Grouted rock bolts subject to axial loading in the field exhibit various failure modes,among which the most predominant one is the bolt-grout interface failure.Thus,mechanical characterization of the grout is essentia...Grouted rock bolts subject to axial loading in the field exhibit various failure modes,among which the most predominant one is the bolt-grout interface failure.Thus,mechanical characterization of the grout is essential for understanding its performance in ground support.To date,few studies have been conducted to characterize the mechanical behaviour of fiber-reinforced grout(FRG)in rock bolt reinforcement.Here we experimentally studied the mechanical behaviour of FRG under uniaxial compression,indirect tension,and direct shear loading conditions.We also conducted a series of pullout tests of rebar bolt encapsulated with different grouts including conventional cementitious grout and FRG.FRG was developed using 15%silica fume(SF)replacement of cement(by weight)and steel fiber to achieve highstrength and crack-resistance to overcome drawbacks of the conventional grout.Two types of steel fibers including straight and wavy steel fibers were further added to enhance the grout quality.The effect of fiber shape and fiber volume proportion on the grout mechanical properties were examined.Our experimental results showed that the addition of SF and steel fiber by 1.5%fiber volume proportion could lead to the highest compressive,tensile,and shear strengths of the grout.The minimum volume of fiber that could improve the mechanical properties of grout was found at 0.5%.The scanning electron microscopy(SEM)analysis demonstrated that steel fibers act as an excellent bridge to prevent the cracks from propagating at the interfacial region and hence to aid in maintaining the integrity of the cementitious grout.Our laboratory pullout tests further confirmed that FRG could prevent the cylindrical grout annulus from radial crack and hence improve the rebar’s load carrying capacity.Therefore,FRG has a potential to be utilized in civil and mining applications where high-strength and crack-resistance support is required.展开更多
Five types of polyurea elastomers were synthesized by changing the isocyanate component and the mechanical properties of polyurea materials were measured. Fiber-reinforced cement boards(FRCB)strengthened by polyurea w...Five types of polyurea elastomers were synthesized by changing the isocyanate component and the mechanical properties of polyurea materials were measured. Fiber-reinforced cement boards(FRCB)strengthened by polyurea with different formulations were processed, and a series of experiments were carried out on the specimens with gas explosion devices. The results showed that the conventional mechanical properties of different types of polyureas had their own advantages. Based on the gas explosion overpressure criterion, the blast resistances of reinforced plates were quantitatively evaluated,and the best polyurea was selected to guide the formulation design. The three typical failure modes of polyurea-reinforced FRCBs were flexural, shear, and flexural-shear failure. Dynamic thermodynamics and shock wave spectral analysis revealed that the polyurea did not undergo a glass transition in the gas explosion tests but retained its elastic properties, allowing it to effectively wrap the fragments formed by the brittle substrates.展开更多
A new degradation function of the friction coefficient is used.Basedon the double shear-lag model and Paris formula,the interracial damage of coated-fiber-reinforced composites under tension-tension cyclic loading is ...A new degradation function of the friction coefficient is used.Basedon the double shear-lag model and Paris formula,the interracial damage of coated-fiber-reinforced composites under tension-tension cyclic loading is studied.The effectsof strength and thickness of the coating materials on the debond stress,debond rateas well as debond length are simulated.展开更多
To understand the enhancing effect and fiber-reinforced mechanism of composite fibers reinforced cement concrete, the influences of composite fibers on micro-cracks and the distribution of composite fibers were evalua...To understand the enhancing effect and fiber-reinforced mechanism of composite fibers reinforced cement concrete, the influences of composite fibers on micro-cracks and the distribution of composite fibers were evaluated by optical electron micrometer(OEM) and scanning electron microscope(SEM). Three kinds of fiber, such as polyacrylonitrile-based carbon fiber, basalt fiber, and glass fiber, were used in the composite fibers reinforced cement concrete. The composite fibers could form a stable structure in concrete after the liquid-phase coupling treatment, gas-liquid double-effect treatment, and inert atmosphere drying. The mechanical properties of composite fibers reinforced concrete(CFRC) were studied by universal test machine(UTM). Moreover, the effect of composite fibers on concrete was analyzed based on the toughness index and residual strength index. The results demonstrated that the composite fibers could improve the mechanical properties of concrete, while the excessive amount of composite fibers had an adverse effect on the mechanical properties of concrete. The composite fibers could significantly improve the toughness index of CFRC, and the increment rate is more than 30%. The composite fibers could form a mesh structure, which could promote the stability of concrete and guarantee the excellent mechanical properties.展开更多
The aim of this study is to present a constitutive model for prediction of the mechanical behavior of fiberreinforced cemented sand. For this purpose, a generalized plasticity constitutive model of sandy soil is selec...The aim of this study is to present a constitutive model for prediction of the mechanical behavior of fiberreinforced cemented sand. For this purpose, a generalized plasticity constitutive model of sandy soil is selected and the parameters of the model are determined for three types of sandy soils using the results of triaxial tests. Next, the proposed model is developed using the existing models based on the physicomechanical characteristics of fiber-reinforced cemented sand. The elastic parameters, flow rule and hardening law of the base model are modified for fiber-reinforced cemented sand. To verify the proposed model, the predicted results are compared with those of triaxial tests performed on fiber-reinforced cemented sand. Finally, the efficiency of the proposed model is studied at different confining pressures, and cement and fiber contents.展开更多
