An experimental investigation was conducted on the flexural behavior of FRP-PVC confined concrete circular tubular members.A total of six specimens were prepared and tested under flexural loading.The main parameters v...An experimental investigation was conducted on the flexural behavior of FRP-PVC confined concrete circular tubular members.A total of six specimens were prepared and tested under flexural loading.The main parameters varied in the tests were the layer of FRP and the strengthening approach of BFRP and CFRP.The failure modes,ultimate bending capacity and stress-strain relation curves were investigated in details.Furthermore,the relation model of moment(M)-curvature(φ)was studied,and on the basis of M-φ relation model,a simplified formula was presented to compute the ultimate bending moment capacity.The results show that the external confinement of concrete specimens by FRP-PVC tubes results in enhancing the ultimate bending strength and ultimate deformation,and the ultimate bending capacity increased with the FRP layers.Simultaneously,the reinforcement effect in CFRP is better than that in BFRP.The ultimate bending moment capacity values predicted by the presented formula agree well with the experimental results,which imply that the presented formula is applicable and efficient for prediction of the ultimate bending moment capacity as well.展开更多
The complete flexural vibration band gaps are studied in the thin plates with two-dimensional binary locally resonant structures, i.e. the composite plate consisting of soft rubber cylindrical inclusions periodically ...The complete flexural vibration band gaps are studied in the thin plates with two-dimensional binary locally resonant structures, i.e. the composite plate consisting of soft rubber cylindrical inclusions periodically placed in a host material. Numerical simulations show that the low-frequency gaps of flexural wave exist in the thin plates. The width of the first gap decreases monotonically as the matrix density increases, The frequency response of the finite periodic thin plates is simulated by the finite element method, which provides attenuations of over 20dB in the frequency range of the band gaps. The findings will be significant in the application of phononic crystals.展开更多
Periodic arrays of hybrid-shunted piezoelectric patches are used to control the band-gaps of phononic metamaterial beams. Passive resistive-inductive （RL） shunting circuits can produce a narrow resonant band-gap （R...Periodic arrays of hybrid-shunted piezoelectric patches are used to control the band-gaps of phononic metamaterial beams. Passive resistive-inductive （RL） shunting circuits can produce a narrow resonant band-gap （RG）, and active negative capacitive （NC） shunting circuits can broaden the Bragg band-gaps （BGs）. In this article, active NC shunting circuits and passive resonant RL shunting circuits are connected to the same piezoelectric patches in parallel, which are usually called hybrid shunting circuits, to control the location and the extent of the band-gaps. A super-wide coupled band-gap is generated when the coupling between RG and the BG occurs. The attenuation constant of the infinite periodic structure is predicted by the transfer matrix method, which is compared with the vibration transmittance of a finite periodic structure calculated by the finite element method. Numerical results show that the hybrid-shunting circuits can make the band-gaps wider by appropriately selecting the inductances, negative capacitances, and resistances.展开更多
According to the theory of phononic crystals, the hydraulic pipeline is designed to be a periodic structure composed of steel pipes and hoses to suppress the vibration of the hydraulic system with band gaps. We presen...According to the theory of phononic crystals, the hydraulic pipeline is designed to be a periodic structure composed of steel pipes and hoses to suppress the vibration of the hydraulic system with band gaps. We present theoretical and experimental investigations into the flexural vibration transfer properties of a high-pressure periodic pipe with the force on the inner pipe wall by oii pressure taken into consideration. The results show that the vibration attenuation of periodic pipe decreases along with the elevation of working pressure for the hydraulic system, and the band gaps in low frequency ranges move towards high frequency ranges. The periodic pipe has good vibration attenuation performance in the frequency range below 1000 Hz and the vibration of the hydraulic system is effectively suppressed. A11 the results are validated by experiment. The experimental results show a good agreement with the numerical calculations, thus the flexural vibration transfer properties of the high- pressure periodic pipe can be precisely calculated by taking the fluid structure interaction between the pipe and oil into consideration. This study provides an effective way for the vibration control of the hydraulic system.展开更多
In this study,we design periodic grille structures on a single homogenous thin plate to achieve anisotropic acoustic metamaterials that can control flexural waves.The metamaterials can achieve the bending control of f...In this study,we design periodic grille structures on a single homogenous thin plate to achieve anisotropic acoustic metamaterials that can control flexural waves.The metamaterials can achieve the bending control of flexural waves in a thin plate at will by designing only one dimension in the thickness direction,which makes it easier to use this metamaterial to design transformation acoustic devices.The numerical simulation results show that the metamaterials can accurately control the bending waves over a wide frequency range.The experimental results verify the validity of the theoretical analysis.This research provides a more practical theoretical method of controlling flexural waves in thin-plate structures.展开更多
