The Experts below are selected from a list of 3162 Experts worldwide ranked by ideXlab platform
Philippe Viot - One of the best experts on this subject based on the ideXlab platform.
-
Multi-scale Foam : 3D structure/compressive behaviour relationship of agglomerated cork
Materialia, 2019Co-Authors: Louise Le Barbenchon, Jérémie Girardot, Jean-benoit Kopp, Philippe ViotAbstract:This study focuses on the microstructural aspects of a cork-based by-product known as agglomerated cork and its influence on the compressive mechanical behaviour. The material consists in granulates of a natural Polymeric Foam - cork - mixed together with a small quantity of a bio-sourced resin. Optical and scanning electron microscopy (SEM) are first used to investigate on the bead geometry and placement and interfaces arrangement. Then X-ray computed tomography allows to study the spatial arrangement of agglomerated cork microstructure and hence to complete and confirm 2D observations. 2D and 3D observations show a transverse anisotropic material which is confirmed by the mechanical tests. SEM pictures demonstrate an intricate and heterogeneous material. Microtomography confirms the presence of macroporosities between cork granulates having a mean volume around 0.1 mm 3 . Cork cell specific geometry is also confirmed. The volume of those cells lies around 10 −5 mm 3 . Finally quasi-static compression tests are run to establish a link between microstructure and mechanical behaviour thanks to digital image correlation (DIC). Cork agglomerate demonstrates strong strain localisation at its surface caused by its multi-scale structure.
-
Polymeric Foam deformation under dynamic loading by the use of the microtomographic technique
Journal of Materials Science, 2007Co-Authors: Philippe Viot, Dominique Bernard, Erwan PlougonvenAbstract:The mechanical behaviour of Polymeric Foams depends on several parameters such as temperature, material density and strain rate. This last point implies that compression tests on conventional testing machines are not sufficient. Study of the behaviour in practical situations requires special apparatus like fly wheels, drop towers or Hopkinson bars, allowing high compression speeds. The polypropylene Foams studied are multi-scale materials; agglomerated beads (2–3 mm in diameter), visible to the naked eye, are composed of microscopic closed cells (a few tens of microns). The response of the material to a shock consists of three regions: an elastic phase, a plastic phase and densification. The plastic phase is of prime interest since a great part of the shock energy is dissipated there. Microtomography was used in order to better understand damage mechanisms during the stress plateau of the plastic phase. The final objective of this work is to determine the strain field of porous materials at several levels of shock. As tomography is not fast enough to directly follow the impact deformation, interrupted impact tests were carried out by controlling the levels of sample deformation. Between each impact step, a microtomographic analysis offers insight on the progressive deformation of the sample. The results of these impact tests completed by a microtomographic visualisation in 2D are presented and commented in this paper.
-
Polymeric Foam behavior under dynamic compressive loading
Journal of Materials Science, 2005Co-Authors: Philippe Viot, F Beani, J L LatailladeAbstract:Polymeric Foams are commonly used in many impact-absorbing applications and thermal-acoustic insulated devices. To improve their mechanical performances, these structures have to be modeled. Constitutive equations (for their macroscopic behavior) have to be identified and then determined by appropriate tests.Tests were carried out on polypropylene Foams under high strain rate compression. In this work, the material behaviour has been determined as a function of two parameters, density and strain rate. Foams (at several densities) were tested on a uniaxial compression for initial strain rates equal to 0.34 s−1 and on a new device installed on a flywheel for higher strain rates. This apparatus was designed in order to do stopped dynamic compression tests on Foam. With this testing equipment, the dynamic compressive behaviour of the Polymeric Foam has been identified in the strain rate range [6.7.10−4s−1, 100s−1].Furthermore, the sample compression was filmed with a high speed camera monitored by the fly wheel software. To complete this work, picture-analysis techniques were used to obtain displacement and strain fields of the sample during its compression. Comparisons between these results and stress-strain responses of polypropylene Foam allow a better understanding of its behaviour. The multiscale damage mechanism, by buckling of the Foam structure, was emphasised from the image analysis.
