An Improved Split-Ring Method for Measuring the Level of Autofrettage in Thick-Walled Cylinders

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Abstract
A simple, yet improved, experimental method for measuring the level of autofrettage in thick-walled cylinders, such as gun barrels, is proposed. A representative ring cut from the barrel serves as the test specimen. The ring is split by cutting it radially, while measuring the released hoop strain at the inner and outer surfaces diametrically opposite from the split line. The opening angle resulting from the spring apart from the ring is also monitored. An analysis based on Hill’s residual stress field yields an approximate relation which readily enables the determination of the prevailing level of autofrettage from strain measurements as well as from the value of the opening angle. This relation is found to be practically universal for all relevant cylinder configurations b/a = 1.6–2.2 and all levels of autofrettage of up to φ = 100 percent.