EFFECTS OF SEQUENTIAL CYCLIC AND MONOTONIC LOADINGS ON DAMAGE ACCUMULATION IN NICKEL-270

Specimens of polycrystalline nickel 270 were tested by subjecting them to loading paths of either (1) monotonic prestrain followed by strain controlled cyclic loading to failure or (2) strain controlled precycl ing followed by monotonic loading to failure. The effects of initial c ondition as produced by cold working or annealing, cyclic strain range , frequency and degree of monotonic prestrain on subsequent fatigue be havior were investigated. The effects of precycling on the subsequent monotonic tensile behavior of the test material were also studied. The heat dissipated from the specimens under fatigue loading was measured . It was found that 76.6% of the irreversible work was dissipated as h eat; the remaining portion caused material damage. The relative effect s of monotonic prestrain on subsequent cyclic behavior were more harmf ul than the effects of precycling on subsequent monotonic behavior. Th e results showed that the energy absorbed by the material, which corre sponds to damage, is a function of various loading parameters and is t herefore path dependent under these conditions. (C) 1998 Elsevier Scie nce Ltd.