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

Long-period fiber grating (LPFG) sensors have been demonstrated to exhibit negative and positive strain sensitivity coefficients with cladding modes of LP05 and LP07, respectively. Their temperature sensitivity remains positive for both cladding modes. Based on the unique properties of CO₂ laser-induced gratings, two designs of LPFG sensors have been presented in this paper for simultaneous strain and temperature measurement. One double-LPFG sensor integrates two separate groups of gratings in series, corresponding to two cladding mode measurements such as LP05 and LP07. It can measure strain and temperature simultaneously with a measurement error of less than 2%. However, the spacer between two tandem gratings can only survive in low temperature environments. The other single-LPFG sensor uses the measurements with two cladding modes on one group of gratings. Under various disturbances, different intrinsic cladding modes of the single LPFG, such as LP05 and LP07, are tracked simultaneously for strain and temperature discrimination. The single-LPFG sensor can measure strains in high temperature up to 700°C.

Localization of low energy impacts on carbon fiber composites is an important aspect of structural health monitoring since it creates subsurface damage which can significantly reduce the stiffness of a component. A novel impact localization method is proposed based on the strain amplitude measured by Fiber Bragg Grating (FBG) sensors. The algorithm is based on the relative placement of all sensors and the maximum strain amplitude measured by each sensor. This method requires minimal knowledge of the material or the structure and a minimum number of sensors. The algorithm showed good results on both simulated and experimental test cases of woven composite plates. It was found that a minimum of five FBG are necessary to accurately predict the impact location on a plate. The algorithm was also tested on a woven composite wing showing good localization along the span of the wing but higher errors along the chord length due to the nonlinearity in the measured strains.

This paper presents a novel Fiber-Bragg Grating interrogation system and its validation for detection of Lambwaves and acoustic emission events on both aluminum and composite substrates. The system utilizes a robust laser demodulation technique for FBG interrogation, based upon a simple laser wavelength tracking scheme. This technique enables detection of much higher frequency strains than previous FBG interrogation techniques, enabling the use of FBG sensors in acousto-ultrasonic structural health monitoring schemes such as Lamb-wave pitch-catch and acoustic emission detection in the presence of a quasistatic strain background. The principles of the FBG interrogation system are presented, including validation of the system for detection of ultrasonic Lamb waves, and results from a 4-point bending test of a braided composite tube wherein the FBG system was used to detect crack-growth induced AE events on the braided tube. The AE data agreed well with damage index values measured by a commercial acousto-ultrasonic system.

Solid oxide fuel cells (SOFC) have been known for their clean and efficient energy conversion. SOFCs utilize a range of ceramic electrolyte materials, with yttria stabilized zirconia (YSZ) as the most common choice. Traditional SOFCs operate at relatively high temperatures (800-1000°C) due to their low oxide ion conductivity and high activation energy. Reducing the operating temperature is important to expand the field of SOFC applications, such as power sources for portable electronics. Reducing the electrolyte thickness by means of thin film deposition techniques to the submicrometer range is one way to reduce the Ohmic loss in SOFCs at lower temperature. In this paper, a miniature thin film fuel cell array is designed and fabricated targeting at reduced operating temperature as a potential portable power source.

Casing pipes in oil well constructions may suddenly buckle inward as their inside and outside hydrostatic pressure difference increases. For the safety of construction workers and the steady development of oil industries, it is critically important to measure the stress state of a casing pipe. This study develops a rugged, real-time monitoring, and warning system that combines the distributed Brillouin Scattering Time Domain Reflectometry (BOTDR) and the discrete fiber Bragg grating (FBG) measurement. The BOTDR optical fiber sensors were embedded with no optical fiber splice joints in a fiber reinforced polymer (FRP) rebar and the FBG sensors were wrapped in epoxy resins and glass clothes, both installed during the segmental construction of casing pipes. In-situ tests indicate that the proposed sensing system and installation technique can survive the downhole driving process of casing pipes, withstand a harsh service environment, and remain in tact with the casing pipes for compatible strain measurements. The relative error of the measured strains between the distributed and discrete sensors is less than 12%. The FBG sensors successfully measured the maximum horizontal principal stress with a relative error of 6.7% in comparison with a cross multi-pole array acoustic instrument.

In recent years, fiber reinforced polymer (FRP) composites have been widely applied in civil engineering for retrofitting or renewal of existing structures. Since FRP composite may degrade when exposed to severe outdoor environments, a serious concern has been raised on its long term durability. In the present study, fiber Bragg grating (FBG) sensors were embedded in glass-, carbon- and basalt-fiber reinforced epoxy based FRP plates with wet lay-up technology, to in-situ monitor the stain changes in FRPs during the curing, and water immersion and freeze-thaw ageing processes. The study demonstrates that the curing of epoxy resin brings in a slight tension strain (e.g., 10 ~ 30 με) along the fiber direction and a high contraction (e.g., ~ 1100με) in the direction perpendicular to the fibers, mainly due to the resin shrinkage. The cured FRP strips were then subjected to distilled water immersion at 80oC and freeze-thaw cycles from -30°C to 30°C. Remarkable strain changes of FRPs due to the variation of the temperatures during freeze-thaw cycles indicate the potential property degradation from fatigue. The maximum strain change is dependent on the fiber types and directions to the fiber. Based on the monitored strain values with temperature change and water uptake content, CTE (coefficient of thermal expansion) and CME (coefficient of moisture expansion) are exactly determined for the FRPs.

