Transactions of Nanjing University of Aeronautics & Astronautics
Volume 32,Issue 3,2015 Table of Contents
2015, 32(3):255-260.
Abstract:
Mode shape has become a hotspot of vibrationbased damage detection in plates. Twodimensional(2D) modal curvature (MC2D), derived from mode shapes, is a prevailing physical quantity used to indicate damage. Unfortunately, the physical mechanism of MC2D for characterizing damage in plates has not been clarified to date. In contrast, onedimensional(1D) modal curvature (MC1D) has explicit physical mechanism to portray damage in beams. Unresolved physical mechanism of MC2D severely hampers its applications for damage identification in plates. To address this deficiency, the clarification mechanism of MC2D is investigated to identify damage. With the clarified mechanism, numerical and experimental cases are used to demonstrate the effectiveness of MC 2D in detecting damage in plates.
Mode shape has become a hotspot of vibrationbased damage detection in plates. Twodimensional(2D) modal curvature (MC2D), derived from mode shapes, is a prevailing physical quantity used to indicate damage. Unfortunately, the physical mechanism of MC2D for characterizing damage in plates has not been clarified to date. In contrast, onedimensional(1D) modal curvature (MC1D) has explicit physical mechanism to portray damage in beams. Unresolved physical mechanism of MC2D severely hampers its applications for damage identification in plates. To address this deficiency, the clarification mechanism of MC2D is investigated to identify damage. With the clarified mechanism, numerical and experimental cases are used to demonstrate the effectiveness of MC 2D in detecting damage in plates.
2015, 32(3):261-267.
Abstract:
Optical fiberbased sensors are usually applied in structural health monitoring (SHM) as part of smart materials. The weak interface between the optical fiber and the host material will reduce the mechanical performance of the smart materials. Normally, the principal parts of the optical fibers are inorganic, while the matrix of host material is organic. These two kinds of materials can not be combined. Microfracture can be found in smart materials. Two methods for improving the interface are proposed. Firstly, the influence of the interface size on the strength is studied. Secondly, interfacial treatment before embedding the optical fiber into the composite is analyzed. Compressive tests of composite laminated specimens are conducted to evaluate the proposed methods. The specimens are produced from T300 Carbon/epoxy prepreg, with different treated optical fiber embedded inside. The experimental results indicate that smaller interface size and proper treatment will strengthen the whole structure.
Optical fiberbased sensors are usually applied in structural health monitoring (SHM) as part of smart materials. The weak interface between the optical fiber and the host material will reduce the mechanical performance of the smart materials. Normally, the principal parts of the optical fibers are inorganic, while the matrix of host material is organic. These two kinds of materials can not be combined. Microfracture can be found in smart materials. Two methods for improving the interface are proposed. Firstly, the influence of the interface size on the strength is studied. Secondly, interfacial treatment before embedding the optical fiber into the composite is analyzed. Compressive tests of composite laminated specimens are conducted to evaluate the proposed methods. The specimens are produced from T300 Carbon/epoxy prepreg, with different treated optical fiber embedded inside. The experimental results indicate that smaller interface size and proper treatment will strengthen the whole structure.
2015, 32(3):268-278.
Abstract:
Since vibration signals of hydraulic pump are mostly nonlinear and traditional fusion algorithm cannot satisfyingly process them, a morphological undecimated wavelet decomposition fusion (MUWDF) algorithm is proposed. Firstly, under the framework of morphological undecimated wavelet decomposition (MUWD), multichannel signals are decomposed. Approximate signals of all decomposition layers are selected by feature energy factor and fused according to the presented fusion rules. Furthermore, specific method for optimal selection of MUWDF parameters is presented to avoid subjective influences. Finally, the proposed algorithm is verified by simulation signals and pump vibration signals.
