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The DSpace digital repository system captures, stores, indexes, preserves, and distributes digital research material.Sun, 31 May 2020 15:47:23 GMT2020-05-31T15:47:23ZA self-affine geometrical model of dynamic RT-PMMA fractures: implications for fracture energy measurements
http://hdl.handle.net/10985/9600
A self-affine geometrical model of dynamic RT-PMMA fractures: implications for fracture energy measurements
KOPP, Jean-Benoit; SCHMITTBUHL, Jean; NOEL, Olivier; FOND, Christophe
Profilometric imaging of fracture surfaces of rubber toughened polymer has been performed at two different resolutions (a) at large scales [10 μ\upmu m–25 mm] using an opto-mechanical profilometer and (b) at small scales [0.195 μ\upmu m–0.48 mm] using an interferometric optical microscope. We introduced a self-affine geometrical model using two parameters: the Hurst exponent and the topothesy. We showed that for rubber toughened materials the approximation of the created surface by a mean flat plane leads to a poor estimation of the dynamic fracture energy GIdcG_{Idc}. The description of the created rough fracture surface by a self-affine model is shown to provide a significantly better approximation. A new and original geometrical method is introduced to estimate self-affine parameters: the 3D surface scaling method. Hurst exponents are shown to be unique, χ=0.6±0.1\chi =0.6\pm 0.1 for the different fracture zones and measurement scales. Topothesy ratios indicate a significant difference of fracture surface roughness amplitude depending on the observation resolution when the detrending technique is not correctly introduced.
Thu, 01 Jan 2015 00:00:00 GMThttp://hdl.handle.net/10985/96002015-01-01T00:00:00ZKOPP, Jean-BenoitSCHMITTBUHL, JeanNOEL, OlivierFOND, ChristopheProfilometric imaging of fracture surfaces of rubber toughened polymer has been performed at two different resolutions (a) at large scales [10 μ\upmu m–25 mm] using an opto-mechanical profilometer and (b) at small scales [0.195 μ\upmu m–0.48 mm] using an interferometric optical microscope. We introduced a self-affine geometrical model using two parameters: the Hurst exponent and the topothesy. We showed that for rubber toughened materials the approximation of the created surface by a mean flat plane leads to a poor estimation of the dynamic fracture energy GIdcG_{Idc}. The description of the created rough fracture surface by a self-affine model is shown to provide a significantly better approximation. A new and original geometrical method is introduced to estimate self-affine parameters: the 3D surface scaling method. Hurst exponents are shown to be unique, χ=0.6±0.1\chi =0.6\pm 0.1 for the different fracture zones and measurement scales. Topothesy ratios indicate a significant difference of fracture surface roughness amplitude depending on the observation resolution when the detrending technique is not correctly introduced.Reevaluation of the diametral compression test for tablets using the flattened disc geometry
http://hdl.handle.net/10985/11248
Reevaluation of the diametral compression test for tablets using the flattened disc geometry
MAZEL, Vincent; GUERARD, Sandra; CROQUELOIS, Benjamin; KOPP, Jean-Benoit; GIRARDOT, Jérémie; DIARRA, Harona; BUSIGNIES, Virginie; TCHORELOFF, Pierre
Mechanical strength is an important critical quality attribute for tablets. It is classically measured, in the pharmaceutical field, using the diametral compression test. Nevertheless, due to small contact area between the tablet and the platens, some authors suggested that during the test, the failure could occur in tension away from the center which would invalidate the test and the calculation of the tensile strength. In this study, the flattened disc geometry was used as an alternative to avoid contact problems. The diametral compression on both flattened and standard geometries was first studied using finite element method (FEM) simulation. It was found that, for the flattened geometry, both maximum tensile strain and stress were located at the center of the tablet, which was not the case for the standard geometry. Experimental observations using digital image correlation (DIC) confirmed the numerical results. The experimental tensile strength obtained using both geometries were compared and it was found that the standard geometry always gave lower tensile strength than the flattened geometry. Finally, high-speed video capture of the test made it possible to detect that for the standard geometry the crack initiation was always away from the center of the tablet.
