Steel-concrete composite structures(SCCS)have been widely used as primary load-bearing components in large-scale civil infrastructures.As the basis of the co-working ability of steel plate and concrete,the bonding sta...Steel-concrete composite structures(SCCS)have been widely used as primary load-bearing components in large-scale civil infrastructures.As the basis of the co-working ability of steel plate and concrete,the bonding status plays an essential role in guaranteeing the structural performance of SCCS.Accordingly,efficient non-destructive testing(NDT)on interfacial debondings in SCCS has become a prominent research area.Multi-channel analysis of surface waves(MASW)has been validated as an effective NDT technique for interfacial debonding detection for SCCS.However,the feasibility of MASW must be validated using experimental measurements.This study establishes a high-frequency data synchronous acquisition system with 32 channels to perform comparative verification experiments in depth.First,the current sensing approaches for high-frequency vibration and stress waves are summarized.Secondly,three types of contact sensors,namely,piezoelectric lead-zirconate-titanate(PZT)patches,accelerometers,and ultrasonic transducers,are selected for MASW measurement.Then,the selection and optimization of the force hammer head are performed.Comparative experiments are carried out for the optimal selection of ultrasonic transducers,PZT patches,and accelerometers for MASW measurement.In addition,the influence of different pasting methods on the output signal of the sensor array is discussed.Experimental results indicate that optimized PZT patches,acceleration sensors,and ultrasonic transducers can provide efficient data acquisition for MASW-based non-destructive experiments.The research findings in this study lay a solid foundation for analyzing the recognition accuracy of contact MASW measurement using different sensor arrays.展开更多
This paper introduced a novel microstructure-based constitutive model designed to comprehensively characterize the intricate mechanical behavior of anisotropic clay rocks under the influence of water saturation.The pr...This paper introduced a novel microstructure-based constitutive model designed to comprehensively characterize the intricate mechanical behavior of anisotropic clay rocks under the influence of water saturation.The proposed model encompasses elastoplastic deformation,time-dependent behavior,and induced damage.A two-step homogenization process incorporates mineral compositions and porosity to determine the macroscopic elastic tensor and plastic yield criterion.The model also considers interfacial debonding between the matrix and inclusions to capture rock damage.The application of the proposed model is demonstrated through an analysis of Callovo-Oxfordian clayey rocks,specifically in the context of radioactive waste disposal in France.Model parameters are determined,followed by numerical simulations of various laboratory tests including lateral decompression tests with constant mean stress,triaxial compression tests under different water saturation conditions,and creep tests.The numerical results are compared with corresponding experimental data to assess the efficacy of the proposed model.展开更多
The interfacial debonding between the active layer and the current collector has been recognized as a critical mechanism for battery fading,and thus has attracted great efforts focused on the related analyses.However,...The interfacial debonding between the active layer and the current collector has been recognized as a critical mechanism for battery fading,and thus has attracted great efforts focused on the related analyses.However,much still remains to be studied regarding practical methods for suppressing electrode debonding,especially from the perspective of mechanics.In this paper,a pre-strain strategy of current collectors to alleviate electrode debonding is proposed.An analytical model for a symmetric electrode with a deformable and limited-thickness current collector is developed to analyze the debonding behavior involving both a pre-strain of the current collector and an eigen-strain of the active layers.The results reveal that the well-designed pre-strain can significantly delay the debonding onset(by up to 100%)and considerably reduce the debonding size.The critical values of the pre-strain are identified,and the pre-strain design principles are also provided.Based on these findings,this work sheds light on the mechanical design to suppress electrode degradation.展开更多
