A new method to predict the ultimate strength of fiber reinforced composites under arbitrary load condition is introduced. The micromechanics strength theory is used to perform the final failure prediction of composit...A new method to predict the ultimate strength of fiber reinforced composites under arbitrary load condition is introduced. The micromechanics strength theory is used to perform the final failure prediction of composite laminates. The theory is based on unit cell analytic model which can provide the ply composite material properties by only using the constituent fiber and matrix properties and the laminate geometric parameters without knowing any experimental information of the laminates. To show that this method is suitable for predicting the strength of composite laminates, the micromechanics strength theory is ranked by comparing it with all the micro-level and the best two macro-level theories chosen from the World Wide Failure Exercise. The results show that this method can be used for predicting strength of any composite laminates and provide a direct reference for composite optimum design.展开更多
This presentation predicts the elastic properties of three-dimensional(3D)orthogonal woven composite(3DOWC)by finite element analysis based on micro/meso repeated unit cell(RUC)models.First,the properties of fiber yar...This presentation predicts the elastic properties of three-dimensional(3D)orthogonal woven composite(3DOWC)by finite element analysis based on micro/meso repeated unit cell(RUC)models.First,the properties of fiber yarn are obtained by analysis on a micro-scale RUC model assuming fibers in a hexagonal distribution pattern in the polymer matrix.Then a full thickness meso-scale RUC model including weft yarns,warp yarns,Z-yarns and pure resin zones is established and full stiffness matrix of the 3DOWC including the in-plane and flexural constants are predicted.For thick 3DOWC with large number of weft,warp layers,an alternative analysis method is proposed in which an inner meso-RUC and a surface meso-RUC are established,respectively.Then the properties of 3DOWC are deduced based on laminate theory and properties of the inner and surface layers.The predicted results by the above two alternative methods are in good experimental agreement.展开更多
The Wigner-Seitz unit cell (rhombus) for a honeycomb lattice fails to establish a k-vector in the 2D space, which is required for the Bloch electron dynamics. Phonon motion cannot be discussed in the triangular coordi...The Wigner-Seitz unit cell (rhombus) for a honeycomb lattice fails to establish a k-vector in the 2D space, which is required for the Bloch electron dynamics. Phonon motion cannot be discussed in the triangular coordinates, either. In this paper, we propose a rectangular 4-atom unit cell model, which allows us to discuss the electron and phonon (wave packets) motion in the k-space. The present paper discusses the band structure of graphene based on the rectangular 4-atom unit cell model to establish an appropriate k-vector for the Bloch electron dynamics. To obtain the band energy of a Bloch electron in graphene, we extend the tight-binding calculations for the Wigner-Seitz (2-atom unit cell) model of Reich et al. (Physical Review B, 66, Article ID: 035412 (2002)) to the rectangular 4-atom unit cell model. It is shown that the graphene band structure based on the rectangular 4-atom unit cell model reveals the same band structure of the graphene based on the Wigner-Seitz 2-atom unit cell model;the π-band energy holds a linear dispersion (ε−k ) relations near the Fermi energy (crossing points of the valence and the conduction bands) in the first Brillouin zone of the rectangular reciprocal lattice. We then confirm the suitability of the proposed rectangular (orthogonal) unit cell model for graphene in order to establish a 2D k-vector responsible for the Bloch electron (wave packet) dynamics in graphene.展开更多
In order to improve the performance degradation prediction accuracy of proton exchange membrane fuel cell(PEMFC),a fusion prediction method(CKDG)based on adaptive noise complete ensemble empirical mode decomposition(C...In order to improve the performance degradation prediction accuracy of proton exchange membrane fuel cell(PEMFC),a fusion prediction method(CKDG)based on adaptive noise complete ensemble empirical mode decomposition(CEEMDAN),kernel principal component analysis(KPCA)and dual attention mechanism gated recurrent unit neural network(DA-GRU)was proposed.CEEMDAN and KPCA were used to extract the input feature data sequence,reduce the influence of random factors,and capture essential feature components to reduce the model complexity.The DA-GRU network helps to learn the feature mapping relationship of data in long time series and predict the changing trend of performance degradation data more accurately.The actual aging experimental data verify the performance of the CKDG method.The results show that under the steady-state condition of 20%training data prediction,the CKDA method can reduce the root mean square error(RMSE)by 52.7%and 34.6%,respectively,compared with the traditional LSTM and GRU neural networks.Compared with the simple DA-GRU network,RMSE is reduced by 15%,and the degree of over-fitting is reduced,which has higher accuracy.It also shows excellent prediction performance under the dynamic condition data set and has good universality.展开更多
