A Study to Determine if a Correlation Exists Between Metal Fatigue Life and the Capability of the Metal to Absorb or Retain an Inert Gas

The purpose of the study was to determine if a correlation exists between stressed metal fatigue and the ability of a metal to absorb or retain inert gas. Aluminum, stainless steel, and normalized steel samples were fatigued to percentages of their normal fatigue life and examined for preferential inert gas absorption in high fatigue regions. The inert gas was krypton, which was enriched with Kr-85, a radioactive tracer, for identification. The procedure was reversed for the same types of metals by allowing krypton absorption into the metals and examining for preferential release from subsequently fatigued areas. Autoradiography and radiometric analysis did not indicate any relationship between release or absorption of krypton and stress fatigue life with one exception; in the case of 4130 steel, limited results indicate that when Kr-85 absorption precedes fatigue, autoradiography and radiometric measurements can detect fatigue near failure. Peripheral results indicate that autoradiography is able to detect cracks in metals whether the inert gas absorption precedes or follows fatigue.