Experimental Investigation on the Effects of Cold Expansion of Fastener Holes

Abstract

A series of experimental investigations concerning the residual stress fields at cold‐expanded fastener holes and of the behavior of fatigue cracks at such holes has been conducted. These studies have included measurement of the initial, cold‐work‐induced residual stress fields at both uncracked and cracked holes and the performance of both constant amplitude and spectrum fatigue crack growth tests.

Numerical study of the optimum degree of cold expansion: Application for the pre-cracked specimen with the expanded hole at the crack tip

“…There have been numerous investigations that have explored the effectiveness of the process in the initiation and growth of fatigue cracks (Ball and Lowry, 1998;Walin, 1993;Herman, 1994;Ghfiri et al, 2000;Chakherlou and Vogwell, 2003;Vogwell et al, 2001;Lacarac et al, 2000). The fatigue lifetime can be improved because the drilling a hole at the crack tip can decrease the notch sharpness; on the other hand, the expansion can induce the residual compressive hoop stresses near the edge of the hole.…”

Finite element analysis of the residual stress by cold expansion method under the influence of adjacent holes

“…These methods improve the fatigue life by developing a compressive residual stress on the area where a fatigue crack is expected to break out. Especially, the cold expansion method has been used most commonly for that purpose since the Boeing Company introduced it [2,3].…”

Residual Stress From Cold Expansion of Fastener Holes: Measurement, Eigenstrain, and Process Finite Element Modeling

“…Chandawanich and Sharpe [7] performed an experimental study of fatigue crack initiation and growth from CX holes in samples made from 7075-T6 aluminum sheet and observed a significant decrease in crack growth rate in CX samples compared to samples without CX, but no effect on crack initiation. Ball and Lowry [8] performed fatigue crack growth experiments under constant and variable amplitude loading, and observed significant increases in fatigue life (total of initiation and growth) for samples with CX. These studies used 3% to 5% CX, where the percentage represents the amount by which the hole radius increases as the mandrel is pulled through the hole (at maximum expansion).…”