A. Launay - Academia.edu (original) (raw)
Papers by A. Launay
Procedia Engineering, 2010
Fatigue life prediction of polymer matrix composites requires the investigation of the cyclic beh... more Fatigue life prediction of polymer matrix composites requires the investigation of the cyclic behavior. This paper deals with the experimental study conducted on a polyamide 66 reinforced with 35 wt% of short glass fibers (PA66 GF35), at room temperature. The material was tested dry-as-molded or at the equilibrium with an air containing 50 % of relative humidity. The dynamic mechanical analysis leads us to focus on the material conditioned at RH=50 %, which appears to exhibit the most complex mechanical effects, and is yet representative of the actual service life. An exhaustive experimental campaign in tensile mode has been carried out, including various strain or stress rates, complex mechanical histories and local thermo-mechanical recording. The material has thus been tested in static tension at stress rates ranging over four decades (from 2.5 to 2500 MPa/s), and also in cyclic tension with loading histories combining creep, stress relaxation or strain recovery steps at different strain/stress levels. Such an extended database allowed us to highlight several mechanical phenomena: at least two characteristic viscous times co-exist, and are independent of any irreversible mechanism. Residual strain appears above a stress threshold, and a kinematic hardening law is suggested to explain tension-relaxation-recovery tests. Eventually, hints of a non-linear viscous flow law and of a cyclic damage law are pointed out.
Procedia Engineering, 2011
ABSTRACT SGFR thermoplastics exhibit a highly non-linear mechanical behavior under complex mechan... more ABSTRACT SGFR thermoplastics exhibit a highly non-linear mechanical behavior under complex mechanical loadings, for various temperature and humidity conditions. A phenomenological constitutive model is proposed; describing several physical mechanisms such as viscoelasticity, thresholdless viscoplasticity and cyclic softening. The anisotropic microstructure resulting from the injection process is taken into account through orientation tensors. (C) 2011 Published by Elsevier Ltd. Selection and/or peer-review under responsibility of ICM11
Components made of short glass fiber reinforced thermoplastics are increasingly used in the autom... more Components made of short glass fiber reinforced thermoplastics are increasingly used in the automotive industry in order to reduce the price and weight of the vehicule. These components are frequently submitted to fatigue loadings during their service conditions. Therefore, a good conception towards the fatigue phenomenon is mandatory. One preliminary need is to model correctly the non linear behavior of such material, which is clearly not an easy task due to the numerous dissipation mechanisms involved and the strong anisotropy induced by the injection process. In this study, we present some results on injected samples with a specific geometrical accident leading to a stress concentration factor Kt=2.5. A specific thermomechanical characterization is done using an infrared camera. Several key informations can be extracted from these experimental data: temperature variations, heat sources, crack initiation localization, crack propagation (detection of the crack vicinity), etc.These data are then compared to numerical simulations involving the simulation of the injection step and finite element analysis using an anisotropic elasto-viscoplastic model. The heat sources obtained with the model are compared the experimental ones. A very good agreement between the experimental data and the numerical ones is found which illustrate the relevancy of the model to capture some key thermomechanical properties of these materials, which is obviously a key element in the fatigue life prediction.
Current …, 2006
CESAR (Simplified Evolution Code Applied to Reprocessing) is a depletion code developed through a... more CESAR (Simplified Evolution Code Applied to Reprocessing) is a depletion code developed through a joint program between CEA and COGEMA. In the late 1980's, the first use of this code dealt with nuclear measurement at the Laboratories of the La Hague reprocessing plant. The use of CESAR was then extended to characterizations of all entrance materials and for characterisation, via tracer, of all produced waste. The code can distinguish more than 100 heavy nuclides, 200 fission products and 100 activation products, and it can characterise both the fuel and the structural material of the fuel. CESAR can also make depletion calculations from 3 months to 1 million years of cooling time. Between 2003-2005, the 5 th version of the code was developed. The modifications were related to the harmonisation of the code's nuclear data with the JEF2.2 nuclear data file. This paper describes the code and explains the extensive use of this code at the La Hague reprocessing plant and also for prospective studies. The second part focuses on the modifications of the latest version, and describes the application field and the qualification of the code. Many companies and the IAEA use CESAR today. CESAR offers a Graphical User Interface, which is very user-friendly.