In this paper, the structural health monitoring of a pre-stressed concrete (PC) structure based on two types of distributed sensing techniques is addressed. The sensing elements are Brillouin scattering-based fiber optic sensors (FOSs) and HCFRP (hybrid carbon fiber reinforced polymer) sensors composed of three types of carbon tows. Both types of sensors are characterized by a broad-based and distributed sensing function. The HCFRP sensors are bonded on PC tendon, steel reinforcing bar, and embedded in tensile and compressive concrete sides with epoxy resins and putties. The FOSs are embedded in the tensile and compressive concrete sides where the HCFRP sensors are embedded as well. The distributed sensors are arranged to detect and monitor the initiation and propagation of cracks, yielding of steel reinforcements and corrosion of PC tendons. The experimental investigations demonstrate that the initiation and location of cracks, yielding of steel reinforcements, corrosion of PC tendons and structural health of PC structures can be effectively detected and monitored with such kinds of distributed sensing systems.

The accurate estimation of fatigue life of metallic structural components in service environments is still a challenge for the aircraft designer or fleet manager. Majority of the current available fatigue life prediction models has deficiency to accurately predict damage under random or flight profile service loads. The inherent accuracy is due to the stochastic nature of crack propagation in metallic structure. In addition, currently no generic prediction model available accounting the load interaction effects due to variable loading. In the present paper we discus the use of a Generic Bayesian framework based Gaussian process approach to probabilistically predict the fatigue damage under complex random and flight profile loading.

This paper presents an initial study on Lamb wave propagation characteristics in z-pin reinforced, co-cured composite pi-joints for the purposes of structural health monitoring (SHM). Pi-joint test articles were designed and created to replicate a co-cured, all composite skin-spar joint found within a typical aircraft wing structure. Because pi-joints exhibit various complex damage modes, formal studies are required if SHM systems are to be developed to monitor these types of joints for potential damage. Experiments were conducted on a undamaged (healthy) and damaged test articles where Lamb waves were excited using one lead zirconate titanate (PZT) transducer. A three-dimensional (3D) scanning laser Doppler vibrometer (LDV) was used to collect high-density scans of both the in-plane and out-of-plane velocity measurements. In the damaged test article, where delamination, matrix cracking, and fiber breakage can clearly be seen, changes in both the fundamental antisymmetric A₀ and symmetric S₀ Lamb wave modes are apparent. In both test articles, the effects of narrow geometry, discontinuity due to the attachment of the web, and thickness has detectable effects on Lamb wave propagation. From the comparisons between Lamb waves propagating through the undamaged and damaged test articles, it is clear that damage can be detected using Lamb waves in z-pin reinforced, co-cured composite pi-joints for this case of extensive damage.

This experimental research investigates the effects of adding z-pins to a carbon fiber reinforced plate (CFRP) on Lamb wave propagation, such as mode conversion and reflections. The motivation for this study is derived from the current and expected future use of z-pins in aircraft structures coupled with the requirement to design structural health monitoring (SHM) systems for detecting damage in regions of composite structures with z-pins. This experimental study is conducted on two 4.8 mm thick CFRP test articles, where one plate has a 20 by 279 mm2 band of z-pins and the other does not. The z-pins have an average diameter of 0.28 mm and are inserted through the thickness of the panel with an area density of 4% before curing. A three-dimensional (3D) laser Doppler vibrometer (LDV) was employed to collect velocity measurements over a 1 mm uniformly-spaced grid of 17,899 scan points. Time-sequenced 3D LDV scans are presented to show that adding this relatively small amount of z-pins to a 4.8 mm thick CFRP has few measureable effects on Lamb wave propagation.

The increased usage of fiber-reinforced polymers (FRP) in recent decades has created a need to monitor the unique response of these materials to impact and fatigue damage. As most traditional nondestructive evaluation methods are illsuited to detecting damage in FRPs, new methods must be created without compromising the high strength-to-weight aspects of FRPs. This paper describes the characterization of carbon nanotube-polyelectrolyte thin films applied to glass fiber substrates as a means for in situ strain sensing in glass fiber-reinforced polymers (GFRP). The layer-by-layer deposition process employed is capable of depositing individual and small bundles of carbon nanotubes within a polyelectrolyte matrix and directly onto glass fiber matrices. Upon film fabrication, the nanocomposite-coated GFRP specimens are mounted in a load frame for characterizing their electromechanical performance. This preliminary results obtained from this study has shown that these thin films exhibit bilinear piezoresistivity. Time- and frequency-domain techniques are utilized to characterize the nanocomposite strain sensing response. An equivalent circuit is also derived from electrical impedance spectroscopic analysis of thin film specimens.

Carbon fiber materials become more and more important for many applications. Unlike metal the technological parameters and certified quality control mechanisms for Raw Carbon Fiber Materials (RCF) have not yet been developed. There is no efficient and reliable testing system for in-line inspections and consecutive manual inspections of RCF and post laminated Carbon Fiber Reinforced Plastics (CFRP). Based upon the multi-frequency Eddy Current system developed at Fraunhofer IZFP, structural and hidden defects such as missing carbon fiber bundles, lanes, suspensions, fringes, missing sewing threads and angle errors can be detected. Using an optimized sensor array and intelligent image pre-processing algorithms, the complex impedance signal can be allocated to different carbon fiber layers. This technique enables the detection of defects in depths of up to 5 layers, including the option of free scale measuring resolution and testing frequency. Appropriate parameter lists for optimal error classifications are available. The dimensions of the smallest detectable flaws are in the range of a few millimeters. Algorithms and basic Eddy Current C-Scan processing techniques for carbon fiber material testing are described in this paper.

