Papers by Author: Olivier Dalverny

Abstract: This paper deals with an identification methodology of the interfacial fracture parameters to predict the lifetime of a metallic brazed joint. The methodology is based on an experimental-numerical study whereby the optimal parameters are obtained. The experimental data, using the scanning electron microscope analysis, allowed approving that failure of the assembly based AuGe solder seems first to appear near the interfaces. These results were confirmed by micrographs analysis of the solder/insert and solder/substrate interfaces. Then, using shear test results and parametric identification coupled with a finite elements model (FEM) simulation, the damage constitutive law of the interfacial fracture based on a bilinear cohesive zone model are identified. The agreement between the numerical results and the experimental data shows the applicability of the cohesive zone model to fatigue crack growth analysis and life estimation of brazed joints.

Abstract: This paper describes a new technique allowing the monitoring of damage in metallic freestanding thin films during micro-tensile test by using electrical characterization. After a presentation of the set-up, results obtained on Aluminium thin coatings by using two calculation methods for damage variable are presented and commented.

Abstract: This paper presents different interests of non destructive full-field measurement. More precisely, it focuses on the characterization and the comparison of the X-ray tomography and two methods of infrared thermography in order to define the defect detection limits and to precise the specific application fields for each technique on multi-layered and sandwich composite structures. The obtained results are qualitatively and quantitatively analyzed.

Abstract: 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.

Abstract: 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.

Abstract: The aim of this work is to identify parameters driving constitutive equations of materials with displacement field measurements carried out by image stereo-correlation during an unidirectional tensile test. We evaluate two identification techniques. The first one is the virtual fields method which consists in writing the principle of virtual work with particular virtual fields. It is generally used in the case of linear elasticity and it requires a perfect knowledge of the model in terms of boundary condition since the virtual fields used must be kinematically admissible. This method allows to determine parameters by a direct and fast calculation, without iterations. The second method is the finite element model updating method. It consists in finding constitutive parameters that achieve the best match between finite element analysis quantities and their experimental counterparts. This method is more adaptable than the virtual field method but it needs to spend more calculation time.

Abstract: This paper presents a Finite Elements Modelling (FEM) based methodology dedicated to the evaluation of the lifetime and the reliability of assemblies involving brittle materials under cyclic loading. It focuses on the particular case of metal bonded Aluminium Nitride (AlN) substrates used in power electronic switch modules. The ceramic fracture criterion was formulated according to the weakest link concept, under Weibull's approach. The material's parameters were determined by running three points bending tests. In order to check the relevancy of the proposed methodology, a non linear thermomechanical Finite Elements Model allowed computing the number of thermal cycles before substrate brittle fracture within a test vehicle, which was then compared to experimental results. Once validated, the methodology was applied to two different configurations of a power switch module, designed for harsh environment aeronautic applications. The corresponding external loading profile was considered to compute and monitor the evolution of the maximal principal stresses within the ceramic substrates whole volumes. Their lifetimes and reliabilities was finally assessed and compared to the applications requirements.

Abstract: The objective of this paper is to present the solution developed to model the chem- ical and thermal coupling occurring in an intensied heat exchanger reactor. The results of this modeling are all the properties of the chemical uid along the conduit, and the temperature distribution in the structure. This will be used to manage a thermal and mechanical reliability study of the heat exchanger reactor.

Abstract: This work studies the reliability of power electronic component in aeronautical environment to the ageing eect of the thermal cycling. The structure fatigue is sensitive to the process assembly conditions especially of the soldering process. To correclty evaluate the reliability of the power module, the identication of the solder behavior is one of the rst steps. Anand Model is here identied. Experimental test have to be established to evaluate the parameters of the law. A srt study is made to evaluate the indetiability of the law according to the dierent experimantal test. Then, the scatter of the parameters is evaluated in a context of time series. In the end, the scatter of the parameters is included in a nite element model to understand the inuence of this scatter on the evaluation of the number of cycle before failure.