut. A penalty approach based on the Coulomb friction model is used to model contact. The results show that these models effectively represent the dynamic behaviour, with different accuracy depending on the model details. The last model simulates the self loosening of a bolt subjected to transversal vibrations.

International audience; Cold expansion of metallic holes is widely used in the aerospace industry as an efficient industrial process for improving fatigue performance of mechanical assemblies. To increase the efficiency of the process, it is worth considering the possibility of carrying out the expansion twice in succession in the same hole. This paper discusses the consequences of such an operation on a single titanium hole through a numerical and experimental study. More precisely, dedicated finite element modelling of the cold expansion process has been developed in order to simulate cases where the expansion is carried out twice: in the same direction and in opposite directions. The residual fields generated are analyzed and the results compared with experimental results. Furthermore, we propose in this study to assess a new methodology for measurement of the intensity of the compressive residual stresses generated at the hole edge. Specifically, we will use the incremental hole drilling technique to characterize the expanded holes, including or not a reaming operation of the cold worked hole. Results show that double expansion has a very positive impact on the homogeneity of the compressive fields generated as long as the direction of expansion is properly selected to guarantee the efficiency of the process.

National audience; La méthode de modélisation discrète des plis (DPM : Discrete Ply Modelling) est une stratégie de modélisation qui a été développé initialement pour la modélisation des impacts basse vitesse/basse énergie sur stratifiés et qui s’est révélée particulièrement efficace. Sa robustesse a été démontrée et elle a été appliquée avec succès à un certain nombre de problématiques : impact sur stratifiés, calcul de l’indentation résiduelle, compression après impact, impact sur chant ou sur zone de reprise de plis. Si elle repose sur maillage complexe qui offre des chemins naturels de fissurations matricielles et de délaminage, elle présente l’avantage de ne reposer que sur 13 paramètres parfaitement objectifs : les constantes élastiques, les contraintes à rupture matrice, les déformations des fibres à rupture en traction, les taux de restitution d’énergie critiques pour les interfaces ainsi que pour les fibres en compression. Cette méthode est aussi insensible par nature aux phénomènes de localisation et permet de représenter physiquement les ruptures observées en pratique. Dans ce papier, on présentera les cas particuliers de l’arrachement et de la rupture trouée en détaillant les particularités de maillage et la corrélation des essais. Des perspectives seront données en ce qui concerne la modélisation et les essais des assemblages en lien en particulier avec l’ANR Vertex.

The bolt as an element which integrates several small parts to a united big structure had been used since a long time ago. This type of impermanent joint holds many advantages in the engineering field such as facilitating the maintenance, particularly at the change of defected part, and also making the delivery of many parts composing a huge structure more sensible by transporting them in diverse modes of transport. One of problems using this type of joint is sometimes it is difficult to assure holes position between parts to be aligned just as designed, in order to facilitate positioning of parts during assembly we could possibly use parts with slotted hole. However, a slotted hole will result in a reduced contact surface between the bolt and parts assembled, therefore the behavior of this type will be clearly different compared to the assembly with normal hole. The research will be conducted with assistance of a finite elements software ABAQUS® for simulating the model along with its parameters and mathematical software Matlab® for interpolating data obtained from the simulation. Firstly, the model will be validated by comparing it to experimental result of research conducted by Bakhiet[1], then its boundary conditions and mesh will be used to next model simulations. Secondly, the parameters of the assembly will be varied such as bolt positions on the part and the modulus Young ratio of bolt and parts. Finally, both assemblies are to be compared (e.g. with normal and slotted hole) and then the assembly’s critical value is to be found by using dimensionless parameters developed by Turgeon and Vadean[2]. From research conducted, we could conclude that the behavior of the assembly, particularly at its fatigue stress produced at the bolt, changes significantly with the variation of the bolt position and also the modulus Young ratio of the bolt and part. A reduced value of fatigue stress produced will be achieved while the bolt position is the nearest possible with respect to the point where load applied. Whereas, a higher modulus Young ratio will convict a higher fatigue stress produced at the bolt