Bridges are an important societal resource used to carry vehicular traffic within a transportation network. As such, the economic impact of the failure of a bridge is high; the recent failure of the I-35W Bridge in Minnesota (2007) serves as a poignant example. Structural health monitoring (SHM) systems can be adopted to detect and quantify structural degradation and damage in an affordable and real-time manner. This paper presents a detailed overview of a multi-tiered architecture for the design of a low power wireless monitoring system for large and complex infrastructure systems. The monitoring system architecture employs two wireless sensor nodes, each with unique functional features and varying power demand. At the lowest tier of the system architecture is the ultra-low power Phoenix wireless sensor node whose design has been optimized to draw minimal power during standby. These ultra low-power nodes are configured to communicate their measurements to a more functionally-rich wireless sensor node residing on the second-tier of the monitoring system architecture. While the Narada wireless sensor node offers more memory, greater processing power and longer communication ranges, it also consumes more power during operation. Radio frequency (RF) and mechanical vibration power harvesting is integrated with the wireless sensor nodes to allow them to operate freely for long periods of time (e.g., years). Elements of the proposed two-tiered monitoring system architecture are validated upon an operational long-span suspension bridge.

A smart antenna has been developed for structural health monitoring. The antenna is based on Monarch's GEN 2 selfstructuring antenna (SSA) technology and provides polarization and beam-diversity for improving signal-to-noise ratio (SNR). The antenna works with University of Michigan's Narada platform, where a microcontroller monitors the RSSI and selects the best beam to maintain reliable RF link. Antenna has two wide beams for each polarization and the beams are selected by applying appropriate DC voltages to the RF switches on the antenna aperture. Paper presents the GEN C antenna, which is a smaller version of the GEN 2B with comparable performance features.

In this paper we focus on the optimal placement of sensors for state estimation-based continuous health monitoring of structures using three approaches. The first aims to minimize the static estimation error of the structure deflections, using the linear stiffness matrix derived from a finite element model. The second approach aims to maximize the observability of the derived linear state space model. The third approach aims to minimize the dynamic estimation error of the deflections using a Linear Quadratic Estimator. Both nonlinear mixed-integer and relaxed convex optimization formulations are presented. A simple search-based optimization implementation for each of the three approaches is demonstrated on a model of the long-span New Carquinez Bridge in California.

A MEMS-based wireless sensor network (WSN) is developed for nondestructive monitoring of pipeline systems. It incorporates MEMS accelerometers for measuring vibration on the surface of a pipe to determine the change in water pressure caused by rupture and the damage location. This system enables various sensor boards and camera modules to be daisychained underground and to transmit data with a shared radio board for data uplink. Challenges include reliable long-range communication, precise time synchronization, effective bandwidth usage, and power management. The low-cost MEMS technology, saved wiring cost, and simple installation without destructive modification enable large-scale deployment at an affordable cost.

Monitoring of fatigue cracks in steel bridges is of interest to bridge owners and agencies. Monitoring of fatigue cracks has been attempted with acoustic emission using either resonant or broadband sensors. One drawback of passive sensing is that the data is limited to that caused by growing cracks. In this work, passive emission was complemented with active sensing (piezoelectric wafer active sensors) for enhanced detection capabilities. Passive and active sensing methods were described for fatigue crack monitoring on specialized compact tension specimens. The characteristics of acoustic emission were obtained to understand the correlation of acoustic emission behavior and crack growth. Crack and noise induced signals were interpreted through Swansong II Filter and waveform-based approaches, which are appropriate for data interpretation of field tests. Upon detection of crack extension, active sensing was activated to measure the crack size. Model updating techniques were employed to minimize the difference between the numerical results and experimental data. The long term objective of this research is to develop an in-service prognostic system to monitor structural health and to assess the remaining fatigue life.

A large scale finite element model with high mesh resolution is established to simulate the ground truth of regular highway pavement structure with subsurface debonding defects. The simulation is motivated by non-destructive testing methods that derive information from the acoustic radiation of the surface wave. These NDT (Non-Destructive Testing) signals come from solid elastic wave propagation beneath pavement surface, which then couple with acoustic wave in air above the pavement surface. In this article, 2 main debonding phenomena, which are conventionally hidden below the pavement surface, are modeled and also compared with a healthy (perfectly intact) pavement structure model. Both the impact-response transient analysis and frequency spectrum analysis have been given to show a new opportunity to detect the subsurface debonding in pavement non-destructively through acoustic signals from heights above the pavement surface which are incorporated with ground truth information.

PMN-PT single crystal 1-3 composite high frequency phased arrays with center frequency of 35 MHz were fabricated and characterized for silicon carbide (SiC) NDE imaging applications. The 35 MHz 64-element array was successfully prototyped using PMN-PT single crystal and PC-MUT technology. The broad bandwidth > 90% and high sensitivity (echo amplitude > 500 mV from the impulse response with 0 gain) was observed with reasonably high uniformity. These high frequency phased arrays are promising for ceramic NDE imaging.

