Proceedings Volume 6531

Nondestructive Characterization for Composite Materials, Aerospace Engineering, Civil Infrastructure, and Homeland Security 2007

cover
Proceedings Volume 6531

Nondestructive Characterization for Composite Materials, Aerospace Engineering, Civil Infrastructure, and Homeland Security 2007

View the digital version of this volume at SPIE Digital Libarary.

Volume Details

Date Published: 5 April 2007
Contents: 7 Sessions, 34 Papers, 0 Presentations
Conference: SPIE Smart Structures and Materials + Nondestructive Evaluation and Health Monitoring 2007
Volume Number: 6531

Table of Contents

icon_mobile_dropdown

Table of Contents

All links to SPIE Proceedings will open in the SPIE Digital Library. external link icon
View Session icon_mobile_dropdown
  • Front Matter: Volume 6531
  • Nondestructive Detection in Structural and Mechanical Systems
  • Nondestructive Evaluation in Composite Materials and Aerospace Engineering
  • Civil Infrastructure Health Monitoring
  • Progress in Nondestructure Evaluation
  • Remote Sensing and Homeland Security Applications
  • Applied Imaging
Front Matter: Volume 6531
icon_mobile_dropdown
Front Matter: Volume 6531
This PDF file contains the front matter associated with SPIE Proceedings Volume 6531, including the Title Page, Copyright information, Table of Contents, Introduction, and the Conference Committee listing.
Nondestructive Detection in Structural and Mechanical Systems
icon_mobile_dropdown
Damage assessment of composite laminate by using fiber optic AE sensor based on fused-tapered coupler
Damage inspection is very important for safe and reliable use of composite materials. Some non-destructive evaluation methods have been used to monitor the damage of composite. It is necessary to develop a novel fiber optic sensor and use it to monitor the damage of composite materials. This paper proposes to make an optic fiber acoustic emission (AE) sensor base on fused-taper fiber optic coupler with low price and high sensitivity, and to monitor the damage of composite materials. To prove the sensitivity of this sensor, Pencil-break test was done. To investigate the failure mode of composite materials, tensile experiment of composite laminate was also carried out. Experiment got lots of acoustic emission data under different tensile stage, Relationship of AE waveform and failure mode was established. It was found that fiber optic AE sensor with high sensitivity was successfully developed, and failure mode of composite materials was identified. This kind of research encourages the belief that the sensor will be used to structural health monitoring of larger composite structures.
Sensing inaccessible damage in a structure using frequency response functions
The use of Frequency Response Functions (FRFs) measured at some points in the accessible area of a structure to detect damage in the inaccessible area is studied, based on the difference in the normalized FRFs from a previous observed state. Numerical simulations and experiments were carried out to investigate the effectiveness of the proposed damage index. Results showed that from the indices at the first flexural resonance mode and in the vicinity of the first resonant frequency, the damage can be accurately detected and located if there is damage in the accessible area. If the damage is in the inaccessible area, the existence of the damage can be successfully ascertained although its location may not be identified accurately. For multi-damage conditions, with damage in both the accessible and inaccessible areas, the proposed method can accurately detect and locate the damage in the measurable area and detect the damage in the inaccessible area. The magnitude of the indices provides useful information with regards to the damage severity.
Soft matter acoustics: non-destructive health monitoring of polymer blend films
Soft matter acoustics is concerned with the application of acoustical techniques in the study of soft matter. In this paper, we demonstrate the use of phase sensitive acoustic microscopy (PSAM) in synchronous mapping of threedimensional heterogeneity of sample soft matter systems: thin film blends of polystyrene (PS) and poly (methylmethacrylate) (PMMA). The use of acoustic phase contrast imaging for cure or health monitoring of polymer systems is discussed.
Quantification of damage detection schemes using receiver operating characteristic (ROC) curves
In this work we detect damage in a composite to metal bolted joint subject to ambient vibrations and strong temperature fluctuations. Damage to the joint is considered to be a degradation of the connection strength implemented by loosening the bolts. The system is excited with a signal that conforms to the Pierson-Moskowitz distribution for wave height and represents a possible loading this component would be subject to in situ. We show that as the bolts are loosened, increasing amounts of nonlinearity are introduced in the form of impact discontinuities and stick-slip behavior. The presence of the nonlinearity, hence the damage, is detected by drawing comparisons between the response data and surrogate data conforming to the null hypothesis of an undamaged, linear system. Two metrics are used for comparison purposes: nonlinear prediction error and the bicoherence. Results are displayed using Receiver Operating Characteristic (ROC) curves. The ROC curve quantifies the trade-off between false positives (type I errors) and false negatives (type II errors). Type I errors can be expressed as the probability of false alarm and 1 - type II error is the probability of detection. We demonstrate that ROC curves provide a unified quantifiable approach for directly comparing the merits of different detection schemes.
