Defence Research and Development Laboratory

This paper compares the applicability of a few theoretical models for determining effective elastic moduli, using published experimental data on ceramic materials in a porosity range of 0–40% and on a cellular material with a porosity of about 90%. As the experimental data for the effective Poisson's ratio involve a large scatter, a set of numerical experiments using the finite element method was carried out to obtain the variation of the effective Poisson's ratio with porosity. These variations show that the effective Poisson's ratio approaches 0.25 with increasing porosity, irrespective of the material Poisson's ratio. The effect of pore shapes on the effective elastic moduli and the Poisson's ratio has also been analyzed using FEM.

The present study reviews the state-of-the-art mechanism for the generation of spark by means of micro-electrochemical discharge machining (µ-ECDM) process. It also describes various electrical and non-electrical parameters, influencing performance of the machining process. In the process, several variants of µ-ECDM process have been outlined which were developed with technological advancements for enhanced performance. The review also makes an in-depth study on advancement of micro- and nano-size tool manufacturing processes by unconventional machining techniques. Finally, it sums up potential of this process for development of various hybrid machining processes to achieve better performance.

In recent years, wire-electrical discharge machining (WEDM) has gained popularity in the industry due to its capability to generate complicated shapes in exotic materials, irrespective of their hardness. Conventional machining of Nimonic C-263 superalloy is an extremely difficult and costly process due to its high hardness and tool wear rate. The present research work investigates the influence of the WEDM process parameters on different performance measures during machining of Nimonic C-263 superalloy. A mathematical model for all four important performance measures, namely, cutting rate, surface roughness, spark gap, and wire wear ratio, was developed and the responses were used for studying the interrelationship between performance measures and process parameters. The optimal settings of operating conditions were predicted using desirability function. The effectiveness of multicut strategy was also investigated in the article.

To determine the most suitable composition for a magnetic field modulation recording, we investigated the static and dynamic recording (optical modulation method) characteristics of a TbFeCo film relative to an external magnetic field. It was made clear that the demagnetizing field is the chief determinant of the external magnetic field intensity and that a medium with a compensation temperature between room temperature and about 100°C is suitable for magnetic field modulation recording. AC/N of 50 dB was obtained by modulating the external magnetic field at 500 kHz. An overwriting on the pre-signal was completely realized up to the frequency of 500 kHz.

In this experimental study, the effects of major laser process control parameters, such as the laser power, beam scanning speed and assisting gas flow rate, on cut surface integrity defined by the kerf width, taper percentage, and the extent of heat affected zone (HAZ) were investigated. Response surface methodology (RSM) along with central composite design (CCD) of the experiment was used to optimize the process parameters to get better-cut surface quality. The optimum values of process parameters corresponding to cut surface with minimum defects are laser power 260 W, cutting speed 4500 mm per min, and assistance gas flow rate 14.23 l/min and the corresponding kerf width, taper percentage, and the width of HAZ are found to be 163.7 µm, 5.75%, and 573.28 µm. The confirmation experiments have been conducted that provide favorable results with an error of 2.70%, 1.87%, and 0.36%, for kerf width, taper percentage, and width of HAZ, respectively.

Using the recently developed computationally efficient model predictive static programming and a closely related model predictive spread control concept, two nonlinear suboptimal midcourse guidance laws are presented in this paper for interceptors engaging against incoming high-speed ballistic missiles. The guidance laws are primarily based on nonlinear optimal control theory, and hence imbed effective trajectory optimization concepts into the guidance laws. Apart from being energy efficient by minimizing the control usage throughout the trajectory (minimum control usage leads to minimum turning, and hence leads to minimum induced drag), both of these laws enforce desired alignment constraints in both elevation and azimuth in a hard-constraint sense. This good alignment during midcourse is expected to enhance the effectiveness of the terminal guidance substantially. Both point mass as well as six-degree-of-freedom simulation results (with a realistic inner-loop autopilot based on dynamic inversion) are presented in this paper, which clearly shows the effectiveness of the proposed guidance laws. It has also been observed that, even with different perturbations of missile parameters, the performance of guidance is satisfactory. A comparison study, with the vector explicit guidance scheme proposed earlier in the literature, also shows that the newly proposed model-predictive-static-programming-based and model-predictive-spread-control-based guidance schemes lead to lesser lateral acceleration demand and lesser velocity loss during engagement.

