The Experts below are selected from a list of 183 Experts worldwide ranked by ideXlab platform
Heiko Thoemen - One of the best experts on this subject based on the ideXlab platform.
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Processing and flexural properties of surface reinforced flat pressed WPC panels
European Journal of Wood and Wood Products, 2013Co-Authors: Henrik Schmidt, Jan T. Benthien, Heiko ThoemenAbstract:While extrusion and injection molding are the common technologies to produce wood-plastic composites (WPC), pressing may be an alternative, particularly when flat products are striven for. In this study, flat pressed WPC panels were surface-reinforced by two different types of thermoplastic face layers to improve flexural properties. The two face materials applied were a commingled fabric made of glass and polypropylene filaments (Twintex^®) and a glass fabric reinforced polypropylene laminate (S-TEX^®). Combination of face layers and WPC panels was achieved in a single and a two stage flat pressing process. Besides studying the effects of reinforcing material and number of process stages, the influence on flexural properties of the reinforced panels was identified. Unreinforced WPC panels were tested for comparison. The reinforced WPC panels exhibited greatly improved flexural properties, with MOE (MOR) values up to nearly 10,000 N/mm² (90 N/mm²). Holz-Kunststoff-Verbundwerkstoffe (wood-plastic composites) (WPC) werden überwiegend im Extrusions- oder Spritzgießverfahren hergestellt. Alternativ hierzu können plattenförmige WPCs mit Hilfe der Flachpresstechnologie hergestellt werden. In dieser Studie wurden flachgepresste WPC-Platten mit zwei verschiedenen thermoplastischen Deckschichtmaterialien verstärkt, um so deren Biegeeigenschaften zu verbessern. Als Deckschichtmaterialien wurden Twintex^®, eine kombinierte Glasfaser-Polypropylenfaser-Matte, sowie S-TEX^®, eine dünne glasfaserverstärkte Polypropylenplatte, verwendet. Die Verbindung zwischen Deckschicht und WPC-Platte wurde in einem ein- und einem zweistufigen Verfahren realisiert. Ergänzend zum Einfluss des Verstärkungsmaterials und der Anzahl der Prozessschritte, wurden die Biegeeigenschaften der verstärkten Platten bestimmt. Als Referenzmaterial dienten unverstärkte WPC-Platten. Durch die Verstärkung der Deckschichten wurde ein Anstieg der Biegeeigenschaften auf einen Wert von fast bist zu 10.000 N/mm^2 (MOE) und 90 N/mm^2 (MOR) erzielt.
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Processing and flexural properties of surface reinforced flat pressed WPC panels
European Journal of Wood and Wood Products, 2013Co-Authors: Henrik Schmidt, Jan T. Benthien, Heiko ThoemenAbstract:While extrusion and injection molding are the common technologies to produce wood-plastic composites (WPC), pressing may be an alternative, particularly when flat products are striven for. In this study, flat pressed WPC panels were surface-reinforced by two different types of thermoplastic face layers to improve flexural properties. The two face materials applied were a commingled fabric made of glass and polypropylene filaments (Twintex®) and a glass fabric reinforced polypropylene laminate (S-TEX®). Combination of face layers and WPC panels was achieved in a single and a two stage flat pressing process. Besides studying the effects of reinforcing material and number of process stages, the influence on flexural properties of the reinforced panels was identified. Unreinforced WPC panels were tested for comparison. The reinforced WPC panels exhibited greatly improved flexural properties, with MOE (MOR) values up to nearly 10,000 N/mm² (90 N/mm²).
Alfonso Maffezzoli - One of the best experts on this subject based on the ideXlab platform.
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Flexural creep behaviour of PP matrix woven composite
Composites Science and Technology, 2007Co-Authors: Antonio Greco, Claudio Musardo, Alfonso MaffezzoliAbstract:Abstract In this work the flexural creep behaviour of polypropylene and glass fibre commingled woven composite (Twintex ® ) sheets has been studied. Test samples were obtained in a compression moulding apparatus at different plate temperatures. Short-term flexural creep tests were run at multiple stress levels. Varying the applied stress level and using the Boltzmann superposition principle the linearity of creep behaviour was tested. In the linear viscoelastic region, creep tests were performed at different temperatures, ranging between 303 and 425 K. Time–temperature superposition principle was applied to build master curve, to predict the creep behaviour of the composite at a single reference temperature and long time scales. The obtained results indicate that higher temperatures of the plates lead to a composite with a lower creep compliance, which was related to the crystalline structure developed in the polymer matrix during cooling, and to a better fibre impregnation. An increase of the temperature of the mould resulted in higher degree of crystallinity of the polymer matrix, and lower final void fraction of the composite, as evidenced by results obtained from density tests, X-ray and DSC analysis. In turn, the higher crystalline fraction and lamellar thickness of crystallites were found to decrease the ductility of the composite, as evidenced from Charpy impact tests.