Mechanics of Materials, 2013
Polymer matrix composites, and especially short glass fiber reinforced polyamides, are widely use... more Polymer matrix composites, and especially short glass fiber reinforced polyamides, are widely used in the automotive industry. Their application on structural components requires a confident mechanical design taking into account the sensivity of their mechanical response to both temperature T and relative humidity H. In this paper, the constitutive model already developed by the authors (Launay et al., 2011) is successfully applied to describe the non-linear cyclic behaviour of a PA66-GF35 under various hygrothermal conditions. The extensive experimental database involves testing conditions under and above the glass transition temperature T g . An equivalence principle between temperature and relative humidity is proposed and validated, since the non-linear mechanical response is shown to depend only on the temperature gap T − T g (H).
International Journal of Plasticity, 2011
Polymer matrix composites are widely used in the automotive industry and undergo fatigue loadings... more Polymer matrix composites are widely used in the automotive industry and undergo fatigue loadings. The investigation of the nonlinear cyclic behaviour of such materials is a required preliminary work for a confident fatigue design, but has not involved many publications in the literature. This paper presents an extensive experimental study conducted on a polyamide 66 reinforced with 35 wt% of short glass fibres (PA66 GF35), at room temperature. The material was tested in two conditions: dry-as-moulded (DAM) and at the equilibrium with air containing 50% of relative humidity (RH50).
International Journal of Fatigue, 2014
Design of SFRP parts against fatigue is clearly not an easy task due to the numerous dissipation ... more Design of SFRP parts against fatigue is clearly not an easy task due to the numerous dissipation mechanisms involved and to the strong anisotropy induced by the injection process. Another difficulty is to evaluate a relevant scale to compute the thermomechanical data, as the complex geometry of the parts can induce a variation within a distance comparable to or lower than the representative scale of the microstructure. In this study, injected samples with a geometry leading to a theoretical stress concentration factor K t ¼ 2:5 are under consideration. The samples are submitted to several cyclic blocks and the temperature fields are measured using an infrared camera. Taking advantage of the good thermal and spatial resolutions, a first analysis is performed on the temperature fields, allowing to highlight the hot spot location and to follow the crack propagation. A specific adiabatic analysis is then suggested in order to measure directly the fields of dissipated energy. To predict this field, a numerical chain is then applied involving the simulation of the injection process and finite elements analysis using an anisotropic elasto-viscoplastic model. The predicted heat sources are compared to the experimental ones for several loading amplitudes and the ability of the approach to catch the experimental fields is finally discussed.
International Journal of Fatigue, 2013
Components made of short fiber reinforced thermoplastics are increasingly used in the automotive ... more Components made of short fiber reinforced thermoplastics are increasingly used in the automotive industry, and more and more frequently subjected to fatigue loadings during their service life. The determination of a predictive fatigue criterion is therefore a serious issue for the designers, and requires the knowledge of the local mechanical response.
International Journal of Fatigue, 2013
Keywords: PA66 GF35 Constitutive model Fiber orientation distribution Nonlinear behavior Anisotro... more Keywords: PA66 GF35 Constitutive model Fiber orientation distribution Nonlinear behavior Anisotropic behavior a b s t r a c t Components made of short glass fiber reinforced (SGFR) thermoplastics are increasingly used in the automotive industry, and more frequently subjected to fatigue loadings during their service life. The determination of a predictive fatigue criterion is therefore a serious issue for the designers, and requires the knowledge of the local mechanical response under a large range of environmental conditions (temperature and relative humidity). As the cyclic behavior of polymeric material is reckoned to be highly nonlinear, even at room temperature, an accurate constitutive model is a preliminary step for confident fatigue design.
Les thermoplastiques renforcés en fibres de verre courtes présentent un comportement mécanique fo... more Les thermoplastiques renforcés en fibres de verre courtes présentent un comportement mécanique fortement non-linéaire lorsqu'ils sont soumis à des chargements cycliques, sous différentes conditions hygrothermiques. Une loi de comportement phénoménologique est proposée de façon à décrire différents mécanismes physiques, tells que la viscoélasticité, la viscoplasticité, l'écrouissage ou l'adoucissement cyclique. La microstructure anisotrope, conséquence de la mise en forme par injection, est prise en compte dans le modèle par l'intermédiaire de tenseurs d'orientation.
Les thermoplastiques renforcés en fibres de verre courtes présentent un comportement mécanique fo... more Les thermoplastiques renforcés en fibres de verre courtes présentent un comportement mécanique fortement non-linéaire lorsqu'ils sont soumis à des chargements cycliques, sous différentes conditions hygrothermiques. Une loi de comportement phénoménologique est proposée de façon à décrire différents mécanismes physiques, tells que la viscoélasticité, la viscoplasticité, l'écrouissage ou l'adoucissement cyclique. La microstructure anisotrope, conséquence de la mise en forme par injection, est prise en compte dans le modèle par l'intermédiaire de tenseurs d'orientation.