This technical note describes an application of nonlinear controllability theory to the problem of spacecraft attitude control using control moment gyroscopes (CMGs). Nonlinear controllability theory is used to show that a spacecraft carrying one or more CMGs is controllable on every angular momentum level set in spite of the presence of singular CMG configurations, that is, given any two states having the same angular momentum, any one of them can be reached from the other using suitably chosen motions of the CMG gimbals. This result is used to obtain sufficient conditions on the momentum volume of the CMG array that guarantee the existence of gimbal motions which steer the spacecraft to a desired spin state or rest attitude.

Abstract A high surface, magnetic Fe 3 O 4 @mesoporouspolyaniline core‐shell nanocomposite was synthesized from magnetic iron oxide (Fe 3 O 4 ) nanoparticles and mesoporouspolyaniline (mPANI). The novel porous magnetic Fe 3 O 4 was obtained by solvothermal method under sealed pressure reactor at high temperature to achieve high surface area. The mesoporouspolyaniline shell was synthesized by in situ surface polymerization onto porous magnetic Fe 3 O 4 in the presence of polyvinylpyrrolidone (PVP) and sodium dodecylbenzenesulfonate (SDBS), as a linker and structure‐directing agent, through ‘blackberry nanostructures’ assembly. The material composition, stoichiometric ratio and reaction conditions play vital roles in the synthesis of these nanostructures as confirmed by variety of characterization techniques. The role of the mesoporouspolyaniline shell is to stabilize the porous magnetic Fe 3 O 4 nanoparticles, and provide direct access to the core Fe 3 O 4 nanoparticles. The catalytic activity of magnetic Fe 3 O 4 @mesoporousPANI nanocomposite was evaluated in the cross‐coupling of aryl chlorides and phenols.

Carbon carbon composites are a new class of engineering materials that are ceramic in nature but exhibit brittle to pseudoplastic behaviour. Carbon-carbon is a unique all-carbon composite with carbon fibre embeded in carbon matrix and is known as an inverse composite. Due to their excellent thermo-structural properties, carbon-carbon composites are used in specialised application like re-entry nose-tips, leading edges, rocket nozzles, and aircraft brake discs apart from several industrial and biomedical applications. The multidirectional carbon-carbon product technology is versatile and offers design flexibility. This paper describes the multidirectional preform and carbon-carbon process technology and research and development activities within the country. Carbon-carbon product experience at DRDL has also been discussed. Development of carbon-carbon brake discs process technology using the liquid impregnation process is described. Further the test results on material characterisation, thermal, mechanical and tribological properties are presented.

The present work deals with the wave dispersion behavior of a rotating nanotube using the nonlocal elasticity theory. The rotating nanobeam is modeled as an Euler–Bernoulli theory. The governing partial differential equation for a uniform rotating beam is derived incorporating the nonlocal scale effects. The spatial variation in centrifugal force is modeled in an average sense. Even though this averaging seems to be a crude approximation, one can use this as a powerful model in analyzing the wave dispersion characteristics of the rotating nanobeam. Spectrum and dispersion curves are obtained as a function of rotating speed and nonlocal scaling parameter. It has been shown that the dispersive flexural wave tends to behave non-dispersively at very high rotation speeds. Understanding the dynamic behavior of rotating nanostructures is important for practical development of nanomachines. At the nanoscale, the nonlocal effects often become more prominent. The numerical results are simulated for a rotating nanobeam as a waveguide. The results can provide useful guidance for the study and design of the next generation of nanodevices such as blades of a nanoturbine, nanogears, nanoscale molecular bearings etc, that make use of the wave propagation properties of rotating single-walled carbon nanotubes.

