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Polymers are currently used in several industrial applications such as the interior components of the vehicle. We find them for example in the design of dashboards or door panels. These materials may be subjected to different types of load like the temperature variation or high strain rates due to crash impact. It is therefore necessary to well understand and to anticipate the complex mechanical behaviour of the polymers. This paper describes the results of experimental research about the dependence between the strain rate and the temperature. The main objective is to be able to model the complete variety of the behaviour in order to predict the risk of failure under dynamic loadings. The material chosen for this study is a copolymer propylene ethylene mineral (talc) filled 15% impact modified.

IF=3.85; International audience; Needed to simulate the behaviour of industrial components through finite element analysis, a continuum damage model formulation for fabric reinforced polymers is provided. Based on the Onera Damage Microstructure Model, it considers the influence of privileged direction of intralaminar matrix damage on the stiffness. In this work, the stored strains are considered as representative of the position of the crack lips. Thus, after calculation of the stresses applied to the crack lips, a friction law has been newly implemented in order to represent the hysteresis loops during cyclic loading. Moreover, the possibility of a shear locking, very common among the textile simulations for large shearing, is introduced with its effect on the matrix damage. The present model is applied to simulate various fabric preforms (woven or non-crimp) under cyclic in-plane shear. Because of similarities of the physical phenomena which occur in each investigated materials, the present model is able to represent a realistic behaviour for every preforms investigated.

In this paper, an original and effective model of behaviour for short-fibre reinforced composites is presented. In particular, complex fibre distributions of orientation can be dealt with in a very easy way, without orientation averaging or additional homogenisation steps. The matrix material has elastoplastic damage behaviour with non-isochoric plastic flow. Ductile damage can be fully anisotropic depending on the reinforcement characteristics. The model is validated for the case of a polypropylene reinforced with short flax fibres. In addition, simulations are performed to investigate the influence of key parameters like fibre length and interfacial shear strength, as well as the impact of progressive debonding at the fibre tips.

Among currently available bio-based polymers, poly(lactic acid) (PLA) has interesting physical and mechanical properties (high tensile strength and stiffness, good processability and biodegradability) but relatively low thermal stability, low toughness and is extremely brittle, all of which can be obstacles to industrial applications. The influence of several additives is investigated in this paper, the aim being to confer mechanical properties to PLA-based compositions suitable for potential use in automotive applications. Comparisons of their mechanical properties with those of a mineral filled polypropylene, as frequently used for automotive applications, show that PLA-plasticizer-impact modifier-nanoclay quaternary compositions represent interesting bio-based alternatives.

In this paper, a behaviour model for damageable elastoplastic materials reinforced with short fibres that have complex orientations is proposed. The composite material is seen as the assembly of the matrix medium and several linear elastic fibre media. Its macroscopic behaviour is computed thanks to an additive decomposition of the state potential, with no need to implement complex methods of homogenisation. A 4th-order tensor that depends on the characteristics of each fibre medium is introduced to model the anisotropic damage of the matrix material induced by the reinforcement, as well as the progressive degradation of the fibre–matrix interface. The division of short fibres into several families means that complex distributions of orientation or random orientation can be easily modelled. The model is tested for the case of a polyamide reinforced with different contents of short-glass fibres with distributed orientations and subjected to uniaxial tensile tests in different loading directions. The comparison of the results with experimental data (extracted from the literature) demonstrates the efficiency of the model.

International audience; A phenomenological finite strain non-associated elastoviscoplastic model coupled with damage is proposed in order to simulate the behaviour of a 20% mineral filled semi-crystalline polymer for a large strain rate range under several loading conditions. In the proposed model, the direct relation between the logarithmic rate of the Eulerian Hencky strain tensor (work-conjugate of the Cauchy stress) with the additively decomposition of the stretching tensor in an elastic and a viscoplastic part is used. The viscoplastic formulation is developed with the association of a pressure dependent yield surface coupled with damage to take the rate and the pressure dependency into account. In order to capture the non-isochoric deformation involving expansion under tensile loading and compaction under compression loading, a viscoplastic potential is developed. This model is implemented in a user-material subroutine in an implicit finite element code with a fully implicit viscoplastic return scheme for solid and shell elements. The particular case of shell elements is dealt with by using a second iteration loop to ensure the zero-normal-stress condition. All the material parameters are identified from experimental tests carried out at several kinds and speed loadings. Numerical responses of the proposed model are close to the experiments for several kinds and speed loadings.

