Michel Dupeux

Stresses, displacements and energy calculations for interfacial dislocations in anisotropic two-phase media

Abstract The problem of finding the elastic stress and displacement field around a straight dislocation at the interface separating two media with the most general anisotropic properties, is reduced, similarly to a treatment by Barnett and Lothe (1974), to the inversion of twelve linear equations with twelve unknowns, using the classical formulations of anisotropic elasticity. The opportunity of including constant terms in the analytical form of the displacements is discussed as well as the presence of a resulting couple on the dislocation. The line energy and dilatation field are deduced. Two examples concerning Al/CuAl 2 and α/β brass phase boundary dislocations are treated numerically with help of a FORTRAN computer program. Noticeable effects of both inhomogeneity and anisotropy are revealed. Results for the displacements, stresses and energies are presented.

Versatile microscopic profilometer-vibrometer for static and dynamic characterization of micromechanical devices

In this paper microscopic interferometry is used for 2D and 3D profiling of micromechanical devices deformation and, is extended to allow vibration spectra measurements on a few microns wide microdevices. This is obtained by adding an apertured photomultiplier with suitable signal processing and subnanometric piezoelectric excitation. Resonant frequencies are detected both from vibrations-induced fringes contrast variations and by using a homemade wide bandwidth (10 MHz) double lock-in amplifier. This allows vibration measurements up to several MHz with a spatial resolution down to 1.25 micrometer and a detection limit of vibrations amplitudes in the 0.2 - 1 nm range. Furthermore the system allows a direct visualization of the whole vibration modes and can be applied for automated bulge testing of membranes. System operation for 3D profilometry, vibrometry and bulge testing is demonstrated on Cr cantilever microbeams and microbridges fabricated by surface micromachining and on membranes. Capabilities of the system for large vibration amplitudes measurements and its extension for on-wafer resonant frequencies measurements by using optical excitation are discussed.

Production of oriented two-phase bicrystals by a diffusion bonding technique

An experimental technique is presented for high temperature solid state diffusion bonding of two different crystals. The relative orientation of the crystals and the orientation of the boundary plane can be chosen arbitrarily. Unwanted recrystallization close to the boundary plane is avoided by precise adjustment of the applied bonding force. Special care is taken for preparation of the contact surfaces of the two crystals, to suppress as far as possible superficial straining and planarity defects on macroscopic and microscopic scales. This technique is of use for any stable two-phase system at thermal equilibrium, and has been applied successfully to obtain Al/Al2Cu and Ag/Cu two-phase bicrystals. With both systems, a one hundred hour high temperature treatment is sufficient to produce interfaces free from embritteling porosites, on areas large enough to allow cutting of specimen for macroscopic mechanical tests. These experimental results and the kinetics of bonding are discussed and compared to the theoretical model proposed by Garmong, Paton and Argon (1975).

Application of the Blister Test to Adhesion Energy Measurements in Metal/Ceramic Film-on-Substrate Systems

The mechanisms of interfacial decohesion of metal/ceramic interfaces are of major importance for the practical use of joints in technical applications. Among other quantitative characteristics, the interfacial fracture energy is one of the most specific of the interface of interest. Nevertheless, very few mechanical tests are available to provide reliable values of this interfacial fracture energy [1–2], first because of the generally unstable character of the fracture process, and second because the measured quantities are highly dependent on the test geometry through the so-called “loading phase angle” (or “mode mixity parameter”) [3–4], which indicates the respective contributions of fracture mode I and mode II to the load applied to the fracture test specimen.

Mixité modale pour une fissure d'interface: Application à l'essai brésilien

ABSTRACT At an interface crack tip, the usual mode I and mode II splitting of the singular stress field is impossible due to a complex exponent, there is a mixity of modes. A direct computation of the complex intensity factor allows to give a precise definition of this mixity. Even if some ambiguities remain, it removes an arbitrary parameter which is the distance where measures or computations must be performed.

Methodology to Determine the Toughness of a Brittle Thin Film by Nanoindentation

Nanoindentation is the most convenient local technique for measuring elastic modulus, hardness, and fracture toughness of dielectric thin films. This approach is applied to bulk silicon and dielectric thin films (porous and non-porous) on silicon substrate. Reproducible stable cracks are generated from the edges of a cube corner indentor. The validity of theoretical model of use to estimate the toughness from cracks length has been checked on these reference cases. To calculate the toughness of thin film on Si substrate, we first established the loading range in which the cracks only affect the thin film without substrate damage. Several corrective terms have been introduced to the classical toughness estimation formula to take into account the proximity of the film/substrate interface and the residual stress pre-existing in the film. This approach is discussed by comparing experimental results obtained including these improvements to literature results.