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Pascal Forquin

Université Grenoble Alpes, Laboratoire Sols, Solides, Structures et Risques - 3SR, Faculty Member

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Webpage: https://3sr.univ-grenoble-alpes.fr/membre/pascal-forquin Chief scientist of the ExperDYN Dynamic testing platform (3SR Lab.)•CURRENT AND FORMER POSITIONS2013 – NowFull Professor (PR1) in Mechanics and Civil Engineering, Univ. Grenoble Alpes (UGA), Laboratory of Soils, Solids, Structures and Risks (3SR), RV Division2011 – 2013Full Professor (PR2) in Mechanics and Civil Engineering, Univ. de Lorraine2005 – 2011 Associate Professor (MCF) in Mechanics and Civil Engineering, Univ. de Lorraine•EDUCATION2010 Ability to Manage Researches (HDR) in Mechanics

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Loughborough University

Vito Tagarielli

Imperial College London

Rebecca Brannon

University of Utah

majid Baniassadi

University of Tehran

Januarti Jaya Ekaputri

Institut Teknologi Sepuluh Nopember

Iolanda Craifaleanu

Technical University Of Civil Engineering, Bucharest

South Valley University

South Ural State University

Universitas Sriwijaya

Sergey Konovalov

Russian Academy of Sciences 1

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Papers by Pascal Forquin

$Research paper thumbnail of Dynamic damage and fracture processes in brittle materials$

Dynamic damage and fracture processes in brittle materials

Brittle materials such as, rocks, concrete and high-performance concrete, glass, ceramics, ice...... more Brittle materials such as, rocks, concrete and high-performance concrete, glass, ceramics, ice..., are materials abundantly present in our everyday life and materials involved in many industrial applications or in various protective solutions. Achieving a good understanding of their strain-rate sensitivity in relation with their microstructure remains a major issue. In addition, the development of micromechanics-based models is of major importance in view of improving the predictive capabilities of analytical and numerical models and in order to better explain the role of material parameters involved in the strain-rate and pressure sensitivity of brittle materials. In the present chapter the damage and fracture processes involved in various brittle materials are discussed. Several experimental techniques offering the capability to characterize and analyse these damage modes are presented. Next, some micromechanics-based models attending to describe these mechanisms are detailed. Experimental and modelling approaches allow highlighting the main microstructural parameters driving the behaviour of brittle materials at high loading rates.

Identification of the Dynamic Tensile Behavior of Geomaterials Based on the Virtual Fields Method and a New Generation-Ultra-High-Speed Camera

Conference proceedings of the Society for Experimental Mechanics, 2016

Dynamic behavior of a granite rock was investigated by using the spalling test method. This techn... more Dynamic behavior of a granite rock was investigated by using the spalling test method. This technique, based on the use of a Hopkinson bar, allows applying a tensile loading at high strain-rates, from a few tens to two hundreds of 1/s, to geomaterials to characterize their dynamic tensile strength. However, the standard ‘Novikov’ processing method providing the spall strength is based on basic assumptions (linear-elastic behavior until the peak). In addition, the post-peak behavior and the kinetics of damage in the material remain unknown. The use of full-field measurement appears to be of great interest to improve the processing method and to obtain more information from the spalling tests.

An experimental method of measuring the confined compression strength of geomaterials

International Journal of Solids and Structures, Jun 1, 2007

Knowledge of the behaviour of geomaterials under confined compression is a prerequisite for any a... more Knowledge of the behaviour of geomaterials under confined compression is a prerequisite for any analysis of their ballistic performance. This study proposes an experimental method of determining the spherical and deviatoric behaviour of these materials under high pressure. Known as the 'quasi-oedometric compression test' it consists of compressing a cylindrical specimen tightly enclosed in a thick confinement vessel. The principles of these quasi-oedometric tests are given first, and the steps taken for their execution, together with an examination of the steel used for the confinement vessel. An original way of analysing the data of the test is presented and validated by numerical simulations. These calculations provide valuable information about the influence of the interface product introduced between the vessel and the specimen, and that of friction. Tests are then presented with specimens of aluminium alloy to validate the experimental setup and the method of analysis. In addition, quasi-oedometric compression tests of cement based material, with and without particles, illustrate the opportunities offered by this testing method, and show that its deviatoric strength and compaction law are significantly improved by ceramic granulates addition.

Experimental study of static and dynamic behavior of concrete under high confinement: Effect of coarse aggregate strength

HAL (Le Centre pour la Communication Scientifique Directe), 2016

This article focuses on the static and dynamic behavior of two concretes under very high pressure... more This article focuses on the static and dynamic behavior of two concretes under very high pressure loaded at different strain rates. Concretes differ by the type of coarse aggregates (limestone or siliceous). Specimens are confined in an elastic steel ring, insuring a quasi-uniaxial strain state of loading during axial compression, the so-called quasi-oedometric compression (QOC) tests. The effect of the loading path is first investigated by comparing their response under static QOC tests to triaxial compression results. Compaction of concrete made with strong siliceous aggregates is much higher in QOC test than in triaxial compression test, contrary to concrete made with soft limestone aggregates. Both concretes are then subjected to Split Hopkinson Pressure Bar testing. At high strain rate volumetric stiffness and deviatoric strength of both concretes are increased. Moreover, the increase of concrete strength with strain rate is more pronounced for concrete made with limestone aggregates than with siliceous aggregates.

