Yazid Madi

Plasmonic mode interferences and Fano resonances in Metal-Insulator-Metal nanostructured interface.

Metal-insulator-metal systems exhibit a rich underlying physics leading to a high degree of tunability of their spectral properties. We performed a systematic study on a metal-insulator-nanostructured metal system with a thin 6 nm dielectric spacer and showed how the nanoparticle sizes and excitation conditions lead to the tunability and coupling/decoupling of localized and delocalized plasmonic modes. We also experimentally evidenced a tunable Fano resonance in a broad spectral window 600 to 800 nm resulting from the interference of gap modes with white light broad band transmitted waves at the interface playing the role of the continuum. By varying the incident illumination angle shifts in the resonances give the possibility to couple or decouple the localized and delocalized modes and to induce a strong change of the asymmetric Fano profile. All these results were confirmed with a crossed comparison between experimental and theoretical measurements, confirming the nature of different modes. The high degree of control and tunability of this plasmonically rich system paves the way for designing and engineering of similar systems with numerous applications. In particular, sensing measurements were performed and a figure of merit of 3.8 was recorded ranking this sensor among the highest sensitive in this wavelength range.

Anisotropic ductile failure of a high-strength line pipe steel

Fracture properties of a mother plate for API grade X100 line pipe were investigated using tensile notched bars, CT and SENB pre-cracked specimens. The material had an anisotropic plastic behaviour due to the thermo-mechanical control rolling process. In addition, anisotropic rupture properties were also observed. Specimens tested along the rolling direction were more ductile and more crack growth resistant than those tested along the long transverse direction. Unit cell calculations were used to show that this fracture behaviour is not related to plastic anisotropy. Assuming that fracture is controlled by internal necking between anisotropically spaced voids, a model combining GTN and Thomason models is proposed which enables describing rupture anisotropy. A modified phenomenological model is also proposed so as to reduce the computational cost.

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.

Effect of Plastic Constraint on Anisotropic Crack Extension in a Grade X63 Line Pipe Steel

The purpose of this work was to evaluate the fracture toughness for different plastic constraint levels of a grade X63 line pipe representative of in-service line pipes in France. This study was carried out for high constraint levels using Compact Tensile (CT) specimens and low constraint levels using Single Edge Notched Tensile (SENT) specimens. Moreover, in order to reduce the amount of tested samples, silicone replicas of crack advance were made all along the test. The results show that the loss of plastic constraint induces J–values about 70% higher compared to high constraint tests. A strong crack growth resistance anisotropy was observed at high constraint. This anisotropy is significantly reduced at low constraint.Copyright

Strain capacity assessment of API X65 steel using damage mechanics

Strain-based design for offshore pipeline requires a considerable experimental work aimed to determine the material fracture toughness and the effective strain capacity of pipe and welds. Continuum damage mechanics can be used to limit the experimental effort and to perform most of the assessment analysis and evaluation in a simulation environment. In this work, the possibility to predict accurately fracture resistance of X65 steel using a CDM model proposed by the authors, is shown. The procedure for material and damage model parameters identification is presented. Damage model predictive capability was demonstrated predicting ductile crack growth in SENB and SENT fracture specimens.

Fracture Behaviour of Mis-Matched Dissimilar Welds: Numerical Simulation Using Local Approach

The safety assessment of welded structures still remains an important industrial problem. In this study, a simple diffusion bonded bi-material jonction has been made in order to analyse the mismatch effect. It consists of an assembly of ferritic and austenitic steels which are representative of nuclear pressure vessel. Each material has been tested using smooth and notched tensile bars. These tests were used to adjust the parameters of local approach based on the Rousselier model. Bi-material structures including notch tensile bars, Charpy specimens and single-edge notch bend specimens were tested and simulated using the Finite Element method. The correct test/computation agreement shows that the adjusted parameters on the homogeneous specimens can be transferred to heterogeneous structures.Copyright