Self-healing materials have received considerable development in the last decade. Recent results have demonstrated healing in polymeric materials via a chemical reaction using a healing agent or response to thermal treatment. The goal of this research is to develop a new composite material, for application in wire insulation, that can detect damage and heal itself using resistance heating. The composite material is composed of a conductive network embedded in a polymer matrix. The conductive network is used for damage detection and resistive heating. A matrix material is used that melts when heated and flows to fill damage. External electronic circuitry is used to implement a damage detection algorithm and apply current for resistive heating. Surlyn 8940 is chosen as the polymer matrix and carbon fibers are selected for the resistive heating elements. Methods for melt processing Surlyn are developed and used to produce Surlyn films and composite samples where carbon fiber is embedded in a Surlyn matrix. A finite element model of the resistive heating process is developed to predict the temperature distribution. Thermal imaging is used to characterize resistive heating while optical microscopy and tensile testing are used to characterize healing. Damage detection using capacitive measurements is demonstrated and characterized. The self-healing composite is placed on top of another conductive material such as in the wire insulation application. Capacitance measurements are made using the conductive network inside the composite is used as one electrode and the wide conductor as the second electrode. / Master of Science

No description available.

A method that can be used to detect damage in structures is developed. This method is based on the convexity of the geometric interpretation of the eigenvalue problem for undamped positive definite systems. The damage detection scheme establishes various damage scenarios which are used as failure sets. These scenarios are then compared to the structure's actual response by measuring the natural frequencies of the structure and using a Euclideian norm. Mathematical models were developed for application of the method on a cantilever beam. Damage occurring at a single location or in multiple locations was estalished and studied. Experimental verification was performed on serval prismatic beams in which the method provided adequate results. The exact location and extent of damage for several cases was predicted. When the method failed the prediction was very close to the actual condition in the structure. This method is easy to use and does not require a rigorous amount of instrumentation for obtaining the experimental data required in the detection scheme. / Ph. D.

No description available.

Many studies have attempted to detect structural damage by examining differences in the frequency response functions of a structure before and after damage. In an experimental setting, this variation can not be attributed solely to the addition of damage. Other sources of variation include testing and structure variation. Examples of testing variation include the error introduced by modal parameter extraction, measurement noise, and the mass loading of the accelerometer. Structure variability is due to slight differences in the supposedly identical structures. Dimensional tolerancing is one example. This study began with six "identical" undamaged aluminum cylinders, of which three were later damaged to varying extents. The frequency response functions of the undamaged and damaged cylinders were measured. Also, the frequency response function of the same undamaged cylinder was measured multiple times to investigate testing variation. The contributions of testing, cylinder, and damage variation to the differences between cylinder responses was elucidated by specifically examining their frequency response functions in two ways: comparing the natural frequencies and directly investigating the entire frequency response function. The curvature of the frequency response functions was then used to determined the presence, location, and severity of the imparted damage. / Master of Science

We discuss a systematic methodology that leads to the reconstruction of the material profile of either single, or assemblies of one-dimensional flexural components endowed with Timoshenko-theory assumptions. The probed structures are subjected to user-specified transient excitations: we use the complete waveforms, recorded directly in the time-domain at only a few measurement stations, to drive the profile reconstruction using a partial-differential-equation-constrained optimization approach. We discuss the solution of the ensuing state, adjoint, and control problems, and the alleviation of profile multiplicity by means of either Tikhonov or Total Variation regularization. We report on numerical experiments using synthetic data that show satisfactory reconstruction of a variety of profiles, including smoothly and sharply varying profiles, as well as profiles exhibiting localized discontinuities. The method is well suited for imaging structures for condition assessment purposes, and can handle either diffusive or localized damage without need for a reference undamaged state. / text