Nondestructive detection of delamination and debonding of CFRP by a laser-based ultrasonic visualization method
J. Takatsubo, S. Yashiro, H. Tsuda, et al.
We have developed a generation pulsed-laser scanning method for visualizing the propagation of ultrasonic waves. While scanning a target object with a pulsed-laser beam to generate thermal-exited ultrasonic waves, we detected the propagated waves with a fixed PZT transducer. Although the detected waves were generated from different irradiation points, we were able to produce moving images of the ultrasound generated at the reception-transducer position by reconstructing the measured waveform data. This method has the following features that make it superior to the conventional visualization methods such as photo-elasticity method, reception probe scanning method and computer simulation. (1) it enables us to visualize ultrasonic waves propagating on a complex-shaped object with curved surfaces, steps, and dents. (2) it provides excellent working efficiency by eliminating the need for adjustments to the laser incidence angle and the focal distance. For these reasons, we believe that this new method can be effectively applied to the inspection of defects in the field. In this study, we examined the applicability of this method to CFRP materials, and the results demonstrate the validity of this method for nondestructive flaw inspection in CFRP-structures.
Responsive satellites and the need for structural health monitoring
Brandon J. Arritt, Amrita Kumar, Steven Buckley, et al.
The United States is striving to develop an Operationally Responsive Space capability. The goal is to be able to deliver tailored spacecraft capabilities to the warfighter as needs arise. This places a premium on the timespan between generating that requirement and having a functioning satellite performing its mission on orbit. Although there is lively debate regarding how to achieve this responsive space capability, one thing remains undeniable; the satellite flight qualification and launch vehicle integration process needs to be dramatically truncated. This paper describes the Air Force Research Laboratory's attempts to validate the use of Structural Health Monitoring (SHM) in lieu of traditional structural flight qualification testing schemes (static and shock loads, random vibration, coupled loads analysis, thermal vacuum testing, etc.) for potential Responsive Space (RS) satellites.
Possibility of electrical discharge pulse sound for hammering test
Yoshiaki Akematsu, Kazuro Kageyama, Naotake Mohri, et al.
In this study, it was investigated that the possibility of electrical discharge pulse sound for new inspection technologies instead of hammering test. Electrical discharge pulse sound was applied for hammering sound and sensor by using sound detection was applied for optical fiber vibration sensor. The numerical analysis result using the FEM and the experiment result along with the single pulse discharge was compared. As the result, it was estimated that the generation factor of the elastic wave was same as the current duration. These results become possible to estimate the propagation characteristic of elastic wave. Evaluation of electrical discharge sound for hammering test by using optical fiber sensor was investigated. Defect shape and scale was estimated from comparison with detected waveform by using optical fiber vibration sensor and simulated waveform. As the results, it was considered that electrical discharge sound was available for hammering test.
A wavelength multiplexed interferometric inertial sensor network for nondestructive evaluation and distributed monitoring
The Fabry-Perot Interferometer based accelerometer is proposed for use in fiber optic sensor networks. Despite the potential for high performance in the detection of vibrations, previously such sensors had limited use in these networks. Since the sensor operates as an optical transmission loss filter, simple serial network implementations are difficult. However, by forming the optical resonance cavity of the sensor with wavelength dependent reflective surfaces, a simply serialized network of sensor can be demonstrated through the wavelength division multiplexing of the interferometric signal fringes. This paper summarizes the concept and experimentally demonstrates and evaluated the serialization of two acceleration sensors.
