A dynamic analysis of necking phenomena

A new approach, based on the phenomena of stress wave propagation, is presented to analyse necking in the uniaxial tension test. The initiation of necking has been associated in this analysis with a stage, wherein the stress level at any section of the specimen acquires an instability stress value, and the stress wave velocity becomes zero at the section concerned. A method to compute the gradual development of the neck as a function of time with the aid of successive strain hardening curves has been developed. Experimental profiles were obtained by testing specimens of aluminium, copper, brass and low carbon steel under tension at two different velocities—one being hundred times that of the other—and unloading them after reaching different stages of necking. These compare well with theoretically obtained profiles.     

Model for optical density of films with grain clustering

In photographic emulsions, grains have been reported to be clustered. A model for the observed optical density in the presence of grain clustering has been developed.     

Effect of jammer power on the performance of adaptive arrays

The effect of jammer power on the performance of adaptive arrays is studied. It is shown that the output signal-to-interference-plus-noise ratio (SINR) of an adaptive array is a function of jammer power. In the presence of a wide-band jammer, the output SINR of the array decreases with an increase in jammer power and eventually goes to zero. Unlike continuous wave (CW) jammers, a wide-band jammer does not go through power inversion. Instead, as the jammer power is increased, the interference-to-noise ratio (INR) at the array output shows oscillations. For large jammer power, the output INR increases with an increase in jammer power.     

The thermal control system

This paper presents the design, analysis and performance of the thermal control system ofAryabhata. A passive thermal control system, using flat absorber-AK-512 black paint for the outer surface of the satellite and a combination of solar reflector-AK-512 white paint and mechanical polishing for the inner surfaces, was employed to maintain the temperature of all the electronics subsystems onboard the satellite within the specified limits of 0°C and 40°C during the operational life of the satellite. The in-flight temperature data obtained from sixteen temperature sensors onboard the satellite was compared with the theoretically predicted temperature values and the agreement was good for all electronic subsystems housed within the framework of the satellite. The observed deviations in temperature for the tape recorder, proportional counter package and gas bottles of the spin-up system are attributed to the assumptions made for the mathematical model. It has been found that by improving these approximations, the deviations could be reduced to negligible values.     

On a numerical solution of the plastic buckling problem of structures

An automated digital computer procedure is presented for the accurate and efficient solution of the plastic buckling problem of structures. This is achieved by a Sturm sequence method employing a bisection strategy, which eliminates the need for having to solve the buckling eigenvalue problem at each incremental (decremental) loading stage that is associated with the usual solution techniques. The plastic bucking mode shape is determined by a simple inverse iteration process, once the buckling load has been established. Numerical results are presented for plate problems with various edge conditions. The resulting computer program written in FORTRAN for the JPL UNIVAC 1108 machine proves to be most economical in comparison with other existing methods of such analysis.     

A test rig for testing radial diffusers

A simple test rig for investigating the performance of vaneless diffusers with diverging walls for centrifugal compressors has been designed, fabricated and satisfactorily tested. The test rig was designed to give values of area ratio from 1·5 to 6 for an included angle of 10°. A uniform flow at the entry of the diffuser had been achieved by the use of a centre body and suction on both the walls. The swirl was zero in all the tests.A maximum Reynolds' number of 2·8 × 10⁵ can be obtained during the tests. Experimental values of the coefficients for losses, the pressure recovery and efficiency were obtained from the measurements of static and stagnation pressures.     

Probable simultaneous response by the response spectrum method of analysis

A new method is proposed in which the response in several modes of vibration under the three components of earthquake is replaced by the response in a small number of equivalent modes.     

A two (multicomponent) unit parallel system with standby and common cause failure

This paper investigates the mathematical model of a system composed of two non-identical active parallel units and one cold standby. A unit has N components, each having a constant failure and repair rate. These vary from component to component. Several reliability characteristics of interest to system designers as well as operations managers have been computed. Results obtained earlier are verified as particular cases.     

Kinetics and mechanisms of pore growth in MgO

Isothermal pore growth occurs in MgO when polycrystalline compacts are annealed in air for long periods of time at temperatures between 1450 and 1650°C. Fractographic examination of the microstructures demonstrates that the pores are trapped along the grain boundaries and at the intersections. The growth occurs as a result of pore dragging by grain boundary in combination with transport of atoms by surface diffusion. The contribution from lattice diffusion and vapour transport becomes increasingly important as the temperature is raised. Finally, as the pores grow in size, they inhibit the normal grain growth in MgO.