Since vibration signals of hydraulic pump are mostly nonlinear and traditional fusion algorithm cannot satisfyingly process them, a morphological undecimated wavelet decomposition fusion (MUWDF) algorithm is proposed. Firstly, under the framework of morphological undecimated wavelet decomposition (MUWD), multichannel signals are decomposed. Approximate signals of all decomposition layers are selected by feature energy factor and fused according to the presented fusion rules. Furthermore, specific method for optimal selection of MUWDF parameters is presented to avoid subjective influences. Finally, the proposed algorithm is verified by simulation signals and pump vibration signals.
2015, 32(3):279-288.
Abstract:
Fatigue damage monitoring is critical metallic structure health monitoring of aircraft. The sensor should be high sensitive, easy to be integrated into structure and well adaptable for poor working conditions. Therefore, an attached eddy current sensor with flexible plane is put forward and its characteristics are analyzed. By extracting material′s conductivity as the crack features, forward semianalytical model is established and parameter optimizations are carried out. Crack perturbation model of attached eddy current sensor is constructed, and perturbation voltages of sensing channels under threedimension structural crack are obtained. To verify the sensor′s performance, monitoring experiment on crack extension is conducted under condition of 3 MHz frequency. The validation experimental results show that perturbation model of 2A12T4 aluminum alloy agrees well with experiment results, and perturbation model errors of four sensing channels are within 25%. The attached eddy current sensor is capable of testing the crack nondestructively and measuring the crack extension zuantitatively with the accuracy of 1 mm.
Fatigue damage monitoring is critical metallic structure health monitoring of aircraft. The sensor should be high sensitive, easy to be integrated into structure and well adaptable for poor working conditions. Therefore, an attached eddy current sensor with flexible plane is put forward and its characteristics are analyzed. By extracting material′s conductivity as the crack features, forward semianalytical model is established and parameter optimizations are carried out. Crack perturbation model of attached eddy current sensor is constructed, and perturbation voltages of sensing channels under threedimension structural crack are obtained. To verify the sensor′s performance, monitoring experiment on crack extension is conducted under condition of 3 MHz frequency. The validation experimental results show that perturbation model of 2A12T4 aluminum alloy agrees well with experiment results, and perturbation model errors of four sensing channels are within 25%. The attached eddy current sensor is capable of testing the crack nondestructively and measuring the crack extension zuantitatively with the accuracy of 1 mm.
2015, 32(3):289-296.
Abstract:
Aiming at the requirements of installation and work environment of metalbased fiber Bragg grating (FBG) sensor, a resistance spot welding method is presented. Firstly, the effect of welding parameters on welding quality is discussed theoretically, and a suitable resistance spot welding method for the metalbased FBG sensor is proposed for the first time. Then through serial resistance spot welding tests, the feasibility and practicability of the method are verified, and optimal welding parameters for two different tested metals are obtained. Fatigue performance test validates FBG sensors installed by the proposed method with good fatigue properties and longterm stable measurement performance. The research results can provide technical guidance for engineering structure longterm safety monitoring.
Aiming at the requirements of installation and work environment of metalbased fiber Bragg grating (FBG) sensor, a resistance spot welding method is presented. Firstly, the effect of welding parameters on welding quality is discussed theoretically, and a suitable resistance spot welding method for the metalbased FBG sensor is proposed for the first time. Then through serial resistance spot welding tests, the feasibility and practicability of the method are verified, and optimal welding parameters for two different tested metals are obtained. Fatigue performance test validates FBG sensors installed by the proposed method with good fatigue properties and longterm stable measurement performance. The research results can provide technical guidance for engineering structure longterm safety monitoring.
2015, 32(3):297-304.
Abstract:
A kind of wireless sensor was previously developed, which is powered and transmit signals wirelessly instead of using an electrical connection to the embedded reinforcement. Based on this technique, the relationship between diameters of corroded sensing steel wires and corrosion levels of steel bars is established by experiments. Quadratic function is utilized to fit the experiment results, and the correlation coefficients are all larger than 0.95. Estimated corrosion levels of commonly used steel bars are given for different diameters of corroded sensing steel wires fractured due to corrosion.
