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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9.

Muhayat et al. (2020)

Fatigue Life of Underwater Wet Welded Low Carbon Steel SS400

Evolution microstructure

The effect of water depth on UWW can increase the value of fatigue and tensile strength. At a depth of 10m increase AF (Accicular Ferrite) on weld metal with grain sizes of 5μm. When the ultrasonic power is increased, the porosity decreases from 1.4% to 0.5% and the hydrogen diffusion content decreases from 24.5 ml to 18.6 ml / 100 gram.

10.

Chen et al. (2020)

Insight into hydrostatic pressure effects on diffusible hydrogen content in wet welding joints using in-situ X-ray imaging method

Defects

3. Fatigue Fatigue is one of the causes of material failure that is not preceded by special features that are showed directly by eyes. Material fatigue occurs due to dynamic loads that are received by material for a long time (Gu et al., 2019). Material fatigue can occur due to brittle of the material until fracture without deformation. Factors that influence material failure due to fatigue in welding are the value of maximum tensile stress, residual stress, the stress concentration, corrosion, temperature, metallurgy structure, and overload by the material (Dieter, 1998). Crack due to fatigue consists of 3 stages, namely: crack initiation, crack propagation and fracture, as shown in figure 1 (Wang et al., 2019). Crack Initiation is an initial crack that occurs on the surface of weak material or an area where there is a concentration of stress on the surface due to repeated loading. Crack Propagation is a phase where the process of the fatigue material stages that experience repeated loading will cause the initial cracking and its propagation phase. At this stage, the initiation crack turns into small cracks (microcracks). Microcrack will spread and join with others, so it will form a large crack (macrocrack) and lead to failure. Fracture is the final stage of the fatigue process. The material will fail to the structure that has loaded so that the structure has fractured. When crack propagation occurs, the cross-section of that section will reduce. At the point where the cross-section of that section is unable to withstand the load. The propagation of a crack occurs so rapidly that the structure will fracture.

Fig. 1 . (a) Crack Initiation; (b) Crack Propagation; dan (c) Fracture (Wang et al., 2019). Fatigue crack propagation rate of da/dN vs ∆ K with a log-log function scale, as shown in figure 2. The fatigue crack propagation of da/dN divides into three regions, namely region 1, 2 and 3. Region 1 (Threshold) is an area that does not occur in the crack propagation process except above the order of 1.0E -10 m/cycle. Region 2 (Paris law) is the region that shows the relationship between the rate of crack propagation ( da/dN ) with the difference in the intensity of the stress ( ∆ K ) that works. Crack propagation rate is the second stage before the fault occurs. Region 3 (final failure) is the area of fatigue propagation process that is very fast so that the tension intensity propagation is above the value of the critical stress intensity (Igwemezie et al., 2019).