This PDF file contains the front matter associated with SPIE Proceedings Volume 6934, including the Title Page, Copyright information, Table of Contents, and the Conference Committee listing.

In this study, a newly-developed technique, so-called "integrated wavelet transform (IWT)", is applied to damage detection of laminated composite beams. The novel IWT technique combines advantages of stationary wavelet transform (SWT) and continuous wavelet transform (CWT) to improve the robustness of wavelet-based modal analysis in damage detection. Two progressive wavelet analysis steps are considered, in which the SWT-based multi-resolution analysis (MRA) is first employed to refine the retrieved mode shapes, followed by the CWT-based multiscale analysis (MSA) to magnify the effect of slight abnormality. The SWT-MRA is utilized to eliminate random noise and regular interferences, separate multiple component signal, and thus extract purer damage information; while the CWT-MSA is employed to smoothen, differentiate or suppress polynomial of mode shapes to magnify the effect of abnormality. The effectiveness of IWT in damage detection is illustrated using the vibration mode shape data acquired from the experimental testing of a cantilever laminated composite beam with a through-width crack. As demonstrated in the successful detection of a crack in composite beams, the progressive wavelet transform analysis using IWT provides a robust and viable technique to identify minor damage in a relatively lower signal-to-noise ratio environment.

The implementation of structural health monitoring systems in modern aircraft structures requires a deeper understanding of impact and piezoelectric generated lamb wave propagation on carbon fibre reinforced plastics. In this paper a digital shearing interferometry method is presented that visualizes lamb waves excited by impact events or piezoelectric actuators. The contactless full field measurement of these waves is realized by a Mach-Zehnder interferometer which combines spatial phase shifting and Shearography. The latter is a laser based technique whereby the first order derivates of the displacement is indicated. Since a dynamical process is observed the spatial phase shifting technique is required. The optical implementation of both techniques within the interferometically setup and experimental results with the possibility to measure the out of plane displacement are presented. Therefore the underlying wavefield is reconstructed from the measured first order derivatives. Subsequently these results are compared with a one point measuring method and FEM simulation.

Since delamination is invisible or difficult to detect visually, the delamination causes low reliability of laminated composites for primary structures. To improve the low reliability, smart systems of delamination identifications in-service are desired. Recently, many researchers have employed an Electrical Resistance Change Method (ERCM) to detect the internal damages of Carbon Fiber Reinforced Plastics (CFRP) laminates. The ERCM does not require expensive instruments. Author's group has already experimentally investigated the applicability of the ERCM for monitoring delamination crack and matrix cracks. In the present paper, therefore, these results performed in the previous papers are briefly explained. These successful results enable us to monitor a lot of information of the CFRP laminates by means of the electrical resistance changes in many applications. In these previous papers, the plate type specimens are small. The effect of plate scale on ERCM is investigated in the present paper. 3-D FEM analyses are conducted to calculate the electrical potential changes caused by delamination for CFRP plates of different sizes and the applicability of ERCM to large CFRP structures is investigated.

Preliminary tests were conducted using frequency response (FR) characteristics to determine damage initiation and growth in a honeycomb sandwich graphite/epoxy curved panel. This investigation was part of a more general study investigating the damage tolerance characteristics of several such panels subjected to quasi-static internal pressurization combined with hoop and axial loading. The panels were tested at the Full-Scale Aircraft Structural Test Evaluation and Research (FASTER) facility located at the Federal Aviation Administration William J. Hughes Technical Center in Atlantic City, NJ. The overall program objective was to investigate the damage tolerance characteristics of full-scale composite curved aircraft fuselage panels and the evolution of damage under quasi-static loading up to failure. This paper focuses on one aspect of this comprehensive investigation: the effect of state-of-damage on the characteristics of the frequency response of the subject material. The results presented herein show that recording the frequency response could be used for real-time monitoring of damage growth and in determining damage severity in full-scale composites fuselage aircraft structures.

