Abstract: MoSi2 based composites have been recognized as a potential candidate materials for high temperature structural applications. Although, MoSi2 has been reinforced by a variety of ceramic particles, ductile phase toughening of MoSi2 has received only limited attention. In the present investigation, ductile refractory metal (Mo and Ta) foils were used as reinforcements in MoSi2 matrix to prepare the laminated composites. 20 vol% SiC particles (SiCp) were also added in MoSi2 matrix to reduce the thermal expansion mismatch between MoSi2 and the ductile metal foils. The improved bonding between MoSi2-SiCp matrix layer and Mo / Ta foils due to reduced residual thermal stresses resulted in significant improvement in the room temperature fracture toughness of both the composite systems over the monolithic MoSi2.
Abstract: Utilization of natural fibers for making composites and employ them in various structural applications due to superior specific properties drawn the attention of researchers in the present scenario. In the present research a new natural fiber i.e. Palm Tree Sprout Leaf (PTSL) is introduced, and is extracted by a novel technique called pure splitting method. Untreated and chemically treated palm tree sprout leaf fiber are reinforced into the polyester matrix for fabricating composites and are tested for determining their mechanical and dielectric properties as per ASTM procedures. Morphological characterization of fiber is also done using Scanning Electron Microscope. Tensile strength and modulus, flexural strength of chemically treated PTSL fiber reinforced polyester composites exhibited a reasonable improvement when compared with the untreated fiber reinforced polyester (FRP) composites. Flexural modulus of PTSL FRP composites is more when compared with chemically treated FRP composites at all volume fractions of fiber. Impact strength of PTSL FRP composites clearly increased with increase in fiber volume fraction. The reasonable values of dielectric strength at various fiber volume fractions exhibited by PTSL FRP composites will give an opportunity for designer in choosing light weight insulating material.
Abstract: The High Velocity Oxy-fuel (HVOF) spray technique has been used by many researchers to deposit composite coatings, but there is less available literature discussing the fabrication of bulk metal matrix composites by this technique. In the current study, aluminum matrix composites with dispersions of alumina (Al2O3) and silicon carbide (SiC) particulates are fabricated by HVOF spray technique. The study comprises the steps of providing the substrate, preparing a mixed powder comprising a first metal powder as a matrix and a second metal powder comprising a ceramic and selected as reinforcement. The detailed procedures to prepare the bulk by using the same are reported. An in-depth characterization of the composite formed has been performed by X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). Hardness of the composite formed is measured on Vickers microhardness tester. This study showed the possibility of fabricating bulk metal matrix composites of larger size by HVOF spray technique.
Abstract: Using the pin on disc wear testing machine the wear characteristics of sisal fibre composite of different content were studied and alignment of fibres in polymer composite were known by scanning electron microscopy. It was observed that when there was no fibre content, the wear was ~25 micron but when the fibre content made 10% to the polymer, the wear increased upto 100 micron and its increased 125 micron at 20% fibre content, after this there is sharp decrease in wear when the sisal fibre content was increased up to 40% and its again reached to 25 micron when the fibre content was increased up to 60% and again after increasing the fibre content 80% the wear gradually increased to 175 micron. Thus to have less wear the fibre content should be 60% in composite.
Abstract: The role of cell wall microstructure in inﬂuencing the mechanical behaviour of closed cell aluminium foam was investigated. The morphologies of the cell wall were characterized by using optical microscopy. An attempt has been made to describe the relationship between the microstructure of cell wall and mechanical properties primarily pertaining to the compressive response. The closed-cell foams in as-foamed and aged condition, having rather similar relative densities and cell structures but significantly different cell-wall microstructure have been examined. It was found that in as foam condition thick dendritic structure is present. On ageing at different temperatures for different duration, it was found that as ageing progresses the dendritic structure break in to finer precipitates resulting in improvement in microstructure of the cell wall. The compression tests also affirm the microstructural contribution to energy absorption capability.