A kind of wireless sensor was previously developed, which is powered and transmit signals wirelessly instead of using an electrical connection to the embedded reinforcement. Based on this technique, the relationship between diameters of corroded sensing steel wires and corrosion levels of steel bars is established by experiments. Quadratic function is utilized to fit the experiment results, and the correlation coefficients are all larger than 0.95. Estimated corrosion levels of commonly used steel bars are given for different diameters of corroded sensing steel wires fractured due to corrosion.
2015, 32(3):305-311.
Abstract:
This study aims to develop a reliable method for locating multiple cracks in a beam using data fusion of multiple curvature mode shapes. The identification of multiple damage in beams based on curvature mode shape has become a research focus in recent decades. However, the curvature mode shape method using a single mode carries limited damage information, and fails to reveal all cracks when multiple damage detection is required. To address this limitation, the curvature mode shape method is further enhanced by a data fusion algorithm to fuse damage information in multiple modes. The effectiveness of the method is proved through a numerical case of a beam with multiple cracks. The applicability of the method is experimentally validated by detecting multiple cracks in a composite laminated beam with mode shapes acquired by a scanning laser vibrometer. The results show that the method of fusing multiple curvature mode shapes carries more complete damage information than the traditional one using a single mode, and can successfully locate all cracks in a damaged beam.
This study aims to develop a reliable method for locating multiple cracks in a beam using data fusion of multiple curvature mode shapes. The identification of multiple damage in beams based on curvature mode shape has become a research focus in recent decades. However, the curvature mode shape method using a single mode carries limited damage information, and fails to reveal all cracks when multiple damage detection is required. To address this limitation, the curvature mode shape method is further enhanced by a data fusion algorithm to fuse damage information in multiple modes. The effectiveness of the method is proved through a numerical case of a beam with multiple cracks. The applicability of the method is experimentally validated by detecting multiple cracks in a composite laminated beam with mode shapes acquired by a scanning laser vibrometer. The results show that the method of fusing multiple curvature mode shapes carries more complete damage information than the traditional one using a single mode, and can successfully locate all cracks in a damaged beam.
2015, 32(3):312-317.
Abstract:
The third damage action, human disruption behavior, is one of the major threats to pipeline operation. It is necessary to monitor and locate the perturbation behavior that may threat pipeline safety in realtime. Therefore, a new pipeline security monitoring system is designed by using linestructure Sagnac optic fiber interferemeter with the characteristic of 3×3 coupler that can modulate the phase of optic signal, with no need for phase modulation and demodulation. The optic structure of the new system is simplified, the signal processing accuracy is improved, and the polarization effect is reduced. The working principle of the monitoring in ideal condition is described, the phase demodulation is analyzed and the location of the possible damage action point is formulated. By using simulink, the optic signal propagation and interference is simulated and interference signals in different frequencies are obtained. The results validate the feasibility of the monitoring system and indicate that the low frequency signal less than 1 kHz resulting from the human damage action can be detected. The disturbance set at 10 km can be located by calculating the demodulation signal accurately over a long monitoring distance.
The third damage action, human disruption behavior, is one of the major threats to pipeline operation. It is necessary to monitor and locate the perturbation behavior that may threat pipeline safety in realtime. Therefore, a new pipeline security monitoring system is designed by using linestructure Sagnac optic fiber interferemeter with the characteristic of 3×3 coupler that can modulate the phase of optic signal, with no need for phase modulation and demodulation. The optic structure of the new system is simplified, the signal processing accuracy is improved, and the polarization effect is reduced. The working principle of the monitoring in ideal condition is described, the phase demodulation is analyzed and the location of the possible damage action point is formulated. By using simulink, the optic signal propagation and interference is simulated and interference signals in different frequencies are obtained. The results validate the feasibility of the monitoring system and indicate that the low frequency signal less than 1 kHz resulting from the human damage action can be detected. The disturbance set at 10 km can be located by calculating the demodulation signal accurately over a long monitoring distance.