Fiber reinforced polymer (FRP) materials are currently used for strengthening civil engineering infrastructures. The strengthening system is dependant on the bond characteristics of the FRP to the external surface of the structure to be effective in resisting the applied loads. This paper presents an innovative self-monitoring FRP strengthening system. The system consists of two components which can be embedded in FRP materials to monitor the global and local behavior of the strengthened structure respectively. The first component of the system is designed to evaluate the applied load acting on a structure based on elongation of the FRP layer along the entire span of the structure. Success of the global system has been demonstrated using a full-scale prestressed concrete bridge girder which was loaded up to failure. The test results indicate that this type of sensor can be used to accurately determine the load prior to failure within 15 percent of the measured value. The second sensor component consists of fiber Bragg grating sensors. The sensors were used to monitor the behavior of steel double-lap shear splices tested under tensile loading up to failure. The measurements were used to identify abnormal structural behavior such as epoxy cracking and FRP debonding. Test results were also compared to numerical values obtained from a three dimensional shear-lag model which was developed to predict the sensor response.

Two types of ultrasonic sensors are presented for structural health monitoring (SHM) and non-destructive testing (NDT) of graphite/epoxy (Gr/Ep) composites of thickness ranging from 1mm to 27.9mm. These piezoelectric film based sensors are fabricated using a sol-gel spray technique. The center operation frequency of these sensors ranged from 1.3MHz to 10.5MHz. For the first sensor type, piezoelectric films of thickness greater than 60μm were deposited directly onto planar and curved Gr/Ep composites surfaces as integrated sensors. Ultrasonic signals propagating in a distance of more than 300mm have been obtained. Anisotropy of 0° and 90° cross ply Gr/Ep composite was measured. For the second sensor type, piezoelectric films were coated onto a 50µm thick polyimide membrane as flexible sensors that could be attached to a host composite structure with planar or curved surfaces. The flexibility of such FUTs is achieved due to the thin polymide, porous PZT/PZT ceramics and electrodes. An induction type non-contact method for the interrogation of the Gr/Ep composites using integrated sensors is also presented. Such non-contact technique may be desired for NDT of rotating composite components.

The residual stresses and mechanisms causing residual stresses in thermoset polymer composites were considered. The relative importance of the different mechanisms was analyzed. The residual stresses were determined analytically by viscoelastic model in addition to an experiment. The linear viscoelastic model was used to calculate of residual stresses in each layer of laminated composites. The fiber Bragg grating (FBG) strain sensor was used to measure the residual stresses throughout cure. The results are agreed well. The viscoelasticity of composites should be considered during calculating the residual stresses, and FBG strain sensor is shown to be a reliable for an accurate measurement of the residual stresses.

Fractal as a novel mathematical tool has a great potential to deal with transit events in a complex waveform. In this paper, fractal is introduced to detect irregularity of vibration mode shapes without using a baseline requirement. Different from the popular Katz's waveform fractal dimension (KWD), a novel approximate waveform capacity dimension (AWCD) specialized in irregularity detection in vibration mode shapes is introduced, from which an AWCD-based modal abnormality algorithm (AWCD-MAA) is established. The fundamental characteristics of AWCD-MAA, such as crack location identification and size quantification, are investigated using an analytical crack model of cantilever beams. An experimental modal shape evaluation of a cracked composite cantilever beam using smart piezoelectric sensors/actuators (i.e., Piezoelectric lead-zirconate-titanate (PZT) and polyvinylidene fluoride (PVDF)) is conducted to confirm the feasibility of the proposed algorithm. The proposed AWCD-MAA is capable of locating and quantifying the crack in a beam-type structure without prior requirement of baseline reference data.

Car manufactures are turning to high pressure hydrogen storage for on-broad power applications. Fiber-composite-wrapped high pressure hydrogen tanks are becoming widely used in onboard vehicle storage applications because of light weight and high strength. It is widely accepted that the worst case of the equipment at operating pressure should be only leakage without the risk of explosion. In order to ensure the safety during the operation course, the damage detection and leakage alert of fiber composite wrapped tank for high pressure hydrogen storage should be investigated. The aim of this paper is to find an effective nondestructive damage detection method for the identification of fatigue cracks on composite wrapped tank. First, a three-dimensional finite-element model is developed as the baseline model. Then fatigue crack in inner aluminum alloy, as the typical damage form, is simulated with the position, length, and direction of the crack as investigation parameters. Two nondestructive damage detection methods are applied to identify whether the damage has occurred based on the natural frequency and mode shapes of the fiber composite wrapped tank. The damage detection capability of each method is studied, and the influence of the vehicle vibration caused by road surface roughness and environment noise on damage detection are discussed. Finally, feasible strategy to alert the leakage of the hydrogen of fiber composite wrapped tanks is suggested.

