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Ramsey, James JehielEffects of Wind on Piezoelectric Lamb Wave-based Health Monitoring
Master of Science, University of Akron, 2006, Mechanical Engineering
Research has been ongoing into embedded NDE (non-destructive evaluation) where an aircraft is continuously monitored by embedded diagnostic systems and only grounded when there is an actual problem. One path of research involves permanently bonding piezoelectric wafers to panels of the aircraft skin and using them as ultrasonic transducers that send Lamb waves into the skin and receive echoes that bounce back from cracks and other damage in it. Such a system must operate in the non-ideal environment to which aircraft are routinely subjected. However, there is little research in the effects of such an environment. In particular, there appears to be no research on how vibration from airflow across the skin of the aircraft in flight may affect embedded NDE involving piezoelectrics. A test specimen was placed in a small wind tunnel with a 1-foot square cross-section and a maximum wind speed of 68 mph. The specimen was a 12 by 24-inch aluminum panel with a wooden frame around its edges to protect its underside from wind. In the first phase of experiments, two piezoelectric wafer transducers were glued to its underside. One transducer sent Lamb wave pulses while the other received them. In the second phase, one transducer was removed and replaced with a half-inch cut in the panel, while the other was set to both transmit pulses and receive their echoes. For both phases, the signal from the transducer receiving the pulses was recorded as the wind speed in the tunnel varied. The shape of the pulses from the receiving transducer remained intact but rode on lower frequency carrier waves whose amplitudes increased with wind speed. Lower frequencies could be filtered out by simply shunting the receiving transducer with a small (< 1 kiloohm) resistor, but this was less effective at higher wind speeds. Such a shunt resistance could be inadvertently introduced by a signal generator, something ignored in previous research. The main obstacle to a piezoelectric embedded NDE appears to be finding an effective filter for the lower frequencies.

Committee:

Yueh-Jaw Lin (Advisor)

Subjects:

Engineering, Mechanical

Keywords:

Piezoelectric; Lamb wave; health monitoring; wind tunnel; non-destructive evaluation; nondestructive evaluation; NDE

Mansour, RabihMode I Interlaminar Fracture Properties of Oxide and Non-Oxide Ceramic Matrix Composites
Doctor of Philosophy, University of Akron, 2017, Mechanical Engineering
This work provides a novel method for determining interlaminar fracture properties at both room and elevated temperature, offering the first glimpse of the interlaminar fracture behavior of CMCs at elevated temperatures. Interlaminar fracture properties play an important role in predicting failure of structural components for CMC materials. Elevated temperatures induce more severe conditions for interlaminar properties resulting in a weaker interlaminar toughness. The main challenges associated with determining interlaminar fracture toughness are the ability to measure crack growth without visual observation and to develop an experimental setup that can be used at both room and high temperature. Hence, a non-visual crack monitoring technique has been successfully introduced to estimate crack length in CMCs using electrical resistance. In a parallel effort, a wedge-loaded double cantilever beam method has been developed to determine the interlaminar fracture properties of CMCs at room and elevated temperatures. It has been found that the wedge method does not depend on the wedge material, as long as the correct coefficient of friction is taken into consideration. Additionally, the wedge method was found to be comparable to the traditional double cantilever beam method. The interlaminar fracture properties depend immensely on the composite microstructure and the weave architecture; the interlaminar crack propagates along the longitudinal fiber tows, passing through the porosities, which serve as stress concentration points. Moreover, depending on the fiber tows orientation along the crack propagation path, a rising or flat R-curve behavior can be seen for the same composite system. High temperature testing revealed that the energy required to initiate a crack at room temperature is greater than that at 815 °C. However, more energy is required to propagate the interlaminar crack at high temperature for some CMC systems (such as PIP SiC/SiNC). This behavior was attributed to softening of the matrix, which was evident when comparing crack growth rate at elevated temperature to room temperature. The data presented provides the first glimpse of the interlaminar fracture properties of CMCs at elevated temperatures. The wedge method was also verified using finite element analysis and micromechanics approaches. However, in order for a model to accurately predict the interlaminar behavior of the material and assist in optimizing specimen’s geometry, the mechanical response of the studied composite should be well-known, especially shear properties. Finally, a method for determining the out-of-plane electrical resistivity for composite materials has been proposed, while introducing the concept of length constant as a composite property. This method was utilized and successfully verified for two ceramic matrix composite systems with significantly different electrical properties. The out-of-plane electrical resistivity was found to be 8-9 times greater than the in-plane electrical resistivity.