This thesis investigates the development of ultrasonic Structural Health Monitoring (SHM) systems, based on guided waves propagation, for the localization of low-velocity impacts and the detection of damage mechanisms in isotropic and anisotropic structures. For the identi- cation of the impact point, two main passive techniques were developed, an algorithm-based and an imaging-based method. The former approach is based on the dierences of the stress waves measured by a network of piezoelectric transducers surface bonded on plate-like structures. In particular, four piezoelectric sensors were used to measure the antisymmetrical A0 Lamb mode in isotropic materials, whilst six acoustic emission sensors were employed to record the wave packets in composite laminates. A joint time-frequency analysis based on the magnitude of the Continuous Wavelet Transform was used to determine the time of arrivals of the wave packets. Then, a combination of unconstrained optimization technique associated to a local Newton's iterative method was employed to solve a system of non linear equations, in order to assess the impact location coordinates and the wave group speeds. The main advantages of the proposed algorithms are that they do not require an a-priori estimation of the group velocity and the mechanical properties of the isotropic and anisotropic structures. Moreover, these algorithms proved to be very robust since they were able to converge from almost any guess point and required little computational time. In addition, this research provided a comparison between the theoretical and experimental results, showing that the impact source location and the wave velocity were predicted with reasonable accuracy. The passive imaging-based method was developed to detect in realtime the impact source in reverberant complex composite structures using only one passive sensor. This technique is based on the re- ciprocal time reversal approach, applied to a number of waveforms stored in a database containing the impulse responses of the structure. The proposed method allows achieving the optimal focalization of the acoustic emission source (impact event) as it overcomes the limitations of other ultrasonic impact localization techniques. Compared to a simple time reversal process, the robustness of this approach is experimentally demonstrated on a stiened composite plate. This thesis also extended active ultrasonic guided wave methods to the specic case of dissipative structures showing non-classical nonlinear behaviour. Indeed, an imaging method of the nonlinear signature due to impact damage in a reverberant complex anisotropic medium was developed. A novel technique called phase symmetry analysis, together with frequency modulated excitation signals, was used to characterize the third order nonlinearity of the structure by exploiting its invariant properties with the phase angle of the input waveforms. Then, a \virtual" reciprocal time reversal imaging process was employed to focus the elastic waves on the defect, by taking advantage of multiple linear scattering. Finally, the main characteristics of this technique were experimentally validated.

This thesis presents a development of Structural Health Monitoring (SHM) and Fault Diagnosis based on Artificial Immune System (AIS), a biology-inspired method motivated from the Biological Immune System (BIS). Using the antigen to model structural health or damage condition of specific characteristics and the antibody to represent an information system or a database that can identify the specific damage pattern, the AIS can detect structural damage and then take action to ensure the structural integrity. In this study the antibodies for SHM were first trained and then tested. The feature space in training includes the natural frequencies and the modal shapes extracted from the simulated structural response data including both free-vibration and seismic response data. The concepts were illustrated for a 2-DOF linear mass-spring-damper system and promising results were obtained. It has shown that the methodology can be effectively used to detect, locate, and assess damage if it occurred. Consistently good results were obtained for both feature spaces of the natural frequencies and the modal shapes extracted from both response data sets. As the only exception, some significant errors were observed in the result for the seismic response data when the second modal shape was used as the feature space. The study has shown great promises of the methodology for structural health monitoring, especially in the case when the measurement data are not sufficient. The work lays a solid foundation for future investigations on the AIS application for large-scale complex structures.

Vibration-based damage detection methods are used in structural applications to identify the global dynamic response of the system. The purpose of the work presented is to exhibit a vibration-based damage detection algorithm that calculates a damage indicator, based on limited frequency bands of the transmissibility function that have high coherence, as a metric for changes in the dynamic integrity of the structure. The methodology was tested using numerical simulation, laboratory experimentation, and field testing with success in detecting, comparatively locating, and relatively quantifying different damages while also parametrically investigating variables which have been identified as issues within similar existing methods. Throughout both the numerical and laboratory analyses, the results were used to successfully detect damage as a result of crack growth or formation of new cracks. Field results using stochastic operational traffic loading have indicated the capability of the proposed methodology in evaluating the changes in the health condition of a section of the bridge and in consistently detecting cracks of various sizes (30 to 60 mm) on a sacrificial specimen integrated with the bridge abutment and a floor beam. Fluctuations in environmental and loading conditions have been known to create some uncertainties in most damage detection processes; however, this work demonstrated that by limiting the features of transmissibility to frequency ranges of high coherence, the effect of these parameters, as compared to the effect of damage, become less significant and can be neglected for some instances. The results of additional field testing using controlled impact forces on the sacrificial specimen have reinforced the findings from the operational loading in detecting damage.