Mesoscopic Modelling of Concrete Under Impact - CSMA2011

Le béton est un matériau difficile à modéliser à cause de sa nature à la fois fragile et hétérog... more Le béton est un matériau difficile à modéliser à cause de sa nature à la fois fragile et
hétérogène. La modélisation mésoscopique présentée est un outil utilisé pour affiner l’échelle d’analyse et étudier l’importance de la microstructure sur la réponse mécanique, particulièrement lorsque le chargement appliqué est très rapide. Des essais d’écaillage et d’impact sur la tranche menés au LEM3 ont ainsi été modélisés en utilisant un modèle d’endommagement anisotrope permettant de prévoir la fragmentation du béton sous impact.

Influence of the Confined Behaviour and the Tensile Strength of Concrete Slabs Under Projectile-Impact

Springer eBooks, Sep 13, 2012

Severe damage modes are observed in concrete structures when subjected to impulse loading as proj... more Severe damage modes are observed in concrete structures when subjected to impulse loading as projectile-impact or blast loading. For instance, the impact of a kinetic penetrator generates scabbing on the front face, radial cracking in the whole target and, for high impact velocities or a thin target, spalling on the rear face. These damage mechanisms may strongly decrease the penetration resistance of concrete structures. On the other hand, high confining pressures in front of the projectile may lead to a micro-cracking and collapse of pores in the vicinity of the tunnel. Moreover both confined and tensile behaviours are influenced by humidity level of the concrete. Therefore the numerical modelling of concrete slabs under projectile-impact relies on the use of coupled modelling in which the hydrostatic and deviatoric behaviours of the concrete under high pressure is modelled in addition to the anisotropic damage induced in dynamic tensile loading. In the present work, a series of numerical simulations of impact tests have been conducted considering different humidity levels and target thicknesses. The confined behaviour of the concrete material is modelled through the KST (Krieg-Sweenson-Taylor) plasticity model. The so-called DFH (Denoual-Forquin-Hild) damage model combined with a cohesion model is used to describe the tensile strength and softening behaviour of concrete in tension. A series of computations have been performed to assess the influence of the confined behaviour and tensile strength on the ballistic performance of concrete slabs.

Investigation of the Mechanical Behaviour of Lingulid Sandstone Emphasizing the Influence from Pre-Existing Structural Defects—Part 2: Dynamic Testing and Numerical Modelling

Applied sciences, Nov 16, 2022

This article is an open access article distributed under the terms and conditions of the Creative... more

Simulations numériques d'essais d'écaillage avec la Méthode des Éléments Discrets

HAL (Le Centre pour la Communication Scientifique Directe), May 16, 2022

-La MED a déjà prouvé sa faculté à modéliser le comportement de matériaux fragiles en régime quas... more -La MED a déjà prouvé sa faculté à modéliser le comportement de matériaux fragiles en régime quasi-statique. Cette étude démontre son potentiel pour représenter le comportement de matériaux fragiles sous sollicitations dynamiques. Les paramètres élastiques microscopiques du modèle MED d'une alumine sont calibrés via des essais quasi-statiques de traction uniaxiale. Le modèle est ensuite utilisé pour simuler la propagation et les interactions d'ondes générées lors d'expériences dynamiques. Les profils de vitesse mesurés lors de l'expérience et calculés avec le modèle MED sont confrontés. Mots clés-Méthode des Éléments Discrets (MED), écaillage, fragmentation dynamique, sensibilité à la vitesse de déformation.

Use of simulated experiments for material characterization of brittle materials subjected to high strain rate dynamic tension

Philosophical Transactions of the Royal Society A, Jan 28, 2017

Use of simulated experiments for material characterization of brittle materials subjected to high... more

An Experimental Method to Characterize the Shear Behaviour of Concrete Under High Confinement

Experimental Mechanics, Apr 1, 2023

Background: Shear behaviour of concrete under high confining pressure has not been thoroughly stu... more Background: Shear behaviour of concrete under high confining pressure has not been thoroughly studied despite being widely observed in concrete structures subjected to high blast loading or projectile impact. Objective: The objective of the present study is to propose an experimental method to investigate the shear behaviour of concrete under high confinement in static conditions. Methods: This method is based on the Punch-Through Shear testing technique. A specimen with two cylindrical notches is first subjected to an active confinement pressure by means of a triaxial cell and an axial loading is then applied to punch through the central part of the specimen. However, in the previous PTS experiments, the inner cylindrical parts being subjected to uniaxial compression, the level of confining pressure applied in the first stage was usually limited to the sample uniaxial compression strength. In the present work, much higher compression stresses of a few hundreds of MPa are applied to the specimen in both radial and axial directions thanks to the small metallic rings used to confine the inner cylindrical parts of the specimen. A series of numerical simulation based on finite-element method is conducted in order to optimize the notches and sample dimensions. Results: Experimental tests conducted on a common concrete showed that the confinement rings successfully prevented any compression damage in the central part during sample pressuring and shearing. The experiments conducted at different levels of confining pressure showed that the higher the confinement level the higher the concrete shear strength. Experiments done with a confining pressure of 100 MPa with two different ligament lengths showed that higher nominal shear stress is obtained with a smaller shear surface. Conclusion The proposed experimental technique allows reaching confining pressure up to 150 MPa (which corresponds to radial stress of 374 MPa in the ligament) and nominal shear strain of about 38% in the ligament of the concrete sample and confirms that the shear strength increases with the level of normal stress applied to the sheared surface.

