Title page for ETD etd-08292008-063445


Type of Document Master's Thesis
Author Halverson, Howard Gerhard
URN etd-08292008-063445
Title Improving fatigue life predictions :theory and experiment on unidirectional and crossply polymer matrix composites
Degree Master of Science
Department Engineering Mechanics
Advisory Committee
Advisor Name Title
Curtin, William A. Jr. Committee Chair
Hajj, Muhammad R. Committee Member
Reifsnider, Kenneth L. Committee Member
Keywords
  • composite
  • fatigue
  • unidirectional
  • crossply
  • prediction
Date of Defense 1996-05-15
Availability restricted
Abstract
A method is presented by which fatigue life predictions of polymer matrix composites may be improved. First a "critical element", whose failure defines global failure of the material. is identified. The global stiffness changes of the specimen during a fatigue test are monitored and taken to be inversely proportional to the increase in applied stress on the critical element. Using a cumulative damage model, the complicated stress history of the critical element is reduced to a "critical element SN curve", which defines the fatigue response of the critical element. The residual strength of the critical element may then be continuously evaluated to predict failure. The statistical nature of material strength is accounted for by forcing the critical element SN Curve to yield a specimen initial strength distribution in fatigue which is equivalent to the quasi-static tensile distribution. In contrast to most methods, the predictions are based on the stiffness history of the specimen in question, rather than on generalized phenomenological models. The critical element SN curve is then applied to (90°/0°) crossply materials to evaluate their fatigue response. Simulations and the variation of experimental parameters are examined for their effect on the predictions.

The unidirectional fatigue predictions were vastly improved over the traditional SN Curve. While the crossply predictions were not as good, they still demonstrated the applicability of the critical element SN curve to a material with a different geometry. Additionally. such a method may have application in real-time durability evaluation of composite components.

Files
  Filename       Size       Approximate Download Time (Hours:Minutes:Seconds) 
 
 28.8 Modem   56K Modem   ISDN (64 Kb)   ISDN (128 Kb)   Higher-speed Access 
[VT] LD5655.V855_1996.H358.pdf 25.14 Mb 01:56:23 00:59:51 00:52:22 00:26:11 00:02:14
[BTD] next to an author's name indicates that all files or directories associated with their ETD are accessible from the Virginia Tech campus network only.

Browse All Available ETDs by ( Author | Department )

dla home
etds imagebase journals news ereserve special collections
virgnia tech home contact dla university libraries

If you have questions or technical problems, please Contact DLA.