Owing to the nature of the stress, corrosion of bridge cable may result in catastrophic failure of the structure. However, using electrochemical techniques isn't fully efficient for the detection and control on line of the corrosion phenomenon. A non-destructive testing method based on acoustic emission technique monitoring bridge cable corrosion was explored. The steel strands were placed at room temperature in 5% NaCl solution. Acoustic emission (AE) characteristic parameters were recorded in the whole corrosion experiment process. Based on the plot of cumulated acoustic activity, the bridge cables corrosion included three stages. It can be clearly seen that different stages have different acoustic emission signal characteristics. The AE characteristic parameters would be increased with cables corrosion development. Finally, the bridge cables corrosion experiment with different stress state and different corrosion environment was performed. The results shows that stress magnitude only affects the bridge cable failure time, however, the AE characteristic parameters value has changed a little. It was verified that AE technique can be used to detect the bridge cable early corrosion, investigating corrosion developing trend, and in monitoring and evaluating corrosion damages.

The constant growth of air traffic leads to increasing demands for the aircraft industry to manufacture airplanes more economically and to ensure a higher level of efficiency, ecology and safety. During the last years important improvements for fuselage structures have been achieved by application of new construction principles, employment of sophisticated and/or alternative materials, and by improved manufacturing processes. In particular the intensified application of fibre-reinforced plastics components is in the focus of current discussions and research. The main goal of an ongoing national project is to improve the existing ultrasonic test technology in such a way that it is optimally suited for the examination of CFRP multilayer structures. The B-Scan and C-Scan results are then used for the visualization of individual layers and the complete layer set-up. First results of the project revealed that with carefully selected transducers and frequencies it is possible to detect defects and irregularities in the layer structure like delaminations, fibre cracking, ondulations, missing layers etc. and even to visualize the fibre orientations in the individual layers.

Among different failure modes observed in structures, loss of stability due to buckling is a major concern. Buckling may be induced because of overload or as a consequence of other types of failures in the structure. This paper examines two techniques, namely, vibration based analysis, and stress wave propagation analysis for detecting this onset of instability. The responses of a bar and a plate are used to illustrate the effectiveness of the two approaches. These analyses were performed through finite element simulations and limited experiments. Changes in vibration frequencies and mode shapes are found to provide good indications of the impending failure as well as its progress. Changes in the wave propagation characteristics showed some limited success in detecting the incipient buckling.

Acoustic emission is a powerful technique for identifying and monitoring the evolution of service induced degradation in structural components and localising damage. The present study is dedicated to the investigation of model composite systems in order to identify, locate and quantify service induced damage. These systems are cross ply translucent glass fibre reinforced composite materials. In cross ply composites, service induced primary damage is manifested in the form of matrix cracking of the off-axis layers. For the purposes of this study, the cross ply composite were subjected to step loading with the concurrent recording of the acoustic activity. At specific intervals of the loading process the propagation characteristics of ultrasonic waves were also recorded using the acoustic emission sensors in a pulser-receiver setup. The acoustic emission activity has been successfully correlated to damage accumulation of the cross ply laminates, while specific acoustic emission indices proved sensitive to the various modes that evolve during the loading.

The acoustic emission (AE) behaviour of steel fibre reinforced concrete is studied in this paper. The experiments were conducted in four-point bending with concurrent monitoring of AE signals. The sensors used, were of broadband response in order to capture a wide range of fracturing phenomena. The results indicate that AE parameters undergo significant changes much earlier than the final fracture of the specimens, even if the AE hit rate seems approximately constant. Specifically, the Ib-value which takes into account the amplitude distribution of the recent AE hits decreases when the load reaches about 60-70 % of its maximum value. Additionally, the average frequency of the signals decreases abruptly when a fracture incident occurs, indicating that matrix cracking events produce higher frequencies than fibre pull-out events. It is concluded that proper study of AE parameters enables the characterization of structural health of large structures in cases where remote monitoring is applied.

Monitoring structural integrity of large planar structures requires normally a relatively dense network of uniformly distributed ultrasonic sensors. A 2-D ultrasonic phased array with all azimuth angle coverage would be extremely useful for the structural health monitoring (SHM) of such structures. Known techniques for estimating direction of arriving (DOA) waves cannot efficiently cope with dispersive and multimodal Lamb waves (LWs). In the paper we propose an adaptive spectral estimation technique capable of handling broadband LWs sensed by 2-D arrays, the modified Capon method. Performance of the technique is evaluated using simulated multiple-mode LWs, and verified using experimental data.

Recently, a new design concept for multifunctional fasteners using smart materials was proposed by the authors. These piezoelectric devices, named 'smart fasteners,' can be fabricated by modifying the design of ordinary fasteners such that they have a piezoelectric transducer and a control unit embedded in their body. These smart fasteners can not only clamp structural members like ordinary fasteners but also induce or detect structural responses. In this paper, the capability of the smart fasteners to excite and detect Lamb waves in the clamped structure for structural health monitoring is presented. For this purpose, a mathematical model for the Lamb wave excitation with the smart fasteners is derived first using the potential function method. By applying the space domain Fourier transform, the model is transformed into the wave number domain where the boundary conditions are applied to get the solution. The obtained solution is then converted back into the physical space using the inverse Fourier transform. Finally, closed-form solutions for the surface displacements are obtained using the residue theorem in the complex plane. With the analytic solutions, mode tuning capabilities of the smart fasteners are analyzed and then experimentally verified.

