Viscoelastic properties identification through innovative Image-Based DMTA strategy

The identification of the high strain-rate properties of materials is an important topic for many engineering applications such as crash worthiness, blast loading, industrial forming, among others. It is also a very challenging experimental task mainly because of the difficulty in measuring impact loads accurately in regimes where inertia effects are significant as well as in presence of heterogeneous deformation states. We present here an innovative identification strategy, using high power ultrasonic loadings together with both InfraRed Thermography, Ultra-High-Speed Imaging and grid method, able to simultaneously characterize the viscoelastic behaviour of polymer materials over a large loading spectrum. The main originalities lies in the fact that heterogeneous stress fields are experimentally reconstructed through acceleration fields measurement and that contrary to conventional DMA, no frequency or temperature sweep is required since the experiment is designed to simultaneously produce both a heterogeneous strain-rate state (up to 400 s-1) and a heterogeneous temperature state (up to the glassy transition point) allowing a local and ?spectral? identification. Moreover, by cooling the sample down, the apparent strain-rate loading range can be significantly increased to fill the gap between servo-hydraulic (10 3 s-1) tests. The present work falls within an effort to invent new high-strain test methodologies based on full field imaging and inverse identification, to both overcome the limits of standard experimental strategies and take advantage of the deformation heterogeneities to achieve a full-characterization of a material from a ?one-shot? test

Experimental and numerical investigation of thermomechanical couplings and energy balance in metallic polycrystals

Les critères de localisation et d endommagement sont généralement basés sur un cadre dissipatif et ce travail s intéresse aux couplages thermomécaniques accompagnant les micromécanismes de déformation. Il repose en partie sur des données expérimentales obtenues précédemment dans le laboratoire par Bodelot pour un polycristal d acier A316L. Ce travail tire profit d'une combinaison de techniques différentes, en particulier de mesures in situ de champs cinématiques et thermiques ainsi que de l Orientation Imaging Microscopy, de la profilométrie et d une micrographie de surface. Différents outils ont été développés afin (1) d'identifier automatiquement les systèmes de glissement activés, (2) d estimer l émissivité de la surface permettant ainsi une détermination des champs thermiques avec une précision de 30 mK, (3) de projeter les champs bruts expérimentaux sur la microstructure et (4) de permettre la modélisation du polycristal et de ses conditions aux limites thermomécaniques réelles dans un cadre de plasticité cristalline dans le code EF Abaqus. Il a notamment été montré que les variations de température fournissent une estimation précise et aisée de la limite d'élasticité macroscopique ainsi que la détermination de la contrainte de cisaillement critique à l'échelle granulaire. En outre, les mesures cinématiques ont permis l'identification des systèmes de glissement activés. Des bilans énergétiques expérimentaux et numériques ont été réalisés et une grande influence de l'hétérogénéité polycristalline sur les mécanismes de stockage d énergie a été soulignée. Les méthodes proposées contribueront à améliorer les critères d endommagement basés sur un cadre dissipatifStrain localization and damage criteria of materials and structures are commonly based on a dissipative framework and this work investigates the thermomechanical couplings accompanying the deformation micromechanisms. It is partly based on experimental data obtained previously in the laboratory by Bodelot for a A316L austenitic stainless steel polycrystal. This work takes profit of a multi-technique approach combining, in particular, in-situ kinematic and thermal fields measurements as well as Orientation Imaging Microscopy, profilometry and surface micrography. Different tools have been developed (1) to automatically identify the activated slip systems directly from the surface micrography, (2) to approach the surface emissivity field allowing an accurate determination of the thermal fields with a 30 mK precision, (3) to project raw experimental fields on the microstructure and (4) to allow the modeling of the polycrystal aggregate and its real thermomechanical boundary conditions by using a crystal plasticity framework within the Abaqus FE code. It has notably been shown that the temperature variations provides an easy and accurate estimation of the macroscopic yield stress at the specimen scale as well as the determination of the Critical Resolved Shear Stress at the intragranular scale. In addition, the local kinematic measurements allow the in-situ identification of the activated slip systems. Experimental and numerical energy balances have been conducted and a great influence of the polycrystalline heterogeneity on the energy storage mechanism has been underlined. The proposed methods would help improving physical based dissipative criteria for damage analysisVILLENEUVE D'ASCQ-ECLI (590092307) / SudocSudocFranceF

Experimental and numerical investigation of thermomechanical couplings and energy balance in metallic polycrystals

