Liang-Jiu Jia

Ductile Fracture Simulation of Structural Steels under Monotonic Tension

This paper aims to predict ductile fracture of mild steel under monotonic loading only from the test results of notchless tensile coupons. A simple fracture model based on the concept of a damage index with only one model parameter is proposed to predict ductile fracture of structural steels. The model is based on an idea of a combination of the void growth model and Miner’s rule in incremental form. Moreover, a new method to modify the true stress-true strain data after necking initiates is proposed, and it is found that the hardening modulus of several structural steels after necking initiates is approximately the same. Finally, ductile fracture of smooth and notched steel specimens is numerically simulated for three types of structural steels, which proves simplicity and acceptable accuracy of the fracture model and the modification method of the true stress-true strain.

Experimental and Numerical Study of Postbuckling Ductile Fracture of Heat-Treated SHS Stub Columns

AbstractPrevious studies have proposed a cyclic ductile fracture model by applying the void growth model and an established rule in incremental form, in which only a monotonic tensile coupon test is required to calibrate the parameters of the fracture model and the corresponding plasticity models. The model parameters were deduced from small-scale hourglass steel coupons, but not from large-scale specimens. In practice, however, ductile fracture after the occurrence of local buckling has been observed in steel members during recent huge earthquakes. This paper aims to establish a simulation method for the postbuckling cracking process on the basis of formerly proposed fracture and plasticity models. Experimental results demonstrate that the ultimate behaviors of heat-treated square hollow section (SHS) stub columns associated with plate buckling and ductile fracture under cyclic loading can be simulated with favorable accuracy.

Experimental and Numerical Study on Ductile Fracture of Structural Steels under Combined Shear and Tension

AbstractDuctile fracture of steel structural members under combined shear and tension was observed in past strong earthquakes, but studies on ductile fracture under the combined stress state have been very limited in the field of steel structures. This study aims to experimentally and numerically investigate the coupling effect of shear stress and tensile stress on ductile fracture of both mild steel and high-strength steel. Two series of specimens are manufactured in which they are under pure shear and combined shear and tension. Meanwhile, a generalized simulation process, including generalization of the whole stress-strain data up to the fracture and fracture parameter calibration using only tensile coupons, is proposed to simulate ductile fracture of different structural steels. The generalized simulation process is proven to be capable of simulating ductile fracture under the combined stress state with good accuracy and simplicity.

Experimental Study on Cracking of Thick-Walled Welded Beam-Column Connections with Incomplete Penetration in Steel Bridge Piers

Fracture of welded beam-column connections was observed in steel moment-resisting frame steel bridge piers during the 1995 Kobe (Hyogoken-Nanbu) Earthquake. In addition, welding defects in fillet welds and full penetration welds were recently reported in existing steel bridges. This paper aims to study the effects of incomplete penetration depth and loading histories on crack initiation and propagation of thick-walled beam-column connections during a strong earthquake event. Five specimens under three different loading histories were loaded quasi-statically, and different cracking modes were observed. The experimental results indicate that the cracking modes are closely correlated with the size of the incomplete penetration depth.

Constitutive Model of Aluminum under Variable-Amplitude Cyclic Loading and Its Application to Buckling-Restrained Braces

AbstractAluminum has been increasingly used in space, building, and other structures owing to its light weight and high durability. The cyclic plasticity of aluminum is of great importance for the ...

Seismic Performance of Compact Beam–Column Connections with Welding Defects in Steel Bridge Piers

AbstractWelding defects and fatigue cracks in full-penetration welded beam–column connections, resulting in partial-penetration welds, are found in existing steel moment-resisting frame bridge piers. The welding defects may have an unfavorable effect on the seismic performance of a large number of existing piers, most of which have been in operation for over 50 years. This study aims to clarify the effects of the weld profile, e.g., weld leg length, penetration depth, and incomplete penetration depth, on seismic performance of the beam–column connections in existing piers with welded box sections. The effect of gusset stiffeners (termed fillets in this paper) at the beam-web-to-column-web joint on the improvement of seismic performance is also studied. In this study, experiments on 10 specimens with different incomplete penetration depths and fillet radii are performed under quasi-static cyclic large displacement loading. Based on the test results, cracks may initiate either at the beam end or at the weld...