Mannur Sundaresan

North Carolina Agricultural and Technical State University | NC A&T · Department of Mechanical Engineering

This paper examines pulse thermographic nondestructive evaluation of flat bottom holes of isotropic materials. Different combinations of defect diameters and depths are considered. Thermographic Signal Reconstruction (TSR) method is used to analyze these results. In addition, a new normalization procedure is used to remove the dependence of thermog...

Thermographic nondestructive evaluation is quick and effective in detecting damage particularly for composite structures. Pulse thermographic nondestructive evaluation (TNDE) technique can potentially provide information on defect dimensions, such as the depth at which the defect is located. However, there are a number of extraneous variables that...

Composite structural members experience extensive and complex damage that accumulate in a relatively steady pace as the structure is quasi-statically loaded. This damage progression which starts as matrix cracks, delaminations, and random fiber breaks, turns unstable when groups of adjacent fibers, ranging from four to ten fibers fail together, aft...

In Pulse Thermographic Nondestructive Evaluation (TNDE), the thermographic signals are heavily influenced by material directionalities, therefore comparison of thermographic results are challenging. In this study a normalization procedure is introduced which simplifies the analysis and requires only break time, equilibrium temperature, and diffusiv...

An important requirement in the thermographic nondestructive evaluation is the identification of actual sound zone or the base line with which the defective areas are compared to determine the actual temperature contrast and the corresponding defect severity. In a part under inspection, the actual sound zone is not known a priori and various approx...

Pulse thermographic nondestructive evaluation (TNDE) technique can be used to estimate defect dimensions, and in particular the depth at which the defect is located. Numerical models of this procedure can aid in the interpretation of experimental results. However, the thermophysical properties of the test object as well as the amount of energy abso...

Guided wave-based technique is one major approach for damage inspection of structures. To detect a small damage, an elastic wave׳s wavelength needs to be in the order of the damage size and hence the frequency needs to be high. Unfortunately, high-frequency wave dynamics always involves complicated wave reflection, refraction and diffraction, and i...

Influence of attenuation on acoustic emission (AE) signals in Carbon Fiber Reinforced Polymer (CFRP) crossply and quasi-isotropic panels is examined in this paper. Attenuation coefficients of the fundamental antisymmetric (A0) and symmetric (S0) wave modes were determined experimentally along different directions for the two types of CFRP panels. I...

A conjugate-pair decomposition (CPD) method is proposed for signal decomposition, dynamics characterization, and nonlinearity identification all in the time domain only. CPD uses the empirical mode decomposition method with signal conditioning techniques to decompose a compound signal into well separated intrinsic mode functions (IMFs) and then use...

Here we present methods for modeling, analysis, and design of metamaterial beams for broadband vibration absorption/isolation. The proposed metamaterial beam consists of a uniform isotropic beam with many small spring-mass- damper subsystems integrated at separated locations along the beam to act as vibration absorbers. For a unit cell of an infini...

This paper presents dynamic characteristics and damage inspection of beams with actual fatigue cracks by using a boundary-effect evaluation method (BEEM) to perform space-wavenumber analysis of operational deflection shapes (ODSs) and a conjugate-pair decomposition (CPD) method to perform time-frequency analysis of dynamic responses of some points...

An experimental and numerical investigation was carried out for the feasibility of determining damage development in carbon/epoxy composite laminates with a circular hole. The study involved flash thermography to map the damaged region in these specimens. First, thermographic response of implanted delaminations in composite laminates was examined u...

Relative motion between surfaces of mechanical parts causes surface wear and damage. The degradation to the surfaces has been monitored using vibration characteristics as well as acoustic emissions generated during the relative surface movements. In particular, acoustic emission signals were found to be sensitive to some of the microscopic processe...

Composite materials are profuse emitters of acoustic emissions (AE) during the occurrence of damage. In some cases, the signals measured are due to growth of noncritical damage. To have a more accurate SHM technique, distinguishing between critical and non-critical damage is necessary. This work focuses on monitoring damage growth and relating AE s...

Acoustic emission signals generated by sliding friction between two flat steel surfaces are characterized. A test fixture to simulate the reciprocating motion between the two surfaces under controlled conditions is developed. Sliding friction under several combinations of surface roughness, relative velocity, and normal pressure was examined. Wideb...

Machine parts often contain components which experience relative motion during service. Relative motion between surfaces causes fatigue crack, wear and eventual surface deterioration. Acoustic emission based machinery condition monitoring is a method which can potentially be used to monitor the state of damage present on surfaces during service. Th...

