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.
| Identifer | oai:union.ndltd.org:VTETD/oai:vtechworks.lib.vt.edu:10919/115790 |
| Date | 17 July 2023 |
| Creators | Stiefvater, Jason Matthew |
| Contributors | Mechanical Engineering, Ng, Wing Fai, Wicks, Alfred L., West, Robert L. |
| Publisher | Virginia Tech |
| Source Sets | Virginia Tech Theses and Dissertation |
| Language | English |
| Detected Language | English |
| Type | Thesis |
| Format | ETD, application/pdf |
| Rights | In Copyright, http://rightsstatements.org/vocab/InC/1.0/ |
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