Discrete Element Approach to Model Advanced Damage in Concrete Structures Under Impact

Springer eBooks, 2022

On the use of the Virtual Fields Method and Ultra High Speed Photography to characterize spalling strength of ordinary concrete

HAL (Le Centre pour la Communication Scientifique Directe), Jun 1, 2017

International audienc

A Shockless Plate-Impact Spalling Technique Based on Wavy-Machined Flyer-Plates to Evaluate the Strain-Rate Sensitivity of Ceramic Tensile Strength

Journal of Dynamic Behavior of Materials, Sep 10, 2021

Silicon carbide ceramics are widely used for armor protection due to their high compressive stren... more Silicon carbide ceramics are widely used for armor protection due to their high compressive strength, high hardness and low density. In the present study, an experimental technique based on the plate-impact technique is developed to measure the tensile strength of ceramic materials. As the strength of ceramics under dynamic loading is highly sensitive to the strain rate, the effort was made to maintain a constant strain rate loading at the failure location. Numerical simulations were used to design several geometries of wavy-machined flyer-plates, which generate a pulse-shaped compressive wave upon impact, with smoothed rising and falling times ranged from 0.65 to 1 $$\upmu$$ μ s. Such shockless plate-impact experiments were performed on a SiC ceramic at impact velocities set between 200 and 450 m/s. Thanks to laser interferometry analysis, the target rear face velocity provides a measurement of the material spall strength at a given strain-rate loading. The strain rate in the failure zone was evaluated via elasto-plastic numerical simulations, using the pulse loading and spall strength determined experimentally. With an appropriate design of the flyer-plate, the plate-impact technique is found to properly allow a well-controlled strain-rate loading around 10 $$^4$$ 4 -10 $$^5$$ 5 s $$^{-1}$$ - 1 with relatively long rising time to be reached. This work is expected to provide a suitable tool to investigate the high strain-rate behavior of ceramic materials.

Computational framework for analysis of contact-induced damage in brittle rocks

International Journal of Solids and Structures, Aug 1, 2019

This paper presents a numerical approach for predicting damage in rock materials caused by contac... more This paper presents a numerical approach for predicting damage in rock materials caused by contact loading. The rock material is modelled using a constitutive description that combines pressure dependent plasticity, for capturing shear deformation under high confining pressure, with an anisotropic damage model for capturing mode I cracking in tension. Material parameters for the model are taken from a recently performed investigation on a granite material. The model has been used to simulate two types of contact loading experiments from the literature, cyclic loading and monotonic loading up to fracture. In order to achieve accurate predictions, the model has been extended to account for small loaded volumes which occur at contact loading. The results show that the main damage mechanism at cyclic loading is crack propagation due to Hertzian stresses whereas in the monotonic experiments sub-surface cracks could initiate. All features measured in the contact loading experiments are captured by the model and hence, the modelling framework is judged to be able to capture contact damage if real stone geometries are studied in FEM.

Experimental Techniques to Characterize the Mechanical Behaviour of Ultra-High-Strength-Concrete Under Extreme Loading Conditions

Conference proceedings of the Society for Experimental Mechanics, 2016

In the present work, three experimental methods have been employed to characterize the dynamic te... more In the present work, three experimental methods have been employed to characterize the dynamic tensile, shear and confined behavior of an UHSC (Ultra-High Strength Concrete) with and without steel fiber reinforcement. On the one hand, a dynamic testing method was developed to investigate the post-peak tensile behavior of UHSC. A Split-Hopkinson Pressure Bar (SHPB) device is used and the notched-concrete sample is glued in-between the input and output bar. A compressive pulse reflects as a tensile pulse leading to the breakage of the sample. In this case a strong influence of fibers is noted. On the other hand, two experimental methods are used to investigate the confined behavior of UHSC under shear and quasi-oedometric loading paths. In the quasi-oedometric compression test the concrete sample is inserted in a confining vessel and axially compressed. Hydrostatic pressure as high as 800 MPa are obtained and the hydrostatic and deviatoric behavior are deduced. The PTS (Punch-Trough-Shear test) provides lateral pressure of over 70 MPa in the sheared zone, high shear strain and leads to a mode II fracturing of the sample. Influence of fibers on the dynamic behavior of UHSC is discussed thanks to the previous experiments.

Single Bunch X-Ray Phase-Contrast Imaging of Dynamic Tensile Failure in Geomaterials

Journal of Dynamic Behavior of Materials, Sep 15, 2022

Granite rock fragmentation at percussive drilling

CRC Press eBooks, May 28, 2013

The aim of this study is to numerically model the fracture system at percussive drilling. Because... more The aim of this study is to numerically model the fracture system at percussive drilling. Because of the complex behavior of rock materials, a continuum approach is employed relying upon a plasticity model with yield surface locus as a quadratic function of the mean pressure in the principal stress space coupled with an anisotropic damage model. In particular, Bohus granite rock is investigated, and the material parameters are defined based on previous experiments. This includes different tests such as direct tension and compression, three-point bending, and quasi-oedometric tests to investigate the material behavior at both tension and confined compression stress states. The equation of motion is discretized using a finite element approach, and the explicit time integration method is employed. Edge-on impact tests are performed, and the results are used to validate the numerical model. The percussive drilling problem is then modeled in 3D, and the bit-rock interaction is considered using contact mechanics. The fracture mechanism in the rock and the bit penetration-resisting force response are realistically captured by the numerical model.

Experimental study of the static and dynamic behavior of pre-stressed concrete subjected to shear loading

Engineering Structures, May 1, 2021

In the present work, the static and dynamic shear strength of concrete is investigated by means o... more In the present work, the static and dynamic shear strength of concrete is investigated by means of Punch-Through Shear (PTS) tests. This experimental method consists in applying an axial load to the central part of the specimen which generates shear stresses in the ligament of the sample. Prior to the shearing stage, the concrete sample is subjected to a lateral confinement pressure that is applied by pre-stressing a metallic cell and then inserting the sample in-between the cell jaws so the confinement stresses are transferred to the concrete specimen during the unloading. The originality of this method lies then in the fact that the level of confinement is better controlled than the experimental protocol which can be found in the literature. A standard hydraulic press was used to conduct quasi-static experiments whereas a modified Split Hopkinson Pressure Bar device was used to perform the dynamic tests. The confinement cell is instrumented with strain gages so the confinement level applied to the ligament of the concrete specimen is measured before and during the shearing stage. The results on two sets of samples (dry and wet) shows that the shear strength is sensitive to the water content with higher values for dry samples and to the applied loading rate, with higher values of dynamic shear strength compared to static ones for both concretes.

