Ductile Crack Initiation Criterion with Mismatched Weld Joints Under Dynamic Loading Conditions

Area of Science:

• Materials Science
• Structural Engineering
• Fracture Mechanics

Background:

• Brittle failure in high toughness steel structures often follows ductile crack initiation and propagation.
• Geometrical discontinuities, particularly in beam-to-column connections, have been linked to brittle failures, as observed after the Hanshin Great Earthquake.
• High triaxial stresses are known to accelerate ductile fracture in steels.

Purpose of the Study:

• To investigate the effects of geometrical heterogeneity and strength mismatches on ductile fracture initiation.
• To analyze the influence of loading rate on the critical conditions for ductile fracture.
• To evaluate the applicability of the two-parameter criterion for predicting ductile crack initiation under various conditions.

Main Methods:

• Applied the two-parameter criterion (equivalent plastic strain and stress triaxiality) to assess ductile cracking.
• Conducted ductile crack initiation tests on circumferentially notched specimens (Charpy type) with and without strength mismatches.
• Performed tests under both static and dynamic tensile loading conditions.

Main Results:

• Geometrical heterogeneity and strength mismatches were found to elevate plastic constraints.
• The two-parameter criterion proved effective in estimating ductile crack initiation.
• Results demonstrated the criterion's transferability across different specimen types and loading rates.

Conclusions:

• The two-parameter criterion provides a reliable and transferable method for evaluating ductile crack initiation.
• This criterion is independent of the presence of strength mismatches and loading rates.
• The findings contribute to a better understanding of brittle failure mechanisms in steel structures.