Thick composite structures under a load pinch

Thick composites are increasingly used in the design of mechanical structures. Combined with low weight, they are generally resistant structures, which can support importante loads. In addition, depending on the number and nature of the materials used, it is possible to adapt properties for specific applications (damping structures).This work proposes the establishment of a new theoretical model of multilayer beam. The model, which is simple and easy handling, is intended for the subsequent establishment of a finite element. The goals are: improve the refinement of the transverse displacement and transverse shear, avoiding the calculation of transverse shear, the use of correction factors, keep only the usual displacement,test the accuracy of the model compared with models from the literature (for an equivalent single-layer approach). The proposed approach is of the kinematics, the form adopted for the displacement field is justified from a dimensional point of view, by the equations of elasticity. The equations of motion and boundary conditions are obtained by applying the principle of virtual power. The validity of the model is tested on problems for which solutions (obtained by previous theories)exist

Effects of the Unified Viscoplastic Formulation and Temperature Terms on the Thermomechanical Behavior of Soldering Materials

Solder materials are critical packaging compounds and due to usually weakest melting temperature among packaging constitutive materials, thus, they are frequently subjected to a multitude of physical phenomena: creep, fatigue and combined hardening effects. The complexity and interaction of such factors must be considered in suitable way in the mechanical behavior modeling using the appropriate material behavior laws. The choice of the mechanical model depends on several factors such as the complexity of constitutive equations to be integrated, the availability and suitability of implementation in the FE codes, the number of parameters to be identified, the capability of the model to represent the most common physical features of the material… Following these observations and in order to deal with these critical remarks, comparisons between the most common unified viscoplastic models should be done in the local and finite element levels for the decision upon the most efficient model. That is the aim of this paper with application to a tin based solder token as the test material

Experimental and mechanical characterizations of a lead free solder alloy for electronic devices

Electronic power modules devices are paramount components in the aeronautical,automotive and military applications. The solder layers are the most critical parts of the module and are usually subjected in their whole life to complex loading conditions. To improve the design task, realistic thermoelastoviscoplastic and lifetime prediction models which can describe efficiently the deformation-damage of the electrical device must be chosen carefully. Some of the most common behavior models are based on the separation between creep and plasticity deformations such as power law, Garofalo, Darveaux… So, to take into account the creep-plasticity interaction, the thermal cycling as well as the hardening-softening effects, unified viscoplastic models are increasingly being used to describe more efficiently the physical state of the material. We propose in this framework a survey of some unified viscoplastic models used in the electronic applications for the viscoplastic modeling of the solder as well as creep-fatigue life prediction rules. The models are used for the characterization of a SnAgCu solder and are briefly compared within tensile, creep data and stabilized responses

Caractérisation expérimentale du comportement mécanique d’assemblage haute température pour l’électronique de puissance

Ce papier a pour objectif l’étude expérimentale du comportement mécanique de deux types de connexions haute température mises en œuvre pour l’assemblage de composants d’électronique de puissance : une jonction réalisée par brasage en phase liquide transitoire (TLPB) d’Ag-In et une autre par brasage d’un eutectique Au88Ge12. Les connexions réalisées à partir d’inserts de cuivre sont caractérisées mécaniquement au moyen d’essais de cisaillement. Une analyse de la microstructure des jonctions en coupe et des faciès de rupture des deux connexions a également été menée. L’ensemble des essais et des analyses permettent de comparer le comportement mécanique et la faisabilité des deux connectiques d’électronique de puissance

Shear Test on CFRP Full-Field Measurement and Finite Element Analysis

The purpose of this work is to study the Iosipescu shear test and more precisely its ability to characterize the shear modulus of a carbone/epoxy composite material. The parameters influencing this identification are the fibre orientation, the geometry of the notch and the boundary conditions. Initially these parameters were studied through the finite element analysis of the shear test. Then, the measurement of the shear strains was carried out by traditional methods of measurement (strain gauges) but also by optical methods. These optical methods: the digital image correlation and the electronic speckle pattern interferometry (ESPI); allow for various levels of loading, to reach a full-field measurement of the shear strain. This enabled us to study the strain distribution on the section between the two notches. The finite element model enabled us to study the parameters influencing the calculation of the shear modulus in comparison with strain gauges, image correlation and ESPI. This work makes it possible to conclude on optimal parameters for the Iosipescu test

Viscoplastic behavior of diamond die attach subjected to high temperature conditions

In power electronic applications, diamond based semi-conductors appears to be a new way to widely increase the capabilities of power electronic converters. The main prospective expected is an increasing in system integration and power capabilities. The Diamonix project concerns the elaboration of a single-crystal diamond substrate with electronic quality and its associated packaging. The designed structure has to resist to temperatures varying between -50°C and +300°C. This paper deals with an experimental and numerical study of the diamond die attach solution. The development of a packaging for diamond component relies in particular on a specific choice of solder’s alloys for the junction die/substrate. To carry out this junction, AuGe and AlSi eutectic alloys were chosen and characterized; the choice of these two kinds of solders i.e. AuGe and AlSi is motivated by the practical elaboration process and the restrictions of hazardous substances (RoHS). The first solder has a melting temperature of 356°C; the second has a higher melting point of 577°C. In this paper, we present some numerical results obtained from FE simulations of two 2D configurations of simplified electronic packaging. The power electronic packaging is composed of a diamond die and a copper metallized Si3N4 ceramic substrate which are brazed together with either AuGe or AlSi solder alloy. To predict the thermomechanical behavior of the solders, a particular constitutive behavior law was implemented as a User MATerial subroutine which is based on a viscoplastic unified McDowell formulation, coupled with porous damage equations. The mechanical law can describe precisely the viscoplastic damage phenomenon of solder subjected to high thermal cycling and to optimize the thermo-mechanical modeling for advanced package developmen