Les critères de localisation et d’endommagement sont généralement basés sur un cadre dissipatif et ce travail s’intéresse aux couplages thermomécaniques accompagnant les micromécanismes de déformation. Il repose en partie sur des données expérimentales obtenues précédemment dans le laboratoire par Bodelot pour un polycristal d’acier A316L. Ce travail tire profit d'une combinaison de techniques différentes, en particulier de mesures in situ de champs cinématiques et thermiques ainsi que de l’Orientation Imaging Microscopy, de la profilométrie et d’une micrographie de surface. Différents outils ont été développés afin (1) d'identifier automatiquement les systèmes de glissement activés, (2) d’estimer l’émissivité de la surface permettant ainsi une détermination des champs thermiques avec une précision de 30 mK, (3) de projeter les champs bruts expérimentaux sur la microstructure et (4) de permettre la modélisation du polycristal et de ses conditions aux limites thermomécaniques réelles dans un cadre de plasticité cristalline dans le code EF Abaqus. Il a notamment été montré que les variations de température fournissent une estimation précise et aisée de la limite d'élasticité macroscopique ainsi que la détermination de la contrainte de cisaillement critique à l'échelle granulaire. En outre, les mesures cinématiques ont permis l'identification des systèmes de glissement activés. Des bilans énergétiques expérimentaux et numériques ont été réalisés et une grande influence de l'hétérogénéité polycristalline sur les mécanismes de stockage d’énergie a été soulignée. Les méthodes proposées contribueront à améliorer les critères d’endommagement basés sur un cadre dissipatifStrain localization and damage criteria of materials and structures are commonly based on a dissipative framework and this work investigates the thermomechanical couplings accompanying the deformation micromechanisms. It is partly based on experimental data obtained previously in the laboratory by Bodelot for a A316L austenitic stainless steel polycrystal. This work takes profit of a multi-technique approach combining, in particular, in-situ kinematic and thermal fields measurements as well as Orientation Imaging Microscopy, profilometry and surface micrography. Different tools have been developed (1) to automatically identify the activated slip systems directly from the surface micrography, (2) to approach the surface emissivity field allowing an accurate determination of the thermal fields with a 30 mK precision, (3) to project raw experimental fields on the microstructure and (4) to allow the modeling of the polycrystal aggregate and its real thermomechanical boundary conditions by using a crystal plasticity framework within the Abaqus FE code. It has notably been shown that the temperature variations provides an easy and accurate estimation of the macroscopic yield stress at the specimen scale as well as the determination of the Critical Resolved Shear Stress at the intragranular scale. In addition, the local kinematic measurements allow the in-situ identification of the activated slip systems. Experimental and numerical energy balances have been conducted and a great influence of the polycrystalline heterogeneity on the energy storage mechanism has been underlined. The proposed methods would help improving physical based dissipative criteria for damage analysi

Étude expérimentale et numérique des couplages thermomécaniques, et bilan d'énergie au sein des polycristaux métalliques

