Tensile properties of elephant grass fiber reinforced polyester composites

Elephant grass stalk fibers were extracted using retting and chemical (NaOH) extraction processes. These fibers were treated with KMnO₄ solution to improve adhesion with matrix. The resulting fibers were incorporated in a polyester matrix and the tensile properties of fiber and composite were determined. The fibers extracted by retting process have a tensile strength of 185 MPa, modulus of 7.4 GPa and an effective density of 817.53 kg/m³. The tensile strength and modulus of chemically extracted elephant grass fibers have increased by 58 and 41%, respectively. After the treatment the tensile strength and modulus of the fiber extracted by retting have decreased by 19, 12% and those of chemically extracted fiber have decreased by 19 and 16%, respectively. The composites were formulated up to a maximum of 31% volume of fiber resulting in a tensile strength of 80.55 MPa and tensile modulus of 1.52 GPa for elephant grass fibers extracted by retting. The tensile strength and the modulus of chemically extracted elephant grass fiber composites have increased by approximately 1.45 times to those of elephant grass fiber composite extracted by retting. The tensile strength of treated fiber composites has decreased and the tensile modulus has shown a mixed trend for the fibers extracted by both the processes. Quantitative results from this study will be useful for further and more accurate design of elephant grass fiber reinforced composite materials.     

Ultrawideband Printed Elliptical Monopole Antennas

Parametric study of ultrawideband printed elliptical monopole antennas have been presented. Design curve for the length of the feed transmission line for various lower band edge frequencies has been generated. Variation of bandwidth with ellipticity ratio of these configurations has also been studied. Experiments have been performed to measure bandwidth and radiation patterns of these configurations, which tally well with simulated results. The elliptical configuration with ellipticity ratio of 1.1 gives ultrawide impedance bandwidth ratio of 12.4:1 as compared to 10.2:1 of the circular monopole antenna. This antenna introduces minimum ringing and distortion/dispersion of the pulse in time domain     

Advanced ceramic tool materials for machining

Cutting tools made of advanced ceramics have the potential for high-speed finish machining as well as for high-removal-rate machining of difficult-to-machine materials. The raw materials used in these ceramics are abundant, inexpensive, and free from strategic materials. In spite of this, solid or monolithic ceramic tools are currently used only to a limited extent partly due to certain limitations of these materials and partly due to the inadequacy of the machine tools used. The advances in ceramic materials and processing technology, the need to use materials that are increasingly more difficult to machine, increasing competition, and the rapidly rising manufacturing costs, have opened new vistas for ceramics in machining applications. The development of ceramic tool materials can be broadly categorized into three types: monolithic forms, thin coatings, and whisker-reinforced composites. Such a classification provides a totally new perspective on ceramic tool materials and broadens their scope considerably, and is justified on the basis that it is the ceramic addition that makes the tool material more effective. A brief overview of these materials is presented in this paper.     

Active eutectoid decomposition in a near-eutectoid zirconium-copper alloy

The decomposition of the beta-phase into the alpha- and the Zr₂Cu-phases has been investigated in a Zr-1.6 wt pct Cu alloy. It has been observed that the decomposition process is extremely rapid and cannot be suppressed even by rapid beta quenching. The product structure obtained on fast cooling consists of a lamellar aggregate of the alpha-phase and a metastable phase which does not have the stoichiometry of the Zr₂Cu-phase. Structurewise, this phase is similar but not identical to the equilibrium phase. A mechanism for this rapid decomposition of the beta-phase has been proposed. It has also been found that the equilibrium Zr₂Cu-phase emerges after short aging treatments at sufficiently high temperatures in the α+Zr₂Cu field.     

Discharge characteristics of orifice meters in sediment-laden flows

Experimental results on the discharge characteristics of concentric orifice meters placed in circular pipes carrying sediment-laden flow in homogeneous and heterogeneous regimes are reported. The experiments were carried out using water as the carrying medium and sand and coal as the sediments. The data cover a range of concentration from 0.5% to 7.0% by volume. The analysis of the data has resulted in graphical predictors which enable determination of the discharge to fairly good accuracy.     

PERFORMANCE CHARACTERISTICS OF SINGLE-STAGE STEAM JET EJECTORS USING TWO SIMPLE MODELS

Two simple models, one of Hougen, Watson and Ragatz (HWR) and the other by Dotterweich and Mooney (DM), are used to compute the motive steam requirements of single-stage steam jet ejectors. Non-idealities associated with the performance of nozzle, diffuser and that of mixing process are accounted for by nozzle and diffuser efficiency factors. Nozzle and diffuser efficiencies between 0.7-0.9 and 0,75-1.0 respectively, are studied for systems, steam-water vapor, steam-air, and steam-hydrocarbons (n-paraffins: C₁ to C₅). The results are compared with the empirical correlations of Power and Ludwig. In addition, the effect of motive steam pressure on steam consumption is investigated. It is found that predicted steam consumptions, when DM model is employed, agree closely with literature data. It is suggested that model predicted values, rather than the empirical plots, be used in any specific case, since empirical correlations represent only averaged values.     

