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1

Memory response on generalized thermoelastic medium in context of dual phase lag thermoelasticity with non-local effect

Tiwari R., Saeed A. M., Kumar R., Kumar A., Singhal A.

Archives of Mechanics

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2022

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Vol. 74, nr 2-3

69--88

EN

Theory of non-local continuum is contemporary appraised and is found to be supplementary coherent to capture the impacts of each and every point of the material at its single point. The conviction of memory dependent derivative is also newly appraised and is observed to be more intuitionistic for predicting the realistic character of the real-world obstacles. Attractiveness of the belief of a memory dependent derivative lies in its unique properties such as its significant constituents – a kernel function and time-delay are freely selected according to the requirement of a problem. The present study comprises a new meticulous thermoelastic heat conduction model for the homogeneous, isotropic, thermoelastic half space medium concerning memory effects and non-local effects. Governing equations are constructed on the basis of the newly appraised non-local generalized theory of thermoelasticity with two phase lags in the frame of a memory dependent derivative. Exact analytical solutions of the physical fields such as dimensionless temperature, displacement as well as thermal stress are evaluated by using a suitable technique of the Laplace transform. Quantitative results are determined in a time-domain for different values of time by taking the numerical inversion of the Laplace transform. Noteworthy role of the constituents of the memory dependent derivative such as kernel function as well as time-delay factor has been scrutinized on the crucial field variables of the medium through computational outcomes. Moreover, the impact of non-local parameter is examined on the variations of field quantities through the quantitative results.

2

Optimization of process parameters of friction stir welded AA5082-AA7075 butt joints using resonance fatigue properties

Kumar G., Kumar R., Kumar R.

Bulletin of the Polish Academy of Sciences. Technical Sciences

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2020

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Vol. 68, nr 1

99--108

EN

In this work, experiments were carried out to quantify the behaviour of friction stir welded (FSW) AA5082-AA7075 butt joints under tensile loading and completely reversed fatigue loading. Different samples were prepared to identify optimum tool rotational and travel speeds to produce FSW AA5082-AA7075 butt joints with the maximum fatigue life. ANOVA was performed, which confirmed that both tool speed nad tool rotation speed affect the tensile strength of the weld. The samples exhibit a considerable difference in their fatigue life and tensile strenght. This difference can be accounted to the presence of welding defects such as surface defects and porosity. S-N curve plotted for the sample shows a significantly high fatigue life at the lower stress ranges. Fracture surfaces were also analysed under scanning electron microscope (SEM). Study of the fracture surface of the sample that failed under fatigue loading showed that the surface was mainly divided in two zones. The first zone was the area of fatigue crack growth where each stress cycle, slowly and gradually, helped in the growth of crack. The second zone was the region of fast fracture where the crack growth resulted in the failure of the joint instantaneously. The fracture surface study of the sample that failed under tensile loading showed that the mode of failure was ductile in nature.

3

Phase-lag effects in skin tissue during transient heating

Kumar R., Vashishth A. K., Ghangas S.

International Journal of Applied Mechanics and Engineering

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2019

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Vol. 24, no. 3

603--623

EN

A three-phase-lag (TPL) model is proposed to describe heat transfer in a finite domain skin tissue with temperature dependent metabolic heat generation. The Laplace transform method is applied to solve the problem. Three special types of heat flux are applied to the boundary of skin tissue for thermal therapeutic applications. The depth of tissue is influenced by the different oscillation heat flux. The comparison between the TPL and dual-phase-lag (DPL) models is analyzed and the effects of phase lag parameters […] and material constant […] on the tissue temperature distribution are presented graphically.

4

Deformation of modified couple stress thermoelastic diffusion in a thick circular plate due to heat sources

Kumar R., Devi S.

Computational Methods in Science and Technology

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2019

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Vol. 25, No. 4

167--176

EN

The aim of this study is to present a mathematical model for predicting the results for displacements, stress components, temperature change and chemical potential with considering independently a particular type of heat source. The general solution for the two-dimensional problem of a thick circular plate with heat sources in modified couple stress thermoelastic diffusion has been obtained in the context of one and two relaxation times. Laplace and Hankel transforms technique is applied to obtain the solutions of the governing equations. Resulting quantities are obtained in the transformed domain. The numerical inversion technique has been used to obtain the solutions in the physical domain. Effects of time on the resulting quantities are shown graphically.

