Characterization of Mechanical and Damping Properties of Nettle and Glass Fiber Reinforced Hybrid Composites

Growing environmental concerns are becoming significant challenges for large-scale applications in the automotive industry. Replacing and hybridizing glass fibers with natural fibers for non-structural applications is one effective way to address this challenge, while retaining the useful properties of both. This paper investigates the mechanical and damping performance of four types of compression-molded materials: polyester matrix (reference), nettle (6% by weight), hybrid 1 (6% glass and 6% nettle by weight), and hybrid 2 (12% glass and 6% nettle by weight), with polyester matrix at an ambient temperature. The tensile tests using digital image correlation (DIC) showed that by adding 6% by weight nettle fibers for polymer matrix tensile modulus increases by 21%. For the hybrid 1 two-layer composite (6% by weight glass and 6% by weight nettle) and the hybrid 2 three-layer composite (12% by weight glass and 6% by weight nettle), it increases by 80% and 101%, respectively. On the other hand, dynamic mechanical analysis (DMA) has been used to assess the damping properties of the materials. The results showed that the loss factor increased by 6~14% for nettle reinforced composite, by 8~25% for hybrid 1 glass-nettle reinforced composite and by 2~15% for hybrid 2 glass-nettle reinforced composite for frequencies around 1.0~2.0 Hz and around 12 Hz corresponding to vehicle body and suspension natural frequencies, respectively. These results showed that glass fibers can be replaced by nettle fibers without compromising performance

Apport de la simulation numérique 3D d’essais d’indentation instrumentée à l’identification d’une loi de comportement élasto-viscoplastique d’un béton à hautes performances

Les bétons à hautes performances (BHP) sont des matériaux hétérogènes à différentes échelles. L’identification des propriétés élasto-viscoplastiques effectives de tels matériaux nécessite d’une part la mesure des propriétés mécaniques à l’échelle de chaque phase constitutive, et d’autre part le recours à une approche par homogénéisation multi-échelle. Le travail présenté dans cet article concerne l’analyse du comportement élasto-viscoplastique de la matrice cimentaire d’un BHP. Une méthodologie d’identification inverse des paramètres des modèles de comportement des quatre phases constitutives de la matrice cimentaire a été développée. Elle se base sur le couplage entre la simulation 3D par la méthode des éléments finis d’un essai de nanoindentation et un procédé d’optimisation numérique des paramètres du modèle. La comparaison des courbes «charge-profondeur de pénétration» expérimentales et numériques pour chaque phase montre la bonne adéquation entre les données expérimentales et les modèles ainsi identifiés

Experimental investigation and constitutive modelling of the deformation behaviour of high impact polystyrene for plug-assisted thermoforming

This paper concerns the experimental and numerical study of the plug-assisted thermoforming process of high impact polystyrene (HIPS). The thermomechanical properties of this polymer were characterized at different temperatures and deformation rates. To study the influence of different parameters in the real conditions of plug-assisted thermoforming process, we carried out “plug-only” tests at different temperatures and plug velocities. To model the deformation behaviour of HIPS, we proposed a thermo-elastic-viscoplastic model, which we have implemented in Abaqus software. A thermo-dependent friction model was also proposed and implemented in Abaqus software. The parameters of the proposed models were identified by the inverse analysis method in the real conditions of plug-assisted thermoforming. The proposed models were validated with “plug-only” tests and plug-assisted thermoforming of yogurt container

Inverse Identification of Single-Crystal Plasticity Parameters of HCP Zinc from Nanoindentation Curves and Residual Topographies

This paper investigates the orientation-dependent characteristics of pure zinc under localized loading using nanoindentation experiments and crystal plasticity finite element (CPFEM) simulations. Nanoindentation experiments on different grain orientations exhibited distinct load–depth responses. Atomic force microscopy revealed two-fold unsymmetrical material pile-up patterns. Obtaining crystal plasticity model parameters usually requires time-consuming micromechanical tests. Inverse analysis using experimental and simulated loading–unloading nanoindentation curves of individual grains is commonly used, however the solution to the inverse identification problem is not necessarily unique. In this study, an approach is presented allowing the identification of CPFEM constitutive parameters from nanoindentation curves and residual topographies. The proposed approach combines the response surface methodology together with a genetic algorithm to determine an optimal set of parameters. The CPFEM simulations corroborate with measured nanoindentation curves and residual profiles and reveal the evolution of deformation activity underneath the indenter

Thermo-viscoplastic numerical modeling of metal forging process by Pseudo Inverse Approach

Constant demands of light-weighting have forced many industries to resort to manufacturing practices that promise a component with a higher strength-to-weight ratio. Hot forging is one such method used to produce parts using difficult-to-form materials as well as to achieve complex geometries. Although numerical methods provide an efficient means to predict the material yield and the stress/strain states of the product at different stages of forming and classical methods are accurate enough to provide a suitable representation of the process, they tend to be computationally expensive. This limits their use in process optimization studies. The Pseudo Inverse Approach (PIA) developed in the context of 2D axisymmetric cold forming, provides a quick and fairly accurate estimate of the stress and strain fields in the final product for a given initial shape. In this work, the PIA is extended to include the thermal and viscoplastic effects associated with the hot forging process. The results are compared with commercially available software based on the classical approaches to show the efficiency and the limitations of PIA