Integrated acoustic emission/vibration sensor for detecting damage in aircraft drive train components
Diaphragm-type couplings are high misalignment torque and speed transfer components used in aircrafts. Crack development in such couplings, or in the drive train in general, can lead to component failure that can bring down an aircraft. Real time detection of crack formation and growth is important to prevent such catastrophic failures. However, there is no single Nondestructive Monitoring method available that is capable of assessing the early stages of crack growth in such components. While vibration based damage identification techniques are used, they cannot detect cracks until they reach a considerable size, which makes detection of the onset of cracking extremely difficult. Acoustic Emission (AE) can detect and monitor early stage crack growth, however excessive background noise can mask acoustic emissions produced by crack initiation. Fusion of the two mentioned techniques can increase the accuracy of measurement and minimize false alarms. However, a monitoring system combining both techniques could prove too large and heavy for the already restricted space available in aircrafts. In the present work, we will present a newly developed integrated Acoustic Emission/Vibration (AE/VIB) combined sensor which can operate in the temperature range of -55°F to 257°F and in high EMI environment. This robust AE/VIB sensor has a frequency range of 5 Hz-2 kHz for the vibration component and a range of 200-400 kHz for the acoustic emission component. The sensor weight is comparable to accelerometers currently used in flying aircraft. Traditional signal processing approaches are not effective due to high signal attenuation and strong background noise conditions, commonly found in aircraft drive train systems. As an alternative, we will introduce a new Supervised Pattern Recognition (SPR) methodology that allows for simultaneous processing of the signals detected by the AE/VIB sensor and their classification in near-real time, even in these adverse conditions. Finally, we will discuss the architecture developed to produce a fully autonomous monitoring tool based on the fusion of the AE and Vibration techniques.
Nondestructive Evaluation in Composite Materials and Aerospace Engineering
icon_mobile_dropdown
The use of composite materials increase the availability of oil and gas and reduce the cost of drilling and production operations
Recognizing the potential benefits, the oil exploration and production industry began to experiment with the field use of composite materials in the last half of the 1900's. Gradually, the inherent reluctance to move "unproven materials" into full operational applications is being overcome. Now, the increased price of crude and the need to locate and produce more oil and gas and to reduce associated costs are forcing an accelerated acceptance and use of composite materials in these operations. As a result, the cost of building, servicing, and maintaining drilling rigs and pipe lines is being reduced. "Thought to be depleted" oil and gas deposits are being revitalized. Technology currently in development and/or in the process of field trial demonstration are showing promise to provide enabling capability for obtaining greater reach in both extended reach and deep water drilling. Smart drill pipes and coiled tubing, able to provide both real-time communication from well head to drill bit and to similarly provide down hole power, have been demonstrated. This paper presents a summary of the current state of the use of composites in the Oil Patch and discusses areas of technology development which must be brought to fruition in order for the oil industry the reap full benefit, such as has been accomplished by the aerospace industry.
Single crystal piezoelectric composites for advanced NDT ultrasound
Xiaoning Jiang, Kevin Snook, Wesley S. Hackenberger, et al.
In this paper, the design, fabrication and characterization of PMN-PT single crystal/epoxy composites are reported for NDT ultrasound transducers. Specifically, 1-3 PMN-PT/epoxy composites with center frequencies of 5 MHz - 40 MHz were designed and fabricated using either the dice-and-fill method or a photolithography based micromachining process. The measured electromechanical coefficients for composites with frequency of 5 MHz - 15 MHz were about 0.78-0.83, and the coupling coefficients for composites with frequencies of 25 MHz- 40 MHz were about 0.71-0.72. The dielectric loss remains low (< 0.05). These properties hold promise for advanced NDT ultrasound applications.
Design of piezoelectric transducers for health monitoring of composite aircraft structures
Tadeusz Stepinski, Marcus Engholm
Composite structures have become a significant part of modern lightweight aircrafts. Contrary to the aluminum panels such structures are susceptible to catastrophic failure without noticeable forewarnings. One possible way of preventing catastrophic failures is integrating health monitoring systems in the critical composite structures of the aircraft. Ultrasonic resonance inspection is especially suitable for the inspection of multilayered composite structures. In our previous works we have described the principle of narrow-band ultrasonic spectroscopy (NBUS), where the surface of an inspected structure is scanned with a resonant transducer whose frequency response is monitored in a narrow frequency band. It has been proven that the NBUS method is capable of detecting both artificial disbonds and real impact defects in carbon fiber composites. In this paper we present design guidelines for optimizing narrow-band electromechanical impedance (NBE/MI) sensors that are to be integrated with a monitored composite structure. The NBE/MI sensor takes the form of a piezoelectric element bonded to the monitored structure. Parameter variations in the inspected structure result in the respective variations of the electrical impedance (admittance) of the piezoelectric sensor. Relation between the state of the inspected structure and the sensor's admittance is estimated using the network representation. Conclusions concerning the proper choice of the operating frequencies suitable for various structures are presented.
