Fatigue Life Prediction Under Multiaxial Variable Amplitude Loading Using A Stress-Based Criterion

Introduction

Engineering components (crankshafts, gas turbines and offshore structures) in service are usually subjected to multiaxial variable amplitude loading. Predicting of fatigue life of materials under multiaxial variable amplitude loading is an important issue and a challenge for engineers. The major complexity is that prediction methods must be able to capture different damage mechanisms of fatigue loading (proportional and non-proportional multiaxiality, mean stress, asynchronous and variable amplitude), especially under random loading in which all these mechanisms may appear.

Numerous methods have been proposed to estimate fatigue life under multiaxial variable amplitude that can be divided into three groups: a group of methods using cycle counting techniques (Bannantine & Socie, 1991; Fatemi & Socie, 1988; Wang & Brown, 1993; Wang & Brown, 1996; Carpinteri, Spagnoli, & Vantadori, 2003; Susmel & Tovo, 2011; Wang & Susmel, 2016), a group of incremental cumulative damage models (Morel, 2000; Saintier et al., 2013; Vu, Halm, & Nadot, 2014), and a group based on spectral analysis (Benasciutti & Tovo, 2005; Lagoda, Macha, & Nielsłony, 2005; Ge, Sun, & Zhou, 2015). Among those groups, the group using cycle counting techniques has been strongly developed. In the low cycle fatigue (LCF) domain, Bannantine and Socie (1991) proposed the use of Smith-Watson-Tooper (SWT) damage parameters and the cycle counting method is applied on the normal strain. Wang and Brown (1993, 1996) proposed a cycle counting method based on two counting variables of shear strains. In the high cycle fatigue (HCF) domain, several methods based on critical plane approaches have been proposed (Carpinteri et al., 2003; Susmel & Tovo 2011; Wang & Susmel, 2016). Although there are some limitations in the use of cycle counting techniques (Banvillet et al., 2004), advantages of these approaches include simple formulation, simple implementation and time-saving calculations. Recently, Wei & Dong (2014) proposed a generalized cycle counting criterion for arbitrary multiaxial fatigue loading conditions, that could be a solution to improve the drawback of classical cycle counting techniques. Vu et al. (2010), Pejkowski & Skibicki (2016) proposed high cycle fatigue criteria for multiaxial loading that reveals advantages of stress-based approach in prediction of the fatigue limit and fatigue life on various materials.

Most fatigue life prediction methods are developed from a multiaxial fatigue criterion. As mentioned above, the multiaxial fatigue criterion must capture correctly different damage mechanisms of fatigue loading. A stress-based multiaxial fatigue criterion proposed recently by Vu et al. (2010) shows a good prediction quality for a wide range of experimental data conducted on various steels in the high cycle fatigue domain. In this paper, a fatigue life prediction method developed from the criterion of Vu et al. will be presented. Brief description of Vu et al. criterion and fatigue life calculation under multiaxial variable amplitude loading is presented in section 2. In section 3, assessment and discussion of the accuracy of the proposed method will be carried out with three different materials from literature (EN-GS800-2 cast iron, 39NiCrMo3 steel and SAE 1045 steel) subjected to different patterns of variable amplitude loading (blocks, non-proportional asynchronous and proportional random loading).