Tribological aspects in modern aircraft industry

Preface : The problem of contact materials subject to relative movement is becoming increasingly important for lifetime of the equipment, pollution and cost in energy. One of the aims of tribology is to understand how friction occurs and wear in dynamical contacts. This can vary considerably depending on the choice of the pair of materials and the experimental device. Few milligrams of material lost in a mechanism is sufficient to make it unusable and cause replacement with significant costs. There is still no specific and general formalism to solve the problem of tribology, that is to say, friction, tearing, wear and lubrication of solid and liquid. Friction behavior or wear depends on complex conditions of stress, environment and physicochemical properties of surfaces, themselves dependent on tribological mechanisms. The intrinsic mechanical properties of materials are complementary and play a direct role in the tribological process. The work presented at the ACMA’14 conferences are multidisciplinary, by interacting mechanics, physical chemistry and materials science on a different scale ranging, the goal is to explain, even if the reactions of the contact surfaces are very complex, the basics of tribology, the process of friction and wear, to apply the test methods on the materials in contact and get material coatings on other surfaces by different methods and processes mechanical, physical and chemical. This special issue of the journal "KEM: Key Engineering Materials" consists of a collection of studies both in the fields of experimental simulation of tribology than the science of surfaces in contact by relative movements in relation to the mechanical properties materials

Contribution of a micromechanics-based approach for reliability assessment

The paper intends to widely develop the use of a new methodology for the design and optimization of composite materials and structures. Based on the coupling of reliability methods and homogenization techniques, such approach allows the integration of uncertainties at different scales in the problem analysis (i.e. from the microscopic scale of the composite material components up to the macroscopic scale of the structure) and the investigation of their consequences in the failure prediction. The principles and implementation steps of such original method have already been described in details (Int. J. Mech. Sci. 53 (2011) 935-945; Eng. Fail. Analysis 18 (2011) 988-998). This work focuses on its application and significant progress allowed in the design phase for engineering composite materials. Illustrations are presented on the case of a civil engineering structure, namely the Laroin footbridge (France) with carbon epoxy stay cables, and highlight reliability-based innovations and exploitations regarding the structure optimization

Mechanical characterization of an Au-Ge solder alloy for high temperature electronic devices

This paper presents a description of the mechanical behaviour of an Au-Ge solder under various loading conditions as well as an elastoviscoplastic modelling. In order to achieve the modelling task, the solder is subjected to a set of shear, creep and fatigue loadings in order to determine the behaviour dependence to the temperature and displacement rate and which could be useful to evaluate the degradation of the material. These tests are realized under a wide range of temperatures, loads and displacement rates for modelling purposes. Then, a unified viscoplastic model is applied to predict correctly the material mechanical responses. The model is correlated with the experimental data

Assemblages structuraux des convertisseurs de puissance

L'accroissement des performances des équipements de Traction ferroviaire, reposait essentiellement jusqu'à maintenant, sur l'intégration des innovations dans le domaine des composants électriques et des matériaux diélectriques mais la standardisation de sous-ensembles réutilisables nous conduit à reconsidérer les assemblages structuraux des coffres de traction (convertisseurs de puissance). Ces coffres de traction sont assemblés actuellement avec des éléments de fixation mécanique (boulon, rivet), le but est donc d'améliorer la connaissance des comportements mécaniques de ces types d'assemblages à travers d'une étude expérimentale basée sur des essais statiques et dynamiques sur des joints boulonnés et rivetés. Ces essais nous ont permis de valider des modèles numériques par des éléments finis en utilisant les codes de calcul ABAQUS et ANSYS. La deuxième partie de la thèse concerne les assemblages par collage structural. Nous avons étudié la possibilité de remplacer les assemblages mécaniques classiques par l'assemblage par collage structural. La première phase de notre travail a été de recenser et sélectionner des adhésifs structuraux susceptibles de répondre à notre cahier de charge. Dans cette partie les travaux suivants ont été réalisés : - Etude des comportements des adhésifs en tant que matériau, ce qui a nécessité de réaliser des éprouvettes massiques. - Réalisation d'essais expérimentaux en statique et en dynamique sur des joints collés avec l'adhésif sélectionné. - Création des modèles numériques non linéaires en 3D sur ABAQUS pour les joints collés. - Etude hygrothermique accélérée afin d'étudier l'effet du vieillissement sur les assemblages collés en fonction de l'humidité et de la température.Increased performance of railway traction equipment, until now relied primarily on the integration of innovations in the field of electrical and dielectric materials, but the standardization of subassemblies reusable us to reconsider the structural assemblies of the traction cubicles (power converters). These cubicles are assembled now with mechanical fasteners (bolts, rivets), the first goal is to improve knowledge of the mechanical behaviour of these types of joints through an experimental study based on statics and dynamics tests of bolted and riveted joints. These tests have allowed us to validate numerical models of finite elements by using the computer codes ABAQUS® and ANSYS®. The second part of the thesis deals with the structural adhesive joints. We studied the possibility of replacing conventional mechanical assembly structural bonding. The first phase of our work was to identify and select structural adhesives that could meet our specifications. In this section the following work has been made: - Study of thermo-mechanical behaviour of the adhesive with the bulk Adhesive Test Specimens. - Statics and dynamics test in the bonded joint. - Non-linear 3D finite elements models. - Hygrothermal accelerated to study the effect of aging on the adhesive according to the humidity and temperature.TOULOUSE-INP (315552154) / SudocSudocFranceF