Fri, 01 Jan 2016 00:00:00 GMThttp://hdl.handle.net/10985/112482016-01-01T00:00:00ZMAZEL, VincentGUERARD, SandraCROQUELOIS, BenjaminKOPP, Jean-BenoitGIRARDOT, JérémieDIARRA, HaronaBUSIGNIES, VirginieTCHORELOFF, PierreMechanical strength is an important critical quality attribute for tablets. It is classically measured, in the pharmaceutical field, using the diametral compression test. Nevertheless, due to small contact area between the tablet and the platens, some authors suggested that during the test, the failure could occur in tension away from the center which would invalidate the test and the calculation of the tensile strength. In this study, the flattened disc geometry was used as an alternative to avoid contact problems. The diametral compression on both flattened and standard geometries was first studied using finite element method (FEM) simulation. It was found that, for the flattened geometry, both maximum tensile strain and stress were located at the center of the tablet, which was not the case for the standard geometry. Experimental observations using digital image correlation (DIC) confirmed the numerical results. The experimental tensile strength obtained using both geometries were compared and it was found that the standard geometry always gave lower tensile strength than the flattened geometry. Finally, high-speed video capture of the test made it possible to detect that for the standard geometry the crack initiation was always away from the center of the tablet.Multi-scale foam : 3D structure/compressive behaviour relationship of agglomerated cork
http://hdl.handle.net/10985/17576
Multi-scale foam : 3D structure/compressive behaviour relationship of agglomerated cork
LE BARBENCHON, Louise; GIRARDOT, Jérémie; KOPP, Jean-Benoit; VIOT, Philippe
This study focuses on the microstructural aspects of a cork-based by-product known as agglomerated cork and its influence on the compressive mechanical behaviour. The material consists in granulates of a natural polymeric foam - cork - mixed together with a small quantity of a bio-sourced resin. Optical and scanning electron microscopy (SEM) are first used to investigate on the bead geometry and placement and interfaces arrangement. Then X-ray computed tomography allows to study the spatial arrangement of agglomerated cork microstructure and hence to complete and confirm 2D observations. 2D and 3D observations show a transverse anisotropic material which is confirmed by the mechanical tests. SEM pictures demonstrate an intricate and heterogeneous material. Microtomography confirms the presence of macroporosities between cork granulates having a mean volume around 0.1 mm 3 . Cork cell specific geometry is also confirmed. The volume of those cells lies around 10 −5 mm 3 . Finally quasi-static compression tests are run to establish a link between microstructure and mechanical behaviour thanks to digital image correlation (DIC). Cork agglomerate demonstrates strong strain localisation at its surface caused by its multi-scale structure.
Tue, 01 Jan 2019 00:00:00 GMThttp://hdl.handle.net/10985/175762019-01-01T00:00:00ZLE BARBENCHON, LouiseGIRARDOT, JérémieKOPP, Jean-BenoitVIOT, PhilippeThis study focuses on the microstructural aspects of a cork-based by-product known as agglomerated cork and its influence on the compressive mechanical behaviour. The material consists in granulates of a natural polymeric foam - cork - mixed together with a small quantity of a bio-sourced resin. Optical and scanning electron microscopy (SEM) are first used to investigate on the bead geometry and placement and interfaces arrangement. Then X-ray computed tomography allows to study the spatial arrangement of agglomerated cork microstructure and hence to complete and confirm 2D observations. 2D and 3D observations show a transverse anisotropic material which is confirmed by the mechanical tests. SEM pictures demonstrate an intricate and heterogeneous material. Microtomography confirms the presence of macroporosities between cork granulates having a mean volume around 0.1 mm 3 . Cork cell specific geometry is also confirmed. The volume of those cells lies around 10 −5 mm 3 . Finally quasi-static compression tests are run to establish a link between microstructure and mechanical behaviour thanks to digital image correlation (DIC). Cork agglomerate demonstrates strong strain localisation at its surface caused by its multi-scale structure.Strain rate effect on the mechanical properties of a glass fibre reinforced acrylic matrix laminate. An experimental approach
http://hdl.handle.net/10985/17357
Strain rate effect on the mechanical properties of a glass fibre reinforced acrylic matrix laminate. An experimental approach
CADIEU, Lucien; KOPP, Jean-Benoit; JUMEL, Julien; BEGA, Jéremy; FROUSTEY, Catherine
The aim of this study is to evaluate the effect of the loading rate on the mechanical properties and damage mechanisms of a Glass/Elium150 laminate composite. Quasi-static indentation (QS) and low energy dynamic impact (DYN) tests which simulate lifetime structural loadings (dropped tool, gravel impacts, …) are lead. A specific experimental approach is developed to compare results of both experiments. The effect of the loading rate on the structural response (stiffness, dissipated energy) of the composite is highlighted. The numerous damage mechanisms involved in the collapse of the material are observed at a microscopic scale using both optical and scanning electron microscopy (SEM). Finally an intra-laminar crack propagation mechanism is described based on post-mortem observations at ply scale to explain the formation of interlaminar cracks