Filament wound pressure vessels have been extensively used in industry and engineering. The existing damage detection and health monitoring methods for these vessels, such as X-ray and ultrasonic scan, can not meet the requirement of online damage detection; moreover optical grating fibre can only sense the local damage, but not the damage far away from the location of sensors. Vibration-based damage detection methods have the potential to meet such requirements. There methods are based on the fact that damages in a structure results in a change in structural dynamic characteristics. A damage detection method based on a residual associated with output-only subspace-based modal identification and global or focused chi^2-tests built on that residual has been proposed and successfully experimented on a variety of test cases. The purpose of this work is to describe the damage detection method and apply this method to assess the composite structure filled with fluid. The results of identification and damage detection will be presented.

Single crystal piezoelectric composite transducers including 75 MHz PC-MUT (piezoelectric composite micromachined ultrasound transducers), diced 10 MHz and 15 MHz 1-3 composite transducers were successfully demonstrated with broad bandwidth and high sensitivity. In this paper, the design, fabrication and characterization of composite transducers are reported. C-scan experiments for SiC ceramic samples were performed using these composite transducers as well as some commercial NDE transducers. The results suggest that significant improvements in resolution and penetration depth can be achieved in C-scan NDE imaging using single crystal composite broadband transducers.

Acoustic emission (AE) was monitored in notched full-scale honeycomb sandwich composite curved fuselage panels during loading. The purpose of the study was to evaluate the AE technique as a tool for detecting notch tip damage initiation and evaluating damage severity in such structures. This evaluation was a part of a more general study on the damage tolerance of six honeycomb sandwich composite curved panels, each containing a different damage scenario. The overall program objective was to investigate the effects of holes and notches on residual strength. The investigation was conducted using the Full-Scale Aircraft Structural Test Evaluation and Research (FASTER) facility located at the Federal Aviation Administration William J. Hughes Technical Center, Atlantic City International Airport, NJ. This paper reports on the AE results recorded during the loading to failure of two selected panels. The results show that damage initiation at the tips of the notches, and its progression along the panel, could be detected and located. These AE results were correlated with the deformation and strain fields measured through strain photogrammetry, throughout loading, at the vicinity of these notches. This correlation aided in interpreting the AE results. While the fretting among the newly created fracture surfaces generated a large number of low-intensity AE signals, the high-intensity signals generated at high load levels provided a good measure for anticipating incipient fracture. Further, the AE results located internal disbonding caused during panel fabrication. The large number of low-intensity AE signals generated from the disbonded regions was associated with the fretting among the disbonded surfaces.

The quantitative measurement of crystallographic texture through determination of the Orientation Distribution Coefficients (ODCs) can provide critical information on a sample's suitability for being utilised in a particular manufacturing process or can be used to measure changes in the microstructure of components in service. Ultrasonic techniques have been developed by previous workers that measure three of the ODCs that describe the orientation probability distribution function for an aggregate of cubic crystallites. Electron Backscatter Diffraction (EBSD), a microscopic technique that measures the crystallographic orientations of individual crystals, has been utilised to offer an alternative method to measuring the complete range of ODCs. As a technique, EBSD provides a much more detailed measurement of texture than ultrasonic measurements ever could. Ultrasonic methods are however non-destructive, can be used on components in service and are quicker in use and are less expensive to implement that EBSD measurements. EBSD is a valuable method in validating ultrasonic measurements, and can help to guide us in determining the limitations of the ultrasonic measurements. Ultrasonic measurement of texture is and will continue to be a useful approach to measuring texture but it does have its limitations for application to real samples. Equally, one has to use EBSD properly if one is to obtain accurate and representative data for the entire sample.

The structural health monitoring of structures during active use (in service) has long been of interest to the NDE community. One technique uses passive ultrasound or Acoustic Emission (AE). However, the interpretation of the AE signals is difficult especially when the operator tries to distinguish between the growth of harmless micro-cracks and the development of harmful delaminations. This paper focuses on two types of structures, i.e., aluminum plates such as used in wing structures in aircraft and graphite plates such as encountered in aircraft disc brakes where carbon-carbon composite is used. The objective in this work is to distinguish the acoustic emissions (AE) caused by delaminations from those associated with microcracking. The technical approach is to use finite element methods (FEM) to simulate AE from sources represented by piezoelectric wafers embedded in the composites. In flat panels of graphite and aluminum-alloy AE waveforms were modeled from transverse cracks and longitudinal delaminations. The results show distinct differences in the amplitudes, durations and frequency content creating a potential avenue for distinguishing between these two flaw types.

