Papers by Author: Mustafa Bakkal

Abstract: In this study, the hybridization effect on the mechanical properties of the natural fiber reinforced composites was investigated. For this purpose, glass fibers in different ratios of 2.5, 5 and 10 wt% were added in the polymer composites with cotton fibers at the ratios of 12.5 and 25 wt%. In order to have better interfacial bonding and increase the effectiveness of glass fiber on the mechanical properties, maleic anhydride coupling agent was added in the hybrid composite structures. At the end of the study, the best ratios of maleic anhydride, cotton and glass fiber for this kind composites were explored with respect to the economical and mechanical concerns. This study suggests that hybridization can be considered as most promising way to improve the mechanical properties for this novel composite materials.

Abstract: This chapter covers the series of machinability evaluation test result and discussions of Zr_52.5Ti₅Cu_17.9Ni_14.6Al₁₀ bulk metallic glass (BMG). These tests are lathe turning, drilling, milling and preliminary level grinding tests. In the continuous machining methods such as turning, drilling and grinding of BMG, above a threshold cutting speed, the low thermal conductivity of BMG leads to chip temperatures high enough to cause the chip oxidation and associated light emission. The high temperature produced by this exothermic chemical reaction causes crystallization within the chips. Chips morphology suggests that increasing amounts of viscous flow control the chip-removal process. Moreover, viscous flow and crystallization can occur during the machining of the bulk metallic glass, even under the high temperature gradient and strain rate. High cutting speed significantly reduced the forces for BMG machining due to thermal softening. However, in intermittent cutting process which is milling, there is no high temperature problem, special burr formations the rollover and the top burr were observed along the slot and achieved good surface roughness, R_a = 0.113 μm, using conventional WC-Co cutting tool. In each method, tests repeated for the conventional materials for comparison purpose. This study concludes the precision machining of BMG is possible with the selection of feasible tools and process parameters for each method.

Abstract: This paper aims to evaluate the machinability of a novel composite material which is textile fabric reinforced composite. In this study, four different cutting tools with different geometries were used due to the lack of information on tool selection for thermoplastic matrix composites. During machining of this novel composite, the fixture design is essential due to the very low elastic modulus of composite plates about 0.5 GPa. After designing special milling fixture, tests were performed in two limit values of cutting parameters, cutting speed and feed rate. Cutting force results, chip and burr formation were evaluated to determine suitable tool and cutting parameter selection.

Abstract: In this study, machinability of Zr-based bulk metallic glass (Zr52.5Ti5Cu17.9Ni14.6Al10) (BMG) material was investigated by conducting a set of milling and drilling experiments. In milling, two different tool paths, spiral and slot milling, were used. To investigate the behavior of BMG in drilling by two different tools at different feed rates, two sets of drilling experiments are conducted. Crown shaped exit burr formation are observed in drilling of BMG. Best results on thrust force, exit burr formation and hole surface roughness is obtained while using micrograin WC tool on BMG drilling. No chip light emission was observed during all tests. This study concludes that BMG can be achieved machining with good surface roughness, (Ra=0.113 µm), using conventional cutting tools.