LOW CYCLE FATIGUE OF THIN COPPER FOILS

摘要

It is well known that the fatigue properties for small scaled structures such as thin foils due to their dimensional constraint cannot be deduced from bulk material. Thus the fatigue properties have to be determined using their practical dimensions. In this investigation S-N curves of Cu foils have been obtained under tension-tension fatigue (R=0). Special emphasis was placed on characterization of microstructural parameters and texture and the thickness being varied between 50μm and 250μm. To obtain deeper insight on the fatigue mechanism cyclic stress-strain (CSS) curves of thin Cu foils were determined as function of thickness (125μm and 250μm) for rolled/annealed material using a multiple step-test. The experiments were performed using a microtensile and a servohydraulic machine (load capacity 500N) in combination with a new noncontacting laser speckle extensometer (with strain resolution of about 1.10~(-5).The results indicate a strong size effect on fracture strain and fatigue life for a comparable ratio of grain size to thickness. A physical explanation is presented on the number of active slip systems and a different state of stress/strain. Based on these findings in a first attempt it seems feasible to predict S-N curves for thin foils.