Manuel François

Strong Improvements of Localized Surface Plasmon Resonance Sensitivity by Using Au/Ag Bimetallic Nanostructures Modified with Polydopamine Films

In the present work, the standard monometallic localized surface plasmon resonance (LSPR) biosensing sensitivity is highly improved when using a new system based on glass substrates modified with high-temperature annealed gold/silver bimetallic nanoparticles (Au/Ag bimetallic NPs) coated with polydopamine films before biomolecule specific immobilization. Thus, different zones of bimetallic NPs are spatially created onto a glass support thanks to a commercial transmission electron microscopy (TEM) grid marker in combination with two sequential evaporations of continuous films of gold (4 nm) and silver (2 nm) and followed by annealing at 500 °C for 8 h. By using the scanning electron microscopy (SEM), it is found that annealed Au/Ag bimetallic NPs have uniform size and shape distribution that exhibited a sharper well-defined LSPR resonant peak when compared with that of monometallic Au NPs and thereby contributing to an improved sensitivity in LSPR biosensor application. The controlled micropatterns consisting of bimetallic particles are used in the construction of LSPR biochips for high-throughput detection of different concentrations of a model antigen named bovine serum albumin (BSA) on a single glass sample, with a lower limit of detection of 0.01 ng/mL under the optimized conditions.

Effect of plastic shearing on damage and texture on Zircaloy-4 cladding tubes : experimental and numerical study

Abstract Experimental evaluation of plastic shearing due to cold rolling Zircaloy-4 (Zy4) cladding tubes has been performed. An experiment design was used to evaluate the influence of three parameters on the shear stress: the feeding, the frequency of rolling steps, and the type of internal lubricant. Calculation and experimental analysis have shown a good correlation between a cumulative damage factor (CDF) and depth of defects in cold-pilgered tubes. The CDF depends strongly on the shear strain e zr . Texture simulations, using a visco-plastic self-consistent (VPSC) model, have been performed and compared with experimental pole figures (PF) obtained by X-ray diffraction. A very good agreement is obtained between experimental and simulated pole figures, specially in radial and axial directions (RD–AD) plane. Results have shown that a shear component in the strain rate tensor is necessary, and that the critical resolved shear stresses (CRSS) must be changed during pilgering to take into account the real pilgering conditions.

Extracting the plastic properties of metal materials from microindentation tests: Experimental comparison of recently published methods

Experimental verifications have been performed on three engineering metals to verify recent methods proposed for extracting stress–strain curves from indentation tests. Their sensitivity to data errors is evaluated. Finally, the factors that might cause the inaccuracy and instability of the proposed methods are discussed, providing information that can be useful for further improving these methods.

The uncertainty of experimental derivatives: application to strain measurement

A procedure is presented to evaluate the uncertainty of derivatives computed from polynomial curves or surfaces fitted to experimental data. The procedure takes into account the uncertainties in the dependent and independent variables and agrees with international recommendations. It is valid independent of the experimental technique from which data are obtained. The application of the procedure is demonstrated by evaluating the uncertainty of strains calculated by differentiation of whole-field displacement data obtained by moire interferometry.

Neutron time-of-flight diffraction used to study aged duplex stainless steel at small and large deformation until sample fracture

Owing to its selectivity, diffraction is a powerful tool for analysing the mechanical behaviour of polycrystalline materials at the mesoscale (phase and/or grain scale). In situ neutron diffraction during tensile tests and elastoplastic self-consistent modelling were used to study slip phenomena occurring on crystallographic planes at small and large deformation. The critical resolved shear stresses in both phases of duplex stainless steel were found for samples subjected to different thermal treatments. The evolution of grain loading was also determined by showing the large differences between stress concentration for grains in ferritic and austenitic phases. It was found that, for small loads applied to the sample, linear elastic deformation occurs in both phases. When the load increases, austenite starts to deform plastically, while ferrite remains in the elastic range. Finally, both phases undergo plastic deformation until sample fracture. By using an original calibration of diffraction data, the range of the study was extended to large sample deformation. As a result, mechanical effects that can be attributed to damage processes initiated in ferrite were observed.

