SAM
https://sam.ensam.eu:443
The DSpace digital repository system captures, stores, indexes, preserves, and distributes digital research material.Wed, 22 May 2019 11:16:56 GMT2019-05-22T11:16:56ZThermoforming of a PMMA transparency near glass transition temperature
http://hdl.handle.net/10985/6684
Thermoforming of a PMMA transparency near glass transition temperature
GILORMINI, Pierre; CHEVALIER, Luc; REGNIER, Gilles
In order to simulate the thermoforming of a transparency, constitutive equations are proposed for the nonlinear viscoelastic behaviour of poly(methyl methacrylate) near glass transition temperature, which include large deformations. In a first step, they are fitted on a set of uniaxial tensionrelaxation tests at various strain levels and strain rates. In a second step, their implementation in a finite element code is performed. Finally, the thermoforming of a transparency at a constant and uniform temperature is simulated and compared with experimental results.
Fri, 01 Jan 2010 00:00:00 GMThttp://hdl.handle.net/10985/66842010-01-01T00:00:00ZGILORMINI, PierreCHEVALIER, LucREGNIER, GillesIn order to simulate the thermoforming of a transparency, constitutive equations are proposed for the nonlinear viscoelastic behaviour of poly(methyl methacrylate) near glass transition temperature, which include large deformations. In a first step, they are fitted on a set of uniaxial tensionrelaxation tests at various strain levels and strain rates. In a second step, their implementation in a finite element code is performed. Finally, the thermoforming of a transparency at a constant and uniform temperature is simulated and compared with experimental results.Legitimate domain of a Newtonian behavior for thermal nanoimprint lithography
http://hdl.handle.net/10985/7175
Legitimate domain of a Newtonian behavior for thermal nanoimprint lithography
TEYSSEDRE, Hubert; GILORMINI, Pierre; LANDIS, Stefan; REGNIER, Gilles
Nanoimprint lithography is an efficient way to reproduce nanostructures down to 20 nanometers in sub-micrometer polymeric films. To optimize this process, simulation using a Newtonian behavior is a cheap and efficient way to predict the polymer flow in micro and nano size cavities. This behavior is nevertheless limited to flows with shear rates below a critical value that can be determined with standard rheology measurements. We have investigated the validity domain of this behavior to simulate thermal NIL. This domain of validity is composed of two uncoupled functions, one for the material properties and the mean pressure applied to the pattern, and one for the geometry considered. The latter function has been determined with numerical simulations using the natural element method. It is demonstrated that knowing the mean applied pressure, the critical shear rate, and the viscosity of the material we are able to determine, depending on stamp geometry, if shear-thinning may or may not occur during an imprinting process.
Tue, 01 Jan 2013 00:00:00 GMThttp://hdl.handle.net/10985/71752013-01-01T00:00:00ZTEYSSEDRE, HubertGILORMINI, PierreLANDIS, StefanREGNIER, GillesNanoimprint lithography is an efficient way to reproduce nanostructures down to 20 nanometers in sub-micrometer polymeric films. To optimize this process, simulation using a Newtonian behavior is a cheap and efficient way to predict the polymer flow in micro and nano size cavities. This behavior is nevertheless limited to flows with shear rates below a critical value that can be determined with standard rheology measurements. We have investigated the validity domain of this behavior to simulate thermal NIL. This domain of validity is composed of two uncoupled functions, one for the material properties and the mean pressure applied to the pattern, and one for the geometry considered. The latter function has been determined with numerical simulations using the natural element method. It is demonstrated that knowing the mean applied pressure, the critical shear rate, and the viscosity of the material we are able to determine, depending on stamp geometry, if shear-thinning may or may not occur during an imprinting process.Crosslink Density Changes during the Hydrolysis of Tridimensional Polyesters
http://hdl.handle.net/10985/8276
Crosslink Density Changes during the Hydrolysis of Tridimensional Polyesters
RICHAUD, Emmanuel; GILORMINI, Pierre; COQUILLAT, Marie; VERDU, Jacques
The hydrolysis of almost ideal networks based on macrodiols of average molar mass about 2 kg mol 1, with L¼18 ester groups per chain is studied. Tensile testing is used to evaluate the crosslink density through the statistical theory of rubber elasticity at two temperatures and three values of relative humidity. A kinetic model for ester consumption including an autocatalysis term is proposed and combined with two original approaches for modeling the crosslink density changes. This allows kinetic parameters of hydrolysis to be determined, and very good predictions are obtained for the variations of crosslink density (or elastic modulus) in the three aging conditions considered. The initial curvature of elastic modulus versus time is predicted positive for weak autocatalysis and negative for strong autocatalysis. The obtained conversion ratio at degelation is found to decrease sharply with the number of esters per elastically active chain
