Crankshaft bending stiffness. During the first stages of dimensioning of an engine, we must define major dimensions in particular those related to the crankshaft. The suitable choice of these coasts, dimensioning for other parts, requires several iterations. In such a situation, it is not easy to have resorts to structural finite-elements analysis which requires important means of calculation and lot of time. Using a simplified model based on beam theory can be useful, fast and sufficiently accurate. The crankshaft is modeled by a cylindrical shaft, composed of four sections with elliptic cross-section. Each section represents a part between two bearings of the crankshaft of a four cylinders on line engine. This work presents a methodology of identification of the geometrical characteristics of the equivalent elliptic cross-sections which must behave like the real crankshaft. Owning the CAD of the crankshaft of a four cylinder engine and the real loading along the combustion cycle we calculate with the finite element method the reactions in the crank journals. By comparison between elasticity with finite elements and strength of material approach we determine the specific inertias of the "crankshaft" beam. This methodology is simple and efficient to be used during quasi static calculations of the crankshaft.
Static seals of confined flow near critical point. The assembly of metal parts that may be encountered in industry (nuclear, space, ...), creates frequently a path of leakage which can let a fluid pass. In this following study, we aim at understanding the phenomenology of a confined flow through the vicinity of critical point and its influence on the leakage rate. This sealing problem was limited to stationary and viscous situations. The leakage geometry has been assimilated to a capillary tube whose the wall temperature is fixed at the fluid critical value. A difference of pressure was imposed between a supercritical inlet and a subcritique outlet. The phenomenological approach has led to highlight the existence of a transition zone crossing the critical point. In this region of strong expansion, has shown the existence of a thermo-mechanical coupling and be taken a into account by the thermal convection joined the conduction to transport heat. It shows that the progression in fluid outwards is slowed by that cap effect.
Failure conditions analysis of looped network pipes due to water hammer phenomenon. A numerical model has been established in order to simulate the propagation of the water-hammer wave into a looped water networks. This model gives information on water hammer waves taking into account the structure of the water network and the lost of pressure. The numerical algorithm gives the value of the maximal fluid pressure induced by water hammer provoked by fast closing valves into network and then the maximal stresses into pipes. These maximal stresses can overcome the admissible stress and lead to failure risks. In this case, the severity of a defect like corrosion crater has been estimate by computing under water hammer pressure the stress distribution at defect tip. This allows to computes the applied notch stress intensity factor. This parameter is introduced into the SINTAP failure assessment diagram into order to determine nodes of the network in critical situation. Conventionally, it is admitted that the risk of failure exists if this safety factor is less than 2. The results indicate almost nodes of the studied network are outside of safe zone in the Failure Assessment Diagram.
In water supply installations, noise pollution often occurs. As a basic component of a system, a flush valve may frequently be a source of noise and vibration generated by cavitation or high turbulence levels. During valve closing or valve opening, cavitation can be a problem. In order to decrease the noise and to improve the design inside a flush valve, some experimental and numerical analyses were carried out in our laboratories. These analyses led to some improvements in the design of the valves. Cavitation occurrence was more specifically addressed, using numerical simulation, and this is the main aim of the present paper. Particularly, the use of a simplified numerical test without cavitation model is compared with one using a cavitation model. In order to define potential cavitation risks in some parts of the valve, it has been found that a simplified approach provides an accurate overview. Computational Fluid Dynamics (CFD) simulations of cavitating flow of water through an industrial flush valve were performed using the Reynolds averaged Navier-Stokes (RANS) equations with a near-wall turbulence model. The flow was assumed turbulent, incompressible and steady. Two commercial CFD codes (Fluent 6.3 and Star CCM+3.04.009) were used to analyse the effects of inlet pressure as well as mesh size and mesh type on cavitation intensity in the flush valve.
This paper explores analytically the nonlinear dynamic behavior of rotors. Coupled nonlinear equations of motion are formulated using Hamilton's principle. The rotor model is composed of a rigid disk and a flexible shaft which is characterized as a beam of circular cross section. Various influences are taken into account like the effect of higher order large deformations, rotary inertia, gyroscopic effect, rotor unbalance and the effect of a dynamic axial force. Forced response due to a mass unbalance is presented first for the linear analysis and then perturbation techniques are used to solve the complete equations of motion including nonlinear terms. Method of multiple scales is applied to examine the nonlinear behaviour of the rotor system. Resonant curves are plotted for different possible resonance conditions. It is concluded that the higher order large deformations and axial force acting dynamically on the rotor have a significant effect on its nonlinear response. This response varies for different parameters of the rotor like an unbalance mass and diameter of the shaft.
