L. Y. Xu

Application of ultrasonic tomography to monitoring gas/liquid flow☆

On the basis that a gas/liquid two-phase flow was considered as a strongly inhomogeneous medium due to the high contrast in acoustic impedance distribution, the authors analysed the inherent dependency of the incomplete tomographic projections on the distribution of bubbles in liquid when using transmission-mode (TM) ultrasound computerized tomography (UCT). A mathematical model describing the acoustic characteristics of this flow was established. A transmission-mode ultrasonic system for tomographic imaging of gas/liquid flow was designed based upon a fast binary back-projection image reconstruction algorithm. Emphasis was made on the evaluation of its performance and its application to flow regime identification. Several flow pattern models were made and the corresponding monitoring results were given. Finally, limitations and possible future implementations of the system are discussed.

Simulation study of the electrode array used in an ERT system

Abstract Using an established finite-element simulation software suite developed in Tianjin, the authors analysed some factors which influenced the sensing field of an electrical resistance tomography (ERT) system. In order to improve the space evenness of the sensing field and ‘focus’ its effective measurement space, the authors described a guard electrode scheme, which improved both the quality of the reconstructed image and the delineation of conductive regions within the vessel.

Fatigue strength improvement of stainless steel using weld toes dressing with low transformation temperature welding wire

Abstract In the present study, low transformation temperature welding wire (LTTW), which can induce residual compressive stress around 304L welded joints, has been developed to improve the fatigue performance of welded joints. Procedure of design and chemical composition of weld metal and deposited metal of LTTW are introduced. The microstructure of weld metal of LTTW is composed of low carbon martensite and residual austenite. The residual stress distribution of a single welding bead of LTTW was measured and the result shows that compressive residual stress is generated. In addition, fatigue test was also carried out on no-load cruciform welded joints of 304L stainless steel under three conditions: as welded, 308L dressing and LTTW dressing. The result shows that the fatigue life of LTTW dressing joints (2×106 cycles) is improved by 14–23 times and 3–6 times compared with that of as welded joints and 308L dressing joints.

Study on residual stress in socket weld by numerical simulation and experiment

In this paper, welding residual stress in socket weld of 304L stainless steel pipe was investigated using numerical simulation and validated by X-ray stress measurement. From the simulation results, the maximum tensile residual stresses were located at weld root and weld toe on both sides of the weld along pipe, which led to the fatigue failure. Pre-bevelling and low transformation temperature (LTT) dressing could decrease tensile residual stress both in hoop and axial direction at weld root and weld toe. After LTT dressing, compressive residual stress was generated throughout weld toe. Compressive stress can delay fatigue crack initiation and propagation. Therefore, pre-bevelling and LTT dressing can improve the fatigue life of socket weld.

Effect of welding on the corrosion behavior of X65/Inconel 625 in simulated solution

Due to excellent mechanical properties and corrosion resistance, the carbon steel/nickel-based alloy has huge potential for using in oil and gas industry. The pipes are usually joined by welding. Hence, it is significant to study the effect of welding on the corrosion properties. A literature search indicates that few studies have been conducted on the corrosion properties. Accordingly, in the present work, electrochemical measurements together with immersion tests were used to analyze the corrosion properties of Inconel 625 clad layers and butt-weld metal. The hardness was also determined. The microstructures, morphological features, and the changes observed in the surface composition were evaluated by X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM), together with energy-dispersive spectroscopy (EDS). The microstructures of Inconel 625 clad layers and butt-weld metal consist of primary γ-Ni solid solution dendritic, γ/laves interdendritic eutectic. Because of the heat effect induced by multi-pass welding, element segregation and more participation of carbide were observed in the butt-weld metal, which could account for higher hardness and inferior corrosion resistance of the butt-weld metal as compared to the clad layer.

The fabrication of highly conductive and flexible Ag patterning through baking Ag nanosphere−nanoplate hybrid ink at a low temperature of 100 °C

With the aim of developing highly conductive ink for flexible electronics on heat-sensitive substrates, Ag nanospheres and nanoplates were mixed to synthesize hybrid inks. Five kinds of hybrid ink and two types of pure ink were written to square shape on Epson photo paper using rollerball pens and sintered at a low temperature (100℃). The microstructure, electrical resistivity, surface porosity, hardness and flexibility of silver patterns were systematically investigated and compared. It was observed that the optimal mixing ratio of nanospheres and nanoplates was 1:1, which equipped the directly written pattern with excellent electrical and mechanical properties. The electrical resistivity was 0.103 μΩ·m, which was only 6.5 times of bulk silver. The enhancement compared to pure silver nanospheres or nanoplates based ink was owing to the combined action of nanospheres and nanoplates. It was a valued way to prepare Ag nanoink with good performance for printed/written electronics.

Effect of Ni-Coated Carbon Nanotubes on the Creep Behavior of Sn-Ag-Cu Solder by Nanoindentation

In the present study, the powder metallurgy route was used to successfully incorporate Ni-coated carbon nanotubes into Sn-Ag-Cu solder, to form a nanocomposite solder. Nanoindentation tests were performed on both composite and Sn-Ag-Cu solder samples to investigate their creep behaviour at room temperature. Characterization results revealed that with the addition of Ni-coated carbon nanotubes, the creep behaviour of composite solder improved significantly as compared to that of the unreinforced solder alloy. Moreover, increasing the maximum load from 20 mN to 100 mN increased the percentage reduction in creep strain rate from 4% to 28%, for the composite compared to its monolithic counterpart after 300 s of holding.Copyright