Wed, 01 Jan 2014 00:00:00 GMThttp://hdl.handle.net/10985/82762014-01-01T00:00:00ZRICHAUD, EmmanuelGILORMINI, PierreCOQUILLAT, MarieVERDU, JacquesThe hydrolysis of almost ideal networks based on macrodiols of average molar mass about 2 kg mol 1, with L¼18 ester groups per chain is studied. Tensile testing is used to evaluate the crosslink density through the statistical theory of rubber elasticity at two temperatures and three values of relative humidity. A kinetic model for ester consumption including an autocatalysis term is proposed and combined with two original approaches for modeling the crosslink density changes. This allows kinetic parameters of hydrolysis to be determined, and very good predictions are obtained for the variations of crosslink density (or elastic modulus) in the three aging conditions considered. The initial curvature of elastic modulus versus time is predicted positive for weak autocatalysis and negative for strong autocatalysis. The obtained conversion ratio at degelation is found to decrease sharply with the number of esters per elastically active chainOn using the leveling of the free surface of a Newtonian fluid to measure viscosity and Navier slip length
http://hdl.handle.net/10985/7394
On using the leveling of the free surface of a Newtonian fluid to measure viscosity and Navier slip length
GILORMINI, Pierre; TEYSSEDRE, Hubert
Measuring the relaxation time involved in the leveling of the free surface of a Newtonian fluid laid on a substrate can give access to material parameters. It is shown here how most favorable pattern geometries of the free surface and film thicknesses can be defined for the measures of viscosity and Navier slip length at the fluid-solid interface, respectively. Moreover, special emphasis is put on the conditions required to avoid shear-thinning by controling the maximum shear rate. For initially sinusoidal patterns with infinitesimal amplitudes, an analytical solution including slip at the fluid-solid interface is used, and numerical simulations based on the natural element method allow to discuss the effect of finite amplitudes. This leads to the definition of a relevance domain for the analytical solution that avoids the need for numerical simulations in practical applications. It is also shown how these results can be applied to crenelated profiles, where Fourier series expansion can be used, but with caution.
Version éditeur : http://rspa.royalsocietypublishing.org/content/469/2160/20130457.short
Tue, 01 Jan 2013 00:00:00 GMThttp://hdl.handle.net/10985/73942013-01-01T00:00:00ZGILORMINI, PierreTEYSSEDRE, HubertMeasuring the relaxation time involved in the leveling of the free surface of a Newtonian fluid laid on a substrate can give access to material parameters. It is shown here how most favorable pattern geometries of the free surface and film thicknesses can be defined for the measures of viscosity and Navier slip length at the fluid-solid interface, respectively. Moreover, special emphasis is put on the conditions required to avoid shear-thinning by controling the maximum shear rate. For initially sinusoidal patterns with infinitesimal amplitudes, an analytical solution including slip at the fluid-solid interface is used, and numerical simulations based on the natural element method allow to discuss the effect of finite amplitudes. This leads to the definition of a relevance domain for the analytical solution that avoids the need for numerical simulations in practical applications. It is also shown how these results can be applied to crenelated profiles, where Fourier series expansion can be used, but with caution.Cyclic and monotonic testing of free and constrained recovery properties of a chemically crosslinked acrylate
http://hdl.handle.net/10985/7759
Cyclic and monotonic testing of free and constrained recovery properties of a chemically crosslinked acrylate
ARRIETA, Juan Sebastian; DIANI, Julie; GILORMINI, Pierre
A chemically crosslinked acrylate network was submitted to various thermomechanical strain and stress recoveries while changing the experimental parameters in order to better define the benefits and the limits of using chemically crosslinked polymers for multicycle applications or applications under external constraints. The results showed that the free recoveries and the constrained recoveries remained the same at the first cycle and during the next ones. It was also shown that the low stress usually generated by a crosslinked network when submitted to a constrained recovery can be significantly increased by choosing suitable experimental conditions.
