Analysis of Multiple Bonded Patch Interaction Simple Design Guidelines for Multiple Bonded Repairs in Close Proximity

Abstract

The use of bonded composite patches to extend the life of aging metal airframes continues to grow as air forces and airline companies operate larger fleets beyond their original design lives. The crack-slowing power of bonded composite patches is well-known; often the process can be accomplished at a few percent of the cost of replacing the damaged component. However, care must be taken in the design of repairs to multiple site fatigue and corrosion damage so the repairs in close proximity do not create additional structural problems by inducing high stresses into the area of the repair.

The current paper discusses recent modeling efforts to quantify the effects of multiple bonded composite patches in close proximity. It is well-established that a single structural repair attracts load into the locally stiffened area around the patch; further, single-sided repairs induce significant bending in the skin. The paper addresses the situation when two or more structural repairs occur near each other, and illustrates with simple design rules the acceptable practices for this case.