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Showing papers by "Charles R. Farrar published in 2007"


Journal ArticleDOI
TL;DR: Technical challenges that must be addressed if SHM is to gain wider application are discussed in a general manner and the historical overview and summarizing the SPR paradigm are provided.
Abstract: This introduction begins with a brief history of SHM technology development. Recent research has begun to recognise that a productive approach to the Structural Health Monitoring (SHM) problem is to regard it as one of statistical pattern recognition (SPR); a paradigm addressing the problem in such a way is described in detail herein as it forms the basis for the organisation of this book. In the process of providing the historical overview and summarising the SPR paradigm, the subsequent chapters in this book are cited in an effort to show how they fit into this overview of SHM. In the conclusions are stated a number of technical challenges that the authors believe must be addressed if SHM is to gain wider acceptance.

2,152 citations


Journal ArticleDOI
TL;DR: In this paper, the authors explicitly state and justify structural health monitoring axioms, and stimulate discussion and thought within the community regarding these axiomatizations, in order to facilitate new researchers in the field a starting point that alleviates the need to review the vast amounts of literature in this field.
Abstract: Based on the extensive literature that has developed on structural health monitoring over the last 20 years, it can be argued that this field has matured to the point where several fundamental axioms, or gen eral principles, have emerged. The intention of this paper is to explicitly state and justify these axioms. In so doing, it is hoped that two subsequent goals are facilitated. First, the statement of such axioms will give new researchers in the field a starting point that alleviates the need to review the vast amounts of literature in this field. Second, the authors hope to stimulate discussion and thought within the community regarding these axioms.

514 citations


Journal ArticleDOI
TL;DR: This paper concludes the theme issue on structural health monitoring (SHM) by discussing the concept of damage prognosis (DP), which attempts to forecast system performance by assessing the current damage state, estimating the future loading environments for that system, and predicting through simulation and past experience the remaining useful life of the system.
Abstract: This paper concludes the theme issue on structural health monitoring (SHM) by discussing the concept of damage prognosis (DP). DP attempts to forecast system performance by assessing the current damage state of the system (i.e. SHM), estimating the future loading environments for that system, and predicting through simulation and past experience the remaining useful life of the system. The successful development of a DP capability will require the further development and integration of many technology areas including both measurement/processing/telemetry hardware and a variety of deterministic and probabilistic predictive modelling capabilities, as well as the ability to quantify the uncertainty in these predictions. The multidisciplinary and challenging nature of the DP problem, its current embryonic state of development, and its tremendous potential for life-safety and economic benefits qualify DP as a ‘grand challenge’ problem for engineers in the twenty-first century.

394 citations


Journal ArticleDOI
TL;DR: In this paper, a wavelet-based signal processing technique has been developed to enhance the time reversibility of Lamb wave in thin composite plates, and the validity of the proposed method is demonstrated through experimental studies in which input signals exerted at piezoelectric (PZT) patches on a quasi-isotropic composite plate are successfully reconstructed by using the time reversal method.

306 citations


Journal ArticleDOI
TL;DR: This paper developed a wireless impedance sensor node equipped with a low-cost integrated circuit chip that can measure and record the electrical impedance of a piezoelectric transducer, a microcontroller that performs local computing and a wireless telemetry module that transmits the structural information to a base station.
Abstract: This paper presents the development and application of a miniaturized impedance sensor node for structural health monitoring (SHM). A large amount of research has been focused on utilizing the impedance method for structural health monitoring. The vast majority of this research, however, has required the use of expensive and bulky impedance analyzers that are not suitable for field deployment. In this study, we developed a wireless impedance sensor node equipped with a low-cost integrated circuit chip that can measure and record the electrical impedance of a piezoelectric transducer, a microcontroller that performs local computing and a wireless telemetry module that transmits the structural information to a base station. The performance of this miniaturized and portable device has been compared to results obtained with a conventional impedance analyzer and its effectiveness has been demonstrated in an experiment to detect loss of preload in a bolted joint. Furthermore, for the first time, we also consider the problem of wireless powering of such SHM sensor nodes, where we use radio-frequency wireless energy transmission to deliver electrical energy to power the sensor node. In this way, the sensor node does not have to rely on an on-board power source, and the required energy can be wirelessly delivered as needed by human or a remotely controlled robotic device.