Acoustic Emissions (AE) has been successfully used with composite structures to both locate and give a measure of damage accumulation. The current experimental study uses AE to monitor large-scale composite modular bridge components. The components consist of a carbon/epoxy beam structure as well as a composite to metallic bonded/bolted joint. The bonded joints consist of double lap aluminum splice plates bonded and bolted to carbon/epoxy laminates representing the tension rail of a beam. The AE system is used to monitor the bridge component during failure loading to assess the failure progression and using time of arrival to give insight into the origins of the failures. Also, a feature in the AE data called Cumulative Acoustic Emission counts (CAE) is used to give an estimate of the severity and rate of damage accumulation. For the bolted/bonded joints, the AE data is used to interpret the source and location of damage that induced failure in the joint. These results are used to investigate the use of bolts in conjunction with the bonded joint. A description of each of the components (beam and joint) is given with AE results. A summary of lessons learned for AE testing of large composite structures as well as insight into failure progression and location is presented.

Due to the state of aging civil infrastructure systems structural health monitoring and nondestructive evaluation have received increased attention recently. Events related to bridge collapses in Pennsylvania (partial) and Minnesota (catastrophic) combined with the levee failures in Louisiana have justifiably drawn the attention of the policy makers and the public at large. Therefore it appears likely that both monitoring efforts of existing systems and the development of more resilient systems will be increased. In the case of civil structures (bridges, dams, levees, and buildings) the most common type of sensors used are strain gages and accelerometers. While these sensors can be useful if used correctly they are limited in the types of data that can be gathered and are not well-suited for many applications. In contrast acoustic emission sensors are very rarely used for civil applications but can in fact provide useful information either as a stand-alone data type or to supplement the data gathered from other sensors. This paper describes several case studies where acoustic emission has been successfully used in civil infrastructure applications and summarizes both the advantages and challenges that are inherent in the method for such applications.

Acoustic emission (AE) characteristic parameters of bridge cable damage were obtained on tensile test. The testing results show that the AE parameter analysis method based on correlation figure of count, energy, duration time, amplitude and time can express the whole damage course, and can correctly judge the signal difference of broken wire and unbroken wire. It found the bridge cable AE characteristics aren't apparent before yield deformation, however they are increasing after yield deformation, at the time of breaking, and they reach to maximum. At last, the bridge cable damage evolution law is studied applying the AE characteristic parameter time series fractal theory. In the initial and middle stage of loading, the AE fractal value of bridge cable is unsteady. The fractal value reaches to the minimum at the critical point of failure. According to this changing law, it is approached how to make dynamic assessment and estimation of damage degrees.

Fiber waviness in laminated composite material is introduced during manufacture because of uneven curing, resin shrinkage, or ply buckling caused by bending the composite lay-up into its final shape prior to curing. The resulting waviness has a detrimental effect on mechanical properties, therefore this condition is important to detect and characterize. Ultrasonic characterization methods are difficult to interpret because elastic wave propagation is highly dependent on ply orientation and material stresses. By comparison, the pulsed terahertz response of the composite is shown to provide clear indications of the fiber waviness. Pulsed Terahertz NDE is an electromagnetic inspection method that operates in the frequency range between 300 GHz and 3 THz. Its propagation is influenced by refractive index variations and interfaces. This work applies pulsed Terahertz NDE to the inspection of a thick composite beam with fiber waviness. The sample is a laminated glass composite material approximately 15mm thick with a 90-degree bend. Terahertz response from the planar section, away from the bend, is indicative of a homogeneous material with no major reflections from internal plies, while the multiple reflections at the bend area correspond to the fiber waviness. Results of these measurements are presented for the planar and bend areas.

This paper describes the utilization of induced radio frequency thermal excitation in conjunction with infrared (IR) imaging for the detection of discontinuities in embedded metal conductive mesh on composite structure. An electric current is inductively generated in the conductive media of the composite using a radio frequency coil held above the surface. As the generated current moves through the composite structure, any perturbation in the current flow caused by discontinuities in the grid or highly resistive areas becomes heated slightly above the surrounding. This small temperature variation is detected in real-time by means of an IR imaging system that includes an IR camera, a computer, and imaging software. The data is depicted as a thermogram on the computer monitor, and can be analyzed using specialized system software. From the detected thermal variations, one can determine electrical conductivity characteristics of the conductive composite layer.