This paper shows that time-frequency analysis is most appropriate for nonlinearity identification, and presents advanced signal processing techniques that combine time-frequency decomposition and perturbation methods for parametric and non-parametric identification of thin-walled structures and other dynamical systems. Hilbert-Huang transform (HHT)...

Mating parts often experience repetitive relative motion termed fretting which results in friction, wear, as well as acoustic emission signals. Acoustic emission signals have the potential for monitoring the condition of the surfaces participating in the frictional process. In structural health monitoring studies, where the focus is on quantifying...

Structural buckling can lead to failure, but beyond the initial onset of buckling there exists a stable region within which there may be no material damage, the structure retains the load carrying capacity, and can recover fully elastically when unloaded. Reclaiming this region as valid design space requires the full understanding of changes in the...

In this research, the acoustic emissions from simulated crack growth and incremental crack growth in a cyclically loaded aluminum panel were detected by acoustic emission sensors. One of these sensors was comprised of an array of thin strips of piezoelectric material bonded to the specimen and electrically connected. The geometry of these sensor st...

The classification of acoustic emission source mechanisms based on features related to the physics of acoustic emission signal generation is considered in this paper. Numerically generated acoustic emission waveforms are used for this purpose. Conventional acoustic emission parameters such as rise-time, duration, and frequency content do not effect...

This paper presents a dynamics-based methodology for accurate damage inspection of thin-walled structures by combining a boundary-effect evaluation method (BEEM) for space-wavenumber analysis of measured operational deflection shapes (ODSs) and a conjugate-pair decomposition (CPD) method for time-frequency analysis of time traces of measured points...

This paper reports on results of training support vector machines (SVMs) to classify the source types of acoustic emission signals using two different sets of waveform features. The first approach used as attributes in training instances eighteen traditional acoustic emission features and used experimental data, while the second approach used six c...

This paper reports on a prototype architecture for structural health monitoring (SHM) systems and reviews the literature in the relevant areas. A wireless sensor network (WSN) infrastructure is generally assumed. A WSN can be extended to a sensor web either in the accessible sense (making resources available on the World Wide Web) or in the collabo...

The acoustic emission (AE) technique is a promising tool for monitoring the integrity of structural members while they are in service. The major obstacle in deploying this technique is the presence of noise from extraneous sources that generate false positives. Identification and separation of noise from crack related signals are of interest. Frict...

Among different failure modes observed in structures, loss of stability due to buckling is a major concern. Buckling may be induced because of overload or as a consequence of other types of failures in the structure. This paper examines two techniques, namely, vibration based analysis, and stress wave propagation analysis for detecting this onset o...

Identification of the source mechanism and measurement of source strength are important requirements for wider field application of the acoustic emission technique. It is difficult to relate a given source event to resulting acoustic emission waveforms in experimental results. However, it is practical to simulate such source events using numerical...

This paper examines the stress waves generated by simulated acoustic emission sources in flat plates and a stiffened panel. The mode conversions and reflections in stiffened panels significantly increase the complexity of the acoustic emission waveforms and hence identifying the source of acoustic emission signals becomes difficult. The waveforms c...

Structural health monitoring of wind turbines is necessitated by the difficulty in manually inspecting a wind turbine to assess safety and consequences of damage. Damage to a blade could dynamically unbalance the turbine, which could destroy the entire machine. Besides the huge financial loss if a turbine fails, safety is a concern for anything nea...

The development of high sensitivity sensors capable of accurately reproducing propagating Lamb waves is crucial for the success of AE based structural health monitoring applications. Plate like members are the most common elements encountered in structural health monitoring. The stress waves propagate as guided waves or Lamb waves in these members....

Structural Health Monitoring (SHM) of a wind turbine blade using a Structural Neural System (SNS) is described in this paper. Wind turbine blades are composite structures with complex geometry and sections that are built of different materials. The 3D structure, large size, anisotropic material properties, and the potential for damage to occur anyw...

A prototype structural neural system (SNS) is tested for the first time and damage detection results are presented in this study. The SNS is a passive online structural health monitoring (SHM) system that mimics the synaptic parallel computation networks present in the human biological neural system. Piezoelectric ceramic sensors and analog electro...

A large number of sensors are required to perform real-time structural health monitoring (SHM) to detect acoustic emissions (AE) produced by damage growth on large complicated structures. This requires a large number of high sampling rate data acquisition channels to analyze high frequency signals. To overcome the cost and complexity of having such...