A combination of experimental measurements and numerical analysis was utilized to study the low-velocity impact damage of domestic carbon fiber-reinforced composites(CFRCs).The results indicated that the low-velocity ...A combination of experimental measurements and numerical analysis was utilized to study the low-velocity impact damage of domestic carbon fiber-reinforced composites(CFRCs).The results indicated that the low-velocity impact damage induced pits and longitudinal cracks on the front side,oblique cracks and delaminationin on the back side.The pit depth increased with the increasing impact energy.It was demonstrated that the numerical analysis strain history curve was similar to the experimentally measured strain history curve,which verified the accuracy of numerical analysis in which the Hashin failure criterion was used.The work provides basic data and theoretical basis for the promotion and application of the domestic carbon fiber,and demonstrates the feasibility of replacing imported carbon fibers with domestic carbon fibers.展开更多
In order to improve the properties of silica sol shell for investment casting process, various contents of cattail fibers were added into the slurry to prepare a fiber-reinforced shell in the present study. The bendin...In order to improve the properties of silica sol shell for investment casting process, various contents of cattail fibers were added into the slurry to prepare a fiber-reinforced shell in the present study. The bending strength of fiber-reinforced shell was investigated and the fracture surfaces of shell specimens were observed using SEM. It is found that the bending strength increases with the increase of fiber content, and the bending strength of a green shell with 1.0 wt.% fiber addition increases by 44% compared to the fiber-free shell. The failure of specimens of the fiber-reinforced green shell results from fiber rupture and debonding between the interface of fibers and adhesive under the bending load. The micro-crack propagation in the matrix is inhibited by the micro-holes for ablation of f ibers in specimens of the f iber-reinforced shell during the stage of being fired. As a result, the bending strength of specimens of the fired shell had no significant drop. Particularly, the bending strength of specimens of the fired shell reinforced with 0.6wt.% fiber reached the maximum value of 4.6 MPa.展开更多
To meet the ever-increasing construction demands around the world during recent years,reinforcement and stabilization methods have been widely used by geotechnical engineers to improve the performances and behavior of...To meet the ever-increasing construction demands around the world during recent years,reinforcement and stabilization methods have been widely used by geotechnical engineers to improve the performances and behavior of fine-grained soils.Although lime stabilization increases the compressive strength of soils,it reduces the soil ductility at the same time.Recent research shows that random fiber inclusion modifies the brittleness of soils.In the current research,the effects of lime and polypropylene(PP)fiber additions on such characteristics as compressive and shear strengths,failure strain,secant modulus of elasticity(E50)and shear strength parameters of mixtures were investigated.Kaolinite was treated with 1%,3% and 5% lime by dry weight of soil and reinforced with 0.1% monovalent PP fibers with the length of 6 mm.Samples were prepared at optimum conditions and cured at 35℃ for 1 d,7 d and 28 d at 90% relative humidity and subsequently subjected to uniaxial and triaxial compression tests(UCT and TCT)under cell pressures of 25 kPa,50 kPa and 100 kPa.Results showed that inclusion of random PP fibers to clay-lime mixtures increases both compressive and shear strengths as well as the ductility.Lime content and curing period were found to be the most influential factors.Scanning electron microscopy(SEM)analysis showed that lime addition and the formation of cementitious compounds bind soil particles and increase soil/fiber interactions at interface,leading to enhanced shear strength.The more ductile the stabilized and reinforced composition,the less the cracks in roads and waste landfill covers.展开更多
An evaluation of existing strength of concrete columns confined with fiber-reinforced polymer( FRP) was presented with extensive collection of experimental data. According to the evaluation results, artificial neural ...An evaluation of existing strength of concrete columns confined with fiber-reinforced polymer( FRP) was presented with extensive collection of experimental data. According to the evaluation results, artificial neural networks( ANNs) model to predict the ultimate strength of FRP confined column with different shapes was proposed. The models had seven inputs including the column length,the tensile strength of the FRP in the hoop direction,the total thickness of FRP,the diameter of the concrete specimen,the elastic modulus of FRP,the corner radius and the concrete compressive strength. The compressive strength of the confined concrete was the output data. The results reveal that the proposed models have good prediction and generalization capacity with acceptable errors.展开更多
In order to investigate the synergistic effect of re-dispersible powder-ethylene-vinyl acetate copolymer(EVA) and polypropylene fiber on the crack resistance of concrete under thermal fatigue loading, the compressive ...In order to investigate the synergistic effect of re-dispersible powder-ethylene-vinyl acetate copolymer(EVA) and polypropylene fiber on the crack resistance of concrete under thermal fatigue loading, the compressive strength, ultimate tensile strength, ultimate tensile strain and tensile modulus of elasticity were tested. In addition, ultrasonic method and scanning electron microscope analysis were used to explain the microstructure mechanism. The results show that polypropylene fiberreinforced concrete presents a better performance on crack resistance than ordinary concrete, and the synergism of EVA and polypropylene fiber can improve the anti-cracking ability of concrete further.展开更多