International audience; A number of experimental studies have demonstrated that pre-tensioning fasteners significantly increases the fatigue life of shear joints. Fatigue life prediction for clamped joints is still a complex and unresolved issue because of the mixed nature of load transfer, which partly occurs by frictional forces. This article presents a calculation method based on a multiaxial-type critical-plane criterion, which determines the fatigue life and fatigue crack initiation site. For this purpose, the values of hydrostatic pressure and amplitude of maximum alternating shear stress on a critical octahedral plane are determined at each point of the structure and for each loading increment, and are used to predict the fatigue life of the joint. A dedicated experimental study was conducted within materials & processes airbus laboratory to validate the numerical results. In addition, a dimensionless parameter Rs is introduced to quantify the proportion of load transferred by friction and by bearing of the bolt, and allows the optimal preload to be approximated, above which value more clamping should not give further improvement. This value characterizes the shift of the crack location from the net section to the outside of the compressed area.

Bolted joints used in aeronautical structures are subject to vibrations, which can result in critical damage either from self-loosening or from fatigue. This study is devoted to the examination of the dynamic behavior of a simple bolted joint assembly subjected to quickly varying transverse load, which induces bending of the jointed plates. The adopted approach is based on finite element method, with a coupled bolt model and a penalty friction model, and implicit time simulation. Numerical result sets are presented and discussed.

Cold expansion of metallic holes is widely used in the aerospace industry for improving the fatigue performance of mechanical assemblies. To increase the efficiency of the process, it is worth considering the possibility of carrying out the expansion twice in succession in the same hole. This paper discusses the consequences of such an operation on a single titanium hole through a numerical and experimental study. More precisely, numerical modeling is developed in order to simulate cases where the expansion is carried out twice: in the same direction and in opposite directions. The residual fields are analyzed and the results compared with experimental results using incremental hole-drilling technique. Results show that double expansion may have a very positive impact on the homogeneity of the compressive fields.

International audience; In aeronautical structures, assemblies with thin laminates are becoming increasingly usual, especially for fuselage design. In these structures, out-of-plane loads can appear in bolted joints and can lead to progressive punching of the fastener’s head in the laminate resulting, in some cases, in a failure mode called pull-through [1]. This complex phenomenon, which occurs in assemblies, was studied firstly by using a simplified ‘‘circular’’ pull-through test method. Qualitative micrographic examinations showed damage very similar to that observed in impacted specimens. The research presented here extends the Discrete Ply Model Method (DPM) developed by Bouvet et al. [2] to this case. The finite elements model is based on a particular mesh taking ply orientations into account. Cohesive elements are placed at the interfaces between solid elements to represent matrix cracks and delamination, thus allowing the natural coupling between these two damage modes to be represented. The model shows good correlation with test results, in terms of load/displacement curve, and correct prediction of the damage map until failure, including the splitting phenomenon.

International audience; Faced with an increasingly fast-changing market, airplane manufacturers have to reduce the development time of their new programs whilst dealing with more and more complex composite structures. The European project Maaximus (More Affordable Aircraft Structure Lifecycle through eXtended, Integrated & Mature nUmerical Sizing) aims at providing methods and tools to enable the fast development and right-first-time validation of a highly optimized composite airframe. In this context, accurate models of fasteners are crucial to ensure correct structure modeling at a higher level. The present study focuses on the mechanical behavior of a threaded assembly subjected to an axial tensile load. After a review of the state-of-the-art in this domain, the first part of the paper shows what benefits can be expected from explicit simulation for large quasistatic models. Parallelization strategies for High-Performance Computing (HPC) are presented, bringing out the need for consistency between the parallelization strategy and the computation structure. These simulation techniques are then applied to the modeling of a tensile test of a fastener. The results of corresponding experiments for two fastener diameters are presented. A successful correlation between simulations and experiments is found, both qualitatively and quantitatively. This study shows the efficiency of a well-chosen resolution algorithm in a coherent HPC environment for solving large non-linear models.

