京都大学 / 0048 / 新制・課程博士 / 博士(農学) / 甲第21140号 / 農博第2266号 / 新制||農||1057(附属図書館) / 学位論文||H30||N5114(農学部図書室) / 京都大学大学院農学研究科森林科学専攻 / (主査)教授 藤井 義久, 教授 吉村 剛, 教授 松浦 健二 / 学位規則第4条第1項該当 / Doctor of Agricultural Science / Kyoto University / DFAM

The application of piezoelectric sensors such as the ultrasonic transducer has significantly enhanced the fields of nondestructive evaluation (NDE). Their application of piezoelectric materials allows for the sensing of low energy, high frequency acoustic emission (AE) events such as fatigue cracking in metals and delamination in composites. Utilizing the physical characteristics of these AE waves, the location of these structural defects can then be source located by means of time-of-flight trilateration. The real time sensing of such events has led to the field of structural health monitoring (SHM) and has revolutionized NDE. Furthermore, with the application of modern micro-electromechanical system-based (MEMS) technology, the fields of NDE and SHM can be improved greatly, and sensing instrumentation simplified. A novel piezoresistive-based MEMS strain sensor is presented as this improvement to NDE and SHM. The ultrathin silicon membrane-based (USM) strain sensor's ability to capture an AE signal is demonstrated by a Hsu-Nielsen source and shows comparable frequency content to a commercial piezoceramic ultrasonic transducer. To the knowledge of the authors, this makes the USM strain sensor the first known piezoresistive strain sensor capable of recording low energy AE. The novel improvements to NDE and SHM arise from the sensor's low minimum detectable strain and wide frequency bandwidth, enabling a dual-use application of both AE and static strain sensing. The USM sensor's ability to document quasi-static bending is demonstrated and once again compared with an ultrasonic transducer, which provides no significant response. This dual-use application is proposed to effectively combine the uses of both strain and ultrasonic transducer sensor types within one sensor, lending itself novel and useful to NDE and SHM. The potential benefits include enhanced sensitivity, reduced sensor size and cost, and reduced instrumentation complexity. / Master of Science / Visual inspection for cracks and defects has long been staples of assessing structural health throughout human history. These surface imperfections are an obvious hindrance to structural integrity and routine observation and inspection is needed to ensure a structure's safety. With the progression of technology and the discovery of piezoelectric materials, more advanced methods have been devised to detect and source locate not only surface level but sub-surface cracking. This has been accomplished through the use of piezoelectric ultrasonic transducers to monitor the propagation of acoustic emission (AE) vibrations, which are the result of energy redistribution by events such as cracking. The remote monitoring of AE events has led to the growth of the nondestructive evaluation (NDE) field, where these cracks and defects can be located by the detection of their AE source. These transducers, however, are met with limitations in their applications. Operating off the piezoelectric effect allows for a superb response to low energy, high frequency excitation characteristic of AE, but results in no response to quasi-static strain measurements, such as that of a slowly applied bending load on a plate. In the work herein, modern micro-electromechanical system (MEMS) based technology is utilized to devise a sensor capable of both AE and static strain measurements. The dual sensing of both of these measurements can allow for the source location of cracking events along with the monitoring of structure strain, effectively combining the use of two sensors into one. This dual-application use can have a great impact on the evaluation of critical structures like bridges and aircraft and simplify and reduce costs inherent to nondestructive evaluation.

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Thesis: Sc. D., Massachusetts Institute of Technology, Department of Mechanical Engineering, 1980 / Includes bibliographical references. / by Afarin Ordubadi. / Sc. D. / Sc. D. Massachusetts Institute of Technology, Department of Mechanical Engineering