In this study,a peridynamic fiber-reinforced concrete model is developed based on the bond-based peridynamic model with rotation effect(BBPDR).The fibers are modelled by a semi-discrete method and distributed with ran...In this study,a peridynamic fiber-reinforced concrete model is developed based on the bond-based peridynamic model with rotation effect(BBPDR).The fibers are modelled by a semi-discrete method and distributed with random locations and angles in the concrete specimen,since the fiber content is low,and its scale is smaller than the concrete matrix.The interactions between fibers and concrete matrix are investigated by the improvement of the bond’s strength and stiffness.Also,the frictional effect between the fibers and the concrete matrix is considered,which is divided into static friction and slip friction.To validate the proposed model,several examples are simulated,including the tensile test and the three-point bending beam test.And the numerical results of the proposed model are compared with the experiments and other numerical models.The comparisons show that the proposed model is capable of simulating the fracture behavior of the fiber-reinforced concrete.After adding the fibers,the tensile strength,bending strength,and toughness of the fiber-reinforced concrete specimens are improved.Besides,the fibers distribution has an impact on the crack path,especially in the three-point bending beam test.展开更多
In the seasonal permafrost region with loess distribution,the influence of freeze-thaw cycles on the engineering performance of reinforced loess must be paid attention to.Many studies have shown that the use of fiber ...In the seasonal permafrost region with loess distribution,the influence of freeze-thaw cycles on the engineering performance of reinforced loess must be paid attention to.Many studies have shown that the use of fiber materials can improve the engineering performance of soil and its ability to resist freeze-thaw cycles.At the same time,as eco-environmental protection has become the focus,which has been paid more and more attention to,it has become a trend to find new environmentally friendly improved materials that can replace traditional chemical additives.The purpose of this paper uses new environmental-friendly improved materials to reinforce the engineering performance of loess,improve the ability of loess to resist freeze-thaw cycles,and reduce the negative impact on the ecological environment.To reinforce the engineering performance of loess and improve its ability to resist freeze-thaw cycles,lignin fiber is used as a reinforcing material.Through a series of laboratory tests,the unconfined compressive strength(UCS)of lignin fiber-reinforced loess under different freeze-thaw cycles was studied.The effects of lignin fiber content and freeze-thaw cycles on the strength and deformation modulus of loess were analyzed.Combined with the microstructure features,the change mechanism of lignin fiber-reinforced loess strength under freeze-thaw cycles was discussed.The results show that lignin fiber can improve the UCS of loess under freeze-thaw cycles,but the strengthening effect no longer increases with the increase of fiber content.When the fiber content is less than 1%,the UCS growth rate of loess is the fastest under freeze-thaw cycles.And the UCS of loess with 1%fiber content is the most stable under freeze-thaw cycles.The freeze-thaw cycles increase the deformation modulus of loess with 1%fiber content,and its ability to resist deformation is obviously better than loess with 1.5%,2%and 3%fiber content.The fiber content over 1%will weaken the strengthening effect of lignin fiber-reinforced loess,and the optimum fiber content of lignin fiber-reinforced loess under freeze-thaw cycles is 1%.展开更多
Silver-based alloys are significant light-load electrical contact materials(ECMs).The trade-off between mechanical properties and electrical conductivity is always an important issue for the development of silver-base...Silver-based alloys are significant light-load electrical contact materials(ECMs).The trade-off between mechanical properties and electrical conductivity is always an important issue for the development of silver-based ECMs.In this paper,we proposed an idea for the regulation of the mechanical properties and the electrical conductivity of Ag-11.40Cu-0.66Ni-0.05Ce(wt%)alloy using in-situ composite fiber-reinforcement.The alloy was processed using rolling,heat treatment,and heavy drawing,the strength and electrical conductivity were tested at different deformation stages,and the microstructures during deformation were observed using field emission scanning electron microscope(FESEM),transmission electron microscope(TEM)and electron backscatter diffraction(EBSD).The results show that the method proposed in this paper can achieve the preparation of in-situ composite fiber-reinforced Ag-Cu-Ni-Ce alloys.After the heavy deformation drawing,the room temperature Vickers hardness of the as-cast alloy increased from HV 81.6 to HV 169.3,and the electrical conductivity improved from 74.3%IACS(IACS,i.e.,international annealed copper standard)to 78.6%IACS.As the deformation increases,the alloy strength displays two different strengthening mechanisms,and the electrical conductivity has three stages of change.This research provides a new idea for the comprehensive performance control of high-performance silver-based ECMs.展开更多
Articular cartilage is a layer of low-friction,load-bearing soft hydrated tissue covering bone-ends in diarthrosis,which plays an important role in spreading the load,reducing the joint contact stress,joint friction a...Articular cartilage is a layer of low-friction,load-bearing soft hydrated tissue covering bone-ends in diarthrosis,which plays an important role in spreading the load,reducing the joint contact stress,joint friction and wear during exercise.The vital mechanical function展开更多
Sizing treatment has shown great potential in improving the interfacial properties of poly(p-phenylene benzodioxazole)(PBO)fiber-reinforced composites,but is severely limited due to the use of flammable and explosive ...Sizing treatment has shown great potential in improving the interfacial properties of poly(p-phenylene benzodioxazole)(PBO)fiber-reinforced composites,but is severely limited due to the use of flammable and explosive organic solvents.Herein,a new high-efficiency waterborne sizing agent has been developed by using functionalized carbon nanospheres(CNSs)as a nano-reinforcement.Due to abundant oxygen-containing groups,the CNSs greatly improves the surface activity,wettability,and roughness of the PBO fibers.As a result,the interfacial shear strength of the CNSs sized fiber-reinforced composite increases by 79.6%compared with that of the pristine fiber-reinforced composite.Moreover,the excellent mechanical and thermal properties of the PBO fibers remain almost unchanged after sizing treatment.Thus,this work provides an environmentally friendly and scalable method for constructing a strong interface between the PBO fibers and the matrix resins,which makes sense in promoting the application of PBO fiber-reinforced composites in aerospace and military industries.展开更多
