Date of Award

Fall 1999

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Mechanical & Aerospace Engineering

Program/Concentration

Aerospace Engineering

Committee Director

Brett A. Newman

Committee Member

Chuh Mei

Committee Member

Jeng-Jong Ro

Call Number for Print

Special Collections; LD4331.E535 Y87

Abstract

This thesis investigates the influence of feedback control, and other factors associated with loading characteristics, on fatigue damage reduction and long-term integrity of aircraft structural components. An actively controlled flexible aircraft model and a new state space modeling procedure for crack growth are utilized to uncover important factors which influence airframe crack growth. A matrix of simulation test cases is constructed to cover such variables as open-loop operation, nominal closed-loop operation, perturbed closed-loop operation (i.e., feedback gain variation), nominal maneuver profile, perturbed maneuver profile (including overload strength and frequency), atmospheric gust, and mean stress level. Simulation output data including crack length vs. number of load cycles is used to predict long-term structural integrity, and more importantly to expose the critical factors influencing this integrity. Results indicate feedback control can provide significant leverage on crack growth. Results also indicate existence of nonintuitive optimal overload strength and frequency values which minimize crack growth. Cases exist where higher overloads reduce crack growth. Such results have important implications for designing new control logic which exploits this behavior.

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DOI

10.25777/xc74-8x95

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