CUMULATIVE FATIGUE DAMAGE UNDER COMPLEX STRAIN HISTORIES

THE ACCUMULATION OF FATIGUE DAMAGE UNDER COMPLEX MECHANICAL HISTORIES IS APPROACHED FROM A CYCLIC DEFORMATION VIEWPOINT. SMOOTH AXIAL SPECIMENS OF SAE 1045 STEEL IN TWO HEAT TREATED CONDITIONS WERE SUBJECTED TO REPEATED BLOCKS OF A VARIETY OF COMPLEX STRAIN HISTORIES AND THE RESULTING STRESS-STRAIN RESPONSES DETERMINED. A NEW DAMAGE EQUATION, BASED ON SIMPLE MATERIALS PROPERTIES, WAS THEN APPLIED TO STABILIZED BLOCKS AND A FATIGUE LIFE PREDICTED. THE METHOD ENTAILS A REVERSAL-BY-REVERSAL STRESS-STRAIN ANALYSIS OF A HISTORY USING THE RATIO OF PLASTIC TO ELASTIC STRAIN RANGE AS A DAMAGE PARAMETER. A COMPUTER PROGRAM WAS DEVELOPED TO PERFORM THE DETAILED DATA REDUCTION AND ANALYSIS AND CAN BE EMPLOYED ON-LINE IN A COMPUTER INTERFACED, CLOSED LOOP TEST SYSTEM. AGREEMENT BETWEEN EXPERIMENTAL AND PREDICTED LIVES IS WITHIN A FACTOR OF TWO OVER THE RANGE OF LIVES INVESTIGATED. /ASTM/