Sciences des matériaux
Measurement of thickness of thin metal sheets by the A0 Lamb mode at low frequency.thickness products
Industrial structures undergo significant stresses during their life and can destroy the environment. This can, in many cases, cause serious damage, often imperceptible. Several methods are used to detect and locate such early stage damage.Lamb waves, which are guided by both surfaces of a planar structure, are good candidates to inspect the plate in a non invasive manner. These waves have the advantage to travel long distances without significant attenuation in the direction of propagation, which allows control quickly, permanently and inreal time, large areas of difficult access. In this work, we present a method to measure the thickness of thin sheets using the propagation of the first anti-symmetric A0 Lamb mode, generated by a piezoelectric transducer. The principle is based on the existing proportionality relationship between the group velocity and thickness of thin metal sheets, at low frequencies. We test this relation on various metallic sheets of thicknesses: 25; 75; 100; 160 and 200 microns. Voir les détails
Mots clés : Lamb waves, group velocity, thickness, Transducer.
SPATIO-TEMPORAL ASPECTS OF THE DOMAIN PROPAGATION IN A SPIN-CROSSOVER LATTICE WITH DEFECT
We study the spatiotemporal formation and spreading of the high-spin state (HS) during the cooperative relaxation of the photo-induced metastable high spin (HS) state at low temperature of anelastic lattice, in the presence of a defect injected in the center of the lattice. For that, we designed a 2D rectangular-shaped lattice with discrete spins coupled by springs. The distances between the sites are spin-dependent which prevents any analytical resolution of the present problem. The elastic coupling between the spin-crossover (SCO) sites results in a long-range effective interactions between the spin states from which originates the complexity and the richness of this problem. The numerical resolution of the problem is performed using Monte Carlo simulations on the spin states and theatomic positions. The simulations are restricted to a lattice with a hole (simulating the defect) with afixed size. The presence of the defect shows the dynamics of the spin-crossover transformations startsfrom one corner of the rectangular lattice and propagates along the width (shortest distance to thesurface).Then a second regime of longitudinal propagation takes place, whose velocity slows down significantly in the vicinity of the defect. Then the interface leaves the defect, where it was pinned atlow velocity and accelerates when it approaches the border of the lattice. We have also investigated the spatial dependence of the displacement field, from which we derived the spatial distribution of the divergence, which directly connects to the distribution of the internal strain and elastic energy. Valuable information is derived from the time-dependence of the total elastic energy in particular around the defect. Voir les détails
Mots clés : Spin Crossover, phase transition, interface propagation, Defects, elasticity, Monte Carlo Simulations
Using Multivariate Statistics & Multi-Scale Entropy to Monitor Gears Degradation and Signal Denoising Strategy using Wavelet Decomposition
This paper focuses on fault diagnosis in gears transmissions driven by induction machines. A new tool of anomaly detection based on multi-scale entropy (MSE) algorithm in conjunction with multivariate statistical approach of the motor current signature analysis (MCSA) is proposed. Simulation results show that the proposed methods are able to detect tooth surface decay in the permanent regime of MCSA. Voir les détails
Mots clés : gear Fault diagnosis, Multi-scale entropy, Induction machine, Wavelet decomposition and principal component analysis.
Stress and temperature effects study on anhysteretic curves behavior of magnetostrictive materials
The present work deals with the effect of stress and temperature on the effective magnetic field which occurs in magnetostrictive materials when it is subjected to external applied field. The magnetostriction is then computed for changes made onstress and temperature respectively. The anhysteretic curves representing the magnetization behavior with applied magnetic field are deduced. The results obtained are comparable with those provided in literature. Voir les détails
Mots clés : Stress, Magnetostrictive materials, Magnetization, Temperature, Stress field, Anhysteretic curve
Defects dispersion studies in composite structures has polymer matrix
The performance / weight composite materials with polymer matrix reinforced by fibers makes them a material of choice for structural applications in many fields such as aerospace and civil engineering. Among these materials, the epoxy matrix composites reinforced carbon fibers are often referred to as having the most interesting mechanical properties due to the remarkable properties of the carbon fibers. The epoxy resin is also involved in obtaining these exceptional properties thanks to its ability to impregnate the fibers well, its chemical and electrical resistance and low retraction during polymerization.Analysis of measurement results of the three pointbending on the composite materials epoxy matrix reinforced with different layers of carbon fibers using Weibull statistics allow us to the highlight the probabilistic aspects of the fracture and the dispersion defects in structures. Voir les détails
Mots clés : composite, fiber, polymer, probability default.
Innovative Eddy Current Probes Characterization Of Micro Defects
In this paper, we designed Eddy Current probes based on two different technologies, depending on the application. The first one is based on traditional probes based on classical winding coils, the second one takes advantage of the small size and high sensitivity of micro-coils etched on a flexible kapton film. Those probes are very efficient in the detection of defects located in complex geometries or in small curvature radius components. The simulation also provides the ability to compare upstream performance of a new probe relative to a conventional sensor and thus guide the choice of investment in innovative technology. Voir les détails
Mots clés : Eddy curren, Defect characterization, Finite Element Method, micro coil, arrayed eddy current sensor
Human Liver Tissue Characterization Using Backscattered Ultrasound Signals Mean Scatterer Spacing
Using the backscattered ultrasound signals, we studied the periodicity of in vitro healthy and pathological liver tissue, we utilized the mean scatterer spacing (MSS) as a parameter of tissue characterization, estimated by: Spectral Auto-Correlation (SAC), Spectral Correlation of the autoregressive model (AR-SAC) and the Discrete Wavelet Technique (DWT), in comparison between this three method, the result of simulation confirm that DWT with Fourier Transform together (DWT with FT) can provide a very effective tool to extract the MSS from such structure and characterize the tissue. Voir les détails
Mots clés : Periodicity, Liver tissue, Mean scatterer spacing, Backscattered Ultrasound Signals
Reconstitution of complex defects with the methodof neural network: Application for the nondestructiveevaluation
in this work, we propose a reconstitution of complex defects starting from the results obtained during a nondestructive testing by eddy currents carried out on aconducting plate by using the neural network. We provided tothe neural network the values of impedance of the differential sensor calculated using a modeling by finite elements.The values of impedance are injected at the input of the neural network and the depth of the defect is recovered in its output, we used the gradient of the error propagation algorithm for performing learning of the neural network. Voir les détails
Mots clés : Neural Network, eddy currents, impedance, complex defect, nondestruction evaluation
Non intrusive stochastic finite elements method applied for non destructives NDT problems
The current work concerns the study of harmful defect detection for the inspected structure by eddy current non destructive testing. So a non intrusive stochastic finite element method was exploited in the case of 2D magnetodynamic equation. The electrical conductivity is considered as random variables and generated using Monte -Carlo method. Voir les détails
Mots clés : Stochastic finite element method, Eddy Current, Conducting plate, Random variable
Temperature Effects on Thin film Based SPR-Sensor
In this paper, using the angle interrogation methods, we simulate the effect of temperature fluctuation on thin film based SPR-sensor. The sensor configuration is a three layer Krestchmann configuration consisting of glass prism, thin metallic layer, and bulk sensing layer. The temperature sensor uses RPS geometry of three interfaces where the refractive index of the layer adjacent to the environment is very sensitive to changes in the environmental temperature. The final results indicate that, as the temperature decreases, Θmin (resonance angle) shift to larger angles and increased in Rmin .These results can be used in the development of chemical, biomedical sensors, is suggested Voir les détails
Mots clés : surface plasmon resonance (SPR), thermo-optic effect, temperature sensor.