A ship's tail shaft has serious flexural vibration due to the cantilevered nature of the propeller's blades.Analysis of the nature frequency of flexural vibration is vital to be able to provide effective shock...A ship's tail shaft has serious flexural vibration due to the cantilevered nature of the propeller's blades.Analysis of the nature frequency of flexural vibration is vital to be able to provide effective shock absorption for a ship's tail shaft.A mathematic model of tail shaft flexural vibrations was built using the transfer matrix method.The nature frequency of flexural vibration for an electrically propelled ship's tail shaft was then analyzed,and an effective method for calculating it was proposed:a genetic algorithm(GA),which calculates the nature frequency of vibration of a system.Sample calculations,with comparisons by the Prohl method under conditions bearing isotropic support,showed this method to be practical.It should have significant impact on engineering design theory.展开更多
Thermal transport properties are investigated for out-of-plane phonon modes （FPMs） and it-plane phonon modes （IPMs） in double-stub graphene nanoribbons （GNRs）. The results show that the quantized thermal conduct...Thermal transport properties are investigated for out-of-plane phonon modes （FPMs） and it-plane phonon modes （IPMs） in double-stub graphene nanoribbons （GNRs）. The results show that the quantized thermal conductance plateau of FPMs is narrower and more easily broken by the double-stub structure. In the straight GNRs, the thermal conductance of FPMs is higher in the low temperature region due to there being less cut-off frequency and more low-frequency excited modes. In contrast, the thermal conductance of IPMs is higher in the high temperature region becau~,＇.e of the wider phonon energy spectrum. Furthermore, the thermal transport of two types of phonon modes can be modulated by the double-stub GNRs, the thermal conductance of FPMs is less than that of IPMs in the low temperatures, but it dominates the contribution to the total thermal conductance in the high temperatures. The modulated thermal conclu~＇tanc：e can provide a guideline for designing high-performance thermal or thermoelectric nanodevices based on graphene.展开更多
For both the vibrating and steady supporting surfaces of a scanning disk in a Besocke-style piezoelectric scanner, a theoretical model is given by considering the nonlinear lateral friction at the micro-contact interf...For both the vibrating and steady supporting surfaces of a scanning disk in a Besocke-style piezoelectric scanner, a theoretical model is given by considering the nonlinear lateral friction at the micro-contact interface between the positioning legs and the supporting surface. Numerical simulations demonstrate that unexpected flexural vibrations can arise from a vibrating ramp, and their frequencies are lower than the eigenfrequencies of the scanner in the linearly elastic regime. The vibrations essentially depend on 1） the vibrational states of the supporting ramp and the steel ball tips on the three piezo- electric positioning legs, and 2） the tribological characteristics of the contacts between the tips and the ramp. The results give an insight into the intrinsic vibrations of the scanners, and are applicable in designing and optimizing piezoelectric scanning systems.展开更多
Extensive research has shown that externally bonded carbon fiber reinforced polymer （CFRP） laminates are particularly suitable for improving the fatigue behavior of reinforced concrete （RC） beams. This paper prese...Extensive research has shown that externally bonded carbon fiber reinforced polymer （CFRP） laminates are particularly suitable for improving the fatigue behavior of reinforced concrete （RC） beams. This paper presents the research on flexural ngidity evolvement laws by testing 14 simple-supported RC beams strengthened with carbon fiber laminates （CFL） under cyclic load, and 2 under monotone load as a reference. The cyclic load tests revealed the peak load applied onto the surface of a supported RC beam strengthened with CFL is linear to the logarithm of its fatigue life, and the flexural rigidity evolvement undergoes three distinct phases： a rapid decrease from the start to about 5% of the fatigue life; an even development from .5% to about 99% of the fatigue life; and a succedent rapid decrease to failure. When the ratio of fatigue ＂cycles to the fatigue life is within 0.0.5 to 0.99, the flexural rigidity varies linearly with the ratio. The peak load does not affect the flexural rigidity evolvement if it is not high enough to make the main reinforcements yield. The dependences of the flexural rigidity of specimens formed in the same group upon their fatigue cycles normalized by fatigue life are almost coincident. This implies the flexural rigidity may be a material parameter independent of the stress level. These relationships of flexural rigidity to fatigue cycles, and fatigue life may be able to provide some hints for fatigue design and fatigue life evaluation of RC member strengthened with CFL; nevertheless the findings still need verifying by more experiments.展开更多
