This PDF file contains the front matter associated with SPIE Proceedings Volume 7294, including the Title Page, Copyright information, Table of Contents, Introduction, and the Conference Committee and Symposium Committee listings.

Nondestructive Evaluation (NDE) and Structural Health Monitoring (SHM) are closely related technologies intended to assure the safe and reliable operation of structural components at an affordable cost. The paper will start with a brief review of common design strategies to assure the structural integrity of components and of the role that NDE and SHM play within those strategies. Included will be a discussion of the metrics used to quantify the effectiveness of NDE and SHM, such as probability of detection (POD), and how these metrics influence the selection of the optimal noninvasive strategy to assure structural integrity. In many cases, this will involve a combination of traditional NDE measurements performed at discrete time intervals and SHM measurements providing information on a continuous or semi-continuous basis at discrete sensor locations. It will then be suggested that NDE/SHM simulators are key engineering tools in designing these specific measurement configurations and in determining the optimum balance between these two measurement philosophies. Included in that discussion will be a review of the development of NDE simulators, a discussion of applications that they are finding in traditional NDE, including Model-Assisted Probability of Detection (MAPOD) determination, and a suggestion of how simulations could be integrated into SHM strategies. The paper will conclude with a discussion of possible future directions.

In this paper, the development of a 35 MHz 64-channel Piezoelectric Composite based Micromachined Ultrasound Transducer (PCMUT) phased array for NDE ultrasound application is presented. A 35 MHz PMN-PT single crystal 1-3 composite based PC-MUT phased array was designed with extensive acoustic field and 1D modeling. The initial modeling results demonstrated that the focused detection resolution (10% of -3 dB beam width) could be as small as 30 μm in the azimuth direction. The maximum imaging depth for ceramic samples is around 20 mm. The PC-MUT array being developed will extend the state-of-art NDE phased array technology from approximately 20 MHz to 35 MHz, which will greatly enhance the imaging resolution for a broad range of NDE ultrasound applications.

This paper describes an approach to measuring internal displacements and strains in metals. The technique has the advantage over optical surface strain measurement techniques in that internal information is obtained. The principle is to use an ultrasonic array to record images of the speckle pattern produced by the material microstructure before and after the application of load. A cross-correlation algorithm is then used to determine the relative displacement of portions of the images between the two load states, and hence the strain field. The mathematical basis of the technique is summarized, and experimental results are presented. The results demonstrate that the technique can be used for example to measure the onset of plasticity and non-uniform strain fields deep in a material.

Acoustic emission (AE) testing is a sensitive technique capable of detecting many types of defect with a sparse sensor array making it an attractive structural health monitoring technology. The widespread application of the technology is limited by a lack of predictive modelling and in part, the lack of quantitative source characteristics. The vast majority of current laboratory AE testing is conducted on small coupons which cannot be used to generate quantitative source characteristics since reflected wave energy from the specimen edges influences the received waveforms. An alternative approach is to test on large specimens where the modal properties of propagating waves can be examined with no influence from reflected wave energy. However, the design and testing of large specimens is not trivial. The work in this paper discusses the design of large fibre reinforced composite (FRC) specimens which are suitable for making quantitative source measurements. The design considerations include the minimum plate dimensions and placement of sensors. A novel technique, referred to as the location-time plot technique, is described which links propagation characteristics, specimen dimensions and sensor locations to map the dispersion of elastic waves in plates. The technique is demonstrated in the design of a simple AE experiment on a highly anisotropic plate. The technique is then used in the design of a practical AE testing arrangement for monitoring delamination from artificial defects in a large FRC plate. Experimental waveforms, recorded using this AE testing arrangement, are presented and are shown to be in agreement with the location-time plot technique.

Surface deterioration is the most common type of concrete damage. In the case of subsurface damage the difficulty of characterization increases as there is no visual evidence of the crack. Additionally since the close to surface layer of the material is intact, the sensitivity of the longitudinal wave velocity, which is typically measured for inspection purposes, is questionable. In the present paper, cracks were created in steel fiber reinforced concrete specimens by four point bending. Wave characteristics were then measured on the intact surfaces (compression side) using common acoustic emission transducers. It was seen that although there was no visual sign of the crack, Rayleigh as well as longitudinal wave velocities were influenced showing clear decrease relatively to the sound material. Additionally other parameters such as the amplitude or energy of the waves were much more sensitive to damage. In order to explain the results, numerical simulations were conducted making a parametric study between the depth of the sound layer, the propagating wavelength and the measured wave parameters. It is concluded that by scanning a surface with simple acoustic one sided measurements, the identification of the location of the subsurface damage is possible, while the propagating wave gives information about the form and depth of the crack.

