Semester

Spring

Date of Graduation

2005

Document Type

Dissertation

Degree Type

PhD

College

Statler College of Engineering and Mineral Resources

Department

Mechanical and Aerospace Engineering

Committee Chair

James Smith.

Abstract

Aging of aircraft structures is mostly associated with fatigue cracking, de-bonding and corrosion. Detection and characterization of the structural defects at the initiation stages makes it a great challenge for any inspection technology. This study proposes a new solution for the nondestructive evaluation problem by using a magnetic flux method for non-ferromagnetic materials and provides a new neural network tool that predicts crack profiles in three dimensions by solving the inverse problem, where available neural networks can solve it in two dimensions only.;The discontinuity resulting from a crack produces disturbance to the distribution of electrical current density in the structure and as a result the magnetic field around the crack will change. The magnitude of the disturbance is determined by the size and shape of the crack. Therefore, it is possible to evaluate the crack area by magnetic field measurements. The magnetic fields from the plate edges and the wires that carry the current are very strong compared to the magnetic field produced by the crack. A new plate, called a dummy plate, is used to minimize the effect of the magnetic fields produced by the plate edges. This study proves the effectiveness of the dummy plate and shows the measurable change in the magnetic signal around the crack.;As a result of this work, a tool is now available that can solve the nondestructive evaluation problem and the inverse problem in three dimensions and has the capability to provide an enhanced assessment tool for judgment and decision-making which will improve the safety of metallic structures and save people lives.

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