General Metasurface Synthesis Based on Susceptibility Tensors

A general method, based on susceptibility tensors, is proposed for the synthesis of metasurfaces transforming arbitrary incident waves into arbitrary reflected and transmitted waves. The proposed method exhibits two advantages: 1)it is inherently vectorial, and therefore better suited for full vectorial (beyond paraxial) electromagnetic problems, 2) it provides closed-form solutions, and is therefore extremely fast. Incidentally, the method reveals that a metasurface is fundamentally capable to transform up to four independent wave triplets (incident, reflected and refracted waves). In addition, the paper provides the closed-form expressions relating the synthesized susceptibilities and the scattering parameters simulated within periodic boundary conditions, which allows one to design the scattering particles realizing the desired susceptibilities. The versatility of the method is illustrated by examples of metasurfaces achieving the following transformations: generalized refraction, reciprocal and non-reciprocal polarization rotation, Bessel vortex beam generation, and orbital angular momentum multiplexing

Experimental and numerical analysis of micromechanical damage in the punching process for High-Strength Low-Alloy steels

Sequential sheet metal forming processes can result in the accumulation of work hardening and damage effects in the workpiece material. The mechanical strength of the final component depends on the “evolution” of these two characteristics in the different production steps. The punching process, which is usually in the beginning of the production chain, has an important impact on the stress, strain and damage states in the punched zones. It is essential that the influence of these mechanical fields be taken into account in the simulation of the forming sequence. In order to evaluate the evolution of each phenomenon, and in particular damage accumulation in the forming process, it is essential to characterize the punching process. The objective of this work is to understand and identify the physical damage mechanisms that occur during the punching operation and to establish relevant numerical models to predict the fracture location. The effect of the punch–die clearance on mechanical fields distribution is also discussed in this work

Numerical integration of an advanced Gurson model for shear loading: Application to the blanking process

A new extension of the Gurson damage model has been proposed recently to predict ductile fracture under shear dominated loads. The aim of this work is to verify the ability of this approach to simulate, in an accurate way, the damage evolution in shearing processes. An implicit stress integration algorithm is then developed to implement the new model in a finite element code. The numerical procedure is checked through simulations of shear and uniaxial tension tests on a single elements. The extended Gurson damage model is tested and applied to the punching process to compare its predictive ability with the original approach. The obtained numerical results are in good agreement with experimental results of the punching process, showing better ductile fracture predictions compared to the original Gurson model

Experimental characterization and numerical modeling of micromechanical damage under different stress states

The use of HSLA steels for the manufacture of automotive components is interesting from an engineering point of view. This family of steels, while possessing high strength, also has good formability and can be used in forming manufacturing processes. In some forming processes such as blanking, shear strain localization occurs, which causes damage and results in the final fracture of the material. This paper presents an experimental study based on in situ tests to understand and identify the physical mechanisms of ductile damage under two stress states: tension and shear. Different macroscopic tests were performed to calibrate a damage model based on a micromechanical approach. This damage model is based on the Gurson–Tvergaard–Needleman theory and presents recent improvements proposed by Nahshon and Hutchinson and by Nielsen and Tvergaard so as to better predict fracture under a wide range of stress states, especially with low levels of stress triaxiality. These extensions have made the identification of the material parameter more complicated. In this work an identification strategy has been proposed using tests on specimens with different shapes. The identified parameter values are validated and the fracture model show good predictive capability over a wide stress state range

Synthesis of Electromagnetic Metasurfaces: Principles and Illustrations

The paper presents partial overview of the mathematical synthesis and the physical realization of metasurfaces, and related illustrative examples. The synthesis consists in determining the exact tensorial surface susceptibility functions of the metasurface, based on generalized sheet transition conditions, while the realization deals with both metallic and dielectric scattering particle structures. The examples demonstrate the capabilities of the synthesis and realization techniques, thereby showing the plethora of possible metasurface field transmission and subsequent applications. The first example is the design of two diffraction engineering birefringent metasurfaces performing polarization beam splitting and orbital angular momentum multiplexing, respectively. Next, we discuss the concept of the "transistor" metasurface, which is an electromagnetic linear switch based on destructive interferences. Then, we introduce a non-reciprocal non-gyrotropic metasurface using a pick-up circuit radiator (PCR) architecture. Finally, the implementation of all-dielectric metasurfaces for spatial dispersion engineering is discussed

Hidrolitički potencijal β-ksilozidaze iz plijesni Talaromyces thermophilus i njezina primjena u kontinuiranoj proizvodnji ksiloze