National audience; Dans les structures aéronautiques, il est de plus en plus fréquent de voir des assemblages mettant en jeu des stratifiés d'épaisseur faible. Dans certains cas comme les jonctions en L, des efforts hors plan apparaissent au niveau de l'assemblage qui peuvent conduire à un mode de rupture appelé quelque fois déboutonnage mais plus couramment par l'anglicisme " pull-through ". Ce mode de rupture est généré par le poinçonnement progressif du stratifié par la tête de la fixation avec parfois au final le passage complet de la tête au travers du stratifié [1]. Des analyses micrographiques qualitatives ont montré que ces endommagements étaient très similaires à ceux observés en impact. De ce fait, il a été envisagé d'étendre l'approche développée par Bouvet et al. [2] à cette problématique. Le modèle éléments finis est basé sur un maillage particulier qui suit les orientations des plis. Des éléments cohésifs sont disposés aux interfaces des éléments volumiques pour pouvoir représenter la fissuration matricielle ou le délaminage et permettre un couplage naturel entre ces deux endommagements. Le modèle permet une bonne comparaison avec les essais réalisés en terme de graphe effort d'arrachement/déplacement de la tête de vis ainsi qu'une prédiction correcte des cartographies d'endommagement.

International audience; A Belleville spring is usually used in mechanical systems to obtain large loads for small distances of travel. Such a spring has a non-linear load-length curve. Moreover, Belleville springs are commonly stacked together in series or in parallel or both. Thus, defining a design that uses Belleville springs is not an easy matter. The existing assistance tool only checks whether a proposed design is acceptable or not. To improve design assistance, we show how optimization processes can be used in order to build a tool that interactively proposes an optimal design directly from the designer’s requirements. The tool presents both an optimal design using a Belleville spring taken from a catalogue and an optimal custom design. An illustrative example is presented to highlight the benefits of using such an assistance tool.

International audience; This paper presents a 3D finite element (FE) model of a thread forming screw assembly process based on the ABAQUS 6.5.4 Explicit software program. The model consists of two principal elements: an M10×12 thread forming screw and a lower 4 mm plate into which the screw taps its threads. The aim was to develop a robust industrial dimensioning tool; the model can be extended to establish the preload and investigate other types of assemblies. A 45 deg sector, which represents 1/8 of the joint, was modeled to maintain a good compromise between calculation time and an accurate representation of the thread forming process. The intent of the study was to analyze the material flow throughout the thread forming process; a parametrical study was also conducted to identify the most influential process parameters. To validate the model, FE numerical simulation results are compared with published experimental results. The study shows that the lead hole diameter has an important influence on the screwing torque.

Dans cet article, nous allons presenter les resultats d'une etude comparative des caracteristiques mecaniques de boulons en acier 42CrMo4 de fabrication standard et speciale. Cette etude porte principalement sur l'influence de la chronologie des phases de fabrication des vis sur les caracteristiques mecaniques statiques et en fatigue. Cette chronologie concerne le traitement thermique et le roulage a froid. Si aucune influence n'est visible sur la tenue statique des boulons, l'influence sur la tenue en fatigue est tres importante. Par ailleurs, independamment du type de fabrication, nous avons remarque que les zones de rupture sont differentes selon que l'on procede a un essai statique ou a un essai de fatigue. Dans le premier cas, la rupture a lieu dans la longueur filetee libre de prise avec l'ecrou tandis qu'en fatigue, la rupture a lieu au niveau du premier filet en prise avec l'ecrou. Ces differences de comportement observees experimentalement sont corroborees par des simulations par la methode des elements-finis que nous avons mises en œuvre dans le cadre d'un travail sur la tenue en service des assemblages boulonnes.

International audience; This paper deals with the dimensioning of two-bolted assemblies made up from joint prismatic subassemblies subjected to fatigue compressive loads coplanar with the screw axis. The presented study is complementary to a previous study relative to tension loading [A. Daidie, J. Chakhari, A. Zghal, Numerical model for bolted T-stubs with two bolt rows, Struct. Eng. Mech. 26 (3) (2007) 343–361]. However, one should note that the two loading cases are not similar since an additional influential corner contact problem occurs in the case of compressive loading. The main development in this paper relative to the previous study [A. Daidie, J. Chakhari, A. Zghal, Numerical model for bolted T-stubs with two bolt rows, Struct. Eng. Mech. 26 (3) (2007) 343–361] is taking into consideration this complex corner contact problem. In this framework, the local deformation between the subassemblies and the corner of the supporting structure is formulated and a non-linear expression of a constrained displacement is established. Moreover, the evolution of the contact zone under the compressive loading, which is not similar in the case of tension loading, is taken into consideration. Consequently, a new extended numerical model for compressive loading is established from unidirectional finite elements and validated by 3D finite element simulations. An algorithm which updates the contact stiffness matrix and sets out forces and displacements at each node of the subassembly is developed using C language program. Finally, a statistical software method is used as in the case of tensile loading. It is important to note that in the case of compressive loading, this statistical software method is not only used to establish the effect of the joint parameters, but also to identify and tune up parameters relative to the complex problem of the corner contact.

