Effect of the matrix behavior on the damage of ethylene–propylene glass fiber reinforced composite subjected to high strain rate tension

This study investigates the origin of the strain rate effect on the mechanical behavior of a discontinuous glass fiber reinforced ethylene–propylene copolymer (EPC) matrix composite. This kind of composite materials are commonly used for automotive functional and structural applications. To this aim, a multi-scale experimental approach is developed. The deformation processes and the damage mechanisms observed at the microscopic scale are related to the material mechanical properties at the macroscopic scale. Tensile tests up to failure and specific interrupted tensile tests have been optimized and performed for high strain rates up to 200 s 1 to quantify the strain rate effect at different scales. High speed tensile tests have also been performed on the pure copolymer matrix. The threshold and the kinetic of damage have been quantified at both microscopic and macroscopic scales. Experimental results show that the composite behavior is strongly strain-rate dependent. The multi-scale analysis leads to the conclusion that the strain rate effect on the damage behavior of the EPC matrix composite is mainly due to the viscous behavior of the EPC matrix. SEM observations and analysis show that a localized deformation in the interface zone around fibers occurs at high strain rates and directly affects the visco-damage behavior. It is established that when the strain rate increases, the local deformation zone around the fibers behaves like a dissipation zone. Consequently, the damage initiation is delayed and the related kinetic is reduced with respect to the quasi-static loading case

Effect of the matrix behavior on the damage of ethylene–propylene glass fiber reinforced composite subjected to high strain rate tension

This study investigates the origin of the strain rate effect on the mechanical behavior of a discontinuous glass fiber reinforced ethylene–propylene copolymer (EPC) matrix composite. This kind of composite materials are commonly used for automotive functional and structural applications. To this aim, a multi-scale experimental approach is developed. The deformation processes and the damage mechanisms observed at the microscopic scale are related to the material mechanical properties at the macroscopic scale. Tensile tests up to failure and specific interrupted tensile tests have been optimized and performed for high strain rates up to 200 s 1 to quantify the strain rate effect at different scales. High speed tensile tests have also been performed on the pure copolymer matrix. The threshold and the kinetic of damage have been quantified at both microscopic and macroscopic scales. Experimental results show that the composite behavior is strongly strain-rate dependent. The multi-scale analysis leads to the conclusion that the strain rate effect on the damage behavior of the EPC matrix composite is mainly due to the viscous behavior of the EPC matrix. SEM observations and analysis show that a localized deformation in the interface zone around fibers occurs at high strain rates and directly affects the visco-damage behavior. It is established that when the strain rate increases, the local deformation zone around the fibers behaves like a dissipation zone. Consequently, the damage initiation is delayed and the related kinetic is reduced with respect to the quasi-static loading case

Computational micro to macro transitions for shape memory alloy composites using periodic homogenization

In the current manuscript, a homogenization framework is proposed for periodic composites with shape memory alloy (SMA) constituents under quasi-static thermomechanical conditions. The methodology is based on the step-by-step periodic homogenization, in which the macroscopic and the microscopic problems of the composite are solved simultaneously. The implementation of the framework is examined with numerical examples on SMA composite laminates. Complexity of the composite nonlinear response and non-proportional stress state in the SMA appears, even in the case of uniaxial macroscopic boundary conditions. Moreover, under certain conditions, the composite laminate can exhibit a non-convex transformation surface. Additionally, the transformation temperatures at various stress levels under isobaric thermal cycling can be quite different between the composite and the pure SMA

Experimental Parameters Identification of Fatigue Damage Model for Short Glass Fiber Reinforced Thermoplastics GFRP

In the present work, a new polycyclic fatigue damage model is formulated and applied for short glass fibre reinforced thermoplastics. The model is able to capture experimental trends observed for the considered composites. The damage growth description involves a set of 20 parameters in the case of a complete 3D –structure. In the current paper, it is considered the particular case of a displacement controlled fatigue tensile test involving 4 damage parameters. The present contribution is a first approach of parameter identification. It is considered a least squares sense based cost function and homogeneous fatigue tests performed on a short glass fibre reinforced polyamide. The identified set of parameters appears to be not depending on the adopted initial values. The model as the parameters determined by the minimisation algorithm, are validated on a fatigue test performed with a different loading condition

