Fatigue life enhancement of fiber metal laminate materials as a result of hole cold expansion

Fiber metal laminate materials (FML), based on a combination of aluminum and glass fibers are being promoted as potential replacements for aluminum based on their lower weight and increased fatigue life. One issue that has not been completely addressed is whether fatigue life enhancement techniques such as cold expansion are effective. Although both experimental and theoretical research has been performed looking at the effect of hole cold expansion in aluminum alloys no research has focused on measuring the fatigue life enhancement that could result from the cold expansion process in FML materials. To investigate the fatigue life enhancement associated with hole cold expansion the fatigue crack initiation period in fiber metal laminate materials both before and after cold expansion was measured. Fatigue crack growth studies were performed on FML 3-3/2 dogbone coupons and crack growth was monitored using a digital camera equipped with a high magnification zoom lens. The images were also analyzed using a digital image correlation system that allows measurement of surface strains during fatigue crack growth. The results showed that cold expansion is very effective in slowing macro-scale crack growth in fiber metal laminate materials but that it does not have a significant effect on retarding short crack formation.Peer reviewed: YesNRC publication: Ye