200 citations


Journal ArticleDOI
TL;DR: In this paper, a damage detection technique was proposed to assess damage in composite plates by using an enhanced time reversal method, where an input signal at an excitation point can be reconstructed if a response signal measured at another point is reemitted to the original excitation points after being reversed in a time domain.
Abstract: A damage detection technique, which does not rely on any past baseline signals, is proposed to assess damage in composite plates by using an enhanced time reversal method. A time reversal concept of modern acoustics has been adapted to guided-wave propagation to improve the detectability of local defects in composite structures. In particular, wavelet-based signal processing techniques have been developed to enhance the time reversibility of Lamb waves in thin composite laminates. In the enhanced time reversal method, an input signal at an excitation point can be reconstructed if a response signal measured at another point is reemitted to the original excitation point after being reversed in a time domain. This time reversibility is based on linear reciprocity of elastic waves, and it is violated when nonlinearity is caused by a defect along a direct wave path. Examining the deviation of the reconstructed signal from the known initial input signal allows instantaneous identification of damage without requiring the baseline signal for comparison. The validity of the proposed method has been exemplified through experimental studies on a quasi-isotropic laminate with delamination.

164 citations



Journal ArticleDOI
TL;DR: In this paper, the monitoring of the composite wing skin-to-spar joint in unmanned aerial vehicles using ultrasonic guided waves was investigated. But the authors focused on the ultrasonic strength of transmission through the joints.
Abstract: This article deals with the monitoring of the composite wing skin-to-spar joint in unmanned aerial vehicles using ultrasonic guided waves The study investigates simulated wing skin-to-spar joints with two different types of bond defects, namely poorly cured adhesive and disbonded interfaces The bond-sensitive feature considered is the ultrasonic strength of transmission through the joints The dispersive wave propagation problem is studied numerically by a semi-analytical finite element method that accounts for viscoelastic damping, and experimentally by ultrasonic testing that uses highly durable, flexible macro fiber composite transducers The discrete wavelet transform is also employed to de-noise and compress the ultrasonic measurements Both numerical and experimental tests confirm that the ultrasonic strength of transmission increases across the defected bonds

111 citations


Journal ArticleDOI
TL;DR: In this paper, a structural health monitoring system for continuous online monitoring of delamination initiation and growth in composite structures is developed for minimizing damage misclassification by developing an instantaneous damage detection scheme that does not rely on past baseline data.
Abstract: A structural health monitoring system is developed for continuous online monitoring of delamination initiation and growth in composite structures. Structural health monitoring problems are often cast in the context of a statistical pattern recognition paradigm, in which a damage state of a structure is inferred by comparing test data with baseline data. However, subtle signal changes due to damage can often be masked by larger ambient variation of operational and environmental conditions of an in-service structure. Therefore, it is critical for the development of a robust monitoring system to minimize false-positive indications of damage caused by the undesired operational and environmental variation of the structure. The issue of minimizing damage misclassification has been addressed in this article by developing an instantaneous damage detection scheme that does not rely on past baseline data. The proposed instantaneous damage diagnosis is based on the concepts of time reversal acoustics and consecutive outlier analysis, and the proposed damage diagnosis has been tested for detecting delamination in composite plates.

101 citations


Journal ArticleDOI
TL;DR: A review of active materials in the context of applications to manufacturing machining processes is provided in this paper, with a discussion of future research areas and a suggests path forward, and a brief overview of experimental and theoretical studies on various process monitoring and control is considered.
Abstract: This paper provides a review of active materials in the context of applications to manufacturing machining processes. The important concepts and background of active materials are briefly introduced. After which, the applications of these materials are discussed as applied to relevant themes in machining processes. A brief overview of research work on experimental and theoretical studies on various process monitoring and control is considered, and several research papers on these topics are cited. This paper concludes with a discussion of future research areas and a suggests path forward.

