Analysis of the calibration of the constants of the Modified Wohler Curve ̈

Resumo

This analysis is based on the critical plane approach combined with the Modified Wohler Curve, using ̈
uniaxial fatigue results, of ASTM743 CA6NM steel, subjected to loading ratios R = (0, −1,
−1
3
,
−2
3
,
1
3
,
2
3
). In
this scenario, we show the indicated procedures to calibrate as constants of the Wohler Curve. We postulate that, ̈
by incorporating the effects of multi-axiality, the critical plane approach parameters can be used successfully in

estimating fatigue life under different test conditions. Thus, unlike the classical approach, the use of this enhance-
ment has the advantage of allowing the construction of the verses relationship, regardless of the type of test used

for calibration. To define the new relationship, a calibration strategy considering the Susmel and Lazzarin critical
plane model is presented.As a result, it was found that from the constants A and b curve by the SN curve, we can
represent an intermediate curve by means of these constants versus the compressibility ratio. This relationship is
influenced by the loading rate of Rρ. This new parameter can be used as a multiaxial fatigue criterion for life
prediction. Regarding the parameter A, for this material presented, for the conditions of R = (−1,
−2
3
,
1
3
,
2
3
),

converged with the Susmel and Lazzarin hypothesis, the curve evolved according to the variation of the compress-
ibility relation, changing a linear behavior. However, for the conditions of R = (0,

−1
3
), there is inconsistency in
the available data about the theory. The tensions increased proportionally to the increase of rho, diverging from
the assumed hypotheses. The b parameter behaved similarly to the A parameter.