Strain hardening cement-based composites(SHCC)beam externally bonded with glass fiber-reinforced polymer(FRP)plate was examined under three-point flexural test.The effects of the type of substrate used(plain cement mo...Strain hardening cement-based composites(SHCC)beam externally bonded with glass fiber-reinforced polymer(FRP)plate was examined under three-point flexural test.The effects of the type of substrate used(plain cement mortar vs.SHCC),the use or not of a FRP plate to strengthen the SHCC beam,and the thickness of the FRP plate on the flexural performances were studied.Results show that the ultimate load of SHCC beams strengthened with FRP plate has improved greatly in comparison with plain SHCC beams.The deformation capacity of beams makes little change with an increase in the thickness of FRP plates.The formation of multiple flexural-shear cracks(MFSC)is the unique feature of SHCC beams bonded with FRP plates under three-point bending.The debonding of the FRP plate is initiated from MFSC.The initiated debonding area(IDA)is formed by the joint points of the flexural-shear cracks with the FRP plate.Then the debonding strain is represented using the average strain of FRP plate within IDA,which decreases with an increase of FRP plate thickness.The experimental values of the debonding strain of SHCC beam reinforced with FRP plate are close to those predicted by the JSCE’s equation.展开更多
The mechanisms of interfacial debonding of particle reinforcedrheological materials are studied. Based on an energy criterion, asimple formula of local critical stress for interfacial debonding isderived and expressed...The mechanisms of interfacial debonding of particle reinforcedrheological materials are studied. Based on an energy criterion, asimple formula of local critical stress for interfacial debonding isderived and expressed in terms of the interfacial energy. Theparticle size effect on interface debond- ing can then be analyzedeasily owing to the fact that critical stress is inverselyproportional to the square root of particle radius. By takingPP/CaCO_3 system as an example, the present energy criterion iscompared with the mechanical debonding criterion, and it is foundthat under the condition that bond strength is equal to matrixstrength and particle radius not over 0.2μm, the mechanicaldebonding cri- terion can be automatically satisfied if the energycirterion is satisfied.展开更多
A new degradation function of the friction coefficient is used.Based on the double shear-lag model and Paris formula,the interracial damage of coated- fiber-reinforced composites under tension-tension cyclic loading i...A new degradation function of the friction coefficient is used.Based on the double shear-lag model and Paris formula,the interracial damage of coated- fiber-reinforced composites under tension-tension cyclic loading is studied.The effects of strength and thickness of the coating materials on the debond stress,debond rate as well as debond length are simulated.展开更多
The sufficient bond between concrete and rock is an important prerequisite to ensure the effect of shotcrete support. However, in cold regions engineering protection system, the bond condition of rock and concrete sur...The sufficient bond between concrete and rock is an important prerequisite to ensure the effect of shotcrete support. However, in cold regions engineering protection system, the bond condition of rock and concrete surface is easily affected by freeze-thaw cycles, resulting in interface damage, debonding and even supporting failure. Understanding the micromechanisms of the damage and debonding of the rock-concrete interface is essential for improving the interface protection.Therefore, the micromorphology, micromechanical properties, and microdebonding evolution of the sandstone-concrete interface transition zone(ITZ) under varying freeze-thaw cycles(0, 5, 10, 15, 20) were studied using scanning electron microscope, stereoscopic microscope, and nano-indentation. Furthermore, the distribution range and evolution process of ITZ affected by freeze-thaw cycles were defined. Major findings of this study are as follows:(1) The microdamage evolution law of the ITZ under increasing freeze-thaw cycles is clarified, and the relationship between the number of cracks in the ITZ and freeze-thaw cycles is established;(2) As the number of freeze-thaw cycles increases, the ITZ's micromechanical strength decreases, and its development width tends to increase;(3) The damage and debonding evolution mechanisms of sandstone-concrete ITZ under freeze-thaw cycles is revealed, and its micromechanical evolution model induced by freeze-thaw cycles is proposed.展开更多
This paper investigates the dynamic behavior of a buried rigid elliptic cylinder partially debonded from surrounding matrix under the action of anti-plane shear waves (SH waves). The debonding region is modeled as an ...This paper investigates the dynamic behavior of a buried rigid elliptic cylinder partially debonded from surrounding matrix under the action of anti-plane shear waves (SH waves). The debonding region is modeled as an elliptic arc-shaped interface crack with non-contacting faces. By using the wave function (Mathieu function) expansion method and introducing the dislocation density function as an unknown variable, the problem is reduced to a singular integral equation which is solved numerically to calculate the near and far fields of the problem. The resonance of the structure and the effects of various parameters on the resonance are discussed.展开更多