Flexural resonance vibrations of piezoelectric ceramic tubes in Besocke-style scanners with nanometer resolution are studied by using an electro-mechanical coupling Timoshenko beam model. Meanwhile, the effects of fri...Flexural resonance vibrations of piezoelectric ceramic tubes in Besocke-style scanners with nanometer resolution are studied by using an electro-mechanical coupling Timoshenko beam model. Meanwhile, the effects of friction, the first moment, and moment of inertia induced by mass loads are considered. The predicted resonance frequencies of the ceramic tubes are sensitive to not only the mechanical parameters of the scanners, but also the friction acting on the attached shaking ball and corresponding bending moment on the tubes. The theoretical results are in excellent agreement with the related experimental measurements. This model and corresponding results are applicable for optimizing the structures and performances of the scanners.展开更多
Our research focused on the analy sis of concrete deterioration mechan ism under the coup ling effects of flexural load,cy clic wetting and dry ing, and sulfate. The relative dy namic modulus of elasticity of a corrod...Our research focused on the analy sis of concrete deterioration mechan ism under the coup ling effects of flexural load,cy clic wetting and dry ing, and sulfate. The relative dy namic modulus of elasticity of a corroded concrete samp le was tested, and scannin g electron microscop e was used to observe the microstructure of concrete under the coup ling effects of flexural load,cy clic wetting and dry ing, and sulf ate. Results manif ested that flexur al load and cy clic wetting and dry ing durin g the concrete service chan ged the corrosion p rocess of the sulfate mediu m in con crete and enh anced the deterioration of con crete p erforman ce.Furthermore, the influencin g p atterns of strength grade of concr ete, mass concentration of sulfate solution, and mineral admixtures on the degree of concrete deterioration were identified.展开更多
Time-dependant reliability is analyzed for the flexural cracking of prestressed concrete bridges under service limit state. The limit state function and random variables are derived from Chinese highway bridge design ...Time-dependant reliability is analyzed for the flexural cracking of prestressed concrete bridges under service limit state. The limit state function and random variables are derived from Chinese highway bridge design specifications. For deterioration of structural performances, chloride-induced reinforcement corrosion is emphasized. Through integrating first order reliability method （FORM） and time discretized approach, the time-variant reliability is evaluated. For illustrative propose, the reliability of a typical simply supported prestressed concrete beam is exemplified.展开更多
A finite element calculation model of corroded RC eccentric compressive members was build using finite element software ANSYS. The model considers the decline of mechanical properties and the effective section of a co...A finite element calculation model of corroded RC eccentric compressive members was build using finite element software ANSYS. The model considers the decline of mechanical properties and the effective section of a corroded steel bar,as well as the deterioration of bond character between corroded reinforcement and concrete. The reliability of the finite element model was evaluated by comparing the results of the finite element calculation with the data from experiments. Based on the finite element analysis results,the influence of corrosion degree,the diameter change of the longitudinal reinforcing bars and the spacing change of stirrups on the flexural stiffness were calculated and analyzed.展开更多
Four kinds of iron oxide pigments were added into wood-fiber/high-density-polyethylene composites （WF/HDPE） at three different concentrations, to determine the effects of pigments on the changes in the color and mec...Four kinds of iron oxide pigments were added into wood-fiber/high-density-polyethylene composites （WF/HDPE） at three different concentrations, to determine the effects of pigments on the changes in the color and mechanical properties of the composites before and after UV accelerated weathering. HDPE, wood fibers, pigments and other processing additives were dry-mixed in a high-speed mixer. The mixtures were extruded by two-step extrusion process with a self-designed twin-screw/single-screw extruder system. Color of the samples was determined according to CIE 1976 L^＊a^＊b^＊ system by a spec- trophotometer and the bending properties were tested to evaluate the mechanical properties before and after accelerated UV weathering. The result shows that the modulus of elasticity of WF/HDPE did not obvi- ously changed after incorporating with the pigments, but the bending strength increased. After accelerated aging for 2000 h, both color and mechanical properties significantly changed. Iron oxide red and black performed better than the other two pigments, and the pigments dosage of 2.28% in the composites is favourable.展开更多
