The prevalence of antibodies against spotted fever group rickettsia (SFGR), murine typhus and Q f... more The prevalence of antibodies against spotted fever group rickettsia (SFGR), murine typhus and Q fever were investigated in wild rats captured in Indonesia. Sera of 327 rats were collected from Jakarta and Boyolali on Java Island. The prevalences of antibodies against SFGR and murine typhus were 128 (39.1%) and 48 (14.7%), respectively. Antibodies against Q fever were not detected in these serum samples. Antibodies against SFGR were found in all species of rats (20.8–51.9%). The antibody positive rate against murine typhus in Rattus norvegicus (38.0%) was significantly higher than that in other rat species (0–4.8%, p < 0.01). The antibody positive rates against SFGR and murine typhus in rats captured in Jakarta were significantly higher than those in rats captured in Boyolali (p < 0.01). In this survey, all species of rats had antibodies against SFGR, indicating that the 4 species of tested rats (R. norvegicus, R. rattus, R. exulans, R. tiomanicus) were infected with SFGR and that SFGR may infest the whole of Java Island. Most of the rats that were antibody-positive against murine typhus were captured in Jakarta. Therefore, R. norvegicus and R. rattus are likely to be important hosts of murine typhus in Jakarta. The antibody-positive rates against SFGR and murine typhus in rats captured in the dry season were significantly higher than those in rats captured in the rainy season. This may coincide with the active periods of ticks and fleas in Indonesia.
Reliable and accurate health monitoring techniques can prevent catastrophic failures of structure... more Reliable and accurate health monitoring techniques can prevent catastrophic failures of structures. Conventional damage detection methods are based on visual or localized experimental methods and very often require prior information concerning the vicinity of the damage or defect. The structure must also be readily accessible for inspections. The techniques are also labor intensive. In comparison to these methods, health-monitoring techniques that are based on the structural dynamic response offers unique information on failure of structures. However, systematic relations between the experimental data and the defect are not available and frequently, the number of vibration modes needed for an accurate identification of defects is much higher than the number of modes that can be readily identified in the experiment. These motivated us to develop an experimental data based detection method with systematic relationships between the experimentally identified information and the analytical or mathematical model representing the defective structures. The developed technique use changes in vibrational curvature modes and natural frequencies. To avoid misinterpretation of the identified information, we also need to understand the effects of defects on the structural dynamic response prior to developing health-monitoring techniques. In this thesis work we focus on two type of defects in composite structures, namely delamination and edge notch like defect. Effects of nonlinearity due to the presence of defect and due to the axial stretching are studied for beams with delamination. Once defects are detected in a structure, next concern is determining the effects of the defects on the strength of the structure and its residual stiffness under dynamic loading. In this thesis, energy release rate due to dynamic loading in a delaminated structure is studied, which will be a foundation toward determining the residual strength of the structure.
Sensors constructed with single-crystal PMN-PT, i.e. Pb(Mg1/3Nb2/3)O3-PbTiO3 or PMN, are develope... more Sensors constructed with single-crystal PMN-PT, i.e. Pb(Mg1/3Nb2/3)O3-PbTiO3 or PMN, are developed in this paper for structural health monitoring of composite plates. To determine the potential of PMN-PT for this application, glass/epoxy composite specimens were created containing an embedded delamination-starter. Two different piezoelectric materials were bonded to the surface of each specimen: PMN-PT, the test material, was placed on one side of the specimen, while a traditional material, PZT-4, was placed on the other. A comparison of the ability of both materials to transmit and receive an ultrasonic pulse was conducted, with the received signal detected by both a second surface-bonded transducer constructed of the same material, as well as a laser Doppler vibrometer (LDV) analyzing the same location. The optimal frequency range of both sets of transducers is discussed and a comparison is presented of the experimental results to theory. The specimens will be fatigued until failure with further data collected every 3,000 cycles to characterize the ability of each material to detect the growing delamination in the composite structure. This additional information will be made available during the conference.