NDI technique development for new technologies
In the aerospace industry, the space industry in particular, there is a persistent emphasis on knowing the quality of the components, assemblies, and systems. The demand for quality in the space industry is driven by the high cost of finding problems late in assembly and the impediments to repairing hardware on orbit. One source of late problems is commonly attributed to the incorporation of new technologies. In this work as part of an effort to identify gaps in a suite of funded technology development efforts, we used the Risk Roadmap amplified from a systems point of view. This methodology resulted in insights into the origins of some of the problems associated with incorporating new technology, and the need for planning for system accommodation. One of the system accommodation efforts identified by this effort was the need for the development of nondestructive evaluation and inspection (NDE/NDI) techniques to begin sooner, at approximately TRL 3, with respect to the technology, in order to avoid causing a program delay. This paper describes the Risk Roadmap and the other views of the data in the development of the associated systems view that led to this insight.
Lamb wave propagation in composite laminates using a higher-order plate theory
A new consistent higher-order plate theory is developed for composites with the aim of accurately and efficiently modeling multiple higher-order Lamb waves over a higher frequency range. The dispersion relations based on this theory that can be analytically determined comprise five symmetric and six anti-symmetric wave modes. Computational procedures for phase and group velocities are discussed. Meanwhile, characteristic wave curves including velocity, slowness, and wave curves are introduced to investigate the dispersive and anisotropic behavior of Lamb wave propagation in composites. From numerical results of Lamb waves in both lamina and symmetric laminate, it shows that the higher-order plate theory not only gives good agreement with three-dimensional (3-D) elasticity theory over a wide high frequency range, but also provides a more robust method than 3-D elasticity theory. This study demonstrates a feasibility of using the proposed theory for realizing near real-time Structural Health Monitoring for composites at a higher frequency range.
A scaleable integrated sensing and control system for NDE, monitoring, and control of medium to very large composite smart structures
Jerry Jones, Valerie Rhoades, Radford Arner, et al.
NDE measurements, monitoring, and control of smart and adaptive composite structures requires that the central knowledge system have an awareness of the entire structure. Achieving this goal necessitates the implementation of an integrated network of significant numbers of sensors. Additionally, in order to temporally coordinate the data from specially distributed sensors, the data must be time relevant. Early adoption precludes development of sensor technology specifically for this application, instead it will depend on the ability to utilize legacy systems. Partially supported by the U.S. Department of Commerce, National Institute of Standards and Technology, Advanced Technology Development Program (NIST-ATP), a scalable integrated system has been developed to implement monitoring of structural integrity and the control of adaptive/intelligent structures. The project, called SHIELD (Structural Health Identification and Electronic Life Determination), was jointly undertaken by: Caterpillar, N.A. Tech., Motorola, and Microstrain. SHIELD is capable of operation with composite structures, metallic structures, or hybrid structures. SHIELD consists of a real-time processing core on a Motorola MPC5200 using a C language based real-time operating system (RTOS). The RTOS kernel was customized to include a virtual backplane which makes the system completely scalable. This architecture provides for multiple processes to be operating simultaneously. They may be embedded as multiple threads on the core hardware or as separate independent processors connected to the core using a software driver called a NAT-Network Integrator (NATNI). NATNI's can be created for any communications application. In it's current embodiment, NATNI's have been created for CAN bus, TCP/IP (Ethernet) - both wired and 802.11 b and g, and serial communications using RS485 and RS232. Since SHIELD uses standard C language, it is easy to port any monitoring or control algorithm, thus providing for legacy technology which may use other hardware processors and various communications means. For example, two demonstrations of SHIELD have been completed, in January and May 2005 respectively. One demonstration used algorithms in C running in multiple threads in the SHIELD core and utilizing two different sensor networks, one CAN bus and one wireless. The second had algorithms operating in C on the SHIELD core and other algorithms running on multiple Texas Instruments DSP processors using a NATNI that communicated via wired TCP/IP. A key feature of SHIELD is the implementation of a wireless ZIGBEE (802.15.4) network for implementing large numbers of small, low cost, low power sensors communication via a meshstar wireless network. While SHIELD was designed to integrate with a wide variety of existing communications protocols, a ZIGBEE network capability was implemented specifically for SHIELD. This will facilitate the monitoring of medium to very large structures including marine applications, utility scale multi-megawatt wind energy systems, and aircraft/spacecraft. The SHIELD wireless network will facilitate large numbers of sensors (up to 32000), accommodate sensors embedded into the composite material, can communicate to both sensors and actuators, and prevents obsolescence by providing for re-programming of the nodes via remote RF communications. The wireless network provides for ultra-low energy use, spatial location, and accurate timestamping, utilizing the beaconing feature of ZIGBEE.