In order to improve inspection result repetition and flaw ration veracity of manual ultrasonic inspection of offshore platform structure, an ultrasonic phased array inspection imaging technology for NDT of offshore platform structures is proposed in this paper. Aimed at the practical requirement of tubular joint welds inspection of offshore platform structures, the ultrasonic phased array inspection imaging system for offshore platform structures is developed, which is composed of computer, ultrasonic circuit system, scanning device, phased array transducer and inspection imaging software system. The experiment of Y shape tubular joint model of 60 degree is performed with the ultrasonic phased array inspection imaging system for offshore platform structures, the flaws characteristic could be exactly estimated and the flaws size could be measured through ultrasonic phased array inspection imaging software system for offshore platform structures. Experiment results show that the ultrasonic phased array inspection imaging technology for offshore platform structures is feasible, the ultrasonic phased array inspection imaging system could detect flaws in tubular joint model, the whole development trend of flaws is factually imaging by the ultrasonic phased array inspection technology of offshore platform structures.

Eddy Current Testing(ECT) has been used in wide field such as airline and power plants for maintenance, ironworks for production. However original flaw shape blur in image by signal of ECT. In our previous work an image reconstruction method from signal had been proposed. The method is based on that simple relationship between signal and source are described by a convolution of response function and flaw shape. The method was able to show more fine image of points flaw, short line flaw, long line flaw than images of those original signal. One difficulty in the method was to determine empirical parameter by trial and error. In this paper, we propose a concept of modified response function and signal that enable to make empirical parameter unnecessary. Those modification process is fully programmable and is carried out automatically. Validity of introducing those modification are considered from mathematical view point. Numerical results shows the method with this concept reconstructed image as same as empirical parameter method.

This paper is focus on the applications of EM sensor on cable force measurement for large bridges. The sensors are entirely suitable for sheathed cables and require no physical contact with the cable itself. In order to meet the requirement of observing structure behavior under extreme events, a high sampling rate of EM technology has been developed. The sampling rate of the EM sensor can be as high as 0.1 Hz which is faster than the current available technology for sensor size of up to 250mm. Both laboratory and field calibrations were conducted. The relationship between the relative incremental permeability and tensile stress is derived from these calibrations. Field measurements on tendons for Stonecutters Bridge in Hong Kong demonstrate the reliability and accuracy of the EM stress sensors using the updated technology.

The complex external environment for civil engineering structures results in the structural vibration properties varying with external conditions, such as humidity and temperature. For the vibration-based structural health monitoring techniques, for example damage identification, modal updating etc., above characteristics will result in the vibration-based techniques invalid. Other researchers have reported that modal frequencies varied significantly due to temperature change, but the humidity affect structural vibration properties in another manner. This paper discusses the variation of frequencies and mode shapes with respect to humidity and temperature changes for concrete structures, for which the changing of moisture will affect the density of materials, and the changing of temperature will affect the stiffness of structures. This paper models these two factors with finite element model approach based on the theoretical analysis, and numerical results obtained on the FE model of a concrete bridge deck are reported.

This paper describes preliminary results towards the development of an innovative NDE/SHM scheme for material characterization and defect detection based on the generation of highly nonlinear solitary waves (HNSWs). HNSWs are stress waves that can form and travel in highly nonlinear systems (i.e. granular, layered, fibrous or porous materials) with a finite spatial dimension independent on the wave amplitude. Compared to conventional linear waves, the generation of HNSWs does not rely on the use of electronic equipment (such as an arbitrary function generator) and on the response of piezoelectric crystals or other transduction mechanism. HNSWs possess unique tunable properties that provide a complete control over tailoring: 1) the choice of the wave's width (spatial size) for defects investigation, 2) the composition of the excited train of waves (i.e. number and separation of the waves used for testing), and 3) their amplitude and velocity. HNSWs are excited onto concrete samples and steel rebar. The first pilot study of this ongoing effort between Caltech and the University of Pittsburgh is presented.