The effect of coatings on the interfacial strength of a hollow glass microsphere/polyester composite and their capacity to endure thermal stresses were studied by mechanical testing and an active Acoustic Emission (AE) method. AE was postulated to provide more local information at or near the glass/polyester interface due to the sensitivity of elastic waves to the rigidity of polymer chains at the glass sphere/polyester interface compared to mechanical testing. Three frequency ranges identified by multivariate statistics yet consolidated for the initial analysis into a band of 140-240 kHz, were found to be changing with the different coated glass filler for different glass content and heating state. Considering the acoustic behavior of the composites containing different levels of glass sphere content (1-10 vol%), a lower concentration (aminoethylamino)-propyl-trimethoxy silane coated glass (AS6), demonstrated the lowest attenuation after heating (associated with higher interfacial strength). As anticipated, the highest attenuation after heating was observed for uncoated glass (16K) due to expectedly weaker associations. Mechanical testing results after heating were consistent with the AE response for AS6 and 16K for this frequency range. Trends in amplitude for the three narrower, frequency ranges of 130-160 kHz, 180-220 kHz and 230-260 kHz were compared against that of 140-240 kHz and very small differences were observed. It was found that the frequency range of 130-60 kHz was more descriptive of the changes of interfacial strength in composites (at 10 vol%), being consistent with the mechanical test results. Considering the AE response at 130-160 kHz and mechanical data, higher concentration (aminoethylamino)-propyl-trimethoxy silane (AS12), better endured thermal stresses compared to other coatings. A smaller trial looked at the effect of moisture aging and subsequent thermal cycling on the glass/polymer interface strength as another method to perturb the interface. Attenuation for the band of 180-260 kHz was studied for aged versus non-aged composites. The commercial coating, L21 demonstrated a better moisture resistance before and after thermal cycling compared to uncoated glass spheres. An improved evaluation of interfacial strength in glass/polyester was expected using AE technique versus mechanical testing due to its higher sensitivity to changes in internal structure, however; no significant improvement compared to mechanical testing was observed, at least based on the analysis technique currently being used. / Thesis / Master of Applied Science (MASc) / Sheet molded compound (SMC) is a polymer material reinforced by fibers providing a combination of light weight and high mechanical properties and is used in automotive industry. Light weight fillers (hollow glass microspheres) are used to obtain further weight reduction; however, addition of these fillers leads to reduced mechanical properties and further problems during painting process known as ‘paint popping’. The former is due to uncertain interfacial state between polymer and fillers and the latter results from different thermal expansion behavior of the polymer and filler materials while the material is exposed to high temperatures for painting process. This research aims to devise a highly sensitive technique and evaluate its suitability compared to mechanical testing for investigation of the origin of aforementioned problems. Acoustic Emission (AE) is a method with high sensitivity to changes in internal structure of the material which is postulated to provide a better insight on material microstructure compared to more commonly used method i.e. mechanical testing. Use of interfacial controlling agents was examined to reduce the problems as a result of introduction of fillers. The effect of using surface modified fillers and the effect of thermal stresses on material was investigated using AE technique. Application of AE method in this study provided a good insight about the changes in material internal structure; however, it did not demonstrate a significant improvement in detecting the origins of studied problems compared to mechanical testing at least based on the analysis technique used in this study.

The acoustic emission technique is an effective way to acquire crack information from material bodies at the microscopic level. Monitoring of the acoustic emission events provides a deeper understanding regarding the structural health status of critical constructions such as bridges, railways, pipelines, pressure vessels, etc. Thanks to the acoustic emission monitoring systems, it is possible to avoid catastrophic events and save lives, time, and money. For this reason, efforts to develop new acoustic emission sensor technologies, as well as the use of current acoustic emission sensors in new research fields, will contribute to the limited literature sources. Optical sensing systems provide good alternatives to the existing sensing technologies because of their wide range of detection bandwidths, adaptation to harsh environments, and low sensitivity to electromagnetic interference. For this reason, the first part of this thesis demonstrates an optoacoustic sensing methodology that enables the detection of acoustic emissions by optics. This sensing system consists of thin-film optical filters (TFOF) and an elastic microcavity layer. The sensing mechanism is similar to the Fabry Perot structures and it relies on resonance shifts of the cavity when there is a change in the cavity thickness similar to the Fabry Perot structures. Thus, the design, fabrication, and demonstration steps of a Fabry Perot elastic microcavity have been presented. Throughout the fabrication efforts, a new deposition protocol was developed. This deposition technique has enabled the deposition of TFOF on flexible substrates via the RF-sputtering technique. Thus, a new sensing configuration has been developed using flexible optical components. In the second chapter, an optical sensing methodology based on tunable spectral filters and flexible optical components is introduced. The design, fabrication, realization, and characterization of a proof-of-concept optomechanical sensor have been presented. The design step includes optical, mechanical, and optoacoustic correlation simulations using the Transfer Matrix Method, finite element analysis, and analytical models. Moreover, the fabrication part includes multilayer deposition on silica and flexible substrates using the RF-Sputtering technique and integration of these optical components into a 3D-printed housing together with electronic components. Eventually, the performance evaluation of the optomechanical sensor has been carried out and the experimental results showed that the sensor resonance frequency is around 515 Hz and the sensor is capable of detecting static loadings from 50 Pa to 235 Pa values. In the fourth chapter, seismic vulnerability analysis of a coupled Tank-Piping System has been performed using traditional acoustic emission sensors. Real-time performance evaluation of the pipeline as well as the structural health status of the critical parts were monitored. As a result, deformation levels of each critical part were investigated, and the processing of acoustic emission signals provided a more in-depth view of damage level of the analyzed components. Throughout the thesis, TFOFs are an integral part of this thesis. Therefore, both the design and simulation of TFOFs play a crucial role throughout this research work. The Transfer Matrix Method is used to simulate the optical performance of TFOFs. Moreover, in the final chapter, an automated design framework is presented for the design of TFOFs using a nature-inspired machine learning approach called Genetic algorithm. This design approach enables the design of sophisticated geometric configurations with unique optical capabilities. Therefore, not only the improvement of sensor response but also the new ways in the development of novel optical systems are demonstrated in this final chapter.

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