As an advanced composite material, the 3D braided composite has received more and more attention in foreign countries. However, it has received less attention in China. The geometric unit cell which can describe the b...As an advanced composite material, the 3D braided composite has received more and more attention in foreign countries. However, it has received less attention in China. The geometric unit cell which can describe the basic structure and the relationship between the braiding angle and geometric parameters of the fabric and fiber volume ratio are given in this paper based on two 3D braiding processes, namely, the four-step and the twostep ones. Several existing mechanical models to predict groperties of the 3D braided comPOsites are discussed and their shortcomings are pointed out herein. Then a new model called the inclined laminal combination model is proposed, which is based on the classical laminated plate theory and can predict the basic mechanical behavior of the two 3D braided composites with four-step or two-step braid. In the model, each yarn in the unit cell is regarded as an inclined laminate and then a 3D analysis is performed. It is found that the predicted mechanical properties of the 3D braided composites by the proposed model are compared well with the experimental data.展开更多
The front-row shading reduction coefficient is a key parameter used to calculate the system efficiency of a photovoltaic(PV)power station.Based on the Hay anisotropic sky scattering model,the variation rule of solar r...The front-row shading reduction coefficient is a key parameter used to calculate the system efficiency of a photovoltaic(PV)power station.Based on the Hay anisotropic sky scattering model,the variation rule of solar radiation intensity on the surface of the PV array during the shaded period is simulated,combined with the voltage-current characteristics of the PV modules,and the shadow occlusion operating mode of the PV array is modeled.A method for calculating the loss coefficient of front shadow occlusion based on the division of the PV cell string unit and Hay anisotropic sky scattering model is proposed.This algorithm can accurately evaluate the degree of influence of the PV array layout,wiring mode,array spacing,PV module specifications,and solar radiation on PV power station system efficiency.It provides a basis for optimizing the PV array layout,reducing system loss,and improving PV system efficiency.展开更多
The 7XXX aluminum alloys having a microstructure with precipitate free zones (PFZ) nearby the grain boundary, have received a great deal of attention due to their high strength, light mass, and yet poor fracture tough...The 7XXX aluminum alloys having a microstructure with precipitate free zones (PFZ) nearby the grain boundary, have received a great deal of attention due to their high strength, light mass, and yet poor fracture toughness. Experimental investigation into the effect of microstructure on the ductility was well established and comprehensive in the literature. A micromechanical model using a unit cell including some voids and relevant microstructural features was created. The competition between intergranular and intragranular fracture was investigated by comparing the void growth velocity between PFZ and matrix. The effects of void aspect ratio, relative PFZ volume, orientation of PFZ on the ductility of 7XXX aluminum alloys were analyzed. The results show that the model can explain the effect of microstructure on the competition between intergranular and intragranular fracture.展开更多
