Contribution of specific work of fracture to size effect in microcutting

Specific work of fracture (R) has been widely used to quantify the energy consumed in formation of new surfaces during metal cutting. R becomes a significant portion of total cutting energy in microcutting, thereby influencing the phenomenon of “size effect. ” Therefore, this work presents an evaluation of specific work of fracture for sharp and rounded-edged tools, knowing cutting forces and shear angles from LS-DYNA simulations of orthogonal microcutting of low-carbon AISI 1215 steel. The R was also evaluated as a function of process parameters such as cutting speed, rake angle, tool edge radius, and uncut chip thickness, so as to illustrate the effect of these variables on the magnitude of R and contribution of R to the specific cutting energy or “size effect.” It is observed that R increases with an increase in uncut chip thickness, whereas it decreases with an increase in cutting speed, rake angle, and tool edge radius. U_R defines the contribution of fracture to the specific cutting energy (U) due to specific work of fracture R. At all the parametric conditions, the contribution of fracture is higher at lower uncut chip thickness and it is of 8–36% in microcutting of AISI 1215 steel.     

High speed versus conventional grinding in high removal rate machining of alumina and alumina–titania

High removal rate (up to 16.6 mm³/s per mm) grinding of alumina and alumina–titania was investigated with respect to material removal and basic grinding parameters using a resin-bond 160 μm grit diamond wheel at the speeds of 40 and 160 m/s, respectively. The results show that the material removal for the single-phase polycrystalline alumina and the two-phase alumina–titania composite revealed identical mechanisms of microfracture and grain dislodgement under the grinding conditioned selected. There were no distinct differences in surface roughness and morphology for both materials ground at either conventional or high speed. An increase in material removal rate did not necessarily worsen the surface roughness for the two materials at both speeds. Also the grinding forces for the two ceramics demonstrated similar characteristics at any grinding speeds and specific removal rates. Both normal and tangential grinding forces and their force ratios at the high speed were lower than those at the conventional speed, regardless of removal rates. An increase in specific removal rate caused more rapid increases in normal and tangential forces obtained at the conventional grinding speed than those at the high speed. Furthermore, it is found that the high speed grinding at all the removal rates exerted a great amount of coolant-induced normal forces in grinding zone, which were 4–6 times higher than the pure normal grinding forces.     

A strategy for efficient and quality cutting of materials with abrasive waterjets considering the variation in orifice and focusing nozzle diameter

In Abrasive Waterjet (AWJ) cutting, orifice and focusing nozzle diameter undergo continuous change in their dimensions due to erosive nature of high velocity abrasive waterjet. This particular phenomenon can affect the efficiency and quality of the process. To achieve maximum efficiency and desired quality with this process, the parameters need to be optimally selected from time to time considering the changes in the dimensions of orifice and focusing nozzle. In an effort to develop strategies for this purpose and to build the knowledge base for adaptive control of the process, the present work aims to study the influence of orifice and focusing nozzle diameter variation on the performance of abrasive waterjets in cutting 6063-T6 aluminum alloy. The performance was assessed in terms of different parameters such as depth of cut, material removal rate, cutting efficiency, kerf geometry and cut surface topography. In order to maintain the desired performance, it is essential to monitor the condition of nozzles and suitably adjust the process parameters with a view to control the process. Towards the latter, the present work attempts to suggest a strategy that can aid in replacing the nozzles at an appropriate time for maintaining the performance of process within certain limits so as to maintain the precision in machining with abrasive waterjets.     

Artificial Neural Network Prediction of Fretting Wear Behavior of Structural Steel,En 24 Against Bearing Steel,En 31

In this study, artificial neural network (ANN) technique is used to predict the friction and wear behavior of various surface-treated structural steel (En 24) fretted against bearing steel (En 31). A three-layer neural network with a back propagation algorithm is used to train the network. Fretting wear volume and coefficient of friction obtained at different normal loads (ranging between 2.4 and 29.4 N) for various treated samples (hardened, thermo-chemically treated, MoS₂ coated) were used in the formation of training data of ANN. Results of the predictions of ANN are in good agreement with the experimental results. The degree of accuracy of predictions was 96.3 and 95.7% for fretting friction coefficient and wear, respectively.     

Dry wear studies on glass-fibre-reinforced epoxy composites

Continuous glass-fibre-reinforced epoxy composites were fabricated and their wear behaviour was studied. A rapid drop in the wear loss occurred with an increase in the sliding speed for the pure epoxy resin while the reinforced sample exhibited a mild decrease, a flat region and then a rise. Optical microscopy examination indicates that the higher wear loss for the composite at higher speeds could be due to loss of glass fibres. The variation in the coefficient of friction, μ, with load and sliding speed was studied. Both the epoxy resin and the composite show a marked dependence of μ on load, which includes a peak. The pure epoxy resin showed no significant dependence of the coefficient of friction on sliding speed whereas the composite shows a peak value, thereby emphasizing the important role of the reinforcing fibres.     