This work deals with the AE behavior of concrete under four-point bending. Different contents of steel fibers were included to investigate their influence on the load-bearing capacity and on the fracture mechanisms. The AE waveform characteristics revealed that, although tension was the dominant mechanism of fracture for the plain material, the increase in the fiber content resulted in extension of the shear failure due to improvement of the weak tensile properties of concrete. Appropriate AE indices employed for early warning prior to macroscopic failure can lead to more suitable design of the reinforcement, in order to withstand the specific stresses.

Acoustic Emission (AE) testing is capable of detecting a wide range of defects using a relatively sparse sensor array and as a result is a candidate structural health monitoring technology. The widespread application of the technology is restricted by a lack of predictive modelling capability and quantitative source characteristic information. Most AE tests are conducted on small coupons where source characteristics are estimated using the early arriving part of the AE signal. The early arriving part of an AE signal, and therefore the source characteristics, are dependent on the source location, source orientation and specimen geometry making them unsuitable for use in predictive models. The work in this paper is concerned with making source characterisation measurements based on the diffuse field of an AE signal. A practical approach for calibrating the diffuse field amplitude is proposed and is demonstrated on AE signals from electrochemically accelerated corrosion of a 316L stainless steel plate. The diffuse field amplitude of several AE events is calculated and reported as an equivalent absolute force. The low signal to noise ratio and high attenuation of elastic wave energy are found to reduce the accuracy of the results.

In this study, CNTs were used as modifiers of the epoxy matrix of quasi-isotropic carbon fibre reinforced laminates. The prepared laminates were subjected to tensile loading and tension-tension fatigue and, the changes in the longitudinal resistance were monitored via a digital multimeter. In addition, Acoustic Emission and Acousto-Ultrasonic techniques were used for monitoring the fatigue process of the laminates. The nano-enhanced laminates on the one hand exhibited superior fatigue properties and on the other hand they demonstrated the full-potential of the material to be used as an integrated sensor to monitor the fatigue life.

Woven fiber composites are currently being investigated due to their advantages over other materials, making them suitable for low weight, high stiffness, and high interlaminar fracture toughness applications such as missiles, body armor, satellites, and many other aerospace applications. Damage characterization of woven fabrics is a complex task due to their tendency to exhibit different failure modes based on the weave configuration, orientation, ply stacking and other variables. A multiscale model is necessary to accurately predict progressive damage. The present research is an experimental study on damage characterization of three different woven fiber laminates under low energy impact using Fiber Bragg Grating (FBG) sensors and flash thermography. A correlation between the measured strain from FBG sensors and the damaged area obtained from flash thermography imaging has been developed. It was observed that the peak strain in the fabrics were strongly dependent on the weave geometry and decreased at different rates as damage area increased due to dissimilar failure modes. Experimental observations were validated with the development of a multiscale model. A FBG sensor placement model was developed which showed that FBG sensor location and orientation plays a key role in the sensing capabilities of strain on the samples.

Fiber reinforced metallic composite materials are being considered for a number of applications because of their attractive mechanical properties as compared to monolithic metallic alloys. An engineered interphase, including the bond strength between the composite's constituents, contributes to a large extent to the improvement of strength and stiffness properties of this class of materials. However, in high temperature applications, where combination of cyclic loading with environmental effects is expected, consideration should be given to interphase degradation, especially in the vicinity of stress risers, such as notches and holes. The applicability of damage tolerance analysis in structural components made of titanium matrix composite materials designed to operate under high temperature environments would depend on the availability of adequate characterization methods for the evaluation of interfacial degradation. The objective of this work is to provide a basic understanding of interfacial degradation mechanisms due to oxidation in environmentally exposed titanium-based composites subjected to cyclic stresses. A nondestructive method has been developed enabling highresolution monitoring of interfacial damage initiation and accumulation as well as surface/subsurface cracking behavior during interrupted fatigue tests. This nondestructive technique is based on surface acoustic wave propagation in the composites and can detect minute changes in elastic properties of the interfacial region due to elevated temperatures as well as oxygen effects.