Hem-fir plywood were exposed to two brown rot fungi, Gloeophyllum trabeum and Postia placenta, and one white rot fungus, Trametes versicolor, to investigate the effect of fungal decay on mechanical properties of plywo...Hem-fir plywood were exposed to two brown rot fungi, Gloeophyllum trabeum and Postia placenta, and one white rot fungus, Trametes versicolor, to investigate the effect of fungal decay on mechanical properties of plywood. Results showed that modulus of rupture （MOR） and modulus of elasticity （MOE） of hem-fir plywood declined significantly by inoculating fungi, and weight loss of sample had a modest decrease. The fungi also made a greater effect on MOR than on MOE. Of three fungi, Postia placenta caused a most significant weight loss, and Gloeophyllum trabeum resulted in a largest flexural properties loss. Substantial declines in MOR and MOE of hem-fir plywood were also observed when the plywood samples were stored under wet conditions over 15 weeks, even in the absence of fungal attack.展开更多
The stability and vibration of a thin elastic helical rod with circular cross section in a viscous medium are discussed. The dynamical equations of the rod in the viscous medium are established in the Frenet coordinat...The stability and vibration of a thin elastic helical rod with circular cross section in a viscous medium are discussed. The dynamical equations of the rod in the viscous medium are established in the Frenet coordinates of the centreline with the Euler angles describing the attitudes of the cross section as variables. We have proved that the Lyapunov and Euler conditions of stability of a helical rod in the space domain are the necessary conditions for the asymptotic stability of the rod in the time domain. The free frequencies and damping coefficients of torsional and flexural vibrations of the helical rod in the viscous medium are calculated.展开更多
In this paper,a modified single-degree-of-freedom(SDOF)model of reinforced concrete(RC)beams under close-in explosion is proposed by developing the specific impulse equivalent method and flexural resistance calculatio...In this paper,a modified single-degree-of-freedom(SDOF)model of reinforced concrete(RC)beams under close-in explosion is proposed by developing the specific impulse equivalent method and flexural resistance calculation method.The equivalent uniform specific impulse was obtained based on the local conservation of momentum and global conservation of kinetic energy.Additionally,the influence of load uniformity,boundary condition and complex material behaviors(e.g.strain rate effect,hardening/softening and hoop-confined effect)was considered in the resistance calculation process by establishing a novel relationship between external force,bending moment,curvature and deflection successively.The accuracy of the proposed model was verified by carrying out field explosion tests on four RC beams with the scaled distances of 0.5 m/kg~(1/3)and 0.75 m/kg~(1/3).The test data in other literatures were also used for validation.As a result,the equivalent load implies that the blast load near the mid-span of beams would contribute more to the maximum displacement,which was also observed in the tests.Moreover,both the resistance model and test results declare that when the blast load becomes more concentrated,the ultimate resistance would become lower,and the compressive concrete would be more prone to softening and crushing.Finally,based on the modified SDOF model,the calculated maximum displacements agreed well with the test data in this paper and other literatures.This work fully proves the rationality of the modified SDOF method,which will contribute to a more accurate damage assessment of RC structures under close-in explosion.展开更多
The demand for building-integrated photovoltaics and portable energy systems based on flexible photovoltaic technology such as perovskite embedded with exceptional flexibility and a superior power-to-mass ratio is eno...The demand for building-integrated photovoltaics and portable energy systems based on flexible photovoltaic technology such as perovskite embedded with exceptional flexibility and a superior power-to-mass ratio is enormous.The photoactive layer,i.e.,the perovskite thin film,as a critical component of flexible perovskite solar cells(F-PSCs),still faces long-term stability issues when deformation occurs due to encountering temperature changes that also affect intrinsic rigidity.This literature investigation summarizes the main factors responsible for the rapid destruction of F-PSCs.We focus on long-term mechanical stability of F-PSCs together with the recent research protocols for improving this performance.Furthermore,we specify the progress in F-PSCs concerning precise design strategies of the functional layer to enhance the flexural endurance of perovskite films,such as internal stress engineering,grain boundary modification,self-healing strategy,and crystallization regulation.The existing challenges of oxygen-moisture stability and advanced encapsulation technologies of F-PSCs are also discussed.As concluding remarks,we propose our viewpoints on the large-scale commercial application of F-PSCs.展开更多
Unusual quadratic dispersion of flexural vibrational mode and red-shift of Raman shift of in-plane mode with increas- ing layer-number are quite common and interesting in low-dimensional materials, but their physical ...Unusual quadratic dispersion of flexural vibrational mode and red-shift of Raman shift of in-plane mode with increas- ing layer-number are quite common and interesting in low-dimensional materials, but their physical origins still remain open questions. Combining ab initio density functional theory calculations with the empirical force-constant model, we study the lattice dynamics of two typical two-dimensional （2D） systems, few-layer h-BN and indium iodide （InI）. We found that the unusual quadratic dispersion of flexural mode frequency on wave vector may be comprehended based on the com- petition between atomic interactions of different neighbors. Long-range interaction plays an essential role in determining the dynamic stability of the 2D systems. The frequency red-shift of in-plane Raman-active mode from monolayer to bulk arises mainly from the reduced long-range interaction due to the increasing screening effect.展开更多
