Determination of the critical plane orientation depending on the fatigue curves for bending and torsion

Abstract

ABSTRACT. This paper contains a proposition setting out a new way of determining an orientation angle of the critical plane. The applied method involves an analysis of fatigue life results' scatter of several selected materials on the basis of a new criterion of multiaxial fatigue. The expression for the equivalent stress was derived on the basis of pure bending and pure torsion. The paper also contains a verification of the effectiveness of the proposed model by analyzing scatter bands and the value of the ratio of normal to shear stresses.

Influence of plastic deformations on both yield strength and torsional fatigue life of non‐ferrous alloys

“…For the 6082‐T6 aluminum alloy, a fatigue life under torsion equal to is assumed, according to the experimental results available in the literature, 31,35,36 and the number of the preloading cycles alternatively applied, , is equal to 20%, 40%, and 60% of . In order to compute the amplitude of the total moment to be controlled during testing, firstly, the amplitude of the shear stress, , is calculated by exploiting the following S – N relation, where the fatigue strength coefficient and the fatigue exponent are provided in previous studies 32–34,37–39 : …”

“…For the CuZn40Pb2 brass alloy, a fatigue life under torsion equal to N ¼ 10 5 is assumed, according to the experimental results available in the literature, 31 and the number of the preloading cycles alternatively applied, n, is equal to 20%, 40%, and 60% of N. In order to compute the amplitude of the total moment to be controlled T A B L E 3 Results in terms of yield strength, σ y , obtained by applying a loading history characterized by a cyclic preloading and then a static tension, for the CuZn40Pb2 brass alloy (left-hand side) and for the 6082-T6 aluminum alloy (right-hand side). For each loading history, the mean value, σ y , is also reported, together with the relative percentage difference with respect to σ s (in italic).…”

“…For the 6082-T6 aluminum alloy, a fatigue life under torsion equal to N ¼ 5 10 ð Þ 4 is assumed, according to the experimental results available in the literature, 31,35,36 and the number of the preloading cycles alternatively applied, F I G U R E 4 Yield strength versus the number of preloading cycles, n, for the (A) CuZn40Pb2 brass alloy and (B) 6082-T6 aluminum alloy. The mean yield strength, σ y , and the yield strength related to the undamaged material, σ s , are also reported for the examined alloys.…”

The generalized criterion of multiaxial random fatigue based on conception proposed by prof. Macha

“…So the question arises what physical quantity we get in effect. It is known from experience that this proposition is successfully used according to this criterion and similar other criteria on in the critical plane where both normal and shear stress are taken into account [17][18][19][20][21][22][23][24].…”

Including the normal to shear stresses ratio in fatigue life estimation for cyclic loadings

“…The critical plain concept is strictly related to the reduction of the multi-axis state to the single-axis equivalent [4]. The course of normal stress turned at angle α with respect to σxx is given by the formula…”