DESIGN AND MANUFACTURING FOR CORROSION FATIGUE LIFE

WHILE CORROSION FATIGUE LIMITS THE USEFUL LIFE OF A LARGE NUMBER OF MECHANICAL COMPONENTS, THERE CURRENTLY ARE NO QUANTIFIED METHODS OF EVALUATING THIS FAILURE MODE WHEN MAKING DESIGN AND MANUFACTURING DECISIONS. SUCH METHODS WOULD ALLOW THE DESIGNER TO EVALUATE ALTERNATE GEOMETRIC FEATURES AFFECTING LOCAL CYCLIC THERMAL AND MECHANICAL STRESSES, AND ALTERNATE MANUFACTURING PROCESSES WHICH PRODUCE DIFFERENT LEVELS OF RESIDUAL STRESS AND CORROSION FATIGUE. THE DEVELOPMENT OF SUCH CORROSION FATIGUE DESIGN ANALYSIS METHODS IS INHIBITED BY THE DIFFICULTY OF RUNNING CONVENTIONAL S-N FATIGUE TESTS IN CORROSIVE ENVIRONMENTS WITH THE MEAN STRESSES OF INTEREST, AND AT THE CYCLIC RATES AND LONG LIVES OF INTEREST IN THE DESIGN OF MOST PLANTS. AN INNOVATIVE METHOD OF USING DA/DN CRACK GROWTH RATE DATA, WHICH IS AN ORDER OF MAGNITUDE EASIER TO GENERATE, AND ALREADY AVAILABLE FOR MANY CONDITIONS OF DESIGN INTEREST, IN ORDER TO DERIVE S-N FATIGUE LIFE CURVES WHICH INCLUDE CORROSION EFFECTS IS BEING INVESTIGATED. RESEARCHERS ARE ADOPTING ELASTICPLASTIC J-INTEGRAL THEORY TO PREDICT THE GROWTH OF CRACKS IN CONVENTIONAL FATIGUE SPECIMENS, AND TO INCLUDE THE EFFECTS OF MORE AGGRESSIVE ENVIRONMENTS ON CRACK INITIATION USING THRESHOLD CRACK GROWTH ANALYSES.