Numerical simulation and experimental validation of the microindentation test applied to bulk elastoplastic materials

The main objective of this work is to compare numerically simulated load?indentation depth curves together with deformation and stress fields underneath a sharp indenter for a set of mystical materials. Firstly, a numerical simulation and experimental validation of the microindentation test applied to three different bulk elastoplastic materials (copper, stainless steel and pure aluminium) using two indenters (Berkovich and spherical) are presented. The simulation of these microindentation tests is carried out using the finite element large strain elastoplastic and contact models. The corresponding results are particularly aimed at addressing the following aspects: the influence of the indenter geometry on both the load?indentation depth curve and range of plastic strains involved in the test, the comparison of the 3D results for the sharp indenter with those of the 2D approximation, the capabilities of the modelling through experimental validation of the numerical predictions and, in addition, an assessment of the indentation size effect. Secondly, the numerical results of Berkovich indentation applied to a set of mystical materials are exhaustively discussed. Although it is effectively shown that these mystical materials exhibit indistinguishable load?penetration depth curves during the loading phase, an important aspect that has not been previously addressed is that some clear differences in their responses are obtained for the unloading stage. Finally, the deformation and stress contours at the maximum indentation force and after unloading are particularly analysed.

Determining Ti-17 β-Phase Single-Crystal Elasticity Constants through X-Ray Diffraction and Inverse Scale Transition Model

The scope of this work is the determination of single-crystals elastic constants (SEC) from X-ray diffraction lattice strains measurements performed on multi-phase polycrystals submitted to mechanical load through a bending device. An explicit three scales inverse self-consistent model is developed in order to express the SEC of a cubic phase, embedded in a multi-phase polycrystal, as a function of its X-ray Elasticity Constants. Finally, it is applied to a two-phases (α+β) titanium based alloy (Ti-17), in order to estimate Ti-17 β-phase unknown SEC. The purpose of the present work is to account the proper microstructure of the material. In particular, the morphologic texture of Ti-17 a-phase, i.e. the relative disorientation of the needle-shaped grains constituting this phase, is considered owing to the so-called Generalized Self-Consistent model.

Modelling of the Ultrasonic Shot Peening Process

The aim of this work is to reach a better understanding of the ultrasonic shot-peening process and, in particular, the evolution of the shot speed distribution. A simple 1D modelling of the interaction between the shots and the sonotrode is carried out. The impact is considered as inelastic with an energy absorption that depends on the speed of the shot. It is found that after about 10 interactions (» 1s) the speed distribution in the chamber follows a Maxwell-Boltzmann distribution, which is the distribution found in a perfect gas at equilibrium. The influence of various process parameters such as the sonotrode amplitude, the vibration frequency on the average speed and on the Almen intensity is studied.

Texture and residual-stresses analysis in Zircaloy-4 cylindrical samples

Texture and residual-stress analysis using X-ray diffraction have been carried out on cylindrical Zircaloy-4 samples in cold-worked and finished state. The (00.2) pole figure of finished tubes shows an important asymmetry in the tangential direction (TD) not observed on unrolled tubes. This asymmetry vanishes at a 5-μm depth. A noticeable variation of the texture index J has been pointed out within the first micrometers from the surface of the tubes. Strain measurements in tangential and longitudinal directions have been carried out on the (10.4) and (20.2) planes. In the tangential (hoop) direction, compressive stress on the outer surface decreases rapidly in the first layers and remains constant at the analysed depth. Axial stress analysis shows the opposite sign for the two different diffracting planes on the cold-worked tubes, indicating the existence of second-order stresses.

A Kinematic Hardening Finite Elements Model to Evaluate Residual Stresses in Shot-Peened Parts, Local Measurements by X-Ray Diffraction

Experimental analysis can be very costly and time consuming when searching for the optimal process parameters of a new shot-peening configuration (new material, new geometry of the part…). The prediction of compressive residual stresses in shot-peened parts has been an active field of research for the past fifteen years and several finite elements models have been proposed. These models, although they give interesting qualitative results, over-estimate, most of the time, the level of the maximal compressive stresses. A better comprehension of the phenomena and of the influence of the parameters used in the model can only carry a notable improvement to the prediction of the stresses. The fact that the loading path is cyclic and is not radial led us to think that a model including kinematic hardening would be better adapted for the modelling of shot peening. In this article we present the results of a simulation of a double impact for several constitutive laws. We study the effect of the chosen constitutive law on the level of residual stresses and, in particular, we show that kinematic hardening, even identified on the same tensile curve than isotropic hardening, leads to lower stress levels as compared with isotropic hardening. Furthermore, the overall shape of the stress distribution within the depth is significantly different for the two types of hardening behaviour. Further, in order to check the modelisations, local measurements were carried on with X-ray diffraction on a large size impact and correlated with the topography of the impact.