Xi Chen - One of the best experts on this subject based on the ideXlab platform.
-
characterization of the compressive deformation behavior with strain rate effect of low density Polymeric Foams
Polymer Testing, 2016Co-Authors: Akio Yonezu, Keita Hirayama, Hiroshi Kishida, Xi ChenAbstract:Abstract This study investigates the compressive deformation behavior of a low-density Polymeric Foam at different strain rates. The material tested has micron-sized pores with a closed cell structure. The porosity is about 94%. During a uni-axial compressive test, the macroscopic stress–strain curve indicates a plateau region during plastic deformation. Finite Element Method (FEM) simulation was carried out, in which the yield criterion considered both components of Mises stress and hydrostatic stress. By using the present FEM and experimental data, we established a computational model for the plastic deformation behavior of porous material. To verify our model, several indentation experiments with different indenters (spherical indentation and wedge indentation) were carried out to generate various tri-axial stress states. From the series of experiments and computations, we observed good agreement between the experimental data and that generated by the computational model. In addition, the strain rate effect is examined for a more reliable prediction of plastic deformation. Therefore, the present computational model can predict the plastic deformation behavior (including time-dependent properties) of porous material subjected to uni-axial compression and indentation loadings.
Simon Ouellet - One of the best experts on this subject based on the ideXlab platform.
-
High Rate Compressive Behaviour of a Dilatant Polymeric Foam
Journal of Dynamic Behavior of Materials, 2018Co-Authors: Kapil Bharadwaj Bhagavathula, Austin Azar, Sukanya Satapathy, Simon Ouellet, Christopher R. Dennison, James David HoganAbstract:Polymeric Foams are an essential part of personal protection equipment, such as helmets and body armor. In this work, the authors study the strain-rate dependent behavior of a dilatant Polymeric Foam, focusing on developing characterization and testing methodologies needed to better understand the links between microstructure and failure in these materials. The authors study these links for a commercially-available shear-thickening Foam, named D3O LITE D. Prior to testing, the pore sizes (82 ± 26 µm), ligament thickness between pores (5–12 µm), and porosity (83 ± 5%) were quantified using scanning electron microscope images. Samples were then tested in compression under quasi-static conditions for a strain rate of 0.04 s−1 using an MTS testing apparatus, and in dynamic conditions using a split Hopkinson pressure bar apparatus for strain rates of 5280–5720 s−1. For both rates, strains upwards of 85% were achieved and this allowed us to examine a variety of material failure behaviors, including elastic collapse, localization, pore collapse, densification and post pore collapse hardening. These mechanisms are observed in-situ during compression experiments using high-speed photography, and linked back to stress–strain responses of the materials. In this material, the elastic collapse stress for quasi-static and dynamic compression conditions was found to be 120 ± 40 kPa and 243 ± 47 kPa, respectively, and elastic modulus were noted of 2.4 ± 0.7 MPa and 3.8 ± 1.2 MPa, respectively. Following the elastic collapse, some unique specimen-scale localization features were observed during the dynamic experiments. These features are unique to dynamic compression and were not observed for the quasi-static case, demonstrating a demonstrating a distinct high-rate behavior for this material, possibly linked to its “shear thickening” label. After densification, complete pore collapse followed by post pore collapse hardening were observed for both strain rates. These results represent some of the first studies on shear-thickening Foams in the literature, and the testing methodologies developed in this study will serve as the foundation for additional experimental and computation studies across a broader range of Foam materials.
