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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 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; 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.

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 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.

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

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; 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.

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.

this article deals with bolted assemblies subjected to transverse loading The design of experiments (DOE) method is applied to this type of assembly in order to analyse the behaviour of the various design parameters. The results of observation come from a finite elements model which was preliminarily validated by an experimental study. A factorial design with six factors and three levels, makes it possible to draw interesting conclusions about the various factors likely to influence the design of this type of connection

Fatigue failure is a common problem with bolted joints. Preloading can often offer great advantage, in that it reduces the intensity of the alternative part of strains. Although it is more and more usual to carry out very precise finite element calculations, it should be highlighted that the error arising from simulations or experiments may be surprisingly great when looking at supplements of strain, i.e. alternative strain. That is one of the reasons why designing preloaded bolted joints requires great care, and sometimes turns out to be impractical. A partnership has been established for several years with a group of industrial manufacturers and users of slewing bearings. The objective is to model a parameterised bolt-assembled slewing bearing system and to develop a simulation tool that • allows us to check resistance of the bolts for maximum load as well as fatigue load • runs much faster than a three-dimensional simulation in order to enable us to compare multiple configurations, in order to be used in early design stages.

International audience; High-pressure squeezing is a technique used for the extraction of the pore water of porous materials such as sediments, soils, rocks, and concrete. The efficiency of extraction depends on the maximum pressures on the materials. This article presents the design of a high-pressure device reaching an axial pressure of 1000MPa which has been developed to improve the efficiency of extraction. The increase in squeezing pressure implies high stresses inside the chamber, so specialized expertise was required to design a safe, functional device that could withstand pressures significantly higher than common laboratory equipment. The design includes finite element calculations, selection of appropriate materials, and descriptive construction details for the apparatus. It also includes an experimental study of the performance of the apparatus in terms of extraction efficiency.

International audience; no abstract