Fatigue crack growth in a lap joint specimen extracted from a retired aircraft fuselage was monitored using bonded continuous acoustic emission sensors. The specimen lasted nearly 350,000 cycles of tension-tension cyclic loading. During this period a large number of acoustic emission signals were collected. Two distinct classes of events were obser...

Detecting and locating damage in structural components and joints that have high feature densities and complex geometry is a difficult problem in the field of structural health monitoring (SHM). Active propagation of diagnostic waves is one approach that is used to detect damage. But small cracks and damage are difficult to detect because they have...

Structural health monitoring is an underlying technology that can help to ensure safe operation and provide cost effective maintenance of advanced composite structures. While several general methods of health monitoring have evolved in recent years, there is still the goal of reducing the overall cost of applying health monitoring to large structur...

The accuracy of locating damage using vibration measurements depends on the number and locations of sensors on the structure. In practical applications, only a limited number of on-board sensors will be available. The limited number of sensors causes spatial aliasing when solving an underdetermined inverse problem to locate damage. In this study, i...

Fatigue crack growth during the service of aging aircrafts has become an important issue and the monitoring of such cracks in hot spots is desirable. A structural health monitoring sensor system that uses acoustic emission technique for monitoring safety of such structures is described in this report. A "continuous sensor" formed by connecting mult...

A small size prototype of a Structural Neural System (SNS) was tested in real time for damage detection in a laboratory setting and the results are presented in this paper. The SNS is a passive online structural health monitoring (SHM) system that can detect small propagating damages in real time before the overall failure of the structure is reali...

This paper focuses on actuating mode shapes of cellulose-based electro-active paper (EAPap) in order to investigate its suitability as actuators. Firstly, actuating mechanism of EAPap is addressed based on intrinsic characteristics of cellulose structures under electric fields. EAPap actuator is then fabricated by embedding gold as electrodes into...

This paper describes a scalable structural health monitoring technique for tracking fatigue damage in metallic and composite structural members. A new type of sensor termed "continuous sensor" was used in this study. It is feasible to integrate this sensor into critical areas of aircraft structure with minimal cost and weight penalty. Panels and jo...

A multiagent architecture for vehicle and structural health monitoring is proposed. A prototype using this architecture was devel- oped using JADE. Critical aspects of the design were verified using the SPIN model checker. The tasks in our framework are related to data- fusion levels and Gibson's realist position on direct perception of objects and...

The possibility of using a laser sensor and piezoelectric patches for vibration suppression on aircraft was demonstrated. The control technique significantly increased the damping ratio and reduced the steady-state vibration of a model wing in a low-speed wind tunnel. The performance could be improved by using actuators that have a large force and...

A multiagent framework for data acquisition, analysis, and diagnosis in health management is proposed. It uses the contract net protocol, a protocol for high-level distributed problem solving that provides adaptive and flexible solutions where task decomposition and assignment of subtasks is natural. Java is used to wrap implementations of existing...

Recently a new structural health monitoring system that employs a "continuous acoustic emission sensor" and an embeddable local processor has been proposed. The development of a processor that integrates the functions of signal conditioning, feature extraction, data storage, and digital communication is currently in progress. A prototype of this lo...

Most structural health monitoring analyses to date have focused on the determination of damage in the form of crack growth in metallic materials or delamination or other types of damage growth in composite materials. However, in many applications, local instability in the form of buckling can be the precursor to more extensive damage and unstable f...

Structural Health Monitoring ideally would check the health of the structure in real time all the time. Simplifying the sensor system and the data acquisition equipment plays a very important role in achieving this goal. This paper discusses a practical technique that uses long continuous sensors and biomimetic signal processing to simplify health...

This paper discusses a proof test procedure for estimating and extending the fatigue life of composite coupons. The estimates were based on the acoustic emission data collected during the described proof test procedure. A group of coupon specimens that included both undamaged as well as damaged ones were tested to verify the ability to estimate the...

Fatigue crack growth during the service of aging aircrafts has become an important issue and the monitoring of such cracks in hot spots is desirable. A structural health monitoring system using an acoustic emission technique under development for monitoring safety of such structures is described in this paper. A "continuous sensor" formed by connec...

Most structural health monitoring analyses to date have focused on the determination of damage in the form of crack growth in metallic materials or delamination or other types of damage growth in composite materials. However, in many applications, local instability in the form of buckling can be the precursor to more extensive damage and unstable f...