Adaptive learning techniques have recently been considered for structural health monitoring applications due to their flexibility and effectiveness in addressing real-world challenges such as variability in the monitoring of environmental and operating conditions. In this paper, an active learning data selection procedure is proposed that adaptively selects the most informative measurements to include, from multiple available measurements, in estimating structural damage. This is important, since not all the measurements may provide useful information and could reduce performance when processed. Within the adaptive learning framework, the data selection problem is formulated to choose those measurements which are most representative of the diversity within a damage state. This is achieved by extracting time-frequency analysis based statistical similarity features from the measurements, and selecting uniformly distributed subsets to build representative reference sets. The utility of the proposed method is demonstrated by improvements in adaptive learning performance for the estimation of fatigue damage in an aluminum compact tension sample.

The quantification of pitting corrosion in terms of material or metal loss is required for the understanding of pipe condition. One approach to accurately map pitting corrosion is with a high-resolution laser scanner. However, this process is time consuming and requires the removal of the pipe segment and sandblasting of its surface. In this study, thermography is considered for the field testing. We investigated the potential of quantifying pitting corrosion with thermography technique. A cleaned pipe was inspected with the pulsed thermography (PT) technique. Extracted signal features were used to characterize metal loss. The algorithms to process PT inspection data and extract signal features to characterize the pitting corrosion are presented in this paper.

In this paper we investigate the performance of defect detection using long duration transient thermography for woven composite laminates subjected to low-velocity impacts. Two types of defects are studied: inclusions represented by foam tabs inserted into the laminate during fabrication and barely visible impact damage due to low-velocity impacts. These defects represent the expected damage states that are necessary for inspection during the service life of a woven composite aircraft component. The long duration transient thermography is demonstrated to successfully detect the embedded inclusions, with a dimension to depth ratio detection capability of approximately 3. It is also demonstrated that the detection of low velocity impact damage with the transient thermography is less successful due to uneven emissivity of the surface. Therefore, processing of the image using a self referencing algorithm is performed which improves the damage detection clarity.

An innovative Line Scanning Thermography (LST) inspection method is being developed as part of a Structural Damage Assessment System to access the health of in-service composite structures. The system utilizes a line heat source to thermally excite the surface inspected and an infrared detector to record the transient surface temperature variation and to detect regions of increased heat resistance associated to interlaminar disbonds, cracks and other imperfections found in composites structures. In this study our efforts towards the applications of LST for the analysis of carbon fiber sandwich composites will be discussed. The LST technique provides a quick and efficient methodology to scan wide areas rapidly. The scanning protocols developed for the detection of sub-surface disbonds (delamination) in composite sandwich parts will be presented. The results presented correspond to scans of test coupons with manufactured defects.

Bonded repair offers significant advantages over mechanically fastened repair schemes as it eliminates local stress concentrations and seals the interface between the mother structure and the patch. However, it is particularly difficult to assess the efficiency of the bonded repair as well as its performance during service loads. Thermography is a particularly attractive technique for the particular application as it is a non-contact, wide field non destructive method. Phase thermography is also offering the advantage of depth discrimination in layered structures such as in typical patch repairs particularly in the case where composites are used. Lock-in thermography offers the additional advantage of on line monitoring of the loaded structure and subsequently the real time evolution of any progressive debonding which may lead to critical failure of the patched repair. In this study composite systems (CFRP plates) with artificially introduced defects (PTFE) were manufactured. The aforementioned methods were employed in order to assess the efficiency of the thermographic technique. The obtained results were compared with typical C-scans.

We present an impulse ultra-wideband (UWB) sensor and demonstrate its sensing capability through various tests. The sensor, consisting of transmitter, receiver and antennas integrated together in a single package, is capable of transmitting impulse signals varying from 450 to 1170 ps and detecting signals up to 5.5 GHz. It has a range resolution of about 1 inch. The system can vary the transmitting pulse duration, thus effectively simulating multiple UWB systems working together consecutively.

We report a millimeter-wave stepped-frequency radar operating from 29.72 to 37.7 GHz for sensing applications. The radar is implemented using coherent super-heterodyne scheme and completely realized using microwave and millimeterwave integrated circuits. The developed radar has been demonstrated for different sensing applications with high accuracy and resolution. It can be used for various sensing applications including pavement and bridge assessment, liquid-level measurement, detection and location of buried mines and unexploded ordnance (UXO), detection of intrusion to structures including important civil facilities, detection of slow moving objects, surveillance and monitoring of hidden activities and objects.

In this study percentage of total kernel mass within a given mass of in-shell peanuts was determined nondestructively using a low-cost RF impedance meter. Peanut samples were divided into two groups, one the calibration and the other the validation group. Each group contained 50 samples of about 100 g of peanuts. Capacitance (C), phase angle (θ) and impedance (Z) measurements on in-shell peanut samples were made at frequencies 1 MHz, 5 MHz and 9 MHz. Ten measurements on each sample set were made, to minimize the errors due to the orientation of the peanuts as they settle between the electrodes of the impedance meter, by emptying and refilling the samples after each measurement. After completing the measurements on each set, the peanuts from that set were shelled, kernels were separated and weighed. Multi linear regression (MLR) calibration equation was developed by correlating the percentage of the kernel mass in a given peanut sample set with the measured capacitance, impedance and phase angle values. This equation was used to predict the kernel mass ratio of the samples from the validation group. The fitness of the MLR equation was verified using Standard Error of Prediction (SEP) and Root Mean Square Error of Prediction (RMSEP). Also, the predictability of total kernel mass ratio was calculated by comparing the mass ratio predicted using MLR model with the actual mass ratio determined using the conventional standard method of visual determination.