Computational-fluid-dynamics-based design and analysis is presented for a full-scale scramjet combustor with kerosene fuel injected from struts placed in the combustor flowpath. Three-dimensional Navier-Stokes equations are solved with a K-e turbulence model using commercial computational-fluid-dynamics software. Combustion is modeled based on infinitely fast chemical kinetics. Lagrangian dispersed-phase analysis is considered for fueldroplet evaporation and mixing in the supersonic stream. Parametric studies are carried out to investigate the effect of combustor-inlet Mach number and total pressure on the flow development process. A higher combustor-entry Mach number and distributed-fuel-injection system will ensure the existence of predominant supersonic flow in the combustor. Simulations are also carried out to investigate two different kinds of fuel injection struts in the scramjet combustor performance. A distributed-fuel -injection system, required to avoid thermal choking, increases the three-dimensionality of the flowfield.

Understanding start–unstart behavior of intakes in hypersonic Mach numbers is essential for seamless operation of scramjet engines. We consider a high compression ratio intake (CR = 40) at a Mach number of M = 6 in this work. Start–unstart characteristics are studied in a hypersonic wind tunnel at a flight realistic Reynolds number (Re = 8.7 × 106/m, M = 6). A flap provided at the rear end of the isolator simulates the effect of backpressure for throttling ratios in the range of 0–0.69. Experiments are conducted in two modes: (a) with the flap fixed at a particular throttling ratio and (b) the flap moved to a particular throttling ratio after the started flow has been established. Unsteady pressure measurements and time-resolved Schlieren visualization are undertaken. Modal analysis of pressure (using fast Fourier transform) and Schlieren images (using dynamic mode decomposition) are carried out. The intake shows started behavior for throttling ratios up to 0.31 and a dual behavior, where it remains started in dynamic flap runs but unstarted in fixed flap runs for throttling ratios of 0.35 and 0.42. The intake exhibits a staged evolution to a large amplitude oscillatory unstart for throttling ratios of 0.55 and 0.69, with frequencies of 950 Hz and 1100 Hz, respectively. For the first time, a staged evolution (5 stages) to a subsonic spillage oscillatory unstart of a hypersonic intake is detailed using corroborative evidence from both time-resolved Schlieren and pressure measurements. A precursor to the final large amplitude oscillatory unstart is identified, and the flow mechanism for sustained oscillations is explained.

The strong evolutionary conservation of the DNA methyltransferase, Dnmt2, is at odds with the absence of phenotypic defects in organisms lacking Dnmt2. The cellular processes where Dnmt2 has a role to play also remain largely undiscovered. Here we show that Dnmt2 is a part of RNA processing machinery during cellular stress. In addition to interacting with proteins involved in RNA processing and cellular stress, Dnmt2 exhibits nucleo-cytoplasmic shuttling in response to cellular stress. Normally present in the nucleus, under conditions of stress, Dnmt2 relocalises to the cytoplasmic Stress Granules and RNA processing bodies. Surprisingly, for a DNA methyltransferase, knockout of which showed no phenotypic defects in several species, our results show that transient transfection of Dnmt2 in mammalian cells causes cell lethality. Interestingly, Dnmt2 overexpression altered the expression of several genes involved in viral infection. Taking into consideration its recently identified role in retrotransposon silencing, the role of Dnmt2 in stress granules could represent a primitive cellular defense mechanism against viral infection.

For the full paper by R. Arundhathi, D. Damodara, Pravin R. Likhar, M. Lakshmi Kantam, P. Saravanan, Travis Magdaleno, and Sun Hee Kwon, in Issue 9, 2011, pp 1591–1600 (DOI: ), the address for co-author P. Saravanan, and Scheme 1 contain errors. The original versions need to be replaced with the following: Affiliation of P. Saravanan: Defence Metallurgical Research Laboratory, Hyderabad 500058, India Scheme 1:1