-
low density polyethylene expanded polystyrene and expanded polypropylene strain rate and size effects on mechanical properties
Polymer Testing, 2016Co-Authors: Duane S Cronin, Simon OuelletAbstract:Abstract Polymeric Foam materials may be used as energy absorbing materials for protection in impact scenarios, and design with these materials requires the mechanical properties of Foams across a range of deformation rates, where high deformation rate testing often requires small samples for testing. Owing to their cellular macrostructure, and the large deformations that occur during loading of Foams, the measured stress-strain response of a Foam material may be influenced by the sample size. In this study, the mechanical properties of three closed-cell Polymeric Foams (Low Density Polyethylene, Expanded Polystyrene and Expanded Polypropylene) at two different densities were investigated over a range of deformation rates from 0.01 s −1 to 100 s −1 . For each Foam material, three different nominal sample sizes (10 mm, 17 mm and 35 mm) were tested. On average, the Polymeric Foam materials exhibited increasing stress with increasing deformation rate, for a given amount of strain. Density variation was identified at the sample level, with smaller samples often exhibiting lower density. Expanded Polystyrene demonstrated the highest variability in sample density and corresponding variability in mechanical response, qualitatively supported by observed variations in the macrostructure of the Foam. Expanded Polypropylene exhibited variability in density with sample size, and observable variability in the material macrostructure; however, the dependence of the measured mechanical properties on sample size was modest. Low Density Polyethylene was found to have a relatively consistent cell size at the macrostructure level, and the material density did not vary significantly with sample size. In a similar manner, the dependence of measured mechanical properties on sample size was modest. The effect of sample size was identified to be material specific, and it is recommended that this be assessed using sample-specific density measurements and considering different sized samples when testing Foam materials.
-
compressive response of Polymeric Foams under quasi static medium and high strain rate conditions
Polymer Testing, 2006Co-Authors: Simon Ouellet, Duane S Cronin, M J WorswickAbstract:Polymeric Foam materials are widely used for impact protection and energy absorption, for which advanced design and modeling requires appropriate material characterization data and constitutive models. The compressive mechanical behavior of three common Polymeric Foams (expanded polystyrene, high-density polyethylene, and polyurethane) has been measured at strain rates ranging from 0.0087 to 2500/s. Although a large amount of compression data is available in the literature, most of this data only addresses strain rates up to 250/s, with higher rate data limited to modest levels of compression. This represents a significant deficit in the current knowledge since many applications are leading to the use of Foams at high rates and significant total deformation. The material characterization was accomplished using a standard compression test device and a drop tower apparatus to achieve rates up to 100/s. A Polymeric split Hopkinson pressure bar apparatus was used to achieve strain rates from 500 to 2500/s. This data has been used to investigate a common Foam constitutive model, and shows that strain rate effects become more pronounced at rates above approximately 1000/s.
Tomasz Sadowski - One of the best experts on this subject based on the ideXlab platform.
-
effective properties for sandwich plates with aluminium foil honeycomb core and polymer Foam filling static and dynamic response
Computational Materials Science, 2011Co-Authors: Tomasz Sadowski, J BecAbstract:Abstract The estimation of static and eigenvibration properties of honeycomb sandwich reinforced by Polymeric Foam were investigated in the paper. A new “real microstructure” numerical 3D FEM model was proposed for the analysis in which the face materials and the honeycomb were modelled by shell elements, whereas filling Foam was modelled by solid elements. Two variants of the honeycomb sandwich panel were considered: with and without polymer Foam filling. Static and modal analyses have been performed in both, filled and hollow cases, to observe the effect of core stabilization with Foam, particularly for higher natural frequencies. The effective properties of the honeycomb sandwich panels were estimated for both considered cases. Similar calculations have been made for the core materials without top and bottom faces and for the sandwich plate without honeycomb core structure (only polymer Foam). One can observe: (1) the substantial increase of the effective elastic properties of the plate; (2) that the eigenvibration properties depend strongly on: the face material, honeycomb core and filling materials properties. The above conclusions are important for design process of structural parts.