Numerical study of high cycle fatigue behaviour of copper polycrystalline aggregates. An analysis of high cycle fatigue behaviour is undertaken via the numerical simulation of polycrystalline aggregates. The metallic material chosen for investigation is Copper, which has a FCC crystalline structure. The REV, which is composed of 300 randomly orientated equiaxed grains, is loaded at the fatigue limit determined at 10(7) cycles. The aim is to calculate the mechanical quantities at the mesoscopic scale (average quantities in the grains) after cyclic stabilisation has been achieved. The results highlight the fact that the mechanical quantities at this scale have a large scatter. A statistical analysis of the response of the aggregate for different loading conditions (tensile, torsion, and in-phase tension-torsion) is done. Thanks to the sufficiently large number of different microstructures investigated, a. critical analysis of the Dang Van and Crossland multiaxial fatigue criteria has been undertaken, using the local mechanical quantities.
A two degrees-of-freedom pneumatically driven parallel robot has been developed for pick-and-place of payloads comprised between 5 and 20 kg using standard double acting cylinders cheaper than electrical motors. After the general presentation of the robot, the actuator models are developed and a novel control strategy is introduced based on a cascade scheme with a predictive position controller and an inner H(infinity) force control. Some experimental results are then presented and analyzed in order to show the effectiveness of the controllers.
Modelling fluid/solid coupling in high temperature assembly processes. A numerical tool for the simulation of the Friction Stir Spot Welding process is developed. The model is based on a fluid/solid coupling which describes the state of the material in the structure. The model includes the P1+/P1 finite-element, developed with a strong thermomechanical coupling, both for fluid and solid behaviours. The coupling, associated with an Arbitrary Eulerian Lagrangian approach, is implemented in a new option of the finite element code SYSWELD (R). We present here a first simulation of the Friction Stir Spot Welding process.
Dynamics of bubbles crossing a liquid-liquid interface. We investigate experimentally and computationally the passage of air bubbles through an initially flat horizontal interface separating two Newtonian liquids. We use various liquids in such a way that their viscosity ratio can vary by more than two orders of magnitude; the density contrast and the interfacial tension also vary to a certain extent. Two different injection systems are used and allow us to generate bubbles with diameters ranging typically from 1 mm to 2 cm, the biggest bubbles being toroidal. In parallel we carry out axisymmetric computations based on two distinct approaches, namely an interface capturing technique (a VOF approach without interface reconstruction) and a Cahn-Hilliard model coupled with the Navier-Stokes equations.
Geometrical modelisation of thread milling process. Milling operation parameters, such as cutting and geometrical parameters, are quite difficult to define because of the variation of chip load during the process. Modeling the cutting forces is an efficient help to evaluate the effects of each parameter with the support of a few number of machining tests, and in order to define the available parameters domain. Nevertheless, the modeling needs improvement to be more precise and consequently be able to compare the effect of changing parameters as tool geometry. Thread milling is a machining technique which can produce both internal and external threads with using a machine tool, a helicoidal interpolation and a tool having the thread profile. This technique has several advantages compared to cut tapping and it is well adapted to the production of high cost parts. From a geometric point of view, thread milling is a quite complex 3D machining problem, due to the tool center trajectory, cutting mill geometry and cutting section. The present study deals with the geometric modeling of thread milling as a preliminary step for cutting force modeling. The developed approach is based on the complete analytical formulation of the mill geometry (cutting edge, rake face, clearance face). A simplified formulation for uncut chip thickness is established and the specificities of some parameters are examined correlating to the tool angle variation.