Strain localization and damage criteria of materials and structures are commonly based on a dissipative framework and this work investigates the thermomechanical couplings accompanying the deformation micromechanisms. It is partly based on experimental data obtained previously in the laboratory by Bodelot for a A316L austenitic stainless steel polycrystal. This work takes profit of a multi-technique approach combining, in particular, in-situ kinematic and thermal fields measurements as well as Orientation Imaging Microscopy, profilometry and surface micrography. Different tools have been developed (1) to automatically identify the activated slip systems directly from the surface micrography, (2) to approach the surface emissivity field allowing an accurate determination of the thermal fields with a 30 mK precision, (3) to project raw experimental fields on the microstructure and (4) to allow the modeling of the polycrystal aggregate and its real thermomechanical boundary conditions by using a crystal plasticity framework within the Abaqus FE code. It has notably been shown that the temperature variations provides an easy and accurate estimation of the macroscopic yield stress at the specimen scale as well as the determination of the Critical Resolved Shear Stress at the intragranular scale. In addition, the local kinematic measurements allow the in-situ identification of the activated slip systems. Experimental and numerical energy balances have been conducted and a great influence of the polycrystalline heterogeneity on the energy storage mechanism has been underlined. The proposed methods would help improving physical based dissipative criteria for damage analysisLes critères de localisation et d’endommagement sont généralement basés sur un cadre dissipatif et ce travail s’intéresse aux couplages thermomécaniques accompagnant les micromécanismes de déformation. Il repose en partie sur des données expérimentales obtenues précédemment dans le laboratoire par Bodelot pour un polycristal d’acier A316L. Ce travail tire profit d'une combinaison de techniques différentes, en particulier de mesures in situ de champs cinématiques et thermiques ainsi que de l’Orientation Imaging Microscopy, de la profilométrie et d’une micrographie de surface. Différents outils ont été développés afin (1) d'identifier automatiquement les systèmes de glissement activés, (2) d’estimer l’émissivité de la surface permettant ainsi une détermination des champs thermiques avec une précision de 30 mK, (3) de projeter les champs bruts expérimentaux sur la microstructure et (4) de permettre la modélisation du polycristal et de ses conditions aux limites thermomécaniques réelles dans un cadre de plasticité cristalline dans le code EF Abaqus. Il a notamment été montré que les variations de température fournissent une estimation précise et aisée de la limite d'élasticité macroscopique ainsi que la détermination de la contrainte de cisaillement critique à l'échelle granulaire. En outre, les mesures cinématiques ont permis l'identification des systèmes de glissement activés. Des bilans énergétiques expérimentaux et numériques ont été réalisés et une grande influence de l'hétérogénéité polycristalline sur les mécanismes de stockage d’énergie a été soulignée. Les méthodes proposées contribueront à améliorer les critères d’endommagement basés sur un cadre dissipati

A novel image-based ultrasonic test to map material mechanical properties at high strain-rates

An innovative identification strategy based on high power ultrasonic loading together with both infrared thermography and ultra-high speed imaging is presented in this article. It was shown to be able to characterize the visco-elastic behaviour of a polymer specimen (PMMA) from a single sample over a range of temperatures and strain-rates. The paper focuses on moderate strain-rates, i.e. from 10 to 200 s−1 , and temperatures ranging from room to the material glass transition temperature, i.e. 110°C. The main originality lies in the fact that contrary to conventional Dynamic Mechanical Thermal Analysis (DMTA), no frequency or temperature sweep is required since the experiment is designed to simultaneously produce both a heterogeneous strain-rate state and a heterogeneous temperature state allowing a local and multi-parametric identification. This article is seminal in nature and the test presented here has good potential to tackle a range of other types of high strain-rate testing situations.<br/

DMTA EXME-D-17-00051

The dataset is associated to the article untitled &#39;A novel image-based ultrasonic test to map material mechanical properties at high strain rates&#39;. This work presents an innovative identification strategy based on high power ultrasonic loading together with both infrared thermography and ultra-high speed imaging. It was shown to be able to characterize the viscoelastic behaviour of a polymer specimen (PMMA) from a single sample over a wide range of temperatures and strain rates. The main originality lies in the fact that contrary to conventional DMT Analysis, no frequency or temperature sweep is required since the experiment is designed to simultaneously produce both a heterogeneous strain-rate state and a heterogeneous temperature state allowing a local and multi-parametric identification. </span

Mechanically robust, electrically stable metal arrays on plasma-oxidized polydimethylsiloxane for stretchable technologies

International audienc

Ultrasonic test for high rate material property imaging

In order to perform experimental identification of high strain rate material models, engineers only have a very limited toolbox based on test procedures developed decades ago. The best example is the so-called Split Hopkinson Pressure Bar (SHPB) which has proved extremely useful but has important intrinsic limitations due to the stringent assumptions required to process the test data. The recent advent of full-field deformation measurements using imaging techniques has allowed novel approaches to be developed and exciting new testing procedures to be imagined for the first time. One can then use this full-field information in conjunction with efficient numerical inverse identification tools such as the Virtual Fields Method (VFM) identify material parameters at high rates. The underpinning novelty is to exploit the inertial effects developed in high strain rate loading.This paper presents results a new inertial ultrasonic test to obtain stress-strain curves at high strain rates (here, up to 300/s). The idea is to excite a flat rectangular specimen at its first longitudinal resonance frequency. Images are recorded with an HPV-1 camera from Shimadzu at 250 kfps. It is shown that meaningful stress-strain curves can be obtained using acceleration as a stress gauge

Photo-hardenable and patternable PDMS/SU-8 hybrid functional material: A smart substrate for flexible systems

International audienc

Controlled mud-crack patterning and self-organized cracking of polydimethylsiloxane elastomer surfaces

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