The capability of embedded piezoelectric wafer active sensors(PWAS)to perform in-situ nondestructive evaluation(NDE)for structural health monitoring(SHM)of reinforced concrete(RC)structures strengthened with fiber rei...The capability of embedded piezoelectric wafer active sensors(PWAS)to perform in-situ nondestructive evaluation(NDE)for structural health monitoring(SHM)of reinforced concrete(RC)structures strengthened with fiber reinforced polymer(FRP)composite overlays is explored.First,the disbond detection method were developed on coupon specimens consisting of concrete blocks covered with an FRP composite layer.It was found that the presence of a disbond crack drastically changes the electromecfianical(E/M)impedance spectrum lneasurcd at the PWAS terlninals.The spectral changes depend on the distance between the PWAS and the crack tip.Second,large scale experiments were conducted on a RC beam strengthened with carbon fiber reinforced polymer(CFRP)composite overlay.The beam was subject to an accelerated fatigue load regime in a three-point bending configuration up to a total of 807,415 cycles.During these fatigue tests,the CFRP overlay experienced disbonding beginning at about 500,000 cycles.The PWAS were able to detect the disbonding before it could be reliably seen by visual inspection.Good correlation between the PWAS readings and the position and extent of disbond damage was observed.These preliminary results demonstrate the potential of PWAS technology for SHM of RC structures strengthened with FRP composite overlays.展开更多
In this paper,we report the study of the process of fabricating a multi-layermetal micro-structure using UV-LIGA overlay technology,includingmask fabrication,substrate treatment,and UV-LIGA overlay processes.To solve ...In this paper,we report the study of the process of fabricating a multi-layermetal micro-structure using UV-LIGA overlay technology,includingmask fabrication,substrate treatment,and UV-LIGA overlay processes.To solve the process problems in the masking procedure,the swelling problemof the first layer of SU-8 thick photoresist was studied experimentally.The 5μmline-width compensation and closed 20μmand 30μmisolation strips were designed and fabricated around the micro-structure pattern.The pore problemin the Ni micro-electroforming layer was analyzed and the electroforming parameters were improved.The pH value of the electroforming solution should be controlled between 3.8 and 4.4 and the current density should be below 3 A/dm^2.To solve the problems of high inner stress and incomplete development of the micro-cylinder hole array with a diameter of 30μm,the lithography process was optimized.The pre-baking temperature was increased via gradient heating and rose every 5℃ from 65℃ to 85℃ and then remained at 85℃ for 50 min–1 h.In addition,the full contact exposure was used.Finally,a multi-layer metal micro-structure with high precision and good quality of microelectroforming layer was fabricated using UV-LIGA overlay technology.展开更多
This research extends ongoing efforts to develop methods for reinforcing damaged main gas pipelines to prevent catastrophic failure.This study establishes the use of scaled-down experimental models for assessing the d...This research extends ongoing efforts to develop methods for reinforcing damaged main gas pipelines to prevent catastrophic failure.This study establishes the use of scaled-down experimental models for assessing the dynamic strength of damaged pipeline sections reinforced with wire wrapping or composite sleeves.A generalized dynamic model is introduced for numerical simulation to evaluate the effectiveness of reinforcement techniques.The model incorporates the elastoplastic behavior of pipe and wire materials,the influence of temperature on mechanical properties,the contact interaction between the pipe and the reinforcement components(including pretensioning),and local material failure under transient internal pressure.Based on these parameters,a finite element model was developed using ANSYS 19.2 to enable parametric studies.The accuracy of the proposed model was verified by comparing the simulation results with the experimental findings.Pipeline section samples containing non-penetrating longitudinal crackswere subjected to comparative analyses and transient pressure until critical failure.The unreinforced and steel wire-wrapped sections were investigated.The results confirm the feasibility of applying the computational model to study the dynamic strength of reinforced damaged pipe sections.Furthermore,pipelines with longitudinal cracks reinforced using circular composite overlays with orthotropic mechanical properties were examined,and recommendations are provided for selecting the geometric parameters of such overlays.展开更多