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Flexural creep behaviour of PP matrix woven composite
Composites Science and Technology, 2007Co-Authors: Aaron Greco, Claudio Musardo, Alfonso MaffezzoliAbstract:In this work the flexural creep behaviour of polypropylene and glass fibre commingled woven composite (Twintex??) sheets has been studied. Test samples were obtained in a compression moulding apparatus at different plate temperatures. Short-term flexural creep tests were run at multiple stress levels. Varying the applied stress level and using the Boltzmann superposition principle the linearity of creep behaviour was tested. In the linear viscoelastic region, creep tests were performed at different temperatures, ranging between 303 and 425 K. Time-temperature superposition principle was applied to build master curve, to predict the creep behaviour of the composite at a single reference temperature and long time scales. The obtained results indicate that higher temperatures of the plates lead to a composite with a lower creep compliance, which was related to the crystalline structure developed in the polymer matrix during cooling, and to a better fibre impregnation. An increase of the temperature of the mould resulted in higher degree of crystallinity of the polymer matrix, and lower final void fraction of the composite, as evidenced by results obtained from density tests, X-ray and DSC analysis. In turn, the higher crystalline fraction and lamellar thickness of crystallites were found to decrease the ductility of the composite, as evidenced from Charpy impact tests. ?? 2006 Elsevier Ltd. All rights reserved.
Remko Akkerman - One of the best experts on this subject based on the ideXlab platform.
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Characterization of the dynamic friction of woven fabrics: Experimental methods and benchmark results
Composites Part A-applied Science and Manufacturing, 2014Co-Authors: Ulrich Sachs, Konstantine A. Fetfatsidis, Josefine Schumacher, Gerhard Ziegmann, Samir Allaoui, Gilles Hivet, Remko Akkerman, Emmanuelle Vidal-sallé, Bernhard Maron, Kristof VancloosterAbstract:A benchmark exercise was conducted to compare various friction test set-ups with respect to the measured coefficients of friction. The friction was determined between Twintex®PP, a fabric of commingled yarns of glass and polypropylene filaments, and a metal surface. The same material was supplied to all benchmark participants and the test conditions were prescribed, making the used set-up the most important variable among the laboratories. Tests at ambient temperature as well as tests above the melting point of polypropylene are part of the benchmark, in order to determine both the dry and hydrodynamic friction characteristics. The dependency on sliding velocity, average pressure and temperature was investigated. Systematic differences are observed between the measurements obtained by the different set-ups, which are discussed and related to design characteristics of the devices. The values obtained in this benchmark are comparable and may serve as a reference to evaluate other friction set-ups. The paper concludes with guidelines for the design of a friction tester
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a friction test benchmark with Twintex pp
Key Engineering Materials, 2012Co-Authors: Ulrich Sachs, Konstantine A. Fetfatsidis, Josefine Schumacher, Gerhard Ziegmann, Samir Allaoui, Gilles Hivet, Emmanuelle Vidalsalle, Remko AkkermanAbstract:This paper presents an update on a friction benchmark, that was proposed during the 13th ESAFORM conference. The goal is to compare different friction test set-ups [1–4] by determining the coefficient of friction (CoF) for Twintex® PP. The benchmark instructions are based on the ASTM standard D1894 [5] but also account for different friction velocities, pressures and temperatures. At the time of writing five research groups contributed to the benchmark, each with a custom designed test set-up, differing in size, mechanism, force control and temperature regulation. All tests will be conducted with woven glass reinforced polypropylene, from the same Twintex® batch. Conclusions will be drawn about the comparability of different testing methods by recognizing and analyzing systematically deviating results.