Journal of Intelligent Material Systems and Structures, 2011
The need to understand and monitor the integrity of structural components made of composite mater... more The need to understand and monitor the integrity of structural components made of composite materials is becoming critical, due to an increase of the use of composites in aerospace, civil, wind energy, and transportation engineering. Off-the-shelf piezoelectric transducers embedded inside the composites or bonded onto the structure surface are a possible solution for on-line structural health monitoring and non-destructive evaluation: they can be used to generate Lamb waves, which are able to detect damage. This article focuses on the behavior of two sets of woven fiberglass/epoxy specimens, one with embedded, one with surface-mounted piezoelectric wafer transducers (lead zirconate titanate). The specimens are tested under axial tensile fatigue at high stress ratio, and the transducers are interrogated in pitch-catch mode at different stages of the specimens' life, while they are subjected to the mean test load (the testing machine is paused). A novel signal processing technique based on wavelet thresholding/denoising and Gabor wavelet transform is discussed. This technique identifies changes in boundary conditions, loading/unloading prior to damage and during damage. It appears to correlate the contour area changes with the so-called characteristic damage state observed in the literature in composite laminates under tensile fatigue.
Fiber reinforced polymer (FRP) composites have been increasingly used for civil infrastructure in... more Fiber reinforced polymer (FRP) composites have been increasingly used for civil infrastructure in recent years, and the applications have promoted interest in health monitoring of structural composites. Although primary layouts of these composite structures are similar, the FRP composites used in civil engineering structures are usually relatively thicker and larger in size. Hence, more power authority is needed in the experimental procedure for health monitoring purposes. In this study, health monitoring of thick composite structures using smart piezoelectric materials is presented. Monitoring technique based on wave propagation is evaluated for possible damage detection in civil composite structures. For comparison purposes, the composite laminated beams with two different thickness are made of E-glass fiber and epoxy resins by vacuum bagging process, and the damage in the form of delamination is created by inserting Teflon sheet between the lamina at certain location. Smart piezoelectric materials are used as both the emitter and receiver of the wave. The exploratory experimental program developed in this study can be used for better understanding of the possibility of wave propagation based technique in health monitoring and damage detection of large civil FRP composite structures.
This is an investigation on the damage behavior of fiberglass/epoxy specimens with embedded piezo... more This is an investigation on the damage behavior of fiberglass/epoxy specimens with embedded piezoelectrics under axial tensile fatigue. The specimen&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39;s local and global damage states are complicated by the specimen&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39;s own stretching under loading, which varies as a function of damage. A signal processing technique based on wavelet transforms is presented: denoised signals are processed with Gabor wavelet transforms, and
There is a pressing need to develop effective techniques for structural health monitoring, so tha... more There is a pressing need to develop effective techniques for structural health monitoring, so that the safety and integrity of the composite structures can be improved. The main objective of this study is to evaluate dynamics-based damage detection techniques for composite laminated plates using smart piezoelectric materials and modern instrumentation like scanning laser vibrometer (SLV). The study comprises of testing an E-glass/epoxy composite plate with an embedded delamination using two different actuator-sensor systems: (1) SLV with PZT (lead-zirconate-titanate) actuators (PZT-SLV), and (2) polyvinylidenefluoride (PVDF) sensors with PZT actuators (PZT-PVDF). The numerical finite element (FE) analysis is also performed to complement the damage detection. The experimental and numerical curvature mode shapes are primarily used to detect the presence, location, and size of the delamination. Three relatively new damage detection algorithms (i.e., simplified gapped smoothing method (GSM), generalized fractal dimension (GFD), and strain energy method (SEM)) are employed to analyze the experimental and numerical curvature mode shape data and uniform load surface (ULS) curvatures. From the damage detection outcomes, it is observed that the PZT-SLV system proves to be more convenient and effective, and it is capable of scanning a large number of points over the entire plate specimens; while the PZT-PVDF system, in which the curvature mode shapes are directly acquired, exhibits good sensitivity to damage. The damage detection algorithms like GSM, GFD and SEM based on the utilization of three consecutive mode curvatures (modes 3-5) and resulting ULS curvature successfully identify the presence, location, and relative size of delamination in the composite plate.
