Daniel Coutellier

Studies of Scale Effects for Crash on Laminated Structures

This work proposes the study of the influence of scaled down ply layout techniques applied in a laminated composite structure submitted to fast dynamics. By its wide-ranging advantages, scale reduction represents a significant stake for engineers. An experimental campaign is carried out on an omega-shaped structure. The energies absorbed, as well as the efforts applied in the composite structure are then compared between the scale 1 prototype with the various models established (scales 1/2 and 1/4). The conclusions generated are numerous. Firstly, in this geometrical configuration, dynamic loading does not have the same effects on the results and, secondly, the relations of similitude used seem to be able to give some solutions, if the same ruin damage modes appear.

Solder fatigue failures in a new designed power module under Power Cycling

Abstract Today a point has been reached where lifetimes of power modules are limited by the standard packaging technologies, such as wire bonding. To surpass these limits, a new power module was designed using Cu clips as interconnects instead of Al wire bonds. With this new design the structure robustness should be improved and lead to a reliability gain but in counterpart it requires an additional solder layer in order to fix the clip onto the die. This paper studies the failure mechanisms occurring in these two solder layers under power cycling. The behavior of solder layers is precisely analyzed by performing power cycling tests and by taking advantage of Finite Elements simulations. Furthermore an experimental and numerical sensitivity study on test parameters is conducted. Results obtained enable the definition of solder lifetime prediction models.

Geometrically nonlinear analysis of two-dimensional structures using an improved smoothed particle hydrodynamics method

Purpose – The purpose of this paper is to present an efficient smoothed particle hydrodynamics (SPH) method particularly adapted for the geometrically nonlinear analysis of structures. Design/methodology/approach – In order to resolve the inconsistency phenomenon which systematically occurs in the standard SPH method at the domain’s boundaries of the studied structure, the classical kernel function and its spatial derivatives were modified by the use of Taylor series expansion. The well-known tensile instabilities inherent to the Eulerian SPH formulation were attenuated by the use of the Total Lagrangian Formulation (TLF). Findings – In order to demonstrate the effectiveness of the present improved SPH method, several numerical applications involving geometrically nonlinear behaviors were carried out using the explicit dynamics scheme for the time integration of the PDEs. Comparisons of the obtained results using the present SPH model with analytical reference solutions and with those obtained using ABAQU...

Un élément multi-matériaux pour l’étude du comportement en crash des structures stratifiées : synthèse et perspectives

Abstract.The materials used within the structures in the field of ground transportation are increasingly complex and it is usual to find numerous composite parts. New laminated materials are appeared, more particularly the multi-layered multi-materials (combining metals such as steel, aluminium… and composite materials such as resins, fibres…). We are to develop a finite element method permitting to study under impact these structures. The latter have been built into an explicit computation software. A synthesis of developments is presented and many perspectives are envisaged.

Post-buckling analysis of thin-walled structures using the SPH method

In this investigation a meshless shell formulation is proposed for the post-buckling analysis of thin-walled structures using a non-linear dynamic explicit scheme. This method is an adaptation of the Smoothed Particle Hydrodynamics (SPH) method to deal with shell-like structures, while keeping its character of a strong formulation based on the principle of collocation directly applied on the differential equilibrium equations. The present SPH formulation is an extension of the continuum-corrected and stabilized SPH method allowing a thin structure to be modeled by using only one layer of particles to represent the shell mid-surface. Application of this method for the post-buckling analysis of several academic examples, shows its interest and its potential especially in terms of CPU computing time saving while keeping a very good level of accuracy compared to the classical SPH method and to the Finite Element method.

Development of a New Methodology for Delamination Detection in Laminated Structures

A new methodology to study the behaviour of delaminated composite structures has been developed. This study can be split up into two parts: The first one is about the detection of delamination in damaged laminated thin structures. In the finite element computational code, those laminated structures are modelled using shell elements. The methodology uses post-process criteria based on fracture mechanics linked with damage mechanics of computational code by the effective stress tensor. In the second place, the influence of delamination over the overall behaviour of the structure is taken into account. This influence is introduced by locally changing the material characterisation, progressively during the loading phase. These integrated effects change the numerical behaviour on loading and energy curves.

Confinement device to assess dynamic crushability of wood material

Cellular materials such as wood are widely and advantageously used as shock absorbers in various transport applications. The design and manufacturing of structures made of these materials require the knowledge of their dynamic compressive properties at various strain rates and stress states. Therefore, it is challenging to conduct dynamic multiaxial stress state experiments and especially on split-Hopkinson pressure bar apparatus where stress hardening increases as a function of velocity. This paper presents the so-called verification and validation methodology for confining solutions dedicated to impact on viscoelastic split-Hopkinson pressure bar system with large diameter bars. The method is a hybrid approach combining finite element analysis and an original experimental validation. Based on finite element results, particular attention is given to the mass, the material and the geometry to minimize the confining device influence on the propagation of elastic waves and thus on the material response of the tested specimens. It is essential to avoid spurious reflected waves at the new interfaces of the system in order to ensure the validity of the experimentation. The numerically predicted solutions are experimentally validated and preliminary results in the context of dynamic loadings using wood material are presented.