Tue, 01 Jan 2019 00:00:00 GMThttp://hdl.handle.net/10985/173572019-01-01T00:00:00ZCADIEU, LucienKOPP, Jean-BenoitJUMEL, JulienBEGA, JéremyFROUSTEY, CatherineThe aim of this study is to evaluate the effect of the loading rate on the mechanical properties and damage mechanisms of a Glass/Elium150 laminate composite. Quasi-static indentation (QS) and low energy dynamic impact (DYN) tests which simulate lifetime structural loadings (dropped tool, gravel impacts, …) are lead. A specific experimental approach is developed to compare results of both experiments. The effect of the loading rate on the structural response (stiffness, dissipated energy) of the composite is highlighted. The numerous damage mechanisms involved in the collapse of the material are observed at a microscopic scale using both optical and scanning electron microscopy (SEM). Finally an intra-laminar crack propagation mechanism is described based on post-mortem observations at ply scale to explain the formation of interlaminar cracksExperimental Investigation and Discrete Element Modelling of Composite Hollow Spheres Subjected to Dynamic Fracture
http://hdl.handle.net/10985/17021
Experimental Investigation and Discrete Element Modelling of Composite Hollow Spheres Subjected to Dynamic Fracture
CORE, Arthur; KOPP, Jean-Benoit; VIOT, Philippe; CHARLES, Jean-Luc; DAU, Frédéric
This paper deals with the characterization and the numerical modelling of the collapse of composite hollow spherical structures developed to absorb energy during high velocity impacts. The structure is composed of hollow spheres (ϕ=2–30 mm) made of epoxy resin and mineral powder. First of all, quasi-static and dynamic (v=5 mm·min−1 to v=2 m·s−1) compression tests are conducted at room temperature on a single sphere to study energy dissipation mechanisms. Fracture of the material appears to be predominant. A numerical model based on the discrete element method is investigated to simulate the single sphere crushing. The stress-strain-time relationship of the material based on the Ree-Eyring law is numerically implemented. The DEM modelling takes naturally into account the dynamic fracture and the crack path computed is close to the one observed experimentally in uniaxial compression. Eventually, high velocity impacts (v>100 m·s−1) of a hollow sphere on a rigid surface are conducted with an air cannon. The numerical results are in good agreement with the experimental data and demonstrate the ability of the present model to correctly describe the mechanical behavior of brittle materials at high strain rate.
Sun, 01 Jan 2017 00:00:00 GMThttp://hdl.handle.net/10985/170212017-01-01T00:00:00ZCORE, ArthurKOPP, Jean-BenoitVIOT, PhilippeCHARLES, Jean-LucDAU, FrédéricThis paper deals with the characterization and the numerical modelling of the collapse of composite hollow spherical structures developed to absorb energy during high velocity impacts. The structure is composed of hollow spheres (ϕ=2–30 mm) made of epoxy resin and mineral powder. First of all, quasi-static and dynamic (v=5 mm·min−1 to v=2 m·s−1) compression tests are conducted at room temperature on a single sphere to study energy dissipation mechanisms. Fracture of the material appears to be predominant. A numerical model based on the discrete element method is investigated to simulate the single sphere crushing. The stress-strain-time relationship of the material based on the Ree-Eyring law is numerically implemented. The DEM modelling takes naturally into account the dynamic fracture and the crack path computed is close to the one observed experimentally in uniaxial compression. Eventually, high velocity impacts (v>100 m·s−1) of a hollow sphere on a rigid surface are conducted with an air cannon. The numerical results are in good agreement with the experimental data and demonstrate the ability of the present model to correctly describe the mechanical behavior of brittle materials at high strain rate.Study of the dynamic fracture of hollow spheres under compression using the Discrete Element Method
http://hdl.handle.net/10985/17251
Study of the dynamic fracture of hollow spheres under compression using the Discrete Element Method
CORE, Arthur; KOPP, Jean-Benoit; GIRARDOT, Jérémie; VIOT, Philippe
Hollow sphere structure (HSS) belongs to cellular solids that have been studied recently for its multiples properties. In our case, HSS aims to absorb soft impacts energy on an airliner cockpit. This structure is investigated because of its promises in term of specific energy dissipated (J.kg1) during impact. First of all, quasi- static and dynamic (v = 5mmmin_1 to v = 2ms4) uniaxial compression tests are conducted at room temperature on a single sphere (D = 30 mm). Rapid crack propagation (RCP) is observed to be predominant at macroscopic scale. The formalism of Linear Elastic Fracture Mechanics (L.E.F.M.) is therefore used to estimate the dynamic energy release rate GIdc . The crack tip location is measured during the crack propagation using a high speed camera. The Discrete Element Method (DEM) is used to simulate the dynamic fracture by implementing a node release technique to perform a generation phase simulation. The dynamic energy release rate can be determined using the experimentally measured crack history. In hollowed spherical structures the numerical results reveal a high proportion of energy dissipated through inertial effects as well as a dependence of the thickness of the skin over the range of 0.04 mm to 1.2 mm. At a crack tip velocity of 0.6 times the Rayleigh wave speed of the material, the dynamic correction factor is less than 0.05. Similar results have been shown for the longitudinal dynamic fracture of polymer pipes. The quantitative results of GIdc are in good agreement with the literature and the present model offers an alternative to the finite element method to simulate the rapid crack propagation.Its use reveals to be an interesting way to model the mechanical behavior of brittle materials.
