Date of Award

12-2014

Degree Name

Doctor of Philosophy

Department

Mechanical and Aerospace Engineering

First Advisor

Dr. Muralidhar K. Ghantasala

Second Advisor

Dr. Daniel Kujawski

Third Advisor

Dr. Peter A. Gustafson

Fourth Advisor

Dr. John Patten

Keywords

Fatigue sensor, fatigue monitoring, structural health monitoring, micro-fabrication, UV lithography, fatigue life

Abstract

A novel fatigue monitoring sensor (FMS) is designed, fabricated and tested for detecting and monitoring the fatigue damage and estimating the remaining life of structures and components subjected to cyclic loads. The concept is based on the characteristics of stress / strain life cycle relationship of engineering materials. Sensor consists of alternate slots and strips having different strain magnification factor with respect to the nominal strain. The sensor is designed in such a way that the strips will experience the strain which closely resemble the actual strain distribution in the notch or critical area of the component. The sensor can be placed outside the notch but still would experience the same fatigue damage as the notch tip. The sensor is attached to the surface of structural member which is being monitored. The strips fail in a sequential manner from the strip experiencing the highest stress/strain magnification to the lowest. Each strip failure corresponds to the particular fatigue damage accumulated by the critical location of the structure being diagnosed. The fatigue sensor monitors the actual fatigue damage of the structural component and can be used for both diagnosis and prognosis of the remaining useful life.

This research mainly involves the design and simulation of the fatigue sensor with respect to different geometrical parameters and materials. Numerical and analytical modeling was carried out to determine the optimal design. The finite element analysis is carried out using COMSOL and ANSYS softwares. Fabrication of the fatigue sensor constitutes a major part too. The prototype fatigue sensors were fabricated using Wire EDM (-Electro Discharge Machining) and microfabrication technologies. Relative advantages of these processes are established and discussed. The commissioning of the sensor with a suitable data acquisition system and testing it under different conditions is also an important part of the work. Analysis of the obtained experimental data constitute the final part.

Access Setting

Dissertation-Open Access

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