The paper presents the initial results on the performance of cellulose-based Electro-Active Papers (EAPap) as actuators. The electro-active papers depend on ion migration and dipole moment for the actuation. EAPap is fabricated by depositing gold electrodes on the top and bottom surfaces of cellophane sheets. Small sheet specimens measuring approxi...

Detecting and locating cracks in structural components and joints that have high feature densities is a challenging problem in the field of Structural Health Monitoring. There have been advances in piezoelectric sensors, actuators, wave propagation, MEMS, and optical fiber sensors. However, few sensor-signal processing techniques have been applied...

A relatively overlooked factor in both global and local methods of health monitoring is the nonlinear stiffness of structures caused by the cycling of cracks and delaminations. Global methods of health monitoring use modal parameters or frequency response functions in an inverse procedure to quantify damage in structures with thick sections. Global...

An embeddable structural health monitoring system has been developed to measure acoustic emission signals generated by incipient damage in Army structures. The structural health monitoring system is built upon two parallel approaches that mimic signal processing in biological nerve cells. One approach uses a continuous sensor formed by a series con...

Piezoelectric ceramic patches are the mainstay for actuating and sensing in smart structures, but these patches are limited in the temperature range in which they can operate. Operation at temperatures above ambient is desired for new applications of smart structures, including in aircraft, turbine engine components, space vehicles, and others. The...

This paper examines the use of continuous sensors to detect damage in composite materials. Continuous sensors contain multiple interconnected sensor nodes that can be integrated into an artificial neural system as an array of sensor nerves. The advantage of this passive health monitoring approach is that the sensor system is highly distributed and...

This paper discusses the use of a vibration method to detect fatigue cracks in inaccessible internal structures. On aircraft, the lower wing panels are highly stressed causing cracks to initiate from fastener holes inside the wing box. The wing panel internal sections are usually inspected using conventional nondestructive inspection techniques aft...

This paper discusses recent advances in modeling and simulation of an artificial neural system and simulation of wave propagation for designing structural health monitoring systems. An artificial neural system was modeled using piezoceramic nerves and electronic components. Wave propagation in a panel is modeled using classical plate theory and a c...

This paper discusses the development of continuous Active Fiber Composite sensors to detect damage in composite materials. Continuous sensors contain multiple interconnected sensor nodes that can be integrated into an artificial neural system as an array of sensor nerves. Continuous sensors have demonstrated a possibility of damage detection in lar...

The concept of a biomimetic sensor system design that can be embedded in aircraft structure is explored in this project. Signal processing techniques for quantifying the sensor responses are studied. In particular, wavelet analysis is used to extract the time frequency information about the acoustic emission (AE) signals and to separate the Lamb wa...

A major concern with ageing aircraft is the deterioration of structural components in the form of fatigue cracks at fastener holes, loose rivets and debonding of joints. These faults in conjunction with corrosion can lead to multiple-site damage and pose a hazard to flight. Developing a simple vibration-based method of damage detection for monitori...

Various techniques have been developed that use changes in the mode shapes, Ritz vectors, or the operational deflection shapes of a structure to detect damage. These techniques generally have been applied using single excitation forces at low frequencies. This paper shows that the frequency range and number of simultaneous excitation forces used si...

An artificial central nervous system has been formed using parallel connected continuous sensors. Continuous sensors are analogous to biological neurons and have multiple piezoceramic sensor elements or receptors. When a neuron receives an acoustic emission signal caused by damage in a structure, the signal is evaluated by the processor of the neur...

A new approach for the Health Monitoring of structural systems is described in this paper. This technique is based on detecting the acoustic emission signals from damage progression in structures using an array of sensory nodes. Two different sensor configurations that could be used for monitoring wide areas on a structure are discussed. An reliabl...

Most structural health monitoring analyses to date have focused on the determination of damage in the form of crack growth in metallic materials or delamination or other types of damage growth in composite materials. However, in many applications local instability in the form of buckling can be the precursor to more extensive damage and unstable fa...

The concept of a continuous sensor for detecting vibration and stress waves in bars is investigated in this paper. This type of sensor is a long tape with a number of sensing nodes that are electrically connected together to form a single sensor with one channel of data output. The spacing of the sensor nodes can be designed such that the sensor is...

This paper discusses the potential for using Piezoceramic and Nanotube materials to develop an artificial neural system for structural health monitoring. An artificial neural system array was modeled using piezoceramic nerves and electronic components. The neural system was simulated using one hundred dual-output sensor nodes on a four-foot square...