基金the National Seienee Foundation through grants NSF#CMS-9908293 and NSF INT-9904493the Federal Highway Administration and the South Carolina Department of TransPortation(projeet Number 614)
文摘The capability of embedded piezoelectric wafer active sensors(PWAS)to perform in-situ nondestructive evaluation(NDE)for structural health monitoring(SHM)of reinforced concrete(RC)structures strengthened with fiber reinforced polymer(FRP)composite overlays is explored.First,the disbond detection method were developed on coupon specimens consisting of concrete blocks covered with an FRP composite layer.It was found that the presence of a disbond crack drastically changes the electromecfianical(E/M)impedance spectrum lneasurcd at the PWAS terlninals.The spectral changes depend on the distance between the PWAS and the crack tip.Second,large scale experiments were conducted on a RC beam strengthened with carbon fiber reinforced polymer(CFRP)composite overlay.The beam was subject to an accelerated fatigue load regime in a three-point bending configuration up to a total of 807,415 cycles.During these fatigue tests,the CFRP overlay experienced disbonding beginning at about 500,000 cycles.The PWAS were able to detect the disbonding before it could be reliably seen by visual inspection.Good correlation between the PWAS readings and the position and extent of disbond damage was observed.These preliminary results demonstrate the potential of PWAS technology for SHM of RC structures strengthened with FRP composite overlays.
文摘In this paper,we report the study of the process of fabricating a multi-layermetal micro-structure using UV-LIGA overlay technology,includingmask fabrication,substrate treatment,and UV-LIGA overlay processes.To solve the process problems in the masking procedure,the swelling problemof the first layer of SU-8 thick photoresist was studied experimentally.The 5μmline-width compensation and closed 20μmand 30μmisolation strips were designed and fabricated around the micro-structure pattern.The pore problemin the Ni micro-electroforming layer was analyzed and the electroforming parameters were improved.The pH value of the electroforming solution should be controlled between 3.8 and 4.4 and the current density should be below 3 A/dm^2.To solve the problems of high inner stress and incomplete development of the micro-cylinder hole array with a diameter of 30μm,the lithography process was optimized.The pre-baking temperature was increased via gradient heating and rose every 5℃ from 65℃ to 85℃ and then remained at 85℃ for 50 min–1 h.In addition,the full contact exposure was used.Finally,a multi-layer metal micro-structure with high precision and good quality of microelectroforming layer was fabricated using UV-LIGA overlay technology.
基金funded by the Science Committee of the Ministry of Science and Higher Education of the Republic of Kazakhstan(Grant No.AP19680589).
文摘This research extends ongoing efforts to develop methods for reinforcing damaged main gas pipelines to prevent catastrophic failure.This study establishes the use of scaled-down experimental models for assessing the dynamic strength of damaged pipeline sections reinforced with wire wrapping or composite sleeves.A generalized dynamic model is introduced for numerical simulation to evaluate the effectiveness of reinforcement techniques.The model incorporates the elastoplastic behavior of pipe and wire materials,the influence of temperature on mechanical properties,the contact interaction between the pipe and the reinforcement components(including pretensioning),and local material failure under transient internal pressure.Based on these parameters,a finite element model was developed using ANSYS 19.2 to enable parametric studies.The accuracy of the proposed model was verified by comparing the simulation results with the experimental findings.Pipeline section samples containing non-penetrating longitudinal crackswere subjected to comparative analyses and transient pressure until critical failure.The unreinforced and steel wire-wrapped sections were investigated.The results confirm the feasibility of applying the computational model to study the dynamic strength of reinforced damaged pipe sections.Furthermore,pipelines with longitudinal cracks reinforced using circular composite overlays with orthotropic mechanical properties were examined,and recommendations are provided for selecting the geometric parameters of such overlays.