The aim of the paper is to discover the general creep mechanisms for the short fiber reinforcement matrix composites (MMCs) under uniaxial stress states and to build a relationship between the macroscopic steady creep...The aim of the paper is to discover the general creep mechanisms for the short fiber reinforcement matrix composites (MMCs) under uniaxial stress states and to build a relationship between the macroscopic steady creep behavior and the material micro geometric parameters. The unit cell models were used to calculate the macroscopic creep behavior with different micro geometric parameters of fibers on different loading directions. The influence of the geometric parameters of the fibers and loading directions on the macroscopic creep behavior had been obtained, and described quantitatively. The matrix/fiber interface had been considered by a third layer, matrix/fiber interlayer, in the unit cells with different creep properties and thickness. Based on the numerical results of the unit cell models, a statistic model had been presented for the plane randomly-distributed-fiber MMCs. The fiber breakage had been taken into account in the statistic model for it starts experimentally early in the creep life. With the distribution of the geometric parameters of the fibers, the results of the statistic model agree well with the experiments. With the statistic model, the influence of the geometric parameters and the breakage of the fibers as well as the properties and thickness of, the interlayer on the macroscopic steady creep rate have been discussed.展开更多
AIM： To examine the human hepatic parenchymal and stromal components in rat liver and the phenotypic changes of human cells in liver of human-rat chimera （HRC） generated by in utero transplantation of human cells d...AIM： To examine the human hepatic parenchymal and stromal components in rat liver and the phenotypic changes of human cells in liver of human-rat chimera （HRC） generated by in utero transplantation of human cells during partial hepatectomy （PHx）-induced liver regeneration. METHODS： Human hepatic parenchymal and stromal components and phenotypic changes of human cells during liver regeneration were examined by flow oytometry, in situ hybridization and immunohistochemistry. RESULTS： ISH analysis positive cells in hepatic demonstrated human Aluparenchyma and stroma of recipient liver. Functional human hepatocytes generated in this model potentially constituted human hepatic functional units with the presence of donor-derived human endothelial and biliary duct cells in host liver. Alpha fetoprotein （AFP）^＋, CD34^＋ and CD45^＋ cells were observed in the chimeric liver on day 10 after PHxinduced liver regeneration and then disappeared in PHx group, but not in non-PHx group, suggesting that dynamic phenotypic changes of human cells expressing AFP, CD34 and CD45 cells may occur during the chimeric liver regeneration. Additionally, immunostaining for human proliferating cell nuclear antigen （PCNA） showed that the number of PCNA-positive cells in the chimeric liver of PHx group was markedly increased, as compared to that of control group, indicating that donor-derived human cells are actively proliferated during PHx-induced regeneration of HRC liver. CONCLUSION： HRC liver provides a tool for investigating human liver regeneration in a humanized animal model.展开更多
基金Funded in part by China Postdoctoral Science Foundation(No.2013M541574)Hi-tech Research and Development Program of China(No.2012AA040209)
文摘A new method to predict the ultimate strength of fiber reinforced composites under arbitrary load condition is introduced. The micromechanics strength theory is used to perform the final failure prediction of composite laminates. The theory is based on unit cell analytic model which can provide the ply composite material properties by only using the constituent fiber and matrix properties and the laminate geometric parameters without knowing any experimental information of the laminates. To show that this method is suitable for predicting the strength of composite laminates, the micromechanics strength theory is ranked by comparing it with all the micro-level and the best two macro-level theories chosen from the World Wide Failure Exercise. The results show that this method can be used for predicting strength of any composite laminates and provide a direct reference for composite optimum design.
基金BASTRI Subtopic Research about Digital Sampler Technology of Body Structure Performance Study Based on Big Data Calculation Model,China(No.MIIT Civil aircraft special purpose MJ-2017-F-20)
文摘This presentation predicts the elastic properties of three-dimensional(3D)orthogonal woven composite(3DOWC)by finite element analysis based on micro/meso repeated unit cell(RUC)models.First,the properties of fiber yarn are obtained by analysis on a micro-scale RUC model assuming fibers in a hexagonal distribution pattern in the polymer matrix.Then a full thickness meso-scale RUC model including weft yarns,warp yarns,Z-yarns and pure resin zones is established and full stiffness matrix of the 3DOWC including the in-plane and flexural constants are predicted.For thick 3DOWC with large number of weft,warp layers,an alternative analysis method is proposed in which an inner meso-RUC and a surface meso-RUC are established,respectively.Then the properties of 3DOWC are deduced based on laminate theory and properties of the inner and surface layers.The predicted results by the above two alternative methods are in good experimental agreement.
