The Development of a Finite Element Program to Model High Cycle Fatigue in Isotropic Plates

<p>As part of a joint AFRL-DAGSI turbine blade research effort a computer program has been developed that uses a von Karman large-deflection two-dimensional finite element approximation to determine stress levels and patterns in isotropic thin plates. The dynamic loading of various plates has been carried out in order to model a high cycle fatigue situation. The research considered the various effects of mode shapes resident frequency non-linear cyclic effect endurance limits and stress variations within a high cycle fatigue environment. Two main initiatives were taken. First a transient analysis tool was developed that calculates stress and displacement patterns over a period of time. This analysis also included the effects of damping. The second initiative developed a tool to calculate the eigenvalues (natural frequencies) and eigenvectors of a plate with a given geometry. The results indicated that it is possible to model fatigue at high frequencies using FE analysis and compare these findings with experimentation incorporating a shaker table. In this research different geometries of plates were investigated to represent turbine blade configurations. One square plate and three trapezoidal plates were investigated. It was found that a linear relationship could be found between the loading amplitude and the resulting maximum stress. This relationship allows for the prediction of the needed loading amplitude to cause high cycle fatigue. It was also determined that by altering the geometry of the plate the needed loading frequency or loading amplitude to reach a stress level that would initiate cracks could be minimized.</p><p>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.</p><p>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.</p><p>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.</p><br>