92 citations



Journal ArticleDOI
TL;DR: In this article, a non-linear feature identification technique for structural damage detection using autoregressive coefficients in the frequency domain auto-regressive model with exogenous (ARX) inputs is presented.

Journal ArticleDOI
TL;DR: This work demonstrates that the parameters of a system of ordinary differential equations may be adjusted via an evolutionary algorithm to produce excitations that improve the sensitivity and robustness to extraneous noise of state-space based damage detection features extracted from the structural response to such excitations.
Abstract: Active excitation is an emerging area of study within the field of structural health monitoring whereby prescribed inputs are used to excite the structure so that damage-sensitive features may be extracted from the structural response. This work demonstrates that the parameters of a system of ordinary differential equations may be adjusted via an evolutionary algorithm to produce excitations that improve the sensitivity and robustness to extraneous noise of state-space based damage detection features extracted from the structural response to such excitations. A simple computational model is used to show that significant gains in damage detection and quantification may be obtained from the response of a spring-mass system to improved excitations generated by three separate representative ordinary differential equation systems. Observed differences in performance between the excitations produced by the three systems cannot be explained solely by considering the frequency characteristics of the excitations. This work demonstrates that the particular dynamic evolution of the excitation applied to the structure can be as important as the frequency characteristics of said excitation if improved damage detection is desired. In addition, the implied existence of a globally optimum excitation (in the sense of improved damage assessment) for the model system is explored.

Proceedings ArticleDOI
06 Apr 2007
TL;DR: In this paper, a Lamb wave propagation-based Structural Health Monitoring (SHM) system is used to identify common features of undamaged paths, which can be used as a baseline for near real-time damage detection.
Abstract: A critical aspect of existing Structural Health Monitoring (SHM) systems is the ability to compare current data obtained from a structure to a prerecorded baseline measurement taken for an undamaged case. Several Lamb wave-based SHM techniques have been successfully developed that use baseline measurements to identify damage in structures. The method developed in this study aims to instantaneously obtain baseline measurements in order to eliminate any complications associated with archiving baseline data and with the effects of varying environmental conditions on the baseline data. The proposed technique accomplishes instantaneous baseline measurements by deploying an array of piezoelectric sensors/actuators used for Lamb wave propagation-based SHM such that data recorded for equidistant sensor-actuator path lengths can be used to instantaneously identify several common features of undamaged paths. Once identified, data from these undamaged paths can be used as a baseline for near real-time damage detection. This method is made possible by utilizing sensor diagnostics, a recently developed technique which minimizes false damage identification and measurement distortion caused by faulty sensors. Several aspects of the instantaneous baseline damage detection method are detailed in this paper including determination of the features best used to identify damage, development of signal processing algorithms used to analyze data, and a comparison of two sensor/actuator deployment schemes.

Proceedings ArticleDOI
06 Apr 2007
TL;DR: A feasibility study of using wireless energy transmission systems to provide a required power for structural health monitoring (SHM) sensor nodes to develop SHM sensing systems which can be permanently embedded in the host structure and do not require an on-board power sources.
Abstract: In this paper, we present a feasibility study of using wireless energy transmission systems to provide a required power for structural health monitoring (SHM) sensor nodes. The goal of this study is to develop SHM sensing systems which can be permanently embedded in the host structure and do not require an on-board power sources. With this approach, the energy will be periodically delivered as needed to operate the sensor node, as opposed to being harvested as in the conventional approaches. The wirelessly transmitted microwave energy is captured by a microstrip patch antenna, and then transformed into DC power by a rectifying circuit and stored in a storage medium to provide the required energy to the sensor and transmitter. Based on the fact that recent networked sensor systems require power on the order of fractions of a watt, it is quite possible to operate such sensing devices completely from the captured wirelessly delivered energy. The method of designing and optimizing a wireless energy transmission system is discussed. This paper also summarizes considerations needed to design such energy delivery systems, experimental procedures and results, and additional issues that can be used as guidelines for future investigations.