Fiber-reinforced polymer(FRP)composites are increasingly popular due to their superior strength to weight ratio.In contrast to significant recent advances in automating the FRP manufacturing process via 3D printing,qu...Fiber-reinforced polymer(FRP)composites are increasingly popular due to their superior strength to weight ratio.In contrast to significant recent advances in automating the FRP manufacturing process via 3D printing,quality inspection and defect detection remain largely manual and inefficient.In this paper,we propose a new approach to automatically detect,from microscope images,one of the major defects in 3D printed FRP parts:fiber-deficient areas(or equivalently,resin-rich areas).From cross-sectional microscope images,we detect the locations and sizes of fibers,construct their Voronoi diagram,and employ-shape theory to determine fiber-deficient areas.Our Voronoi diagram and-shape construction algorithms are specialized to exploit typical characteristics of 3D printed FRP parts,giving significant efficiency gains.Our algorithms robustly handle real-world inputs containing hundreds of thousands of fiber cross-sections,whether in general or non-general position.展开更多
The compressive mechanical properties,failure modes and foam filler strengthening mechanism and effect of a short basalt fiber-reinforced epoxy resin composite grid beetle elytron plate with a polyvinyl chloride(PVC)f...The compressive mechanical properties,failure modes and foam filler strengthening mechanism and effect of a short basalt fiber-reinforced epoxy resin composite grid beetle elytron plate with a polyvinyl chloride(PVC)foam-filled core(GBEPfc)are investigated via compression experiments and the finite element method.The results are compared with those of a grid plate(GPfc)with the same wall thickness as the GBEPfc.Additionally,a fully integrated preparation method and process are developed for the GBEPfc,with a material composition that is close to the structure and composition of the organism.Increases of more than 20%in the specific compressive strength and specific energy absorption of the GBEPfcrelative to the GPfcare ascertained.The foam provides a constraining force for the fiber composite structure;consequently,the trabeculae and honeycomb walls of the core transition from a lower-order deformation that easily occurs to a higher-order deformation that occurs less readily.The interaction between the core composite structure and PVC foam is described.The GBEPfcdeveloped in this paper is simple in structure and easy to prepare,and the material composition is close to biological prototypes and materials used in practical engineerings,which lays a foundation for the application of beetle elytron plates.展开更多
Fiber-reinforced composites are a popular lightweight materials used in a variety of engineering applications,such as aerospace,architecture,automotive,and marine construction,due to their attractive mechanical proper...Fiber-reinforced composites are a popular lightweight materials used in a variety of engineering applications,such as aerospace,architecture,automotive,and marine construction,due to their attractive mechanical properties.Constructing lattice materials from fiber-reinforced composites is an efficient approach for developing ultra-lightweight structural systems with superior mechanical proper-ties and multifunctional benefits.In contrast to corrugated,foam,and honeycomb core materials,composite lattice materials can be manufactured with various architectural designs,such as woven,grid,and truss cores.Moreover,lattice materials with open-cell topology provide multifunctional advantages over conventional closed-cell honeycomb and foam structures and are thus highly desirable for developing aerospace systems,hypersonic vehicles,long-range rockets and missiles,ship and naval structures,and protective systems.The objective of this study is to review and analyze dynamic mechanical behavior performed by different researchers in the area of composite lattice materials and to highlight topics for future research.展开更多
The development of multiscale fiber-reinforced composite powders is an effective way to improve the mechanical properties and functionality of additively manufactured parts.Herein,a novel thermally induced precipitati...The development of multiscale fiber-reinforced composite powders is an effective way to improve the mechanical properties and functionality of additively manufactured parts.Herein,a novel thermally induced precipitation process is proposed for preparing multiscale fiber-reinforced powders.A systematic evaluation was conducted to explore the main factors influencing powder morphology,powder flow,and microstructure.In the powder-forming mechanism,the polymer matrix is coated on the microfiber,and a film of carbon nanotubes covers the powder surface,which is promoted by heterogeneous nucleation.The composite powders comprised polyamide 12,carbon fiber(CF),and carbon nanotubes,which have been successfully applied in powder bed fusion processes including selective laser sintering(SLS).Smooth flow and powder deposition were observed,and the composite components obtained via SLS were well-fabricated using the optimized process parameters.A CF loading ratio of up to 66.7 wt%and homogeneous fiber distribution within the matrix were successfully achieved.展开更多
The use of composite sandwich structures with cellular cores is prevalent in lightweight designs owing to their superior energy-absorbing abilities.However,current manufacturing processes,such as hot-press molding and...The use of composite sandwich structures with cellular cores is prevalent in lightweight designs owing to their superior energy-absorbing abilities.However,current manufacturing processes,such as hot-press molding and mold pressing,require multiple steps and complex tools,thus limiting the exploration of advanced sandwich structure designs.This study reports a novel multi-material additive manufacturing(AM)process that allows the single-step production of continuous fiber-reinforced polymer composite(CFRPC)sandwich structures with multiscale cellular cores.Specifically,the integration of CFRPC-AM and in situ foam AM processes provides effective and efficient fabrication of CFRPC panels and multiscale cellular cores with intricate designs.The cellular core design spans three levels:microcellular,unit-cell,and graded structures.Sandwich structures with a diverse set of unit-cell designs,that is,rhombus,square,honeycomb,and re-entrant honeycomb,were fabricated and their flexural behaviors were studied experimentally.The results showed that the sandwich structure with a rhombus core design possessed the highest flexural stiffness,strength,and specific energy absorption.In addition,the effect of the unit-cell assembly on the flexural performance of the CFRP composite sandwich structure was examined.The proposed design and fabrication methods open new avenues for constructing novel and high-performance CFRPC structures with multiscale cellular cores that cannot be obtained using existing approaches.展开更多
