Available at: http://digitalcommons.calpoly.edu/theses/1023
Date of Award
MS in Aerospace Engineering
Effect of Fatigue Cycle Loading Amplitude Tension-Tension on Composite Laminated Plates with Delamination
Composite materials provide many mechanical advantages; however, they are susceptible to failure or delamination due to impact, high concentrated stresses and fatigue produced by high loading and dripping weight due to poor manufacturing processes yielding to delamination. The objective of enhancing delamination in the laminated composite structural panel’s elements is to control the response of the composite structures in order to prevent catastrophic failure due to excessive deformation. The main scope of this thesis is to study the effect of a different amplitude fatigue cycle in tension-tension on a carbon fiber laminated composite plates with initial delamination to determine the maximum number of loading cycles required to propagate the initial delamination and failure through the preformed delamination. The study also, will encompass the comparison with numerical analysis models using Nastran/Patran software .
The laminate composite plates were fabricated with woven prepreg carbon fiber with an initial delamination and tested under tensile and constant amplitude cycle loading. The tensile characteristics of the laminated composite plates were determined using the standard test. The number of the fatigue cyclic was determined for fatigue tests with different maximum stresses of 72 .5%, 69.5%, 66.5%, 63.5%, and 60.5% from the average ultimate failure loading. A linear static numerical analysis was performed using MSC Patran/Nastran to correlate a finite element model and test data for the tensile load cases. The finite element model was validated by comparing the deformation shape and the predicted high stress concentration areas of the test specimen during the experimental analysis with the predicted numerical analysis.
The flexural stiffness is predicted to be reduced by approximately 200% by the addition of an initial delamination. The fatigue life of the laminated composite plates tested would extend over 20000 cycles at a load rate between 55% and 60% of the ultimate failure loading if the input load drops above 10%. The numerical analysis performed showed a difference of 41% to the experimental analysis.