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Today polymer materials are frequently used in the transport domain with more severe specication requirements. The behaviour modeling and failure prediction have consequently become a priority. In this paper, an elastoviscoplastic... more
Today polymer materials are frequently used in the transport domain with more severe specication requirements. The behaviour modeling and failure prediction have consequently become a priority. In this paper, an elastoviscoplastic behaviour model is presented, with non associated plasticity, damage and strain rate eect, which represents the observed behaviours of a semi-crystalline polymer under dynamic loading.
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Understanding the human body response during impact has become a primary concern, especially in the field of ballistic impacts. Among various materials employed as human body substitutes, synthetic gel named SEBS is used in the present... more
Understanding the human body response during impact has become a primary concern, especially in the field of ballistic impacts. Among various materials employed as human body substitutes, synthetic gel named SEBS is used in the present study. Mechanical characterization from quasi-static to very high strain rates are performed allowing the constitutive modeling of the gel material and its implementation in an explicit finite element code. Tensile testing are completed using appropriate tensile fixtures and specific strain measurement and point out a hyperelastic behavior (strain over 300%) with strain rate sensitivity. Compression tests are performed from static strain rates to dynamic strain rates using for very high strain rates polymeric split Hopkinson bars and high-speed imaging. Mooney-Rivlin hyperelastic material model with specific strain rate dependence is implemented using optimization process by inverse method of dynamic compression testing results for material parameters identification. The material law is employed during modeling of direct impact of less lethal kinetic energy projectiles over various velocities and gives satisfactory results compared to the experimental impact analysis.
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In the field of biomechanics, numerical procedures can be used to understand complex phenomena that cannot be analyzed with experimental setups. The use of experimental data from human cadavers can present ethical issues that can be... more
In the field of biomechanics, numerical procedures can be used to understand complex phenomena that cannot be analyzed with experimental setups. The use of experimental data from human cadavers can present ethical issues that can be avoided by utilizing biofidelic models. Biofidelic models have been shown to have far-reaching benefits, particularly in evaluating the effectiveness of protective devices such as body armors. For instance, numerical twins coupled with a biomechanical model can be used to assess the efficacy of protective devices against intense external forces. Similarly, the use of human body surrogates in experimental studies has allowed for biomechanical studies, as demonstrated by the development of crash test dummies that are commonly used in automotive testing. This study proposes using numerical procedures and simplifying the structure of an existing biofidelic FE model of the human thorax as a preliminary step in building a physical surrogate. A reverse engineer...
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In this paper, a previously developed viscoelastic-viscoplastic behaviour model for short-fibre-reinforced thermoplastics (SFRT) is enriched with matrix ductile damage and fibre/matrix interfacial debonding constitutive laws. Aiming at... more
In this paper, a previously developed viscoelastic-viscoplastic behaviour model for short-fibre-reinforced thermoplastics (SFRT) is enriched with matrix ductile damage and fibre/matrix interfacial debonding constitutive laws. Aiming at industrial applications, model development takes special care to ensure a relatively easy characterisation of material parameters, as illustrated with case of a short-glass-fibre-reinforced polypropylene. Numerical simulations are done to assess the capability of the model to account for all specificities of SFRT behaviour with a particular attention paid on the coupled influence of strain rate and microstructure configuration on the initiation and development of matrix damage and fibre/matrix debonding.
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In the sectors of activity such as the automotive industry, polymers are definitively present into the different components of the vehicle. These materials may be subjected to high loads such as crash impact. Therefore, they have to meet... more
In the sectors of activity such as the automotive industry, polymers are definitively present into the different components of the vehicle. These materials may be subjected to high loads such as crash impact. Therefore, they have to meet strong requirements in terms of safety regulations. It is so important to know and to anticipate the behavior of the material in a wide strain rate and temperature range in order to predict the risk of failure.
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For automotive suppliers, it is essential to model the behavior of thermoplastics under crash loading and for a large range of temperature typically from -30° until 85°c. Thermoplastics are very sensitive to both strain rate and... more
For automotive suppliers, it is essential to model the behavior of thermoplastics under crash loading and for a large range of temperature typically from -30° until 85°c. Thermoplastics are very sensitive to both strain rate and temperature with an inverse relation: hardening with strain rate and softening with temperature. Generally, a large experimental campaign has to be carried out to identify different behavior laws of the material, each of them for a specific range of strain rate and temperature. Then, according to the characteristics of the loading case, e.g. impact, corresponding behavior laws are chosen in the database to run the numerical simulations. This results in an important experimental cost and a large database to manage. It is then interesting to explore the time-temperature equivalence of thermoplastics to act on both aspects. Relations between strain rate and temperature sensitivities are identified through dynamic mechanical analysis (DMA) in the viscoelastic do...
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A constitutive model of viscous behaviour of short-fibre reinforced composites (SFRC) where complex distributions of fibre orientations are taken into account is proposed in this work. The approach considered for the computation of... more
A constitutive model of viscous behaviour of short-fibre reinforced composites (SFRC) where complex distributions of fibre orientations are taken into account is proposed in this work. The approach considered for the computation of composite macroscopic behaviour is based on an additive decomposition of the state potential. The SFRC is assimilated to an assembly of several fibre media embedded in a polymeric matrix medium. One of the main assets of this approach is the possibility to model reinforcement with complex distributions of fibre orientations. Moreover, this decomposition allows the implementation of complex behaviour laws coupled with damage models. The polymeric matrix behaviour is typically strain-rate sensitive, i.e. viscoelastic-viscoplastic. This property has to be taken into account when the modelling of the composite behaviour over a large range of strain rate is intended. Therefore, a viscoelastic constitutive model, based on a generalised Maxwell model, and a visc...
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Many constitutive models were developed in the literature to model the complex behaviour of polymer materials. These models can be sorted in two categories: the physical based models where the microstructure of the material is taken into... more
Many constitutive models were developed in the literature to model the complex behaviour of polymer materials. These models can be sorted in two categories: the physical based models where the microstructure of the material is taken into account for representing the macroscopic behaviour [1,2] and the phenomenological based models where the material discontinuities, in the microstructural scale, are homogenised in a representative volume element. In this way, elasto-plastic constitutive models based on the “overstress” concept (VBO) [3] using the unified state variable theory were extended for polymeric materials [4,5]. The addition of mineral fillers in the semi-crystalline matrix increases the cavitation phenomenon. In this case, the viscoelastic-viscoplastic deformation of the material is accompanied by damage in the form of nucleation, growth and coalescence of cavities. Many damage model were developed for polymer application in order to represent this phenomenon [6,7,8,9]. The...
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The use of Layered Fabric Reinforced Polymers (LFabRP) in the automotive industry is growing significantly. A new material model was developed for the LFabRP to improve the predictability of low-speed impact simulations by means of Finite... more
The use of Layered Fabric Reinforced Polymers (LFabRP) in the automotive industry is growing significantly. A new material model was developed for the LFabRP to improve the predictability of low-speed impact simulations by means of Finite Element Analysis (FEA). The delamination evaluation is included within the material model. It allows to describe the behaviour of a layered material by using only one shell element through-the-thickness and takes into account the delamination effects. By ensuring the internal energy equivalence between both element and material model theories, a realistic strain field for layered material is provided to the intralaminar material model. The intralaminar material model is based on a pre-existing continuum damage model (Onera Damage Model). To improve the efficiency and the precision for the modelling of LFabRP, friction mechanisms, a rheological viscoelastic model and a smeared crack approach for the fibre failure were introduced. The validation of t...