Papers by Author: Mahmood Anwar

Abstract: Recently, Composite Sandwich Panel (CSP) technology considerably influenced the design and fabrication of high performance structures. Although using CSP increases the reliability of structure, the important concern is to understand the complex deformation and damage evolution process. This study is focused on the flexural and indentation behavior of CSP made of chopped strand mat glass fiber and polyester matrix as face sheets and polyurethane foam as foam core subject to flexural and indentation loading condition. A setup of three-point bending and indentation test is prepared using different strain rates of 1mm/min, 10mm/min, 100mm/min and 500mm/min to determine the effects of strain rate on flexural and indentation behavior of CSP material. The load-extension, stress-extension response and energy absorption of the panel show the relation between the flexural and indentation behavior of panels to strain rate as by increasing the strain rate, the flexural properties and the energy absorption of panel are increased.

Abstract: Wear on Co-Cr-Mo biomedical implants is still a major issue especially for applications in articulation joints like in total ankle, knee and hip arthroplasty. Generation of excessive wear particles can coagulate in body tissues which later cause inflammation, bone loss and necrosis. Modification of implant surfaces is a common technique for increasing the hardness and thus minimizing these effects. In this study, thermal oxidation method was carried out on the Co-Cr-Mo to investigate the effects of different pretreatment processes and surface roughness on the hardness of oxide layer formed. Prior to oxidation process, all samples were annealed and pickled to remove residual stress and oxide scales respectively. The oxidation process was done inside furnace under atmospheric condition for 3 hours at 1160 °C. The metallic compositions, surface morphology and hardness of the oxide layer formed on the substrate were verified using X-ray diffraction (XRD), scanning electron microscope and micro-Vickers hardness analysis respectively. It is found that mechanical pretreatment provides oxide/carbide layer with higher hardness than chemical pretreatment method. It is believed that remnants of polishing diamond pastes trapped in roughness valleys react with metal matrix and later transform into carbides during oxidation process. In contrast, initial surface roughness of the substrate has no significant effect on the hardness of oxide/carbide layer.

Abstract: Wear debris and metal ion release generated during application of biomedical devices would cause adverse cellular response, inflammation and pain in the human body. Modifying of implant surface with rutile structure is one of the methods to reduce these problems. In the present study, an attempt was made to evaluate the effect of thermal oxidation temperature on surface morphology and structure of the Ti13Nb13Zr biomedical material. The substrates were heated at varied temperatures of 550°C, 700°C and 850°C for 9 hours and cooled inside muffle furnace at a constant rate of 5oC/min. Scanning electron microscopy and x-ray diffractive were employed to evaluate the surface morphology and analyze the structure of the oxidized substrates respectively. All thermally oxidized samples exhibit the presence of oxides without spallation regardless of the thermal oxidation temperatures. Surface morphology of oxidized substrates changes from smooth to nodular particles-like shape when the oxidation temperature increases from low to high. Rutile structure dominants the surface area when the substrate is thermally oxidized at 850 °C.

Abstract: Titanium alloys are commonly used in biomedical application in hard tissues replacement especially for knee and hip implants. Surface modifications are required prior to diamond coating process for improving tribological and wear properties of the titanium alloy. In this study, experiments were carried out to investigate the effects of different carburizing times on the adhesion strength of carbide layer formed on the Ti-6Al-7Nb. Prior to carburization process, all samples were treated to remove residual stress and oxide scales by annealing and pickling processes respectively. Hard wood charcoal powder was used as a medium. The carburizing process was carried out for 6, 12 and 24 hours at 950 °C under normal atmospheric condition. Surface morphology, carbide layer thickness and adhesion strength were evaluated using SEM, XRD, 3D Surface Profilometer and Blast Wear Tester (BWT). It is found that a mixture of oxide and carbide layers formed on the substrate and the thickness of these layers increases with carburizing time. It is also revealed that the 24 hr carburizing time provides the strongest adhesion strength among the three and TiC as the dominant layer.