Open Access

ARTICLE

Bonded Composite Patch Geometry Effects on Fatigue Crack Growth in Thin and Thick Aluminum Panels¹

S. Mall^2,3, J. J. Schubbe^1,4

1 The views expressed in this article are those of the authors and do not reflect the official policy or position of the United States Air Force, Department of Defense, or the U.S. Government
2 Department of Aeronautics and Astronautics, Air Force Institute of Technology, Wright-Patterson Air Force Base, OH
3 To whom correspondence be addressed at AFIT/ENY, Bldg. 640, 2950 Hobson Way, Air Force Institute of Technology, Wright-Patterson AFB, OH, 45433-7765, Tel: 937-255-3636 x4587, email: Shankar.Mall@afit.edu
4 Mechanical Engineering Department, U.S. Naval Academy, Annapolis, MD

Structural Longevity 2009, 2(1), 25-47. https://doi.org/10.3970/sl.2009.002.025

Abstract

Effects of various geometric factors on the crack growth behavior of thin and thick aluminum panels repaired with asymmetric boron/epoxy bonded composite patch were investigated. Two widths, three patch lengths, three panel thicknesses and several patch-to-panel stiffness ratios were considered. Asymmetric repair introduces initial thermal curvature (or bending) in the repaired panels. The radius of curvature decreased with increase in the patch length in the thicker plates (6.350 or 4.826 mm thickness). On the contrary, the radius of curvature in the thin plate (i.e. 3.175 mm thickness) increased with increase in the patch length. The effects of stiffness ratio and patch width on the initial curvature of the asymmetrically repaired panel depended upon the length of the bonded patch, thickness of the repaired panel and stiffness ratio. There was increase in the fatigue life of the repaired panel with increase of stiffness ratio at a given patch length for all three thicknesses. For repairs of stiffness ratio equal to 1.0, the patch length had practically no or small effect on fatigue life of the repaired thick panels, but increase in patch length improved the fatigue life of the repaired thin panel. Overall, the effects of stiffness ratio and patch length on the fatigue life improvement of the repaired panel are complex which require further studies. The crack growth rate in the thick repaired panels (6.350 or 4.826 mm thickness) up to crack length before any debond occurred was not affected by the patch length. On the other hand, the longer patch decreased in the crack growth rate relative to the shorter patch in the thin repaired panel (3.175 mm). The higher stiffness ratio provided the lower crack growth rate or longer fatigue life for both thin and thick repaired plate for a given patch length. Finally, there was no effect of the patch width on the crack growth rates up to crack length equal to the uniform width of patch. There was similar growth pattern of debond (i.e. only near the immediate area of the crack), regardless of patch length and width as well as stiffness ratio up to the crack length either equal to uniform width of the patch (i.e. before patch taper portion) or when it would have grown unstable in the unrepaired specimen. Thereafter, a significant debond growth occurred.

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