Journal of Intelligent Material Systems and Structures, 2007
In this article, a combined analytical and experimental damage assessment method using curvature ... more In this article, a combined analytical and experimental damage assessment method using curvature mode shapes is developed. The curvature mode is selected due to its sensitivity to the presence of the damage and the localized nature of the changes. An analytical relationship between the damaged and the healthy beams is formulated, for which the effect of damage in the form of stiffness loss is accounted. This relationship is later used to estimate the extent of damage from the experimentally identified changes in structural dynamic characteristics. Surface-bonded piezoelectric sensors are used to directly acquire the curvature modes of composite structures, which simplify the identification procedure. The specimens are made of carbon/epoxy laminated composite beams. Several different types of damages are introduced in the beams (i.e., delamination, impact, and saw-cut damages) to simulate possible damage scenarios. Several limitations and remarks of the proposed experimental and damage identification approaches are discussed. The study shows that the present technique using curvature mode shapes and piezoelectric materials can be used effectively to locate the damage in the laminated composite structures.
Structural Health Monitoring-an International Journal, 2004
Many composite materials and structures are susceptible to defects, which can significantly reduc... more Many composite materials and structures are susceptible to defects, which can significantly reduce the strength of structures and may grow to failure. To avoid the catastrophic failure of structures, development of a reliable method of structural health monitoring is one of the most important keys in maintaining the integrity and safety of structures. Dynamic response-based damage detection offers a simple procedure as an alternative to the conventional nondestructive evaluation techniques. However, this technique depends on the quality of measured data for its identification accuracy. In this article, experimental aspects of dynamic response-based damage detection technique on carbon/ epoxy composites are addressed. Smart piezoelectric materials are used as sensors or actuators to acquire the curvature modes of structures. These materials are surface-bonded to the beams. An impulse hammer is used as an actuating source as well. Four types of damage detection algorithms are evaluated for several possible damage configurations with two different excitation sources. The quality of damage identification with the four different detection algorithms is discussed. These experimental damage identification techniques using curvature modes and piezoelectric materials can be effectively used in damage detection and health monitoring of composite structures.
Accurate interpretation of data measurement is a major challenge for development of reliable and ... more Accurate interpretation of data measurement is a major challenge for development of reliable and effective diagnostic system. This paper presents experimental results of a proposed damage identification candidate based on Lamb wave propagation analysis. Carbon/epoxy laminated composite plate specimens with various damage, i.e., delamination and impact damage, are evaluated. Damage location is extracted from the measured time history data of the propagated wave and the wave traveling time. Assuming the wave propagates with a constant speed, the summation of the distance from the transmitter to the damage and the distance from the damage to the receiver is constant. The possible damage location combining with the locations of the transmitter and receiver forms an elliptical path, where the locations of the transmitter and receiver serve as the foci of the ellipse. Piezoelectric transducers (PZTs) are used as the wave transmitters and receivers. Post-processing of the recorded signals using wavelet transform allows better isolation of the interested propagation mode and the extraction of the traveling time, which enhance the accuracy of damage localization. Results of the damage location estimation are presented.