Committee:

Gregory Morscher, Dr. (Advisor); Minel Braun, Dr. (Committee Member); Kwek-Tze Tan, Dr. (Committee Member); Gary Doll, Dr. (Committee Member); Alper Buldum, Dr. (Committee Member)

Subjects:

Materials Science; Mechanical Engineering

Keywords:

Ceramic Matrix Composites; Interlaminar Fracture Properties; Elevated Temperature Properties; Non-Destructive Evaluation; Electrical Resistance

Mejia, Paloma YasminSmart Systems for Damage Detection and Prognosis
Bachelor of Science in Applied Science, Miami University, 2005, School of Engineering and Applied Science - Manufacturing Engineering
Health monitoring of structures aims to characterize, asses, and predict damage initiation and propagation. Studies in this field are utilized to provide a damage analysis of structures that allows time-consuming inspections to be avoided. The aim of this work is to use experimental and computational tools to identify key parameters that characterize damage initiation and propagation. More specifically, this thesis will focus on experimental and computational modeling of damaged and healthy automotive exhaustive hangers to determine the main mechanical parameters that will serve to identify damage. The results obtained from computer simulations and laboratory experiments are thoroughly compared and analyzed to observe the changes in mechanical properties of the structure. The evolution of damage in the structure will translate in alterations in its mechanical properties. This report starts by providing a brief introduction to the field of health monitoring and a literature review of available methods for damage identification and prediction. The research approach is also described to introduce the reader to the main tools used in this study. Sections on experimental and computational analysis of the results follow which provides the main findings of this work. Finally, the conclusions and future work section of the report provides a summary of the main findings and the potential usage of these in future studies in the field of prognosis.

Committee:

Amit Shukla (Advisor)

Subjects:

Engineering, Mechanical

Keywords:

damage detection; non-destructive evaluation

Liu, XiaodongEffects of stress on intergranular corrosion and intergranular stress corrosion cracking in AA2024-T3
Doctor of Philosophy, The Ohio State University, 2005, Materials Science and Engineering
High strength AA2024-T3 alloy has pronounced susceptibility to intergranular corrosion (IGC) and intergranular stress corrosion cracking (IGSCC), which seriously limits the lifetime as engineering materials. Conventional investigation methods constrained a single crack per specimen can not characterize and evaluate multiple IGC cracks exist in real structures. In this study, a number of specially designed approaches have been developed to allow better understanding of the effects of applied and residual tensile and compressive stresses on growth kinetics of IGC and IGSCC in AA2024-T3. The stressed foil penetration technique and microfocal x-ray radiography along with electrochemical measurements are primarily used in this study. The breakdown potential was lower and the passive current density was higher under tension compared to unstressed samples. Microfocal x-ray radiography analysis resulted in IGSCC kinetics and characterized the morphology of individual cracks and generated the kinetics of localized IGC growth, which is not limited to the formation of a single crack and the competition between SCC cracks can be studied. Tensile stress along the transverse direction promotes linking of the IGC on the edges of the elongated grains to form a fracture surface that is nominally perpendicular to the transverse stress. Arrest marks were observed on the fracture surface associated with the transition from IGC to IGSCC. The current oscillations suggest that the linking process is discontinuous in nature. A constant load setup along with x-ray radiography was used to monitor multiple IGSCCs grow and competition. Interestingly, it was found in every experiment that the crack that resulted in ultimate failure was not the longest crack at early stages of the experiment, and long cracks tended to stop growing. The stifling of cracks appeared to intersect triple points at grain ends. The local grain boundary composition, and interaction between the susceptible microstructure and local environment under tensile stress are associated with intermittent anodic dissolution of precipitates and the adjacent grain boundaries in AA 2024-T3. The application of compressive stress at a level halfway to yield significantly reduced the growth kinetics of IGC in the perpendicular direction, but did not eliminate it totally. The breakdown and repassivation potentials increased, and passive current density decreased for samples under compression or with compressive residual stress.