Procedia Engineering, 2010
Fatigue life prediction of polymer matrix composites requires the investigation of the cyclic beh... more Fatigue life prediction of polymer matrix composites requires the investigation of the cyclic behavior. This paper deals with the experimental study conducted on a polyamide 66 reinforced with 35 wt% of short glass fibers (PA66 GF35), at room temperature. The material was tested dry-as-molded or at the equilibrium with an air containing 50 % of relative humidity. The dynamic mechanical analysis leads us to focus on the material conditioned at RH=50 %, which appears to exhibit the most complex mechanical effects, and is yet representative of the actual service life. An exhaustive experimental campaign in tensile mode has been carried out, including various strain or stress rates, complex mechanical histories and local thermo-mechanical recording. The material has thus been tested in static tension at stress rates ranging over four decades (from 2.5 to 2500 MPa/s), and also in cyclic tension with loading histories combining creep, stress relaxation or strain recovery steps at different strain/stress levels. Such an extended database allowed us to highlight several mechanical phenomena: at least two characteristic viscous times co-exist, and are independent of any irreversible mechanism. Residual strain appears above a stress threshold, and a kinematic hardening law is suggested to explain tension-relaxation-recovery tests. Eventually, hints of a non-linear viscous flow law and of a cyclic damage law are pointed out.
Procedia Engineering, 2011
ABSTRACT SGFR thermoplastics exhibit a highly non-linear mechanical behavior under complex mechan... more ABSTRACT SGFR thermoplastics exhibit a highly non-linear mechanical behavior under complex mechanical loadings, for various temperature and humidity conditions. A phenomenological constitutive model is proposed; describing several physical mechanisms such as viscoelasticity, thresholdless viscoplasticity and cyclic softening. The anisotropic microstructure resulting from the injection process is taken into account through orientation tensors. (C) 2011 Published by Elsevier Ltd. Selection and/or peer-review under responsibility of ICM11
Components made of short glass fiber reinforced thermoplastics are increasingly used in the autom... more Components made of short glass fiber reinforced thermoplastics are increasingly used in the automotive industry in order to reduce the price and weight of the vehicule. These components are frequently submitted to fatigue loadings during their service conditions. Therefore, a good conception towards the fatigue phenomenon is mandatory. One preliminary need is to model correctly the non linear behavior of such material, which is clearly not an easy task due to the numerous dissipation mechanisms involved and the strong anisotropy induced by the injection process. In this study, we present some results on injected samples with a specific geometrical accident leading to a stress concentration factor Kt=2.5. A specific thermomechanical characterization is done using an infrared camera. Several key informations can be extracted from these experimental data: temperature variations, heat sources, crack initiation localization, crack propagation (detection of the crack vicinity), etc.These data are then compared to numerical simulations involving the simulation of the injection step and finite element analysis using an anisotropic elasto-viscoplastic model. The heat sources obtained with the model are compared the experimental ones. A very good agreement between the experimental data and the numerical ones is found which illustrate the relevancy of the model to capture some key thermomechanical properties of these materials, which is obviously a key element in the fatigue life prediction.
Current …, 2006
CESAR (Simplified Evolution Code Applied to Reprocessing) is a depletion code developed through a... more CESAR (Simplified Evolution Code Applied to Reprocessing) is a depletion code developed through a joint program between CEA and COGEMA. In the late 1980's, the first use of this code dealt with nuclear measurement at the Laboratories of the La Hague reprocessing plant. The use of CESAR was then extended to characterizations of all entrance materials and for characterisation, via tracer, of all produced waste. The code can distinguish more than 100 heavy nuclides, 200 fission products and 100 activation products, and it can characterise both the fuel and the structural material of the fuel. CESAR can also make depletion calculations from 3 months to 1 million years of cooling time. Between 2003-2005, the 5 th version of the code was developed. The modifications were related to the harmonisation of the code's nuclear data with the JEF2.2 nuclear data file. This paper describes the code and explains the extensive use of this code at the La Hague reprocessing plant and also for prospective studies. The second part focuses on the modifications of the latest version, and describes the application field and the qualification of the code. Many companies and the IAEA use CESAR today. CESAR offers a Graphical User Interface, which is very user-friendly.
