The Experts below are selected from a list of 156 Experts worldwide ranked by ideXlab platform
Mehdi Hojjati - One of the best experts on this subject based on the ideXlab platform.
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bending behavior of multilayered textile Composite Prepregs experiment and finite element modeling
Materials & Design, 2017Co-Authors: Hassan Alshahrani, Mehdi HojjatiAbstract:Abstract An accurate model and assessment of out-of-plane bending properties can improve the forming predictions of multilayered textile Prepregs using a suitable modeling technique. This paper aims to investigate the bending properties of multilayered textile thermosetting Composite Prepregs under conditions relevant to the forming process. A finite element model based on a viscoelastic approach has been developed to predict the bending behavior of different stacking sequences at different processing parameters, including temperature and rate. This model allows the modeler to determine the correct bending parameter values to set during the forming simulation process. The effect of stacking sequences on out-of-plane bending deformation was studied experimentally and numerically through the developed modeling methodology. Furthermore, the paper analyzes the feasibility of using a viscoelastic material model to model the bending behavior of rate-dependent material and its application in forming simulation. A comparison between elastic and viscoelastic material models showed the importance of considering the rate dependency to describe the bending behavior of prepreg materials. The experimental and numerical results show that the bending properties strongly depend on the fabric lay-up inside multiple stacked plies. Bending and friction properties were also found to significantly influence the occurrence of wrinkles during the forming simulation.
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A new test method for the characterization of the bending behavior of textile Prepregs
Composites Part A-applied Science and Manufacturing, 2017Co-Authors: Hassan Alshahrani, Mehdi HojjatiAbstract:Abstract To improve forming simulation outcomes for Composite Prepregs and predict wrinkle formation, the bending behavior of prepreg materials must be correctly characterized. This paper proposes a new loading-rate control bending test in which the sample deflection and applied rate are controlled by a linear actuator while the load required to achieve this deflection is recorded by a miniature-load cell. An investigation of out-of-plane bending behavior as well as viscoelastic behavior at the forming process conditions of woven fabric out-of-autoclave Prepregs was undertaken using this method. The experimental results show that the proposed bending test provides sufficient control of the deflection shape, testing rates, and processing temperatures within the range of thermosetting resin. Furthermore, the bending results reveal the rate dependency and viscoelastic nature of the materials. A method is developed to derive the bending stiffness from the nonlinear relationship between bending moment and curvature.
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influence of double diaphragm vacuum compaction on deformation during forming of Composite Prepregs
Journal of Science: Advanced Materials and Devices, 2016Co-Authors: Hassan Alshahrani, Mehdi HojjatiAbstract:Abstract During the diaphragm forming process, a vacuum seal is applied between the upper and lower diaphragms to compact and hold the laminate. Therefore, a thorough characterization of the in-plane shear behavior of fabrics under diaphragm forming conditions must take into account the effect of vacuum-sealing and compaction between the two diaphragms during bias extension. The study presented here examined the shear angles of out-of-autoclave 8-harness satin woven carbon/epoxy Prepregs under diaphragm compaction. A bias extension test was conducted to study the effect of diaphragm compaction and ply interactions on shear properties. The test was performed at different compaction levels, and changes in shear angle with respect to vacuum levels and diaphragm compaction forces were observed. The contribution of diaphragm material and ply interaction to shear stiffness was evaluated and compared with results from a direct bias extension test. The samples were tested at both room temperature and at elevated temperatures using a radiant heater. The results show that shear angle decreases significantly as vacuum pressure and compaction is applied between the two diaphragms. This finding indicates that vacuum levels and compaction forces have a significant influence on the deformation limit and wrinkling onset during the diaphragm forming process.
Hassan Alshahrani - One of the best experts on this subject based on the ideXlab platform.