The interfacial debonding in fiber-reinforced plastic(FRP)strengthened repair material will affect the bonding strength and lead to failure of the repair without warning.Unfortunately the interfacial damage is normall...The interfacial debonding in fiber-reinforced plastic(FRP)strengthened repair material will affect the bonding strength and lead to failure of the repair without warning.Unfortunately the interfacial damage is normally invisible and often in the form of a patch rather than a through-width crack.Therefore,a debonding patch detection technique based on fiber optic interferometry is proposed.A quasi-impulse loading is applied with a rubberhead hammer and the total elongation of a surface-mounted optical fiber along the length of the repair material is measured as a function of load position.When a debonding patch is present,the induced sudden slope or sign change on the plot of fiber integral strain v.s.load position will reveal the extent and the location of the debonded area.The results of the study indicate that the proposed technique is applicable for debonding patch detection in repaired members under various support conditions.展开更多
With the increasingly use of FRC (fiber-reinforced composite) in urban lifelines, me-chanical properties investigation is very important for disaster resistance, especiallythe investigation of fatigue properties. Base...With the increasingly use of FRC (fiber-reinforced composite) in urban lifelines, me-chanical properties investigation is very important for disaster resistance, especiallythe investigation of fatigue properties. Based on the shear-lag model, an usual com-posite model under cyclic loading is established. According to the Paris formula, therelationship between interfacial fatigue parameters and the number of cycles is ob-tained under the cyclic loading. Interfocial fatigue properties of this model and thegrowth of the interfacial fatigue crack are analyzed. And the Poisson ratio is consid-ered also.展开更多
A generalized solution was obtained for the partially debonded elliptic inhomogeneity problem in piezoelectric materials under antiplane shear and inplane electric loading using the complex variable method. It was ass...A generalized solution was obtained for the partially debonded elliptic inhomogeneity problem in piezoelectric materials under antiplane shear and inplane electric loading using the complex variable method. It was assumed that the interfacial debonding induced an electrically impermeable crack at the interface. The principle of conformal transformation and analytical continuation were employed to reduce the formulation into two Riemann-Hilbert problems. This enabled the determination of the complex potentials in the inhomogeneity and the matrix by means of series of expressions. The resulting solution was then used to obtain the electroelastic fields and the energy release rate involving the debonding at the inhomogeneity-matrix interface. The validity and versatility of the current general solution have been demonstrated through some specific examples such as the problems of perfectly bonded elliptic inhomogeneity, totally debonded elliptic inhomogeneity, partially debonded rigid and conducting elliptic inhomogeneity, and partially debonded circular inhomogeneity.展开更多
External bonding of fiber reinforced polymer (FRP) composites on the concrete structures has been proved to be an effective and efficient way to strengthen concrete structures. For a FRP strengthened concrete beam, ...External bonding of fiber reinforced polymer (FRP) composites on the concrete structures has been proved to be an effective and efficient way to strengthen concrete structures. For a FRP strengthened concrete beam, it is usually observed that the failure occurs in the concrete and a thin layer of concrete is attached on the surface of the debonded FRP plate. To study the debond behavior between concrete and FRP composites, an analytical model based on the three-parameter model is developed to study the debonding behavior for the FRP-to-concrete joint under pure shearing. Then, nonlinear FEM analysis is conducted to verify the PrOposed analytical model. The FEM results shows good agreement with the results from the model. Finally, with the analytical model, sensitivity analyses are performed to study the effect of the interracial parameters or the ~eometric parameters on the debondin~ behavior.展开更多
The axial loading in rockbolts changes due to stress redistribution and rheology in the country rock mass.Such a change may lead to debonding at rockbolt to grout interface or rupture of the rockbolt.In this study,bas...The axial loading in rockbolts changes due to stress redistribution and rheology in the country rock mass.Such a change may lead to debonding at rockbolt to grout interface or rupture of the rockbolt.In this study,based on laboratory experiments,ultrasonic guided wave propagation in fully grouted rockbolt under different pull-out loads was investigated in order to examine the resultant debonding of rockbolt.The signals obtained from the ultrasonic monitoring during the pull-out test were processed using wavelet multi-scale analysis and frequency spectrum analysis,the signal amplitude and the amplitude ratio(Q)of low frequency to high frequency were defined to quantify the debonding of rockbolt.In addition to the laboratory test,numerical simulation on the effect of the embedment