Vibration-based damage detection (VBDD) methods are structural health monitoring techniques that utilize changes to the dynamic characteristics of a structure (i.e. its natural frequencies, mode shapes, and damping properties) as indicators of damage. While conceptually simple, considerable research is still required before VBDD methods can be applied reliably to complex structures such as bridges. VBDD methods require reliable estimates of modal parameters (notably natural frequencies and mode shapes) in order to assess changes in the condition of a structure. This thesis presents the results of experimental and numerical studies investigating a number of issues related to the potential use of VBDD techniques in the structural health monitoring of bridges, the primary issue being the influence of the excitation source.<p> Two bridges were investigated as part of this study. One is located on Provincial Highway No. 9 over the Red Deer River south of Hudson Bay, Saskatchewan. The other is located near the Town of Broadview, Saskatchewan, off Trans-Canada Highway No. 1, 150 km east of the City of Regina. Field tests and numerical simulations were conducted using different types of excitation to evaluate the quality of the modal properties (natural frequencies and mode shapes) calculated using these excitation types, and thus to evaluate the performance of VBDD techniques implemented using the resulting modal data. Field tests were conducted using different sources of dynamic excitation: ambient, traffic excitation, and impact excitation. The purpose of field testing was to study the characteristics and repeatability of the modal parameters derived using the different types of dynamic excitation, and to acquire data that could be used to update a FE model for further numerical simulation.<p> A FE model of the Red Deer River bridge, calibrated to match the field measured dynamic properties, was subjected to different types of numerically simulated dynamic excitation with different noise (random variations) levels added to them. The types of dynamic excitation considered included harmonic forced excitation, random forced excitation and the subsequent free vibration decay, impact excitation, and different models of truck excitation. The bridge model was subjected to four different damage scenarios; in addition, six VBDD methods were implemented to evaluate their ability to identify and localize damage. The effects of uncertainty in the definition of controlled-force excitation sources and variation in measurement of the bridge response were also investigated.<p> Field tests on the Hudson Bay bridge showed that excitation induced by large trucks generally produced more reliable data than that of smaller vehicles due to higher signal-to-noise ratios in the measured response. It was also found that considering only the free vibration phase of the response after the vehicle left the bridge gave more reliable data. Impact excitation implemented the on Hudson Bay bridge using a spring-hammer yielded repeatable and high quality results, while using a heavy weight delectometer for impact excitation on the Broadview bridge produced results of lesser quality due to the occurrence of multiple strikes of the impact hammer. In general, wind induced vibration measurements taken from both bridges were less effective for defining modal properties than large vehicle loading or impact excitation. All of the VBDD methods examined in this study could detect damage if the comparison was made between modal parameters acquired by eigenvalue analyses of two FE models of the bridge, before and after damage. However, the performance of VBDD methods declined when the dynamic properties were calculated from response time histories and noise was introduced. In general, the damage index method performed better than other damage detection methods considered.<p> Numerical simulation results showed that harmonic excitation, impact excitation, and the free decay phase after random excitation yielded results that were consistent enough to be used for the identification of damage. The reliability of VBDD methods in detecting damage dropped once noise was introduced. Noise superimposed on the excitation force had little effect on the estimated modal properties and the performance of VBDD methods. On the other hand, noise superimposed on the measured dynamic response had a pronounced negative influence on the performance of the VBDD methods.