PSI - Issue 27

Ericha Dwi Wahyu Syah Putri et al. / Procedia Structural Integrity 27 (2020) 54–61 Putri et al. / Structural Integrity Procedia 00 (2019) 000 – 000

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Fig 2. da/dN vs ∆ K curve (Igwemezie et.al., 2019)

The strength of fatigue and fatigue life can be determined by testing by giving a rotating loading bending using the S-N curve method. S-N curve is a fatigue curve which is a graph of the relationship between fatigue strength ( S : Strength) and the number of loading cycles ( N : Number of Stress Cycles). The S-N curve has the disadvantage of being unable to predict local plastic deformations and the effects of stresses. Figure 3, shows that the horizontal axis is data on the number of loading cycles, and the vertical axis shows the strength of material fatigue (Dieter 1988). Range 10 0 ≤ ≤10 3 is low cycle fatigue (low cycles fatigue), range ≥10 3 is high cycle fatigue (high cycles fatigue), and the cycle range 10 7 to 10 8 there are three areas of the specimen, which means the specimen has not broken when the test stop. This condition is called the endurance limit of the material in receiving the fatigue load (endurance limit), and the stress level is called the endurance stress ( σe ). If you want to plan components that have a safe lifetime or even infinite life, the applied voltage level must be below the endurance limit of the component (Dieter 1988).

Fig. 3. S-N curve (Dieter 1988).

Arias and A. Q. Bracarense (2017) researched the characteristics of fatigue crack propagation at UWW conducted on land and water. Underwater welding is carried out at water depths of 10 and 60 by modelling using a hyperbaric chamber. This test shows that the characteristic of fatigue crack propagation at UWW at a depth of 60 m causes the crack propagation rate to be unstable compared to UWW at a depth of 10 m and welding on land. It causes the formation of porosity defects in large quantities. The defects in the weld metal will stop the crack propagation rate, so the fatigue strength of the material will increase. (Arias and Bracarense, 2017). Based on the problems, it is necessary to have an effective method to increase the fatigue resistance of underwater welding. Marquez et al. (2019) assume that heat treatment is the best way to improve the mechanical properties and microstructure of material from a welded joint. The application of heat treatments such as preheating, post-weld heat treatment, or both. Zhang et al. (2019) argue that the Post Weld Heat Treatment (PWHT) carried out after the welding process. This process can change the microstructure of the material into homogeneous. It aims to prevent the failure of materials such as cracking. Cracks can arise due to high residual stresses and changes in the mechanical properties of welding materials. Residual stress occurs in the area around the welding joint. Residual stress can cause fatigue crack propagation if the material subject to dynamic loads on an ongoing basis. Hamid et al. (2018) explain the changes in the microstructure of the material after going through the PWHT process. The result of PWHT on base metal area