Civil Infrastructure Health Monitoring
icon_mobile_dropdown
Structural identification, damage identification and structural health monitoring
There are numerous Structural identification (StrId) methods and techniques. The purpose of StrId in the civil infrastructure arena include: a) design validation of new structures, b) condition assessment of existing structures, c) analytical model updating of existing and new structures, and d) damage identification (DmId) of existing structures. Many StrId researchers utilized StrId methods for DmId. However, not all StrId methods are suited for DmId and not all damages are possible to be identified by popular StrId methods. This paper investigates the relationship between StrId methods and DmId. We investigate which StrId method is suited for DmId for the type of damages that may affect civil infrastructure. It will be shown that some damages can be identified by StrId methods, while some other damages need specific methods that are not within the conventional realm of StrId methods. Some guidelines for choosing StrId methods that are appropriate for DmId are given.
Application of statistical pattern classification methods for damage detection to field data
Carlos Cabrera, Allen Cheung, Pooya Sarabandi, et al.
The field of Structural Health Monitoring (SHM) has received considerable attention for its potential applications to monitoring civil infrastructure. However, the damage detection algorithms that form the backbone of these systems have primarily been tested on simulated data instead of full-scale structures because of the scarcity of real structural acceleration data. In response to this deficiency in testing, we present the performance of two damage detection algorithms used with ambient acceleration data collected during the staged demolition of the fullscale Z24 Bridge in Switzerland. The algorithms use autoregressive coefficients as features of the acceleration data and hypothesis testing and Gaussian Mixture Modeling to detect and quantify damage. While experimental or numerically simulated data have provided consistently positive results, field data from real structures, the Z24 Bridge, show that there can be significant false positives in the predictions. Difficulties with data collection in the field are also revealed pointing to the need for careful signal conditioning prior to algorithm application.
Application of PDE methods for image-based concrete surface damage detection
Tremendous progress has been achieved in image analysis and processing, and in particular, the use of partial differential equation (PDE) methods in image analysis has proliferated in recent years. However, PDE methods have seen little application to optical image-based structural damage detection for civil systems. This paper applies the Chan-Vese active contour model and its level set representation to detect concrete surface damage, in this case concrete cracks, in optical images. The detected cracks can be further characterized by extracted geometric quantities including their width, length and area of coverage, and associated with engineering design. With regard to crack width extraction, an approximate method is proposed, which relies on solving for a signed distance function. We test these methods by using synthetic images as well as real multi-temporal images from a laboratory experiment. This paper illustrates that using the proposed methods, cracks with complex topographical patterns can be successfully detected with sufficient accuracy.
Long term health monitoring systems for bridges
A number of efforts had been sought to instrument bridges for the purpose of structural monitoring and assessment. The outcome of these efforts, as gauged by advances in the understanding of the definition of structural damage and their role in sensor selection as well as in the design of cost and data-effective monitoring systems, has itself been difficult to assess. The authors' experience with the design, calibration, and operation of a monitoring system for the Kishwaukee Bridge in Illinois has provided several lessons that bear upon these concerns. The systems have performed well in providing a continuous, low-cost monitoring platform for bridge engineers with immediate relevant information. Experiences learned from the design and installation of health monitoring systems for several major long span bridges in Japan and China will be addressed.
Integrity monitoring of an old steel bridge using fiber optic distributed sensors based on Brillouin scattering
Branko Glišić, Daniele Posenato, Daniele Inaudi
Götaälvbron, the bridge over Göta river, was built in thirties and is now more than seventy years old. The steel girders were cracked and two issues are in cause of steel cracking: fatigue and mediocre quality of the steel. The bridge authorities repaired the bridge and decided to keep it in service for the next fifteen years, but in order to increase the safety and reduce uncertainties related to the bridge performance an integrity monitoring system has been mandatory. The main issue related to selection of the monitoring system has been the total length of the girders which is for all the nine girders more than 9 km. It was therefore decided to monitor the most loaded five girders (total length of 5 km approximately) and logically a fiber optic distributed sensing system have been selected. For the first time a truly distributed fiber optic sensing system, based on Brillouin scattering effect, is employed on such large scale to monitor new crack occurrence and unusual strain development. The monitoring system itself, the monitoring strategy, challenges related to installation and the data management are presented in this paper.