文摘Grouted rock bolts subject to axial loading in the field exhibit various failure modes,among which the most predominant one is the bolt-grout interface failure.Thus,mechanical characterization of the grout is essential for understanding its performance in ground support.To date,few studies have been conducted to characterize the mechanical behaviour of fiber-reinforced grout(FRG)in rock bolt reinforcement.Here we experimentally studied the mechanical behaviour of FRG under uniaxial compression,indirect tension,and direct shear loading conditions.We also conducted a series of pullout tests of rebar bolt encapsulated with different grouts including conventional cementitious grout and FRG.FRG was developed using 15%silica fume(SF)replacement of cement(by weight)and steel fiber to achieve highstrength and crack-resistance to overcome drawbacks of the conventional grout.Two types of steel fibers including straight and wavy steel fibers were further added to enhance the grout quality.The effect of fiber shape and fiber volume proportion on the grout mechanical properties were examined.Our experimental results showed that the addition of SF and steel fiber by 1.5%fiber volume proportion could lead to the highest compressive,tensile,and shear strengths of the grout.The minimum volume of fiber that could improve the mechanical properties of grout was found at 0.5%.The scanning electron microscopy(SEM)analysis demonstrated that steel fibers act as an excellent bridge to prevent the cracks from propagating at the interfacial region and hence to aid in maintaining the integrity of the cementitious grout.Our laboratory pullout tests further confirmed that FRG could prevent the cylindrical grout annulus from radial crack and hence improve the rebar’s load carrying capacity.Therefore,FRG has a potential to be utilized in civil and mining applications where high-strength and crack-resistance support is required.
基金funded by National Natural Science Foundation of China(No.12002392).
文摘Five types of polyurea elastomers were synthesized by changing the isocyanate component and the mechanical properties of polyurea materials were measured. Fiber-reinforced cement boards(FRCB)strengthened by polyurea with different formulations were processed, and a series of experiments were carried out on the specimens with gas explosion devices. The results showed that the conventional mechanical properties of different types of polyureas had their own advantages. Based on the gas explosion overpressure criterion, the blast resistances of reinforced plates were quantitatively evaluated,and the best polyurea was selected to guide the formulation design. The three typical failure modes of polyurea-reinforced FRCBs were flexural, shear, and flexural-shear failure. Dynamic thermodynamics and shock wave spectral analysis revealed that the polyurea did not undergo a glass transition in the gas explosion tests but retained its elastic properties, allowing it to effectively wrap the fragments formed by the brittle substrates.
基金The subject supported by the National Natural Science Foundation of China(No.59778034)Teaching and Research Award Program for Outstanding Young Teachers in Higher Education Institutions of MOEChina and The Hong Kong Polytechnic University(G-S737)
文摘A new degradation function of the friction coefficient is used.Basedon the double shear-lag model and Paris formula,the interracial damage of coated-fiber-reinforced composites under tension-tension cyclic loading is studied.The effectsof strength and thickness of the coating materials on the debond stress,debond rateas well as debond length are simulated.
基金Funded by the National Natural Science Foundation of China(No.51778479).
文摘To understand the enhancing effect and fiber-reinforced mechanism of composite fibers reinforced cement concrete, the influences of composite fibers on micro-cracks and the distribution of composite fibers were evaluated by optical electron micrometer(OEM) and scanning electron microscope(SEM). Three kinds of fiber, such as polyacrylonitrile-based carbon fiber, basalt fiber, and glass fiber, were used in the composite fibers reinforced cement concrete. The composite fibers could form a stable structure in concrete after the liquid-phase coupling treatment, gas-liquid double-effect treatment, and inert atmosphere drying. The mechanical properties of composite fibers reinforced concrete(CFRC) were studied by universal test machine(UTM). Moreover, the effect of composite fibers on concrete was analyzed based on the toughness index and residual strength index. The results demonstrated that the composite fibers could improve the mechanical properties of concrete, while the excessive amount of composite fibers had an adverse effect on the mechanical properties of concrete. The composite fibers could significantly improve the toughness index of CFRC, and the increment rate is more than 30%. The composite fibers could form a mesh structure, which could promote the stability of concrete and guarantee the excellent mechanical properties.
文摘The aim of this study is to present a constitutive model for prediction of the mechanical behavior of fiberreinforced cemented sand. For this purpose, a generalized plasticity constitutive model of sandy soil is selected and the parameters of the model are determined for three types of sandy soils using the results of triaxial tests. Next, the proposed model is developed using the existing models based on the physicomechanical characteristics of fiber-reinforced cemented sand. The elastic parameters, flow rule and hardening law of the base model are modified for fiber-reinforced cemented sand. To verify the proposed model, the predicted results are compared with those of triaxial tests performed on fiber-reinforced cemented sand. Finally, the efficiency of the proposed model is studied at different confining pressures, and cement and fiber contents.
