Development of a Multiaxial Fatigue Damage Model for High Strength Alloys Using a Critical Plane Methodology

Abstract

The prediction of fatigue life for metallic components subjected to complex multiaxial stress states is a challenging aspect in design. Equivalent-stress approaches often work reasonably well for uniaxial and proportional load paths; however, the analysis of nonproportional load paths brings forth complexities, such as the identification of cycles, definition of mean stresses, and phase shifts, that the equivalent-stress approaches have difficulties in modeling. Shear-stress based critical-plane approaches, which consider the orientation of the plane on which the crack is assumed to nucleate, have shown better success in correlating experimental results for a broader variety of load paths than equivalent-stress models. However, while the interpretation of the ancillary stress terms in a critical-plane parameter is generally straightforward within proportional loadings, there is often ambiguity in the definition when the loading is nonproportional. In this study, a thorough examination of the variables responsible for crack nucleation is presented in the context of the critical-plane methodology. Uniaxial and multiaxial fatigue data from Ti–6Al–4V and three other alloys, namely, Rene’104, Rene’88DT, and Direct Age 718, are used as the basis for the evaluation. The experimental fatigue data include axial, torsional, proportional, and a variety of nonproportional tension/torsion load paths. Specific attention is given to the effects of torsional mean stresses, the definition of the critical plane, and the interpretation of normal stress terms on the critical plane within nonproportional load paths. A new modification to a critical-plane parameter is presented, which provides a good correlation of experimental fatigue data.

Cumulative model of very high cycle fatigue

“…The predicting decrease of VNCF in conditions of two‐axial cyclic tension is in satisfied agreement with published experimental data 25 for the Ti‐alloy Ti − 6 Al − 4 V and R =− 1; R = 0.1; R = 0.5.…”

“…Consider predicting results of tests of VHCF of steel in standing contact 25 , 26 in condition of repeating local normal pressure. Use the following assessments of the surface stresses near the circular boundary of the loaded site of half‐space 27 : where σ r , σ ϕ , σ Z are the stresses in radial, circumferential and axial directions; q the normal contact pressure.…”

“…In Fig. 6 the predicted values q are compared with the published data 25 . The used data is presented in Table 3.…”

Investigation of the multiaxial fatigue behaviour of 316 stainless steel based on critical plane method

“…The quality of the predictions depends on the type and quality of the experimental information used for feeding the model and the loading conditions . Sophisticated damage parameters that include several loading effects have been presented . Good correlation between experimental and estimated fatigue lives has been observed for a number of cases.…”

A modification of Smith–Watson–Topper damage parameter for fatigue life prediction under non‐proportional loading

“…Though it is very difficult to solve the multiaxial fatigue problem, fundamental understanding of this problem is essential for the reliability assessment under realistic service condition and is valuable for the design and maintenance against fatigue failures. 2,[4][5][6][7][8][9][10] This critical plane concept first used in stress-based criteria, was subsequently introduced to strain-based criteria and then to energy-based criteria. Although the life prediction technique has been made extensive progress in the past decades, yet there is no simple theory of fatigue that can be applied to wide class of materials and loading conditions, nor there exist a universal model of fatigue damage.…”