Search

A new path‐independent multiaxial fatigue damage parameter σn*, which is defined as the largest normal stress range between adjacent turning points of the maximum shear stress on the critical plane, is proposed to describe multiaxial fatigue damage. By combining the maximum normal stress σn,max or the largest normal stress range σn* with the maximum shear stress range on the critical plane, two axial equivalent stress modification factors, keqσ and keqσ*, are proposed, which can account for the influence of non‐proportional additional hardening. The sensitivity of the proposed axial equivalent stress modification factors to multiaxial variable amplitude loading sequences is analyzed. Furthermore, two new multiaxial fatigue damage models based on the axial equivalent stress modification factors are proposed to estimate fatigue life. The applicability of the presented methodology was verified by the experimental data of En15R steel and 7050‐T7451 aluminum alloy, and the results showed that the predicted fatigue lifetimes agree well with the experimental data under variable amplitude multiaxial loading. [ABSTRACT FROM AUTHOR]

• AMed Ti-6Al-4V with different sizes via ultrasonic cycling up to very-high-cycle regime. • S - N data showing size effect: large sized specimens with small fatigue life or strength. • A new probabilistic control volume scheme to predict fatigue property of large specimens. • A size sensitivity exponent to quantify size effect on fatigue property of AMed alloys. • A general form of probabilistic control volume model to unify original and new models. The effect of specimen size on the fatigue performance of additively manufactured (AMed) Ti-6Al-4V is investigated in this paper. The fatigue tests of Ti-6Al-4V specimens made by laser powder bed fusion were conducted via ultrasonic axial cycling up to very-high-cycle regime with stress ratio R = –1. The S - N data of five group specimens show an evident size effect, that is, with the increase of specimen size, the fatigue life or fatigue strength decreasing gradually. A new probabilistic control volume scheme is developed to evaluate the fatigue life of large sized specimens by the tested data of small sized specimens. The applicability of the proposed model is validated by the present data and those of our previous investigation. Moreover, a general form of probabilistic control volume model is derived to show the original and present models are the special cases for conventional cast and AMed alloys. [ABSTRACT FROM AUTHOR]

A new calculation approach is suggested to the fatigue life evaluation of notched specimens under multiaxial variable amplitude loading. Within this suggested approach, if the computed uniaxial fatigue damage by the pure torsional loading path is larger than that by the axial tension–compression loading path, a shear strain‐based multiaxial fatigue damage parameter is assigned to calculate multiaxial fatigue damage; otherwise, an axial strain‐based multiaxial fatigue damage parameter is assigned to calculate multiaxial fatigue damage. Furthermore, the presented method employs shear strain‐based and axial strain‐based multiaxial fatigue damage parameters in substitution of equivalent strain amplitude to consider the influence of nonproportional additional hardening. The experimental data of GH4169 superalloy and 7050‐T7451 aluminium alloy notched components are used to illustrate the presented multiaxial fatigue lifetime estimation approach for notched components, and the results reveal that estimations are accurate. [ABSTRACT FROM AUTHOR]

An innovative numerical methodology is presented for fatigue lifetime estimation of notched bodies experiencing multiaxial cyclic loadings. In the presented methodology, an evaluation approach of the local nonproportionality factor F for notched specimens, which defines F as the ratio of the pseudoshear strain range at 45° to the maximum shear plane and the maximum shear strain range, is proposed and discussed deeply. The proposed evaluation method is incorporated into the material cyclic stress‐strain equation for purpose of describing the nonproportional hardening behavior for some material. The comparison between multiaxial elastic‐plastic finite element analysis (FEA) and experimentally measured strains for S460N steel notched specimens shows that the proposed nonproportionality factor estimation method is effective. Subsequently, the notch stresses and strains calculated utilizing multiaxial elastic‐plastic FEA are used as input data to the critical plane‐based fatigue life prediction methodology. The prediction results are satisfactory for the 7050‐T7451 aluminum alloy and GH4169 superalloy notched specimens under multiaxial cyclic loading. [ABSTRACT FROM AUTHOR]