This paper deals with the modelling of the behaviour of short-fibre reinforced composites. The composite is seen as an assembly of a matrix medium and of several fibre media. Each fibre medium, characterised by its own orientation of fibres and volume fraction, is considered as a one-dimensional elastic medium. The matrix material has an elastoplastic behaviour. All types of hardening laws can be considered, thanks to a valuable adaptivity of the modelling. The use of the Drucker–Prager criterion for plasticity and non-associative plasticity rules allow to deal with compressible plastic flow. Moreover, all kind of orientation of fibres, in particular random orientations and imperfect alignments, can be modelled in a simple way. The influence of the fibres’ orientation on the mechanical response of a polymer matrix composite subjected to tensile/compression tests is analysed in detail. Finally, simulated behaviours of composites are compared to experimental data found in the literature.

IF=2.371; International audience; Short-flax-fibre-composite materials are appealing for technical applications thanks to renewability, biodegradability but also potentially high ratio rigidity/density of flax fibres, in particular. However, the significant variability of technical flax fibres’ constitutive, geometrical and mechanical properties and especially lack of quantitative knowledge about its real impact on composite behaviour still prevent a widespread use of such composites. To overcome this obstacle, this study gives qualitative and quantitative information about impact of variability of flax fibre properties on numerically assessed tensile behaviour of short-flax-fibre-reinforced polypropylene, with particular attention paid to the determination of lower bound of composite behaviour. Different fibre contents and orientations, including in-plane random and distributed orientations, are considered. Results reveal that range of variation of composite behaviour strongly depends on weight of fibre contribution to composite response. It is therefore directly related to fibre content and orientation but also indirectly to manufacturing process, since this latter governs fibre orientation.

This paper deals with a viscoelastic–viscoplastic model for semi-crystalline polymers in crash applications. A polymer behaviour model is implemented in the commercial PAM CRASH© code thanks to a user material card. Global variables (load, displacement) and local variables (strain) are validated on flat and notched tensile specimens by comparing the numerical responses with data obtained by digital image correlation.

The increasing use of structural adhesives in industry encourages the need for a detailed description of their mechanical behaviour. In this paper, a structural adhesive, named BETAMATE 1496V™, which has been specially designed for applications in the automotive industry (crashworthiness) has been studied. The propose is to obtain as near a possible, a complete description of the mechanical behaviour by means of new measurement techniques, applied over a large range of strain rates using different kinds of loading devices. These results lead to important findings which we believe will have an impact on finite element modeling.

IF=2.035; International audience; Mechanical behaviour of short-fibre reinforced composites (SFRC) can be affected by numerous damage phenomena. This paper focuses on the modelling of fibre/matrix debonding initiated at fibre tips, which is the dominant damage mechanism when a majority of short-fibres are subjected to local tensile loadings. A failure criterion for SFRC is proposed based on a critical amount of voids located in debonded areas. Very accurate mechanical states at break can be predicted for SFRC with complex fibre distribution of orientation, for different kinds of uniaxial and biaxial tensile loadings.

International audience; Crashworthiness performance of automotives by introducing new materials is of high interest based on the global mass’ reduction of cars. Bonded techniques are tested at present with respect to the reduction of the mass/energy’s ratio combined with recycling processes. In this study, a compression test program is performed on a bulk structural adhesive under a very large range of strain rates, thus [0.1; 5000]/s. Uniaxial compression tests at 0.1 and 50/s are achieved using a high-speed hydraulic testing machine. A split Hopkinson bar’ device made of PA66 is experimented so as to characterize soft materials in the upper domain of strain rates, thus [500; 5000]/s. A special mold is used for the preparation of the adhesive plates. Two sheets are prepared (thickness 4 mm with 1 MPa pressure and 6 mm with 4 MPa pressure) in order to consider the effect of the pressure during the curing process. Water jet technique is used to extract cylindrical samples from the plates with accurate dimensions. The identification of the compression behaviour of the structural adhesive is lead with objective to find material parameters of a modified G’sell model for finite element modeling of crashworthiness.