lengths on ultrasonic guided wave propagation in rockbolt was conducted by using a damage-based model,and the debonding between rockbolt and cement mortar was numerically examined.It was confirmed that the ultrasonic guided wave propagation in rockbolt was very sensitive to the debonding because of pull-out load,therefore,the critical bond length could be calculated based on the propagation of guided wave in the grouted rockbolt.In time domain,the signal amplitude in rockbolt increased with pull-out load from 0 to 100 kN until the completely debonding,thus quantifying the debonding under the different pull-out loads.In the frequency domain,as the Q value increased,the debonding length of rockbolt decreased exponentially.The numerical results confirmed that the guided wave propagation in the fully grouted rockbolt was effective in detecting and quantifying the debonding of rockbolt under pull-out load.展开更多
Bused on the generalized self-consistent finite element iterative averaging method.this paper studied the effects of the fiber-end debonding on the axially tensile elasto- plastic properties of SiC whiskers reinforced...Bused on the generalized self-consistent finite element iterative averaging method.this paper studied the effects of the fiber-end debonding on the axially tensile elasto- plastic properties of SiC whiskers reinforced Aluminium matrix composite for variouscases of different.fiber's fiber's aspect ratios and volume fractions Compared with the casesof perfect interface.it could be concluded that the effects of fiber-end debonding willbecome weaker with the fiber aspect ratio increasing and greater as the fiber volumefraction increases.展开更多
This study aims to investigate the effects of interfacial debonding and fiber volume fraction on the stressstrain behavior of the fiber reinforced metal matrix composites subjected to off-axis loading.The generalized ...This study aims to investigate the effects of interfacial debonding and fiber volume fraction on the stressstrain behavior of the fiber reinforced metal matrix composites subjected to off-axis loading.The generalized method of cells(GMC)is used to analyze a representative element whose fiber shape is circular.The constant compliant interface model(CCI)is also adopted to study the response of composites with imperfect interfacial bonding.Results show that for the composites subjected to off-axis loading,the mechanical behaviors are affected appreciably by the interfacial debonding and the fiber volume fraction.展开更多
The collapse pressure is a key parameter when RTPs are applied in harsh deep-water environments.To investigate the collapse of RTPs,numerical simulations and hydrostatic pressure tests are conducted.For the numerical ...The collapse pressure is a key parameter when RTPs are applied in harsh deep-water environments.To investigate the collapse of RTPs,numerical simulations and hydrostatic pressure tests are conducted.For the numerical simulations,the eigenvalue analysis and Riks analysis are combined,in which the Hashin failure criterion and fracture energy stiffness degradation model are used to simulate the progressive failure of composites,and the“infinite”boundary conditions are applied to eliminate the boundary effects.As for the hydrostatic pressure tests,RTP specimens were placed in a hydrostatic chamber after filled with water.It has been observed that the cross-section of the middle part collapses when it reaches the maximum pressure.The collapse pressure obtained from the numerical simulations agrees well with that in the experiment.Meanwhile,the applicability of NASA SP-8007 formula on the collapse pressure prediction was also discussed.It has a relatively greater difference because of the ignorance of the progressive failure of composites.For the parametric study,it is found that RTPs have much higher first-ply-failure pressure when the winding angles are between 50°and 70°.Besides,the effect of debonding and initial ovality,and the contribution of the liner and coating are also discussed.展开更多
Introducing Neutral Polymeric bonding agents(NPBA) into the Nitrate Ester Plasticized Polyether(NEPE)propellant could improve the adhesion between filler/matrix interface, thereby contributing to the development of ne...Introducing Neutral Polymeric bonding agents(NPBA) into the Nitrate Ester Plasticized Polyether(NEPE)propellant could improve the adhesion between filler/matrix interface, thereby contributing to the development of new generations of the NEPE propellant with better mechanical properties. Therefore,understanding the effects of NPBA on the deformation and damage evolution of the NEPE propellant is fundamental to material design and applications. This paper studies the uniaxial tensile and stress relaxation responses of the NEPE propellant with different amounts of NPBA. The damage evolution in terms of interface debonding is further investigated using a cohesive-zone model(CZM). Experimental results show that the initial modulus and strength of the NEPE propellant increase with the increasing amount of NPBA while the elongation decreases. Meanwhile, the relaxation rate slows down and a higher long-term equilibrium modulus is reached. Experimental and numerical analyses indicate that interface debonding and crack propagation along filler-matrix interface are the dominant damage mechanism for the samples with a low amount of NPBA, while damage localization and crack advancement through the matrix are predominant for the ones with a high amount of NPBA. Finally, crosslinking density tests and simulation results also show that the effect of the bonding agent is interfacial rather than due to the overall crosslinking density change of the binder.展开更多
