Multiaxial low‐cycle fatigue life evaluation under different non‐proportional loading paths

Abstract

This paper presents analytical and experimental investigations for fatigue lives of structures under uniaxial, torsional, multiaxial proportional, and non‐proportional loading conditions. It is known that the rotation of principal stress/strain axes and material additional hardening due to non‐proportionality of cycle loading are the 2 main causes resulting in shorter fatigue lives compared with those under proportional loading. This paper treats these 2 causes as independent factors influencing multiaxial fatigue damage and proposes a new non‐proportional influencing parameter to consider their combined effects on the fatigue lives of structures. A critical plane model for multiaxial fatigue lives prediction is also proposed by using the proposed non‐proportional influencing factor to modify the Fatemi‐Socie model. The comparison between experiment results and theoretical evaluation shows that the proposed model can effectively predict the fatigue life due to multiaxial non‐proportional loading.

Use of an energy‐based/critical plane model to assess fatigue life under low‐cycle multiaxial cycles

“…There are two categories of approaches for this purpose, ie, semi‐empirical models and incremental plasticity models. The semi‐empirical model developed by Kanazawa and Chen is a frequently used choice, which has been adopted recently by Shamsaei and Qu . It can be seen as a modification of Ramberg‐Osgood equation, in which the cyclic strength coefficient K ′ is calibrated to capture the effect of NP loading, such that where F NP and α NP are the nonproportionality of loading path and the NP hardening coefficient, respectively.…”

“…Unfortunately, although the modified Ramberg‐Osgood equation may be capable of calculating SWT parameter, it has been proved to be ineffective to calculate cyclic plastic strain energy under NP loading . Moreover, the multiplication of F NP and α NP is potentially invalid to consider the effect of NP loading when it is used for materials without NP hardening (ie, α NP = 0). As a consequence, incremental plasticity models are normally recommended to obtain the area of stabilized hysteresis loop under NP loading.…”

Evaluation of the Fatemi‐Socie damage parameter for the fatigue life calculation with application of the Chaboche plasticity model

“…7,24,25,36,37 In a few papers, 7,13,17,24,25 the k value is expressed as a function of the number of reversals to failure, ie, k(2N f ), but without direct application to the Fatemi-Socie parameter. 7,24,25,36,37 In a few papers, 7,13,17,24,25 the k value is expressed as a function of the number of reversals to failure, ie, k(2N f ), but without direct application to the Fatemi-Socie parameter.…”

“…[38][39][40][41][42] Fatemi and Socie 5 define the critical plane by the plane with the highest shear strain amplitude. 13,14,47 In multiple articles, 8,12,22,36,37 the problem of searching the critical plane for the Fatemi-Socie model is simplified by the assumption that the critical plane is perpendicular to a specimen surface, and as a result, the plane orientation is described by only a single angular displacement. But, under the nonproportional loading, the rotating principal axes of strain tensor cause that a shape of the resolved shear strain path on the arbitrary plane generates nonuniqueness of the measure of the shear strain amplitude.…”

Prediction of multiaxial fatigue life for complex three‐dimensional stress state considering effect of additional hardening

“…It is accepted that material additional hardening can significantly reduce the fatigue lives of components in multiaxis loading condition.8, Take 304 stainless steel for example, when the amount of additional cyclic hardening are doubling, the multiaxial fatigue life will reduce 90%, but the more severe forms tend to occur in inconel 718 alloy, of which the life decreased 50%, while additional cyclic hardening increased 10% under the multiaxial loading path . Based on the numerous researches in the last few decades, two conclusions were obtained: Additional cyclic hardening of materials has a strong link with material properties, such as stacking fault energy a representative property here; loading environments, such as the direction and amplitude of applied loads, can significantly affect the amount of additional cyclic hardening. Given the two points above, in order to consider the effect of additional cyclic hardening in multiaxial loading condition thoroughly, it is evident that material properties and loading environments should be taken as an important component for fatigue damage parameter in life prediction model.…”