Abstract
The formation and propagation of cracks occur through irreversible dislocation movements at notches, material defects, and grain boundaries. Since this process is partly thermally controlled, the resistance to dislocation movements at low temperatures increases. This slows both fatigue initiation and fatigue crack propagation. From recent experimental data, it can be seen that fatigue crack growth is accelerated below the fatigue transition temperature (FTT) that correlates with the ductile-brittle transition temperature (DBTT) found by well-known fracture mechanics tests, i.e., Charpy impact, fracture toughness, and CTOD. Hence, this study investigates the relation between FTT and DBTT in S500 high-strength steel base material and welded joints at low temperatures using fatigue crack growth, fracture toughness tests as well as scanning electron microscopy. From the tests, an almost constant decrease in fatigue crack propagation rate is determined with decreasing test temperature even below the DBTT. At −100 °C, the fatigue crack propagation rate is about half of the rate observed at room temperature for both base material and weld metal.
Highlights
Low temperatures cause challenging conditions for the structural integrity of steel structures in Arctic regions [1]
This study investigated the relation between the fatigue transition temperature and the ductile-brittle transition temperature by means of fatigue crack propagation tests at constant stress intensity factor range and fracture mechanics tests (i.e., Charpy impact, fracture toughness), respectively
From the tests, an almost constant decrease in fatigue crack propagation rate is determined with decreasing test temperature even below the ductile-brittle transition temperature of the weld metal
Summary
Low temperatures cause challenging conditions for the structural integrity of steel structures in Arctic regions [1]. The combination of high ice-related loads and low temperatures is difficult to account for in design [7,8,9,10,11,12,13,14,15,16,17,18]. This problem is amplified by the lack of comprehensive guidance for lowtemperature fatigue strength assessment of steel structures. A better understanding of the effect of temperature on fatigue damage mechanisms (fatigue crack initiation and propagation) is required to avoid detrimental fatigue performance at low temperatures and to use the beneficial effect of improved fatigue strength above the FTT, see Braun and Ehlers [23]
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