基金National Natural Science Foundation of China under Grant (Nos.52192662,52020105005,51908320)the Beijing Nova Program under Grant No.20220484012+1 种基金the Interdisciplinary Research Project for Young Teachers of USTB (Fundamental Research Funds for the Central Universities,FRF-IDRY-22-013)the Key Laboratory for Intelligent Infrastructure and Monitoring of Fujian Province (Huaqiao University,IIM-01-05)。
文摘Steel-concrete composite structures(SCCS)have been widely used as primary load-bearing components in large-scale civil infrastructures.As the basis of the co-working ability of steel plate and concrete,the bonding status plays an essential role in guaranteeing the structural performance of SCCS.Accordingly,efficient non-destructive testing(NDT)on interfacial debondings in SCCS has become a prominent research area.Multi-channel analysis of surface waves(MASW)has been validated as an effective NDT technique for interfacial debonding detection for SCCS.However,the feasibility of MASW must be validated using experimental measurements.This study establishes a high-frequency data synchronous acquisition system with 32 channels to perform comparative verification experiments in depth.First,the current sensing approaches for high-frequency vibration and stress waves are summarized.Secondly,three types of contact sensors,namely,piezoelectric lead-zirconate-titanate(PZT)patches,accelerometers,and ultrasonic transducers,are selected for MASW measurement.Then,the selection and optimization of the force hammer head are performed.Comparative experiments are carried out for the optimal selection of ultrasonic transducers,PZT patches,and accelerometers for MASW measurement.In addition,the influence of different pasting methods on the output signal of the sensor array is discussed.Experimental results indicate that optimized PZT patches,acceleration sensors,and ultrasonic transducers can provide efficient data acquisition for MASW-based non-destructive experiments.The research findings in this study lay a solid foundation for analyzing the recognition accuracy of contact MASW measurement using different sensor arrays.
文摘This paper introduced a novel microstructure-based constitutive model designed to comprehensively characterize the intricate mechanical behavior of anisotropic clay rocks under the influence of water saturation.The proposed model encompasses elastoplastic deformation,time-dependent behavior,and induced damage.A two-step homogenization process incorporates mineral compositions and porosity to determine the macroscopic elastic tensor and plastic yield criterion.The model also considers interfacial debonding between the matrix and inclusions to capture rock damage.The application of the proposed model is demonstrated through an analysis of Callovo-Oxfordian clayey rocks,specifically in the context of radioactive waste disposal in France.Model parameters are determined,followed by numerical simulations of various laboratory tests including lateral decompression tests with constant mean stress,triaxial compression tests under different water saturation conditions,and creep tests.The numerical results are compared with corresponding experimental data to assess the efficacy of the proposed model.
基金Project supported by the National Natural Science Foundation of China(Nos.12072183,11872236,12172205)the Key Research Project of Zhejiang Laboratory of China(No.2021PE0AC02)。
文摘The interfacial debonding between the active layer and the current collector has been recognized as a critical mechanism for battery fading,and thus has attracted great efforts focused on the related analyses.However,much still remains to be studied regarding practical methods for suppressing electrode debonding,especially from the perspective of mechanics.In this paper,a pre-strain strategy of current collectors to alleviate electrode debonding is proposed.An analytical model for a symmetric electrode with a deformable and limited-thickness current collector is developed to analyze the debonding behavior involving both a pre-strain of the current collector and an eigen-strain of the active layers.The results reveal that the well-designed pre-strain can significantly delay the debonding onset(by up to 100%)and considerably reduce the debonding size.The critical values of the pre-strain are identified,and the pre-strain design principles are also provided.Based on these findings,this work sheds light on the mechanical design to suppress electrode degradation.
基金This work is supported by National Natural Science Foundation of China(51608406)the Fundamental Research Funds for the Central Universities(201114013).