文摘The Wigner-Seitz unit cell (rhombus) for a honeycomb lattice fails to establish a k-vector in the 2D space, which is required for the Bloch electron dynamics. Phonon motion cannot be discussed in the triangular coordinates, either. In this paper, we propose a rectangular 4-atom unit cell model, which allows us to discuss the electron and phonon (wave packets) motion in the k-space. The present paper discusses the band structure of graphene based on the rectangular 4-atom unit cell model to establish an appropriate k-vector for the Bloch electron dynamics. To obtain the band energy of a Bloch electron in graphene, we extend the tight-binding calculations for the Wigner-Seitz (2-atom unit cell) model of Reich et al. (Physical Review B, 66, Article ID: 035412 (2002)) to the rectangular 4-atom unit cell model. It is shown that the graphene band structure based on the rectangular 4-atom unit cell model reveals the same band structure of the graphene based on the Wigner-Seitz 2-atom unit cell model;the π-band energy holds a linear dispersion (ε−k ) relations near the Fermi energy (crossing points of the valence and the conduction bands) in the first Brillouin zone of the rectangular reciprocal lattice. We then confirm the suitability of the proposed rectangular (orthogonal) unit cell model for graphene in order to establish a 2D k-vector responsible for the Bloch electron (wave packet) dynamics in graphene.
基金funded by Shaanxi Province Key Industrial Chain Project(2023-ZDLGY-24)Industrialization Project of Shaanxi Provincial Education Department(21JC018)+1 种基金Shaanxi Province Key Research and Development Program(2021ZDLGY13-02)the Open Foundation of State Key Laboratory for Advanced Metals and Materials(2022-Z01).
文摘In order to improve the performance degradation prediction accuracy of proton exchange membrane fuel cell(PEMFC),a fusion prediction method(CKDG)based on adaptive noise complete ensemble empirical mode decomposition(CEEMDAN),kernel principal component analysis(KPCA)and dual attention mechanism gated recurrent unit neural network(DA-GRU)was proposed.CEEMDAN and KPCA were used to extract the input feature data sequence,reduce the influence of random factors,and capture essential feature components to reduce the model complexity.The DA-GRU network helps to learn the feature mapping relationship of data in long time series and predict the changing trend of performance degradation data more accurately.The actual aging experimental data verify the performance of the CKDG method.The results show that under the steady-state condition of 20%training data prediction,the CKDA method can reduce the root mean square error(RMSE)by 52.7%and 34.6%,respectively,compared with the traditional LSTM and GRU neural networks.Compared with the simple DA-GRU network,RMSE is reduced by 15%,and the degree of over-fitting is reduced,which has higher accuracy.It also shows excellent prediction performance under the dynamic condition data set and has good universality.
文摘As an advanced composite material, the 3D braided composite has received more and more attention in foreign countries. However, it has received less attention in China. The geometric unit cell which can describe the basic structure and the relationship between the braiding angle and geometric parameters of the fabric and fiber volume ratio are given in this paper based on two 3D braiding processes, namely, the four-step and the twostep ones. Several existing mechanical models to predict groperties of the 3D braided comPOsites are discussed and their shortcomings are pointed out herein. Then a new model called the inclined laminal combination model is proposed, which is based on the classical laminated plate theory and can predict the basic mechanical behavior of the two 3D braided composites with four-step or two-step braid. In the model, each yarn in the unit cell is regarded as an inclined laminate and then a 3D analysis is performed. It is found that the predicted mechanical properties of the 3D braided composites by the proposed model are compared well with the experimental data.
基金This work was supported by the Global Energy Interconnection Group Limited Science&Technology Project(Project No.:SGGEIG00JYJS1900046).
文摘The front-row shading reduction coefficient is a key parameter used to calculate the system efficiency of a photovoltaic(PV)power station.Based on the Hay anisotropic sky scattering model,the variation rule of solar radiation intensity on the surface of the PV array during the shaded period is simulated,combined with the voltage-current characteristics of the PV modules,and the shadow occlusion operating mode of the PV array is modeled.A method for calculating the loss coefficient of front shadow occlusion based on the division of the PV cell string unit and Hay anisotropic sky scattering model is proposed.This algorithm can accurately evaluate the degree of influence of the PV array layout,wiring mode,array spacing,PV module specifications,and solar radiation on PV power station system efficiency.It provides a basis for optimizing the PV array layout,reducing system loss,and improving PV system efficiency.