The process of ultrasonic shot peening has been studied from two aspects: (a) a 3D numerical model of shot motion in the peening chamber based on the theory of granular gases, (b) an experimental setup developed for measuring shot velocity distribution in the chamber and impact locations on the peened surface. The aim of such study is to propose an experimental method providing shot trajectories in order to validate the 3D model for the process parameter optimization, used for example in the aeronautic industry. The presented results illustrate the value of the model in the understanding and mastering of the process, as well as its usefulness, on one hand for the design of peening chambers, and on the other hand for a better definition of numerical models that help to predict residual stresses generated in the peened material.
Cette etude experimentale presente l’etude du comportement mecanique d’un polyamide 66 (PA66) renforce par des fibres de verre courtes frequemment utilisees dans l’industrie automobile. Afin d’etudier l’influence de la teneur en humidite, de la quantite de fibres de verre introduite dans la matrice et de la vitesse de deplacement, une serie d’essais de traction a ete realisee sur du polyamide renforce ou non avec des fibres de verre courtes a differents fractions volumiques : 10, 20 et 30 wt%. Les resultats montrent la dependance du materiau aux differents parametres cites precedemment. La technique de thermographie infrarouge (IR) a ete utilisee pour determiner l’evolution de la temperature a la surface des materiaux au cours des essais de traction. Un processus de localisation de la dissipation thermique a pu etre identifie a partir des images thermiques.
This paper investigates the flow boiling heat transfer in microchannels with the aim of developing compact cooling systems which can be adapted to miniaturized power components. Nano- and micro-surface treatments were used as innovative techniques to improve the heat transfer performance as well as to delay the intermittent dryout. It was observed that the micro-structured surfaces show significant enhancements (up to 85%) in heat transfer compared to the smooth surfaces. Especially, using the highly-wetted structured surface, the intermittent dryout is improved.
Characterization of the mechanical properties by nanoindentation of a treatment of diffusion and a coating for the improvement wear resistance of low carbon steels. The superficial zone is very often the part of a component which undergoes the strongest constraints, it is also this zone which is exposed to frictions and the chemical attacks. The surface treatments are largely used to solve the problems of wear, chemical attack, corrosion or fatigue. This work concerns the development of a surface conversion treatment by diffusion precipitation. This process of superficial hardening allows to increase and to improve the superficial properties of materials and more particularly those of the tools. It is proposed in this work, to search the conditions for obtaining a chromium carbide known by these properties of wear, corrosion and oxidation resistance, starting from a treatment carried out in three stages: the first stage is a pack carburizing (pack cementation) by carbon on two low carbon steels: the XC18 and the 16MC5. The second stage, concerns the deposition on the surface of treated steels a metallic chromium film of a few mu m. In the third stage the parts previously obtained are heated at high temperature to convert the surface chrome species into carbide by diffusion of carbon from the cemented zone towards surface chrome species to obtain by precipitation of chromium carbide. The characterization of the mechanical properties (hardness and Young modulus) by nanoindentation of the samples obtained is carried out in this work.
Crytalline plasticity constitutive equations for BCC steel at low temperature. The prediction of the irradiation-induced evolution of the ductile-fragile transition curve of pressure vessel steels is a major research topic in the nuclear industry. Multiscale approaches starting from ab initio scale up to macroscopic continuum mechanics are currently investigated through the European project PERFORM60. At the intermediate level of cristal plasticity, several effects need to be described accurately before considering the introduction of irradiation hardening mechanisms; such as the thermal activity of dislocations slip, the different mobilities between screw and edge dislocations at low temperature. These effects should be introduced in a cristal plasticity law used in finite-element simulations of polycrystalline aggregates. Accordingly, a new cristal plasticity law is proposed in this paper based on a critical analysis of previous numerical results obtained with a discrete dislocations dynamics code.
Behaviour of cellular material under dynamic loadings. Part 2: a multi-scale approach. A multi scale methodology is proposed for the study of the cellular material behavior under dynamic loading. The behavior of polymeric foams studied depends on the constitutive material and the morphology of the porous structure. The cellular material of this study is constituted of millimetric porous beads, these beads are themselves constituted of microscopic closed cells. The methodology proposed to model the multi scale morphology of the structure (the scales of beads and cells) of the cellular material; it consists in implementing simple mechanical models at the different scales to reproduce the complex physical phenomenon observed and to model the macroscopic response of the foam. The observation and the analysis of physical phenomenon is the first step of the multi scale modeling. This paper describes the experimental and numerical methods used to observe and describe the structure of the cellular material, and quantify deformations and damages of these structures at the scales of beads and cells. Two ways of modeling were investigated: a finite-element model to represent the bead structure and another approach, more original, by the use of a modified discrete element model to model the microscopic structure of the cells.