As costs associated with wireless sensing technologies continue to decline, it has become feasible to deploy dense networks of tens, if not hundreds of wireless sensors within a single structural system. Additionally, many state-of-the-art wireless sensing platforms now integrate low-power microprocessors and high-precision analog-to-digital converters in their designs. As a result, data processing tasks can be efficiently distributed across large networks of wireless sensors. In this study, a parallelized model updating algorithm is designed for implementation within a network of wireless sensing prototypes. Using a novel parallel simulated annealing search method optimized for in-network execution, this algorithm efficiently assigns model parameters so as to minimize differences between an analytical model of the structure and wirelessly collected sensor data. Validation of this approach is provided by updating a lumped-mass shear structure model of a six-story steel building exposed to seismic base motion.

A novel real-time radar NDE technique for the in-depth inspection of glass fiber reinforced polymer (GFRP)-retrofitted concrete columns is proposed. In this technique, continuous wave radar signals are transmitted in the far-field region (distant inspection), and reflected signals are collected by the same signal transmitter. Collected radar signals are processed by tomographic reconstruction methods for real-time image reconstruction. In-depth condition in the near-surface region of GFRP-concrete systems is revealed and evaluated by reconstructed images.

A GIS-based data management system has been proposed for pavement management due to the spatial capability in organizing diverse geo-referenced information. The technology can be further enhanced by nondestructive distributed sensing. To target a wide study area, this research proposes a low-cost vibro-acousto passive sensing technique that embeds within roadways for long-term sensing. Using self-sustaining MEM sensors, the technology detects acoustic signals and use relative rating to assess pavement conditions. The detection technique echoes the traditional chain-drag technology in that the same sound detection is deployed. Coupling with previously established AMPIS pavement imaging and distress detection technique, the proposed system can evolve to be a more powerful new-generation GIS-PMS. This paper introduces the system concept and describes the philosophy behind the system and some of the challenges that we are currently attempting to solve.

In recent years, wireless sensors technologies are attracted many researchers in the field of structural health monitoring (SHM) of civil, mechanical and aerospace systems. Another potential application of wireless sensors is in the Vehicle-Infrastructure Integration (VII) which is an initiative by the U.S. Department of Transportation to improve road safety and reduce congestion, through as part of its Intelligent Transportation System program. However, fundamental issues remain unresolved before a broad application of the wireless SHM or VII sensor network concept is the question of sustainable power source for each independent sensor mounted on infrastructures. With a vast number of sensors nodes/networks in the infrastructure, connecting them to the grid power source is simply uneconomical in the era of wireless technology. The other option, which is providing power to each sensor from battery sources, has its own setbacks, as batteries can only provide power for a limited period, have to be replaced periodically (often difficult and costly), and their disposal creates environmental hazard. This study addresses the feasibility of energy harvesting from the ambient vibration of transportation infrastructures to power wireless sensors. Based on the vibration responses from simulation and field tests, vehicle induced vibrations on bridge and pavement were obtained and the theoretical power output from such vibration sources were computed. The expected results from this study will be demonstrated by avoiding complex wiring to the sensors by which the associated cost of wiring and batteries will be significantly reduced, and at the same time the technology can easily be deployed, meaning it is one step forward in improving the SHM and VII applications.

For sensor operation or remote interrogation of existing infrastructures, power is one of the key issues in wireless sensing technology. The novel energy harvesting technique and its integration with wireless sensing systems are vital to the next generation structural health monitoring systems. Energy harvesting devices convert the ambient energy surrounding the wireless sensors into electrical energy to extend the lifetime or reach unlimited lifespan of wireless sensors. Mechanical vibrations, existing almost everywhere, have been investigated as a promising energy source for wireless sensors in many applications. Piezoelectric generators are the primary method for converting the vibration energy into electrical energy. Most piezoelectric vibration energy harvesters studied so far are based on simple cantilever-based design with resonant frequency matching the environmental resonant frequency. However, the energy conversion efficiency of this type of vibration energy harvester drops dramatically if the environmental frequency and the frequency of the energy harvester are mismatched. This paper proposes a novel multi-mode piezoelectric vibration energy harvester that is suitable for structural health monitoring in an environment with multiple dominant vibration modes. The multi-mode piezoelectric vibration energy harvester has distributed stiffness and mass and has multiple resonant frequencies adapted to the environmental vibration modes. A multi-mode energy harvester with two interested resonant modes is used as an example to demonstrate this new concept. The multi-mode energy harvester is modeled using Finite Element Method. The efficiency of the multi-mode piezoelectric energy harvester is compared with that of existing cantilever-based piezoelectric energy harvester.