2015, 32(3):318-324.
Abstract:
Bolted connections are commonly used in aerospace structures. Once the bolts on the aircraft are damaged or loose, the consequence will be disastrous. Therefore, monitoring bolt loosening is especially required. However, periodic manual inspection costs much money and time. And it is very difficult to achieve multipoint monitoring for many bolted structures in an aircraft. Therefore, a lowcost, reliable detection method based on wireless sensor networks is presented. The reed switch is selected as a sensor for bolt loosening monitor. The chip PT2262 and PT2272 are chosen as hardware codec chip for multipoint placement. A wireless transmitter and receiver circuit is designed on 315 MHz frequency. The codec chip and the wireless transmission are triggered by the reed switches. Ｂolt loosening is detected by the receiving terminal and indicated by light and sound alarms. The wireless transmitter and ｔｈｅ receiver circuit are test ed and the monitoring system is erified by experiments. The results show that bolt loosening can be effectively detected within 300 m. The developed sensor network is expected to solve multipoint bolt detection problems and provide a low cost and reliable monitoring technology.
Bolted connections are commonly used in aerospace structures. Once the bolts on the aircraft are damaged or loose, the consequence will be disastrous. Therefore, monitoring bolt loosening is especially required. However, periodic manual inspection costs much money and time. And it is very difficult to achieve multipoint monitoring for many bolted structures in an aircraft. Therefore, a lowcost, reliable detection method based on wireless sensor networks is presented. The reed switch is selected as a sensor for bolt loosening monitor. The chip PT2262 and PT2272 are chosen as hardware codec chip for multipoint placement. A wireless transmitter and receiver circuit is designed on 315 MHz frequency. The codec chip and the wireless transmission are triggered by the reed switches. Ｂolt loosening is detected by the receiving terminal and indicated by light and sound alarms. The wireless transmitter and ｔｈｅ receiver circuit are test ed and the monitoring system is erified by experiments. The results show that bolt loosening can be effectively detected within 300 m. The developed sensor network is expected to solve multipoint bolt detection problems and provide a low cost and reliable monitoring technology.
2015, 32(3):325-333.
Abstract:
Since health monitoring of shield tunnels generally employs multiple sensors belonging to different types, a fine analysis on massive monitoring data, as well as further quantitative health grading, is really challenging. An optimized fuzzy clustering analysis method based on the fuzzy equivalence relation is proposed for health monitoring of shield tunnels. Clustering results are autogenerated by using fuzzy similarityvalued map. The results follow the idea of unsupervised classification. Moreover, a onvenient new health index HI is proposed for a fast tunnelhealth grading. A case study on Nanjing Yangtze River Tunnel is presented to validate this method. Three types of indicators, namely soil pressure, pore water pressure and steel strain, are used to develop the clustering model. The clustering results are verified by analyzing the engineering geological conditions; the validity and the efficacy of the proposed method are also emonstrated. Further, the fuzzy clustering analy sis also represents a potential for identifying abnormal monitoring data. This investigation indicates the fuzzy clustering analysis method is capable of characterizing the fuzziness of tunnel health, and beneficial to clarify the tunnel health evaluation uncertainties.
Since health monitoring of shield tunnels generally employs multiple sensors belonging to different types, a fine analysis on massive monitoring data, as well as further quantitative health grading, is really challenging. An optimized fuzzy clustering analysis method based on the fuzzy equivalence relation is proposed for health monitoring of shield tunnels. Clustering results are autogenerated by using fuzzy similarityvalued map. The results follow the idea of unsupervised classification. Moreover, a onvenient new health index HI is proposed for a fast tunnelhealth grading. A case study on Nanjing Yangtze River Tunnel is presented to validate this method. Three types of indicators, namely soil pressure, pore water pressure and steel strain, are used to develop the clustering model. The clustering results are verified by analyzing the engineering geological conditions; the validity and the efficacy of the proposed method are also emonstrated. Further, the fuzzy clustering analy sis also represents a potential for identifying abnormal monitoring data. This investigation indicates the fuzzy clustering analysis method is capable of characterizing the fuzziness of tunnel health, and beneficial to clarify the tunnel health evaluation uncertainties.