Metallic Hydrogen

One of the great challenges in condensed matter physics has been to produce metallic hydrogen (MH) in the laboratory. There are two approaches: solid molecular hydrogen can be compressed to high density at extreme pressures of order 5–6 megabars. The transition to MH should take place at low temperatures and is expected to occur as a structural first-order phase transition with dissociation of molecules into atoms, rather than the closing of a gap. A second approach is to produce dense molecular hydrogen at pressures of order 1–2 megabars and heat the sample. With increasing temperature, it was predicted that molecular hydrogen first melts and then dissociates to atomic metallic liquid hydrogen as a first-order phase transition. We have observed this liquid–liquid phase transition to metallic hydrogen, also called the plasma phase transition. In low-temperature studies, we have pressurized HD to over 3 megabars and observed two new phases. Molecular hydrogen has been pressurized to 4.2 megabars. A new phase transition has been observed at 3.55 megabars, but it is not yet metallic.     

Evaluation of carbide grades and a new cutting geometry for machining titanium alloys

A new cutting geometry consisting of a high clearance angle (from 10° to 15°) together with a high negative rake angle (from ?10° to ?15°) is proposed for increasing cemented tungsten carbide tool life during the machining of titanium alloys. This geometry would allow the use of a conventional insert (with an included angle of 90°) of any suitable shape (e.g. round, square or triangular) on a modified tool holder. The new geometry is found to yield longer tool life than does a high clearance angle (+15°) alone or a conventional tool with a low negative rake angle (?5°) and a low clearance angle (+5°). Further, the lower cobalt grade (Carboloy grade 999) and finer carbide grain size tools (Carboloy grade 895) are found to yield longer tool life than the higher cobalt grade medium carbide grain size tools (Carboloy grade 883), which are currently the most commonly used grade. A new ceramic tool material, an Si-Al-O-N compound, is found not to be suitable for machining titanium alloys because of rapid wear.     

UNIFIED APPROACH AND INTERACTIVE PROGRAM FOR THERMAL ANALYSIS OF VARIOUS MANUFACTURING PROCESSES WITH APPLICATION TO MACHINING

Analytical approach to thermal aspects of various manufacturing processes, such as machining, grinding, polishing, welding, heat treatment, laser processing, and tribology was used by many researchers between the late 1930s and early 1940s. That was the golden period when Blok introduced the heat partition concept in 1937; Jaeger developed the heat source method in 1942; and Rosenthal introduced the moving heat source theory in 1946. Starting from the Fourier's partial differential equation (PDE) of heat conduction, researchers have addressed various manufacturing processes using different approaches, namely, separation of variables, Fourier transform, Laplace transform, Bessel function, and Green's function methods. Consequently, it has become difficult to conceive a unified analytical approach of the various manufacturing processes based on the review of the literature as one approach differs from the other quite significantly and integration of them would be a formidable task, if not an impossible task. In contrast, using the Jaeger's classical heat source method and appropriate heat source (shape, size, and distribution) we developed a unified analytical approach to address the thermal aspects of various manufacturing processes. Such an approach, to the best of our knowledge, has never been attempted before and lends itself to the development of a user friendly interactive programming software that can be extremely valuable in practice. In this paper, we used Jaeger's classical heat source method, modified Hahn's oblique moving heat source for the shear plane heat source, Blok's ingenious heat partition method, and Chao and Trigger's functional analysis approach to illustrate the analysis of the temperature distribution in the work material, chip, and cutting tool in machining.     

Towards control of carbon nanotube synthesis process using prediction-based fast Monte Carlo simulations

Precise control of the lengths of carbon nanotube (CNT) and other nanostructures is important for various industrial applications. However, time-resolution (∼1 min) of current in situ measurements does not allow control of lengths to within 20 nm. We present an approach to combine intermittent in situ measurements with length estimates from a fast atomistic Monte Carlo (MC) simulation of CNT synthesis. The MC simulation time was reduced by >70% through prediction of the nonlinear and nonstationary growth increments, and initialization of relaxation process (the most computationally intensive step in MC simulations) with the near-optimum predicted positions, leading to one of the longest (∼194 nm) CNTs from atomistic simulations. A utility function of growth predictions was defined so that its maximization specified the end-point of the synthesis process. Extensive simulation studies indicate that the approach can be used to control CNT lengths to within 1 nm of specifications.