Lead Zirconate Titanate (PZT) transducers have been extensively used in the electromechanical impedance (EMI) based structural health monitoring (SHM). Many EMI models have been developed for damage assessment, mostly focusing on single damage identification. However, in real life, structures are frequently subjected to multiple or progressive damages. Specifically, structural components such as beams and columns are subjected to loading, vibration, wear and tear which could cause multiple damages. Once damages occur, they usually propagate along certain directions due to continuous usage or inadequate protection. Moreover the increase in severity of damages may lead to failure of the structural components or even the whole structure. The EMI technique which is based on the electromechanical interaction between the PZT transducer and its host structure has been found to be effective in damage detection. However, systematic study on monitoring the progressive of damage in multiple directions in the structures is still in need. In this paper, the EMI technique using surface bonded PZT transducers is employed to obtain the structural health signature. Experimental tests are carried out to study the damage propagation on aluminum plates, where damages are created along the length and width directions of the plates by drilling holes in sequence. Structural health signatures are obtained for each damage state and compared with the signature of non-damage state, followed by the discussion on the characteristics of damage propagation. In addition, for different damaged states, finite element modeling is carried out to verify the experimental signatures. The acquired numerical results are analyzed both qualitatively and quantitatively. Both experimental and numerical results demonstrate the capability of EMI technique for damage propagation monitoring.

Quadrangular grid method is presented for simulating the propagation of elastic stress waves in two dimensional orthotropic midia. The investigated lumps are constructed among the auxiliary quadrangular grids. The dynamic equations of the investigated lump are given by integreting along the boundary of the investigated lump. The algorithm is obtained by computing the nodal displacements and the central point stresses of the quadrangular grids alternately in time domain. The numerical results are compared with the solutions of the finite element method. The results demonstrate that the quadrangular grid method is of much higher calculational speed than the finite element method. The stress wave propagation is simulated numerically in an orthotropic plate with a hole. Finally, stress wave propagation in two layers of different media is studied and the example shows the features of the reflected and refracted wave propagations.

Work at the Pacific Northwest National Laboratory has demonstrated that ultrasonic property measurements can be effectively employed for the rapid and accurate classification/discrimination of liquids in small, carry-on, standard "stream-of-commerce" containers. This paper focuses on a set of laboratory measurements acquired with the PNNL prototype device as applied to several types of liquids (including threat liquids and precursor chemicals) to the manufacture of LEs in small commercially available plastic containers.

The increase of terrorism and its global impact has made the screening of the contents of liquid-filled containers a necessity. The ability to evaluate the contents of a container rapidly and accurately is a critical tool in maintaining global safety and security. Due to the immense quantities and large variety of containers shipped worldwide, there is a need for a technology that enables rapid and effective ways of conducting non-intrusive container inspections. Such inspections can be performed utilizing "through-transmission" or "pulse-echo" acoustic techniques, in combination with multiple frequency excitation pulses or waveforms. The challenge is combining and switching between the different acoustic techniques without distorting the excitation pulse or waveform, degrading or adding noise to the receive signal; while maintaining a portable, low-power, low-cost, and easy to use system. The Pacific Northwest National Laboratory (PNNL) has developed a methodology and prototype device focused on this challenge. The prototype relies on an advanced diplexer circuit capable of rapidly switching between both "through-transmission" and "pulse-echo" detection modes. This type of detection requires the prototype to isolate the pulsing circuitry from the receiving circuitry to prevent damage and reduce noise. The results of this work demonstrate that an advanced diplexer circuit can be effective; however, some bandwidth issues exist. This paper focuses on laboratory measurements and test results acquired with the PNNL prototype device as applied to several types of liquid-filled containers. Results of work conducted in the laboratory will be presented and future measurement platform enhancements will be discussed.

Maritime security personnel have a need for advanced technologies to address issues such as identification, confirmation or classification of substances and materials in sealed containers, both non-invasively and nondestructively in field and first response operations. Such substances include items such as hazardous/flammable liquids, drugs, contraband, and precursor chemicals used in the fabrication of illicit materials. Our initial efforts focused specifically on a commercial portable acoustic detector technology that was evaluated under operational conditions in a maritime environment. Technical/operational limitations were identified and enhancements were incorporated that would address these limitations. In this paper, application-specific improvements and performance testing/evaluation results will be described. Such enhancements will provide personnel/users of the detector a significantly more reliable method of screening materials for contraband items that might be hidden in cargo containers.

