No abstract

The effect of welding heat input on the fatigue life of a quenched boron steel and ferrite-bainite (FB) steel lap joint was investigated. Boron steel was quenched and welded with FB steel in heat input ranging from 0.29 to 0.67 kJ/mm. Boron, which can increase hardenability, affected the microstructure and hardness of the weld metal and heat affected zone (HAZ). The hardness of the weld metal and HAZ increased with decreasing welding heat input, and the high hardness of the weld metal and boron steel HAZ prevented the initiation of cracks in the stress concentration area around the bead. The bead width increased with increasing heat input, and the results of finite element method (FEM) showed that the maximum stress in the notch of the weld joint decreased when the bead width was increased. That is to say, the fatigue life increased when the weld joint had wider bead width. Finally, while the fatigue life was affected by the residual stress, the variation of the welding heat input used in this study had hardly any affect on the residual stress distribution.

Abstract:The stress concentration of lock-claws, which are one of the important parts for pneumatic fitting for a flexible tube connection, was investigated by finite element simulation. In this study, the generation of the local plastic deformation was predicted when the tube was hooked up to a pneumatic fitting in order to disperse the stress concentration, and design optimization was carried out using the Taguchi method. For the optimization, the outer width, bending angle, and inner radius of the lock-claws are used as main variables. As a result, their respective contribution ratios are revealed as 81.3%, 10.9%, and 1.5%. The ratio of the total stress distribution was improved by 4% compared with the initial design of the lock-claws. † Corresponding Author, suhch@dmi.re.kr

The impact of process conditions on the structure of thermal oxides formed on AlN was determined by high resolution transmission electron microscopy (HRTEM). Oxidation for 2 hours at 800 °C produced mostly amorphous oxide layers whereas oxidation for 6 hours at 1000 °C produced partly crystalline and epitaxial oxide layers. The crystalline oxide was mostly single phase α -Al 2 O 3 except at the surface where it was a mixture of γ -Al 2 O 3 and α -Al 2 O 3 . Prior to oxidation AlN crystal was almost free of defects. The AlN contained a high density of defects, and measurable amounts of oxygen and nitrogen near the interface when oxidized at 800 °C but it was nearly defect-free, and nitrogen-and oxygen-free for oxidation at 1000 °C. This could be due to the rapid out diffusion of nitrogen and oxygen at higher temperature leading to equilibrium throughout the sample.