Application of ultra-high speed photography in identification of the dynamic tensile response of quasi-brittle materials

This paper investigates the application of CMOS-based ultra-high speed camera in characterising m... more This paper investigates the application of CMOS-based ultra-high speed camera in characterising materials under dynamic tensile loading. A single Hopkinson bar test is used to induce an axial stress wave in the sample and a grid pattern is filmed during the test to obtain time-resolved full-field kinematic measurements. Then the acceleration fields are used to reconstruct the stress information and identify material response. Quasi-brittle materials (e.g. rocks and concrete) present a particular experimental challenge due to small deformation and low stress level at failure. The Shimadzu HPV-X2 acquisition system has been applied for such purpose and its performance was investigated by first performing a spalling test on an aluminium benchmark sample and then applied to testing ordinary concrete.

Investigation of the Mechanical Behaviour of Lingulid Sandstone Emphasising the Influence from Pre-Existing Structural Defects, Part 1: Model Identification Based on Static Experiments

Applied sciences, Oct 25, 2022

This article is an open access article distributed under the terms and conditions of the Creative... more

$Research paper thumbnail of Dynamic damage and fracture processes in brittle materials$

Dynamic damage and fracture processes in brittle materials

Brittle materials such as, rocks, concrete and high-performance concrete, glass, ceramics, ice...... more Brittle materials such as, rocks, concrete and high-performance concrete, glass, ceramics, ice..., are materials abundantly present in our everyday life and materials involved in many industrial applications or in various protective solutions. Achieving a good understanding of their strain-rate sensitivity in relation with their microstructure remains a major issue. In addition, the development of micromechanics-based models is of major importance in view of improving the predictive capabilities of analytical and numerical models and in order to better explain the role of material parameters involved in the strain-rate and pressure sensitivity of brittle materials. In the present chapter the damage and fracture processes involved in various brittle materials are discussed. Several experimental techniques offering the capability to characterize and analyse these damage modes are presented. Next, some micromechanics-based models attending to describe these mechanisms are detailed. Experimental and modelling approaches allow highlighting the main microstructural parameters driving the behaviour of brittle materials at high loading rates.

Identification of the Dynamic Tensile Behavior of Geomaterials Based on the Virtual Fields Method and a New Generation-Ultra-High-Speed Camera

Conference proceedings of the Society for Experimental Mechanics, 2016

Dynamic behavior of a granite rock was investigated by using the spalling test method. This techn... more Dynamic behavior of a granite rock was investigated by using the spalling test method. This technique, based on the use of a Hopkinson bar, allows applying a tensile loading at high strain-rates, from a few tens to two hundreds of 1/s, to geomaterials to characterize their dynamic tensile strength. However, the standard ‘Novikov’ processing method providing the spall strength is based on basic assumptions (linear-elastic behavior until the peak). In addition, the post-peak behavior and the kinetics of damage in the material remain unknown. The use of full-field measurement appears to be of great interest to improve the processing method and to obtain more information from the spalling tests.

An experimental method of measuring the confined compression strength of geomaterials

International Journal of Solids and Structures, Jun 1, 2007

Knowledge of the behaviour of geomaterials under confined compression is a prerequisite for any a... more Knowledge of the behaviour of geomaterials under confined compression is a prerequisite for any analysis of their ballistic performance. This study proposes an experimental method of determining the spherical and deviatoric behaviour of these materials under high pressure. Known as the 'quasi-oedometric compression test' it consists of compressing a cylindrical specimen tightly enclosed in a thick confinement vessel. The principles of these quasi-oedometric tests are given first, and the steps taken for their execution, together with an examination of the steel used for the confinement vessel. An original way of analysing the data of the test is presented and validated by numerical simulations. These calculations provide valuable information about the influence of the interface product introduced between the vessel and the specimen, and that of friction. Tests are then presented with specimens of aluminium alloy to validate the experimental setup and the method of analysis. In addition, quasi-oedometric compression tests of cement based material, with and without particles, illustrate the opportunities offered by this testing method, and show that its deviatoric strength and compaction law are significantly improved by ceramic granulates addition.

Experimental study of static and dynamic behavior of concrete under high confinement: Effect of coarse aggregate strength

HAL (Le Centre pour la Communication Scientifique Directe), 2016

This article focuses on the static and dynamic behavior of two concretes under very high pressure... more This article focuses on the static and dynamic behavior of two concretes under very high pressure loaded at different strain rates. Concretes differ by the type of coarse aggregates (limestone or siliceous). Specimens are confined in an elastic steel ring, insuring a quasi-uniaxial strain state of loading during axial compression, the so-called quasi-oedometric compression (QOC) tests. The effect of the loading path is first investigated by comparing their response under static QOC tests to triaxial compression results. Compaction of concrete made with strong siliceous aggregates is much higher in QOC test than in triaxial compression test, contrary to concrete made with soft limestone aggregates. Both concretes are then subjected to Split Hopkinson Pressure Bar testing. At high strain rate volumetric stiffness and deviatoric strength of both concretes are increased. Moreover, the increase of concrete strength with strain rate is more pronounced for concrete made with limestone aggregates than with siliceous aggregates.