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bending behavior of textile thermosetting Composite Prepregs during forming processes
2017Co-Authors: Hassan AlshahraniAbstract:Composite materials are increasingly replacing metals for many modern structures used in the aerospace and automotive industry. Textile Composites are favored due to their superior forming capabilities to produce complex shapes. However, the formability of a textile Composite is limited by failure modes, such as wrinkling, which remain challenging issues during the forming process. The ability to accurately predict wrinkles and ultimately prevent them during the forming process is highly desirable for process optimization in an industrial environment. The success or failure of Composite formation is determined by the properties of the material that is undergoing the deformation. A significant amount of time and effort has been devoted to characterizing and modeling these properties. Therefore, to predict those defects, a thorough understanding of the deformation behavior of textile-woven Prepregs is required. Out-of-plane bending is one of the deformation mechanisms that govern the appearance of wrinkles during Composite forming. This thesis therefore presents an experimental, theoretical, and numerical study on the out-of-plane bending behavior of woven out-of-autoclave Prepregs with application in forming simulations. Within this thesis, a new test method for characterizing the bending behavior of prepreg materials at forming conditions was developed based on a vertical cantilever test associated with a linear actuator and load cell. This test method allowed for sufficient control of the deflection shape, testing rates, and processing temperatures within the range of the thermosetting resin. Investigations for out-of-plane bending behavior and viscoelastic behavior in the forming process conditions were undertaken using the developed test method. Through the cantilever beam theory, where the prepreg yarn is composed of two external viscoelastic polymer plies with a linear elastic ply, a theoretical model is proposed to estimate the bending stiffness over a range of processing conditions. A new approach for considering the testing rate and temperature with respect to a reference value is also established. Experimental tests were carried out to estimate the model parameters and to validate the proposed model. The predicted bending stiffness was found to be in a good agreement with experimental values at selected conditions. However, there were slight differences due to the complexity of the undulation in the woven fabric structure. Then, a finite element model for the bending behavior of multilayered Prepregs was developed by considering the actual bending behavior of the material. The prepreg ply was modeled by incorporating the characterized behavior of intra-ply shear and inter-ply friction. The effect of stacking sequences on out-of-plane bending deformation during the forming process was studied experimentally and numerically. Moreover, the feasibility of using a viscoelastic approach and its application in forming simulations were analyzed. Finally, a series of real forming experiments using a double diaphragm process were carried out to investigate the formability of textile out-of-autoclave thermoset Prepregs over complex geometry for aerospace applications. A one-step procedure was used for both the forming and curing processes using the same experimental setup. A finite element model was developed to simulate the double diaphragm forming process, with consideration for the diaphragm material properties at forming conditions. In addition, important considerations, such as local fiber compressive stresses, shear angle distributions, and stacking lay-up sequences, were analyzed to identify the potential causes of wrinkles in the formed parts. The resulting knowledge from the modeling methodology allowed the designers to reliably choose the appropriate stacking sequences and suitable process parameters for complex structures prior to conducting expensive trial and error tests.
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bending behavior of multilayered textile Composite Prepregs experiment and finite element modeling
Materials & Design, 2017Co-Authors: Hassan Alshahrani, Mehdi HojjatiAbstract:Abstract An accurate model and assessment of out-of-plane bending properties can improve the forming predictions of multilayered textile Prepregs using a suitable modeling technique. This paper aims to investigate the bending properties of multilayered textile thermosetting Composite Prepregs under conditions relevant to the forming process. A finite element model based on a viscoelastic approach has been developed to predict the bending behavior of different stacking sequences at different processing parameters, including temperature and rate. This model allows the modeler to determine the correct bending parameter values to set during the forming simulation process. The effect of stacking sequences on out-of-plane bending deformation was studied experimentally and numerically through the developed modeling methodology. Furthermore, the paper analyzes the feasibility of using a viscoelastic material model to model the bending behavior of rate-dependent material and its application in forming simulation. A comparison between elastic and viscoelastic material models showed the importance of considering the rate dependency to describe the bending behavior of prepreg materials. The experimental and numerical results show that the bending properties strongly depend on the fabric lay-up inside multiple stacked plies. Bending and friction properties were also found to significantly influence the occurrence of wrinkles during the forming simulation.
Philippe Boisse - One of the best experts on this subject based on the ideXlab platform.
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consolidation modeling during thermoforming of thermoplastic Composite Prepregs
Materials, 2019Co-Authors: Hu Xiong, Nahiene Hamila, Philippe BoisseAbstract:This article describes the modeling of the compaction/consolidation behavior of thermoplastic Composite Prepregs during the thermoforming process. The proposed model is principally based on a generalized Maxwell approach. Within a hyperelastic framework, viscoelasticity is introduced for the compaction mode in addition to the in-plane shearing mode by taking into account the influence of the resin and its flow during consolidation. To reveal the evolution of the consolidation level, which reflects the number of voids in the Composite, an intimate contact model was used during the process. The model was characterized by a compaction test at a high temperature. It was implemented into a recently developed prismatic solid-shell finite element. The analysis of the thermoforming of a double dome demonstrated the relevance of the consolidation computation in determining the process parameters leading to a Composite part free of voids.