In this paper, a novel vibration-based methodology for fast inverse identification of delamination in E-glass/epoxy composite panels has been proposed with experimental demonstration using a scanning laser vibrometer (SLV). The methodology consists of 1) a parameter subset selection for delamination damage localization and 2) iterative inverse eigenvalue analysis for damage quantification. It can potentially lead to a functional formulation relating spatial and global damage indices such as curvature damage factor to local damage parameters. The functional relationship will be suitable to fast or real-time in-situ delamination damage identification. To accomplish the objectives, a shear-locking free higher-order finite element model has been combined with a micromechanics theory-based continuum damage model as an identification model for locating delamination. Applications of the proposed methodology to an Eglass/ epoxy panel [CSM/UM1208/3 layers of C1800]s = [CSM/0/(90/0)3]s with delamination have been demonstrated both numerically and experimentally using a piezoelectric actuator, a PVDF sensor and non-contact measuring SLV. Experimental modal analysis has been successfully conducted using the sample specimen to demonstrate the proposed methodology.

This paper proposes a new method using substructure potential energy, which is capable of accurately estimating the damage magnitude of multiple members, and particularly advantageous for sandwich panels with lattice cores. While other existing damage severity estimation methods require the information of several modes of the whole structure, the new method utilizes only a small number of measurement locations for sandwich structure. The performance of the proposed method is compared with existing damage detection methods using a set of numerical simulations that are demonstrated for a sandwich panel based on synthetic data generated from finite element models.

Thermal protection system is one of the key technology of reusable launch vehicle (RLV). After C/C and ceramic-matrix composite used in space orbiter, one new-typed thermal protection systems (TPS)-ARMOR TPS is coming forth. ARMOR TPS is means adaptable, robust, metallic, operable, reusable TPS. The ARMOR TPS has many advantages, for example: fixing easily, longer life, good properties, short time of maintenance and service. The ARMOR TPS is one of important candidate structure of RLV. ARMOR thermal protection system in foreign countries for reusable launch vehicle is used instead of the traditional ceramic-matrix composite thermal protection system and C/C thermal protection system. Also the constituent feature of ARMOR thermal protection system is much better than the traditional TPS. In comparison with traditional TPS, the ARMOR TPS will be the best selection for all kinds of RLV. So the ARMOR thermal protection system will be used in aviation and spaceflight field more and more widely because of its much better performance. ARMOR TPS panel is above the whole ARMOR TPS, and the metal honeycomb sandwich structure is the surface of the ARMOR TPS panel. So the metal honeycomb sandwich structure plays an important role in the ARMOR TPS, while it bears the flight dynamic pressure and stands against the flight dynamic calefaction. The metal honeycomb sandwich structure is made using the technique of the whole braze welding. In the course of the vacuum high temperature braze welding, its surface will appear concave. The reasons which lead to the shortage are summarized and discussed. The difference of thermal expansion coefficient and pressure between the core and the panels may be the chief reasons. This paper will analyze the mechanics behavior of metal honeycomb sandwich structure in the course of the vacuum high temperature braze welding, then make sure the reasons and get a way to solve it. Haynes214 is a good material of face sheet at present. γ - TiAl and microlaminate materials are the candidate materials in the future.