Corrosion induced bridge deck delamination is a common problem in reinforced concrete decks. While condition assessment can be done using a number of traditional and NDE methods, the presented study concentrates on a complementary use of five NDE techniques: impact echo (IE), ground penetrating radar (GPR), half-cell potential (H-C), ultrasonic surface waves (USW) and electrical resistivity (ER). Each of the five techniques has its advantages and limitations. However, each of them can contribute to a more comprehensive assessment of the condition of a deck. For example, GPR can identify deteriorated bridge deck areas, while IE can accurately detect and characterize delaminations in the deck. USW, on the other hand, provides information about material degradation through a measurement of concrete elastic moduli. Finally, H-C will provide information about the likelihood for active corrosion, while ER will assess potential for corrosive environment. There are also secondary benefits of the use of the five techniques, like e.g. mapping of concrete cover from GPR surveys. A brief overview of the techniques and their complementary use illustrated by the results from deck testing on several bridges is presented. The presented surveys were conducted on both decks (typical thickness 7 to 9 inches) and slabs (typical thickness 14-20 inches), some with an additional PC overlay. Results include delamination maps from IE, attenuation maps from GPR, modulus distribution maps from USW, H-C potential maps, and resistivity maps from ER. Some of the results are validated through a series of "ground truth" measurements, like inspection of cores taken from the decks.

In this paper, a structural behavior monitoring (SBM) based maintenance methodology is conceptualized to combine the advantages of visual inspection and state-of-the-art instrumentation. It depends on the data taken from the instrumentation in the decision-making process of infrastructure maintenance schedule. As such, SBM must address key factors such as the ease and cost effectiveness of sensor deployment, reliability in measurement, and quality of measured data. SBM is focused on major failure mechanisms in structural engineering, and use of advanced distributed sensors for behavior-related or mission critical data collection from representative 'hot spot' areas or part of a structure that will likely experience damage or significant deterioration. SBM has several unique attributes such as damage transfer mechanisms in sensor designs, coupled local and global measurements, multi-parameter monitoring for system behaviors, and integrated monitoring and mitigation strategies. They are discussed and illustrated with examples in this paper. Example structural behaviors include, but not limited to, concrete crack and spalling, steel yielding and corrosion, debonding, member buckling, foundation scour, and fatigue.

In this paper, a distant acoustic-laser NDE technique is proposed, utilizing a high powered standoff parametric acoustic array (PAA) and laser Doppler vibrometry (LDV), for the detection of debonding and delamination in multi-layer composite systems. Fiber-reinforced polymer wrapped concrete cylinder specimens with artificial defect were manufactured and used in the validation of the technique. Low-frequency (50 Hz 2 kHz) and highfrequency (2 kHz 7 kHz) focused sound waves were generated by PAA, and surface dynamic signatures of the specimens were remotely measured by LDV. From the results it is found that the proposed technique successfully captures the presence of near-surface debonding/delamination.

This paper addresses the potential applications of terrestrial 3D LiDAR scanning technologies for bridge monitoring. High resolution ground-based optical-photonic images from LiDAR scans can provide detailed geometric information about a bridge. Applications of simple algorithms can retrieve damage information from the geometric point cloud data, which can be correlated to possible damage quantification including concrete mass loss due to vehicle collisions, large permanent steel deformations, and surface erosions. However, any proposed damage detection technologies should provide information that is relevant and useful to bridge managers for their decision making process. This paper summaries bridge issues that can be detected from the 3D LiDAR technologies, establishes the general approach in using 3D point clouds for damage evaluation and suggests possible bridge state ratings that can be used as supplements to existing bridge management systems (BMS).

This paper describes the identification of finite dimensional, linear, time-invariant models of a 4-story building in the state space representation using multiple data sets of earthquake response. The building, instrumented with 31 accelerometers, is located on the University of California, Irvine campus. Multiple data sets, recorded during the 2005 Yucaipa, 2005 San Clemente, 2008 Chino Hills, and 2009 Inglewood earthquakes, are used for identification and validation. Considering the response of the building as the output and the ground motion as the input, the state space models that represent the underlying dynamics of the building in the discrete-time domain corresponding to each data set are identified. The four state space models identified demonstrate that the response of the building is amplitude dependent with the response frequency, and damping, being dependent on the magnitude of ground excitation. The practical application of this finding is that the consistency of this building response to future earthquakes can be quickly assessed, within the range of ground excitations considered (0.005g - 0.074g), for consistency with prior response - this assessment of consistent response is discussed and demonstrated with reference to the four earthquake events considered in this study. Inclusion of data sets relating to future earthquakes will enable the findings to be extended to a wider range of ground excitation magnitudes.

The Zhanjiang Bay Bridge is a cable stayed bridge with a main span of 480m. Structural behavior due to thermal effects is presented in this paper in according to data received from a health monitoring system (HMS) since 2006. Data obtained from the analysis includes temperature gradients and time lags in the steel box girder, concrete tower, and stayed cables. By comparing the measured and calculated thermal displacements, it was possible to estimate the unmeasured thermal gradient on the surface of the towers as well as to determine that one of the expansion joints was likely constrained and contributing to the bridges asymmetrical displacement.