In a framework of developing a structural health monitoring for civil infrastructure, the damage ... more In a framework of developing a structural health monitoring for civil infrastructure, the damage identification procedure based on dynamic response for fiber reinforced polymer (FRP) sandwich composites is evaluated. In this paper, an experimental damage identification procedure based on structural dynamic responses and using smart sensors is conducted. Damage identification is estimated from comparison of dynamic responses of healthy and damaged FRP sandwich beams. Correspondingly, based on the relationship between the changes of mechanical properties and the related changes of dynamic responses (i.e., the curvature mode shapes in this study), damage magnitude is quantified. The composite sandwich beams are made of E-glass fiber and polyester resin, and the core consists of the corrugated cells in a sinusoidal configuration. Artificial damage is created between the interface of core and faceplate and also in the core of sandwich beam to simulate core-faceplate debonding and core crushing, respectively. Using piezoelectric smart sensors, dynamic responses data is collected and dynamic characteristics of the sandwich structure are extracted, from which the location and magnitude of the damage are evaluated. As demonstrated in this study, the present dynamic responsebased procedure using smart sensors can be effectively used to assess damage and monitor structural health of FRP honeycomb sandwich structures.
A reliable and effective damage detection technique is one of the significant tools to maintain t... more A reliable and effective damage detection technique is one of the significant tools to maintain the safety and integrity of structures. A dynamic response offers viable information for the identification of damage in the structures. However, the performance of such dynamics-based damage detection depends on the quality of measured data and the effectiveness of data processing algorithms. In this article, the experimentally measured data of two sensor systems, i.e., a surfacebonded piezoelectric sensor system and a noncontact scanning laser vibrometer (SLV) system, are studied, and their effectiveness in damage identification of composite laminated beams is compared. Three dynamics-based damage detection algorithms are evaluated using the data acquired from these two measurement systems. The curvature mode shape is selected as a parameter to locate damage due to its sensitivity. The piezoelectric sensors directly acquire the curvature mode shapes of the structures, while the SLV measures the displacement mode shapes. The difference in the measurement characteristics of these systems and their influence in the damage identification performance are addressed. The beam specimens Downloaded from are made of E-glass/epoxy composites, and several different types of damages are introduced in the beams (i.e., delaminations, and impact and saw-cut damages). This study provides a thorough assessment of the two sensor systems in damage detection of composite laminated beams and verifies the validity of dynamics-based damage detection methodology in locating the local defects in composite structures.
In this study, the guided wave technique is applied to nondestructively assess the damage in vari... more In this study, the guided wave technique is applied to nondestructively assess the damage in various engineering materials, like alumina, laminated composites, and composite sandwiches. A combined theoretical, numerical and experimental investigation of the pulse-echo method using piezoelectric sensors and actuators is conducted. The dispersion effect of wave guides on these materials is first analyzed, and the transient propagation process of wave guides and its interaction with inside damages are then numerically simulated. The implementations of the pulse echo method are illustrated in experimental testing and damage detection of aluminum beams, carbon/epoxy laminated composite plates, and composite sandwich beams. In particular, the experimental results on damage detection of the composite sandwich beams are reported and discussed. As illustrated in this study, the pulse-echo method combined with piezoelectric material can be used effectively to locate damage in various engineering materials and structures.
In this paper, a combined analytical and experimental study of dynamic characteristics of honeyco... more In this paper, a combined analytical and experimental study of dynamic characteristics of honeycomb composite sandwich structures in bridge systems is presented, and a relatively simple and reliable dynamic experimental procedure to estimate the beam bending and transverse shear stiffness is proposed. This procedure is especially practicable for estimating the beam transverse shear stiffness, which is primarily contributed by the core and is usually difficult to measure. The composite sandwich beams are made of E-glass fiber and polyester resins, and the core consists of the corrugated cells in a sinusoidal configuration. Based on the modeling of equivalent properties for the face laminates and core elements, analytical predictions of effective flexural and transverse shear stiffness properties of sandwich beams along the longitudinal and transverse to the sinusoidal core wave directions are first obtained. Using piezoelectric sensors, the dynamic response data are collected, and the dynamic characteristics of the sandwich structures are analyzed, from which the flexural and transverse shear stiffness properties are reduced. The experimental stiffness results are then compared to the analytical stiffness properties, and relatively good correlations are obtained. The proposed dynamic tests using piezoelectric sensors can be used effectively to evaluate the dynamic characteristics and stiffness properties of large sandwich structures suitable for highway bridge applications.
