PSI - Issue 48

Haris Nubli et al. / Procedia Structural Integrity 48 (2023) 73–80 Nubli et al. / Structural Integrity Procedia 00 (2023) 000 – 000

78

6

SS400 mild steel

-25 -80 -70 -70 -49

HSLA EH32 FH32

(Majzoobi et al., 2016)

(Noh et al., 2018)

9Cr-1Mo Steel

(Chatterjee et al., 2014)

5. Correlation to Sub-zero Temperature of DH36 Steel In this paper, a correlation analysis is conducted to show the strength of association and directionality between input and output variables. To account for the robustness of the analysis in the presence of tight ranks and outliers, the Kendall rank correlation is utilized. The Kendall rank correlation generates correlation coefficients ranging from -1.0 to 1.0, where ±1.0 represents a perfect degree of association between the variables. A negative correlation coefficient indicates a negative relationship between the variables (Magiya, 2019). Figure 4 presents a heatmap generated from the findings of Section 3, focusing on DH36 high-strength steel. The Kendall rank correlation includes input parameters such as temperature (T), specimen thickness (t), and strain rate (έ) in relation to the output variables of the ultimate tensile strength ( σut ) and fracture strain ( εf ). In the cryogenic tensile test of DH36 steel, the analysis reveals that the increase in ultimate tensile strength is influenced by a reduction in temperature, indicating a hardening effect attributed to sub-zero temperatures. The association between ultimate tensile strength and temperature exhibits a negative correlation, implying that lower temperatures result in higher ultimate tensile strength. The second most influential association with ultimate tensile strength is observed with the strain rate, displaying a proportional relationship. Regarding fracture strain, there is a positive correlation with specimen thickness, indicating a modest association of 0.2. Conversely, the strain rate exhibits an inverse correlation with fracture strain, implying that higher strain rates result in shorter fracture strains. Furthermore, temperature demonstrates a relatively weaker correlation with fracture strain, suggesting that DH36 steel may exhibit a minor increase in brittleness at lower temperatures.

1.00 Kendall rank

0.80

0.60

εf

-0.68

0.2

-0.073

0.40

0.20

0.00

−0.20

−0.40

σut

0.15

0.067

-0.71

−0.60

−0.80

−1.00

t

έ

T

Fig. 4. Heatmap of Kendall rank correlation for the effect of temperature to the strength of DH36.

6. Concluding Remarks In conclusion, a comprehensive understanding of the hazards and mechanical behavior associated with cryogenic tem peratures is crucial for the design and operation of LNG-carrying ships. The following key points summarize the findings: