This paper examines the longitudinal tensile behavior and failure mechanism of a new unidirectional carbon fiber reinforced aluminum composite through experiments and simulations.A Weibull distribution model was estab...This paper examines the longitudinal tensile behavior and failure mechanism of a new unidirectional carbon fiber reinforced aluminum composite through experiments and simulations.A Weibull distribution model was established to describe the fiber strength dispersion based on single-fiber tensile tests for carbon fibers extracted from the composite.The constitutive models for the matrix and interface were established based on the uniaxial tensile and single-fiber push-out tests,respectively.Then,a 3D micromechanical numerical model,innovatively considering the fiber strength dispersion by use of the weakest link and Weibull distribution theories,was estab-lished to simulate the progressive failure behavior of the composite under longitudinal tension.Due to the dispersion of fiber strength,the weakest link of the fiber first fractures,and stress concentra-tion occurs in the surrounding fibers,interfaces,and matrix.The maximum stress concentration fac-tor for neighboring fibers varies nonlinearly with the distance from the fractured fiber.Both isolated and clustered fractured fibers are present during the progressive failure process of the composite.The expansion of fractured fiber clusters intensifies stress concentration and material degradation which in turn enlarges the fractured fiber clusters,and their mutual action leads to the final collapse of the composite.展开更多
A framework is presented to quantify the objective-level resilience of reinforced concrete liners of circular tunnels when exposed to enclosed vehicle fire hazards.By assessing the loss of functionality due to fire-in...A framework is presented to quantify the objective-level resilience of reinforced concrete liners of circular tunnels when exposed to enclosed vehicle fire hazards.By assessing the loss of functionality due to fire-induced damage,the framework enables a decision-basis evaluation of the efficiency of various fire mitigation methods for spe-cific tunnel conditions.In this study,the fire-induced damage of concrete tunnel liners due to strength loss and spalling is stochastically simulated and classified based on typical post-fire repair procedures and damage evalu-ation.The resilience assessment is conducted using Monte Carlo Simulation in combination with a fast-running tool for calculating the thermal impact from vehicle fires on the inside surface of the tunnel liner(developed by the authors in previous work).The proposed approach accounts for uncertainties associated with both the vehicle fire(particularly the combustion energy)and the tunnel conditions(i.e.,geometry,dimensions,and the presence of longitudinal ventilation and/or fixed fire-fighting systems(FFFS)).A parametric case study is used to quantitatively demonstrate the effectiveness of FFFS for reducing post-fire losses of tunnel functionality.Other parameters such as tunnel dimensions,traffic restrictions for vehicles with heavy fire hazard risk,and installation or upgrade of the tunnel ventilation system show somewhat less effectiveness for reducing fire-induced damage.展开更多
The intestinal wall is considered as a highly composite heterogeneous tissue characterized by a strong nonlinear stress-strain passive response with an exponential stiffening effect at higher deformations.The conventi...The intestinal wall is considered as a highly composite heterogeneous tissue characterized by a strong nonlinear stress-strain passive response with an exponential stiffening effect at higher deformations.The conventional theory of fiber-reinforced elastic solids allows one to describe the anisotropic strain energy as a function of the pseudo-invariants arising from the coupling of the elastic deformation and the direction of fiber reinforcement.In this paper,a multi-layer finite element model of the intestine walls is developed,based on an anisotropic hyperelastic theory of the layered structure,in which each layer may be considered as a composite reinforced by two families of fibers that are arranged in symmetrical spirals.A potential is proposed to model the intestine walls as a fiber-reinforced composite consisting of two directions of muscle-fiber reinforcement and a cross-ply collagen arrangement.Moreover,finite element simulations of a specimen cut from the intestinal walls were carried out by using the same form of strain-energy function,described by a well-known Gasser-Ogden-Holzapfel(GOH)model,for each layer.The model parameters were optimized by fitting the model to the experimental stress-stretch responses in both longitudinal and circumferential directions.In order to verify the proposed model,finite element analyses were carried out to investigate the distributions of equivalent stress in the intestine after the complete deployment of capsule robot legs.展开更多
Caching and sharing the content files are critical and fundamental for various future vehicular applications.However,how to satisfy the content demands in a timely manner with limited storage is an open issue owing to...Caching and sharing the content files are critical and fundamental for various future vehicular applications.However,how to satisfy the content demands in a timely manner with limited storage is an open issue owing to the high mobility of vehicles and the unpredictable distribution of dynamic requests.To better serve the requests from the vehicles,a cache-enabled multi-layer architecture,consisting of a Micro Base Station(MBS)and several Small Base Stations(SBSs),is proposed in this paper.Considering that vehicles usually travel through the coverage of multiple SBSs in a short time period,the cooperative caching and sharing strategy is introduced,which can provide comprehensive and stable cache services to vehicles.In addition,since the content popularity profile is unknown,we model the content caching problems in a Multi-Armed Bandit(MAB)perspective to minimize the total delay while gradually estimating the popularity of content files.The reinforcement learning-based algorithms with a novel Q-value updating module are employed to update the caching files in different timescales for MBS and SBSs,respectively.Simulation results show the proposed algorithm outperforms benchmark algorithms with static or varying content popularity.In the highspeed environment,the cooperation between SBSs effectively improves the cache hit rate and further improves service performance.展开更多
基金the National Natural Science Foundation of China(No.52165018)the Jiangxi Key Laboratory of Forming and Joining Technology for Aerospace Component,China(No.EL202303270)the Jiangxi Provincial Department of Science and Technology,China(No.20225BCJ22002)
文摘This paper examines the longitudinal tensile behavior and failure mechanism of a new unidirectional carbon fiber reinforced aluminum composite through experiments and simulations.A Weibull distribution model was established to describe the fiber strength dispersion based on single-fiber tensile tests for carbon fibers extracted from the composite.The constitutive models for the matrix and interface were established based on the uniaxial tensile and single-fiber push-out tests,respectively.Then,a 3D micromechanical numerical model,innovatively considering the fiber strength dispersion by use of the weakest link and Weibull distribution theories,was estab-lished to simulate the progressive failure behavior of the composite under longitudinal tension.Due to the dispersion of fiber strength,the weakest link of the fiber first fractures,and stress concentra-tion occurs in the surrounding fibers,interfaces,and matrix.The maximum stress concentration fac-tor for neighboring fibers varies nonlinearly with the distance from the fractured fiber.Both isolated and clustered fractured fibers are present during the progressive failure process of the composite.The expansion of fractured fiber clusters intensifies stress concentration and material degradation which in turn enlarges the fractured fiber clusters,and their mutual action leads to the final collapse of the composite.