Mesoscopic Modelling of Concrete Under Impact - CSMA2011

Le béton est un matériau difficile à modéliser à cause de sa nature à la fois fragile et hétérog... more Le béton est un matériau difficile à modéliser à cause de sa nature à la fois fragile et
hétérogène. La modélisation mésoscopique présentée est un outil utilisé pour affiner l’échelle d’analyse et étudier l’importance de la microstructure sur la réponse mécanique, particulièrement lorsque le chargement appliqué est très rapide. Des essais d’écaillage et d’impact sur la tranche menés au LEM3 ont ainsi été modélisés en utilisant un modèle d’endommagement anisotrope permettant de prévoir la fragmentation du béton sous impact.

Influence of the Confined Behaviour and the Tensile Strength of Concrete Slabs Under Projectile-Impact

Springer eBooks, Sep 13, 2012

Severe damage modes are observed in concrete structures when subjected to impulse loading as proj... more Severe damage modes are observed in concrete structures when subjected to impulse loading as projectile-impact or blast loading. For instance, the impact of a kinetic penetrator generates scabbing on the front face, radial cracking in the whole target and, for high impact velocities or a thin target, spalling on the rear face. These damage mechanisms may strongly decrease the penetration resistance of concrete structures. On the other hand, high confining pressures in front of the projectile may lead to a micro-cracking and collapse of pores in the vicinity of the tunnel. Moreover both confined and tensile behaviours are influenced by humidity level of the concrete. Therefore the numerical modelling of concrete slabs under projectile-impact relies on the use of coupled modelling in which the hydrostatic and deviatoric behaviours of the concrete under high pressure is modelled in addition to the anisotropic damage induced in dynamic tensile loading. In the present work, a series of numerical simulations of impact tests have been conducted considering different humidity levels and target thicknesses. The confined behaviour of the concrete material is modelled through the KST (Krieg-Sweenson-Taylor) plasticity model. The so-called DFH (Denoual-Forquin-Hild) damage model combined with a cohesion model is used to describe the tensile strength and softening behaviour of concrete in tension. A series of computations have been performed to assess the influence of the confined behaviour and tensile strength on the ballistic performance of concrete slabs.

Investigation of the Mechanical Behaviour of Lingulid Sandstone Emphasizing the Influence from Pre-Existing Structural Defects—Part 2: Dynamic Testing and Numerical Modelling

Applied sciences, Nov 16, 2022

This article is an open access article distributed under the terms and conditions of the Creative... more

Simulations numériques d'essais d'écaillage avec la Méthode des Éléments Discrets

HAL (Le Centre pour la Communication Scientifique Directe), May 16, 2022

-La MED a déjà prouvé sa faculté à modéliser le comportement de matériaux fragiles en régime quas... more -La MED a déjà prouvé sa faculté à modéliser le comportement de matériaux fragiles en régime quasi-statique. Cette étude démontre son potentiel pour représenter le comportement de matériaux fragiles sous sollicitations dynamiques. Les paramètres élastiques microscopiques du modèle MED d'une alumine sont calibrés via des essais quasi-statiques de traction uniaxiale. Le modèle est ensuite utilisé pour simuler la propagation et les interactions d'ondes générées lors d'expériences dynamiques. Les profils de vitesse mesurés lors de l'expérience et calculés avec le modèle MED sont confrontés. Mots clés-Méthode des Éléments Discrets (MED), écaillage, fragmentation dynamique, sensibilité à la vitesse de déformation.

Use of simulated experiments for material characterization of brittle materials subjected to high strain rate dynamic tension

Philosophical Transactions of the Royal Society A, Jan 28, 2017

Use of simulated experiments for material characterization of brittle materials subjected to high... more

An Experimental Method to Characterize the Shear Behaviour of Concrete Under High Confinement

Experimental Mechanics, Apr 1, 2023

Background: Shear behaviour of concrete under high confining pressure has not been thoroughly stu... more Background: Shear behaviour of concrete under high confining pressure has not been thoroughly studied despite being widely observed in concrete structures subjected to high blast loading or projectile impact. Objective: The objective of the present study is to propose an experimental method to investigate the shear behaviour of concrete under high confinement in static conditions. Methods: This method is based on the Punch-Through Shear testing technique. A specimen with two cylindrical notches is first subjected to an active confinement pressure by means of a triaxial cell and an axial loading is then applied to punch through the central part of the specimen. However, in the previous PTS experiments, the inner cylindrical parts being subjected to uniaxial compression, the level of confining pressure applied in the first stage was usually limited to the sample uniaxial compression strength. In the present work, much higher compression stresses of a few hundreds of MPa are applied to the specimen in both radial and axial directions thanks to the small metallic rings used to confine the inner cylindrical parts of the specimen. A series of numerical simulation based on finite-element method is conducted in order to optimize the notches and sample dimensions. Results: Experimental tests conducted on a common concrete showed that the confinement rings successfully prevented any compression damage in the central part during sample pressuring and shearing. The experiments conducted at different levels of confining pressure showed that the higher the confinement level the higher the concrete shear strength. Experiments done with a confining pressure of 100 MPa with two different ligament lengths showed that higher nominal shear stress is obtained with a smaller shear surface. Conclusion The proposed experimental technique allows reaching confining pressure up to 150 MPa (which corresponds to radial stress of 374 MPa in the ligament) and nominal shear strain of about 38% in the ligament of the concrete sample and confirms that the shear strength increases with the level of normal stress applied to the sheared surface.