The prevalence of antibodies against spotted fever group rickettsia (SFGR), murine typhus and Q f... more The prevalence of antibodies against spotted fever group rickettsia (SFGR), murine typhus and Q fever were investigated in wild rats captured in Indonesia. Sera of 327 rats were collected from Jakarta and Boyolali on Java Island. The prevalences of antibodies against SFGR and murine typhus were 128 (39.1%) and 48 (14.7%), respectively. Antibodies against Q fever were not detected in these serum samples. Antibodies against SFGR were found in all species of rats (20.8–51.9%). The antibody positive rate against murine typhus in Rattus norvegicus (38.0%) was significantly higher than that in other rat species (0–4.8%, p < 0.01). The antibody positive rates against SFGR and murine typhus in rats captured in Jakarta were significantly higher than those in rats captured in Boyolali (p < 0.01). In this survey, all species of rats had antibodies against SFGR, indicating that the 4 species of tested rats (R. norvegicus, R. rattus, R. exulans, R. tiomanicus) were infected with SFGR and that SFGR may infest the whole of Java Island. Most of the rats that were antibody-positive against murine typhus were captured in Jakarta. Therefore, R. norvegicus and R. rattus are likely to be important hosts of murine typhus in Jakarta. The antibody-positive rates against SFGR and murine typhus in rats captured in the dry season were significantly higher than those in rats captured in the rainy season. This may coincide with the active periods of ticks and fleas in Indonesia.
Reliable and accurate health monitoring techniques can prevent catastrophic failures of structure... more Reliable and accurate health monitoring techniques can prevent catastrophic failures of structures. Conventional damage detection methods are based on visual or localized experimental methods and very often require prior information concerning the vicinity of the damage or defect. The structure must also be readily accessible for inspections. The techniques are also labor intensive. In comparison to these methods, health-monitoring techniques that are based on the structural dynamic response offers unique information on failure of structures. However, systematic relations between the experimental data and the defect are not available and frequently, the number of vibration modes needed for an accurate identification of defects is much higher than the number of modes that can be readily identified in the experiment. These motivated us to develop an experimental data based detection method with systematic relationships between the experimentally identified information and the analytical or mathematical model representing the defective structures. The developed technique use changes in vibrational curvature modes and natural frequencies. To avoid misinterpretation of the identified information, we also need to understand the effects of defects on the structural dynamic response prior to developing health-monitoring techniques. In this thesis work we focus on two type of defects in composite structures, namely delamination and edge notch like defect. Effects of nonlinearity due to the presence of defect and due to the axial stretching are studied for beams with delamination. Once defects are detected in a structure, next concern is determining the effects of the defects on the strength of the structure and its residual stiffness under dynamic loading. In this thesis, energy release rate due to dynamic loading in a delaminated structure is studied, which will be a foundation toward determining the residual strength of the structure.
Sensors constructed with single-crystal PMN-PT, i.e. Pb(Mg1/3Nb2/3)O3-PbTiO3 or PMN, are develope... more Sensors constructed with single-crystal PMN-PT, i.e. Pb(Mg1/3Nb2/3)O3-PbTiO3 or PMN, are developed in this paper for structural health monitoring of composite plates. To determine the potential of PMN-PT for this application, glass/epoxy composite specimens were created containing an embedded delamination-starter. Two different piezoelectric materials were bonded to the surface of each specimen: PMN-PT, the test material, was placed on one side of the specimen, while a traditional material, PZT-4, was placed on the other. A comparison of the ability of both materials to transmit and receive an ultrasonic pulse was conducted, with the received signal detected by both a second surface-bonded transducer constructed of the same material, as well as a laser Doppler vibrometer (LDV) analyzing the same location. The optimal frequency range of both sets of transducers is discussed and a comparison is presented of the experimental results to theory. The specimens will be fatigued until failure with further data collected every 3,000 cycles to characterize the ability of each material to detect the growing delamination in the composite structure. This additional information will be made available during the conference.