International audience; Bolted bearing connections are one of the most important connections in some industrial structures, and manufacturers are always looking for a quick calculation model for a safe design. In this context, all the analytical and numerical models reduce the global study to the study of the most critical sector. Therefore, the main inputs for these models are the maximal equivalent contact load and the corresponding contact angle. Thus, a load distribution calculation model that takes all the important parameters, such as the stiffness of the supporting structure and the variation in the contact angle, into consideration is needed. This paper presents a 3D finite element (FE) simplified analysis of load distribution and contact angle variation in a slewing ball bearing. The key element of this methodology, which is based on the Hertz theory, is modeling the rolling elements under compression by nonlinear traction springs between the centers of curvature of the raceways. The contact zones are modeled by rigid shells to avoid numerical singularities. Each raceway curvature center is coupled to the corresponding contact zone by rigid shells. The main contribution of this method is not only the evaluation of the contact loads with a relatively reduced calculation time but also the variation in the contact angle from the deformed coordinates of the curvature centers. Results are presented for several loading cases: axial loading, turnover moment, and a combined loading of axial force and turnover moment. The influence of the most important parameters such as the contact angle, the stiffness of the bearings, and the supporting structure is discussed. Finally, a preliminary experimental validation is conducted on a standard ball bearing. The results presented in this paper seem encouraging. The FE study shows an important influence of several parameters and a good correlation with experimental results. Consequently, this model can be extended to other types of slewing bearings such as roller bearings. Moreover, it can be implemented in complex industrial structures such as cranes and lifting devices to determine the corresponding load distributions and contact angles and, consequently, the most critical sector.

International audience; Self-loosening of bolts is a problem encountered in many industrial fields, and especially in aviation. The purpose of this paper is to study the self-loosening phenomenon numerically through an assembly consisting of two plates assembled by a bolt and subjected to a transversal dynamic load. First, a 3D finite element model is developed, with contact elements and all geometrical details, including the real thread geometry with its helix angle. This leads to many degrees of freedom and long calculation time. Then a 1D simulation is made, based on a simplified model with only 4 degrees of freedom and few contact conditions. Calculation is nearly instantaneous. Both models describe the succession of sticking and slipping on contact surfaces and predict loosening of the assembly. They provide close results. The next step will be to compare their behaviour with an experimental approach, in order to validate and fit the models.

International audience; This paper presents an evaluation of the influence of the cold expansion process on the fatigue performance of holes in hard alloys, as such materials are involved in an increasing number of aeronautical applications. Fatigue enhancement could bring significant savings for numerous possible industrial applications. However, although the cold expansion of aluminium holes has been studied widely, there have been few publications concerning this process in hard alloys and there is currently very few research activities on technique dedicated to high strength metallic holes. Thus, this work aims to define an approach to understand why processes and methodologies are suitable for obtaining effective expansion of these materials. In this article, the response of expanded holes is studied, considering various experimental parameters and for a wide range of expansion ratios. The influence on the fatigue strength of Ti-6Al-4V tensile specimens is also reported for various expansion ratios, more precisely \textquotedblleftstandard\textquotedblright expansion ratios and high expansion ratios. Then, a specific numerical modelling of the process is presented, which enables us to understand the impact of high expansion ratios in titanium holes and the influence on fatigue performance. A very good correlation between experimental and numerical results is observed.

International audience; This article presents a numerical tool for dimensioning two-threaded fasteners connecting prismatic parts subjected to fatigue tension loads that are coplanar with the screw axis. A simplified numerical model is developed from unidirectional finite elements, modeling the connected parts and screws with bent elements and the elastic contact layer between the parts with springs. An algorithm updating the contact stiffness matrix, calculating forces and displacements at each node of the structure and thus normal stresses in the screws in both static and fatigue is further developed using C language. An experimental study is also conducted in parallel with the numerical approach to validate the developed model assumptions, the numerical model and the 3D finite element results. Since stiffness values for the compressive zones in the parts are analytically difficult to determine, a statistical software method is used, from which a tuning factor is derived for identifying these stiffness values. The method is also applied to set out the influence of each parameter on the fatigue behaviour of each screw. Finally, the developed model will be used to establish a new, sophisticated, fast and accurate tool for dimensioning bolted mechanical structures.