Discrete Element Approach to Model Advanced Damage in Concrete Structures Under Impact

Springer eBooks, 2022

On the use of the Virtual Fields Method and Ultra High Speed Photography to characterize spalling strength of ordinary concrete

HAL (Le Centre pour la Communication Scientifique Directe), Jun 1, 2017

International audienc

A Shockless Plate-Impact Spalling Technique Based on Wavy-Machined Flyer-Plates to Evaluate the Strain-Rate Sensitivity of Ceramic Tensile Strength

Journal of Dynamic Behavior of Materials, Sep 10, 2021

Silicon carbide ceramics are widely used for armor protection due to their high compressive stren... more Silicon carbide ceramics are widely used for armor protection due to their high compressive strength, high hardness and low density. In the present study, an experimental technique based on the plate-impact technique is developed to measure the tensile strength of ceramic materials. As the strength of ceramics under dynamic loading is highly sensitive to the strain rate, the effort was made to maintain a constant strain rate loading at the failure location. Numerical simulations were used to design several geometries of wavy-machined flyer-plates, which generate a pulse-shaped compressive wave upon impact, with smoothed rising and falling times ranged from 0.65 to 1 $$\upmu$$ μ s. Such shockless plate-impact experiments were performed on a SiC ceramic at impact velocities set between 200 and 450 m/s. Thanks to laser interferometry analysis, the target rear face velocity provides a measurement of the material spall strength at a given strain-rate loading. The strain rate in the failure zone was evaluated via elasto-plastic numerical simulations, using the pulse loading and spall strength determined experimentally. With an appropriate design of the flyer-plate, the plate-impact technique is found to properly allow a well-controlled strain-rate loading around 10 $$^4$$ 4 -10 $$^5$$ 5 s $$^{-1}$$ - 1 with relatively long rising time to be reached. This work is expected to provide a suitable tool to investigate the high strain-rate behavior of ceramic materials.

Computational framework for analysis of contact-induced damage in brittle rocks

International Journal of Solids and Structures, Aug 1, 2019

This paper presents a numerical approach for predicting damage in rock materials caused by contac... more This paper presents a numerical approach for predicting damage in rock materials caused by contact loading. The rock material is modelled using a constitutive description that combines pressure dependent plasticity, for capturing shear deformation under high confining pressure, with an anisotropic damage model for capturing mode I cracking in tension. Material parameters for the model are taken from a recently performed investigation on a granite material. The model has been used to simulate two types of contact loading experiments from the literature, cyclic loading and monotonic loading up to fracture. In order to achieve accurate predictions, the model has been extended to account for small loaded volumes which occur at contact loading. The results show that the main damage mechanism at cyclic loading is crack propagation due to Hertzian stresses whereas in the monotonic experiments sub-surface cracks could initiate. All features measured in the contact loading experiments are captured by the model and hence, the modelling framework is judged to be able to capture contact damage if real stone geometries are studied in FEM.

Experimental Techniques to Characterize the Mechanical Behaviour of Ultra-High-Strength-Concrete Under Extreme Loading Conditions

Conference proceedings of the Society for Experimental Mechanics, 2016

In the present work, three experimental methods have been employed to characterize the dynamic te... more In the present work, three experimental methods have been employed to characterize the dynamic tensile, shear and confined behavior of an UHSC (Ultra-High Strength Concrete) with and without steel fiber reinforcement. On the one hand, a dynamic testing method was developed to investigate the post-peak tensile behavior of UHSC. A Split-Hopkinson Pressure Bar (SHPB) device is used and the notched-concrete sample is glued in-between the input and output bar. A compressive pulse reflects as a tensile pulse leading to the breakage of the sample. In this case a strong influence of fibers is noted. On the other hand, two experimental methods are used to investigate the confined behavior of UHSC under shear and quasi-oedometric loading paths. In the quasi-oedometric compression test the concrete sample is inserted in a confining vessel and axially compressed. Hydrostatic pressure as high as 800 MPa are obtained and the hydrostatic and deviatoric behavior are deduced. The PTS (Punch-Trough-Shear test) provides lateral pressure of over 70 MPa in the sheared zone, high shear strain and leads to a mode II fracturing of the sample. Influence of fibers on the dynamic behavior of UHSC is discussed thanks to the previous experiments.

Single Bunch X-Ray Phase-Contrast Imaging of Dynamic Tensile Failure in Geomaterials

Journal of Dynamic Behavior of Materials, Sep 15, 2022

Granite rock fragmentation at percussive drilling

CRC Press eBooks, May 28, 2013

The aim of this study is to numerically model the fracture system at percussive drilling. Because... more The aim of this study is to numerically model the fracture system at percussive drilling. Because of the complex behavior of rock materials, a continuum approach is employed relying upon a plasticity model with yield surface locus as a quadratic function of the mean pressure in the principal stress space coupled with an anisotropic damage model. In particular, Bohus granite rock is investigated, and the material parameters are defined based on previous experiments. This includes different tests such as direct tension and compression, three-point bending, and quasi-oedometric tests to investigate the material behavior at both tension and confined compression stress states. The equation of motion is discretized using a finite element approach, and the explicit time integration method is employed. Edge-on impact tests are performed, and the results are used to validate the numerical model. The percussive drilling problem is then modeled in 3D, and the bit-rock interaction is considered using contact mechanics. The fracture mechanism in the rock and the bit penetration-resisting force response are realistically captured by the numerical model.