A small volume fraction of Carbon Nanotubes (CNTs) added in a polymeric matrix increases significantly the mechanical properties of the polymers. It is experimentally determined from the TEM images of CNT-based nanocomposites that nanotubes don't stand straight in their embedded matrix and they have some curvature in their shape. The load transfer mechanism between CNT and polymer matrix is also one of the most important issues which is not understood explicitly, yet. In this paper a wavy Single Walled Carbon Nanotube (SWCNT) is modeled as inclusion in a polymer matrix and its effective mechanical properties is studied. This model is based on using 3-D Representive Volume Element (RVE) with long wavy CNT inclusions. The CNT is modeled as a continuum hollow cylindrical shape elastic material with some curvature in its shape. The effect of the waviness of the CNT inclusions and its parameters is studied. We used a new approach in the modeling of interaction between the CNT/matrix at the interface. This approach consists of modeling the physical interaction between CNT and polymeric matrix from point of view of the classical contact phenomenon between two flexible bodies. The results of this new approach are compared with perfectly bonded interface and also those obtained from the rule of mixtures. Results show that the Effective Young Modulus (EYM) of the CNT-based nanocomposites for modeling the interaction of CNT/polymer from the point of view of classical contact approach is slightly smaller than the perfectly bonded condition and is more near to experimental reports. It is also showed that increasing the amplitude of wavy CNT or decreasing its wavelength decreases the EYM of the CNT-based nanocomposites s which is in good agreement with the literature. There were also, a linear relation between the EYM of the CNT-based nanocomposites and the volume fraction of CNT inclusions which was observed by the other authors.

The long-term deterioration of large-scale infrastructure systems is a critical national problem that if left unchecked, could lead to catastrophes similar in magnitude to the collapse of the I-35W Bridge. Fortunately, the past decade has witnessed the emergence of a variety of sensing technologies from many engineering disciplines including from the civil, mechanical and electrical engineering fields. This paper provides a detailed overview of an emerging set of sensor technologies that can be effectively used for health management of large-scale infrastructure systems. In particular, the novel sensing technologies are integrated to offer a comprehensive monitoring system that fundamentally addresses the limitations associated with current monitoring systems (for example, indirect damage sensing, cost, data inundation and lack of decision making tools). Self-sensing materials are proposed for distributed, direct sensing of specific damage events common to civil structures such as cracking and corrosion. Data from self-sensing materials, as well as from more traditional sensors, are collected using ultra low-power wireless sensors powered by a variety of power harvesting devices fabricated using microelectromechanical systems (MEMS). Data collected by the wireless sensors is then seamlessly streamed across the internet and integrated with a database upon which finite element models can be autonomously updated. Life-cycle and damage detection analyses using sensor and processed data are streamed into a decision toolbox which will aid infrastructure owners in their decision making.

The objective of this paper is to present a 'straw-person' framework that appears to be a practical first step towards a more transparent, objective, quantitative and risk-based approach to bridge assessment and prioritization. While the framework presented is qualitative in nature it has distinct advantages over the current approach in that (a) it explicitly recognizes key performance limit states, (b) directly addresses bridge hazards, vulnerabilities, and exposures, (c) incorporates the uncertainty associated with various assessment techniques and provides flexibility for their implementation, and (d) provides a means to capture (in a useable format) expert knowledge and heuristics from top bridge engineers. In addition to the straw-person framework, the paper presents a rudimentary classification system to illustrate one approach to implementation. A series of case studies are then presented to demonstrate the potential value of this approach in distinguishing between bridges that are essentially "equivalent" based on the current assessment procedure. In addition, these case studies also serve to illustrate that the proposed approach may be utilized with existing inspection data. The paper concludes with some observations and comments regarding the straw-person framework presented.

To develop a simple method for detecting and monitoring FRP-concrete debonding with the use of distributed Brillouinbased fiber optic strain sensor, this study proposes a model that takes into consideration both the steady and the transient Brillouin interaction states. Assuming that the transient term has an analogous effect on the steady state term, two parameters, the effective transient length and the intensity reduction ratio, are introduced. The proposed model shows that the stimulated Brillouin signal intensity distribution at the specific frequency, which corresponds to the maximum strain at the debonded region, is sensitive to the occurrence of debonding. For evaluation of the model, experiments are carried out on a reinforced concrete beam retrofitted with glass FRP sheets on which sensing fibers are mounted, and the results agree with the observation. This numerical and experimental study demonstrates the effectiveness of the proposed model that incorporates not only the steady Brillouin interaction state. The model enables debonding detection without baseline measurement, leveraging the stimulated Brillouin scattering principle with high spatial resolution and high accuracy.

This paper presents a field experiment on monitoring of reflective cracks in highway asphalt overlay using a Brillouin scattering based distributed optical fiber sensor. With wheel loading above the joint of existing underlying pavement, the distributed strain of the overlay near the joint was examined. An initial crack was evaluated and predicted from the measured strain distribution. Then the progress of the reflective crack was investigated based on monitoring of the strain distribution of the overlay and the underlying pavement. Within the measurements at three typical times, the contribution of the wheel loading and the asphalt shrinkage induced by the temperature variation are all analyzed and compared.