Structural health monitoring of Lindquist bridge
D. D. Sargent, E. R. Murison, B. Bakht, et al.
Many forestry bridges in Canada are typically single-lane, single span structures with two steel plate girders and a deck comprising of precast reinforced concrete panels. The concept of arching in deck slabs was utilized in the steel-free precast panels used in the Lindquist Bridge in British Columbia, Canada. The panels were completely devoid of tensile reinforcement and transverse confinement to the panels was provided by external steel straps. After the bridge was constructed in 1998, electrical strain gauges were installed on the girders and straps. Static and dynamic load tests were performed. The cracks on the top and bottom of the deck were mapped in 1999 and 2003. In 2006, a load test and crack mapping were performed on the bridge. The strain readings in the straps were compared with the data obtained 8 years prior. After analysis of the strain gauge readings, conclusions were drawn on the performance of the bridge. The cracks were formed to accommodate arching action and it was concluded that the bridge is still performing as it was designed.
Monitoring fatigue life in concrete bridge deck slabs
J. Newhook, V. Limaye
Concrete bridge deck slabs are the most common form of bridge deck construction in short and medium span bridge structures in North America. Understanding and monitoring the condition of these bridge decks is an important component of a bridge management strategy. Progressive deterioration due to fatigue occurs in concrete decks due to the large number of cycles of heavy wheels loads and normally manifests itself as the progressive growth of cracks in the top and underside of the deck slab. While some laboratory fatigue testing programs have been reported in the literature, there is very little information on proposed techniques to monitor this phenomenon. This paper discusses the issue of how fatigue monitoring may be included as part of a structural health monitoring system for bridges. The paper draws upon previously published experimental results to identify the main characteristics of fatigue damage and structural response for concrete bridge deck slabs. Several means of monitoring this response are then evaluated and monitoring methods are proposed. A specific field structure monitoring program is used to illustrate the application of the concept. The cases study examines several sensor systems and discusses the various limitations and needs in this area. The results are of interest to both the general area of structural health monitoring as well as fatigue monitoring specifically.
Self repair of impact, higher energy impact, and earthquake damage in infrastructure systems made of polymers and concrete
Self repair for structures, which I invented in 1989, is designed to incorporate hollow vessels, usually fibers, which will release a repairing agent when the structure is damaged, so that the repairing agent will fill delaminations, voids and cracks, thus healing both matrix voids and rebonding fibers. The repaired damage will enable continued function and prevent further degradation to catastrophic failure. Repaired damage will enable applications to be utilized under current standard operating procedure without reduction in performance due to impacts The benefits are: 1) safety of bridges and highways, lives saved, money saved 2) reduced maintenance expenditure, 3) extended life cycle and reduced maintenance costs 4) lighter weight infrastructure components such as bridges due to a reduction in overdesign safety measures. The benefit is truly in the economy, readiness, and effectiveness of all infrastructure applications Two materials are important in infrastructure as the matrix material, polymers and concrete. Natural Process Design, Inc. works in both areas to develop self repair.. A small part of that research is presented here.
Predicting deflections of a simply supported pre-stressed concrete girder subjected to static loads from observed strains
Aftab Mufti, Leslie Jaeger, Chad Klowak, et al.
Deflections of structures, such as bridge girders, are often the most difficult to monitor. Strain measurement is relatively simple with the use of electronic strain gauges, fiber optic sensors, or other strain measuring devices. This paper investigates two different methods for predicting or monitoring the deflection of a simply-supported full-scale bridge girder subjected to a partially distributed uniform load using strain measurements. A full-scale pre-stressed concrete bridge girder was instrumented and tested under a static monotonic load in the linear elastic range. This paper highlights the experimentally measured deflections along the length of one half of the girder and compares them to theoretically predicted deflections and deflections predicted using numerical integration along with harmonic analysis of curvatures determined from theoretical and observed experimental strains. Experimental test results indicate that estimating deflections from observed strains is feasible within the linear-elastic range of such girders. The methods outlined for predicting deflections of full-scale pre-stressed concrete bridge girders from observed strains are a valuable tool for structural engineers and for the periodic and continuous monitoring of civil structures such as bridges.