基金Financial support for this project has been provided by the U.S.De-partment of Transportation(Grant#69A3551747118)via the Univer-sity Transportation Center for Underground Transportation Infrastruc-ture(UTC-UTI)at the Colorado School of Mines(CSM).
文摘A framework is presented to quantify the objective-level resilience of reinforced concrete liners of circular tunnels when exposed to enclosed vehicle fire hazards.By assessing the loss of functionality due to fire-induced damage,the framework enables a decision-basis evaluation of the efficiency of various fire mitigation methods for spe-cific tunnel conditions.In this study,the fire-induced damage of concrete tunnel liners due to strength loss and spalling is stochastically simulated and classified based on typical post-fire repair procedures and damage evalu-ation.The resilience assessment is conducted using Monte Carlo Simulation in combination with a fast-running tool for calculating the thermal impact from vehicle fires on the inside surface of the tunnel liner(developed by the authors in previous work).The proposed approach accounts for uncertainties associated with both the vehicle fire(particularly the combustion energy)and the tunnel conditions(i.e.,geometry,dimensions,and the presence of longitudinal ventilation and/or fixed fire-fighting systems(FFFS)).A parametric case study is used to quantitatively demonstrate the effectiveness of FFFS for reducing post-fire losses of tunnel functionality.Other parameters such as tunnel dimensions,traffic restrictions for vehicles with heavy fire hazard risk,and installation or upgrade of the tunnel ventilation system show somewhat less effectiveness for reducing fire-induced damage.
文摘The intestinal wall is considered as a highly composite heterogeneous tissue characterized by a strong nonlinear stress-strain passive response with an exponential stiffening effect at higher deformations.The conventional theory of fiber-reinforced elastic solids allows one to describe the anisotropic strain energy as a function of the pseudo-invariants arising from the coupling of the elastic deformation and the direction of fiber reinforcement.In this paper,a multi-layer finite element model of the intestine walls is developed,based on an anisotropic hyperelastic theory of the layered structure,in which each layer may be considered as a composite reinforced by two families of fibers that are arranged in symmetrical spirals.A potential is proposed to model the intestine walls as a fiber-reinforced composite consisting of two directions of muscle-fiber reinforcement and a cross-ply collagen arrangement.Moreover,finite element simulations of a specimen cut from the intestinal walls were carried out by using the same form of strain-energy function,described by a well-known Gasser-Ogden-Holzapfel(GOH)model,for each layer.The model parameters were optimized by fitting the model to the experimental stress-stretch responses in both longitudinal and circumferential directions.In order to verify the proposed model,finite element analyses were carried out to investigate the distributions of equivalent stress in the intestine after the complete deployment of capsule robot legs.
基金supported in part by the Natural Science Foundation of China(62002138)the Open Research Project of the State Key Laboratory of Industrial Control Technology,Zhejiang University,China(ICT2022B26).
文摘Caching and sharing the content files are critical and fundamental for various future vehicular applications.However,how to satisfy the content demands in a timely manner with limited storage is an open issue owing to the high mobility of vehicles and the unpredictable distribution of dynamic requests.To better serve the requests from the vehicles,a cache-enabled multi-layer architecture,consisting of a Micro Base Station(MBS)and several Small Base Stations(SBSs),is proposed in this paper.Considering that vehicles usually travel through the coverage of multiple SBSs in a short time period,the cooperative caching and sharing strategy is introduced,which can provide comprehensive and stable cache services to vehicles.In addition,since the content popularity profile is unknown,we model the content caching problems in a Multi-Armed Bandit(MAB)perspective to minimize the total delay while gradually estimating the popularity of content files.The reinforcement learning-based algorithms with a novel Q-value updating module are employed to update the caching files in different timescales for MBS and SBSs,respectively.Simulation results show the proposed algorithm outperforms benchmark algorithms with static or varying content popularity.In the highspeed environment,the cooperation between SBSs effectively improves the cache hit rate and further improves service performance.