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Forming simulation sensitivity study of the double-dome benchmark geometry
Key Engineering Materials, 2012Co-Authors: Bert Rietman, Sebastiaan Haanappel, René Ten Thije, Remko AkkermanAbstract:Simulations of manufacturing processes are of utmost importance in order to check on process feasibility of composites products already during the design phase. In order to benchmark the different software for (thermo)forming simulations of textiles and composites a benchmark geometry was agreed during previous Esaform conferences. Round 2 results have led to the insight that a stronger definition of the benchmark was needed, see [1]. The geometry, referred to as double-dome, combines doubly curved regions with steep walls and small radii. Therefore it may be considered critical with respect to forming behavior. As testing material a Twintex comingled glass/PP both as plain and twill weave woven fabric were chosen [2]. This paper addresses the simulation of the double-dome with the finite-element software Aniform. Shear angles, draw-in and the possible presence of wrinkles will be taken into account and compared to round 2 results of other participants. Additionally, a numerical sensitivity study of material and process parameters will be presented in order to identify major influences on the forming results. The paper concludes with a number of recommendations for further research as well as possible improvements for numerical modeling. [1] Sargent et.al., “Benchmark study of finite element models for simulation the thermostamping of woven-fabric reinforced composites”. Proceedings of the 13th Esaform Conference, Brescia 2010. [2] Cao et.al., “Characterisation of mechanical behaviour of woven fabrics: experimental methods and benchmark results”, Composites Part A: Applied Science and Manufacturing, 2008
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a lubrication approach to friction in thermoplastic composites forming processes
Composites Part A-applied Science and Manufacturing, 2011Co-Authors: R Ten H W Thije, Remko Akkerman, M P Ubbink, L Van Der MeerAbstract:Friction is an important phenomenon that can dominate the resulting product geometry of thermoplastic composites upon forming. A model was developed that predicts the friction between a thermoplastic laminate and a rigid tool. The model is based on the Reynolds equation for thin film lubrication and assumes hydrodynamic lubrication on a meso-mechanical level. The frictional properties are calculated, solely based on the rheological properties of the matrix constituent and the fabric weave geometry. The results have been validated against pull-out experiments of a 2 × 2 twill polypropylene (Twintex) weave at melt temperatures.
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Friction testing of thermoplastic composites
2011Co-Authors: Ulrich Sachs, Sebastiaan Haanappel, Bert Rietman, Remko AkkermanAbstract:Friction phenomena play a major role in thermoplastic composite forming processes. In order to make use of the large potential these materials have, accurate CAE tools are needed that as a consequence incorporate temperature, pressure and velocity dependent friction behavior. To obtain a sound understanding of friction behavior a large number of friction measurement set-ups have been described in literature. A benchmark to compare different testing methods was proposed during the Esaform2010 conference. In this paper the material (Twintex PP) and testing conditions for the benchmark are briefly revisited and first testing results employing the in-house developed friction tester are presented. It is observed that the results reproduce very well at different conditions. Based on the Hersey number the Stribeck curve for the tested material combination is derived. It is concluded that a full state of hydrodynamic lubrication was reached with friction coefficients between 0.15 and 0.5. This opens up good perspectives for numerical modeling since all parameters are readily available in process simulations. Future comparisons within the context of the benchmark will assess the quantitative level of the identified coefficients of friction.
Henrik Schmidt - One of the best experts on this subject based on the ideXlab platform.
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Processing and flexural properties of surface reinforced flat pressed WPC panels
European Journal of Wood and Wood Products, 2013Co-Authors: Henrik Schmidt, Jan T. Benthien, Heiko ThoemenAbstract:While extrusion and injection molding are the common technologies to produce wood-plastic composites (WPC), pressing may be an alternative, particularly when flat products are striven for. In this study, flat pressed WPC panels were surface-reinforced by two different types of thermoplastic face layers to improve flexural properties. The two face materials applied were a commingled fabric made of glass and polypropylene filaments (Twintex^®) and a glass fabric reinforced polypropylene laminate (S-TEX^®). Combination of face layers and WPC panels was achieved in a single and a two stage flat pressing process. Besides studying the effects of reinforcing material and number of process stages, the influence on flexural properties of the reinforced panels was identified. Unreinforced WPC panels were tested for comparison. The reinforced WPC panels exhibited greatly improved flexural properties, with MOE (MOR) values up to nearly 10,000 N/mm² (90 N/mm²). Holz-Kunststoff-Verbundwerkstoffe (wood-plastic composites) (WPC) werden überwiegend im Extrusions- oder Spritzgießverfahren hergestellt. Alternativ hierzu können plattenförmige WPCs mit Hilfe der Flachpresstechnologie hergestellt werden. In dieser Studie wurden flachgepresste WPC-Platten mit zwei verschiedenen thermoplastischen Deckschichtmaterialien verstärkt, um so deren Biegeeigenschaften zu verbessern. Als Deckschichtmaterialien wurden Twintex^®, eine kombinierte Glasfaser-Polypropylenfaser-Matte, sowie S-TEX^®, eine dünne glasfaserverstärkte Polypropylenplatte, verwendet. Die Verbindung zwischen Deckschicht und WPC-Platte wurde in einem ein- und einem zweistufigen Verfahren realisiert. Ergänzend zum Einfluss des Verstärkungsmaterials und der Anzahl der Prozessschritte, wurden die Biegeeigenschaften der verstärkten Platten bestimmt. Als Referenzmaterial dienten unverstärkte WPC-Platten. Durch die Verstärkung der Deckschichten wurde ein Anstieg der Biegeeigenschaften auf einen Wert von fast bist zu 10.000 N/mm^2 (MOE) und 90 N/mm^2 (MOR) erzielt.