Progress in Nondestructure Evaluation
icon_mobile_dropdown
Progress in air-coupled ultrasound
Subash Jayaraman, Dominik Pellkofer, Ian Lucas, et al.
A variety of industrial and everyday non-destructive inspection applications exist where the target material/product is inaccessible or, contact with the material is prohibited. In such cases, air-coupled ultrasonic techniques play a major role but commonly significant transmission loss is known to occur. Therefore, it becomes imperative to know the amount of absolute wave mechanical strain achieved in materials embedded in gaseous medium, for certain applications. Thus, the overall objective of this work was to establish simulated results and specific experimental verifications of the numerical modeling, and develop guidelines in the use of matching layers to maximize the wave mechanical strain imparted to materials. A Laser Doppler Vibrometer was used to obtain the displacements/strains induced in the materials. Coupled Acoustic Piezoelectric Analysis (CAPA), coupled field finite element method software was used to perform the simulations. The applications considered in this work include metallic targets inside an enclosed container, food products and also elastomeric composites such as automotive tires.
Terahertz NDE application for corrosion detection and evaluation under shuttle tiles
Robert F. Anastasi, Eric I. Madaras, Jeffrey P. Seebo, et al.
Pulsed Terahertz NDE is being examined as a method to inspect for possible corrosion under Space Shuttle Tiles. Other methods such as ultrasonics, infrared, eddy current and microwave technologies have demonstrable shortcomings for tile NDE. This work applies Terahertz NDE, in the frequency range between 50 GHz and 1 THz, for the inspection of manufactured corrosion samples. The samples consist of induced corrosion spots that range in diameter (2.54 to 15.2 mm) and depth (0.036 to 0.787 mm) in an aluminum substrate material covered with tiles. Results of these measurements are presented for known corrosion flaws both covered and uncovered and for blind tests with unknown corrosion flaws covered with attached tiles. The Terahertz NDE system is shown to detect all artificially manufactured corrosion regions under a Shuttle tile with a depth greater than 0.13 mm.
Capacitance sensors for the nondestructive measurement of moisture content in in-shell peanuts
Chari V. Kandala, Chris L. Butts
Moisture content (MC) in peanuts is measured at various stages of their processing and storage in the peanut industry. A method was developed earlier that would estimate the MC of a small sample of in-shell peanuts (peanut pods) held between two circular parallel-plates, from the measured values of capacitance and phase angle at two frequencies 1 and 5 MHz. These values were used in an empirical equation, developed using the capacitance and phase angle values of samples of known MC levels, to obtain the average MC values of peanut samples with moisture contents in the range of 7 to 18%. In the present work, two rectangular parallel-plates were mounted inside a vertical cylinder made of acrylic material and filled with about 100 g of in-shell peanuts and their average mc was determined from a similar empirical equation. The calculated MC values were compared with those obtained by the standard air-oven method. For over 85% of the samples tested in the moisture range between 6% and 22% the MC values were found to be within 1% of the air-oven values. Ability to determine the average MC of slightly larger quantities of in-shell peanuts without shelling and cleaning them, as being done presently, will save time, labor and sampling material for the peanut industry.
Filtering of NDT signals obtained from wrapped steel cables
The main cables of suspension bridges are often wrapped with a steel wire, in order to compact the cable and hold it in shape. If a non-destructive evaluation by means of magnetic methods is performed on such a cable, disturbances due to the wrapping can be expected in the measured signal. In the presented work, these disturbances shall be quantified and compared to the flaw signals. Different approaches for the separation of the disturbance and the flaw signal are discussed. Additionally, the possibility to detect wire breaks and corrosion within an unwrapped steel cross-section could be shown in laboratory measurements. The influence of the wrapping was investigated using finite element (FE) simulations and experimental laboratory measurements. A parameter study was performed in order to obtain data in which the components from a flaw and the wrapping can be separated. The parameters varied in this study were chosen depending on the prospect of success and the cost of the realization. Using these data sets different filtering methods, such as wavelet analysis, were implemented. A final comparison of the different methods suggests the most efficient way to assess the condition of such cable systems using magneto-inductive testing. Finally, it can be concluded that the use of FE simulation is a very useful tool for the development of new data analysis methods, even if a real set-up and data from measurements exist.