IF=2.01; International audience; A specific damage characterization method using Digital Image Correlation for semi-crystalline polymers is proposed for a wide range of strain rates. This damage measurement is an extension of the SEĖ method [16] which was developed to characterize the behaviour laws at constant strain rates of polymeric materials. This procedure is compared to the well-known damage characterization by loss of stiffness technique under quasi-static loading. In addition, an in-situ tensile test, carried out in a microtomograph, is used to observe the cavitation phenomenon in real time. The different ways used to evaluate the damage evolution are compared and the proposed technique is also suitable for measuring the ductile damage observed in semi-crystalline polymers under dynamic loading.

The use of fabric reinforced polymers in the automotive industry is growing significantly. The high specific stiffness and strength, the ease of shaping as well as the great impact performance of these materials widely encourage their diffusion. The present model increases the predictability of explicit finite element analysis and push the boundaries of the ongoing phenomenological model. Carbon fibre composites made up various preforms were tested by applying different mechanical load up to dynamic loading. This experimental campaign highlighted the physical mechanisms affecting the initial mechanical properties, namely intra- and interlaminar matrix damage, viscoelasticty and fibre failure. The intralaminar behaviour model is based on the explicit formulation of the matrix damage model developed by the ONERA as the given damage formulation correlates with the experimental observation. Coupling with a Maxwell-Wiechert model, the viscoelasticity is included without losing the direct explicit formulation. Additionally, the model is formulated under a total Lagrangian scheme in order to maintain consistency for finite strain. Thus, the material frame-indifference as well as anisotropy are ensured. This allows reorientation of fibres to be taken into account particularly for in-plane shear loading. Moreover, fall within the framework of the total Lagrangian scheme greatly makes the parameter identification easier, as based on the initial configuration. This intralaminar model thus relies upon a physical description of the behaviour of fabric composites and the numerical simulations show a good correlation with the experimental results.

International audience; Damage evolution and characterization in semi-crystalline polymer filled with particles under various loadings is still a challenge. A specific damage characterization method using Digital Image Correlation is proposed for a wide range of strain rates considering tensile tests with hydraulic jacks as well as Hopkinson's bars. This damage measurement is obtained by using and adapting the SEE method [1] which was developed to characterize the behaviour laws at constant strain rates of polymeric materials in dynamic. To validate the characterization process, various damage measurement techniques are used under quasi-static conditions before to apply the procedure in dynamic. So, the well-known damage characterization by loss of stiffness technique under quasi-static loading is applied to a polypropylene. In addition, an in-situ tensile test, carried out in a microtomograph, is used to observe the cavitation phenomenon in real time. A good correlation is obtained between all these techniques and consequently the proposed technique is supposed suitable for measuring the ductile damage observed in semi-crystalline polymers under dynamic loading. By applying it to the semi-crystalline polymer at moderate and high speed loadings, the damage evolution is measured and it is observed that the damage evolution is not strain rate dependent but the failure strain on the contrary is strain rate dependent.

International audience; Epoxy resins are widely used in Carbon Fiber Reinforced Polymers (CFRPs) for the aeronautical industry. They must ensure cohesion in most of the structural composite parts incorporated into the modern manufactured aircrafts. So fracture properties of epoxy resins are essential features to resist critical decohesions in case of impact. Surprisingly however, there are few experimental studies dedicated to the dynamic fracture of these thermoset polymers. Therefore, this research aims at developing an experimental procedure to characterize the dynamic fracture toughness of epoxy resins during propagation. Since glassy polymers exhibit viscous fracture, the crack speed å is known for influencing the toughness of these materials. Then a strain gage method is proposed to determine the mode I dynamic energy release rate G ID for various crack speeds å. Thus an experimental set-up is defined to simultaneously implement strain gage measurement and high speed cinematography. Finally, preliminary results are briefly reported to demonstrate the method validity.

