Identifier

etd-10282011-162414

Degree

Doctor of Philosophy (PhD)

Department

Mechanical Engineering

Document Type

Dissertation

Abstract

Health monitoring of the composite structures is an important issue that must be addressed. Embedded sensors could be an effective way to monitor the health of composite structures continuously and which could also avoid the catastrophic failures of composite structures. Piezoelectric-fiber-composite sensors (PFCS) made from micro-sized Lead Zirconate Titanate (PZT) fibers have great advantages over the traditional bulk PZT sensors for embedded sensor applications. PFCS as an embedded sensor will be an ideal choice to continuously monitor the stress/strain levels and health conditions of composites. This work presents a critical study on using PFCS as an effective embedded sensor within the composite structures. Firstly, a series of carefully planned experiments are conducted to study the sensor performance based on characteristics like transfer function, sensitivity, nonlinearity, resolution, and noise levels. A numerical simulation study is performed to understand the local stress/strain field near the embedded sensor region inside composite specimen. High stress-concentration regions are observed near the embedded sensor corner edge. In-plane tensile, in plane tension-tension fatigue, flexural, and short beam strength tests are performed to evaluate the strengths/behavior of the composites (composite laminates and composite sandwich structures) containing embedded PFCS sensor. Overall PFCS seems to have high compatibility with composites and the reduction in strength values are within the permissible limits. Embedded PFCS’s voltage output response under tension-tension fatigue loading conditions has been recorded simultaneously to study their ability to detect the changes in input loading conditions. A linear relationship has been observed between the changes in the output voltage response of the sensor and changes in the input stress amplitude. This means that by constantly monitoring the output response of the embedded PFCS, one could effectively monitor the magnitude of stress/strain acting on the structure. Experiments are also performed to explore the ability of the embedded PFCS to detect the damages in the structures using modal analysis and impact techniques. PFCS are able to detect defects like delamination and cracks inside the composite structure using these two methods. Hence embedded PFCS could be an effective method to monitor the health of the composite structures’ in-service conditions.

Date

2011

Document Availability at the Time of Submission

Secure the entire work for patent and/or proprietary purposes for a period of one year. Student has submitted appropriate documentation which states: During this period the copyright owner also agrees not to exercise her/his ownership rights, including public use in works, without prior authorization from LSU. At the end of the one year period, either we or LSU may request an automatic extension for one additional year. At the end of the one year secure period (or its extension, if such is requested), the work will be released for access worldwide.

Committee Chair

Wahab, M. A.

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