文摘Strain hardening cement-based composites(SHCC)beam externally bonded with glass fiber-reinforced polymer(FRP)plate was examined under three-point flexural test.The effects of the type of substrate used(plain cement mortar vs.SHCC),the use or not of a FRP plate to strengthen the SHCC beam,and the thickness of the FRP plate on the flexural performances were studied.Results show that the ultimate load of SHCC beams strengthened with FRP plate has improved greatly in comparison with plain SHCC beams.The deformation capacity of beams makes little change with an increase in the thickness of FRP plates.The formation of multiple flexural-shear cracks(MFSC)is the unique feature of SHCC beams bonded with FRP plates under three-point bending.The debonding of the FRP plate is initiated from MFSC.The initiated debonding area(IDA)is formed by the joint points of the flexural-shear cracks with the FRP plate.Then the debonding strain is represented using the average strain of FRP plate within IDA,which decreases with an increase of FRP plate thickness.The experimental values of the debonding strain of SHCC beam reinforced with FRP plate are close to those predicted by the JSCE’s equation.
基金the Nationai Natural Science Foundation of China(19632030 and 19872007)Natural Science Foundation of Jiangsu Province
文摘The mechanisms of interfacial debonding of particle reinforcedrheological materials are studied. Based on an energy criterion, asimple formula of local critical stress for interfacial debonding isderived and expressed in terms of the interfacial energy. Theparticle size effect on interface debond- ing can then be analyzedeasily owing to the fact that critical stress is inverselyproportional to the square root of particle radius. By takingPP/CaCO_3 system as an example, the present energy criterion iscompared with the mechanical debonding criterion, and it is foundthat under the condition that bond strength is equal to matrixstrength and particle radius not over 0.2μm, the mechanicaldebonding cri- terion can be automatically satisfied if the energycirterion is satisfied.
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.Based on the double shear-lag model and Paris formula,the interracial damage of coated- fiber-reinforced composites under tension-tension cyclic loading is studied.The effects of strength and thickness of the coating materials on the debond stress,debond rate as well as debond length are simulated.
基金supported by the National Natural Science Foundation of China (Grant No.41772333)the National Natural Science Foundation of Shaanxi Province, China (Grant No.2018JQ5124)the New-Star Talents Promotion Project of Science and Technology of Shaanxi Province, China (Grant No.2019KJXX049)。
文摘The sufficient bond between concrete and rock is an important prerequisite to ensure the effect of shotcrete support. However, in cold regions engineering protection system, the bond condition of rock and concrete surface is easily affected by freeze-thaw cycles, resulting in interface damage, debonding and even supporting failure. Understanding the micromechanisms of the damage and debonding of the rock-concrete interface is essential for improving the interface protection.Therefore, the micromorphology, micromechanical properties, and microdebonding evolution of the sandstone-concrete interface transition zone(ITZ) under varying freeze-thaw cycles(0, 5, 10, 15, 20) were studied using scanning electron microscope, stereoscopic microscope, and nano-indentation. Furthermore, the distribution range and evolution process of ITZ affected by freeze-thaw cycles were defined. Major findings of this study are as follows:(1) The microdamage evolution law of the ITZ under increasing freeze-thaw cycles is clarified, and the relationship between the number of cracks in the ITZ and freeze-thaw cycles is established;(2) As the number of freeze-thaw cycles increases, the ITZ's micromechanical strength decreases, and its development width tends to increase;(3) The damage and debonding evolution mechanisms of sandstone-concrete ITZ under freeze-thaw cycles is revealed, and its micromechanical evolution model induced by freeze-thaw cycles is proposed.
文摘This paper investigates the dynamic behavior of a buried rigid elliptic cylinder partially debonded from surrounding matrix under the action of anti-plane shear waves (SH waves). The debonding region is modeled as an elliptic arc-shaped interface crack with non-contacting faces. By using the wave function (Mathieu function) expansion method and introducing the dislocation density function as an unknown variable, the problem is reduced to a singular integral equation which is solved numerically to calculate the near and far fields of the problem. The resonance of the structure and the effects of various parameters on the resonance are discussed.