Development of a robotic cell for trimming of composite parts. Robot machining is a new challenge in robotics as it requires both high stiffness and accuracy of the robot at hand. Until now, machining operations have been mainly realized with numerical-control machine-tools. This paper pertains to the optimization of the use of industrial robots for finishing tasks knowing the process cutting phenomena and the robot stiffness. Composite parts trimming is used as an illustrative machining operation in the framework of this paper. On the one hand, the robot was modeled and its joint stiffness values were identified. On the other hand, tests for composites parts trimming were performed in order to determine optimal cutting conditions guaranteeing the integrity (a good quality of) the part and satisfying productivity. Moreover, cutting forces were measured during the tests thanks to a wrench sensor mounted on the robot end-effector. From those two parallel studies and from a given placement of the part into the robot workspace, the robot end-effector displacements can be determined. Then those displacements could be minimized by determining the best placement of the part into the robot workspace. For operations that hardly stress the robot this solution can significantly reduce the robot end-effector displacements, without modifying the robot control.
Computer simulation of the laminar flow in stirred tanks generated by the proximity impellers of a mono and double screws type with simple and modified profiles. In this paper, the hydrodynamic characteristics of stirred tanks equipped with a mono and double screws with both classic and modified profiles have been numerically investigated. The computer simulations are conducted within a computational fluid dynamic (CFD) code, based on resolution of the Navier-Stokes equations with a finite volume discretization. The numerical results showed that the velocity field is more efficient with the modified screw profile than the one with a simple profile. In the case of the double screw, the importance of viscous dissipation and pumping has been assessed. Also, the pumping and the energetic efficiency reach the highest values. The good agreement between the numerical results and the experimental data confirm the validity of the analysis method.
We study the dynamic response to small acoustic oscillations of a vaporizing droplet in shape of a pastille (a small liquid cylinder, called "pastille" in the sequel, the height of which being smaller than the radius of the base). Contrary to some previously proposed models, where the thermal convection effect inside the droplet is often neglected, the continuously fed pastille-shaped model takes into account the effects of both thermal convection and conduction. Curves related to different heat exchange coefficients are presented for the frequency response of the vaporization rate. The case where the feeding process at the bottom of the pastille is assumed isothermal (isothermal bottom regime) is compared to the one where the feeding process at the bottom of the pastille is adiabatic (adiabatic bottom regime). The response factor curves for the pure conduction model of the spherical droplet and for the present model of the "equivalent pastille" are also compared. The temperature field perturbation is then examined. As well as for the evaporation mass flow rate perturbation, comparisons are made between the regime with an isothermal bottom and the one with an adiabatic bottom. We find that, in spite of some divergences observed between the various cases, the frequency response of a droplet submitted to acoustic oscillations presents also some common points. It is shown that the life time (or residence time), the thermal diffusion time, and the period of the harmonic perturbation do intervene strongly in the behaviour of the vaporizing pastille. The liquid propulsion is a possible application of this basic study conducted as part of a thesis.
In mass production, the customer defines the constraints of assembled products by functional and quality requirements. The functional requirements are expressed by the designer through the chosen dimensions, which are linked by linear equations in the case of a simple stack-up or non-linear equations in a more complex case. The customer quality requirements are defined by the maximum allowable number of out-of-tolerance assemblies. The aim of this paper is to prove that quality requirements can be accurately predicted in the design stage thanks to a better knowledge of the statistical characteristics of the process. The authors propose an approach named Advanced Probability based Tolerance Analysis (APTA), assessing the defect probability (called P-D) that the assembled product has of not conforming to the functional requirements. This probability depends on the requirements (nominal value, tolerance, capability levels) set by the designer for each part of the product and on the knowledge of production devices that will produce batches with variable statistical characteristics (mean value, standard deviation). The interest of the proposed methodology is shown for linear and non-linear equations related to industrial products manufactured by the RADIALL SA Company.