文摘An experimental investigation was conducted on the flexural behavior of FRP-PVC confined concrete circular tubular members.A total of six specimens were prepared and tested under flexural loading.The main parameters varied in the tests were the layer of FRP and the strengthening approach of BFRP and CFRP.The failure modes,ultimate bending capacity and stress-strain relation curves were investigated in details.Furthermore,the relation model of moment(M)-curvature(φ)was studied,and on the basis of M-φ relation model,a simplified formula was presented to compute the ultimate bending moment capacity.The results show that the external confinement of concrete specimens by FRP-PVC tubes results in enhancing the ultimate bending strength and ultimate deformation,and the ultimate bending capacity increased with the FRP layers.Simultaneously,the reinforcement effect in CFRP is better than that in BFRP.The ultimate bending moment capacity values predicted by the presented formula agree well with the experimental results,which imply that the presented formula is applicable and efficient for prediction of the ultimate bending moment capacity as well.
基金Project supported by the State Key Development Program for Basic Research of China （Grant No 51307） and the National Natural Science Foundation of China （Grant No 50575222）.
文摘The complete flexural vibration band gaps are studied in the thin plates with two-dimensional binary locally resonant structures, i.e. the composite plate consisting of soft rubber cylindrical inclusions periodically placed in a host material. Numerical simulations show that the low-frequency gaps of flexural wave exist in the thin plates. The width of the first gap decreases monotonically as the matrix density increases, The frequency response of the finite periodic thin plates is simulated by the finite element method, which provides attenuations of over 20dB in the frequency range of the band gaps. The findings will be significant in the application of phononic crystals.
基金supported by the National Natural Science Foundation of China(Grant Nos.51275519 and 51175501)
文摘Periodic arrays of hybrid-shunted piezoelectric patches are used to control the band-gaps of phononic metamaterial beams. Passive resistive-inductive （RL） shunting circuits can produce a narrow resonant band-gap （RG）, and active negative capacitive （NC） shunting circuits can broaden the Bragg band-gaps （BGs）. In this article, active NC shunting circuits and passive resonant RL shunting circuits are connected to the same piezoelectric patches in parallel, which are usually called hybrid shunting circuits, to control the location and the extent of the band-gaps. A super-wide coupled band-gap is generated when the coupling between RG and the BG occurs. The attenuation constant of the infinite periodic structure is predicted by the transfer matrix method, which is compared with the vibration transmittance of a finite periodic structure calculated by the finite element method. Numerical results show that the hybrid-shunting circuits can make the band-gaps wider by appropriately selecting the inductances, negative capacitances, and resistances.
文摘According to the theory of phononic crystals, the hydraulic pipeline is designed to be a periodic structure composed of steel pipes and hoses to suppress the vibration of the hydraulic system with band gaps. We present theoretical and experimental investigations into the flexural vibration transfer properties of a high-pressure periodic pipe with the force on the inner pipe wall by oii pressure taken into consideration. The results show that the vibration attenuation of periodic pipe decreases along with the elevation of working pressure for the hydraulic system, and the band gaps in low frequency ranges move towards high frequency ranges. The periodic pipe has good vibration attenuation performance in the frequency range below 1000 Hz and the vibration of the hydraulic system is effectively suppressed. A11 the results are validated by experiment. The experimental results show a good agreement with the numerical calculations, thus the flexural vibration transfer properties of the high- pressure periodic pipe can be precisely calculated by taking the fluid structure interaction between the pipe and oil into consideration. This study provides an effective way for the vibration control of the hydraulic system.
文摘In this study,we design periodic grille structures on a single homogenous thin plate to achieve anisotropic acoustic metamaterials that can control flexural waves.The metamaterials can achieve the bending control of flexural waves in a thin plate at will by designing only one dimension in the thickness direction,which makes it easier to use this metamaterial to design transformation acoustic devices.The numerical simulation results show that the metamaterials can accurately control the bending waves over a wide frequency range.The experimental results verify the validity of the theoretical analysis.This research provides a more practical theoretical method of controlling flexural waves in thin-plate structures.