基金supported by the National Natural Science Foundation of China(No.51278156)the Basic Project of Shenzhen Science & Technology Program(No.JCYJ2017030155815876)
文摘The interfacial debonding in fiber-reinforced plastic(FRP)strengthened repair material will affect the bonding strength and lead to failure of the repair without warning.Unfortunately the interfacial damage is normally invisible and often in the form of a patch rather than a through-width crack.Therefore,a debonding patch detection technique based on fiber optic interferometry is proposed.A quasi-impulse loading is applied with a rubberhead hammer and the total elongation of a surface-mounted optical fiber along the length of the repair material is measured as a function of load position.When a debonding patch is present,the induced sudden slope or sign change on the plot of fiber integral strain v.s.load position will reveal the extent and the location of the debonded area.The results of the study indicate that the proposed technique is applicable for debonding patch detection in repaired members under various support conditions.
基金This work was supported by the National Natural Science Foundation of China(No.59778034)the Science Foundation of Hebei province(No.03276901)
文摘With the increasingly use of FRC (fiber-reinforced composite) in urban lifelines, me-chanical properties investigation is very important for disaster resistance, especiallythe investigation of fatigue properties. Based on the shear-lag model, an usual com-posite model under cyclic loading is established. According to the Paris formula, therelationship between interfacial fatigue parameters and the number of cycles is ob-tained under the cyclic loading. Interfocial fatigue properties of this model and thegrowth of the interfacial fatigue crack are analyzed. And the Poisson ratio is consid-ered also.
文摘A generalized solution was obtained for the partially debonded elliptic inhomogeneity problem in piezoelectric materials under antiplane shear and inplane electric loading using the complex variable method. It was assumed that the interfacial debonding induced an electrically impermeable crack at the interface. The principle of conformal transformation and analytical continuation were employed to reduce the formulation into two Riemann-Hilbert problems. This enabled the determination of the complex potentials in the inhomogeneity and the matrix by means of series of expressions. The resulting solution was then used to obtain the electroelastic fields and the energy release rate involving the debonding at the inhomogeneity-matrix interface. The validity and versatility of the current general solution have been demonstrated through some specific examples such as the problems of perfectly bonded elliptic inhomogeneity, totally debonded elliptic inhomogeneity, partially debonded rigid and conducting elliptic inhomogeneity, and partially debonded circular inhomogeneity.
基金the National Basic Research Program of China (973 Project) (No. 2009CB623200)National Natural Science Foundation of China (No. 50808043)+1 种基金the Doctoral Program of Higher Education of China (No. 20070286024)the Priority Academic Program Development of Jiangsu Higher Education Institutions
文摘External bonding of fiber reinforced polymer (FRP) composites on the concrete structures has been proved to be an effective and efficient way to strengthen concrete structures. For a FRP strengthened concrete beam, it is usually observed that the failure occurs in the concrete and a thin layer of concrete is attached on the surface of the debonded FRP plate. To study the debond behavior between concrete and FRP composites, an analytical model based on the three-parameter model is developed to study the debonding behavior for the FRP-to-concrete joint under pure shearing. Then, nonlinear FEM analysis is conducted to verify the PrOposed analytical model. The FEM results shows good agreement with the results from the model. Finally, with the analytical model, sensitivity analyses are performed to study the effect of the interracial parameters or the ~eometric parameters on the debondin~ behavior.
基金This work is funded by the National Science Foundation of China(Grant Nos.U1906208,52104157,51904056 and 51874069)and the Fundamental Research Funds for the Central Universities of China(Grant Nos.N2101028 and N2101015).
文摘The axial loading in rockbolts changes due to stress redistribution and rheology in the country rock mass.Such a change may lead to debonding at rockbolt to grout interface or rupture of the rockbolt.In this study,based on laboratory experiments,ultrasonic guided wave propagation in fully grouted rockbolt under different pull-out loads was investigated in order to examine the resultant debonding of rockbolt.The signals obtained from the ultrasonic monitoring during the pull-out test were processed using wavelet multi-scale analysis and frequency spectrum analysis,the signal amplitude and the amplitude ratio(Q)of low frequency to high frequency were defined to quantify the debonding of rockbolt.In addition to the laboratory test,numerical simulation on the effect of the embedment lengths on ultrasonic guided wave propagation in rockbolt was conducted by using a damage-based model,and the debonding between rockbolt and cement mortar was numerically examined.It was confirmed that the ultrasonic guided wave propagation in rockbolt was very sensitive to the debonding because of pull-out load,therefore,the critical bond length could be calculated based on the propagation of guided wave in the grouted rockbolt.In time domain,the signal amplitude in rockbolt increased with pull-out load from 0 to 100 kN until the completely debonding,thus quantifying the debonding under the different pull-out loads.In the frequency domain,as the Q value increased,the debonding length of rockbolt decreased exponentially.The numerical results confirmed that the guided wave propagation in the fully grouted rockbolt was effective in detecting and quantifying the debonding of rockbolt under pull-out load.