Composite materials are playing a vital role in aerospace industries due to its attractive thermal, mechanical and environmental properties. Especially, in aerospace applications where the weight factor is a concern, it offers good strength-to-weight ratio over metals, thus making a viable alternative. Apart from this, it gives high fatigue strength, light weight, increased corrosion resistance, improved fire resistance and also provides an ability to manufacture complex shapes. The steady increase in the use of Glass fiber/ carbon fiber composites has brought tremendous changes in aerospace industries. The diversified application of composite materials motivated the scientists to use in different fields where its predominant properties have given value addition to the product. However, it generates waste composite material during manufacturing as well as end of life. The composites waste should be collected, segregated and safely disposed as per the environmental legislation available in this country. Further, the waste generated by aerospace (defence& space) industry is minimum compared to the composite waste generated by the commercial industries. Composite waste disposal is relatively new area in India which is necessary to discuss for protecting the environment. Hence, selection of suitable environmental friendly as well as cost effective composite disposal method is necessary at this stage for aero space industries. In this paper, an attempt has been made to assess the existing disposal methods in the world and suggest suitable disposal method which is applicable for aerospace Industries.

Titanium and its alloys are joined by various welding processes. However, Fusion welding of titanium alloys resulted solidification problems like porosity, segregation and columnar grains. The problems occurred in conventional welding processes can be resolved using a solid state welding i.e. friction stir welding. Aluminium and Magnesium alloys were welded by friction stir welding. However alloys used for high temperature applications such as titanium alloys and steels are arduous to weld using friction stir welding process because of tool limitations. Present paper summarises the studies on joining of Titanium alloys using friction stir welding with different tool materials. Selection of tool material and effect of welding conditions on mechanical and microstructure properties of weldments were also reported. Major advantage with friction stir welding is, we can control the welding temperature above or below β-transus temperature by optimizing the process parameters. Stir zone in below beta transus condition consists of bi-modal microstructure and microstructure in above β-transus condition has large prior β- grains and α/β laths present in the grain. Welding experiments conducted below β- transus condition has better mechanical properties than welding at above β-transus condition. Hardness and tensile properties of weldments are correlated with the stir zone microstructure.

Realizing organic electronics through the realm of ionic liquids and polymerized ionic liquids.

An international association advancing the multidisciplinary study of informing systems. Founded in 1998, the Informing Science Institute (ISI) is a global community of academics shaping the future of informing science.

Fiber Bragg Grating-based accelerometers are being used in structural health monitoring as they offer several advantages over their electrical counterparts. In this paper, the concept of a novel T-shaped cantilever-based mechanical sensor head is proposed on which the two Fiber Bragg Gratings are integrated in a differential sensing configuration to realize an optical accelerometer. This elegant design simultaneously achieves the dual goals of sensitivity enhancement, and self-temperature compensation. A mathematical model of the accelerometer is developed, and numerical simulations are carried out for three mechanical sensor head designs. A prototype is fabricated and characterized to prove the design. The sensitivity of 821 pm/g of is achieved with a linearity of 99.7%, cross-axis sensitivity of 0.3%, and natural frequency of 64 Hz; self-temperature compensation is achieved with an error of 0.07 pm/°C.

Prediction of weld bead geometry is always an interesting and challenging research topic as it involves understanding of complex multi input and multi output system. The weld bead geometry has a profound impact on the load bearing capability of a weld joint, which in-turn decides the performance in real time service conditions. The present study introduces a novel approach of detecting a relationship between weld bead geometry and mechanical properties (e.g. tensile load) for the purpose of catering the best the process could offer. The significance of the proposed approach is demonstrated by a case of dissimilar aluminium alloy (AA2219 and AA5083) electron beam welds. A mathematical model of tensile braking load as a function of geometrical attributes of weld bead geometry is presented. The results of investigation suggests the effective thickness of weld - a geometric parameter of weld bead has the most significant influence on tensile breaking load of dissimilar weld joint. The observations on bead geometry and the mechanical properties (microhardness, ultimate tensile load and face bend angle) are correlated with detailed metallurgical analysis. The fusion zone of dissimilar electron beam weld has finer grain size with a moderate evaporation and segregation of alloying elements magnesium and copper respectively. The mechanical properties of weld joint are controlled by optimum bead geometry and HAZ softening in weaker AA5083 Al alloy.