• Structural Engineering and Mechanics
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• v.70 no.4
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• pp.499-511
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• 2019

In this study, the axial compressive behavior of novel quadruple C-channel built-up cold-formed steel columns with different slenderness ratio was investigated, using the experimental and numerical analysis. The axial compressive capacity and failure modes of the columns were obtained and analyzed. The finite element models considering the geometry, material and contact nonlinearity were developed to simulate and analyze the structural behavior of the columns further. There was a great correlation between the numerical analyses and test results, which indicated that the finite element model was reasonable and accurate. Then influence of, slenderness ratio, flange width-to-thickness ratio and screw spacing on the mechanical behavior of the columns were studied, respectively. The tests and numerical results show that due to small slenderness ratio, the failure modes of the specimens are generally local buckling and distortional buckling. The axial compressive strength and stiffness of the quadruple C-channel built-up cold-formed steel columns decrease with the increase of maximum slenderness ratio. When the screw spacing is ranging from 150mm to 450mm, the axial compressive strength and stiffness of the quadruple C-channel built-up cold-formed steel columns change little. The axial compressive capacity of quadruple C-channel built-up cold-formed steel columns increases with the decrease of flange width-thickness ratio. A modified effective length factor is proposed to quantify the axial compressive capacity of the quadruple C-channel built-up cold-formed steel columns with U-shaped track in the ends.

• Journal of the Korean institute of surface engineering
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• v.40 no.6
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• pp.254-257
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• 2007

TiN coating on tool steel has been widely used for the improvement of durability of tools. In this work, radical nitriding(RN) is carried out on SKD61 at $450^{\circ}C$ for 5 hours in the ammonia gas pressure $2.7{\times}10^3\;Pa$. The TiN coating is carried out by arc ion plating(AIP) with the process parameters: arc power 150 A, bias voltage -50V, coating time 40 minutes and nitrogen gas pressure $4{\times}10^3\;Pa$. Hardness, elastic modulus, friction coefficient and adhesion of TiN coating on substrates of both TiN/SKD61 and TiN/RN SKD61 coatings are investigated comparatively. The primary crystalline faces of TiN surface are(200) and(111) for TiN/SKD61 and TiN/RN SKD61 respectively. In addition to the primary phase, Fe phase exists in TiN/SKD61 coating, but not in TIN/RN SKD61. The hardness of TiN/RN SKD61 is about 700 Hv, 250 Hv(56%) higher than that of TiN/SKD61 at the near interface of TiN and substrates. At the TiN surface, hardness of TiN/RN SKD61 is 2,149 Hv, 71 Hv(3%) higher than that of TiN/SKD61. The elastic modulus of TiN coating is improved to 26.7 GPa(6%) by radical nitriding. The adhesion is improved by the RN coating showing no spalling. buckling and chipping on the scratch test track which are shown on the non-RN TiN/SKD61.