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The Air Force Institute of Technology, in conjunction with the Structural Health Monitoring branch of the Air Force Research Laboratory, is researching methods of determining effects of notch location and size on beam structures using modal frequency analysis. This thesis explores the ability to detect included notches of varying magnitudes and locations within the frequency domain of an isotropic cantilever beam. A series of experiments employing centerline-notched 2024 T3 and 2024 O aluminum beams was used to determine whether natural frequency measurement in beam structures is a valid mechanism for damage detection. Each specimen was excited by a strain actuator and the dynamic beam response measured using a laser Doppler vibrometer, thereby obtaining eigenvalues and eigenvectors for each case. Results are analyzed for frequency degradation trends based on location, notch length, and vibration mode. Correlation is made between experimentally observed values, ABAQUS modeling, and a series of MATLAB predictions utilizing a finite element solution approach developed by Perel and Palazotto (2002). It is determined that modal frequency analysis is an adequate global indicator of damage presence and magnitude, which reduces global stiffness. Damage location is not easily identifiable from the data. It is also determined that ABAQUS and the MATLAB solution approach are accurate to within 10% of experimental resonant frequency values for short notch lengths and low vibration modes, but highly deviant from experiment for longer notch lengths and higher modes. Residual stresses contained in the 2024 T3 specimens from cold working are determined to have minimal effect on beam dynamics.This work has been selected by scholars as being culturally important, and is part of the knowledge base of civilization as we know it. This work was reproduced from the original artifact, and remains as true to the original work as possible. Therefore, you will see the original copyright references, library stamps (as most of these works have been housed in our most important libraries around the world), and other notations in the work.This work is in the public domain in the United States of America, and possibly other nations. Within the United States, you may freely copy and distribute this work, as no entity (individual or corporate) has a copyright on the body of the work.As a reproduction of a historical artifact, this work may contain missing or blurred pages, poor pictures, errant marks, etc. Scholars believe, and we concur, that this work is important enough to be preserved, reproduced, and made generally available to the public. We appreciate your support of the preservation process, and thank you for being an important part of keeping this knowledge alive and relevant.
