PSI - Issue 71

Pramod Ravindra Kushwaha et al. / Procedia Structural Integrity 71 (2025) 74–81

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4.4 Percentage time elapsed in hump appearance The appearance of the hump (which is material behaviour that suggests a transition in creep mechanism or a localized material response) was observed earlier in the creep curve with an increase in load. It appeared after 48 hours, 21 hours, and 14 hours at loads of 650 N, 700 N, and 750 N, respectively. The percentage time elapsed is the ratio of time at which hump appeared in punch displacement curve to the rupture life (equation 1). % = ℎ x100 (1) Percentage time elapsed for the load was found to be 54.4%, 42.0% and 39.8%, respectively. The percentage time elapsed for the hump appearance is shown in the Fig. 7. It can be seen that the fraction of life elapsed decreased as the load was increased and the graph showed negative slope behavior. This implies that as the load increased a smaller fraction of the total life was elapsed by the time the hump appears. The average slope at the hump was found to be 0.014, 0.024 and 0.024 at 650 N, 700 N, and 750 N, respectively which was increasing with load and an indicative of a higher rate of damage accumulation or stress under higher loads. The change in the mechanism was accelerated, demonstrating its sensitivity to load.

% elapsed time for hump

Fig. 7. Percentage time elapsed with respect to SPC load

Fig. 8. Variation of minimum deflection rate with load for Su-263 at 650 °C