The corrected Paris equation taking into account the stress ratio and biaxial constraint along the crack front

A methodology for assessing the durability of a cyclically loaded plate with a through crack I tape has been proposed, taking into account the biaxial constraint along the crack front and the stress ratio. It has been established that in domestic and foreign literature there are no works in which the prediction of fatigue crack growth was carried out taking into account the stress ratio, as well as non-singular terms ( T xx - and T zz -stresses) of the stress field ahead of the crack tip front, which describe the constraint across and along the crack tip front, respectively. The calculation of the fatigue crack growth rate was carried out using the corrected Paris equation, in which the range of the effective stress intensity factor (SIF) is substituted instead of the range of the effective SIF. An expression for the effective SIF was proposed in the authors’ earlier works, which, in addition to the usual SIF, includes the T xx - and T zz -stresses. The published works of other authors, which present the fatigue crack growth rate for various stress ratios for structural steel, aluminum and titanium alloys, are analyzed. It was shown that for each of the materials, the power-law exponent m is virtually independent of the stress ratio. Conversely, the parameter C depends significantly on the stress ratio and this dependence is close to linear. It was established that for considered materials, the dependence of the parameter C on the asymmetry coefficient can be described by a single equation, which includes only the value of the parameter C obtained under a positive pulsation or symmetric loading cycle. The results of the calculations for the durability of a cyclically loaded plate with a mode I crack I are presented, taking into account the biaxial constraint along the crack front and the stress ratio. It is shown that for the positive stress ratio, the proposed method, taking into account the influence of the stress ratio on the parameter C , leads to a conservative assessment of the durability compared to a calculation that does not take this influence into account. For the negative stress ratio, on the contrary, the durability values obtained using the method that does not take into account the influence of the stress ratio on C , lead to a conservative estimate, that is, to underestimated values.