Processing of Graphene/CNT-Metal Powder

In recent days, the demand for powder metallurgy components has increased due to unusual combination of properties. Carbon allotropes such as graphene and CNT are the novel material to enhance the properties of powder metallurgy component. However, processing of such materials is in infancy stage due lack of advance processing technique. This can be addressed through integration of several fabrication techniques to meet the industrial demands. The processing method and its important parameter will define the final property of the component. Such materials have found its applications in various fields like, sports, bio implants, aerospace and automobile sector

Tribological Aspects of Graphene-Aluminum Nanocomposites

Graphene is a new class of material in carbon group with strong sp2—hybridized 2D-sheet like nanomaterial. In order to make an effective utilization of their astounding properties, they are currently used in the form of reinforcements in various proportions in metals and its alloys to fabricate the nanocomposites. Graphene is incorporated in oil and grease at nano range that results in higher load-carrying capacity compared with that of raw grease and oils without additives, which shows that graphene possesses self-lubricating capacity. Graphene is a planar sheet-like structure (2D), with more contact surface area in the developed composites that can make them suitable for industrial applications with well-established tribological performance. The novelty of this work focuses on the role of graphene addition in enhancing the wear performance aluminum composites to replace the conventional materials by graphene composite combinations. The current chapter explains the processing and tribological performance of graphene-aluminum composites and its effect with various hybrid combinations of MWCNT/SiC/Al2O3. Dispersion of graphene is carried out through ultrasonic liquid processor followed by ball-milling aluminum powder. Thus prepared precursors are vacuum-pressed and microwave-sintered. Graphene in the nanocomposites has resulted in significantly improving the tribological properties, where it gives the wear resistance by creating a solid, lubricant layer between the sliding surfaces

A FEA simulation study of ball end mill for fixed 3+1 / 3+2 axis machining of Ti-6Al-4V.

This paper presents a Finite Element Analysis (FEA) simulation study conducted on ball endmill for fixed 3 + 1 and 3 + 2 axis orientations for machining Ti-6Al-4 V. This work adopts a tungsten carbide (WC) ∅18.6 mm diametrical/6fluted ball endmill to analyse maximum principal elastic strain (ϵmax-max-principal-elastic), maximum principal stress (σmax-principal)along with cutting tools forces in the axial (Fz), radial (Fy), tangential (Fx) and total (Ftotal) directions. The machining orientations considered for 3 + 1 and 3 + 2 axis are (i) tilt angles of 5°, 10°, 15° & 20° and (ii) lead angles of 5°, 10° & 15° with a constant fixed tilt angle of 10°. The cutting speed and feed rate per tooth is taken as 450 m/min and 0.5 mm/tooth. These are based on a high speed machining (HSM) scenario and has been dynamically simulated for a maximum of 175,000 cycles. From the simulation study considered at 16-20 valid cutting points, it can be noticed that in 3 + 1 axis, for a tilt angle of 10° and 3 + 2 axis for a Tilt 10°/Lead 10° the σmax-principaland ϵmax-max-principal-elasticare higher when compared with all tilt/lead angles. In case of total forces (Ftotal) from all 3 directions (Fx, Fyand Fz) not much variation can be noticed for different tilt/lead angles, but higher values are recorded with 3 + 1 axis at 5° tilt angle and 3 + 2 axis at tilt/lead angle of 10°. The paper provides a critical comparative study on the 3 + 1/ 3 + 2 axis orientations highlighting the cutting strain/stress with tool forces at valid cutting points considering entry, middle and exit region of the blank by emphasizing the importance of cutting tool design parameters

Birth Mass Is the Key to Understanding the Negative Correlation Between Lifespan and Body Size in Dogs

Larger dog breeds live shorter than the smaller ones, opposite of the mass-lifespan relationship observed across mammalian species. Here we use data from 90 dog breeds and a theoretical model based on the first principles of energy conservation and life history tradeoffs to explain the negative correlation between longevity and body size in dogs. We found that the birth/adult mass ratio of dogs scales negatively with adult size, which is different than the weak interspecific scaling in mammals. Using the model, we show that this ratio, as an index of energy required for growth, is the key to understanding why the lifespan of dogs scales negatively with body size. The model also predicts that the difference in mass-specific lifetime metabolic energy usage between dog breeds is proportional to the difference in birth/adult mass ratio. Empirical data on lifespan, body mass, and metabolic scaling law of dogs strongly supports this prediction

Processing, Characterization, and Properties of alpha-Al2O3-AA2900 Composites for Aerospace Brake Pad Applications

