Defence Research and Development Laboratory

About: Defence Research and Development Laboratory is a facility organization based out in Hyderabad, India. It is known for research contribution in the topics: Turbulence & Mach number. The organization has 404 authors who have published 420 publications receiving 4183 citations. The organization is also known as: DRDL.

Temperature effects on wave propagation in nanoplates

Abstract: In this paper, the thermal effects on the ultrasonic wave propagation characteristics of a nanoplate are studied based on the nonlocal continuum theory. The nonlocal governing equations are derived for the nanoplate under thermal environment. The axial stress caused by the thermal effects is considered. The wave propagation analysis is carried out using spectral analysis. The influences of the nonlocal small scale coefficient, the room or low temperature, the high temperature and the axial half wave numbers on the wave dispersion properties of nanoplate are also discussed. Numerical results show that the small scale effects and the thermal effects are significant for larger half wavenumbers. The results are qualitatively different from those obtained based on the local plate theory and thus, are important for the development of graphene-based nanodevices such as strain sensor, mass and pressure sensors, atomic dust detectors, and enhancer of surface image resolution.

Effect of beam oscillation on fatigue life of Ti–6Al–4V electron beam weldments

Abstract: The present study deals with the effect of beam oscillation technique using elliptical waveform on fatigue life of Ti–6Al–4V electron beam weldments. Autogenous full penetration bead-on-plate electron beam welds were made with and without beam oscillation. Some welds were subjected to post-weld heat treatment (PWHT) at two different temperatures (700 and 900 °C). Room temperature hardness, tensile properties and fatigue life of the weldments in the as-welded and PWHT conditions were studied and correlated with the microstructure. The beam oscillated weldments exhibited lower strength (hardness) compared to those made without beam oscillation. This was attributed to wider diffusional α plates in the beam oscillated welds due to lower cooling rates. The beam oscillated weldments exhibited inferior fatigue lives compared with unoscillated weldments owing to the presence of wider α platelets in the former. As the width of α platelets in the weldments subjected to PWHT at 700 °C was smaller than that in the weldments subjected to PWHT at 900 °C, they exhibited longer fatigue lives.

Effect of tungsten content on microstructure and mechanical properties of swaged tungsten heavy alloys

Abstract: This paper describes the effect of tungsten content on microstructure and mechanical properties of swaged Co-containing tungsten heavy alloys with varying tungsten (90W–7Ni–2Fe–1Co, 93W–4.9Ni–1.4Fe–0.7Co and 95W–3.5Ni–1Fe–0.5Co). With increasing tungsten while tensile strength goes through a maximum, both percent elongation and impact energy decrease. Microstructure and fractographic analyses have been carried out in order to explain the trends in mechanical properties. Predominant transgranular fracture of tungsten grains combined with ductile dimple failure of the matrix in 90% W alloy is responsible for superior properties of this alloy in comparison to the alloy with 95% W. The highest tensile strength attained in 93% W alloy is attributed to predominant cleavage failure of W-grains. The results clearly indicate that the matrix volume fraction, contiguity and matrix mean path greatly influence the mechanical properties of tungsten heavy alloys.

Nonlinear free flexural vibration of thin circular cylindrical shells

Abstract: Introduction T HE early development on the topic of nonlinear vibrations of isotropic circular cylindrical shells is well documented by Evensen. In 1976, Raju and Rao presented a finite-element solution, and Evensen commented that the authors had ignored the physics of the problem that thin shells bend more readily than they stretch. Subsequently, Prathap pointed out some inconsistencies in the mathematical analysis carried out by Evensen and also in the physical behavior of the three-term model of Dowell and Ventres. The comments made in Ref. 4 led to reinvestigation of the earlier problem in the present study. The axisymmetric part of the assumed deflected shape plays an important role in the nonlinear behavior of the shell, and so two appropriate threeterm mode shapes for the transverse displacement are chosen. The modal equations obtained by the Galerkin method are solved by the fourth-order Runge-Kutta method to obtain the amplitude-frequency relationship. The numerical results based on the present study and on the analysis of Evensen are compared with the existing experimental values.