Cellulose–Polyvinyl Alcohol–Nano-TiO2 Hybrid Nanocomposite: Thermal,Optical, and Antimicrobial Properties against Pathogenic Bacteria

Cellulose fiber-reinforced composite has received great attention due to the high strength, stiffness, biodegradability, and renewability of the excellent natural biomaterials. Cellulose nanofibers for the development of organic–inorganic hybrid composite is relatively new filed of research. Cellulose macro and nanofibers can be used as reinforcement in the hybrid composite because of improved mechanical, thermal, optical, electrical, morphological, and biological properties. The hybrid nanocomposites were synthesized by an in situ sol–gel process in the presence of coupling agent. The sol–gel process has definitely proven its potential by providing the synthesis of various functional organic–inorganic hybrid nanocomposites through an in situ sol–gel process. The hybrid nanocomposites have been prompted by the ability to control the morphology of final materials. The photoluminescence spectral studies indicate that the emission shifts toward higher wavelength (326–532?nm) accompanied by a reduction in impurity centers with increasing concentration of poly(vinyl alcohol)–TiO₂ and hybrid nanocomposite. The final nanostructured TiO₂ hybrid nanocomposites with particle size ranging from 0.32 to 20?nm were characterized by Field -emission transmission electron microscopy (FE-TEM) analysis. Furthermore, cellulose–poly(vinyl alcohol)–nano-TiO₂ hybrid composite was characterized by Fourier transform infrared, X-ray diffraction, UV, Thermogravimetric analysis (TGA), Differential scanning calorimetry (DSC), FE-SEM–EDX, Field-emission scanning electron microscopy (FE-SEM), and FE-TEM analysis. The different analysis results of the hybrid composite indicate the optical transparency, optical properties, T_g, crystallinity, thermal stability, and controlled morphology of hybrid nanocrystalline composites. Finally, the cellulose–poly(vinyl alcohol)—nano-TiO₂ hybrid nanocomposites were tested against pathogens such as Gram-positive Bacteria Bacillus cereus and Gram-negative Escherichia coli for antimicrobial activity. These results show that the hybrid composite exhibited excellent antimicrobial properties against pathogens.     

Frequency equation for the submicron CMOS ring oscillator using the first order characterization

By utilizing the first order behavior of the device,an equation for the frequency of operation of the submicron CMOS ring oscillator is presented.A 5-stage ring oscillator is utilized as the initial design,with different Beta ratios,for the computation of the operating frequency.Later on,the circuit simulation is performed from 5-stage till 23-stage,with the range of oscillating frequency being 3.0817 and 0.6705 GHz respectively.It is noted that the output frequency is inversely proportional to the square of the device length,and when the value of Beta ratio is used as 2.3,a difference of 3.64％ is observed on an average,in between the computed and the simulated values of frequency.As an outcome,the derived equation can be utilized,with the inclusion of an empirical constant in general,for arriving at the ring oscillator circuit's output frequency.     

Investigation of factors contributing depolarization in offset reflector antenna and trimmed‐reflector offset parabolic antenna with lower cross‐polarization

This article outlines impact of various factors on cross‐polarization characteristics of offset reflector antenna for communication spacecraft with smaller sized bus at C band. Effects of different parameters are considered in rigorous analysis of the antenna. Measured and predicted performances are found in agreement. To fulfill specific requirement of higher edge‐of‐coverage gain (>26 dBi) and higher cross‐polarization discrimination (XPD > 30 dB) over a wider coverage and dual linear polarization under the imposed constraints, a novel trimmed‐reflector offset parabolic antenna (TROPA) is devised. This interesting configuration is obtained by trimming both sides parallel to symmetrical plane of a parabolic offset reflector antenna. Parametric study of trimming distance versus its impact on cross‐polarization is also presented. The TROPA acquires wider bandwidth, simplification in its mechanical design and manufacturing, and offers low weight and compactness. It is also shown that trimmed reflector has almost even RF performance in presence of spacecraft body and other antenna. © 2012 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2012.     

Finite-state abstractions on Arabic morphology

There has been much interest recently in two-level and associative models for handling morphologically rich inflectional languages. Such models are claimed to have advantages over generative, rule-based approaches in terms of not just conceptual appropriateness but also computational efficiency. The claim with regard to the former is that, whilst generative approaches to morphology may well be useful for inflectionally simple natural languages such as English (where most of the processing is carried out at the sentence level, with dictionaries and lexicons being accessed to identify secondary inflectional information once primitive words are found), this approach is not at all suitable for inflectionally rich languages where grammatical information is carried not by the combination or pattern of distinct and separate words which make up the sentence but by the combination or pattern of inflections within a word where, for instance, there are no clear boundaries between morphological constituents. The claim with regard to the latter is that many generative approaches to natural language are inefficient and, in some cases, computationally intractable, because of the heavy memory and processing demand placed on implementing actual models based on these approaches for anything more than a constrained fragment of a language. This paper describes an application of finite-state automata for Arabic noun inflections which leads to abstractions based on network topology as well as the form and content of network arcs. The idea of specific automata for specific inflection types inheriting some or all of the nodes, arc form and arc content of abstract automata representing more abstract classes of inflection is also introduced. This can lead to novel linguistic generalities and applications, as well as advantages in terms of procedural efficiency and representation.