We report here the enhanced hemicellulase production by a Talaromyces thermophilus strain in a fed-batch fermentation using 3.6-litre laboratory-controlled bioreactor. When grown on wheat bran, this fungus produces a wide spectrum of polysaccharide-hydrolysing enzymes, mainly endo-β-1,4-xylanase (27 U/mL), β-xylosidase (1.4 U/mL), α-L-arabinofuranosidase (1.05 U/mL) and β-D-mannosidase (0.78 U/mL). The β-xylosidase was purified and shown to hydrolyse xylobiose and short xylooligosaccharides, but it was inactive on xylan. It released xylose from xylooligosaccharides with a degree of polymerisation ranging from 2 to 5. Talaromyces thermophilus β-xylosidase activity was unaffected by high glucose or arabinose concentration (0.5 M) and retained 75 % of its original activity in the presence of 133 mM xylose. Chitosan-immobilised β-xylosidase was used in a continuous process of conversion of wheat bran hydrolysate to xylose in a packed bed reactor. Xylose production of 18.6 mg/g was reached after six hours in the bioreactor and was twofold higher than that produced by the free enzyme. The produced xylose was further converted into xylitol using the crude intracellular enzyme of Talaromyces thermophilus.U radu je opisana mogućnost povećanja proizvodnje hemicelulaze s pomoću soja plijesni Talaromyces thermophilus u šaržnom procesu s pritokom supstrata provedenom u laboratorijski kontroliranom bioreaktoru zapremnine 3,6 L. Na podlozi je od pšeničnih mekinja plijesan proizvela različite enzime što hidroliziraju polisaharide, kao što su: endo-β-1,4-ksilanaza (27 U/mL), β-ksilozidaza (1,4 U/mL), α-L-arabinofuranozidaza (1,05 U/mL) i β-D-manozidaza (0,78 U/mL). Pročišćena je β-ksilozidaza hidrolizirala ksilobiozu i kratkolančane ksilooligosaharide, dok u prisutnosti ksilana nije bila aktivna. Stupanj je polimerizacije ksiloze iz oligosaharida bio u rasponu od 2 do 5. Visoka koncentracija (0,5 M) glukoze ili arabinoze nije utjecala na aktivnost β-ksilozidaze iz plijesni Talaromyces thermophilus, koja je zadržala 75 % aktivnosti u prisutnosti 133 mM ksiloze. U kontinuiranoj proizvodnji ksiloze iz hidrolizata pšeničnih mekinja u reaktoru s nasutim slojem nosača korištena je β-ksilozidaza imobilizirana na kitozanu. Prinos ksiloze od 18,6 mg/g postignut je nakon 6 sati u bioreaktoru, što je dvostruko više od prinosa postignutog pomoću slobodnog enzima. Dobivena je ksiloza prevedena u ksilitol pomoću nepročišćenog intracelularnog enzima iz plijesni Talaromyces thermophilus

Caractérisation expérimentale et contribution à la modélisation numérique de l'endommagement en cisaillement des aciers HLE. Applications au procédé de poinçonnage

L objectif principal de ces travaux de thèse est de caractériser lecomportement et l endommagement d un matériau HLE durant le procédé depoinçonnage. Ils comportent dans un premier temps, une étude expérimentale quirepose sur des observations micrographiques et des essais macroscopiques àdifférents états de contrainte, afin d identifier les mécanismes physiquesd endommagement mis en jeu. Cette étude est complétée par une modélisationnumérique du modèle d endommagement de Gurson modifié en cisaillement et sonimplémentation dans ABAQUS/Explicit. Une stratégie d identification des paramètresmatériau basée sur une large gamme de configurations expérimentales a été mise enplace. Des essais de poinçonnage ont été réalisés en faisant varier le jeu poinçon-matrice, afin de tester la capacité prédictive du modèle de Gurson modifié par rapportau modèle de GTN classique et à un critère découplé basé sur l initiation de rupture.L influence du jeu poinçon-matrice sur la qualité de découpe et sur les niveaux desétats de contrainte et de déformation a été également mise en évidence. Lesprédictions de rupture obtenues par cette approche et pour le matériau étudié sont enbon accord avec les observations expérimentales. Il reste à valider le modèle pourdes configurations de couples matériau/procédé plus étendues et à réaliser sonenchainement avec les autres procédés de mise en forme.The main objective of this thesis is to characterize the behavior anddamage of a HSLA materials during the punching process. They comprise in a firsttime, an experimental study based on micrographic observations and macroscopictests at different stress states to identify the physical mechanisms of damage set in.This study is complemented by a numerical simulation modeling of a Gurson damagemodel modified in shear case and its implementation in ABAQUS / Explicit. Anidentification strategy of material parameters based on a wide range of experimentalconfigurations has been realized. Punching tests were performed by varying thepunch-die clearance to test the predictive ability of the modified Gurson modelcompared to the standard GTN model and to decoupled criterion based on the ductilefracture initiation. The influence of the punch-die clearance blanking quality and instress and strain states levels was also highlighted. Predictions of fracture obtainedby this approach and for the material studied are in good agreement withexperimental observations. It remains to validate the model for larger couple smaterial/process configurations and realize its concatenation with other formingprocesses.PARIS-Arts et Métiers (751132303) / SudocSudocFranceF

Influence of the edge rounding process on the behaviour of blanked parts: numerical predictions with experimental correlation

Blanking of sheet metal is an important forming process in the automotive industry for the manufacture of mechanical components. The final component shape, obtained at the end of bending or deep-drawing processes, often has sharp edges due to the blanking operation. Concerning passenger safety components, like seat belt anchors, rounding of the edges by punching is necessary to avoid cutting the belt material. In addition to removing the sharp edges, the punching results in work hardening of the material in the rounded zones which results in an increase in the local resistance of the material. In this study, a high-strength low-alloy steel (HSLA S500MC) has been tested with the aim of quantifying the blanking and edge rounding operations. The mechanical behaviour of test specimens is investigated by means of tensile tests and the material is characterised in terms of Vickers micro-hardness. Numerical simulations of the edge rounding process are developed using previously identified material behaviour laws. The residual stress fields are characterised and compared to experimental results. This is done so that numerical simulation can be done in the future to prediction the in-service behaviour of the component. Specimens with rounded edges are compared to specimens that were not submitted to the rounding operation. It is shown that Edge Rounding by Punching improves the component resistance, therefore justifying the use of this process in the manufacture of automotive safety components