Committee:

Gerald Frankel (Advisor)

Keywords:

High Strength Aluminum Alloy; Intergranular Corrosion; Stress Corrosion Cracking; Environmental Induced Cracking; Non-Destructive Evaluation; X-ray radiography; In Situ Study SCC; Foil Penetration Technique; Multiple Intergranular Cracking.

Kowalski, Benjamin JohnTransient SH-Wave Interaction with a Cohesive Interface
Master of Science, The Ohio State University, 2014, Mechanical Engineering
Characterization of material damage at the interface between two bodies using non-destructive evaluation (NDE) techniques is a field of study that is important from the point of view of both, research and application. In order to provide useful design engineering tools to the practicing engineer in the field of NDE it is necessary to build robust models that can be easily implemented. In the present thesis SH body waves are chosen as a representative candidate to assess material damage and degradation at an interface. In addition a well-established material damage law in the form of cohesive zones from fracture mechanics is considered. The combined effects of transient wave motion and the cohesive boundary condition at the interface are studied in order to develop a methodology for potential use in an NDE application scenario. Parameter variation studies offer promising results to the practicing engineer. Specifically, the trends of displacement and traction along the interface are evaluated between the bonded and damaged material conditions. Parameter variations allow for insight into how altering the material parameters and wave setup affect macro-behavior of the interface.

Committee:

Prasad Mokashi (Advisor); Daniel Mendelsohn (Committee Member)

Subjects:

Engineering; Mechanical Engineering; Mechanics

Keywords:

Non-destructive Evaluation; Wave Propagation; Cohesive Zones; Boundary Element Method; Computational Mechanics; Applied Mechanics

Appleby, Matthew P.High Temperature Damage Characterization Of Ceramic Composites And Protective Coatings
Doctor of Philosophy, University of Akron, 2016, Mechanical Engineering
Novel high-temperature experiments were conducted in ordered to address some of the most critical life-limiting issues facing woven melt-infiltrated, silicon carbide (SiC) fiber-reinforced SiC ceramic matrix composites (CMCs) as well as protective thermal and environmental barrier coatings (T/EBC). Heating of specimens was achieved using laser-based approaches that simulate the high heat-flux thermal gradient environments that these materials will be subjected to in service. Specialized non-destructive evaluation (NDE) and inspection techniques were developed to investigate damage modes and material response. First, in order to examine the capabilities of utilizing the emerging technique of electrical resistance (ER) measurement for use in high temperature mechanical testing in SiC/SiC CMCs, the temperature dependent ER response of several systems was determined. A model was developed to establish the contribution to overall ER from the individual composite constituents and applied thermal gradient. Then, elevated temperature tensile tests were performed to characterize the damage of composite materials to localized stress concentrations. Further experiments were done to assess the differences in damage mechanisms and retained tensile strength properties of uncoated SiC/SiC CMCs and EBC-CMC systems after prolonged exposure to high pressure, high velocity water vapor containing environments. Differences in damage modes were described using ER monitoring and post-test inspection. Localized strain fields were measured using a novel digital image correlation (DIC) technique and stress-dependent matrix crack accumulation was monitored using in-situ modal acoustic emission (AE). Coupled AE and thermography measurements were also used to describe failure of protective ceramic coatings due to the life-limiting case of thermal cyclic loading. Due to the complex nature of T/EBC failure, the decrease in coating life and durability due to thermal stress concentrations and degradation via molten calcium-magnesium-aluminosilicate (CMAS) infiltration was also examined. Finally, the use of ER measurements for damage characterization was extended to the complex case of creep and stress-rupture of damaged and undamaged composites as well as the dramatic increase in stress-rupture life to SiC/SiC CMCs from environmental barrier coatings. Post-test microscopy was performed to further explain differences in material response and damage morphology.