Mon, 01 Jan 2018 00:00:00 GMThttp://hdl.handle.net/10985/172512018-01-01T00:00:00ZCORE, ArthurKOPP, Jean-BenoitGIRARDOT, JérémieVIOT, PhilippeHollow sphere structure (HSS) belongs to cellular solids that have been studied recently for its multiples properties. In our case, HSS aims to absorb soft impacts energy on an airliner cockpit. This structure is investigated because of its promises in term of specific energy dissipated (J.kg1) during impact. First of all, quasi- static and dynamic (v = 5mmmin_1 to v = 2ms4) uniaxial compression tests are conducted at room temperature on a single sphere (D = 30 mm). Rapid crack propagation (RCP) is observed to be predominant at macroscopic scale. The formalism of Linear Elastic Fracture Mechanics (L.E.F.M.) is therefore used to estimate the dynamic energy release rate GIdc . The crack tip location is measured during the crack propagation using a high speed camera. The Discrete Element Method (DEM) is used to simulate the dynamic fracture by implementing a node release technique to perform a generation phase simulation. The dynamic energy release rate can be determined using the experimentally measured crack history. In hollowed spherical structures the numerical results reveal a high proportion of energy dissipated through inertial effects as well as a dependence of the thickness of the skin over the range of 0.04 mm to 1.2 mm. At a crack tip velocity of 0.6 times the Rayleigh wave speed of the material, the dynamic correction factor is less than 0.05. Similar results have been shown for the longitudinal dynamic fracture of polymer pipes. The quantitative results of GIdc are in good agreement with the literature and the present model offers an alternative to the finite element method to simulate the rapid crack propagation.Its use reveals to be an interesting way to model the mechanical behavior of brittle materials.Reinforcement of cellular materials with short fibres: Application to a bio-based cork multi-scale foam
http://hdl.handle.net/10985/17736
Reinforcement of cellular materials with short fibres: Application to a bio-based cork multi-scale foam
LE BARBENCHON, Louise; KOPP, Jean-Benoit; GIRARDOT, Jérémie; VIOT, Philippe
A bio-sourced foam, agglomerated cork, was chosen to evaluate the influence of short fibres on the mechanical behaviour of cellular materials. The final material was obtained by mixing cork particles with a thermoset resin. Rigid short fibres were then added before uni-axial compression. Enhancing the foam’s mechanical properties without increasing the density is a current problem in transport industries. In this article, we demonstrate how the addition of short fibres strongly modifies the mechanical behaviour of agglomerated foam materials. Dynamic Mechanical Analysis technique revealed that the glass temperature was greater for reinforced foams and more energy loss by heat in visco-elasticity was also noticed for this material. In quasi-static compression, rigidity was strongly enhanced, causing absorbed energy before densification to increase. Maximal force and displacement before fracture were studied by applying Mode I fracture tests, and both were improved by the addition of short fibres. The mesoscopic and microscopic observations revealed it was linked to fracture me- chanisms, most of which happen inside cork beads for the reinforced cellular material. The properties of agglomerated foams may then be improved and tailored by the addtion of short fibres and make weight saving possible in several industrial applications.
