Regression Models for the Effect of Stress Ratio on Fatigue Crack Growth Rate

USING THE EXPERIMENTAL AND THEORETICAL RESULTS OF PREVIOUS RESEARCH WORK, THE AUTHOR PRESENTS A PROBABILISTIC DESCRIPTION OF CONSTANT STRESS AMPLITUDE FATIGUE-TEST RESULTS. THIS DESCRIPTION INCLUDES THE S-N CURVES (OR EQUIPROBABILITY OF FRACTURE CURVES), P-S CURVES (OR STRESS-RESPONSE CURVES), P-N CURVES (CUMULATIVE DISTRIBUTION FUNCTIONS OF FATIGUE ENDURANCES), AND ACCOUNTS FOR THE OCCURRENCE OF RUNOUTS. A METHOD OF ESTIMATION OF THE MODEL COEFFICIENTS WHICH USES THE INFORMATION PROVIDED BY ALL THE SPECIMENS TESTED (BROKEN OR UNBROKEN) IS ALSO PRESENTED. THE APPLICATION OF THIS METHOD IS DEMONSTRATED THROUGH FIVE EXAMPLES FOR EACH OF WHICH SEVERAL HUNDRED TEST RESULTS ARE AVAILABLE. /ASTM/