Date of Award

6-1997

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Department of Aeronautics and Astronautics

First Advisor

Shankar Mall, PhD

Abstract

Post-repair fatigue crack growth was investigated in 3.175, 4.826, and 6.35 mm thick aluminum panels asymmetrically repaired with boron/epoxy composite patches bonded to the plates with FM73 sheet adhesive. Patches were uniaxial with patch to panel stiffness ratios ranging from 0.46 to 1.3. Experimental fatigue tests were carried out at 120 MPa, R=0.1, and 10 Hz (sinusoidal) to measure patched and unpatched face crack lengths, center crack opening displacements, and selected strains. Crack growth data was acquired using optical, eddy current, and post-test analysis methods. Crack growth rates were calculated using the incremental polynomial method. A three-layer Mindlin plate finite element model was used as an analytical technique to predict patched and unpatched face reaction loads and displacements. These parameters, in conjunction with the modified crack closure method, were then used to compute crack growth rates for the specimens using experimentally determined material constants and the Paris Law relationship. Comparisons of the experimental to analytical curvatures of repaired panels showed excellent agreement. Crack growth rate predictions fall consistently within their experimental counterparts at the unpatched face. The present analysis is, thus, an effective tool to investigate the behavior of fatigue crack growth in aluminum panels repaired with composite patches.

AFIT Designator

AFIT-DS-ENY-97-04

DTIC Accession Number

ADA327983

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