Vibration based damage assessment of structures can be formulated as an optimization problem with the objective of minimizing the error between the measured and simulated responses of the structure by updating analytical model parameters. In this study, genetic algorithm (GA) and pattern search technique are combined in a hybrid optimization framework for finite element (FE) model updating using two objective functions defined in time and modal domains. The proposed model updating techniques have been applied to experimental data recorded during a shake table test on a quarter-scale model of a two span reinforced concrete bridge. The bridge was subjected to a series of seismic base excitations with increasing intensities introducing progressive real damage to the structure. Bridge responses to intermediate low amplitude white noise excitations are used for the purpose of modal identification and damage assessment. The FE model parameters are updated at different stages of the experiment. This study shows that damage throughout the structure can be accurately and consistently detected, located and quantified using the proposed model updating techniques.

The global mechanical behaviors of Sutong Bridge, China, the longest cable-stayed bridge in the world, are presented by using measurements from field static load tests compared with numerical analysis in this paper. A total of 37 loading cases with 64 test trucks, each being 300kN in weight, were conducted on 10 key sections to investigate the bridge behavior. The level of loading is about 50-88% of the code-specified serviceability load. A three-dimensional finite-element model is developed and calibrated to match the experiment data. The results show that, under the load test conditions, the incremental deflections, stresses as well as cable force of the structure are linearly proportional to the incremental loads. Moreover, the transverse shear lag effects of the steel box girder are significant and the longitudinal stress distributions in the slabs and diaphragms of the box girder are non-uniform. A good agreement is achieved between the experimental tests and the numerical simulations based on the nonlinear theories of long span bridges.

Laser-based scanning can provide a precise surface profile. It has been widely applied to the inspection of pipe inner walls and is often used along with other types of sensors, like sonar and close-circuit television (CCTV). These measurements can be used for pipe deterioration modeling and condition assessment. Geometric information needs to be extracted to characterize anomalies in the pipe profile. Since the laser scanning measures the distance, segmentation with a threshold is a straightforward way to isolate the anomalies. However, threshold with a fixed distance value does not work well for the laser range image due to the intensity inhomogeneity, which is caused the uncontrollable factors during the inspection. Thus, a local binary fitting (LBF) active contour model is employed in this work to process the laser range image and an image phase congruency algorithm is adopted to provide the initial contour as required by the LBF method. The combination of these two approaches can successfully detect the anomalies from a laser range image.

Ultrasonic waves have been used to monitor early age microstructure development in cementitious materials. The conventional ultrasonic setups typically measure longitudinal (P) waves in fresh cement pastes and need access two sides of the specimen. This type of setup is not suitable for in-situ field testing. In this study, embedded piezoelectric bender elements were used to generate and measure both P and shear (S) waves in fresh cement pastes. The shear waves were observed at very early age of the cement hydration. The velocities of P and S waves are obtained from B-scan images of a collection of recorded signals over time. Experimental results indicate that the shear wave velocity is closely related to the setting time of cement pastes and less affected by air contents than the P wave velocity. Shear modulus and Poisson's ratios of the cement pates are derived from the measured P and S wave velocities.

Vibration analysis of structures with uncertainty is challenging for a variety of reasons. In addition to the difficulty in quantifying uncertainties in the finite element model, analyzing a model with known uncertainties is generally computationally costly, especially for a system with large number of degrees of freedom. This paper explores incorporating uncertainty analysis into one typical order-reduction technique, the component mode synthesis (CMS) method. We first provide a derivation of the general approximation formula for the free interface CMS method, followed by a Monte Carlo sampling-based procedure directly utilizing the reduced-order model. Through numerical analysis, this paper demonstrates the feasibility and numerical accuracy of uncertainty analysis of periodic structures using CMS-based reduced order modeling.

The early detection of damage in structural or mechanical systems is of vital importance. With early detection, the damage may be repaired before the integrity of the system is jeopardized, resulting in monetary losses, loss of life or limb, and environmental impacts. Among the various types of structural health monitoring techniques, vibration-based methods are of significant interest since the damage location does not need to be known beforehand, making it a more versatile approach. The non-destructive damage detection method used for the experiments herein is a novel vibration-based method which uses an index called the EMD Energy Damage Index, developed with the aim of providing improved qualitative results compared to those methods currently available. As part of an effort to establish the integrity and limitation of this novel damage detection method, field testing was completed on a mechanical pipe joint on a condensation line, located in the physical plant of Dalhousie University. Piezoceramic sensors, placed at various locations around the joint were used to monitor the free vibration of the pipe imposed through the use of an impulse hammer. Multiple damage progression scenarios were completed, each having a healthy state and multiple damage cases. Subsequently, the recorded signals from the healthy and damaged joint were processed through the EMD Energy Damage Index developed in-house in an effort to detect the inflicted damage. The proposed methodology successfully detected the inflicted damages. In this paper, the effects of impact location, sensor location, frequency bandwidth, intrinsic mode functions, and boundary conditions are discussed.

Various nondestructive evaluation methods using the propagating velocity and attenuation of an ultrasonic wave have been studied. The ultrasonic wave attenuation is more sensitive on evaluating to damage assessment in the medium than the ultrasonic wave velocity method. In this paper, the nondestructive evaluation technique using self-compensating frequency response function is proposed to measure the quantitative ultrasonic wave attenuation on cement-based materials. The proposed technique is able to measure inherent attenuation of material, not its relative attenuation. In advance, the reproducibility and relevancy of proposed technique are validated by an experimental comparison of conventional measurement and proposed ultrasonic wave attenuation measurement on cement-based material. In addition, the ultrasonic attenuation measurements are able to characterize the size distribution and volume fraction of entrained air voids in cement-based materials.