Modèle d'homogénéisation analytique pour la torsion de plaques orthotropes de type carton ondulé

International audienceCet article présente un modèle d’homogénéisation pour la torsion de plaques orthotropes. Pour un carton ondulé, la rigidité de torsion suivant la direction CD (Cross Direction) est calculée analytiquement selon la théorie de torsion de poutre à parois minces fermées. Nous avons montré que la rigidité de torsion suivant la direction MD (Machine Direction) est négligeable par rapport à celle suivant CD. La cohérence des théories de torsion de poutre et de plaque est étudiée afin d’appliquer correctement les rigidités de torsion de poutre à la simulation de plaques homogénéisées

Modèle d'homogénéisation élasto-plastique pour des structures composites

International audienceCet article présente un modèle d'homogénéisation élasto-plastique pour des structures composites de type carton ondulé. Une plaque composée de deux couches planes et d'une couche ondulée est modélisée par une plaque orthotrope homogène. L'homogénéisation est réalisée par une intégration locale à travers l'épaisseur dans chaque couche, suivie d'une cummlation des contributions des trois couches. Un modèle élasto-plastique en contraintes planes est adopté pour modéliser le comportement des papiers cartons. Notre H-modèle est implémenté dans le code de calcul Abaqus à l'aide du sous-programme utilisateur Ugens. Les résultats obtenus par le H-modèle sont comparés à ceux obtenus par les simulations 3D du carton ondulé avec des éléments de coque. La comparaison montre l'efficacité et la précision de notre modèle d'homogénéisation élasto-plastique

A Displacement Based Analytical Model to Determine Residual Stress Components in a Finite Elastic Thin Plate with Hole-Drilling Method

International audienceIn order to measure the residual stress components in an elastic thin plate, the hole-drilling strain-gage method has been used. This method enables to determine the relation between the magnitudes and directions of the principal stresses and the strain relaxation about the hole. In the existing analytical models based on stress field, the formulations associated with the hole-drilling method are based on the assumption of an infinite plate, this may cause some errors for a finite plate and it’s difficult to validate these solutions by FE methods. Furthermore, in the composite, the displacement field is continuous but the stress field is not necessarily continuous, the displacement field based method has to be used. In the present paper an analyt-ical model based on a displacement field described by a function with coefficients to determine for a finite round thin plate is presented. The coefficients used in the displacement field are independent on the three residual stress components, and they are determined by minimization of the internal strain energy during the hole-drilling process. Once the coefficients in the dis-placement field are determined, three strains measured in three radial directions are utilized to determine the three residual stress components. The proposed analytical model can be also adapted to infinite plate by assuming that the diameter of the round plate tends to infinite

Analytical Homogenization for Honeycomb Sandwich Plates with Skin and Height Effects

International audienceNumerical modeling of honeycomb sandwich plates is too tedious and time consuming. The analytical homogenization enables to obtain an equivalent homogeneous solid and its elastic stiffness. In this paper, the skin effect is considered for the in-plane shear and torsion problems, in which the two skins are relatively rigid. Homogenization models using trigonometric function series and energy method is proposed to study the influence of the honeycomb height on these moduli. The comparison between our H-model and Abaqus 3D modeling has shown very good agreement

Shock Response Spectrum Analysis of Fatigued Runners

International audienceThe purpose of this study was to determine the effect of fatigue on impact shock wave attenuation and assess how human biomechanics relate to shock attenuation during running. In this paper, we propose a new methodology for the analysis of shock events occurring during theproposed experimental procedure. Our approach is based on the Shock Response Spectrum (SRS), which is a frequency-based function that is used to indicate the magnitude of vibration due to a shock or a transient event. Five high level CrossFit athletes who ran at least three times per week and who were free from musculoskeletal injury volunteered to take part in this study. Two Micromachined Microelectromechanical Systems (MEMS) accelerometers (RunScribe®, San Francisco, CA, USA) were used for this experiment. The two RunScribe pods were mounted on top of the foot in the shoelaces. All five athletes performed three maximum intensity runs: the 1st run was performed after a brief warmup with no prior exercise, then the 2nd and the 3rd run were performed in a fatigued state. Prior to the 2nd and the 3rd run, the athletes were asked to perform at maximum intensity for two minutes on an Assault AirBike to tire them. For all five athletes, there was a direct correlation between fatigueand an increase in the aggressiveness of the SRS. We noticed that for all five athletes for the 3rd run the average SRS peaks were significantly higher than for the 1st run and 2nd run (p < 0.01) at the same natural frequency of the athlete. This confirms our hypothesis that fatigue causes a decrease in the shock attenuation capacity of the musculoskeletal system thus potentially involving a higher risk of overuse injury