Jh. Bulloch, FATIGUE THRESHOLD IN STEELS - MEAN STRESS AND MICROSTRUCTURE INFLUENCES, International journal of pressure vessels and piping, 58(1), 1994, pp. 103-127
Tle purpose of the present paper was (i) to closely investigate the ef
fect of R-ratio on a large variety of microstructures commonly found i
n low C steels and (ii) to assess the predictability of a selection of
approaches or models which deal specifically with R-ratio effects on
threshold fatigue stress intensity range values, DELTAK(th). Essential
ly the extent of the R-ratio response on the DELTAK(th) was found to b
e significantly microstructure dependent but the trends were by no mea
ns simple. Generally the predictions of the various models dealing wit
h R-ratio-DELTAK(th) trends exhibited poor commonality with the experi
mentally determined DELTAK(th) values. Marked complex yield strength s
igma(y) effects on DELTAK(th) were observed at low R-ratio levels (R c
ongruent-to 0), viz. (a) DELTAK(th) levels initially increased with si
gma(y), (b) attained a maximum DELTAK(th) value of 9 MPa square-root m
which remained constant with increasing sigma(y) level over the range
300-500 MPa and (c) above sigma(y) congruent-to 600 MPa DELTAK(th) de
creased with sigma(y).