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Processing and flexural properties of surface reinforced flat pressed WPC panels
European Journal of Wood and Wood Products, 2013Co-Authors: Henrik Schmidt, Jan T. Benthien, Heiko ThoemenAbstract:While extrusion and injection molding are the common technologies to produce wood-plastic composites (WPC), pressing may be an alternative, particularly when flat products are striven for. In this study, flat pressed WPC panels were surface-reinforced by two different types of thermoplastic face layers to improve flexural properties. The two face materials applied were a commingled fabric made of glass and polypropylene filaments (Twintex®) and a glass fabric reinforced polypropylene laminate (S-TEX®). Combination of face layers and WPC panels was achieved in a single and a two stage flat pressing process. Besides studying the effects of reinforcing material and number of process stages, the influence on flexural properties of the reinforced panels was identified. Unreinforced WPC panels were tested for comparison. The reinforced WPC panels exhibited greatly improved flexural properties, with MOE (MOR) values up to nearly 10,000 N/mm² (90 N/mm²).
Seung-hwan Chang - One of the best experts on this subject based on the ideXlab platform.
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Comparative study of healing fractured tibia assembled with various composite bone plates
Composites Science and Technology, 2020Co-Authors: Ali Mehboob, Syed Hasan Askari Rizvi, Seung-hwan Chang, Hassan MehboobAbstract:Abstract This study introduces innovative hybrid-type (Magnesium wire/poly-lactic acid–glass/polypropylene composite (Mg/PLA–Twintex[0]2nT) and bio glass fibers/poly-lactic acid–glass/polypropylene composite (BGF/PLA–Twintex[0]2nT)) partially biodegradable composites for comparison with conventional metallic stainless steel (SS) and fully biodegradable composite bone plates (i.e. Mg/PLA and BGF/PLA), as well as for analyzing their effect towards the healing of fractured healthy and diseased bones. Two different diffusion coefficients are introduced as the biological parameter (0.01 and 0.04 mm2/day) to mimic the blood supply of the diseased and healthy bones. The time-dependent tainted mechanical properties of the degradable composites are implemented to the degradable parts of the bone plates. As hypothesised, we found stress alleviations of 72.36%, 58.82%, 64.82%, and 59.71% in the screws with the diseased bones and alleviations of 84.64%, 72.67%, 77.26%, and 70.8% with the healthy bones in the BGF/PLA, Mg/PLA, BGF/PLA–Twintex[0]2nT, and Mg/PLA–Twintex[0]2nT composite bone plates, respectively. These results were then compared with those for the SS plates on the 28th day of healing. The maximum healing performance was predicted for the hybrid composites as opposed to the degradable and SS implants, thereby confirming the superiority of the proposed composites.
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Biomechanical design of a composite femoral prosthesis to investigate the effects of stiffness, coating length, and interference press fit
Composite Structures, 2018Co-Authors: Faris Tarlochan, Ali Mehboob, Hassan Mehboob, Seung-hwan ChangAbstract:Abstract Traditionally, high stiffness hip prostheses are associated with aseptic loosening. Hence, the effects of stiffness, coating length, and interference press fit on load sharing and micro-movements are investigated for a better understanding from a mechanical perspective. A simplified 3D model of the femur and prostheses composed of cobalt chrome (CoCr), titanium (Ti), and glass/polypropylene (Twintex [0]2nT) composite are constructed. Three interference fits corresponding to 5, 25, and 50 µm are used with half, three-quarter, and full lengths of coating that are used to assemble the prostheses with bones to investigate micro-movements at the bone-prosthesis interfaces, interfacial failure, and stress transfer to the bone. The reaction forces of body weight and muscular forces in the femur are used to simulate the FE model. The results indicate that the CoCr and Ti prostheses exhibit low micro-movements at the proximal end and high micro-movements at the distal end and vice versa for the Twintex [0]2nT composite prosthesis. Uniformity of stress transfer to the bone along the prosthesis efficiently increases with increases in the coating lengths and interference press fits for all the cases. A fully coated length of Twintex [0]2nT composite prosthesis with a 50-µm interference press fit provides the most efficient load sharing and stress transfer to the bone and micro-movements at the bone–prosthesis interface.
