A BASIC STUDY ON FATIGUE GAUGE MADE OF ELECTROPLATED COPPER FOIL - (EFFECTS OF UNDERSTRESS)

Fundamental investigations are made regarding the phenomena of slip band initiation and grown grain initiation in an electroplated copper foil under variable amplitude stress which consists of overstress and understress. The applicability of the copper foil to the fatigue gauge which detects fatigue damage is discussed. It is found that the modified Miner's rule does not hold for the slip band and grown grain initiation under two-level single block loading and two-level multiple loading composed of overstress and understress. The cumulative cycle ratio in these cases is dependent on load history. It is also found that fatigue damage during understress applied after overstress is greater in the early period of the cycles. The deviation from the modified Miner's rule, however, can be said to be small. Furthermore, it is found that the fraction of grown grains initiated under variable stress is dependent on the equivalent stress. This enables the evaluation of the equivalent stress based on the fraction of grown grains.