Recent structural health monitoring techniques have focused on developing global sensor systems that can detect damage on large structures. The approach presented here uses a piezoelectric sensor array system that mimics the biological nervous system architecture to measure acoustic emissions and dynamic strains in structures. The advantage of this...

Damage detection can increase safety, extend serviceability, reduce maintenance costs, and define reduced operating limits for structures. Vibration-based methods are a new approach for damage detection and are more globally sensitive to damage than localized methods such as ultrasonic and eddy current methods. The interpretation of vibration respo...

Structural health monitoring research is being performed by NCA&T, the NREL and Sandia Laboratories to develop a''Smart Blade'' with an embedded sensor system integrated into the blade by the manufacturer to continuously monitor the condition of the loading in the blade and reduce or prevent fatigue damage of the blade. This will reduce maintenance...

Building artificial nerves for smart structures and for structural health monitoring is discussed. Structural Health Monitoring refers to using in-situ sensors to monitor the strains and strain waves and from these interpret the health of a structure in real-time. This will allow a structure to be operated at its maximum performance and efficiency...

Piezoceramic materials used for the actuating and sensing of smart structures are limited in the temperature range in which they can operate. Operation at temperatures above ambient is desired for many applications including aircraft, turbine engine housings and others. The decrease in actuation and sensing capability with increasing temperature is...

Piezoelectric materials are opening the door for the design of large smart structures. To explore what possibilities there might be for building practical smart structures, a review of the characteristics and methods of processing piezoelectric active materials is given. The advantages and limitations of using the different forms of piezoelectric m...

In this paper, distributed sensors are evaluated for structural health monitoring. A distributed sensor is formed by electrically connecting a number of acoustic emission sensor nodes in series. The individual nodes are placed at strategic locations on the structure. This arrangement allows the detection of acoustic emissions occurring at multiple...

Health monitoring of aerospace structures can be done using an active interrogation approach with diagnostic Lamb waves. Piezoelectric patches are often used to generate the waves, and it is helpful to understand how these waves propagate through a structure. To give a basic understanding of the actual physical process of wave propagation, a model...

Structural condition monitoring refers to using in-situ sensors to monitor the internal loads and the health of a structure in real-time. This will allow a structure to be operated at its maximum performance and efficiency while minimizing the fatigue damage. To achieve this on a large structure, new highly distributed sensor concepts are investiga...

A distributed in-situ sensor that can simplify structural health monitoring is investigated in this paper. The distributed sensor can detect damage within the coverage area of the sensor by measuring acoustic emissions, but it cannot exactly locate the damage source due to the continuous nature of the sensor. A simulation and experiment showed that...

The use of composites in the transportation industry is hindered by their susceptibility to damage. Defects that occur during manufacturing or an impact during normal operation can significantly reduce the strength of the composite. Consequently, methods of structural health monitoring (SHM) are needed to verify and continuously monitor the integri...

This is an overview paper that discusses the concept of an embeddable structural health monitoring system for use in composite and heterogeneous material systems. The sensor system is formed by integrating groups of autonomous unit cells into a structure, much like neurons in biological systems. Each unit cell consists of an embedded processor and...

Piezoelectric materials are opening the door for the design of large smart structures. To explore what possibilities there might be for building practical smart structures, a review of the characteristics and methods of processing piezoelectric active materials is given. The advantages and limitations of using the different forms of piezoelectric m...

The main and tail rotor systems of a helicopter must be maintained in a damage-free condition to ensure the safety of the helicopter. The components of the rotor system require regular maintenance and inspection, and some of the components are difficult to inspect. Accordingly, an integrated sensor system that continuously monitors the structural i...

Simulation and testing to develop an Intelligent Blade for wind turbines is presented in this paper. The concept blade has an integrated sensor system for structural health monitoring that will continuously monitor the condition of the blade, warn of initiating damage, and provide instant information that can be used to regulate loading in the blad...

An active fiber composite tape with segmented electrodes was modeled for use as a continuous sensor for structural health monitoring of plate structures. The material has unidirectional piezoceramic fibers with interdigital electrodes on the top and bottom surfaces and is poled in the fiber direction. The elastic response of a plate with the modele...

This is an overview paper that discusses the concept of an embeddable structural health monitoring system for use in composite and heterogeneous material systems. The sensor system is formed by integrating groups of autonomous unit cells into a structure, much like neurons in biological systems. Each unit cell consists of an embedded processor and...