Damping capacity, strain hardening and fatigue

An electromagnetic method of exciting torsional resonance vibrations is described. For some alloys of aluminium, notably binary alloys containing 5% and 11% of magnesium, vibrational strains of sufficient magnitude to cause fatigue cracks can be developed by this method at frequencies of the order of one kilocycle per second. During vibration, measurements are made of the damping capacity of the specimens to provide information concerning strain hardening and energy conversion within the specimens up to the time when failure occurs by fatigue. Fatigue failure of the two binary alloys containing magnesium is shown to be preceded by strain hardening. The endurance of individual specimens is related to the amount of irreversible strain imposed per cycle, failure occurring when the cumulative internal strain approaches a limiting value.