Applied Mechanics and Materials Vols. 592-594

Abstract: This study reports the development of Al-TiC metal matrix composites with 2.5 % of TiC is developed using in-situ route by the reaction of carbon powder and halide salt K₂TiF₆ with the aluminium melt. The composites were fabricated using stir casting process by varying three different factors such as temperature, addition time and holding time. The experimental trials are decreased using L₉ Orthogonal array in taguchi design. The prepared composite specimen was characterized using XRD, hardness, and Microstructure examination using optical microscopy.

Abstract: Ultrasonic Non-destructive testing is a well known technique for inspecting fiber reinforced composite structures however; its capability is severely limited by the high attenuation in thick and multi layer structures. Guided wave ultrasonic inspection has been reported to be useful tool for quantitative identification of composite structures. It takes advantage of tailoring / generating desired ultrasonic wave modes (Symmetric and anti-symmetric) for improved transmission through the composite structure. For this, guided waves have to be generated selectively by precisely placing transducer at an angle to the test surface. Automation of two axis fixture for transmission and reception of transducers have to be used for avoiding manual errors. The captured signals have to be processed in order to extract useful information from the received ultrasonic signals. The proposed project aims at developing automated guided wave inspection methods along with digital signal processing for generating dispersion curves for thick composited. Using test laminates with implanted defects, methodology for thick composite inspection with guided wave ultrasonic’s will be established. For this data will be captured and analyzed using Labview software.

Abstract: The material development is aimed at utilizing a suitable Metal Alloy in combination with a most appropriate plastic material considering the achievement of desirable basic features of Smart materials like Shape Memory Effect, Flexibility, recovery time etc. In the present work shape memory composites were developed using Ni-Ti alloy as reinforcement into the epoxy matrix. To understand the recovery and the influence of the Young’s modulus of the matrix, three different combinations of epoxy and hardeners are used. This experiment has considered different combinations of Ni-Ti SMA wire spacing, Ni-Ti SMA wire orientations and Epoxy Mix proportions. The experiments are designed based on ‘Taguchi’s’ L9 orthogonal arrays. ‘Taguchi’s’ method combined with S/N ratio of analysis is used as the statistical tool for optimization of the most recommendable combination of the newly developed SMA polymer composite material. This is due to the special intention of finalizing the most advantageous product in view of physical properties, percentage shape recovery, recovery time etc.

Abstract: Tool based mechanical micromachining technology is gaining importance in MEMS device fabrication because of its ability to machine 3D micro features on different engineering materials. This paper presents the development of tool based mechanical micromachining center with piezoactuated workpiece feeding system. A high speed spindle is used to rotate the micromilling/drilling tool at a speed of 12,000 to 60,000 rpm. A thermoelectric based liquid cooling system is developed to control the temperature of the high speed spindle at a set value. Along with the X-Y positioning system, the workpiece is also mounted on a piezoactuator to provide Z-axis motion during machining operation. An electrical continuity based tool-workpiece contact detection system is developed to overcome premature tool failure during initial tool registration with the workpiece. Based on the developed tool-workpiece contact sensor, an in-situ measurement system is developed to measure the micromachining depth. Experiments were conducted to measure the performance of spindle cooling system and in-situ measurement system.

Abstract: This present paper is an investigation made to study the un-lubricated sliding wear behavior of Al6061 alloy composites reinforced with graphite particulates of size 100-125 μm. The content of graphite in the alloy was varied from 6-9% in steps of 3 wt. %. The liquid metallurgy technique was used to fabricate the composites. A pin-on-disc wear testing machine was used to evaluate the volumetric wear loss, in which a hardened EN32 steel disc was used as the counter face. The results indicated that the volumetric wear loss of the composites was lesser than that of the Al6061 matrix alloy and it further decreased with the increase in graphite content up-to 6 wt.%. For composites containing 9 wt. % of graphite particulates, the volumetric wear loss was more than that of 6wt. % composites, but lesser than base matrix alloy. However, the material loss in terms of wear volume increased with the increase in load and sliding speed, both in case of composites and the alloy.