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Biomechanical simulation of healing process of fractured femoral shaft applied by composite intramedullary nails according to fracture configuration
Composite Structures, 2018Co-Authors: Ali Mehboob, Seung-hwan ChangAbstract:Abstract Flexible composite implants are receiving increased attention in this modern era of orthopedics for the stabilization of long bone fractures because they facilitate tissue development in calluses. An endochondral ossification process involves generation of calluses, and it is well known that this significantly affects the stabilization and healing of the broken bones. Therefore, the exact configuration of callus formation is highly important for the accurate simulation of bone healing. In this study, finite element analysis was performed to estimate the external callus shape by using the rejection coefficient (RC) algorithm. Regarding the application of a fractured femur by an intramedullary (IM) nail, the bone healing simulation was conducted by employing the biphasic mechano-regulation algorithm according to the fracture type (transverse (0°) and oblique (35°)), fracture location (proximal, medial, and distal ends), and nail property. The simulation results revealed that a glass/polypropylene fabric composite (Twintex [0] 2nT ) IM nail, which has the similar Young’s modulus to the cortical bone, provided the most appropriate bio-mechanical environment for bone healing.
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Influence of initial biomechanical environment provided by fibrous composite intramedullary nails on bone fracture healing
Composite Structures, 2017Co-Authors: Ali Mehboob, Seung-hwan Chang, Hassan Mehboob, Faris TarlochanAbstract:Abstract Long bone fractures are primarily treated with internal fixation devices, and intramedullary (IM) nails are the most commonly used. Reamed and unreamed surgical procedures are commonly used to attach IM nails to fractured bones. It is believed that the use of flexible composites contributes to successful fracture healing because of the desirable initial interfragmentary movement (IFM) provided by the material. This finite element study was conducted to understand the influence of initial IFM on the healing process by using various IM nail materials (stainless steel, carbon/epoxy composites (WSN3k [0] 2nT , WSN3k [±30] nT ) and glass/polyprophylene (Twintex [0] 2nT ) composite). Reamed and unreamed IM nails were used to investigate the effects of mesenchymal cell activities, deviatoric strain, and body fluid flow in calluses on bone healing. The results showed that unreamed IM nails promoted healing because of a 40% increase in initial cells supplied to the central callus, compared to reamed nails. The most suitable initial interfragmentary strains (IFS) (18.3% and 6.85%, reamed and unreamed) were provided by the flexible Twintex [0] 2nT IM nail and this induced 38% and 40.33% healing performances by the reamed and unreamed IM nails, respectively.
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Effect of composite intramedullary nails (IM) on healing of long bone fractures by means of reamed and unreamed methods
Composite Structures, 2017Co-Authors: Ali Mehboob, Seung-hwan Chang, Hassan Mehboob, Faris TarlochanAbstract:Abstract Complications are common during bone fracture healing owing to incompatibility of the implants. Flexible fibrous composite materials are promising materials that offer excellent biomechanical compatibility. Flexible composite fixation devices provide enough initial fracture stabilization and an adequate environment to promote the desired secondary healing process. Fractures fixed with reamed and unreamed intramedullary (IM) nails exhibit advantages and disadvantages. In this study, the effect of reamed and unreamed IM nails made of stainless steel and various composites (WSN3 k [0] 2nT , WSN3 k [±30] nT , and Twintex [0] 2nT ) on the bone healing process was studied. A finite element model and mechano-regulation algorithm with deviatoric strain and fluid flow were programmed to estimate the healing process. A suitable biophysical environment was predicted for successful bone healing. The Twintex [0] 2nT IM nail contained 19.57% and 33.44% lower stress than that of the stainless steel at day 1, reducing the stress shielding effect. The body weight carried by the bone was 72.8% higher in the Twintex [0] 2nT nail with a maximum relief of 79.8% in stresses relative to the stainless steel IM nail at final day of healing confirming the maximum healing.