Experimental Parameters Identification of Fatigue Damage Model for Short Glass Fiber Reinforced Thermoplastics GFRP

In the present work, a new polycyclic fatigue damage model is formulated and applied for short glass fibre reinforced thermoplastics. The model is able to capture experimental trends observed for the considered composites. The damage growth description involves a set of 20 parameters in the case of a complete 3D –structure. In the current paper, it is considered the particular case of a displacement controlled fatigue tensile test involving 4 damage parameters. The present contribution is a first approach of parameter identification. It is considered a least squares sense based cost function and homogeneous fatigue tests performed on a short glass fibre reinforced polyamide. The identified set of parameters appears to be not depending on the adopted initial values. The model as the parameters determined by the minimisation algorithm, are validated on a fatigue test performed with a different loading condition

Effect of the matrix behavior on the damage of ethylene–propylene glass fiber reinforced composite subjected to high strain rate tension

This study investigates the origin of the strain rate effect on the mechanical behavior of a discontinuous glass fiber reinforced ethylene–propylene copolymer (EPC) matrix composite. This kind of composite materials are commonly used for automotive functional and structural applications. To this aim, a multi-scale experimental approach is developed. The deformation processes and the damage mechanisms observed at the microscopic scale are related to the material mechanical properties at the macroscopic scale. Tensile tests up to failure and specific interrupted tensile tests have been optimized and performed for high strain rates up to 200 s 1 to quantify the strain rate effect at different scales. High speed tensile tests have also been performed on the pure copolymer matrix. The threshold and the kinetic of damage have been quantified at both microscopic and macroscopic scales. Experimental results show that the composite behavior is strongly strain-rate dependent. The multi-scale analysis leads to the conclusion that the strain rate effect on the damage behavior of the EPC matrix composite is mainly due to the viscous behavior of the EPC matrix. SEM observations and analysis show that a localized deformation in the interface zone around fibers occurs at high strain rates and directly affects the visco-damage behavior. It is established that when the strain rate increases, the local deformation zone around the fibers behaves like a dissipation zone. Consequently, the damage initiation is delayed and the related kinetic is reduced with respect to the quasi-static loading case

Actuateur aérodynamique actif en alliage à mémoire de forme pour roue de véhicule automobile

ACTUATEUR AÉRODYNAMIQUE ACTIF EN AMF POUR ROUE DE VÉHICULE AUTOMOBILE La présente invention concerne un actuateur (12) pour pale (10) de roue de véhicule automobile, comprenant un fil métallique avec, successivement, un premier tronçon (12.1) s’étendant longitudinalement depuis une première extrémité (12.4) jusqu’à une zone intermédiaire (12.3) dudit fil métallique, et un deuxième tronçon (12.2) s’étendant longitudinalement depuis la zone intermédiaire jusqu’à une deuxième extrémité (12.5) dudit fil métallique, la zone intermédiaire étant apte à s’engager en rotation avec la pale et le premier tronçon étant à mémoire de forme de manière à pouvoir faire pivoter la pale suivant la température du fil métallique ; remarquable en ce que la zone intermédiaire est d’un seul tenant avec les premier et deuxième tronçons du fil métallique et forme un pliage dudit fil métallique. (Figure à publier avec l'abrégé : Figure 5

Dialogue essais - simulation et identification de lois de comportement d'alliage à mémoire de forme en chargement multiaxial

