Ultra-Low Cyclic Fatigue Fracture of Q235B and Q345B Steels and Their Butt Welded Joints

다국어 초록 (Multilingual Abstract)

Earthquake-induced fractures in steel structures are characterised by high-strain low-cycle conditions. In order to investigate the ultra-low cyclic fatigue fracture of steel welded joints under earthquakes, two most commonly used structural steels (Q235B and Q345B) and the corresponding welds were studied by experiments and numerical analysis in this paper.
Specimens were extracted from the base material, the weld metal and the heat aff ected zone to investigate the behaviour in diff erent parts of the welded joint. Eighteen smooth round bars were tested under large strain amplitudes, the hysteretic properties, damage degradation characteristics and failure process were analyzed. Constitutive model named Chaboche model was calibrated to describe the cyclic hardening behaviour of these materials. Seventy-two notched round bars with three diff erent notch sizes and two loading protocols were tested to study the fracture behaviour of diff erent materials at different stress triaxialities and diff erent strain amplitudes. Two micromechanical fracture models: cyclic void growth model and degraded signifi cant plastic strain model were calibrated based on the test results. The micromechanical models and Chaboche model were incorporated into numerical simulations by software ABAQUS with subroutine VUMAT to predict the materials fracture. The results show that the failure process under cyclic loads is opposite to that of monotone loads. The dissipation capacity of Q345B is superior to that of Q235B. The fracture resistance deteriorate more in the weld zone under the same loading conditions. The validated models can be used to eff ectively and accurately evaluate the fracture in steel welded connections under ULCF conditions.

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