SEDL / STP / STP927-EB / STP29061S

Enhanced Stop-Drill Repair Procedure for Cracked Structures

Landy, MA
Engineering manager, Fatigue Technology, Inc., Seattle, WA

Armen, H
Group head and Engineering specialist, Structural Mechanics, Grumman Aerospace Corp., Bethpage, NY

Eidinoff, HL
Group head and Engineering specialist, Structural Mechanics, Grumman Aerospace Corp., Bethpage, NY

Pages: 31    Published: Jan 1986

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Abstract

A repair technique for cracked structures that consists of stop drilling the crack tip is examined. This repair procedure is enhanced by cold expanding the stop-drill hole and by installation of an interference-fit fastener. An experimental and analytical investigation of the effectiveness of the enhanced stop-drill procedure is presented. The analysis consists of elastic-plastic stress analysis utilizing the finite element approach to determine residual stress distributions, stress intensity factors around the stop-drill holes due to cold expansion, and stress intensity factors along the fatigue crack paths followed by crack initiation and crack growth life predictions. Comparisons of the life predictions and fatigue test data are also presented. The results indicate that cold expansion and interference-fit fastener installation improve the fatigue performance of stop-drill holes through crack tips by factors ranging from 3 to 20.