2015, 32(3):334-340.
Abstract:
Electromagnetic emission induced during concrete fracturing is of great significance to health monitoring of concrete structures. A coupled stress electricity model is established by analyzing the interaction between stress and electricity during concrete fracturing. And based on this model, the electromagnetic radiation parameters are calculated. The theoretical calculation is well coincident with experimental results. This work provides theoretical support for concrete testing system.
Electromagnetic emission induced during concrete fracturing is of great significance to health monitoring of concrete structures. A coupled stress electricity model is established by analyzing the interaction between stress and electricity during concrete fracturing. And based on this model, the electromagnetic radiation parameters are calculated. The theoretical calculation is well coincident with experimental results. This work provides theoretical support for concrete testing system.
2015, 32(3):341-347.
Abstract:
Stability and accuracy of the imaging results are still unmet practical demands for ultrasonic computed tomography (CT) of concrete material. To address these issues, a CT technique based on simulated annealing genetic algorithm (SAGA) is presented in this work. Firstly, a natural weight matrix with clear physical meaning is introduced in the inverse algorithm and then a quadric broadening objective function is formed according to the propagation characteristics of ultrasound in concrete. After that, the simulated annealing (SA) searching is added to speed up the inverse process and to improve the convergence and stability of the algorithm. Finally, the ptimal inverse imaging results have been achieved by variable ectopic adaptive genetic algorithm. The numerical simulation experiments have shown that the usage of the correct priori information and the excellent characteristic of SAGA in searching the global minimum value of the function have produced accurate and effective results with stable umerical values. The imaging resolution is improved and the imagining results reflecting the inner defections of the tested objects are more reliable and accurate.
Stability and accuracy of the imaging results are still unmet practical demands for ultrasonic computed tomography (CT) of concrete material. To address these issues, a CT technique based on simulated annealing genetic algorithm (SAGA) is presented in this work. Firstly, a natural weight matrix with clear physical meaning is introduced in the inverse algorithm and then a quadric broadening objective function is formed according to the propagation characteristics of ultrasound in concrete. After that, the simulated annealing (SA) searching is added to speed up the inverse process and to improve the convergence and stability of the algorithm. Finally, the ptimal inverse imaging results have been achieved by variable ectopic adaptive genetic algorithm. The numerical simulation experiments have shown that the usage of the correct priori information and the excellent characteristic of SAGA in searching the global minimum value of the function have produced accurate and effective results with stable umerical values. The imaging resolution is improved and the imagining results reflecting the inner defections of the tested objects are more reliable and accurate.
2015, 32(3):348-354.
Abstract:
Plastic pipe reinforced by cross helically wound steel wires (PSP) is a new plasticmatrix steel composite pipe developed in China. To investigate the stress of PSP under foundation settlement, a finite element model (FEM) is proposed. The stresses and strains of PSP are obtained by the FEM analysis. The mechanic behavior of PSP subject to a foundation settlement is analyzed. Finally, the influence factor analysis of settlement deformation, such as settlement depth, overlying soil depth, diameter of PSP and inner pressure of PSP, are discussed.
Plastic pipe reinforced by cross helically wound steel wires (PSP) is a new plasticmatrix steel composite pipe developed in China. To investigate the stress of PSP under foundation settlement, a finite element model (FEM) is proposed. The stresses and strains of PSP are obtained by the FEM analysis. The mechanic behavior of PSP subject to a foundation settlement is analyzed. Finally, the influence factor analysis of settlement deformation, such as settlement depth, overlying soil depth, diameter of PSP and inner pressure of PSP, are discussed.
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