基金the National Natural Science Foundation under Grant No.50675162
文摘A ship's tail shaft has serious flexural vibration due to the cantilevered nature of the propeller's blades.Analysis of the nature frequency of flexural vibration is vital to be able to provide effective shock absorption for a ship's tail shaft.A mathematic model of tail shaft flexural vibrations was built using the transfer matrix method.The nature frequency of flexural vibration for an electrically propelled ship's tail shaft was then analyzed,and an effective method for calculating it was proposed:a genetic algorithm(GA),which calculates the nature frequency of vibration of a system.Sample calculations,with comparisons by the Prohl method under conditions bearing isotropic support,showed this method to be practical.It should have significant impact on engineering design theory.
基金Project supported by the Science Funds from the Educational Bureau of Hunan Province,China(Grant No.16C0468)the China Postdoctoral Science Foundation(Grant No.2016M602421)+1 种基金the Science and Technology Plan of Hunan Province,China(Grant No.2015RS4002)the Natural Science Foundation of Hunan Province,China(Grant No.2015JJ2050)
文摘Thermal transport properties are investigated for out-of-plane phonon modes （FPMs） and it-plane phonon modes （IPMs） in double-stub graphene nanoribbons （GNRs）. The results show that the quantized thermal conductance plateau of FPMs is narrower and more easily broken by the double-stub structure. In the straight GNRs, the thermal conductance of FPMs is higher in the low temperature region due to there being less cut-off frequency and more low-frequency excited modes. In contrast, the thermal conductance of IPMs is higher in the high temperature region becau~,＇.e of the wider phonon energy spectrum. Furthermore, the thermal transport of two types of phonon modes can be modulated by the double-stub GNRs, the thermal conductance of FPMs is less than that of IPMs in the low temperatures, but it dominates the contribution to the total thermal conductance in the high temperatures. The modulated thermal conclu~＇tanc：e can provide a guideline for designing high-performance thermal or thermoelectric nanodevices based on graphene.
基金supported by the National Basic Research Program of China (Grant No. 2012CB921504)the National Natural Science Foundation of China (Grant Nos. 11004099,1174142,and 11274169)+2 种基金the Natural Science Foundation of Jiangsu Province of China (Grant No. BK2012721)the Fundamental Research Funds for the Central Universities (Grant No. 1126020435)the Priority Academic Program Development of Jiangsu Higher Education Institutions
文摘For both the vibrating and steady supporting surfaces of a scanning disk in a Besocke-style piezoelectric scanner, a theoretical model is given by considering the nonlinear lateral friction at the micro-contact interface between the positioning legs and the supporting surface. Numerical simulations demonstrate that unexpected flexural vibrations can arise from a vibrating ramp, and their frequencies are lower than the eigenfrequencies of the scanner in the linearly elastic regime. The vibrations essentially depend on 1） the vibrational states of the supporting ramp and the steel ball tips on the three piezo- electric positioning legs, and 2） the tribological characteristics of the contacts between the tips and the ramp. The results give an insight into the intrinsic vibrations of the scanners, and are applicable in designing and optimizing piezoelectric scanning systems.
基金National Natural Science Foundation of China (No.10272047)the Natural Science Foundation of Guangdong Province (No.020856)
文摘Extensive research has shown that externally bonded carbon fiber reinforced polymer （CFRP） laminates are particularly suitable for improving the fatigue behavior of reinforced concrete （RC） beams. This paper presents the research on flexural ngidity evolvement laws by testing 14 simple-supported RC beams strengthened with carbon fiber laminates （CFL） under cyclic load, and 2 under monotone load as a reference. The cyclic load tests revealed the peak load applied onto the surface of a supported RC beam strengthened with CFL is linear to the logarithm of its fatigue life, and the flexural rigidity evolvement undergoes three distinct phases： a rapid decrease from the start to about 5% of the fatigue life; an even development from .5% to about 99% of the fatigue life; and a succedent rapid decrease to failure. When the ratio of fatigue ＂cycles to the fatigue life is within 0.0.5 to 0.99, the flexural rigidity varies linearly with the ratio. The peak load does not affect the flexural rigidity evolvement if it is not high enough to make the main reinforcements yield. The dependences of the flexural rigidity of specimens formed in the same group upon their fatigue cycles normalized by fatigue life are almost coincident. This implies the flexural rigidity may be a material parameter independent of the stress level. These relationships of flexural rigidity to fatigue cycles, and fatigue life may be able to provide some hints for fatigue design and fatigue life evaluation of RC member strengthened with CFL; nevertheless the findings still need verifying by more experiments.