基金Funded by the Fundamental Research Funds for the Central Universities(No.2018IB001)and the National High-tech Research and Development Program of China(863 Program)(No.2013AA031306)。
文摘A combination of experimental measurements and numerical analysis was utilized to study the low-velocity impact damage of domestic carbon fiber-reinforced composites(CFRCs).The results indicated that the low-velocity impact damage induced pits and longitudinal cracks on the front side,oblique cracks and delaminationin on the back side.The pit depth increased with the increasing impact energy.It was demonstrated that the numerical analysis strain history curve was similar to the experimentally measured strain history curve,which verified the accuracy of numerical analysis in which the Hashin failure criterion was used.The work provides basic data and theoretical basis for the promotion and application of the domestic carbon fiber,and demonstrates the feasibility of replacing imported carbon fibers with domestic carbon fibers.
基金financially supported by the Foundation for Chunhui Program of the Ministry of Education of the People's Republic of China under contract No.Z2011-062
文摘In order to improve the properties of silica sol shell for investment casting process, various contents of cattail fibers were added into the slurry to prepare a fiber-reinforced shell in the present study. The bending strength of fiber-reinforced shell was investigated and the fracture surfaces of shell specimens were observed using SEM. It is found that the bending strength increases with the increase of fiber content, and the bending strength of a green shell with 1.0 wt.% fiber addition increases by 44% compared to the fiber-free shell. The failure of specimens of the fiber-reinforced green shell results from fiber rupture and debonding between the interface of fibers and adhesive under the bending load. The micro-crack propagation in the matrix is inhibited by the micro-holes for ablation of f ibers in specimens of the f iber-reinforced shell during the stage of being fired. As a result, the bending strength of specimens of the fired shell had no significant drop. Particularly, the bending strength of specimens of the fired shell reinforced with 0.6wt.% fiber reached the maximum value of 4.6 MPa.
文摘To meet the ever-increasing construction demands around the world during recent years,reinforcement and stabilization methods have been widely used by geotechnical engineers to improve the performances and behavior of fine-grained soils.Although lime stabilization increases the compressive strength of soils,it reduces the soil ductility at the same time.Recent research shows that random fiber inclusion modifies the brittleness of soils.In the current research,the effects of lime and polypropylene(PP)fiber additions on such characteristics as compressive and shear strengths,failure strain,secant modulus of elasticity(E50)and shear strength parameters of mixtures were investigated.Kaolinite was treated with 1%,3% and 5% lime by dry weight of soil and reinforced with 0.1% monovalent PP fibers with the length of 6 mm.Samples were prepared at optimum conditions and cured at 35℃ for 1 d,7 d and 28 d at 90% relative humidity and subsequently subjected to uniaxial and triaxial compression tests(UCT and TCT)under cell pressures of 25 kPa,50 kPa and 100 kPa.Results showed that inclusion of random PP fibers to clay-lime mixtures increases both compressive and shear strengths as well as the ductility.Lime content and curing period were found to be the most influential factors.Scanning electron microscopy(SEM)analysis showed that lime addition and the formation of cementitious compounds bind soil particles and increase soil/fiber interactions at interface,leading to enhanced shear strength.The more ductile the stabilized and reinforced composition,the less the cracks in roads and waste landfill covers.
基金National Natural Science Foundation of China(No.51278391)
文摘An evaluation of existing strength of concrete columns confined with fiber-reinforced polymer( FRP) was presented with extensive collection of experimental data. According to the evaluation results, artificial neural networks( ANNs) model to predict the ultimate strength of FRP confined column with different shapes was proposed. The models had seven inputs including the column length,the tensile strength of the FRP in the hoop direction,the total thickness of FRP,the diameter of the concrete specimen,the elastic modulus of FRP,the corner radius and the concrete compressive strength. The compressive strength of the confined concrete was the output data. The results reveal that the proposed models have good prediction and generalization capacity with acceptable errors.
基金Funded by National Key R&D Program(No.2016YFC0701003)of Chinathe Fundamental Research Funds for the Central Universities
文摘In order to investigate the synergistic effect of re-dispersible powder-ethylene-vinyl acetate copolymer(EVA) and polypropylene fiber on the crack resistance of concrete under thermal fatigue loading, the compressive strength, ultimate tensile strength, ultimate tensile strain and tensile modulus of elasticity were tested. In addition, ultrasonic method and scanning electron microscope analysis were used to explain the microstructure mechanism. The results show that polypropylene fiberreinforced concrete presents a better performance on crack resistance than ordinary concrete, and the synergism of EVA and polypropylene fiber can improve the anti-cracking ability of concrete further.
基金The authors are pleased to acknowledge the support by the National Natural Science Foundation of China through contract/Grant Nos.11772237,11472196 and 11172216to acknowledge the open funds of the State Key Laboratory of Structural Analysis for Industrial Equipment(Dalian University of Technology)through contract/Grant No.GZ19110.
文摘In this study,a peridynamic fiber-reinforced concrete model is developed based on the bond-based peridynamic model with rotation effect(BBPDR).The fibers are modelled by a semi-discrete method and distributed with random locations and angles in the concrete specimen,since the fiber content is low,and its scale is smaller than the concrete matrix.The interactions between fibers and concrete matrix are investigated by the improvement of the bond’s strength and stiffness.Also,the frictional effect between the fibers and the concrete matrix is considered,which is divided into static friction and slip friction.To validate the proposed model,several examples are simulated,including the tensile test and the three-point bending beam test.And the numerical results of the proposed model are compared with the experiments and other numerical models.The comparisons show that the proposed model is capable of simulating the fracture behavior of the fiber-reinforced concrete.After adding the fibers,the tensile strength,bending strength,and toughness of the fiber-reinforced concrete specimens are improved.Besides,the fibers distribution has an impact on the crack path,especially in the three-point bending beam test.