Experimental study of the static and dynamic behavior of pre-stressed concrete subjected to shear loading

Engineering Structures, May 1, 2021

In the present work, the static and dynamic shear strength of concrete is investigated by means o... more In the present work, the static and dynamic shear strength of concrete is investigated by means of Punch-Through Shear (PTS) tests. This experimental method consists in applying an axial load to the central part of the specimen which generates shear stresses in the ligament of the sample. Prior to the shearing stage, the concrete sample is subjected to a lateral confinement pressure that is applied by pre-stressing a metallic cell and then inserting the sample in-between the cell jaws so the confinement stresses are transferred to the concrete specimen during the unloading. The originality of this method lies then in the fact that the level of confinement is better controlled than the experimental protocol which can be found in the literature. A standard hydraulic press was used to conduct quasi-static experiments whereas a modified Split Hopkinson Pressure Bar device was used to perform the dynamic tests. The confinement cell is instrumented with strain gages so the confinement level applied to the ligament of the concrete specimen is measured before and during the shearing stage. The results on two sets of samples (dry and wet) shows that the shear strength is sensitive to the water content with higher values for dry samples and to the applied loading rate, with higher values of dynamic shear strength compared to static ones for both concretes.

Application of ultra-high speed photography in identification of the dynamic tensile response of quasi-brittle materials

This paper investigates the application of CMOS-based ultra-high speed camera in characterising m... more This paper investigates the application of CMOS-based ultra-high speed camera in characterising materials under dynamic tensile loading. A single Hopkinson bar test is used to induce an axial stress wave in the sample and a grid pattern is filmed during the test to obtain time-resolved full-field kinematic measurements. Then the acceleration fields are used to reconstruct the stress information and identify material response. Quasi-brittle materials (e.g. rocks and concrete) present a particular experimental challenge due to small deformation and low stress level at failure. The Shimadzu HPV-X2 acquisition system has been applied for such purpose and its performance was investigated by first performing a spalling test on an aluminium benchmark sample and then applied to testing ordinary concrete.

Investigation of the Mechanical Behaviour of Lingulid Sandstone Emphasising the Influence from Pre-Existing Structural Defects, Part 1: Model Identification Based on Static Experiments

Applied sciences, Oct 25, 2022

This article is an open access article distributed under the terms and conditions of the Creative... more

Damage in Armor Ceramics Subjected to High-Strain-Rate Dynamic Loadings: The Spherical Expansion Shock Wave Pyrotechnic Test

by Pascal Forquin and Antonio Cosculluela

Handbook of Damage Mechanics; Nano to Macro Scale for Materials and Structures, 2022

For shielding type or armor applications, it is important to know the state of the material well ... more For shielding type or armor applications, it is important to know the state of the material well after the passage of the divergent spherical wave which comes off in front of the impactor projectile. The objective of this chapter is to present an experimental technique which make it possible to load materials in a large range of dynamic strain and stress: The Spherical Expansion Shock Wave Pyrotechnic Test. The paths of loading, the observed micro-physical phenomena and the associated behaviors of two brittle materials (two ceramics) are described. A particular focus is made on the influence of the microstructure and the nature of the ceramic on their dynamic behavior. Numerical simulations are presented. Some of them give the history of the states of strain and stress as well as contribute to the understanding of the physical phenomenology; the others report on the experimental mechanical behavior of these ceramics. This chapter show that is important to consider the state of the material after being submitted to an initial divergent spherical wave before modelling the mechanical response of the material in a shielding type structure. These analyses allow to better consider physical phenomena in the mechanical behavior modelling and so the improvement of the mechanical strength/density ratio of the constituent materials of these kind of structures.

Damage in Armor Ceramics Subjected to High-Strain-Rate Dynamic Loadings: The Edge-On Impact Test

Handbook of Damage Mechanics; Nano to Macro Scale for Materials and Structures, 2022

The objective of this chapter devoted to "Damage in armor ceramics subjected to high-strain-rate ... more The objective of this chapter devoted to "Damage in armor ceramics subjected to high-strain-rate dynamic loadings" is dedicated to the Edge-On-Impact testing technique. This experimental method is commonly used to investigate the high strain-rate tensile damage induced in armor ceramics when subjected to impact loading. The principle of EOI test is the following: a metallic cylindrical projectile hits the edge of a rectangular tile which thickness is generally smaller than the projectile diameter. The compressive strength of ceramics being much higher than their tensile strength, tensile damage occurs without inducing any compressive damage near the impact point. This anisotropic damage, called multiplefragmentation process, is composed of a large number of oriented cracks. Two testing configurations are generally considered. In the so-called open configuration an ultra-high-speed camera is used to visualize the fragmentation process as function of time. In the sarcophagus configuration, a metallic or polymeric casing is used to keep the fragments in place so the damage pattern can be analyzed further by microscopy or X-ray micro-tomography analysis. Next the damage pattern can be compared to numerical predictions. In this chapter, a short review of experimental works proposed in the literature based on the use of EOI tests is presented. A numerical study is introduced to assess the loading history and loading-rate involved in such test. Next, experimental results conducted with 4 silicon carbide ceramics are presented. Finally, these experiments are numerically simulated in a FE code with the DFH (Denoual-Forquin-Hild) anisotropic damage model and the final damage patterns are compared to post-mortem observation in terms of cracking density. Last, the strengths, weaknesses and drawbacks of EOI tests are discussed.