Journal of Intelligent Material Systems and Structures, 2011
The need to understand and monitor the integrity of structural components made of composite mater... more The need to understand and monitor the integrity of structural components made of composite materials is becoming critical, due to an increase of the use of composites in aerospace, civil, wind energy, and transportation engineering. Off-the-shelf piezoelectric transducers embedded inside the composites or bonded onto the structure surface are a possible solution for on-line structural health monitoring and non-destructive evaluation: they can be used to generate Lamb waves, which are able to detect damage. This article focuses on the behavior of two sets of woven fiberglass/epoxy specimens, one with embedded, one with surface-mounted piezoelectric wafer transducers (lead zirconate titanate). The specimens are tested under axial tensile fatigue at high stress ratio, and the transducers are interrogated in pitch-catch mode at different stages of the specimens' life, while they are subjected to the mean test load (the testing machine is paused). A novel signal processing technique based on wavelet thresholding/denoising and Gabor wavelet transform is discussed. This technique identifies changes in boundary conditions, loading/unloading prior to damage and during damage. It appears to correlate the contour area changes with the so-called characteristic damage state observed in the literature in composite laminates under tensile fatigue.
Fiber reinforced polymer (FRP) composites have been increasingly used for civil infrastructure in... more Fiber reinforced polymer (FRP) composites have been increasingly used for civil infrastructure in recent years, and the applications have promoted interest in health monitoring of structural composites. Although primary layouts of these composite structures are similar, the FRP composites used in civil engineering structures are usually relatively thicker and larger in size. Hence, more power authority is needed in the experimental procedure for health monitoring purposes. In this study, health monitoring of thick composite structures using smart piezoelectric materials is presented. Monitoring technique based on wave propagation is evaluated for possible damage detection in civil composite structures. For comparison purposes, the composite laminated beams with two different thickness are made of E-glass fiber and epoxy resins by vacuum bagging process, and the damage in the form of delamination is created by inserting Teflon sheet between the lamina at certain location. Smart piezoelectric materials are used as both the emitter and receiver of the wave. The exploratory experimental program developed in this study can be used for better understanding of the possibility of wave propagation based technique in health monitoring and damage detection of large civil FRP composite structures.
This is an investigation on the damage behavior of fiberglass/epoxy specimens with embedded piezo... more This is an investigation on the damage behavior of fiberglass/epoxy specimens with embedded piezoelectrics under axial tensile fatigue. The specimen&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39;s local and global damage states are complicated by the specimen&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39;s own stretching under loading, which varies as a function of damage. A signal processing technique based on wavelet transforms is presented: denoised signals are processed with Gabor wavelet transforms, and
There is a pressing need to develop effective techniques for structural health monitoring, so tha... more There is a pressing need to develop effective techniques for structural health monitoring, so that the safety and integrity of the composite structures can be improved. The main objective of this study is to evaluate dynamics-based damage detection techniques for composite laminated plates using smart piezoelectric materials and modern instrumentation like scanning laser vibrometer (SLV). The study comprises of testing an E-glass/epoxy composite plate with an embedded delamination using two different actuator-sensor systems: (1) SLV with PZT (lead-zirconate-titanate) actuators (PZT-SLV), and (2) polyvinylidenefluoride (PVDF) sensors with PZT actuators (PZT-PVDF). The numerical finite element (FE) analysis is also performed to complement the damage detection. The experimental and numerical curvature mode shapes are primarily used to detect the presence, location, and size of the delamination. Three relatively new damage detection algorithms (i.e., simplified gapped smoothing method (GSM), generalized fractal dimension (GFD), and strain energy method (SEM)) are employed to analyze the experimental and numerical curvature mode shape data and uniform load surface (ULS) curvatures. From the damage detection outcomes, it is observed that the PZT-SLV system proves to be more convenient and effective, and it is capable of scanning a large number of points over the entire plate specimens; while the PZT-PVDF system, in which the curvature mode shapes are directly acquired, exhibits good sensitivity to damage. The damage detection algorithms like GSM, GFD and SEM based on the utilization of three consecutive mode curvatures (modes 3-5) and resulting ULS curvature successfully identify the presence, location, and relative size of delamination in the composite plate.