基金This study was supported in part by the Earthquake Science and Technology Development Fund,Gansu Earthquake Agency(Grant Nos.2021M7,2019Q08)the Construction Project of Scientific Research team of Seismological Bureau of Gansu Province(Grant No.2020TD-01-01)the National Natural Science Foundation of China(Grant No.51778590).
文摘In the seasonal permafrost region with loess distribution,the influence of freeze-thaw cycles on the engineering performance of reinforced loess must be paid attention to.Many studies have shown that the use of fiber materials can improve the engineering performance of soil and its ability to resist freeze-thaw cycles.At the same time,as eco-environmental protection has become the focus,which has been paid more and more attention to,it has become a trend to find new environmentally friendly improved materials that can replace traditional chemical additives.The purpose of this paper uses new environmental-friendly improved materials to reinforce the engineering performance of loess,improve the ability of loess to resist freeze-thaw cycles,and reduce the negative impact on the ecological environment.To reinforce the engineering performance of loess and improve its ability to resist freeze-thaw cycles,lignin fiber is used as a reinforcing material.Through a series of laboratory tests,the unconfined compressive strength(UCS)of lignin fiber-reinforced loess under different freeze-thaw cycles was studied.The effects of lignin fiber content and freeze-thaw cycles on the strength and deformation modulus of loess were analyzed.Combined with the microstructure features,the change mechanism of lignin fiber-reinforced loess strength under freeze-thaw cycles was discussed.The results show that lignin fiber can improve the UCS of loess under freeze-thaw cycles,but the strengthening effect no longer increases with the increase of fiber content.When the fiber content is less than 1%,the UCS growth rate of loess is the fastest under freeze-thaw cycles.And the UCS of loess with 1%fiber content is the most stable under freeze-thaw cycles.The freeze-thaw cycles increase the deformation modulus of loess with 1%fiber content,and its ability to resist deformation is obviously better than loess with 1.5%,2%and 3%fiber content.The fiber content over 1%will weaken the strengthening effect of lignin fiber-reinforced loess,and the optimum fiber content of lignin fiber-reinforced loess under freeze-thaw cycles is 1%.
基金supported by the National Natural Science Foundation of China(Nos.52022011,52090041,and 51921001)the Beijing Nova Programs,China(No.Z191100001119125).
文摘Silver-based alloys are significant light-load electrical contact materials(ECMs).The trade-off between mechanical properties and electrical conductivity is always an important issue for the development of silver-based ECMs.In this paper,we proposed an idea for the regulation of the mechanical properties and the electrical conductivity of Ag-11.40Cu-0.66Ni-0.05Ce(wt%)alloy using in-situ composite fiber-reinforcement.The alloy was processed using rolling,heat treatment,and heavy drawing,the strength and electrical conductivity were tested at different deformation stages,and the microstructures during deformation were observed using field emission scanning electron microscope(FESEM),transmission electron microscope(TEM)and electron backscatter diffraction(EBSD).The results show that the method proposed in this paper can achieve the preparation of in-situ composite fiber-reinforced Ag-Cu-Ni-Ce alloys.After the heavy deformation drawing,the room temperature Vickers hardness of the as-cast alloy increased from HV 81.6 to HV 169.3,and the electrical conductivity improved from 74.3%IACS(IACS,i.e.,international annealed copper standard)to 78.6%IACS.As the deformation increases,the alloy strength displays two different strengthening mechanisms,and the electrical conductivity has three stages of change.This research provides a new idea for the comprehensive performance control of high-performance silver-based ECMs.
基金National Natural Science Foundation of China,10872147Natural Science Foundation of Tianjin,09JCYBJC1400
文摘Articular cartilage is a layer of low-friction,load-bearing soft hydrated tissue covering bone-ends in diarthrosis,which plays an important role in spreading the load,reducing the joint contact stress,joint friction and wear during exercise.The vital mechanical function
基金financially supported by the National Natural Science Foundation of China (No. 51903237)Beijing Natural Science Foundation (No. 2222091)
文摘Sizing treatment has shown great potential in improving the interfacial properties of poly(p-phenylene benzodioxazole)(PBO)fiber-reinforced composites,but is severely limited due to the use of flammable and explosive organic solvents.Herein,a new high-efficiency waterborne sizing agent has been developed by using functionalized carbon nanospheres(CNSs)as a nano-reinforcement.Due to abundant oxygen-containing groups,the CNSs greatly improves the surface activity,wettability,and roughness of the PBO fibers.As a result,the interfacial shear strength of the CNSs sized fiber-reinforced composite increases by 79.6%compared with that of the pristine fiber-reinforced composite.Moreover,the excellent mechanical and thermal properties of the PBO fibers remain almost unchanged after sizing treatment.Thus,this work provides an environmentally friendly and scalable method for constructing a strong interface between the PBO fibers and the matrix resins,which makes sense in promoting the application of PBO fiber-reinforced composites in aerospace and military industries.