Proceedings ArticleDOI
06 Apr 2007
TL;DR: Nastran et al. as discussed by the authors developed a specialized test-bed for composite UAVs, which consists of four 2.61 m all-composite test-pieces, a series of detailed finite element models of the test-piece and their components, and a dynamic testing setup including a mount for simulating the cantilevered operation configuration of real UAV.
Abstract: In order to facilitate damage detection and structural health monitoring (SHM) research for composite unmanned aerial vehicles (UAV) a specialized test-bed has been developed. This test-bed consists of four 2.61 m all-composite test-pieces emulating composite UAV wings, a series of detailed finite element models of the test-pieces and their components, and a dynamic testing setup including a mount for simulating the cantilevered operation configuration of real wings. Two of the wings will have bondline damage built in; one undamaged and one damaged wing will also be fitted with a range of embedded and attached sensors-piezoelectric patches, fiber-optics, and accelerometers. These sensors will allow collection of realistic data; combined with further modal testing they will allow comparison of the physical impact of the sensors on the structure compared to the damage-induced variation, evaluation of the sensors for implementation in an operational structure, and damage detection algorithm validation. At the present time the pieces for four wings have been fabricated and modally tested and one wing has been fully assembled and re-tested in a cantilever configuration. The component part and assembled wing finite element models, created for MSC.Nastran, have been correlated to their respective structures using the modal information. This paper details the design and manufacturing of the test-pieces, the finite element model construction, and the dynamic testing setup. Measured natural frequencies and mode shapes for the assembled cantilevered wing are reported, along with finite element model undamaged modal response, and response with a small disbond at the root of the top main spar-skin bondline.

Proceedings ArticleDOI
10 Apr 2007
TL;DR: In this article, a PZT sensor diagnostic and validation procedure that performs in-situ monitoring of structural health monitoring (SHM) applications is presented, where the authors quantify and classify several key characteristics of temperature change and develop effcient signal processing techniques to account for those variations in the sensors diagnosis process.
Abstract: This paper presents a piezoelectric sensor diagnostic and validation procedure that performs in-situ monitoring of the operational status of piezoelectric (PZT) sensor/actuator arrays used in structural health monitoring (SHM) applications The validation of the proper function of a sensor/actuator array during operation, is a critical component to a complete and robust SHM system, especially with the large number of active sensors typically involved The method of this technique used to obtain the health of the PZT transducers is to track their capacitive value, this value manifests in the imaginary part of measured electrical admittance Degradation of the mechanical/electrical properties of a PZT sensor/actuator as well as bonding defects between a PZT patch and a host structure can be identified with the proposed procedure However, it was found that temperature variations and changes in sensor boundary conditions manifest themselves in similar ways in the measured electrical admittances Therefore, we examined the effects of temperature variation and sensor boundary conditions on the sensor diagnostic process The objective of this study is to quantify and classify several key characteristics of temperature change and to develop effcient signal processing techniques to account for those variations in the sensor diagnosis process In addition, we developed hardware capable of making the necessary measurements to perform the sensor diagnostics and to make impedance-based SHM measurements The paper concludes with experimental results to demonstrate the effectiveness of the proposed technique


