Ductile Fracture Behaviour of Q690 High Strength Steel Under Monotonic Tensile Actions
The increasing utilization of high-strength Q690 steel in engineering structures is attributed to its superior strength-to-weight ratio.Understanding the ductile tensile fracture behavior of Q690 steel is crucial for investigating bolted connections between Q690 members.To address this,a comprehensive pilot study was conducted using conventional ductile fracture analysis methods,including the Void Growth Model(VGM)and the Stress Modified Critical Strain(SMCS)model.Through monotonic tensile tests on standard and notched coupons of varying radii,the true stress-strain relationship as well as the plastic fracture strains were directly measured for different triaxiality ratios of Q690 steel.Then the fracture surface of tested coupons was observed under SEM,and the failure mode was distinguished.After analyzing the valleys and plateaus formed by the dimples,and the characteristic length of Q690 steel was calculated,which was used as the mesh size of the subsequent numerical model.Advanced finite element models were then used to calibrate and validate the fracture parameters of VGM and SMCS model by examining the stress state at the fracture initiation point and predicting load-extension characteristics and elongations at fracture.The numerical results revealed that both the VGM and SMCS models failed to provide satisfactory predictions for elongations at fracture in the test coupons,and the prediction error of them reached 31%and 39%respectively.As a result,a modified void growth model was proposed,which considered the influence of stress triaxiality on the fracture strain.Notably,the numerical analysis showed a good agreement between predicted and measured values of elongations at fracture in the tested coupons,and the average prediction error was controlled with 5%.This study highlights the importance of understanding the ductile fracture behavior of Q690 steel and introduces a promising new fracture parameter for improved fracture analysis accuracy.
high strength steelductile fractureSEMfracture prediction
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