We are developing a Structure Health Assessment and Warning System (SHAWS) based on building displacement measurements and wireless communication. SHAWS will measure and predict the stability/instability of a building, determine whether it is safe for emergency responders to enter during an emergency, and provide individual warnings on the condition of the structure. SHAWS incorporates remote sensing nodes (RSNs) installed on the exterior frame of a building. Each RSN includes a temperature sensor, a three-axis accelerometer making static-acceleration measurements, and a ZigBee wireless system (IEEE 802.15.4). The RSNs will be deployed remotely using an air cannon delivery system, with each RSN having an innovative adhesive structure for fast (<10 min) and strong installation under emergency conditions. Once the building has moved past a threshold (~0.25 in./building story), a warning will be issued to emergency responders. In addition to the RSNs, SHAWS will include a base station located on an emergency responder's primary vehicle, a PDA for mobile data display to guide responders, and individual warning modules that can be worn by each responder. The individual warning modules will include visual and audio indicators with a ZigBee receiver to provide the proper degree of warning to each responder.

The Health Monitor System (HMS) is a low-cost, low-power, battery-powered device capable of measuring temperature, humidity, and shock. Many mission-critical items are susceptible to shock damage. To help prevent shock damage, assets often are placed in robust custom containers with shock damping and absorption devices. Assets are still at risk of damage while in their protective containers. Having a Health Monitor attached to an asset or container allows the status of the asset to be determined. The Health Monitor can measure, record, store, analyze, and display to the user if a shock event has occurred that puts the asset at risk of failure. Extensive shock testing and algorithm implementation were required to develop a Health Monitor that uses a single-point 3-axis accelerometer to determine the type, height, and severity of a shock event.

Dampers are the key devices for vibration control of structures. The mechanisms of current dampers are internal friction or viscous flow to dissipate external mechanical energies by heat. The high-heat generation potentially causes thermal problems to decrease the durability of dampers. Owing to the surface-tension dominated nanoflow on the porous particles, colloidal dampers have been recently developed with low-heat generation and high damping efficiency. In this paper, a new type of colloidal dampers are designed and fabricated. Its heat generation and hysteresis loops are tested. It is found that the heat generation of the colloidal dampers is below 4% of that of hydraulic dampers with the same energy dissipation capacity. Meanwhile, the hysteresis loops reveal that the colloidal dampers are highly nonlinear devices. We introduce an efficient algorithm to retrieve its instant stiffness and damping coefficients from measured hysteresis loops under cyclic excitations at different frequencies. The retrieved stiffness and damping coefficients are plotted against damping forces or inner pressures. We find that, at low frequencies, the colloidal dampers exhibit the states with negative stiffness and negative damping coefficients; nevertheless, at the frequencies above 6Hz, both the stiffness and the damping coefficients are positive. Frequency is one of the key parameters dominating the damping mechanism of the colloidal dampers.

Structural Health Monitoring (SHM) that uses integrated sensor network to provide real-time monitoring of in-service structures can improve the safety and reliability of the structures significantly. Acellent Technologies' SHM systems based on SMART technology consists of the integrated sensor network, diagnosis hardware platform and the diagnosis software. This paper introduces the latest SMART damage detection hardware platform - ScanGenie and the new analysis software for damage detection in composite and metal structures. The ScanGenie is a portable high-performance hardware that provides many features such as through-transmission, pulse-echo, temperature measurement, self-diagnosis, sensor diagnosis, etc. The new analysis software is based on the ScanGenie hardware to provide functions such as temperature compensation, auto-gain adjustment, impedance-based diagnosis and probability of detection. The system can be used for damage detection in most composite and metal structures such as aircraft, spacecraft and civil infrastructures.

This paper describes the use of decision fusion strategy in damage detection. These techniques fuse multiple individual damage detection measures to form a detector with higher probabilities of correct detection than that attainable with any of the individual measures. In this paper, these technique is applied to vibration-based damage detection methods. As a demonstration of the methodology, the first step was to fabricate an experimental fixture which the vibration properties of damaged and undamaged structures can be measured. The experimental results with the undamaged structural model provided information for producing an improved theoretical and numerical model of the mechanics via model updating techniques. Three common vibration-based damage detection methods using a varied multi-resolution on the experimental results were implemented to identify the damage that occurred in the structure. Finally, the strategy to join the information from the three methods with multi-resolution decision fusion rules is introduced. The fused results are shown to be superior to that from only one method.