The definitive version is available at http://onlinelibrary.wiley.com/doi/10.1002/app.39813/full
Wed, 01 Jan 2014 00:00:00 GMThttp://hdl.handle.net/10985/77592014-01-01T00:00:00ZARRIETA, Juan SebastianDIANI, JulieGILORMINI, PierreA chemically crosslinked acrylate network was submitted to various thermomechanical strain and stress recoveries while changing the experimental parameters in order to better define the benefits and the limits of using chemically crosslinked polymers for multicycle applications or applications under external constraints. The results showed that the free recoveries and the constrained recoveries remained the same at the first cycle and during the next ones. It was also shown that the low stress usually generated by a crosslinked network when submitted to a constrained recovery can be significantly increased by choosing suitable experimental conditions.On modeling shape memory polymers as elastic two-phase composite materials
http://hdl.handle.net/10985/6558
On modeling shape memory polymers as elastic two-phase composite materials
GILORMINI, Pierre; DIANI, Julie
A model has been proposed recently, which describes the experimentally observed mechanical behavior of some shape memory polymers. It considers a purely thermoelastic behavior, without strain rate effects, and assumes essentially that the polymer can be considered as a two-phase composite, with glassy and rubbery phases having volume fractions that depend on temperature only. Since a uniform stress hypothesis was used in the original formulation, with an inconsistency when thermal expansion was considered, this model is revisited here by taking advantage of the many results that have been established in the theory of composite materials. It is shown, especially, that a uniform strain hypothesis is more appropriate than assuming a uniform stress.
Sun, 01 Jan 2012 00:00:00 GMThttp://hdl.handle.net/10985/65582012-01-01T00:00:00ZGILORMINI, PierreDIANI, JulieA model has been proposed recently, which describes the experimentally observed mechanical behavior of some shape memory polymers. It considers a purely thermoelastic behavior, without strain rate effects, and assumes essentially that the polymer can be considered as a two-phase composite, with glassy and rubbery phases having volume fractions that depend on temperature only. Since a uniform stress hypothesis was used in the original formulation, with an inconsistency when thermal expansion was considered, this model is revisited here by taking advantage of the many results that have been established in the theory of composite materials. It is shown, especially, that a uniform strain hypothesis is more appropriate than assuming a uniform stress.On the role of hydrogen bonding on water absorption in polymers
http://hdl.handle.net/10985/12814
On the role of hydrogen bonding on water absorption in polymers
GILORMINI, Pierre; VERDU, Jacques
A kinetic model is proposed for the absorption of water in polymers. The process of bonding-debonding water molecules is described by two opposite reactions with different rate constants, and the key role of the concentration of traps by hydrogen bonding in the polymer matrix is highlighted. These three parameters are combined such that an equation is obtained that generalizes the model proposed by Carter and Kibler, with an additional, crossed, term. Numerical application is performed for the diffusion-absorption of water in a plane polymer sheet, and the parameter ranges where a quasi-Fickian water uptake curve is obtained are defined. The associated apparent diffusivity is shown to obey a hyperbolic variation with equilibrium water uptake for homologous series of polymers, which is in agreement with previous experimental observations.
Mon, 01 Jan 2018 00:00:00 GMThttp://hdl.handle.net/10985/128142018-01-01T00:00:00ZGILORMINI, PierreVERDU, JacquesA kinetic model is proposed for the absorption of water in polymers. The process of bonding-debonding water molecules is described by two opposite reactions with different rate constants, and the key role of the concentration of traps by hydrogen bonding in the polymer matrix is highlighted. These three parameters are combined such that an equation is obtained that generalizes the model proposed by Carter and Kibler, with an additional, crossed, term. Numerical application is performed for the diffusion-absorption of water in a plane polymer sheet, and the parameter ranges where a quasi-Fickian water uptake curve is obtained are defined. The associated apparent diffusivity is shown to obey a hyperbolic variation with equilibrium water uptake for homologous series of polymers, which is in agreement with previous experimental observations.A numerical study of the influence of polydispersity on the behaviour until break of a reinforced hyperelastic material with a cohesive interface
http://hdl.handle.net/10985/9629
A numerical study of the influence of polydispersity on the behaviour until break of a reinforced hyperelastic material with a cohesive interface
TOULEMONDE, Paul-Aymé; DIANI, Julie; GILORMINI, Pierre; DESGARDIN, Nancy
Solid propellants manufacturers commonly monitor the granulometries of the explosive fllers they introduce in the material to pack high fller volume fraction and thus obtain satisfactory energetic performance. However, to our knowledge, the effect of a mix of small and large particles in the micrometric size range in flled elastomers has not yet been fully understood. This work aims at producing a better understanding of the underlying mechanisms that take place in a bidisperse flled elastomer composite under uniaxial loading by using finite element simulations. An original process for creating bidisperse microstructures is proposed and analyzed. The key role of the fller/matrix interface is emphasized through the use of a cohesive zone model. Plane- strain simulations in uniaxial tension of such cells with different fractions of large and small particles are performed.