It is a rare opportunity to monitor a damaged structure due to extensive cracking. The progress of cracks is of primary concern for maintenance. However, it is difficult to distinguish the extension due to structural degradation from temperature to traffic. A Structural Health Monitoring System (SHMS) was installed in a PC box-girder bridge in order to monitor the crack development. This SHMS has continuously worked for 7 years. The temperature and traffic load patterns were deduced from raw data by using correlation techniques. Although, crack opening displacement (COD) due to temperature of daily and yearly seasonal cycles is much larger than the COD due to trucks, the overall fatigue effect due to traffic is much larger than the temperature effect because of its sheer numbers, about 3000 per day. Overweight trucks are usually allowed with permit in major interstate highway. However, frequency change due to local fatigue of crack is negligible. This research can be helpful to explain why frequency is insensitive to local damage.

In the distant detection of debonding in glass fiber reinforced polymer (GFRP)-retrofitted concrete systems using radar NDE techniques, revealing the presence of debonding in reconstructed images is essential to the success of the techniques. An optimization scheme based on mathematical morphology is proposed for determining the optimal measurement and processing parameters in a distant radar NDE technique for debonding detection. Inverse synthetic aperture radar (ISAR) and backprojection algorithms are applied in the technique. Measurement (incident frequency and angle) and processing (frequency bandwidth and angular range) parameters are defined in this work. Performance of the optimization scheme is validated by laboratory ISAR measurements on GFRP-retrofitted concrete cylinders using radar signals in 8-18 GHz. From the results it is shown that better detection can be achieved by optimized measurements and processing.

Some early designs of Electromagnetic Acoustic Transducers (EMATs) used electromagnets to provide the strong magnetic field required for the transducer to operate. The advent of a new generation of permanent magnets such as NdFeB, with magnetic fields approaching 1T, meant that many EMAT designs switched over to using these small, compact and relatively inexpensive magnets. Typically, most modern EMATs make use of permanent magnets since they can exert high magnetic fields with compact structures. There are certain limitations when using permanent magnets, and their low Curie points of between 80-150C limit their practicality for high temperature testing without using water cooled transducers. In this work we have employed a pulsed electromagnet to provide the magnetic field. Pulsing the magnet dramatically reduces the average power required, keeping the supply more compact and less complex. It has the added advantage on ferritic steels, of resulting in much larger amplitude ultrasonic signals and improved signal to noise when compared with EMATs which use the strongest permanent magnets available.

The contrast in the dielectric constant between a landmine and the surrounding soil is one of the most important parameters to be considered when using ground penetrating radar (GPR) for landmine detection. In this paper, we discuss available models for the prediction of the dielectric constant from soil physical properties including bulk density, particles density soil texture, and water content. We predict the effects of such properties on the antipersonnel (AP) landmine detection performance of GPR in an application in Iran. Initially, available soil geophysical information was used from four types of soil selected from Iranian mine-affected areas. Subsequently, a pedotransfer model was developed to predict whether or not field conditions are appropriate for use of GPR instruments. The predictions outcome obtained through usage of this model was based on different soil textures at various soil water contents. Knowledge of soil texture, dry bulk density, and water content are necessary to determine whether soil conditions are suitable for utilization of GPR mine detection. The developed model presented here can be useful for making this determination. Finally, the graphical user interface (GUI) of the pedotransfer model was calculated and presented herein. This software package facilitates the analysis of complex dielectric constant of soil as well as attenuation of GPR signals. The developed package is also capable of plotting the complex dielectric constant of soil coupled with attenuation of GPR signals versus soil physical properties.

