Experimental Investigation of Wear Characteristics on Manganese Phosphate Coated AISI D2 Steel

Sivakumaran Ilaiyavel,Alankaram Venkatesan 한국정밀공학회 2012 International Journal of Precision Engineering and Vol. No.

Manganese Phosphate is an Industrial coating used to reduce friction and improve lubrication in sliding components. In this study, the tribology behavior of uncoated, manganese phosphate coated, Manganese Phosphate with Molybdenum disulphide (MoS2) coated AISI D2 steels was investigated. The Surface morphology of manganese phosphate coatings was examined by Scanning Electron Microscope (SEM) and Energy Dispersive X-ray Spectroscopy (EDX). The wear tests were performed in a pin on disk apparatus as per ASTM G-99 Standard. The wear resistance of the coated steel was evaluated through pin on disc test using a sliding velocity of 0.35 m/s under normal load of 10 to 60 N at the controlled condition of temperature and humidity. The Coefficient of friction and wear loss were evaluated. The temperature rise after 15 min and 30 min were recorded for each load. Wear pattern of uncoated, manganese phosphate coated and Manganese Phosphate with Molybdenum disulphide (MoS2) coated pins were captured using Scanning Electron Microscope (SEM). Based on the results of the wear test, the manganese phosphate with Molybdenum disulphide (MoS2) coating exhibited the lowest average coefficient of friction 0.15 and the lowest wear loss 0.6 mm3 under 60 N loads.

Measurement and assessment of imperfections in plasma cut-welded H-shaped steel columns

K. S. Sivakumaran,P. Arasaratnam,Kim J. R. Rasmussen 국제구조공학회 2006 Steel and Composite Structures, An International J Vol.6 No.6

H-shaped welded steel column members are fabricated by welding together pre-cut flanges and the web. Modern fabricators are increasingly using plasma-cutting technique instead of traditional flame cutting. Different fabrication techniques result in different degrees of geometric imperfections and residual stresses, which can have considerable influence on the strength of steel columns. This paper presents the experimental investigation based temperature profiles, geometric imperfections, and built-in residual stresses in plasma cut-welded H-shaped steel column members and in similar flame cut-welded H-shaped steel columns. Temperature measurements were taken during and immediately after the cutting operations and the welding operations. The geometric imperfections were established at closely spaced grid locations on the original plates, after cutting plates into plate strips, and after welding plate strips into columns. Geometric imperfections associated with plasma cut element and members were found to be less than those of the corresponding elements and members made by flame cutting. The “Method of Section” technique was used to establish the residual stresses in the plate, plate strip, and in the welded columns. Higher residual stress values were observed in flame cut–welded columns. Models for idealized residual stress distributions for plasma cut and flame cut welded sections have been proposed.

Melatonin Protects Human Adipose-Derived Stem Cells from Oxidative Stress and Cell Death

Tan, Shaun S.,Han, Xiaolian,Sivakumaran, Priyadharshini,Lim, Shiang Y.,Morrison, Wayne A. Korean Society of Plastic and Reconstructive Surge 2016 Archives of Plastic Surgery Vol.43 No.3

Background Adipose-derived stem cells (ASCs) have applications in regenerative medicine based on their therapeutic potential to repair and regenerate diseased and damaged tissue. They are commonly subject to oxidative stress during harvest and transplantation, which has detrimental effects on their subsequent viability. By functioning as an antioxidant against free radicals, melatonin may exert cytoprotective effects on ASCs. Methods We cultured human ASCs in the presence of varying dosages of hydrogen peroxide and/or melatonin for a period of 3 hours. Cell viability and apoptosis were determined with propidium iodide and Hoechst 33342 staining under fluorescence microscopy. Results Hydrogen peroxide (1-2.5 mM) treatment resulted in an incremental increase in cell death. 2 mM hydrogen peroxide was thereafter selected as the dose for co-treatment with melatonin. Melatonin alone had no adverse effects on ASCs. Co-treatment of ASCs with melatonin in the presence of hydrogen peroxide protected ASCs from cell death in a dose-dependent manner, and afforded maximal protection at $100{\mu}M$ (n=4, one-way analysis of variance P<0.001). Melatonin co-treated ASCs displayed significantly fewer apoptotic cells, as demonstrated by condensed and fragmented nuclei under fluorescence microscopy. Conclusions Melatonin possesses cytoprotective properties against oxidative stress in human ASCs and might be a useful adjunct in fat grafting and cell-assisted lipotransfer.

Melatonin Protects Human Adipose-Derived Stem Cells from Oxidative Stress and Cell Death

Shaun S. Tan,Xiaolian Han,Priyadharshini Sivakumaran,,Shiang Y. Lim,Wayne A. Morrison 대한성형외과학회 2016 Archives of Plastic Surgery Vol.43 No.3

Background Adipose-derived stem cells (ASCs) have applications in regenerative medicine based on their therapeutic potential to repair and regenerate diseased and damaged tissue. They are commonly subject to oxidative stress during harvest and transplantation, which has detrimental effects on their subsequent viability. By functioning as an antioxidant against free radicals, melatonin may exert cytoprotective effects on ASCs. Methods We cultured human ASCs in the presence of varying dosages of hydrogen peroxide and/or melatonin for a period of 3 hours. Cell viability and apoptosis were determined with propidium iodide and Hoechst 33342 staining under fluorescence microscopy. Results Hydrogen peroxide (1–2.5 mM) treatment resulted in an incremental increase in cell death. 2 mM hydrogen peroxide was thereafter selected as the dose for co-treatment with melatonin. Melatonin alone had no adverse effects on ASCs. Co-treatment of ASCs with melatonin in the presence of hydrogen peroxide protected ASCs from cell death in a dose-dependent manner, and afforded maximal protection at 100 μM (n=4, one-way analysis of variance P<0.001). Melatonin co-treated ASCs displayed significantly fewer apoptotic cells, as demonstrated by condensed and fragmented nuclei under fluorescence microscopy. Conclusions Melatonin possesses cytoprotective properties against oxidative stress in human ASCs and might be a useful adjunct in fat grafting and cell-assisted lipotransfer.

Flexural behavior of steel storage rack base-plate upright connections with concentric anchor bolts

Xianzhong Zhao,Zhaoqi Huang,Yue Wang,Ken S. Sivakumaran 국제구조공학회 2019 Steel and Composite Structures, An International J Vol.33 No.3

Steel storage racks are slender structures whose overall behavior and the capacity depend largely on the flexural behavior of the base-plate to upright connections and on the behavior of beam-to-column connections. The base-plate upright connection assembly details, anchor bolt position in particular, associated with the high-rise steel storage racks differ from those of normal height steel storage racks. Since flexural behavior of high-rise rack base connection is hitherto unavailable, this investigation experimentally establishes the flexural behavior of base-plate upright connections of high-rise steel storage racks. This investigation used an enhanced test setup and considered nine groups of three identical tests to investigate the influence of factors such as axial load, base plate thickness, anchor bolt size, bracket length, and upright thickness. The test observations show that the base-plate assembly may significantly influence the overall behavior of such connections. A rigid plate analytical model and an elastic plate analytical model for the overall rotations stiffness of base-plate upright connections with concentric anchor bolts were constructed, and were found to give better predictions of the initial stiffness of such connections. Analytical model based parametric studies highlight and quantify the interplay of components and provide a means for efficient maximization of overall rotational stiffness of concentrically anchor bolted high-rise rack base-plate upright connections.