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Constant-level, completely reversed bending fatigue tests were conducted on unmachined, mechanically machined, and chemically machined aluminum and titanium alloy sheet panels. All unmachined panels had lower fatigue strengths than machined panels because of stress concentration factor differences at the failure locations. No appreciable differences in fatigue strength occurred as a direct result of the type of machining, but the fatigue lives were inversely proportional to the surface finish of the panels. Early chemical machining produced pitted and undercut radii that reduced the fatigue strength below that of mechanically machined panels. Reworking the pitted, undercut, land-edge radii increased the fatigue strength by a small amount. Polishing the mechanically machined land-edge radii resulted in a small decrease in fatigue strength because of the undercut radii that were produced. Chemical machining of one titanium alloy produced a variable land edge radius that resulted in a higher fatigue strength than for mechanically machined panels with a constant radius. Remachining of chemically machined land edge radii while maintaining the surface finish and land-edge radii geometry had no affect on the fatigue strength.
fatigue (materials), fatigue tests, aircraft structures, aluminum alloys, titanium alloys, machining, chemical milling, surface finish, stress raisers
Whaley, R. E.
Senior engineer, McDonnell Aircraft Corp., St. Louis, Mo.