Committee:

Gregory Morscher (Advisor); Manigandan Kannan (Committee Member); Kwek Tze Tan (Committee Member); Craig Menzemer (Committee Member); Alper Buldum (Committee Member)

Subjects:

Mechanical Engineering

Keywords:

ceramic matrix composites; environmental barrier coatings, thermal barrier coatings; non-destructive evaluation; electrical resistance; acoustic emission; digital image correlation

Niroula, KushalAcoustic Monitoring of the Main Suspension Cables of the Anthony Wayne Bridge
Master of Science, University of Toledo, 2014, Civil Engineering
The 82 year old Anthony Wayne Bridge (AWB) in Toledo, Ohio is undergoing an extensive rehabilitation in two phases starting in construction season 2014. The plan is to first replace the approaches and rehabilitate the superstructure. Upon completion of the superstructure rehabilitation, steps to preserve the main suspension cables will be taken. Prior to taking action to preserve the cables, however, it is necessary to evaluate the condition of the cables. Therefore, as part of cable condition evaluation, an acoustic monitoring system was installed on July 2011 and has been continuously monitoring the main cables since then. Acoustic emission (AE) is a non-destructive technique which is practical for monitoring elements of bridges where invasive inspection is either difficult or costly. The AE system can be accessed remotely in real time and it does not cause any interruption to traffic. In the case of a suspension bridge, main cables are of primary concern as their condition cannot be assessed externally unlike other bridge components and they are fracture critical. This paper presents a case study on the application of the acoustic emission technique to the main cables of the AWB. Several laboratory experiments were planned and executed to develop understanding of the potential AE sources. Wire breaks were the primary AE sources under concern. Rain and frictional activities induced by traffic and wind events would create secondary and/or noise sources. The rain, friction and wire break were all simulated in the laboratory and it was verified that, by using a combination of parameters along with signal signatures, a wire break signal can be discriminated against other secondary or noise sources. The AE monitoring system on the AWB uses a series of 7 algorithms that analyze the parameters of each detected AE event. For each feature that meets or exceeds the value of the classification, it is assigned a source type ranging from 0 to 7. Thus for a wire break, the AE signal would meet or exceed all 7 criteria and would receive a `source type’ classification of `7’. The analysis of the data collected on the AWB during January 2013 to June 2013 (excluding May 2013) showed very high acoustic activity near sensors 1, 2, 14 and 15. After further examination it was found that those activities were of frictional nature caused by weather events and traffic induced movements. Many AE events were classified as high as `source type 6’ that occurred during extreme weather events and there was not any `source type 7’ event. This suggests that no wire breaks have been recorded so far. No wire breaks were discovered during the 2012 invasive inspection too, which supports the results from AE monitoring. Meanwhile, the system was unable to capture the signal produced by cutting of wire samples during the invasive inspection and this challenges the reliability of the monitoring system. An `Auto Sensor Test’ performed in March 2014 indicates that there has been degradation in the system’s performance. Many of the sensors do not seem to have proper coupling, thereby causing difficulty in effective signal-source interpretation. Very few AE events were observed in a review of data from the bridge closure period that started on March 17, 2014.