his work deals with the study of fracture behavior of silicon carbide particle-reinforced (SiCp) A359 aluminum alloy matrix composites using an innovative nondestructive method based on lock-in thermography. The heat wave, generated by the thermo-mechanical coupling and the intrinsic energy dissipated during mechanical cyclic loading of the sample, was detected by an infrared camera. The coefficient of thermo-elasticity allows for the transformation of the temperature profiles into stresses. A new procedure was developed to determine the crack growth rate using thermographic mapping of the material undergoing fatigue: (a) The distribution of temperature and stresses at the surface of the specimen was monitored during the test. To this end, thermal images were obtained as a function of time and saved in the form of a movie. (b) The stresses were evaluated in a post-processing mode, along a series of equally spaced reference lines of the same length, set in front of the crack-starting notch. The idea was that the stress monitored at the location of a line versus time (or fatigue cycles) would exhibit an increase while the crack approaches the line, then attain a maximum when the crack tip was on the line. Due to the fact that the crack growth path could not be predicted and was not expected to follow a straight line in front of the notch, the stresses were monitored along a series of lines of a certain length, instead of a series of equally spaced points in front of the notch. The exact path of the crack could be easily determined by looking at the stress maxima along each of these reference lines. The thermographic results on the crack growth rate of the metal matrix composite (MMC) samples with three different heat treatments were correlated with measurements obtained by the conventional compliance method, and found to be in agreement.

In this study, a mechanical shaker operating at low frequencies is demonstrated to be a viable excitation source for vibrothermography. Additionally, a low-cost transduction approach based on commercially available piezoelectric materials (PZT) is investigated. These PZT transducers are assessed for their excitation efficiency to allow crack detection in metallic structures. Cracks as small as 1 mm are detected using the mechanical shaker regardless of a beam structure orientation or crack location. Although the low-cost PZT-based transduction approach had sufficient excitation power to generate vibration, localized heat generation was not observed at crack locations.

Moisture and oil contents are important quality factors often measured and monitored in the processing and storage of food products such as corn and peanuts. For estimating these parameters for peanuts nondestructively a parallel-plate capacitance sensor was used in conjunction with an impedance analyzer. Impedance, phase angle and dissipation factor were measured for the parallel-plate system, holding the in-shell peanut samples between its plates, at frequencies ranging between 1MHz and 30 MHz in intervals of 0.5 MHz. The acquired signals were analyzed with discrete wavelet analysis. The signals were decomposed to 6 levels using Daubechies mother wavelet. The decomposition coefficients of the sixth level were passed onto a stepwise variable selection routine to select significant variables. A linear regression was developed using only the significant variables to predict the moisture and oil content of peanut pods (inshell peanuts) from the impedance measurements. The wavelet analysis yielded similar R² values with fewer variables as compared to multiple linear and partial least squares regressions. The estimated values were found to be in good agreement with the standard values for the samples tested. Ability to estimate the moisture and oil contents in peanuts without shelling them will be of considerable help to the peanut industry.

A versatile and broad-field technique, sonic thermography uses high intensity acoustic waves to induce frictional heating at defect locations and the thermal signature is then detected using IR imaging. Sonic thermography has the potential to be used as a quantitative technique for difficult inspection problems. One example is the inspection of interference fit fasteners. In the case of poorly fitted interference fasteners, the acoustic waves induce relative motion between the fastener and host, causing frictional heating which can then be detected. The preliminary results of an inspection of interference fit levels in fastened metallic plates, reminiscent of the F-111C wing skin, are discussed. By improving the repeatability of the acoustic energy transfer, the heat detected using the IR thermographic system can be correlated to the interference fit levels of the fasteners. The results provide encouragement for the development of a quantitative assessment capability, however one of the remaining critical issues, which has hindered the use of sonic thermography as a quantitative technique, is the poor repeatability of acoustic excitations. This paper will also report on an experimental study which investigates this repeatability issue, in particular the role of the interface material used between the horn tip and the structure to enhance energy transfer.

This article describes the development of a fiber optic accelerometer based on Fiber Bragg Gratings (FBG). The accelerometer, designed for the structural health monitoring of bridges, utilizes a lumped mass attached to a stretched FBG. Acceleration is measured by the FBG in response to the vibration of the fiber optic mass system. The wavelength shift of FBG is proportional to the change in acceleration, and the gauge factor pertains to the shift in wavelength as a function of acceleration. The accelerometer was first evaluated in laboratory settings and then employed in a demonstration project for condition assessment of a bridge. Laboratory experiments included a series of low frequency low amplitude sinusoidal excitation tests to evaluate the sensitivity and frequency resolution of the proposed sensor. Two series of multiplexed FBG accelerometers were utilized to assess the dynamic properties of a bridge under ambient vibration conditions. The Frequency Domain Decomposition method was employed to identify the mode shapes and natural frequencies of the bridge. Results were compared with the data acquired from the conventional accelerometers.

