Guillaume Montay

The beginnings of plasmomechanics: towards plasmonic strain sensors

This article exposes the beginnings of a new field which could be named as “plasmomechanics”. Plasmomechanics comes from the convergence between mechanics and plasmonics. Here we discuss a relatively recent topic whose technological aim is the development of plasmonic strain sensors. The idea is based on the ability to deduce Au nanoparticles (NPs) distance distributions from polarized optical extinction spectroscopy which could thus give access to material strains. Variations of interparticle distances distributions can indeed lead to variations of plasmonic coupling and thus to material color change as shown here experimentally and numerically for random Au NP assemblies deposited onto elastomer films.

An Advanced Residual Stress Determination for 3D Cylinder Structure

For measuring in-depth residual stress in 3D cylinder structure easily in this paper, the semi-destructive incremental hole drilling technique combined with finite element method is used, the calibration coefficients of 3D cylinder components are calculated, and the relationship between strain and stress is determined, the changes of calibration coefficients are analysed, the residual stress of one steering joint of automobile is measured, and the errors of residual stress are discussed.

Determination of the Residual Stresses in Composite Laminate Using the Compliance Method

Residual stresses play an important role on the mechanical behavior of composite laminate. The development of new methods to determine the residual stresses gradient within the laminates is necessary. This article presents the adaptation of the compliance method in the case of composite laminates carbon/epoxy [02/902]s. The incremental drilling of a constant width groove allows for each increment to measure the strains (using strain gages) and displacements (using an optical device) of particularly points of the structure surface. These experimental data are compared with results given by a finite elements simulation. This comparison allows to raise the residual stresses in the composite laminate.

Study of Residual Stresses in Complex Parts by Experimental and Numerical Methods

Residual stresses can occur in many engineering components such as aircraft and aerospace. They can be caused by the forces and thermal gradient imposed during the forming process. Compressive stresses are sometimes purposely induced in near surface of materials by shot peening to help resist crack growth and fracture of components and to increase the working life under fatigue load. The knowledge of the magnitude and the distribution of the residual stresses, allows the engineer to optimize the forming operation and the materials choice. Theoretical elastic analyses to characterize the calibration coefficients developed under both plane stress conditions are proposed. These coefficients are used to link measured surface and/or subsurface strain to the residual stress. Three dimensional finite element analysis were developed and used to predict the magnitude and the direction of principal residual stresses in the depth of the material. The effect of sample geometry is studied of spherical samples on the calibration coefficient.

Microstructure, Hardness, and Residual Stress Distributions in T-Joint Weld of HSLA S500MC Steel

Abstract This paper investigates the characterization of the microstructure, hardness, and residual stress distributions of MIG-welded high-strength low-alloy S500MC steel. The T-joint weld for 10-mm-thick plates was joined using a two passes MIG welding technology. The contour method was performed to measure longitudinal welding residual stress. The obtained results highlighted a good correlation between the metallurgical phase constituents and hardness distribution within the weld zones. In fact, the presence of bainite and smaller ferrite grain size in the weld-fusion zone might be the reason for the highest hardness measured in this region. A similar trend of the residual stress and hardness distributions was also obtained.

Effect of Hemp Fibre Morphology on the Mechanical Properties of Vegetal Fibre Composite Material

The hemp fibres present specific fibre morphology and a complex non homogeneous cross section which changes in function of the location along the fibre length. Thus the mechanical properties of hemp fibres request a specific characterization method. In this study, firstly, a digital treatment method was developed allowing to consider different geometrical modelling methods: homogeneous or non-homogenous cross section, average global cross section, and cross section measured at the rupture location, including a 3D CAD model reconstruction of the fibre.

Mechanical Modeling of Hemp Fibres Behaviour Using Digital Imaging Treatment

These last years, hemp fibres are using as reinforcement for compounds based on polymer in different industrial manufacturing for their interesting mechanical and ecological properties. The hemp fibres present a non constant cross section and complex geometry that can have a high effect on their mechanical properties. The mechanical properties of hemp fibres (Young moduli, longitudinal stress and failure strain) are rather difficult and request a specific characterization method. In this study, a micro-traction test coupled with a numerical imaging treatment and a finite elements method are used. The mechanical tensile test allows to determinate the evolution of the traction load in function of the displacement until the fibre crack. The numerical imaging allows to measure finely the hemp cross section along the fibre and aims to reconstruct a 3D hemp fibre object model from an image sequence captured by a mobile camera. And lastly, the finite elements method allows to take the real fibre geometry into consideration for the mechanical characterization using inverse optimization simplex method.

Strain Rate Evolution in Aluminium Alloy Measured by ESPI during Tensile Test

The original and significant achievement of this work is to analyse strain rate field in aluminium alloy sheets during micro tensile test. In-plane Electronic Speckle Pattern Interferometry is used to follow the evolution of the local strain in real time. This paper is based on the detection of the localization on a relatively small area of the analysed specimen: less than 5mm × 4mm area. Moreover the speed of the tensile machine is very low, 0.2 to 0.1µm/s. The phase shifting technique is used to obtain the fringes representative of the material displacement. We can therefore get a very good accuracy in the material displacement. A heterogeneity in strain rate field can be noticed from a deformation stage which doesn’t coincide with the one calculated by the classic Considère’s criterion (dF=0) for the diffuse neck initiation (or plastic instability). We also show, the moment when one of the two slip bands systems becomes predominant, and even only one band continues to exist, this occurring widely before fracture. Finally, the fracture of the specimen occurs across this remaining band. The total strain is measured with a second camera, in white light, and is correlated together with the strain rate field to study the localization.

A new Approach in Residual Stresses Analysis by Speckle Interferometry

The knowledge of residual stresses allows a reliable prediction of structure performances evolution, such as service life [1-3]. In this paper, we develop a new method for residual stresses determination combining Electronic Speckle Pattern Interferometry (ESPI) with the machining of a groove. The internal stress field is perturbed as the depth of the groove is increased incrementally. The structure finds a new equilibrium state generating displacements which are measured using ESPI. This method was tested on an aluminium alloy AU4G plate treated locally by an ultrasonic shot-peening. The investigation of the images obtained with the phase shifting technique and fringe patterns, makes it possible to analyze, simultaneously, the stress profile along two directions: along the depth of the structure, and along the groove direction.

Evaluation of Residual Stresses in Dissimilar Weld Joints

Dissimilar metal joints between pipes of ferritic and austenitic steels are present in primary coolant circuit of pressurized water reactors. Over the last years in particular in USA and Japan, stress corrosion cracks, often associated with weld repairs, have been observed for some dissimilar welds made with an Inconel filler metal. The integrity of this type of components is thus a major safety issue. In this context, the goal of this work is to evaluate the welding residual stresses field for a dissimilar weld joint. A representative bi-metallic tubular weld joint was fabricated and residual stresses profiles in the different weld zones were evaluated by means of the hole drilling and neutron diffraction methods.