基金Project(2005CB623706) supported by the National Basic Research Program of China
文摘The 7XXX aluminum alloys having a microstructure with precipitate free zones (PFZ) nearby the grain boundary, have received a great deal of attention due to their high strength, light mass, and yet poor fracture toughness. Experimental investigation into the effect of microstructure on the ductility was well established and comprehensive in the literature. A micromechanical model using a unit cell including some voids and relevant microstructural features was created. The competition between intergranular and intragranular fracture was investigated by comparing the void growth velocity between PFZ and matrix. The effects of void aspect ratio, relative PFZ volume, orientation of PFZ on the ductility of 7XXX aluminum alloys were analyzed. The results show that the model can explain the effect of microstructure on the competition between intergranular and intragranular fracture.
文摘The aim of the paper is to discover the general creep mechanisms for the short fiber reinforcement matrix composites (MMCs) under uniaxial stress states and to build a relationship between the macroscopic steady creep behavior and the material micro geometric parameters. The unit cell models were used to calculate the macroscopic creep behavior with different micro geometric parameters of fibers on different loading directions. The influence of the geometric parameters of the fibers and loading directions on the macroscopic creep behavior had been obtained, and described quantitatively. The matrix/fiber interface had been considered by a third layer, matrix/fiber interlayer, in the unit cells with different creep properties and thickness. Based on the numerical results of the unit cell models, a statistic model had been presented for the plane randomly-distributed-fiber MMCs. The fiber breakage had been taken into account in the statistic model for it starts experimentally early in the creep life. With the distribution of the geometric parameters of the fibers, the results of the statistic model agree well with the experiments. With the statistic model, the influence of the geometric parameters and the breakage of the fibers as well as the properties and thickness of, the interlayer on the macroscopic steady creep rate have been discussed.
基金Supported by The National Natural Science Foundation of China, No. 30271177 and No. 39870676the Major Scienceand Technology Projects of Guangdong Province, No. B602+4 种基金the Natural Science Foundation of Guangdong Province, No.021903the Science and Technology Planning Project of Guangdong Province, No. 2009B060300008the Science and Technology Projects of Guangzhou City, No. 2002Z2E0121the Medical Scientific Research Foundation of Guangdong Province, No. A2007359the Science and Technology Talented Man Foundation of Outstanding Young and Middle-aged People of Southern Medical University,the Special Fund of Scientific Instrument Collaborative Share-net in Guangzhou, No. 2006176
文摘AIM： To examine the human hepatic parenchymal and stromal components in rat liver and the phenotypic changes of human cells in liver of human-rat chimera （HRC） generated by in utero transplantation of human cells during partial hepatectomy （PHx）-induced liver regeneration. METHODS： Human hepatic parenchymal and stromal components and phenotypic changes of human cells during liver regeneration were examined by flow oytometry, in situ hybridization and immunohistochemistry. RESULTS： ISH analysis positive cells in hepatic demonstrated human Aluparenchyma and stroma of recipient liver. Functional human hepatocytes generated in this model potentially constituted human hepatic functional units with the presence of donor-derived human endothelial and biliary duct cells in host liver. Alpha fetoprotein （AFP）^＋, CD34^＋ and CD45^＋ cells were observed in the chimeric liver on day 10 after PHxinduced liver regeneration and then disappeared in PHx group, but not in non-PHx group, suggesting that dynamic phenotypic changes of human cells expressing AFP, CD34 and CD45 cells may occur during the chimeric liver regeneration. Additionally, immunostaining for human proliferating cell nuclear antigen （PCNA） showed that the number of PCNA-positive cells in the chimeric liver of PHx group was markedly increased, as compared to that of control group, indicating that donor-derived human cells are actively proliferated during PHx-induced regeneration of HRC liver. CONCLUSION： HRC liver provides a tool for investigating human liver regeneration in a humanized animal model.
