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        Nanotribological behavior of diamond surfaces using molecular dynamics with fractal theory and experiments

        Jen-Fin Lin,Te-Hua Fang,Cheng-Da Wu,Ko-Han Houng 한국물리학회 2010 Current Applied Physics Vol.10 No.1

        The frictional and indented behavior of a diamond asperity on a diamond plate was carried out using a molecular dynamics (MD) and experiments. The contact load, contact area, dynamic frictional force,and dynamic frictional coefficient increased as the contact interference increased at a constant loading velocity. The microcontact and frictional behavior can be evaluated between a rigid smooth hemisphere to a deformable rough flat plane by combined the deformed behavior of the asperity obtained from MD results with the fractal and statistic parameters. The comparison and the discrepancy of simulated results and nanoindentation and scratching experimental results will be discussed.

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        Establishment of the Model Widely Valid for the Melting and Vaporization Zones in Selective Laser Melting Printings Via Experimental Verifications

        Chang-Shuo Chang,Kuan-Ta Wu,Chang-Fu Han,Tsung-Wen Tsai,Sung-Ho Liu,Jen-Fin Lin 한국정밀공학회 2022 International Journal of Precision Engineering and Vol.9 No.1

        The thermally affected material properties operating in the three phases and porosity variations in the SS316L steel powder have been introduced to the numerical analyses for the transient volumetric heat source (Q) models developed for the solid powder, melting, and vaporization regions in the selective laser melting (SLM). The bulk Q is thus a function of these heat sources and their ratio defined for the liquid and vapor phases. The heat conduction developed for the solid powders with porosity strings the heat convection with Q as the moving heat source to solve two-dimensional temperature distributions efficiently without the confinement of operating conditions and phase presumption. The specimens with single- and multiple-track printings are prepared to investigate the effects of incident energy density (E) and power intensity (I o) on the geometries of single-track printings and the areal surface roughness (Sa) values of the multiple-track printings with 0 and 50% overlap ratios. Laser power and scanning velocity are the controlling factors for the melting pool depth D and width W . D and W become the governing factors for the keyhole with evaporations, which affects the height H of single track after solidification. The W and D results predicted by the theoretical models developed in this study have an error range, 5–20%, compared to the experimental ones, which is much lower than those reported in the literatures (Gusarov et al. in J Heat Transf 131(7):072101, 2009. https ://doi.org/10.1115/1.31092 45 ; Hussein et al. in Mater Des 52:638–647, 2013. https ://doi.org/10.1016/j.matde s.2013.05.070 ; Yin et al. Int J Adv Manuf Technol 83(9–12): 1847–1859, 2016. https ://doi.org/10.1007/s0017 0-015-7609-x ; Andreotta et al. in Finite Elem Anal Des 135: 36–43, 2017. https ://doi.org/10.1016/j.finel .2017.07.002 ). The contact angle ( ϕ * ) is defined as a function of single-track width ( W ) and solidification height ( H ). ϕ * and Sa are significantly reduced as an E is applied beyond its critical value (47.62–57.14 J/mm 3 ). Significant change in Sa is ascribed to the big difference in the morphology and its surface pattern when E or I o reaches its critical value.

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