Effect of hardness on multiaxial fatigue behaviour and some simple approximations for steels

Abstract

A B S T R A C T Constant-amplitude in-phase and 90 • out-of-phase axial-torsional fatigue tests were conducted on tubular specimens made from a medium-carbon steel with three hardness levels obtained from normalizing, quenching and tempering and induction hardening to find the effect of hardness on multiaxial fatigue behaviour. In addition, the same loadings were applied on the normalized solid specimens to investigate the effect of specimen geometry on multiaxial fatigue life. Similar fatigue life variation as a function of hardness was found for in-phase and out-of-phase loadings, with higher ductility beneficial in low-cycle fatigue (LCF) and higher strength beneficial in high-cycle fatigue (HCF). Multiaxial fatigue data were satisfactorily correlated for all hardness levels with the Fatemi-Socie parameter. Furthermore, in order to predict multiaxial fatigue life of steels in the absence of any fatigue data, the Roessle-Fatemi hardness method was used. Multiaxial fatigue lives were predicted fairly accurately using the Fatemi-Socie multiaxial model based on only the hardness level of the material. The applicability of the prediction method based on hardness was also examined for Inconel 718 and a stainless steel under a wide range of loading conditions. The great majority of the observed fatigue lives were found to be in good agreement with predicted lives.Keywords hardness effect on fatigue life; life prediction; multiaxial fatigue. N O M E N C L A T U R EA = specimens' cross-section area b = axial fatigue strength exponent b • = shear fatigue strength exponent b = equivalent fatigue strength exponent c = axial fatigue ductility exponent c • = shear fatigue ductility exponent c = equivalent fatigue ductility exponent E = modulus of elasticity G = shear modulus HB = Brinell hardness k = material constant in the Fatemi-Socie parameter 2N f = reversals to failure r m = mid-section radius T = torque ε = axial strain ε e = elastic axial strain ε p = plastic axial strain ε = equivalent strainCorrespondence: Ali Fatemi.

An overview of Direct Laser Deposition for additive manufacturing; Part II: Mechanical behavior, process parameter optimization and control

“…1% to 2%). Therefore, higher ductility leads to a longer life in LCF, and this was confirmed by Shamsaei and Fatemi for medium carbon steels [117].…”

Numerical fatigue life analysis of a high frequency mechanical impact treated industrial component based on damage mechanics models

“…High crack initiation predictability with an acceptable scatter of AE 3 is shown by numerous experimental investigations [29][30][31].…”

“…As mentioned, k is depending on the number of cycles N. An approximation of k by HB and N is also given as followed [31]:…”

“…For low and medium carbon steels like SAE 1050, SAE 1090 and SAE 1541 the approximation shows a high agreement. This approximation was extended to multiaxial fatigue [31]. For this, the von Mises criterion was used correlating Equation 2 with Equation 3 and Equation 4 by translating the strain-life properties for axial strain to shear with…”

“…According to recommendations the material parameter in the shear crack initiation model regulating the stress sensitivity is set to k = 1 [27,31,32]. Finally the damage sum D and therefore the number of variable amplitude load cycles n = 1/D and the number of subsequent constant amplitude load cycles N was calculated by Equation 3.…”