Abstract: In the present investigation, effect of minor additions of magnesium (Mg) content on the dry sliding wear behavior of A356 alloy has been reported. Alloy composition, normal pressures and sliding distances on A356 alloy has been studied. The worn surfaces were characterized by SEM microanalysis. The results indicate that, the wear rate of A356 alloy increases with increase in normal pressures and sliding distances in all the cases and decreases with 0.7% Mg addition to the A356 alloy. This is due to the change in microstructure resulting in improvement of hardness and strength of the alloy. The worn surface study indicates that, the formation of oxide layer between the mating surfaces during sliding improves sliding wear performance.

Abstract: This paper presents the mechanical and machinability properties of aluminium 6061 alloy reinforced with boron carbide composite is compared with the addition of graphite particles with AlB₄C. The composites were fabricated by stir casting process. The experimental results showed that the hardness of the composite increases with the increasing addition of boron carbide. Tests for machinability characteristics was carried out with carbide tool at different cutting speeds keeping feed and depth of cut as constant. The machining tests revealed that the addition of graphite to Al-B₄C composite has enhanced its machining properties.

Abstract: Thermosetting and thermoplastic resins are becoming widely accepted alternate materials in engineering industry. Industries seek alternate materials starting from containers to aircraft parts for reducing weight and increasing durability. Mere resin based plastic components may not fulfil these requirements. Fiber materials are added in composites to increase the strength, whereas filler materials are generally inert materials which are added to reduce material cost and to improve the mechanical properties such as hardness and wear resistance to some extent. In this paper the effect of carbon fibre, silica and fly-ash particulate addition on the tensile and impact behaviour of polyester and epoxy resin are investigated. The composite laminates were fabricated by hand layup method and cured in room temperature. Tensile and impact properties are increased on addition of carbon fiber up to 30% by weight. Addition of fly-ash particulate and silica in micron sizes decresed the tensile and impact strength.

Abstract: Carbidic Austempered Ductile Iron (CADI) is a recent addition to the Austempered Ductile Iron (ADI) family. The effect of chills on the microstructure and mechanical properties of CADI was investigated after Austempering. Three samples of chromium alloyed CADI, the first sample without chill, the second sample with bottom chill and the third sample with bottom and side chills were produced in order to evaluate the effect of chills on its mechanical properties. The samples were austenised for 2 hours at 925° C and then austempered at 325° C for 2 hours in a salt bath furnace. The microstructural features of the as-cast and the austempered CADI samples were analysed using Optical Microscope and Scanning Electron Microscope (SEM). The mechanical properties of the CADI samples (as-cast and austempered) were evaluated for hardness, impact and wear. By austempering at 325° C for 2 hours a typical microstructure of bainite was produced in all the three samples. Hardness and wear resistance of austempered samples produced using bottom and side chills were considerably higher than the corresponding values in samples produced without using any chill and also by using only bottom chill. This enhanced mechanical property in the bottom and side chill sample is attributed to the presence of bainite, carbides and more of uniform fine graphite nodules.

Abstract: NiTi shape memory alloys usually consist of binary alloys of nickel and titanium concentrations near the equiatomic composition. Due to high hardness of NiTi alloys, the traditional machining processes are not able to machine these alloys. Nontraditional processes like electro discharge machining (EDM) ; due to their unique mechanism of material removal are useful alternatives in such case.The overall machining performance of electro discharge machining process depends on the electrical, thermal properties of both tool and workpiece materials. Cryogenic treatment has a history of improving mechanical, electrical, and thermal properties of materials. Recently, very few researchers applied cryogenic cooling and treatment of workpiece and tool in conventional EDM and found notable improvement in machining performance. In this study, NiTi shape memory alloys was subjected to around-185C for cryogenic treatment and the effects of cryogenic treatments on the machiniability of NiTi shape memory alloys workpieces in electro discharge machining have been investigated. The electrical conductivity of workpiece exceptionally improved. Experimental results showed about 19% increase in material removal rate of cryogenic treated workpieces. Variations in tool wear rate was found to be marginal.