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Thermomechanical analysis, modelling and simulation of the forming of pre-impregnated thermoplastics Composites
Composites Part A-applied Science and Manufacturing, 2015Co-Authors: E. Guzman-maldonado, Nahiene Hamila, Philippe Boisse, Jérôme BikardAbstract:Abstract In this paper, the viscoelastic behaviours of pre-impregnated (prepreg) thermoplastic Composites are analysed using the bias-extension test. A new constitutive model is proposed in order to simulate the forming of thermoplastic Composite Prepregs at the macroscopic scale. The model is based on a continuous approach. Hyperelastic behaviours are associated with dry reinforcements. Four principal deformation modes, all considered independent, define the hyperelastic potential: the elongation in warp direction, the elongation in weft direction, the in-plane shear strain and the bending contribution. Experience shows that viscoelastic behaviour is mainly associated with the in-plane shear deformation. A non-linear visco-hyperelastic model based on the generalisation of Maxwell rheological model is considered for this type of deformation mode. The finite element simulation of a stamping case using this model is introduced. The influence of temperature on the forming stage and the performance of the model are evaluated.
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thermomechanical analysis of thermoplastic Composite Prepregs using bias extension test
Journal of Thermoplastic Composite Materials, 2014Co-Authors: Peng Wang, Nahiene Hamila, Pierre Pineau, Philippe BoisseAbstract:The results of in-plane shear tests performed on 5-hardness satin woven carbon/polyphenylene sulphide and polyetheretherketone thermoplastic Prepregs are described in this article. The experimental...
Steven Nutt - One of the best experts on this subject based on the ideXlab platform.
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void formation in Composite Prepregs effect of dissolved moisture
Composites Science and Technology, 2010Co-Authors: Lessa Kay Grunenfelder, Steven NuttAbstract:Abstract Void formation as a function of resin moisture content was investigated to better understand and control process defects in Composite parts made from prepreg. In this study, uncured prepreg was conditioned at 70%, 80% and 90% relative humidity and at 35 °C. Conditioned prepreg was laid up into quasi-isotropic laminates and cured using vacuum bag only (VBO) processing (low-pressure), and autoclave processing. Moisture uptake in the resin was measured using coulometric Fischer titration. Void content was measured by image analysis of polished sections of cured laminates. Void fractions increased substantially with increasing moisture content in VBO processed laminates, while autoclave-processed parts remained void-free. Experimental results were consistent with trends predicted using a diffusion-based analytical model. The findings are discussed in the context of causes of voids in prepreg Composites.
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Void formation in Composite Prepregs – Effect of dissolved moisture
Composites Science and Technology, 2010Co-Authors: Lessa Kay Grunenfelder, Steven NuttAbstract:Abstract Void formation as a function of resin moisture content was investigated to better understand and control process defects in Composite parts made from prepreg. In this study, uncured prepreg was conditioned at 70%, 80% and 90% relative humidity and at 35 °C. Conditioned prepreg was laid up into quasi-isotropic laminates and cured using vacuum bag only (VBO) processing (low-pressure), and autoclave processing. Moisture uptake in the resin was measured using coulometric Fischer titration. Void content was measured by image analysis of polished sections of cured laminates. Void fractions increased substantially with increasing moisture content in VBO processed laminates, while autoclave-processed parts remained void-free. Experimental results were consistent with trends predicted using a diffusion-based analytical model. The findings are discussed in the context of causes of voids in prepreg Composites.
Xiongqi Peng - One of the best experts on this subject based on the ideXlab platform.
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an anisotropic hyperelastic constitutive model for thermoplastic woven Composite Prepregs
Composites Science and Technology, 2016Co-Authors: Youkun Gong, Xiongqi PengAbstract:Abstract A hyperelastic constitutive model is developed to characterize the anisotropic and large deformation behavior of woven thermoplastic Composite Prepregs during thermo-forming process. In the model, a strain energy function representing the material behavior of melting prepreg is additively decomposed into three parts nominally representing the energy contributions from the matrix, fiber and their interaction, respectively. The proposed constitutive model is demonstrated on a balanced 2 × 2 twill glass/PP prepreg. The specific forms of the strain energy functions are determined by fitting uni-axial tensile and bias extension tests of the Prepregs at melting temperature. The developed model is then applied to simulation of a benchmark double dome thermo-forming, demonstrating that it is highly suitable for predicting the large deformation behavior of woven Prepregs during thermo-forming process. The effects of matrix on forming simulation results are also investigated.