68 research outputs found

    Microstructural evolution of Ti6Al4V in ultrasonically assisted cutting: numerical modelling and experimental analysis

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    This paper aims to elucidate the effect of ultrasonically assisted cutting (UAC) on microstructure in a machined surface and a chip of Ti6Al4V alloy. To investigate microstructural evolution, a FE-based cutting model with an enhanced material formulation and temperature dependent material properties was developed. A Johnson-Mehl-Avrami-Kolmogorov (JMAK) model for the Ti6Al4V alloy was employed to simulate dynamic recrystallization and predict a resultant grain size. Due to a specific thermomechanical load in UAC, the distributions of strains, strain rates and temperatures in a workpiece in the machining process were investigated. In this study, five points under the machined surface and ten points under the unmachined one were tracked to compare the evolution of a grain size and its average magnitude in the alloy subjected to conventional cutting (CC) and UAC. Besides of numerical modelling and experimental studies for the resultant grain size were compared and additional validation using microhardness measurements were conducted. The results showed that the average grain size of the machined surface and the chip in case of UAC was larger and more uniform than that in case of CC. The study also presents discussions about the effect of a vibration amplitude, a feed rate and a cutting speed on the average grain size in machining of Ti6Al4V. The comparison between CC and UAC indicates that the change in average grain size in UAC was smaller than that in CC, thus demonstrating a lower level of damage in UAC

    Improved analytical prediction of chip formation in orthogonal cutting of titanium alloy Ti6Al4V

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    The aim of this paper is to propose an analytical model of chip formation for precise prediction of orthogonal cutting of Ti6Al4V. This alloy is used broadly in aerospace components; hence, prediction of thermomechanical parameters of its orthogonal cutting is crucial for various industrial applications. The suggested analytical model needs only cutting parameters and tool geometry as input; it can predict not only cutting forces but also main features of a primary shear zone and a tool-chip interface. A non-equidistant shear zone model is employed to calculate shear strains and a shear strain rate in the primary shear zone, and a simplified heat-transfer equation is used for temperature. A Calamaz-modified Johnson-Cook material model that accounting for flow softening at high strains and temperature-dependent flow softening is applied to assess shear stresses in the primary shear zone. In addition, a shear-angle solution is modified for Ti6Al4V. At the tool-chip interface, a contact length, equivalent strain and an average temperature rise are defined. Besides, the effect of sliding and apparent friction coefficients is investigated. For a sawtooth chip produced in the cutting process of Ti6Al4V, the segmented-chip formation is analysed. A chip-segmentation frequency and other parameters of the sawtooth chip are also obtained. The predicted results are compared with experimental data with the cutting forces, tool-chip contact length, shear angle and chip-segmentation frequency calculated with the developed analytical model showing a good agreement with the experiments. Thus, this analytical model can elucidate the mechanism of the orthogonal cutting process of Ti6Al4V including predictive capability of continuous and segmented chip formation

    Enhanced machinability of SiC-reinforced metal-matrix composite with hybrid turning

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    Particle-reinforced metal-matrix composites are promising engineering materials thanks to their superior mechanical and thermal properties. However, their poor machinability is a deterrent for use in wider applications, due to the presence of hard ceramic particles, which results in rapid tool wear during machining. Ultrasonically assisted turning (UAT) is a hybrid machining technique, in which the cutting tool is made to vibrate at high frequencies and low amplitudes. In this study, the machinability and tool wear of machining SiCp/Al metal matrix-composite was compared for dry UAT and conventional turning with the use of a cemented carbide (WC) and a polycrystalline diamond (PCD) tool. With the use of ultrasonic assistance, a significant reduction in cutting forces was achieved with a slight increase in cutting temperature. Continuous and semi-continuous chips were obtained in UAT, with better surface topography. A chip-formation mechanism in UAT show increased ductility of the workpiece material when subjected to a repeated high-frequency microchipping process. Abrasive and adhesive wear occurred on the WC tool in both conventional turning and UAT. However, the machined surface obtained in UAT with a WC tool was comparable and sometimes even better than that achieved with the PCD too

    Improvements of machinability of aerospace-grade Inconel alloys with ultrasonically assisted hybrid machining

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    Aerospace-grade Ni-based alloys such as Inconel 718 and 625 are widely used in the airspace industry thanks to their excellent mechanical properties at high temperatures. However, these materials are classified as ‘difficult-to-machine’ because of their high shear strength, low thermal conductivity, tendency to work-harden and presence of carbide particles in their microstructure, which lead to rapid tool wear. Machining-induced residual stresses in a machined part is an important parameter which is assessed since it can be used to evaluate overall structural resilience of the component and its propensity to fatigue failure in-service. Ultrasonically assisted turning (UAT) is a hybrid machining technique, in which tool-workpiece contact conditions are altered by imposing ultrasonic vibration (typical frequency ~ 20 kHz) on a tool’s movement in a cutting process. Several studies demonstrated successfully the resulting improvements in cutting forces and surface topography. However, a thorough study of UAT-induced residual stresses is missing. In this study, experimental results are presented for machining Inconel 718 and 625 using both conventional turning (CT) and UAT with different machining parameters to investigate the effect on cutting forces, surface roughness and residual stresses in the machined parts. The study indicates that UAT leads to significant cutting force reductions and improved surface roughness in comparison to CT for cutting speeds below a critical level. The residual stresses in machined workpiece show that UAT generates more compressive stresses when compared to those in CT. Thus, UAT demonstrates an overall improvement in machinability of Inconel alloys