Journal of Intelligent Material Systems and Structures, 2007
In this article, a combined analytical and experimental damage assessment method using curvature ... more In this article, a combined analytical and experimental damage assessment method using curvature mode shapes is developed. The curvature mode is selected due to its sensitivity to the presence of the damage and the localized nature of the changes. An analytical relationship between the damaged and the healthy beams is formulated, for which the effect of damage in the form of stiffness loss is accounted. This relationship is later used to estimate the extent of damage from the experimentally identified changes in structural dynamic characteristics. Surface-bonded piezoelectric sensors are used to directly acquire the curvature modes of composite structures, which simplify the identification procedure. The specimens are made of carbon/epoxy laminated composite beams. Several different types of damages are introduced in the beams (i.e., delamination, impact, and saw-cut damages) to simulate possible damage scenarios. Several limitations and remarks of the proposed experimental and damage identification approaches are discussed. The study shows that the present technique using curvature mode shapes and piezoelectric materials can be used effectively to locate the damage in the laminated composite structures.
Structural Health Monitoring-an International Journal, 2004
Many composite materials and structures are susceptible to defects, which can significantly reduc... more Many composite materials and structures are susceptible to defects, which can significantly reduce the strength of structures and may grow to failure. To avoid the catastrophic failure of structures, development of a reliable method of structural health monitoring is one of the most important keys in maintaining the integrity and safety of structures. Dynamic response-based damage detection offers a simple procedure as an alternative to the conventional nondestructive evaluation techniques. However, this technique depends on the quality of measured data for its identification accuracy. In this article, experimental aspects of dynamic response-based damage detection technique on carbon/ epoxy composites are addressed. Smart piezoelectric materials are used as sensors or actuators to acquire the curvature modes of structures. These materials are surface-bonded to the beams. An impulse hammer is used as an actuating source as well. Four types of damage detection algorithms are evaluated for several possible damage configurations with two different excitation sources. The quality of damage identification with the four different detection algorithms is discussed. These experimental damage identification techniques using curvature modes and piezoelectric materials can be effectively used in damage detection and health monitoring of composite structures.
Accurate interpretation of data measurement is a major challenge for development of reliable and ... more Accurate interpretation of data measurement is a major challenge for development of reliable and effective diagnostic system. This paper presents experimental results of a proposed damage identification candidate based on Lamb wave propagation analysis. Carbon/epoxy laminated composite plate specimens with various damage, i.e., delamination and impact damage, are evaluated. Damage location is extracted from the measured time history data of the propagated wave and the wave traveling time. Assuming the wave propagates with a constant speed, the summation of the distance from the transmitter to the damage and the distance from the damage to the receiver is constant. The possible damage location combining with the locations of the transmitter and receiver forms an elliptical path, where the locations of the transmitter and receiver serve as the foci of the ellipse. Piezoelectric transducers (PZTs) are used as the wave transmitters and receivers. Post-processing of the recorded signals using wavelet transform allows better isolation of the interested propagation mode and the extraction of the traveling time, which enhance the accuracy of damage localization. Results of the damage location estimation are presented.