基金Project supported by the National Basic Research Program of China (Grant No. 2012CB921504)the National Natural Science Foundation of China (Grant Nos. 11004099 and 11174142)+1 种基金the State Key Laboratory of Acoustics of the Chinese Academy of Sciencesthe Priority Academic Program Development of Jiangsu Higher Education Institutions
文摘Flexural resonance vibrations of piezoelectric ceramic tubes in Besocke-style scanners with nanometer resolution are studied by using an electro-mechanical coupling Timoshenko beam model. Meanwhile, the effects of friction, the first moment, and moment of inertia induced by mass loads are considered. The predicted resonance frequencies of the ceramic tubes are sensitive to not only the mechanical parameters of the scanners, but also the friction acting on the attached shaking ball and corresponding bending moment on the tubes. The theoretical results are in excellent agreement with the related experimental measurements. This model and corresponding results are applicable for optimizing the structures and performances of the scanners.
基金Funded by Fujian Education Department(Nos.JA11329 and JA12412)Quanzhou(Fujian)Techno logy Research and Development Program(Nos.2013Z158,2013Z47,and 2010G7)
文摘Our research focused on the analy sis of concrete deterioration mechan ism under the coup ling effects of flexural load,cy clic wetting and dry ing, and sulfate. The relative dy namic modulus of elasticity of a corroded concrete samp le was tested, and scannin g electron microscop e was used to observe the microstructure of concrete under the coup ling effects of flexural load,cy clic wetting and dry ing, and sulf ate. Results manif ested that flexur al load and cy clic wetting and dry ing durin g the concrete service chan ged the corrosion p rocess of the sulfate mediu m in con crete and enh anced the deterioration of con crete p erforman ce.Furthermore, the influencin g p atterns of strength grade of concr ete, mass concentration of sulfate solution, and mineral admixtures on the degree of concrete deterioration were identified.
文摘Time-dependant reliability is analyzed for the flexural cracking of prestressed concrete bridges under service limit state. The limit state function and random variables are derived from Chinese highway bridge design specifications. For deterioration of structural performances, chloride-induced reinforcement corrosion is emphasized. Through integrating first order reliability method （FORM） and time discretized approach, the time-variant reliability is evaluated. For illustrative propose, the reliability of a typical simply supported prestressed concrete beam is exemplified.
基金The National Natural Science Foundation of China (No.50578068)
文摘A finite element calculation model of corroded RC eccentric compressive members was build using finite element software ANSYS. The model considers the decline of mechanical properties and the effective section of a corroded steel bar,as well as the deterioration of bond character between corroded reinforcement and concrete. The reliability of the finite element model was evaluated by comparing the results of the finite element calculation with the data from experiments. Based on the finite element analysis results,the influence of corrosion degree,the diameter change of the longitudinal reinforcing bars and the spacing change of stirrups on the flexural stiffness were calculated and analyzed.
基金supported by the National Natural Science Foundation of China (30671644, 30771680)
文摘Four kinds of iron oxide pigments were added into wood-fiber/high-density-polyethylene composites （WF/HDPE） at three different concentrations, to determine the effects of pigments on the changes in the color and mechanical properties of the composites before and after UV accelerated weathering. HDPE, wood fibers, pigments and other processing additives were dry-mixed in a high-speed mixer. The mixtures were extruded by two-step extrusion process with a self-designed twin-screw/single-screw extruder system. Color of the samples was determined according to CIE 1976 L^＊a^＊b^＊ system by a spec- trophotometer and the bending properties were tested to evaluate the mechanical properties before and after accelerated UV weathering. The result shows that the modulus of elasticity of WF/HDPE did not obvi- ously changed after incorporating with the pigments, but the bending strength increased. After accelerated aging for 2000 h, both color and mechanical properties significantly changed. Iron oxide red and black performed better than the other two pigments, and the pigments dosage of 2.28% in the composites is favourable.
基金This research was supported by Forest Research Labora-tory, Oregon State University
文摘Hem-fir plywood were exposed to two brown rot fungi, Gloeophyllum trabeum and Postia placenta, and one white rot fungus, Trametes versicolor, to investigate the effect of fungal decay on mechanical properties of plywood. Results showed that modulus of rupture （MOR） and modulus of elasticity （MOE） of hem-fir plywood declined significantly by inoculating fungi, and weight loss of sample had a modest decrease. The fungi also made a greater effect on MOR than on MOE. Of three fungi, Postia placenta caused a most significant weight loss, and Gloeophyllum trabeum resulted in a largest flexural properties loss. Substantial declines in MOR and MOE of hem-fir plywood were also observed when the plywood samples were stored under wet conditions over 15 weeks, even in the absence of fungal attack.