    Preparation of Hydrophilic Encapsulated Carbon Nanotubes with Polymer Brushes and Its Application in Composite Hydrogels

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    Carbon nanotubes can be used as promising reinforcement materials to improve the mechanical properties of hydrogels, but their poor dispersibility in aqueous solution severely limits their application in preparation of composite hydrogels. Therefore, to develop method for modification of carbon nanotubes is still highly desired. In this paper, a facile approach for preparation of the hydrophilic carbon nanotube was reported. The encapsulated multiwalled carbon nanotubes (E-CNT-PAA) with cross-linked shell structure were obatined through the self-assembly of the amphipathic azide diblock copolymers poly­(acrylic acid)-<i>b</i>-poly­(4-vinylbenzyl azide-<i>co</i>-styrene) (PAA-<i>b</i>-(PVBA-<i>co</i>-PS)), and the cross-linking of inside azide groups under UV irradiation. The encapsulated MWCNT was characterized by FT-IR, Raman and TEM. It was demonstrated that the dispersibility of the hydrophilic encapsulated MWCNTs was related to the length of the poly­(acrylic acid) brushes. Subsequently, thermal-responsive composite hydrogels (PNIPAM/E-CNT-PAA) were prepared by in situ polymerization of <i>N</i>-isopropylacrylamide (NIPAM) in the solution of dispersed E-CNT-PAA. The results showed that the composite hydrogels possessed high mechanical properties compared to the pure PNIPAM hydrogel. The tensile strength and elongation of the composite hydrogels were highly dependent on the content of the modified MWCNTs. The composite hydrogels with 0.46 wt % MWCNTs exhibited tensile strength of 97.7 kPa and elongation of 465%, which were at least 3.5× higher than those of the PNIPAM hydrogel. Moreover, the composite hydrogels displayed significant and reversible stimuli-responsiveness

    A Diheteroatom Fluoroalkylation Reagent for Preparation of S- and N‑Containing Fluoroalkyl Compounds and Sulfonic Acid Polymer

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    The first stable diheteroatom fluoroalkylation reagent, 2-((2-azido-1-chloro-1,2,2-trifluoro­ethyl)­thio)­pyrimidine (ACTP), has been prepared by a novel method. By using this reagent, various fluorinated thioethers and sulfones have been successfully prepared. The dearylation and dearylation–oxida­tion of fluoroalkyl 2-pyrimidyl sulfone in one-pot reaction were investigated systematically, and the results demonstrated that both fluoroalkyl sulfinates and sulfonates could be obtained in high yields. In addition, ACTP proved to be useful for the preparation of a fluorinated sulfonic acid proton-exchange membrane

    Facile and Highly Efficient Strategy for Synthesis of Functional Polyesters via Tetramethyl Guanidine Promoted Polyesterification at Room Temperature

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    A facile and highly efficient strategy for the synthesis of functional polyesters from 10-undecenoic acid, which is abundantly available and derived from ricin oil, has been successfully achieved using 1,1,3,3-tetramethyl guanidine (TMG) as a promoter at room temperature. The experimental results indicate that high molecular weight polyesters have been obtained and a variety of functional groups, such as alkenyl, alkynyl, nitro, epoxy, hydroxyl, and bromoisobutyrate, can be incorporated as pendant groups. The structures of the obtained polymers were demonstrated by <sup>1</sup>H and <sup>13</sup>C NMR spectroscopy and their thermal properties were studied by DSC and TGA

    Novel Reversible Mechanochromic Elastomer with High Sensitivity: Bond Scission and Bending-Induced Multicolor Switching

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    Although the rational designed mechanochromic polymer (MCP) materials have evoked major interest and experienced significant progress recently, it is still a great challenge to develop a facile and effective strategy for preparation of reversible broad-spectrum MCPs with a combination of wide-range color switch ability and high sensitivity, which thus make it possible to mimic gorgeous color change as in nature. Herein, we designed and synthesized a novel rhodamine-based mechanochromic elastomer. Our results demonstrated that the elastomer exhibited very promising and unique properties. Three primary fluorescence colors were presented during continuous uniaxial extension and relaxing process, and reversible broad-spectrum fluorescence color change could be achieved consequently. The fluorescence quantum yield of the opened zwitterion of this new mechanophore was as high as 0.67. In addition, the elastomer showed very high sensitivity to stress with a detectable activation strain of ∼0.24, which was much smaller than those reported in the previous literature reports. Meantime, the easy-to-obtain material, facile preparation, and good mechanical property also made it suitable for potential practical applications

    Table_S1 – Supplemental material for High expression of Aurora-B is correlated with poor prognosis and drug resistance in non-small cell lung cancer

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    <p>Supplemental material, Table_S1 for High expression of Aurora-B is correlated with poor prognosis and drug resistance in non-small cell lung cancer by JingJing Yu, Jing Zhou, Fei Xu, Wei Bai and Wei Zhang in The International Journal of Biological Markers</p
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