Thu, 01 Jan 2015 00:00:00 GMThttp://hdl.handle.net/10985/96292015-01-01T00:00:00ZTOULEMONDE, Paul-AyméDIANI, JulieGILORMINI, PierreDESGARDIN, NancySolid propellants manufacturers commonly monitor the granulometries of the explosive fllers they introduce in the material to pack high fller volume fraction and thus obtain satisfactory energetic performance. However, to our knowledge, the effect of a mix of small and large particles in the micrometric size range in flled elastomers has not yet been fully understood. This work aims at producing a better understanding of the underlying mechanisms that take place in a bidisperse flled elastomer composite under uniaxial loading by using finite element simulations. An original process for creating bidisperse microstructures is proposed and analyzed. The key role of the fller/matrix interface is emphasized through the use of a cohesive zone model. Plane- strain simulations in uniaxial tension of such cells with different fractions of large and small particles are performed.Direct experimental evidence of time-temperature superposition at finite strain for an amorphous polymer network
http://hdl.handle.net/10985/9223
Direct experimental evidence of time-temperature superposition at finite strain for an amorphous polymer network
DIANI, Julie; GILORMINI, Pierre; ARRIETA, Juan Sebastian
The time-temperature superposition property of an amorphous polymer acrylate network is characterized at infinitesimal strain by standard dynamic mechanical analysis tests. Comparison of the shift factors determined in uniaxial tension and in torsion shows that both tests provide equivalent time-temperature superposition properties. More interestingly, finite strain uniaxial tension tests run until break at constant strain rate show that the acrylate network exhibits the same time-temperature superposition property at finite strain as at infinitesimal strain. Such original experimental evidence provides new insight for finite strain constitutive modelling of polymer amorphous networks.
Thu, 01 Jan 2015 00:00:00 GMThttp://hdl.handle.net/10985/92232015-01-01T00:00:00ZDIANI, JulieGILORMINI, PierreARRIETA, Juan SebastianThe time-temperature superposition property of an amorphous polymer acrylate network is characterized at infinitesimal strain by standard dynamic mechanical analysis tests. Comparison of the shift factors determined in uniaxial tension and in torsion shows that both tests provide equivalent time-temperature superposition properties. More interestingly, finite strain uniaxial tension tests run until break at constant strain rate show that the acrylate network exhibits the same time-temperature superposition property at finite strain as at infinitesimal strain. Such original experimental evidence provides new insight for finite strain constitutive modelling of polymer amorphous networks.Experimental study and numerical simulation of the vertical bounce of a polymer ball over a wide temperature range
http://hdl.handle.net/10985/7694
Experimental study and numerical simulation of the vertical bounce of a polymer ball over a wide temperature range
DIANI, Julie; GILORMINI, Pierre; AGBOBADA, Gerry
The dependence to temperature of the rebound of a solid polymer ball on a rigid slab is investigated. An acrylate polymer ball is brought to a wide range of temperatures, covering its glass to rubbery transition, and let fall on a granite slab while the coe cient of restitution, duration of contact, and force history are measured experimentally. The ball fabrication is controlled in the lab, allowing the mechanical characterization of the material by classic dynamic mechanical analysis (DMA). Finite element simulations of the rebound at various temperatures are run, consider- ing the material as viscoelatic and as satisfying a WLF equation for its time-temperature superposition property. A comparison between the experiments and the simulations shows the strong link between viscoelasticity and time-temperature superposition properties of the material and the bounce characteristics of the ball.
Wed, 01 Jan 2014 00:00:00 GMThttp://hdl.handle.net/10985/76942014-01-01T00:00:00ZDIANI, JulieGILORMINI, PierreAGBOBADA, GerryThe dependence to temperature of the rebound of a solid polymer ball on a rigid slab is investigated. An acrylate polymer ball is brought to a wide range of temperatures, covering its glass to rubbery transition, and let fall on a granite slab while the coe cient of restitution, duration of contact, and force history are measured experimentally. The ball fabrication is controlled in the lab, allowing the mechanical characterization of the material by classic dynamic mechanical analysis (DMA). Finite element simulations of the rebound at various temperatures are run, consider- ing the material as viscoelatic and as satisfying a WLF equation for its time-temperature superposition property. A comparison between the experiments and the simulations shows the strong link between viscoelasticity and time-temperature superposition properties of the material and the bounce characteristics of the ball.