Les travaux présentés ont consisté à développer des stratégies d'identification performantes des paramètres des lois de comportement superélastique des Alliages à Mémoire de Forme (AMF). L'objectif est de disposer d'une solution complète de caractérisation, d'identification, et de simulation de structures en AMF soumises à des sollicitations complexes. Une base de données expérimentale unifiée pour un alliage de NiTi superélastique a été établie pour une multitude de trajets de déformation multiaxiaux et à différentes températures : en traction homogène, en compression, en traction-compression et en traction-traction. Une caractérisation expérimentale a été développée sur une plate-forme multiaxiale assemblée au laboratoire durant ce travail. L'emploi de la corrélation d'images a permis d'enrichir la base de données expérimentale en déterminant pour chaque essai les champs cinématiques. Cette collection d'essais a permis de montrer l'importante différence de comportement observée entre les directions de laminage et transverse, bien que le matériau soit faiblement texturé. Des procédures d'identification du comportement thermomécanique des AMF ont été mises en place, basées sur la construction et minimisation d'une fonction objectif régularisée. La première est basée sur l'exploitation des courbes contrainte-déformation moyennes sous chargement homogène et unixial. La seconde exploite la richesse des champs de déformations mesurés en essai hétérogène. Les deux stratégies ont permis d'identifier les huit paramètres gouvernant le comportement superélastique du modèle de Chemisky et al. (Chemisky et al. 2011). Des différences entre les jeux de paramètres identifiés sont caractéristiques des effets d'anisotropie observés. Le succès de cette stratégie démontre sa pertinence et est encourageant pour l'identification de paramètres de lois de comportement anisotropes.In this work, efficient identification strategies were developed to determine the characteristic parameters of the thermomechanical behavior of pseudoelastic Shape Memory Alloys (SMA). The aim is to obtain a complete solution for characterization, identification and numerical simulation of SMA structures undergoing multiaxial loading paths. A unified experimental database has been constructed to characterize the behavior of superelastic NiTi SMAs. This database includes tension, compression, tension-tension and tension-compression multiaxial tests at different temperatures. A characterization methodology has been developed on a multiaxial testing setup, which has been assembled in the laboratory during this Ph.D. project. Vital information about the strain fields for each test is added to the experimental database through the use of Digital Image Correlation. A significant difference in the thermomechanical behavior between the rolling and transverse directions has been observed, even when the specimens are not strongly textured. Two strategies were developed that rely on the minimization of a regularized cost function for identification of thermomechanical constitutive law parameters. The first identification procedure is based on uniaxial homogeneous tests at different temperatures. In the other strategy the information of strain fields of heterogeneous tests are utilized. In each case, the eight material parameters of the constitutive law of Chemisky et al. (Chemisky et al. 2011) have been identified. A difference between the identified parameters in the rolling and transverse direction is noted and corresponds to the effect of anisotropy. Nevertheless, the capabilities of the relevant identification strategies shall allow the determination of the parameters of anisotropic constitutive laws.PARIS-Arts et Métiers (751132303) / SudocSudocFranceF

A multi-scale approach to model the curing process in magneto-sensitive polymeric materials

Coopération ENSAM/University of Erlangenpolymers. In the case of magneto-sensitive polymers, micron-size ferromagnetic particles are mixed with a liquid polymeric matrix in the uncured stage. The polymer curing process is a complex process that transforms a fluid to a solid with time. To transfer the constituent parameter information from the micro-scale to the macro-scale for a composite magneto-mechanically coupled polymeric material, an extended Mori–Tanaka semi-analytic homogenization procedure is utilized. The stiffness gaining phenomenon as in the case of a curing process is realized by time-dependent material parameters appearing within the composite piezomagnetic material tensors. Moreover, to compute the volume reduction during curing, a magnetic induction dependent shrinkage model is proposed. Several numerical examples show that the model proposed herein can capture major observable phenomena in the curing process of polymers under magneto-mechanically coupled infinitesimal deformations

Cyclic loading effects on NITI alloys under biaxial conditions

In this work, the influence of the direction and the history of thermomechanical loading of NiTi shape memory alloys on the overall material behavior is experimentally investigated. In the first part, cyclic biaxial mechanical loading has been applied to cross-shaped specimens under constant temperature. The residual strains of selected points from the sample surface are extracted and analyzed. The second part of the study concerns thermomechanical testing of textured samples cut from a laminated plate under complex cyclic loading at different temperature levels. The evolution of residual strains and the transformation threshold are correlated to the history of loading and the amplitude of transformation strain. Anisotropic effects are studied by performing those same experiments on different directions according to the rolling direction of the laminated plate