A fiber optic Bragg grating based acoustic emission sensor system is developed to provide on-line monitoring of cracks or leaks in reactor vessel head penetration of nuclear power plants. Various type of fiber Bragg grating sensor including the variable length of sensing part was fabricated and prototype sensor system was tested by using PZT pulser and pencil lead break sources. In this study, we developed a cantilever type fiber sensor to enhance the sensitivity and to resonant frequency control. Two types of sensor attachment were used. First, the fiber Bragg grating sensor was fully bonded to the surface using bonding agent. Second one is that one part of fiber was partially bonded to surface and the other part of fiber will be remained freely. The resonant frequency of the fiber Bragg grating sensor will depend on the length of sensing part. Various kinds of resonant type fiber Bragg grating acoustic emission sensors were developed. Also several efforts were done to enhance the sensitivity of FBG AE sensor, which include FBG spectrum optimization and electrical and optical noise reduction. Finally, based on the self-developed acquisition system, a series of tests demonstrate the ability of the developed fiber sensor system to detect a pencil lead break event and continuous leak signal.

The stay cables are generally regarded as the most critical component of the cable-stayed bridges. Normal vehicle loads will cause fatigue damage of the cables made of parallel steel wire. In addition, the stay cables also suffer from the challenges of corrosion, fatigue and their coupled effects. Therefore it is important to detect the damage of wires with the cables before the cables fails catastrophically. Structural health monitoring (SHM) is now regarded as an essential tool to evaluate the status of the structure. In this paper, a corroded parallel steel wire, which are removed from a real bridge, was carried out under the fatigue loading to simulate the damage procedure, i.e. the producing and propagation of damage or crack. Piezoelectric transformers bonded to the cable are used to monitor and evaluate the damage propagation during the test. Moreover, the fatigue properties of corroded parallel wire cable are investigated in this paper.

Optical interferometry techniques can be use for the first time to measure the surface resistivity/conductivity of silicon wavers without any physical contact. This can be achieved by applying an electrical potential across the waver and measuring the electronic current flow across the waver as a result of the electrical potential. In the mean time, optical iterferometry techniques such as holographic interferometry can be used in situ to measure the orthogonal surface displacement of the waver, as a result of the applied electrical potential. In addition, a mathematical model can be derived in order to correlate the ratio of the electrical potential to the electronic current flow (electrical potential/electronic Current flow=resistance) and to the surface (orthogonal) displacement of the waver. In other words, a proportionality constant (surface resistivity or conductivity=1/ surface resistivity) between the measured electrical resistance and the surface displacement (by the optical interferometry techniques) can be obtained. Consequently the surface resistivity/ and conductivity of the waver can be determined, without any physical contact.

An extensive model test program had been carried out to investigate the issues of ice loading on bridge pier model. This paper investigated design principle of three kinds of FBG sensor modules, including FBG-based displacement sensor module, FBG-based strain sensor module and FBG-based force sensor module. A series of calibration tests of all FBG sensors had been made to detect the sensitivity of FBG sensor modules previously. There were 12 FBG-based sensors applied to monitor the failure progress and to predict the cracking inside the bridge pier model. The results of the ice loading tests proved that the FBG-based sensor had many advantages, characterized by its small size, high precision, easier installation, water resistance and cold resistance, demonstrating promising potentials in cracking and failure monitoring of bridge pier model.

Seismic damage to buried pipelines is mainly caused by permanent ground displacements, typically concentrated in the vicinity of the fault line in the soil. In particular, a pipeline crossing the fault plane is subjected to significant bending, shear, and axial forces. While researchers have explored the behavior of segmented metallic pipelines under permanent ground displacement, comparatively less experimental work has been conducted on the performance of segmented concrete pipelines. In this study, a large-scale test is conducted on a segmented concrete pipeline using the unique capabilities of the NEES Lifeline Experimental and Testing Facilities at Cornell University. A total of 13 partial-scale concrete pressure pipes (19 cm diameter and 86 cm long) are assembled into a continuous pipeline and buried in a loose granular soil. Permanent ground displacement that places the segmented concrete pipeline in compression is simulated through the translation of half of the soil test basin. A dense array of sensors including linear variable differential transducers, strain gauges, and load cells are installed along the length of the pipeline to measure its response to ground displacement. Response data collected from the pipe suggests that significant damage localization occurs at the ends of the segment crossing the fault plane, resulting in rapid catastrophic failure of the pipeline.