International audience; Managing the axial stiffness of various components in a bolted joint is a major industrial concern for modelling different tightening processes and for accurate fatigue dimensioning. This paper presents a new approach for calculating the axial stiffness of the several elements of a bolt (the head and the engaged part), the nut and the fastened plates. Finite element modelling based on deformation energy improves the existing models and take in to account the type of materials and coefficients of friction of various elements in contact. From these corrections, approaches for axial stiffness calculation based on empirical formulas are proposed for easier application and for future FE modelling bolted joints using beam elements. Finally, the theoretical study is validated by an original experimental approach.

International audience; This paper investigates the behavior of large diameter bearing bolted joint in order to evaluate fatigue resistance of the screws. Based on experimental results, a sector of a slewing bearing is modeled using 3D finite elements. The model is built via hypothesis of sine-distributed efforts on the roller tracks. The simulations are carried out for the most loaded screw, which is located in the symmetry plane. Experimental measures on equipped screws are checked against numerical 3D simulations. This validates the numerical modeling method. Then the numerical model is used to evaluate the influence of several geometrical and physical parameters. The preload intensity reveals to be the major parameter. The bushes’ height affects load filtering and improves fatigue strength of the screws. The height of the mounting tubes smoothes potential stiff points. The friction coefficient between the ring and the mounting is investigated as well. Eventually, several observations are made which lead to design recommendations for fatigue sizing of the slewing bearing screwed joints.

International audience; In the field of structural stress analysis and especially in transitory dynamics (crash and impact simulations), study/design accuracy requires increasingly predictive models. A compromise between cost and precision entails modelling and simplification of all the link elements. Riveting is a particularly sensitive case. The characteristics needed to ensure effective modelling are indeed difficult to measure. This paper presents adjustment of a numerical model simulating a riveted link using a number of different approaches. The results analysis considerably improve knowledge about the riveting process and behaviour of riveted links. This study will pave the way for resistance tests to be conducted in order to numerically characterise riveted links under load. The aim is to develop an approach that reduces the model size and calculation time without adversely affecting the validity of the simulation results, and to show the effect of strains and residual stresses on the link in post-riveting.

International audience; Braided pneumatic artificial muscles, and in particular the better known type with a double helical braid usually called the McKibben muscle, seem to be at present the best means for motorizing robot-arms with artificial muscles. Their ability to develop high maximum force associated with lightness and a compact cylindrical shape, as well as their analogical behavior with natural skeletal muscle were very well emphasized in the 1980s by the development of the Bridge-stone " soft robot " actuated by " rubbertuators ". Recent publications have presented ways for modeling McKibben artificial muscle as well as controlling its highly non-linear dynamic behavior. However , fewer studies have concentrated on analyzing the integration of artificial muscles with robot-arm architectures since the first Bridge-stone prototypes were designed. In this paper we present the design of a 7R anthropomorphic robot-arm entirely actuated by antagonistic McKibben artificial muscle pairs. The validation of the robot-arm architecture was performed in a teleoperation mode.

International audience; The main industrial programs for spring design do not make most of the powerful capabilities for optimization currently available. Usually, such software simply provides comprehensive validation tools. This paper introduces an advanced sizing tool for compression spring design. This tool can be used at any design stage and involves a specification sheet to provide data including interval values. Interval analysis and optimization processes are then run to provide the best design as output. High-level assistance functionalities are also presented and illustrated through a case study.

In the field of design and manufacturing in mechanical engineering, it is difficult to give an overview of lecturing steps because of the splitting up of required knowledge and the expertise level of the teachers. According to the OPALYS project objectives, we present the application of an approach of documents sharing enabled by the use of XML language. We detail the chosen conformity structure for the various kinds of documents. We also detail the choices that were made in order to create links between the documents, while the authors did not know exactly their integration context. The main encountered difficulty is related to the XML tools that did not yet become mature enough for not expert users. The developed demonstrator is then presented in its main functionalities and highlights the relevancy of our approach.