In a framework of developing a structural health monitoring for civil infrastructure, the damage ... more In a framework of developing a structural health monitoring for civil infrastructure, the damage identification procedure based on dynamic response for fiber reinforced polymer (FRP) sandwich composites is evaluated. In this paper, an experimental damage identification procedure based on structural dynamic responses and using smart sensors is conducted. Damage identification is estimated from comparison of dynamic responses of healthy and damaged FRP sandwich beams. Correspondingly, based on the relationship between the changes of mechanical properties and the related changes of dynamic responses (i.e., the curvature mode shapes in this study), damage magnitude is quantified. The composite sandwich beams are made of E-glass fiber and polyester resin, and the core consists of the corrugated cells in a sinusoidal configuration. Artificial damage is created between the interface of core and faceplate and also in the core of sandwich beam to simulate core-faceplate debonding and core crushing, respectively. Using piezoelectric smart sensors, dynamic responses data is collected and dynamic characteristics of the sandwich structure are extracted, from which the location and magnitude of the damage are evaluated. As demonstrated in this study, the present dynamic responsebased procedure using smart sensors can be effectively used to assess damage and monitor structural health of FRP honeycomb sandwich structures.
A reliable and effective damage detection technique is one of the significant tools to maintain t... more A reliable and effective damage detection technique is one of the significant tools to maintain the safety and integrity of structures. A dynamic response offers viable information for the identification of damage in the structures. However, the performance of such dynamics-based damage detection depends on the quality of measured data and the effectiveness of data processing algorithms. In this article, the experimentally measured data of two sensor systems, i.e., a surfacebonded piezoelectric sensor system and a noncontact scanning laser vibrometer (SLV) system, are studied, and their effectiveness in damage identification of composite laminated beams is compared. Three dynamics-based damage detection algorithms are evaluated using the data acquired from these two measurement systems. The curvature mode shape is selected as a parameter to locate damage due to its sensitivity. The piezoelectric sensors directly acquire the curvature mode shapes of the structures, while the SLV measures the displacement mode shapes. The difference in the measurement characteristics of these systems and their influence in the damage identification performance are addressed. The beam specimens Downloaded from are made of E-glass/epoxy composites, and several different types of damages are introduced in the beams (i.e., delaminations, and impact and saw-cut damages). This study provides a thorough assessment of the two sensor systems in damage detection of composite laminated beams and verifies the validity of dynamics-based damage detection methodology in locating the local defects in composite structures.
In this study, the guided wave technique is applied to nondestructively assess the damage in vari... more In this study, the guided wave technique is applied to nondestructively assess the damage in various engineering materials, like alumina, laminated composites, and composite sandwiches. A combined theoretical, numerical and experimental investigation of the pulse-echo method using piezoelectric sensors and actuators is conducted. The dispersion effect of wave guides on these materials is first analyzed, and the transient propagation process of wave guides and its interaction with inside damages are then numerically simulated. The implementations of the pulse echo method are illustrated in experimental testing and damage detection of aluminum beams, carbon/epoxy laminated composite plates, and composite sandwich beams. In particular, the experimental results on damage detection of the composite sandwich beams are reported and discussed. As illustrated in this study, the pulse-echo method combined with piezoelectric material can be used effectively to locate damage in various engineering materials and structures.
In this paper, a combined analytical and experimental study of dynamic characteristics of honeyco... more In this paper, a combined analytical and experimental study of dynamic characteristics of honeycomb composite sandwich structures in bridge systems is presented, and a relatively simple and reliable dynamic experimental procedure to estimate the beam bending and transverse shear stiffness is proposed. This procedure is especially practicable for estimating the beam transverse shear stiffness, which is primarily contributed by the core and is usually difficult to measure. The composite sandwich beams are made of E-glass fiber and polyester resins, and the core consists of the corrugated cells in a sinusoidal configuration. Based on the modeling of equivalent properties for the face laminates and core elements, analytical predictions of effective flexural and transverse shear stiffness properties of sandwich beams along the longitudinal and transverse to the sinusoidal core wave directions are first obtained. Using piezoelectric sensors, the dynamic response data are collected, and the dynamic characteristics of the sandwich structures are analyzed, from which the flexural and transverse shear stiffness properties are reduced. The experimental stiffness results are then compared to the analytical stiffness properties, and relatively good correlations are obtained. The proposed dynamic tests using piezoelectric sensors can be used effectively to evaluate the dynamic characteristics and stiffness properties of large sandwich structures suitable for highway bridge applications.
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