Conventional ultrasonic NDT techniques are limited in their ability to detect small defects by the diffraction limit, that is there is much reduced sensitivity to defects smaller than the wavelength of the interrogating ultrasonic wave. While not a major issue for most inspection, this problem becomes particularly significant for the detection of fatigue damage prior to crack formation. In this regime conventional NDT has proven to be inadequate. For this reason significant effort has been expended on the development of non-linear techniques. These techniques rely on deviations of the material from linear stress strain behaviour which create harmonics in the resulting frequency response. Evidence suggests that changes to a materials condition, such as fatigue damage, change this non-linear response. This paper presents a non-linear inspection method using a non-collinear interaction. This technique has several advantages over other harmonic approaches in that there is spatial separation, modal separation and frequency separation of the non-linear signal. This allows the origin of the non-linear signal and underlying noise levels to be well defined. The capability of the technique is demonstrated using plastically strained material and samples subjected to low cycle fatigue.

With the large span, the high redundancy and three-dimensional overall stress in the space structure, there are further applications in the civil engineering programs. However, due to the more members, the scatter force path and the complex diversity force transmission modes, which may lead to the complex stress than the ordinary structures in the space ones. In this paper, firstly, the structural strain responses have been analyzed through the numerical simulation with snow loading in the national aquatics center (water cube). Then, according to the strains monitoring data and the relation feature between the temperature loading and structural temperature strains collected from the strain monitoring system on the effect of the snow loading in the national aquatics center, the temperature loading strains are to be separated from the snow loading strains with the neural network technique, from which the monitoring data are got in numerical statement and analyzed, meantime, with which the above numerical simulation results are to be checked and evaluated. The analysis results shown, in summer, owning to the high alteration amplitude of the temperature difference, the temperature loading is the control loading to the space structure; on the other hand, in winter, due to the temperature difference reducing during the process of snowfall, the control loading in the structure is to be transferred from the temperature loading to the snow loading, the effect of the snow loading to the space structure can not to be ignored.

An original method, measurement devices and software tool for examination of magneto-mechanical phenomena in wide range of SMART applications is proposed. In many Hi-End market constructions it is necessary to carry out examinations of mechanical and magnetic properties simultaneously. Technological processes of fabrication of modern materials (for example cutting, premagnetisation and prestress) and advanced concept of using SMART structures involves the design of next generation system for optimization of electric and magnetic field distribution. The original fast and higher than million point static resolution scanner with mulitsensor probes has been constructed to measure full components of the magnetic field intensity vector H, and to visualize them into end user acceptable variant. The scanner has also the capability to acquire electric potentials on surface to work with magneto-piezo devices. Advanced electronic subsystems have been applied for processing of results in the Magscaner Vison System and the corresponding software - Maglab has been also evaluated. The Dipole Contour Method (DCM) is provided for modeling different states between magnetic and electric coupled materials and to visually explain the information of the experimental data. Dedicated software collaborating with industrial parametric systems CAD. Measurement technique consists of acquiring a cloud of points similarly as in tomography, 3D visualisation. The actually carried verification of abilities of 3D digitizer will enable inspection of SMART actuators with the cylindrical form, pellets with miniature sizes designed for oscillations dampers in various construction, for example in vehicle industry.

Optical interferometry techniques was used for the first time to measure the surface resistivity/conductivity of anodized aluminium samples in aqueous solution without any physical contact. The anodization process (oxidation) of the aluminium samples was carried out in different sulphuric acid solutions (1.0-2.5 % H₂SO₄), by the technique of electrochemical impedance spectroscopy (EIS), at room temperature. In the mean time, the real-time holographic interferometric was carried out to measure the thickness of anodized (oxide) film of the aluminium samples during the anodization processes. Then, the alternating current (AC) impedance (resistance) of the anodized aluminium samples was determined by the technique of electrochemical impedance spectroscopy (EIS) in different sulphuric acid solutions (1.0-2.5 % H₂SO₄) at room temperature. In addition, a mathematical model was derived in order to correlate between the AC impedance (resistance) and to the surface (orthogonal) displacement of the samples in solutions. In other words, a proportionality constant (surface resistivity or conductivity=1/ surface resistivity) between the determined AC impedance (by EIS technique) and the orthogonal displacement (by the optical interferometry techniques) was obtained. Consequently the surface resistivity (ρ) and conductivity (σ) of the aluminum samples in solutions were obtained. Also, electrical resistivity values (ρ) from other source were used for comparison sake with the calculated values of this investigation. This study revealed that the measured value of the resistivity for the anodized aluminium samples were 2.8×10⁹, 7×10¹², 2.5×10¹³, and 1.4 ×10¹² Ohms-cm in 1.0%,1.5%, 2.0%, and 2.5 % H₂SO₄ solutions, respectively. In fact, the determined value range of the resistivity is in a good agreement with the one found in literature for the aluminium oxide ,85% Al₂O₃ (5×10¹⁰ Ohms-cm in air at temperature 30C°), 96% Al₂O₃ (1×10¹⁴ Ohms-cm in air at temperature 30C°), and 99.7% Al₂O₃ (>1×10¹⁴ Ohmscm in air at temperature 30C°).