文摘Fiber-reinforced polymer(FRP)composites are increasingly popular due to their superior strength to weight ratio.In contrast to significant recent advances in automating the FRP manufacturing process via 3D printing,quality inspection and defect detection remain largely manual and inefficient.In this paper,we propose a new approach to automatically detect,from microscope images,one of the major defects in 3D printed FRP parts:fiber-deficient areas(or equivalently,resin-rich areas).From cross-sectional microscope images,we detect the locations and sizes of fibers,construct their Voronoi diagram,and employ-shape theory to determine fiber-deficient areas.Our Voronoi diagram and-shape construction algorithms are specialized to exploit typical characteristics of 3D printed FRP parts,giving significant efficiency gains.Our algorithms robustly handle real-world inputs containing hundreds of thousands of fiber cross-sections,whether in general or non-general position.
基金supported by the National Natural Science Foundation of China(Grant No.51875102)。
文摘The compressive mechanical properties,failure modes and foam filler strengthening mechanism and effect of a short basalt fiber-reinforced epoxy resin composite grid beetle elytron plate with a polyvinyl chloride(PVC)foam-filled core(GBEPfc)are investigated via compression experiments and the finite element method.The results are compared with those of a grid plate(GPfc)with the same wall thickness as the GBEPfc.Additionally,a fully integrated preparation method and process are developed for the GBEPfc,with a material composition that is close to the structure and composition of the organism.Increases of more than 20%in the specific compressive strength and specific energy absorption of the GBEPfcrelative to the GPfcare ascertained.The foam provides a constraining force for the fiber composite structure;consequently,the trabeculae and honeycomb walls of the core transition from a lower-order deformation that easily occurs to a higher-order deformation that occurs less readily.The interaction between the core composite structure and PVC foam is described.The GBEPfcdeveloped in this paper is simple in structure and easy to prepare,and the material composition is close to biological prototypes and materials used in practical engineerings,which lays a foundation for the application of beetle elytron plates.
基金National Science Foundations of China,Grant/Award Numbers:11572100,11302060,11432004,11421091,12061160461Program for Outstanding Young Scholars in Harbin Institute of Technology+3 种基金Natural Scientific Research Innovation Foundation in Harbin Institute of Technology,Grant/Award Number:HIT.NSRIF.2014025Science and Technology on Advanced Composites in Special Environment LaboratoryAlexander von Humboldt Foundation(University of Siegen,Germany),Grant/Award Number:1155520National Science Foundation(NSF),Grant/Award Number:CMMI-1634560。
文摘Fiber-reinforced composites are a popular lightweight materials used in a variety of engineering applications,such as aerospace,architecture,automotive,and marine construction,due to their attractive mechanical properties.Constructing lattice materials from fiber-reinforced composites is an efficient approach for developing ultra-lightweight structural systems with superior mechanical proper-ties and multifunctional benefits.In contrast to corrugated,foam,and honeycomb core materials,composite lattice materials can be manufactured with various architectural designs,such as woven,grid,and truss cores.Moreover,lattice materials with open-cell topology provide multifunctional advantages over conventional closed-cell honeycomb and foam structures and are thus highly desirable for developing aerospace systems,hypersonic vehicles,long-range rockets and missiles,ship and naval structures,and protective systems.The objective of this study is to review and analyze dynamic mechanical behavior performed by different researchers in the area of composite lattice materials and to highlight topics for future research.
基金This work was supported by National Natural Science Foundation of China(Grant Nos.551905439,U1930207).
文摘The development of multiscale fiber-reinforced composite powders is an effective way to improve the mechanical properties and functionality of additively manufactured parts.Herein,a novel thermally induced precipitation process is proposed for preparing multiscale fiber-reinforced powders.A systematic evaluation was conducted to explore the main factors influencing powder morphology,powder flow,and microstructure.In the powder-forming mechanism,the polymer matrix is coated on the microfiber,and a film of carbon nanotubes covers the powder surface,which is promoted by heterogeneous nucleation.The composite powders comprised polyamide 12,carbon fiber(CF),and carbon nanotubes,which have been successfully applied in powder bed fusion processes including selective laser sintering(SLS).Smooth flow and powder deposition were observed,and the composite components obtained via SLS were well-fabricated using the optimized process parameters.A CF loading ratio of up to 66.7 wt%and homogeneous fiber distribution within the matrix were successfully achieved.
基金supported by National Natural Science Foundation of China(Grant No.52105261)Shenzhen Science and Technology Inno-vation Committee of China(Grant No.JCYJ20210324104610028)Department of Education of Guangdong Province of China(Grant No.2022ZDZX3020).
文摘The use of composite sandwich structures with cellular cores is prevalent in lightweight designs owing to their superior energy-absorbing abilities.However,current manufacturing processes,such as hot-press molding and mold pressing,require multiple steps and complex tools,thus limiting the exploration of advanced sandwich structure designs.This study reports a novel multi-material additive manufacturing(AM)process that allows the single-step production of continuous fiber-reinforced polymer composite(CFRPC)sandwich structures with multiscale cellular cores.Specifically,the integration of CFRPC-AM and in situ foam AM processes provides effective and efficient fabrication of CFRPC panels and multiscale cellular cores with intricate designs.The cellular core design spans three levels:microcellular,unit-cell,and graded structures.Sandwich structures with a diverse set of unit-cell designs,that is,rhombus,square,honeycomb,and re-entrant honeycomb,were fabricated and their flexural behaviors were studied experimentally.The results showed that the sandwich structure with a rhombus core design possessed the highest flexural stiffness,strength,and specific energy absorption.In addition,the effect of the unit-cell assembly on the flexural performance of the CFRP composite sandwich structure was examined.The proposed design and fabrication methods open new avenues for constructing novel and high-performance CFRPC structures with multiscale cellular cores that cannot be obtained using existing approaches.
