Potential fatigue strength improvement of AA 5083-H111 notched parts by wire brush hammering: Experimental analysis and numerical simulation

The effects of milling as machining process and a post-machining treatment by wire-brush hammering, on the near surface layer characteristics of AA 5083-H111 were investigated. Surface texture, work-hardening and residual stress profiles were determined by roughness measurement, scanning electron microscope (SEM) examinations, microhardness and X-ray diffraction (XRD) measurements. The effects of surface preparation on the fatigue strength were assessed by bending fatigue tests performed on notched samples for two loading stress ratios R0.1 and R0.5. It is found that the bending fatigue limit at R0.1 and 107 cycles is 20% increased, with respect to the machined surface, by wire-brush hammering. This improvement was discussed on the basis of the role of surface topography, stabilized residual stress and work-hardening on the fatigue-crack network nucleation and growth. The effects biaxial residual stress field and surface work-hardening were taken into account in the finite element model. A multi-axial fatigue criterion was proposed to predict the fatigue strength of aluminum alloy notched parts for both machined and treated states

Experimental investigation on micromachining of epoxy/graphene nano platelet nanocomposites

This paper investigates the effect of graphene nano platelet (GNP) content (%weight fraction) on the machinability of epoxy/GNP nanocomposites. The machinability of nanocomposites with varying loadings of GNP content was evaluated experimentally through the characterisation of cutting forces, surface morphology, chip morphology and tool wear. The minimum chip thickness phenomena of epoxy/GNP occurred at feed per tooth (FPT) between 0.2 and 0.4 μm. In order to achieve to better surface quality, the FPT should be over 0.4 μm. Epoxy/GNP with 1.0 wt% nanocomposite has produced the highest cutting force of a feed rate of ~ 3 N at 12 μm/rev. Epoxy/GNP nanocomposites exhibit the different cracking tendencies compared with plain epoxy, and the tool wear for GNP/epoxy nanocomposites is very small compared with metal nanocomposites. There is no significant difference in slot width accuracy between different types of tools, such as uncoated tool, diamond-like carbon-coated and diamond-coated tools

Effect of calcium carbonate replacement on workability and mechanical strength of portland cement concrete

Abstract. The continued growth of the world construction sectors has resulted in high demand for concrete materials. The innovation of using filler as a replacement for cement is becoming a trend in order to reduce the cement consumption and provide benefit in various ways. Hence forth, 10% of cement was replaced by the calcium carbonate (CaCO3) in this study. CaCO3 is a natural material, which has a finer particles size as compared to the cement particles. This improves particle packing of concrete and give spacer effect. The concrete with CaCO3 replacement possess a higher slump, which increased the workability. The specimens were prepared in 150mm x 150mm x 150mm mould. At 28 days, the water absorbed by hardened concrete was lower for CaCO3 as microscopy analysis indicates very low porosity in CaCO3 concrete. Mechanical properties tests were conducted in 3, 7 and 28 days. The CaCO3 helps to increase the early strength, due to the accelerator effect and high rate of hydration which hardens the concrete quicker. At matured age, the concrete with the CaCO3 addition exhibits lower strength as compared with concrete without CaCO3, but still within the target strength. Keywords: Calcium carbonate, ordinary Portland cement, particle packing, concrete workability and strengt

Effect of microwave sintering treatment to the flank wear of titanium carbide tools in milling operations

The paper reports the research on the improvement of tool wear resistant of Titanium Carbide (TiC) cutting tool after microwave post sintering treatment. Titanium Carbide square milling insert was microwave sintered at 600°C with 15 minutes of holding time. The face milling operations were conducted to Carbon Steel S45C block (130 mm x 95 mm x 40 mm) by using both of original and microwave sintered insert at 5 different cutting speed (60, 90 , 120 , 150 and 180 m/min), constant feed rate (0.2 mm/tooth) and constant depth of cut(0.2 mm/tooth). The flank wear of the insert was measured every nearest 10th minute of complete cutting passes. The results of the experiment show that microwave post sintering treatment improves the tool resistant of the TiC insert. The flank wear of the sintered insert is lower at any machining time and all cutting speed. The research also found that the percentage of the improvement is lower at higher cutting speed compare to lower cutting speed

Carbon nanotubes/low density polyethylene composite films for strain sensing

Carbon nanotubes (CNTs) are known to have remarkable mechanical and electrical properties. One of those properties is piezoresistance which makes them suitable to be used in the field of strain sensing. Multi-walled nanotubes (MWNTs) were incorporated in low-density polyethylene (LDPE) matrix to form composite film sensors with different concentrations of 1, 2, 3.5, 5, 6.5, and 8 weight%. The fabrication of such composite was carried out using solid-state mixing, followed by melt blending process. Both extrusion and compression molding processes were used where compression showed more promising results in terms of electrical conductivity. Two types of molds were examined in compression molding, namely flash type mold and a positive type mold. The positive type mold showed better control over process parameters. Furthermore two types of multi-walled carbon nanotubes of different aspect ratios were investigated using the positive type mold to examine their effect on the composite conductivity. The ones with the higher aspect ratio showed much higher conductivity. Strain sensitivity measurements were carried out on composite film samples at percolation threshold and beyond and gauge factors were obtained which showed significantly higher sensitivity than that of conventional strain gauges

Micro-Electro Discharge Machining: Principles, Recent Advancements and Applications

Micro electrical discharge machining (micro-EDM) is a thermo-electric and contactless process most suited for micro-manufacturing and high-precision machining, especially when difficult-to-cut materials, such as super alloys, composites, and electro conductive ceramics, are processed. Many industrial domains exploit this technology to fabricate highly demanding components, such as high-aspect-ratio micro holes for fuel injectors, high-precision molds, and biomedical parts.Moreover, the continuous trend towards miniaturization and high precision functional components boosted the development of control strategies and optimization methodologies specifically suited to address the challenges in micro- and nano-scale fabrication.This Special Issue showcases 12 research papers and a review article focusing on novel methodological developments on several aspects of micro electrical discharge machining: machinability studies of hard materials (TiNi shape memory alloys, Si3N4–TiN ceramic composite, ZrB2-based ceramics reinforced with SiC fibers and whiskers, tungsten-cemented carbide, Ti-6Al-4V alloy, duplex stainless steel, and cubic boron nitride), process optimization adopting different dielectrics or electrodes, characterization of mechanical performance of processed surface, process analysis, and optimization via discharge pulse-type discrimination, hybrid processes, fabrication of molds for inflatable soft microactuators, and implementation of low-cost desktop micro-EDM system