基金Project supported by the National Natural Science Foundation of China （Grant No 10472067）.
文摘The stability and vibration of a thin elastic helical rod with circular cross section in a viscous medium are discussed. The dynamical equations of the rod in the viscous medium are established in the Frenet coordinates of the centreline with the Euler angles describing the attitudes of the cross section as variables. We have proved that the Lyapunov and Euler conditions of stability of a helical rod in the space domain are the necessary conditions for the asymptotic stability of the rod in the time domain. The free frequencies and damping coefficients of torsional and flexural vibrations of the helical rod in the viscous medium are calculated.
基金National Natural Science Foundation of China(Grant No.12102337)to provide fund for conducting experiments。
文摘In this paper,a modified single-degree-of-freedom(SDOF)model of reinforced concrete(RC)beams under close-in explosion is proposed by developing the specific impulse equivalent method and flexural resistance calculation method.The equivalent uniform specific impulse was obtained based on the local conservation of momentum and global conservation of kinetic energy.Additionally,the influence of load uniformity,boundary condition and complex material behaviors(e.g.strain rate effect,hardening/softening and hoop-confined effect)was considered in the resistance calculation process by establishing a novel relationship between external force,bending moment,curvature and deflection successively.The accuracy of the proposed model was verified by carrying out field explosion tests on four RC beams with the scaled distances of 0.5 m/kg~(1/3)and 0.75 m/kg~(1/3).The test data in other literatures were also used for validation.As a result,the equivalent load implies that the blast load near the mid-span of beams would contribute more to the maximum displacement,which was also observed in the tests.Moreover,both the resistance model and test results declare that when the blast load becomes more concentrated,the ultimate resistance would become lower,and the compressive concrete would be more prone to softening and crushing.Finally,based on the modified SDOF model,the calculated maximum displacements agreed well with the test data in this paper and other literatures.This work fully proves the rationality of the modified SDOF method,which will contribute to a more accurate damage assessment of RC structures under close-in explosion.
基金supported by the National Key Research and Development Program of China(2022YFB4200052)the National Natural Science Foundation of China(No.21975088)+2 种基金the Department of Science and Technology of Hubei Province(2022EHB009)the China Postdoctoral Science Foundation(2022M711236)S.A.thanks European Research Council(MOLEMAT-726360)for support.
文摘The demand for building-integrated photovoltaics and portable energy systems based on flexible photovoltaic technology such as perovskite embedded with exceptional flexibility and a superior power-to-mass ratio is enormous.The photoactive layer,i.e.,the perovskite thin film,as a critical component of flexible perovskite solar cells(F-PSCs),still faces long-term stability issues when deformation occurs due to encountering temperature changes that also affect intrinsic rigidity.This literature investigation summarizes the main factors responsible for the rapid destruction of F-PSCs.We focus on long-term mechanical stability of F-PSCs together with the recent research protocols for improving this performance.Furthermore,we specify the progress in F-PSCs concerning precise design strategies of the functional layer to enhance the flexural endurance of perovskite films,such as internal stress engineering,grain boundary modification,self-healing strategy,and crystallization regulation.The existing challenges of oxygen-moisture stability and advanced encapsulation technologies of F-PSCs are also discussed.As concluding remarks,we propose our viewpoints on the large-scale commercial application of F-PSCs.
基金Project supported by the Major Program of Aerospace Advanced Manufacturing Technology Research Foundation from NSFC and CASC,China(Grant No.U1537204)the National Key Research and Development Program of China(Grant No.2017YFA0206301)the National Natural Science Foundation of China(Grant No.51702146)
文摘Unusual quadratic dispersion of flexural vibrational mode and red-shift of Raman shift of in-plane mode with increas- ing layer-number are quite common and interesting in low-dimensional materials, but their physical origins still remain open questions. Combining ab initio density functional theory calculations with the empirical force-constant model, we study the lattice dynamics of two typical two-dimensional （2D） systems, few-layer h-BN and indium iodide （InI）. We found that the unusual quadratic dispersion of flexural mode frequency on wave vector may be comprehended based on the com- petition between atomic interactions of different neighbors. Long-range interaction plays an essential role in determining the dynamic stability of the 2D systems. The frequency red-shift of in-plane Raman-active mode from monolayer to bulk arises mainly from the reduced long-range interaction due to the increasing screening effect.