Damage in Concrete Subjected to Impact Loading

by Pascal Forquin and P. Forquin

Handbook of Damage Mechanics; Nano to Macro Scale for Materials and Structures, 2021

This chapter aims to illustrate the damage modes observed in concrete structures subjected to hig... more This chapter aims to illustrate the damage modes observed in concrete structures subjected to highstrain-rate and impact loadings. During the impact of soft or hard projectile against a concrete target complex high-stresses and strain-rates-transient dynamic loading develops leading to various damage modes such as cratering on the front face, crushing and shearing in the projectile-target contact area, radial fracturing in the whole target and, in case of the perforation, spalling on the rear face. In order to improve the constitutive models and numerical tools used to describe projectile-target interaction these damage modes need to be studied and better understood. The present chapter first illustrates various observations of fracturing processes in concrete targets reported in different experimental works. Next, "laboratory impact experiments" in which the damage modes were carefully analyzed are presented. In addition, various experimental techniques that are used to analyze the strength and damage of concrete under high-strain-rates are illustrated. The expected damage modes induced under impact loading depending on the level of confinement and strain-rates are summarized. Finally, based on the experimental data of spalling tests and quasi-oedometric compression tests a coupled plasticity-damage model is fitted and numerical calculations are used to predict the ballistic performances of a common concrete.

Investigation of the Quasi-Static and Dynamic Confined Strength of Concretes by Means of Quasi-Oedometric Compression Tests

Compressive Strength of Concrete, 2019

For the two last decades, the quasi-oedometric compression testing method has been widely employe... more For the two last decades, the quasi-oedometric compression testing method has been widely employed to characterize the quasi-static and dynamic confined response of concrete and rock-like materials. It consists of compressing a cylindrical specimen tightly enclosed in a thick confinement vessel for determining the hydrostatic and deviatoric behaviors of these materials under pressure ranging from few tens to a thousand of MPa. Large capacity hydraulic press can be used for quasistatic loading whereas large-diameter Split-Hopkinson Pressure Bar can be employed to characterize the dynamic response of the tested samples. This chapter describes the principle of this testing technique, the processing method, validation tools provided in the literature and some key-results obtained regarding the influence of concrete composition, particles reinforcement, free water content and the loading-rates on the hydrostatic and deviatoric behaviors of concretes.

Dynamic behaviour of concrete and cementitious materials

Dynamic Behavior of Materials, 2024

Understanding the dynamic response of concrete and cement-based materials is essential for design... more Understanding the dynamic response of concrete and cement-based materials is essential for designing structures that can withstand intense loading conditions, including civil, defense, and critical infrastructures. This chapter provides a comprehensive review of the latest advancements in the mechanical characterization of concrete and cementitious materials under dynamic loading. It focuses on understanding the fracture behavior exhibited by these materials and discusses the challenges encountered during high strain rate testing. By gaining insights into the dynamic behavior of these materials, engineers and researchers can enhance their ability to develop resilient and robust structures capable of withstanding extreme loading conditions.

Dynamic behaviour of concrete and cementitious materials

Dynamic Behavior of Materials, 2024

Understanding the dynamic response of concrete and cement-based materials is essential for design... more Understanding the dynamic response of concrete and cement-based materials is essential for designing structures that can withstand intense loading conditions, including civil, defense, and critical infrastructures. This chapter provides a comprehensive review of the latest advancements in the mechanical characterization of concrete and cementitious materials under dynamic loading. It focuses on understanding the fracture behavior exhibited by these materials and discusses the challenges encountered during high strain rate testing. By gaining insights into the dynamic behavior of these materials, engineers and researchers can enhance their ability to develop resilient and robust structures capable of withstanding extreme loading conditions.

Dynamic behaviour of ceramic materials

Dynamic Behavior of Materials, 2024

Although the dynamic behaviour of ceramics is less well-known than that of other material familie... more Although the dynamic behaviour of ceramics is less well-known than that of other material families such as metals, polymers, composites or even geomaterials, these materials are nonetheless widely used in many fields under dynamic or shock loading. Under such extreme conditions, these materials exhibit damage and deformation modes that are difficult to observe under static loading. For this reason, the study of their behaviour under high strain-rate is a major challenge. These materials combine low density compared to dense materials like steels with interesting, and even exceptional properties under compressive loadings over a wide temperature range, making them particularly valuable as part of shielding solutions against high-speed impact or high-energy-density pulse loading. On the other hand, these materials exhibit low toughness and ductility in the absence of confinement, which explains their ability to fragment under dynamic tensile loading. In addition, the damage and deformation modes in these materials are particularly sensitive to microstructural parameters such as sintering defects, flaws, grain boundaries, secondary phases. The experimental study of the dynamic behaviour of these materials requires the use of specific experimental methods to characterize their strength under high-rate tension, as well as under high confinement pressure in their pristine (unfragmented) or fragmented states. On the other hand, plasticity and anisotropic damage models must be developed and implemented in numerical codes, considering the influence of loading-rate, level of confinement pressure and deformation or fragmentation state of the ceramic material. This chapter provides a non-exhaustive summary of the work available in the literature on these topics.

$Research paper thumbnail of Dynamic damage and fracture processes in brittle materials$

Dynamic damage and fracture processes in brittle materials

Dynamic Behavior of Materials, 2024

Brittle materials such as, rocks, concrete and high-performance concrete, glass, ceramics, ice...... more Brittle materials such as, rocks, concrete and high-performance concrete, glass, ceramics, ice..., are materials abundantly present in our everyday life and materials involved in many industrial applications or in various protective solutions. Achieving a good understanding of their strain-rate sensitivity in relation with their microstructure remains a major issue. In addition, the development of micromechanics-based models is of major importance in view of improving the predictive capabilities of analytical and numerical models and in order to better explain the role of material parameters involved in the strain-rate and pressure sensitivity of brittle materials. In the present chapter the damage and fracture processes involved in various brittle materials are discussed. Several experimental techniques offering the capability to characterize and analyse these damage modes are presented. Next, some micromechanics-based models attending to describe these mechanisms are detailed. Experimental and modelling approaches allow highlighting the main microstructural parameters driving the behaviour of brittle materials at high loading rates.