Wireless sensing has been widely explored in recent years for structural monitoring and dynamic testing. The limitations of current wireless sensor networks have been identified with regard to limited power supply, communication bandwidth, communication range, computing power, etc. The cost of most wireless structural sensors is still prohibitive for dense instrumentation on large civil structures. To address the above challenges, this research proposes a new methodology for structural health monitoring based upon mobile sensor networks. In this research, prototype mobile sensing nodes have been developed using magnet-wheeled cars as the sensor carriers. These mobile sensing nodes can maneuver upon structures built with ferromagnetic materials. Performance of the prototype mobile sensing system has been validated on a laboratory steel frame. Modal analysis for the frame structure is conducted using the data collected by the mobile sensing nodes. This exploratory work illustrates the flexible spatial resolutions offered by mobile sensors, which represent a transformative change from the fixed spatial resolution provided by traditional static sensors.

Acellent Technologies, Inc. developed a smart structural health monitoring (SHM) sensor network that can autonomously assess in real time the structural stability of buildings. The sensor network uses piezoelectric actuators and sensors to characterize damage in, and monitor the rigidity of components of the building primary structure. Additionally, temperature sensors are integrated into the proposed sensor network to monitor the temperature of the structural components. Acellent's existing sensor network SMART Layer technology was used as the basis for the proposed development. The modifications to our existing technology included a redesigned sensor/actuator arrangement, the development of a SmartDAQ sensor package with the required sensor and electronics, and additional software that provides a map of the structural damage, temperature and rigidity information. This will be useful to provide a real time assessment of the building structural integrity. The data will be available for display to provide and early warning to first responders and emergency personnel to ensure their safety prior to entering the building.

The goal of this research is to establish a methodology for damage detection in unreinforced and z-fiber reinforced cocured composite pi- joints using lamb wave based structural health monitoring technique. Because of the lack of natural reinforcement in the thickness direction, delamination has been a predominant failure mode besides other failure modes in laminated composites. Z-fiber reinforcement is one of the ways of controlling or delaying delamination and thus, delaying the failure. Here, DCB (Double Cantilever Beam) and Pi-Joint specimens, with and without z-fiber reinforcement, are considered for experimental analysis. Damage is experimentally induced in the specimen under static loading. Lamb wave propagation based structural health monitoring is performed using PZT sensors in a pitch-catch arrangement. Amplitude vs. time and amplitude vs. frequency response are plotted for various excitation frequencies. At lower frequencies (particularly at 20 KHz), pure A0 mode is generated, which is confirmed by out of phase response of simultaneous PZT sensors. From the response data analysis, presence of damage in unreinforced, z-fiber reinforced DCB and pi-joint specimens is confirmed.

rent routine inspection practices for bridge health monitoring are not sufficient for the timely identification of areas of concern or to provide enough information to bridge owners to make informed decisions for maintenance prioritization. Continuous monitoring is needed for long term evaluation from an integrated sensing system that would act as a monitoring and early warning alarm system and be able to communicate the information from the bridge directly to the bridge owners for potential and immediate action. To address this urgent highway bridge health monitoring need, a joint venture research has been initiated by incorporating novel and promising sensing approach based on piezoelectricity together with energy harvesting to reduce the dramatic uncertainty inherent into any inspection and maintenance plan. In the system, the damage detection and classification is focused on the use of piezoelectric wafer active sensors (PWAS) at both active (Lamb wave interrogation) mode and passive (acoustic emission) mode on steel bridge. For efficient energy usage, the active mode will be triggered when acoustic emission caused by the structural change is detected. In the active sensing mode, computed array imaging will be used to detect the presence of crack and to track its growth. To further quantify the crack growth, damage physics based damage indicator will be defined and used to trace the crack growth as well.