-
analysis of structural performance of sandwich plates with Foam filled aluminum hexagonal honeycomb core
Computational Materials Science, 2009Co-Authors: Vyacheslav N Burlayenko, Tomasz SadowskiAbstract:Exploitation experience of honeycomb sandwich structures has shown that one of the most frequently encountered in-service problems is debonding at the interface between face sheets (skins) and core. Filling of honeycomb type cores with Foam allows to enhance the damage resistance to the debonding propagation, but on the other hand it changes the structural responses of sandwich structure. The aim of the paper is to estimate of a Polymeric Foam influence on the free vibration and buckling characteristics of sandwich plates with a hexagonal honeycomb core. The analyses of sandwich plates with hollow and Foam-filled honeycomb cores are carried out using the commercially available finite element code ABAQUS. The sandwich plates were modelled on the basis of simplified three-layered continuum models. The displacement-based homogeneous technique using finite element method (FEM) is applied to evaluate the effective elastic properties of core for both hollow and filled with Foam honeycomb cores. The comparative results of load carrying capacities and magnitudes of natural frequencies of the sandwich plates are presented. The structural benefits of Foam-filled sandwich plates are briefly discussed.
A Othman - One of the best experts on this subject based on the ideXlab platform.
-
investigating the crushing behavior of quasi static oblique loading on Polymeric Foam filled pultruded composite square tubes
Composites Part B-engineering, 2016Co-Authors: A Othman, Shahrum Abdullah, A K Ariffin, Nik Abdullah Nik MohamedAbstract:Abstract The behavior of Foam-filled core composite is vastly superior as a material in terms of its mechanical and physical properties. The present paper describes the performance of polyurethane (PU) Foam as an internally-reinforced filler material on pultruded composite square cross-section tubes made of E-glass/polyester resin and subjected to axial and oblique loading. In this research study, Foam-filled core composites of three different wall thicknesses and densities were examined experimentally. The capacity of a structure to absorb large amounts of energy during crush regimes is a major concern in the design of crashworthy structures. Various loads were applied to different angle cross-head platens to assess their energy absorption capacity based on quasi-static load–displacement curves. In addition, the interaction properties of the composite and the Foam core sheets during the loadings were discussed. Experimental results indicated that the crashworthy structure of the polyurethane (PU) Foam-filled specimen enhanced the specific and quasi-static absorbed energies more than the empty composite tubes.
-
investigating the quasi static axial crushing behavior of Polymeric Foam filled composite pultrusion square tubes
Materials & Design, 2014Co-Authors: A Othman, A K Ariffin, Siti Norul Huda Sheikh Abdullah, Nik Abdullah Nik MohamedAbstract:Abstract The capability of structures to absorb large amounts of energy is a crucial factor, particularly for structural components of vehicles, in reducing injury in case of collision. In this study, an experimental investigation was conducted to study the crashworthiness of Polymeric Foam-filled structures to the pultruded square cross-section E-Glass fiber-reinforced polyester composite tube profiles. Quasi-static compression was applied axially to composite tubes to determine the response of the quasi-static load displacement curve during progressive damage. Three pultruded composite tube wall thicknesses at different sizes were examined, and the effects of crushing behavior and failure modes were analyzed and discussed. Experimental results indicated that the Foam-filled profile is superior to the non-filled Foam composite tube profile in terms of the capacity to absorb specific energy.
-
on the crushing behavior of Foam filled composite tubes under compressive loading
Advanced Materials Research, 2012Co-Authors: A Othman, Shahrum Abdullah, A K Ariffin, Nik Abdullah Nik Mohamed, Helmi RashidAbstract:The present papers determine the effect of composite pultrusion square tubes E-glass polyester empty and Polymeric Foam-filled subjected to axial compressive loading. The specimens of square composite pultrusion were compressed experimentally under axial loadings to examine the effect of empty and Polymeric Foam-filled with different wall-thickness. The wall-thickness was used in this study were 2.1 and 2.4 mm. During the experimental observation, three characteristic crushing stages were identified as initial peak load, progressive crushing and compaction zone stages. The composite pultrusion square tube profile were analyzed and investigated in terms of crashworthiness parameters to meet the improvement of structural material widely used in automobile, aerospace and marine applications. Result obtained from experimental analysis such that initial peak load, mean load, energy absorption and specific energy absorption versus displacement curves were compared for each specimen. Results showed that the tubes energy absorption was affected significantly by different tube profile. It is also found that the Polymeric Foam-filled exhibit superb crashworthy structure on specific absorbed energy and the amount of initial peak load, mean load and absorbed energy recorded higher than the empty tube profiles.