Abstract: A two noded active sandwich beam element is formulated by employing layerwise Timoshenko’s beam theory. Displacement continuity conditions are imposed between different layers of the sandwich. This element is used to model an adaptive sandwich beam with macro-fiber composite (MFC) as extension actuator and shear actuated fiber composite (SAFC) as shear actuator. Influence of thickness and volume fraction of the active fiber (PZT-5A and single crystal PMN-PT) in the composite actuators on the actuation performance of the sandwich beam is investigated. Based on several numerical experiments, it is found that the PMN-PT based shear actuators give maximum actuation authority for the volume fraction of the fibers in the range of 80%-85%, whereas in case of PZT-5A based shear actuators the actuation authority remains maximum for the fiber volume fractions 80% and above.
Abstract: Composite materials are increasingly used in aerospace, naval and automotive vehicles due to their high specific strength and stiffness. In the area of Non destructive testing, ultrasonic C-scans are used frequently to detect defects in composite components caused during fabrication and damage resulting from service conditions. Ultrasonic testing uses transmission of high frequency sound waves into a material to detect imperfections or to locate changes in material properties. The most commonly used ultrasonic testing technique is pulse echo and through transmission wherein sound is introduced into a test object and reflections (echoes) are returned to a receiver from internal imperfections. Under low-velocity impact loading delaminating is observed to be a major failure mode. This report presents the use of above two techniques to detect the damage in glass fiber reinforced plastic (GFRP) laminates. Pulse echo is used to locate the exact position of damage and through transmission is used to know the magnitude of damage in composite. This paper work will be carried out on two different thicknesses and at impact energy levels varying from 7 to 53J. The ensuring delamination damage will be determined by ultrasonic C-scans using the pulse-echo immersion method for through transmission. Delamination areas were quantified accurately by processing the raw image data using a digital image processing technique. Based on the data obtained, correlation will be established between the delamination area and the impact energy.
Abstract: This work studied the ball indentation test at room temperature to characterize the local tensile properties of bi-metallic weld joints. The weld specimens used were fabricated by joining between SA 508 Gr. 3 ferritic steel and Type 304LN stainless steel with Alloy 82 buttering on the ferritic steel side and Alloy 82/182 weld metal. The test results showed that yield stress (YS) of weld metal was slightly higher than that of Type 304 and smaller than that of SA508 Gr.3, and ultimate tensile stress (UTS) of weld metal was similar as those of Type 304 and SA508 Gr.3 base metals. Also, the values of YS and UTS of buttering layer (Alloy 82) were nearly same as those of weld metal. Heat-affected-zones (HAZs) showed higher YS and UTS values compared to their base metals.
Abstract: Cast magnesium AZ91D, used for cases, covers and housings, for consumer electronics faces increased requirements on aesthetically pleasing surfaces. The casting conditions have strong effect on as-cast surface roughness for thin-walled castings. This is currently not well understood. In the current study surface roughness was measured parallel and perpendicular to the filling direction and on both sides on straight flat thin speci¬men. The parameters studied were First and Second phase injection speed, Cooling time, and Melt temperature. The Fix and Moving side die tempera¬tures were varied, with the fix side was kept hotter. A D-Optimal experimental design was used resulting in 31 different settings. The re¬sults showed that roughness was decreased by mini¬mizing the temperature difference between the two die halves, increasing cooling time and first phase injection speed. Increasing the second phase injection speed increased roughness.
Abstract: A356 aluminium alloy has a wide applicability in the manufacturing of automotive parts. Cooling slope (CS) rheocasting process has been used in the present work to produce A356 billets having near spherical morphology of primary Al phase. Absence of dendritic primary phase, observed in case conventionally cast A356 alloy, and finer distribution of secondary eutectic Si phase within the matrix establishes the usefulness of the CS casting route. Near spherical primary phase in the rheocast alloy ensures better strength, elongation properties and structural integrity in the produced billets. The liquid melt is allowed to flow through the cooling slope after pouring at 6500C. Rapid heat exchange between the flowing melt and slope wall and the atmosphere facilitates heterogeneous nucleation of α-Al phase on the cooling slope wall. Shear driven flow of the solidifying melt is found responsible for separation of α-Al phase from the slope wall and generation of nearly spherical morphology of the primary phase in the microstructure. Grain refiner addition in the melt leads to enhance the primary α-Al percentage in the microstructure and also aids to the improvement of degree of sphericity and reduction of spheroid size. So, grain refining helps to improve the strength, elongation and fracture properties of rheocast billets further.