Date of Award
Yun Bo Yi
Composites, FBG sensors, Monitoring, Polymers, Residual stresses, Strains
By embedding both a single fiber Bragg grating (FBG) sensor and a thermocouple (TC) during the manufacturing for extreme environment applications of certain classes of materials such as metals and polymers, a novel in-situ approach was developed to precisely monitor their entire manufacturing processes. This novel monitoring technique was able to identify many characteristic points during the curing of room and high-temperature epoxies and the solidification processes of metal alloys composed of tin and bismuth which were selected in this research purely for verification purposes. Some of the characteristic points identified for the epoxies were: (i) the gel point, (ii) the start of cure, (iii) the end of cure, (iv) the end of the manufacturing cycle, etc. For the tin/bismuth alloys, the technique was used for the first time to (i) identify the beginning and end of solidification and (ii) to construct the phase diagram of the alloys. It was demonstrated that the FBG sensor-based technique is better suited than the existing TC-based technique to detect the phase transitions of the alloys. The solidification process of water was also monitored and compared to the solidification process of the metals. The water solidification research was subsequently extended to simulate ice formation on transmission line conductors and to determine if the newly proposed FBG/TC method could be used as an ice monitoring method in service.
A novel heat balance approach was presented to identify the degree of cure for the epoxies and to estimate the end of solidification in the alloys. The heat balance approach was verified using the Flory-Stockmayer theory for identifying the gel point in polymers. By using the FBG measurements and a combination of linear elastic models, a novel, yet straightforward approach was presented to determine the residual stresses in a single fiber/polymer composite. Further, multiple factors that impact the calculation of axial strain evolution using fiber Bragg grating (FBG) sensors were thoroughly investigated and verified by analyzing the cooling of the epoxies, the tin/bismuth alloys, and ice.
The proposed monitoring technique could significantly improve the current capability to (i) measure the degree of cure of polymers, (ii) determine the residual strains and stresses in single fiber composites with polymer and metal matrices, (iii) assess the strain evolution during the solidification of metals, (iv) recreate the phase diagrams of metal alloys, (v) estimate stresses in solidified metal parts, (vi) monitor icing and deicing on transmission lines, and many others. Since the specimen preparation is straightforward, the proposed method can be routinely practiced, and the measurements can be completely automated. The techniques could provide a much-needed tool for rapid but accurate assessment of materials for extreme environment applications.
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Khadka, Sabuj, "Monitoring of State Transitions in Extreme Environment Application Materials Using Fiber Bragg Grating Sensors" (2022). Electronic Theses and Dissertations. 2024.
Received from ProQuest
Mechanical engineering, Materials science