FATIGUE GAUGE UTILIZING SLIP-INITIATION PHENOMENON IN ELECTROPLATED COPPER FOIL

Fundamental experiments are carried out to examine the parameter that dominates the slip-band initiation in electroplated copper foil under the condition where the mean stress as well as the stress amplitude varies. In the case of constant-amplitude stressing, the relation between the critical stress for the slip-band initiation sigma(p) and the number of cycles N is well represented by sigma(p)(alpha)N=C. In other words, the slip bands appear when the total hysteresis energy applied to the copper foil attains a critical value. In the case of variable stresses, the range-pair mainly dominates the occurrence of the slip bands, and Miner's linear cumulative damage rule holds for the accumulation of the fatigue damage for the slip-band initiation. Accordingly, the parameter (SIGMAsigma(i)(alpha)n(i)/SIMGAn(i))1/alpha is equivalent to the critical stress sigma(p) under constant amplitude stressing, where sigma(i) and n(i) are the stress amplitude and the number of cycles counted by the range-pair method, respectively, and alpha is the exponent of the sigma(p)-N relation. Based on these results, the applicability of the copper foil to the fatigue gage that accumulates and indicates a load experience is discussed