Committee:

Douglas Nims (Advisor); Douglas Nims (Committee Chair); Brian Randolph (Committee Member); Ahalapitiya Jayatissa (Committee Member)

Subjects:

Civil Engineering; Electrical Engineering

Keywords:

Acoustic Monitoring, Main Suspension Cables, Structural Health Monitoring, Non-Destructive Evaluation, Anthony Wayne Bridge, Acoustic Emission

Brath, Alexander J.Advanced techniques for ultrasonic imaging in the presence of material and geometrical complexity
PhD, University of Cincinnati, 2017, Engineering and Applied Science: Aerospace Engineering
The complexity of modern engineering systems is increasing in several ways: advances in materials science are leading to the design of materials which are optimized for material strength, conductivity, temperature resistance etc., leading to complex material microstructure; the combination of additive manufacturing and shape optimization algorithms are leading to components with incredibly intricate geometrical complexity; and engineering systems are being designed to operate at larger scales in ever harsher environments. As a result, at the same time that there is an increasing need for reliable and accurate defect detection and monitoring capabilities, many of the currently available non-destructive evaluation techniques are rendered ineffective by this increasing material and geometrical complexity. This thesis addresses the challenges posed by inspection and monitoring problems in complex engineering systems with a three-part approach. In order to address material complexities, a model of wavefront propagation in anisotropic materials is developed, along with efficient numerical techniques to solve for the wavefront propagation in inhomogeneous, anisotropic material. Since material and geometrical complexities significantly affect the ability of ultrasonic energy to penetrate into the specimen, measurement configurations are tailored to specific applications which utilize arrays of either piezoelectric (PZT) or electromagnetic acoustic transducers (EMAT). These measurement configurations include novel array architectures as well as the exploration of ice as an acoustic coupling medium. Imaging algorithms which were previously developed for isotropic materials with simple geometry are adapted to utilize the more powerful wavefront propagation model and novel measurement configurations.

Committee:

Francesco Simonetti, Ph.D. (Committee Chair); Gui-Rong Liu, Ph.D. (Committee Member); Peter Nagy, Ph.D. (Committee Member)

Subjects:

Acoustics

Keywords:

Ultrasonics;Non-destructive evaluation;Anisotropy;Guided wave tomography;Total focusing method

Gordon, Neal AMaterial Health Monitoring of SIC/SIC Laminated Ceramic Matrix Composites With Acoustic Emission And Electrical Resistance
Master of Science in Engineering, University of Akron, 2014, Mechanical Engineering
Ceramic matrix composites (CMC) composed of Hi-Nicalon Type S™ fibers, a boron-nitride (BN) interphase, and pre-impregnated (pre-preg) melt-infiltrated silicon / silicon-carbide (SiC) matrix have been studied at room-temperature consisting of unidirectional and cross-ply laminates. Quasi-static, hysteretic and uniaxial tensile tests were done in conjunction with a variety of temporary, laboratory-based material health-monitoring techniques such as electrical resistance (ER) and acoustic emission (AE). The mechanical stress-strain relationship paired with electrical and acoustic measurements were analyzed to expand upon current composite knowledge to develop a more fundamental understanding of the failure of brittle matrix laminates, their constituents, and interactions. In addition, a simple but effective method was developed to allow visual confirmation of post-test crack spacing via microscopy. To enhance fidelity of acquired data, some specimens were heat-treated (i.e. annealing) in order to alter the residual stress state. Differences in location, acoustic frequency, and magnitude of matrix cracking for different lay-ups have been quantified for unidirectional and [0/90] type architectures. Empirical results shows complex hysteretic mechanical and electrical behavior due to fiber debonding and frictional sliding of which no general model exists to capture the essence of this CMC system. The results of this work may be used in material research and development, stress analysis and design verification, manufacturing quality control, and in-situ system and component monitoring.

Committee:

Gregory Morscher, Dr. (Advisor); Wieslaw Binienda, Dr. (Committee Member); Tirumalai Srivatsan, Dr. (Committee Member)

Subjects:

Aerospace Materials; Mechanical Engineering

Keywords:

Ceramic Matrix Composite,CMC;Aerospace;Non-Destructive Evaluation,NDE;Structural Health Monitoring,SHM;Composites;Acoustic Emission;Electrical Resistance