PSI - Issue 33

Aprianur Fajri et al. / Procedia Structural Integrity 33 (2021) 19–26 Fajri et. al/ Structural Integrity Procedia 00 (2019) 000–000

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Fig. 2 shows the approach commonly used in calculations using FEM-based CAE Software. The method is divided into two types, namely macro-scale and micro-scale. The macro-scale approach investigates fatigue life because of the influence of energy that works. It is assumed that objects in good condition and did not have the initial crack. Otherwise, on microscale approach, the objects are considered to have crack initiation and encroachment of damages due to the influence of dynamic load (Ye et al., 2014) 3.1. Stress life approach Stress life is essentially comparing factual stress in the structure with fatigue test data in the form of an S-N curve (see Fig. 3a). This approach is efficient when investigating fatigue phenomena in the elastic range (Ringsberg et al., 2014). If used in nonlinear conditions, the result is less accurate because stress is local, where the value results from calculating the magnitude of the force divided by the cross-sectional area. Materials in nonlinear conditions will experience a permanent change in cross-sectional area. This approach ignores crack initiation and its propagation in predicting component life (Gdoutos et al., 2003). There are several types of stress-life procedures, including the global response that considers stress conditions on whole structure (Zhang et al., 2018), the hot-spot stress approach, and the effective notch stress approach, which only investigates conditions in certain areas (Tasdemir and Nohut, 2012). (a) (b)

Fig. 3. The fatigue data of stainless steel from the lab test; (a) S-N curve for stress life approach; and (b) strain-life curve.

3.2. Strain life approach The strain life approach is comparing factual strains at the structures against strain curves from the lab test (see Fig. 3b). This approach is suitable for investigating fatigue phenomena in both linear and nonlinear conditions. The strain-life approach is usually used to investigate low cycle fatigue, which is very difficult to solve using stress life based (Dong et al., 2021). The downside is that parameter input is very complex, which will affect computing time.