Mechanics of Materials, 2013
Polymer matrix composites, and especially short glass fiber reinforced polyamides, are widely use... more Polymer matrix composites, and especially short glass fiber reinforced polyamides, are widely used in the automotive industry. Their application on structural components requires a confident mechanical design taking into account the sensivity of their mechanical response to both temperature T and relative humidity H. In this paper, the constitutive model already developed by the authors (Launay et al., 2011) is successfully applied to describe the non-linear cyclic behaviour of a PA66-GF35 under various hygrothermal conditions. The extensive experimental database involves testing conditions under and above the glass transition temperature T g . An equivalence principle between temperature and relative humidity is proposed and validated, since the non-linear mechanical response is shown to depend only on the temperature gap T − T g (H).
International Journal of Plasticity, 2011
Polymer matrix composites are widely used in the automotive industry and undergo fatigue loadings... more Polymer matrix composites are widely used in the automotive industry and undergo fatigue loadings. The investigation of the nonlinear cyclic behaviour of such materials is a required preliminary work for a confident fatigue design, but has not involved many publications in the literature. This paper presents an extensive experimental study conducted on a polyamide 66 reinforced with 35 wt% of short glass fibres (PA66 GF35), at room temperature. The material was tested in two conditions: dry-as-moulded (DAM) and at the equilibrium with air containing 50% of relative humidity (RH50).
International Journal of Fatigue, 2014
Design of SFRP parts against fatigue is clearly not an easy task due to the numerous dissipation ... more Design of SFRP parts against fatigue is clearly not an easy task due to the numerous dissipation mechanisms involved and to the strong anisotropy induced by the injection process. Another difficulty is to evaluate a relevant scale to compute the thermomechanical data, as the complex geometry of the parts can induce a variation within a distance comparable to or lower than the representative scale of the microstructure. In this study, injected samples with a geometry leading to a theoretical stress concentration factor K t ¼ 2:5 are under consideration. The samples are submitted to several cyclic blocks and the temperature fields are measured using an infrared camera. Taking advantage of the good thermal and spatial resolutions, a first analysis is performed on the temperature fields, allowing to highlight the hot spot location and to follow the crack propagation. A specific adiabatic analysis is then suggested in order to measure directly the fields of dissipated energy. To predict this field, a numerical chain is then applied involving the simulation of the injection process and finite elements analysis using an anisotropic elasto-viscoplastic model. The predicted heat sources are compared to the experimental ones for several loading amplitudes and the ability of the approach to catch the experimental fields is finally discussed.
International Journal of Fatigue, 2013
Components made of short fiber reinforced thermoplastics are increasingly used in the automotive ... more Components made of short fiber reinforced thermoplastics are increasingly used in the automotive industry, and more and more frequently subjected to fatigue loadings during their service life. The determination of a predictive fatigue criterion is therefore a serious issue for the designers, and requires the knowledge of the local mechanical response.
International Journal of Fatigue, 2013
Keywords: PA66 GF35 Constitutive model Fiber orientation distribution Nonlinear behavior Anisotro... more Keywords: PA66 GF35 Constitutive model Fiber orientation distribution Nonlinear behavior Anisotropic behavior a b s t r a c t Components made of short glass fiber reinforced (SGFR) thermoplastics are increasingly used in the automotive industry, and more frequently subjected to fatigue loadings during their service life. The determination of a predictive fatigue criterion is therefore a serious issue for the designers, and requires the knowledge of the local mechanical response under a large range of environmental conditions (temperature and relative humidity). As the cyclic behavior of polymeric material is reckoned to be highly nonlinear, even at room temperature, an accurate constitutive model is a preliminary step for confident fatigue design.
Les thermoplastiques renforcés en fibres de verre courtes présentent un comportement mécanique fo... more Les thermoplastiques renforcés en fibres de verre courtes présentent un comportement mécanique fortement non-linéaire lorsqu'ils sont soumis à des chargements cycliques, sous différentes conditions hygrothermiques. Une loi de comportement phénoménologique est proposée de façon à décrire différents mécanismes physiques, tells que la viscoélasticité, la viscoplasticité, l'écrouissage ou l'adoucissement cyclique. La microstructure anisotrope, conséquence de la mise en forme par injection, est prise en compte dans le modèle par l'intermédiaire de tenseurs d'orientation.
Les thermoplastiques renforcés en fibres de verre courtes présentent un comportement mécanique fo... more Les thermoplastiques renforcés en fibres de verre courtes présentent un comportement mécanique fortement non-linéaire lorsqu'ils sont soumis à des chargements cycliques, sous différentes conditions hygrothermiques. Une loi de comportement phénoménologique est proposée de façon à décrire différents mécanismes physiques, tells que la viscoélasticité, la viscoplasticité, l'écrouissage ou l'adoucissement cyclique. La microstructure anisotrope, conséquence de la mise en forme par injection, est prise en compte dans le modèle par l'intermédiaire de tenseurs d'orientation.