DETECTION OF FATIGUE DAMAGE OF POLYCRYSTALLINE ALUMINUM BY EXOELECTRON EMISSION MEASUREMENTS

The optically stimulated exoelectron emission from the annealed pure polycrystalline aluminum was continuously measured in air at room temperature during the fatigue process under the reversed bending stress using a picoammeter. The exoelectron emission (EE) increased with the number of fatigue cycles during the early stages, and then reached a peak at about 10-20% of the fatigue life. Increase of EE corresponded to the exposure of the fresh surface produced by persistent slip bands. EE showed a peak when the rate of EE decay exceeded that of the fresh surface formation. This method may well be applicable to other pure metals and alloys.