Wed, 01 Jan 2020 00:00:00 GMThttp://hdl.handle.net/10985/177362020-01-01T00:00:00ZLE BARBENCHON, LouiseKOPP, Jean-BenoitGIRARDOT, JérémieVIOT, PhilippeA bio-sourced foam, agglomerated cork, was chosen to evaluate the influence of short fibres on the mechanical behaviour of cellular materials. The final material was obtained by mixing cork particles with a thermoset resin. Rigid short fibres were then added before uni-axial compression. Enhancing the foam’s mechanical properties without increasing the density is a current problem in transport industries. In this article, we demonstrate how the addition of short fibres strongly modifies the mechanical behaviour of agglomerated foam materials. Dynamic Mechanical Analysis technique revealed that the glass temperature was greater for reinforced foams and more energy loss by heat in visco-elasticity was also noticed for this material. In quasi-static compression, rigidity was strongly enhanced, causing absorbed energy before densification to increase. Maximal force and displacement before fracture were studied by applying Mode I fracture tests, and both were improved by the addition of short fibres. The mesoscopic and microscopic observations revealed it was linked to fracture me- chanisms, most of which happen inside cork beads for the reinforced cellular material. The properties of agglomerated foams may then be improved and tailored by the addtion of short fibres and make weight saving possible in several industrial applications.Rapid crack propagation in PA11: An application to pipe structure
http://hdl.handle.net/10985/17335
Rapid crack propagation in PA11: An application to pipe structure
KOPP, Jean-Benoit; FOND, Christophe; HOCHSTETTER, Gilles
Dynamic fracture mechanism in Polyamide 11 (PA11) material has been described at laboratory scale to access to an intrinsic material parameter. A liquid transportation application is considered with polymer pipes. A preliminary numerical analysis of the rapid crack propagation (RCP) in polymer pipe is firstly realised. Two boundary conditions, imposed displacement or pressure, are numerically investigated. The work of external forces is not negligible for pressurized polymer pipe. A reliable estimate of the dynamic energy release rate GId is in this last case not guaranteed. To limit unwanted structural effects a specific experimental device has been used to ensure a permanent regime of RCP in Pre-Stressed Pipe Specimen (PS2). Experimental dynamic fracture tests are realised with Polyamide 11 PS2. Dynamic instabilities inducing “ring-off” and “snake” mechanisms which could appear during full-scale test are not observed with this new test. A finite element procedure is used to estimate the material toughness GID of PA11. Knowing the crack tip location during RCP inertia effects (i.e. kinetic energy) are quantified. The mean crack tip velocity is observed not to change in PA11 whatever the crack configuration (branching or not). This velocity is known to be the crack branching velocity (≈0.6cR). The average dynamic energy release rate 〈GID〉 is equal to 1.5± 0.1 kJm−2 at the crack branching velocity. The nontrivial fracture surface roughness is observed with a scanning electron microscope.
Mon, 01 Jan 2018 00:00:00 GMThttp://hdl.handle.net/10985/173352018-01-01T00:00:00ZKOPP, Jean-BenoitFOND, ChristopheHOCHSTETTER, GillesDynamic fracture mechanism in Polyamide 11 (PA11) material has been described at laboratory scale to access to an intrinsic material parameter. A liquid transportation application is considered with polymer pipes. A preliminary numerical analysis of the rapid crack propagation (RCP) in polymer pipe is firstly realised. Two boundary conditions, imposed displacement or pressure, are numerically investigated. The work of external forces is not negligible for pressurized polymer pipe. A reliable estimate of the dynamic energy release rate GId is in this last case not guaranteed. To limit unwanted structural effects a specific experimental device has been used to ensure a permanent regime of RCP in Pre-Stressed Pipe Specimen (PS2). Experimental dynamic fracture tests are realised with Polyamide 11 PS2. Dynamic instabilities inducing “ring-off” and “snake” mechanisms which could appear during full-scale test are not observed with this new test. A finite element procedure is used to estimate the material toughness GID of PA11. Knowing the crack tip location during RCP inertia effects (i.e. kinetic energy) are quantified. The mean crack tip velocity is observed not to change in PA11 whatever the crack configuration (branching or not). This velocity is known to be the crack branching velocity (≈0.6cR). The average dynamic energy release rate 〈GID〉 is equal to 1.5± 0.1 kJm−2 at the crack branching velocity. The nontrivial fracture surface roughness is observed with a scanning electron microscope.