文摘Bused on the generalized self-consistent finite element iterative averaging method.this paper studied the effects of the fiber-end debonding on the axially tensile elasto- plastic properties of SiC whiskers reinforced Aluminium matrix composite for variouscases of different.fiber's fiber's aspect ratios and volume fractions Compared with the casesof perfect interface.it could be concluded that the effects of fiber-end debonding willbecome weaker with the fiber aspect ratio increasing and greater as the fiber volumefraction increases.
基金supported by the National Natural Science Foundation of China(No.51175401)Shaanxi Province Project(No.2011kjxx06)
文摘This study aims to investigate the effects of interfacial debonding and fiber volume fraction on the stressstrain behavior of the fiber reinforced metal matrix composites subjected to off-axis loading.The generalized method of cells(GMC)is used to analyze a representative element whose fiber shape is circular.The constant compliant interface model(CCI)is also adopted to study the response of composites with imperfect interfacial bonding.Results show that for the composites subjected to off-axis loading,the mechanical behaviors are affected appreciably by the interfacial debonding and the fiber volume fraction.
基金financially supported by National Natural Science Foundation of China(Grant Nos.52088102,51879249)Fundamental Research Funds for the Central Universities(Grant No.202261055)。
文摘The collapse pressure is a key parameter when RTPs are applied in harsh deep-water environments.To investigate the collapse of RTPs,numerical simulations and hydrostatic pressure tests are conducted.For the numerical simulations,the eigenvalue analysis and Riks analysis are combined,in which the Hashin failure criterion and fracture energy stiffness degradation model are used to simulate the progressive failure of composites,and the“infinite”boundary conditions are applied to eliminate the boundary effects.As for the hydrostatic pressure tests,RTP specimens were placed in a hydrostatic chamber after filled with water.It has been observed that the cross-section of the middle part collapses when it reaches the maximum pressure.The collapse pressure obtained from the numerical simulations agrees well with that in the experiment.Meanwhile,the applicability of NASA SP-8007 formula on the collapse pressure prediction was also discussed.It has a relatively greater difference because of the ignorance of the progressive failure of composites.For the parametric study,it is found that RTPs have much higher first-ply-failure pressure when the winding angles are between 50°and 70°.Besides,the effect of debonding and initial ovality,and the contribution of the liner and coating are also discussed.
基金National Natural Science Foundation of China(U22B20131)for supporting this project.
文摘Introducing Neutral Polymeric bonding agents(NPBA) into the Nitrate Ester Plasticized Polyether(NEPE)propellant could improve the adhesion between filler/matrix interface, thereby contributing to the development of new generations of the NEPE propellant with better mechanical properties. Therefore,understanding the effects of NPBA on the deformation and damage evolution of the NEPE propellant is fundamental to material design and applications. This paper studies the uniaxial tensile and stress relaxation responses of the NEPE propellant with different amounts of NPBA. The damage evolution in terms of interface debonding is further investigated using a cohesive-zone model(CZM). Experimental results show that the initial modulus and strength of the NEPE propellant increase with the increasing amount of NPBA while the elongation decreases. Meanwhile, the relaxation rate slows down and a higher long-term equilibrium modulus is reached. Experimental and numerical analyses indicate that interface debonding and crack propagation along filler-matrix interface are the dominant damage mechanism for the samples with a low amount of NPBA, while damage localization and crack advancement through the matrix are predominant for the ones with a high amount of NPBA. Finally, crosslinking density tests and simulation results also show that the effect of the bonding agent is interfacial rather than due to the overall crosslinking density change of the binder.