Remote Sensing and Homeland Security Applications
icon_mobile_dropdown
Performance evaluation of decentralized wireless sensing and control in civil structures
A structural control system consists of sensors, controllers, and actuators integrated in a single network to effectively mitigate building vibration during external excitations. The costs associated with high-capacity actuators and system installation are factors impeding the wide spread adoption of structural control technology. Wireless communication can potentially lower installation costs by eliminating coaxial cables and offer better flexibility and adaptability in the design of a structural control system. This paper introduces a prototype wireless sensing and control unit that can be incorporated in a real-time structural control system. Tests are conducted using a 3-story half-scale laboratory structure instrumented with magnetorheological dampers to validate the feasibility of the wireless structural control system. This paper also addresses the serious issue of time delay and communication range inherent to wireless technologies. Numerical simulations using different decentralized structural control strategies are conducted on a 20-story steel structure controlled by semi-active hydraulic dampers.
A passive wireless displacement sensor for structural health monitoring of civil structures
A. Hladio, D. Card, D. J. Thomson, et al.
A passive wireless displacement sensor suitable for use in civil structural health monitoring applications is presented. The sensor is based on a resonant electromagnetic cavity with one end of the cavity formed by a flexible membrane. A rod attached to the membrane causes the dimensions of the cavity to change when the rod is displaced. The change in dimensions causes a shift the resonant frequency of the cavity that is directly related to the displacement of the rod. In the example shown the shift is 7 MHz per mm for a cavity with a resonant frequency of 2450 MHz. Using a pulse echo interrogation technique resonant shifts of 100 kHz are resolvable. In the laboratory, displacements of 0.014 mm were measurable, with the distance between the interrogator and the sensor of up to 4.5 m.
Significance evaluation of geometric features in classification of chinese facial images
In this paper, multivariable linear regression analysis was employed to obtain the relationship among facial geometric features, and a discriminant function was used to evaluate the significance of different features. Finally, classification rates were compared with different combinations of geometric features. The results showed that the geometric feature with more significance probably improved the classification performance in the cases studied.
Applied Imaging
icon_mobile_dropdown
On an image reconstruction method for ECT
An image by Eddy Current Testing(ECT) is a blurred image to original flaw shape. In order to reconstruct fine flaw image, a new image reconstruction method has been proposed. This method is based on an assumption that a very simple relationship between measured data and source were described by a convolution of response function and flaw shape. This assumption leads to a simple inverse analysis method with deconvolution.In this method, Point Spread Function (PSF) and Line Spread Function(LSF) play a key role in deconvolution processing. This study proposes a simple data processing to determine PSF and LSF from ECT data of machined hole and line flaw. In order to verify its validity, ECT data for SUS316 plate(200x200x10mm) with artificial machined hole and notch flaw had been acquired by differential coil type sensors(produced by ZETEC Inc). Those data were analyzed by the proposed method. The proposed method restored sharp discrete multiple hole image from interfered data by multiple holes. Also the estimated width of line flaw has been much improved compared with original experimental data. Although proposed inverse analysis strategy is simple and easy to implement, its validity to holes and line flaw have been shown by many results that much finer image than original image have been reconstructed.
Sampling phased array: a new technique for signal processing and ultrasonic imaging
M. Kröning, A. Bulavinov, K. M. Reddy, et al.
Different signal processing and image reconstruction techniques are applied in ultrasonic non-destructive material evaluation. In recent years, rapid development in the fields of microelectronics and computer engineering lead to wide application of phased array systems. A new phased array technique, called "Sampling Phased Array" has been developed in Fraunhofer Institute for nondestructive testing. It realizes unique approach of measurement and processing of ultrasonic signals. The sampling phased array principle make use of the measurement of elementary waves generated by individual elements of sensor array to reconstruct the composite phased array signal for any arbitrary angle or focus depth. The use of special signal processing and image reconstruction algorithms, allows generating A-Scans of several angles and / or Sector-Scan, which can be implemented in real time. With parallel computing structures, this principle is used for automatic testing systems at very high inspection speed. A comparative study was done with Conventional Phased Array system and Sampling Phased Array technique. The study shows that the signal characteristics in both techniques are equal. In addition, the Sampling Phased Array technique is significantly beneficial in the many aspects like quality of information in specific cases, inspection speeds and adaptability to specific inspection tasks in comparison to conventional Phased Array. The electronics was developed as a development platform for high speed automated ultrasonic inspection systems for process integrated testing and also for testing of critical components. The development results, including relevant test methodology and electro-technical/electronic aspects are presented in the current work.