Fatigue strength of fillet‐welded joints at subzero temperatures

Abstract

Ships and offshore structures may be operated in areas with seasonal freezing temperatures and extreme environmental conditions. While current standards state that attention should be given to the validity of fatigue design curves at subzero temperatures, studies on fatigue strength of structural steel at subzero temperatures are scarce. This study addresses the issue by analysing the fatigue strength of welded steel joints under subzero temperatures. Although critical weld details in large welded structures are mostly fillet‐welded joints, most published data are based on fatigue crack growth rate specimens cut out of butt‐welded joints. This study analyses fillet‐welded specimens at −20°C and −50°C against controls at room temperature. Significantly higher fatigue strength was measured in comparison to estimates based on international standards and data from design codes even at temperatures far below the allowed service temperature based on fracture toughness results.

Application of local approaches to the assessment of fatigue test results obtained for welded joints at sub-zero temperatures

“…The comparison with a fatigue design curve based on a fixed slope exponent of = 3 leads therefore to an increased standard deviation of the data deviation at sub-zero temperatures than for room temperature. Moreover, the fracture surfaces presented in Braun et al [5] support this conclusion. Finally, significant differences in prediction accuracy between the different methods are apparent in…”

“…This study investigated the applicability of local fatigue assessment methods for welded joints in engineering structures exposed to sub-zero temperatures. For this purpose, fatigue test results by Braun et al [5] of two fillet weld details with weld toe and weld root failure made of two structural steels in the temperature range of 20 °C down to -50 °C were evaluated using different structural-and notch stress methods found in international standards and literature. The results are compared to the nominal stress approach.…”

“…All results are corrected to a stress ratio of = 0.5 based on the mean stress correction factors calculated by Braun et al [5] to allow a comparison with fatigue design curves (1.02 and 1.08 for S235 and S500, respectively, and both joint types). All cruciform joints failed from the weld root, in particular the results for sub-zero temperatures lie far above the corresponding design curve FAT36.…”

Extension of the strain energy density method for fatigue assessment of welded joints to sub‐zero temperatures

“…41 The specimens were produced from two structural steels: a normalised steel (S235J2+N) and a fine-grained thermomechanically rolled steel (S500G1+M) with the mechanical properties listed in Table 2. All specimens were welded by means of flux-cored arc welding process, see Braun et al 39 for further details. Before the test, the misalignment and local weld geometry of every specimen were measured based on the curvature method (see other studies 43,44 ).…”

Requirements for stress gradient‐based fatigue assessment of notched structures according to theory of critical distance

“…In order to analyse the applicability of TCD methods for fatigue assessment, the determined requirements for stress gradient based fatigue assessment of notched structures according to TCD need to be applied to fatigue test data. For this purpose, fatigue test data obtained for butt‐welded joints with artificial notches obtained by Fischer et al 45 and fatigue test data at low temperatures 51 are currently assessed and will be published in the near future.…”