Replacing high-strength frictional materials with lightweight composite alternatives is currently a global challenge for researchers. In this work, aluminum alloy (AA2900)-based metal-matrix composites reinforced with 6 wt.% α-alumina were fabricated then subjected to T6 heat treatment followed by case hardening. The resulting composite samples exhibited improved hardness, strength behavior, and stress–strain behavior along with good ductility and formability when microwave sintered. Good microstructural bonding was observed for all samples, which can be attributed to the finer α-Al2O3 particulates used as the reinforcement and the microwave sintering process. The mechanical and wear properties of the composites were compared with existing aerospace brake pad material. Data for wear characteristics versus the number of landings for the existing brake pad material were considered as the benchmark data, and the feasibility of replacing it with the developed composites was evaluated

Characterization Studies on Graphene-Aluminium Nano Composites for Aerospace Launch Vehicle External Fuel Tank Structural Application

From the aspect of exploring the alternative lightweight composite material for the aerospace launch vehicle external fuel tank structural components, the current research work studies three different grades of Aluminium alloy reinforced with varying graphene weight percentages that are processed through powder metallurgy (P/M) route. The prepared green compacts composite ingots are subjected to microwave processing (Sintering), hot extruded, and solution treated (T6). The developed Nano-graphene reinforced composite is studied further for the strength–microstructural integrity. The nature of the graphene reinforcement and its chemical existence within the composite is further studied, and it is found that hot extruded solution treated (HEST) composite exhibited low levels of carbide (Al4C3) formations, as composites processed by microwaves. Further, the samples of different grades reinforced with varying graphene percentages are subjected to mechanical characterisation tests such as the tensile test and hardness. It is found that 2 wt% graphene reinforced composites exhibited enhanced yield strength and ultimate tensile strength. Microstructural studies and fracture morphology are studied, and it is proven that composite processed via the microwave method has exhibited good ductile behaviour and promising failure mechanisms at higher load levels

Selective laser melting of Al–Si–10Mg alloy: microstructural studies and mechanical properties assessment

Additive Manufacturing (AM) technique is widely recognized by aerospace sectors for its potential to fabricate complex shape components directly from a Computer-Aided Model data (CAM). Selective Laser Melting (SLM) is an innovative method high degree of adaptability among different AM techniques. SLM is one of the AM techniques adopted to produce the three-dimensional complex shape components. Current research work focuses on fabricating an Al–Si–10Mg aluminium alloy by SLM process which is studied for the influence of scanning speed and build orientation on the mechanical strength and surface finish of the as built component compared with as casted specimen. The importance of the sample studied for the scanning speed and built direction is relatively essential exclusively for dynamic applications. The as-built samples surface micrographs was surprisingly refined with a progressively reduced grain size diameter from 7.2 μm to 5.5 μm by increasing scanning speed compared to that of AlSi10Mg parts (∼9.1 μm). The mean layer thickness increased from 20 μm to 30 μm by decreasing the scanning speed from 500 mm/s to 200 mm/s. Attractive advantage of the Orowan mechanism, fine grain strengthening, and the graded interfacial layer, a considerably-high microhardness (135 ± 3.1HV), and enhanced mechanical properties were achieved

Tribological behavior of 316L stainless steel reinforced with CuCoBe + diamond composites by laser sintering and hot pressing: a comparative statistical study

The aim of this work was to perform a statistical analysis in order to assess how the tribological properties of a laser textured 316L stainless steel reinforced with CuCoBe - diamond composites are affected by diamond particles size, type of technology (laser sintering and hot pressing) and time of tribological test. The analysis started with the description of all response variables. Then, by using IBM® SPSS software, the Friedman’s test was used to compare how the coefficient of friction varied among samples in five-time points. From this test, results showed that there was no statistically significant difference in the coefficient of friction mean values over the selected time points. Then, the two-samples Kolmogorov-Smirnov (K-S) test was used to test the effect of the diamond particles size and the type of technology on the mean of the coefficient of friction over time. The results showed that, for both sintering techniques, the size of the diamond particles significantly affected the values of the coefficient of friction, whereas no statistical differences were found between the tested sintering techniques. Also, the two-way ANOVA test was used to evaluate how these factors influence the specific wear rate, which conducted to the same conclusions drawn for the previous test. The main conclusion was that the coefficient of friction and the specific wear rate were statistically affected by the diamond particles size, but not by the sintering techniques used in this work.This work was supported by FCT national funds, under the national support to R&D units grant, through the reference projects UIDB/04436/2020 and UIDP/04436/2020. Additionally, this work was supported by FCT with the reference projects UIDB/00319/2020 and PTDC/CTM-COM/30416/2017