Proceedings ArticleDOI
06 Apr 2007
TL;DR: In this article, a meta-model based correlation technique was used on a composite UAV wing and associated finite element (FE) model, which was validated on a composite plate structure.
Abstract: The current work details the implementation of a meta-model based correlation technique on a composite UAV wing test piece and associated finite element (FE) model. This method involves training polynomial models to emulate the FE input-output behavior and then using numerical optimization to produce a set of correlated parameters which can be returned to the FE model. After discussions about the practical implementation, the technique is validated on a composite plate structure and then applied to the UAV wing structure, where it is furthermore compared to a more traditional Newton-Raphson technique which iteratively uses first-order Taylor-series sensitivity. The experimental testpiece wing comprises two graphite/epoxy prepreg and Nomex honeycomb co-cured skins and two prepreg spars bonded together in a secondary process. MSC.Nastran FE models of the four structural components are correlated independently, using modal frequencies as correlation features, before being joined together into the assembled structure and compared to experimentally measured frequencies from the assembled wing in a cantilever configuration. Results show that significant improvements can be made to the assembled model fidelity, with the meta-model procedure producing slightly superior results to Newton-Raphson iteration. Final evaluation of component correlation using the assembled wing comparison showed worse results for each correlation technique, with the meta-model technique worse overall. This can be most likely be attributed to difficultly in correlating the open-section spars; however, there is also some question about non-unique update variable combinations in the current configuration, which lead correlation away from physically probably values.

01 Jan 2007
TL;DR: The Los Alamos Dynamic Summer School (LADSS) as mentioned in this paper is a joint LANL/UCSD degree program with a unique focus in validated simulations, structural health monitoring, and damage prognosis.
Abstract: Los Alamos National Laboratory (LANL) and the University of California, San Diego (UCSD) have taken the unprecedented step of creating a collaborative, multi-disciplinary graduate education program and associated research agenda called the Engineering Institute. The technology thrust of the Engineering Institute is damage prognosis, a multidisciplinary engineering science concerned with assessing the current condition and predicting the remaining life of a wide variety of structural systems. The mission of the Engineering Institute is to develop a comprehensive approach for conducting LANL mission-driven, multidisciplinary engineering research and to improve recruiting, revitalization and retention of the current and future staff necessary to support LANL’s nuclear weapons stockpile stewardship responsibilities. The components of the Engineering Institute to be discussed in this paper are 1) the Los Alamos Dynamic Summer School (LADSS), 2) a joint LANL/UCSD degree program with a unique focus in validated simulations, structural health monitoring, and damage prognosis, 3) joint LANL/UCSD research projects, and 4) industry short courses. This program is a possible model for future industry/government interactions with university partners.

Proceedings ArticleDOI
06 Apr 2007
TL;DR: A suite of signal processing algorithms are employed and grouped into one package to improve the damage detection capability and contributes to and enhances the visibility and interpretation of the active-sensing methods related to damage identification in a structure.
Abstract: In this study, a novel approach of integrating data interrogation algorithms of active sensing methods for structural health monitoring (SHM) applications, including Lamb wave propagation, impedance method, and sensor-diagnostics, is presented. Contrary to most active-sensing SHM techniques, which utilize only a single signal processing method for damage identification, a suite of signal processing algorithms are employed and grouped into one package to improve the damage detection capability. A MatLab-based user interface called H.O.P.S. (Health Of Plate Structures) was created, which allows the analyst to configure the data acquisition system and display the results from each damage identification algorithm for side-by-side comparison. This side-by-side comparison of results simplifies the task of identifying the relative effectiveness and sensitivity of each algorithm. By grouping a suite of algorithms into one package, this study contributes to and enhances the visibility and interpretation of the active-sensing methods related to damage identification in a structure.

24 Jun 2007
TL;DR: Phillip Cornwell, the authors is a Professor of Mechanical Engineering at the Rose-Hulman Institute of Technology (RHT) in New York, who has received an SAE Ralph R. Teetor Educational Award in 1992 and the Dean's Outstanding Teacher award at RHT in 2000.
Abstract: Phillip Cornwell, Rose-Hulman Institute of Technology Phillip Cornwell is a Professor of Mechanical Engineering at Rose-Hulman Institute of Technology. He received his Ph.D. from Princeton University in 1989 and his present interests include structural dynamics, structural health monitoring, and undergraduate engineering education. Dr. Cornwell has received an SAE Ralph R. Teetor Educational Award in 1992, and the Dean’s Outstanding Teacher award at Rose-Hulman in 2000.