A damage model is integrated into the explicit finite element framework to predict the damage evolution which occurs under dynamic loading in the crash or stamping process. This damage model is based on the description of the nucleation, growth and coalescence of the microvoids. This damage process leads to the progressive loss of the stress-carrying capacity leading to rupture. The model is adapted to take the material behaviour anisotropy and damage anisotropy into account. An inverse method is developed to identify the material parameters by correlating an experimental and numerical measurement with a tensile test on a notched specimen. This identification methodology is applied to an aluminium part cut from an extruded tube. The material parameters are identified and the ductile rupture is predicted.

Finite element analyses of backward can extrusion are performed with two punch dimensions to enhance the sliding or the sticking of workpiece material at the punch nose contact surface. The punch geometry effect on the effective plastic strain and hydrostatic stress distributions are discussed and the evolution of microvoid volume fraction during the whole extrusion is predicted.

Numerical simulations of the cold stamping process of bars are performed with pore free and porous materials. An isotropic elasto-plastic potential with three material parameters is used to compute the porosity evolution. The damage model takes into account the void nucleation, growth and coalescence. The numerical simulations of the cold stamping process of bars are carried out with ASTRID finite element code for pore free and porous material to enhance the modifications of the dimensions and bulk properties of the forging product occurring with the damage evolution.

Improvement of automotives’ crashworthiness is of high interest for governments prior to objectives focused on the reduction of passengers’ injuries. In these recent years, steel industries have studied the dynamic behaviour of tapered side rails so as to increase the capacities of energy absorption combined with light-weight aspects. On the basis of the global mass’ reduction of cars, bonded techniques have been tested with respect to the reduction of the mass/energy’s ratio. In this study, a test programme has been performed on a structural adhesive under a very large range of strain rates, thus [0.1;5000] /s. For that, a split Hopkinson bars device made of PA66 has been used so as to access to materials responses in the upper domain of strain rates, thus [500;5000] /s. To complete the expected domain of strain rates, compression tests have been done using a high-speed hydraulic machine on the same geometry from 0.1 up to 50 /s. A special mould has been machined and 2 sheets have prepared (thickness: 4 and 6 mm) in order to consider the effect of the pressure during the curing process. Water jet technique has been used to extract cylindrical samples from the sheet with accurate dimensions.

A damage model is integrated into the explicit finite element framework to predict the damage evolution which occurrs under dynamic loading in the crash or stamping process. This damage model is based on the description of the growth, nucleation and coalescence of the microvoids. The microvoid growth is related to the plastic incompressibility equation. The microvoid nucleation is controlled by either the plastic strain or stress. The microvoid coalescence is described by a specific function. This damage process leads to the progressive loss of the structure stress carrying capacity. The ductile fracture occurs once it has vanished. The model is adapted to take the material behaviour anisotropy and damage anisotropy into account. The sensitivity of the damage evolution under dynamic loadings in the case of porous strain rate sensitive material is analysed using single tensile tests. Static and dynamic tensile tests of a notched specimen are performed. Influences of the strain rate and the shape of specimen on the failure mode and loss of the structure’s stress carrying capacity are shown.

To predict damage evolution occurring under dynamic loading, a damage model is implemented inside the explicit finite element framework. The damage model is based on the description of the growth, the nucleation and the coalescence of the microvoids. The microvoid growth is related to the plastic incompressibility relation. The microvoid nucleation is either controlled by the plastic strain or by the stress. The microvoid coalescence is described by a specific function. This damage process leads to the progressive loss of the stress carrying capacity of the structure. The ductile fracture occurs when the stress carrying capacity of the structure vanishes. The sensitivity of damage volution under dynamic loading in the case of porous strain rate sensitive material is analysed using single tensile tests. The dynamic bending test of a cantilever beam with a U-cross-section is performed. The influence of the strain rate on the deformed shape and on the loss of the structure's stress carrying capacity is shown.