5

Response of thermoelastic interactions in micropolar porous circular plate with three phase lag model

Kumar R., Miglani A., Rani R.

Mechanics and Mechanical Engineering

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2018

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Vol. 22, nr 4

999--1014

EN

The present study deals with a homogeneous and isotopic micropolar porous thermoelastic circular plate by employing eigenvalue approach in the three phase lag theory of thermoelasticity due to thermomechanical sources. The expressions of components of displacements, microrotation, volume fraction field, temperature distribution, normal stress, shear stress and couple shear stress are obtained in the transformed domain by employing the Laplace and Hankel transforms. The resulting quantities are obtained in the physical domain by employing the numerical inversion technique. Numerical computations of the resulting quantities are made and presented graphically to show the effects of void, phase lags, relaxation time, with and without energy dissipation.

6

A two dimensional axisymmetric thermoelastic diffusion problem of micropolar porous circular plate with dual phase lag model

Kumar R., Miglani A., Rani R.

Mechanics and Mechanical Engineering

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2018

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Vol. 22, nr 4

1389--1406

EN

In the present work, we consider a two dimensional axisymmetric problem of micropolar porous circular plate with thermal and chemical potential sources in the context of the theory of dual phase lag generalized thermoelastic diffusion. The potential functions are used to analyze the problem. The Laplace and Hankel transforms techniques are used to find the expressions of displacements, microrotation, volume fraction field, temperature distribution, concentration and stresses in the transformed domain. The inversion of transforms based on Fourier expansion techniques is applied to obtain the results in the physical domain. The numerical results for resulting quantities are obtained and depicted graphically. Effect of porosity, LS theory and phase lag are presented on the resulting quantities. Some particular cases are also deduced.

7

Reflection of PlaneWaves at Micropolar Piezothermoelastic Half-space

Kumar R., Sharma N., Lata P., Marin M.

Computational Methods in Science and Technology

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2018

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Vol. 24, No. 2

113--124

EN

A problem of reflection at a free surface of micropolar orthotropic piezothermoelastic medium is discussed in the present paper. It is found that there exist five type plane waves in micropolar orthotropic piezothermoelastic medium, namely quasi longitudinal displacement wave (quasi LD wave), quasi thermal wave (quasi T wave), quasi CD-I, quasi CD-II wave and electric potential wave (PE wave). The amplitude ratios corresponding to reflected waves are obtained numerically. The effect of angle of incidence and thermopiezoelectric interactions on the reflected waves are studied for a specific model. Some particular cases of interest are also discussed.

8

Dynamics of suspended sediment load with respect to summer discharge and temperatures in Shaune Garang glacierized catchment, Western Himalaya

Kumar R., Kumar R., Singh S., Singh A., Bhardwaj A., Kumari A., Randhawa S. S., Saha A.

Acta Geophysica

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2018

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Vol. 66, no. 5

1109--1120

EN

The observed and predicted rise in temperature will have deleterious impact on melting of snow and ice and form of precipitation which is already evident in Indian Himalayan Region. The temperature-dependent entities like discharge and sediment load will also vary with the observed and predicted rise posing environmental, social and economic threat in the region. There is little known about sediment load transport in relation to temperature and discharge in glacierized catchments in Himalaya mainly due to the scarcity of ground-based observation. The present study is an attempt to understand the suspended sediment load and transportation in relation to variation in discharge and temperature in the Shaune Garang catchment. The result shows strong dependence of sediment concentration primarily on discharge (R2 = 0.84) and then on temperature (R2 = 0.79). The catchments with similar geological and climate setting were observed to have comparatively close weathering rate. The sediment load was found to be higher in the catchments in eastern and central part of Indian Himalayan Region in comparison with western part due to dominance of Indian Summer Monsoon leading to high discharge. The annual physical weathering rate in Shaune Garang catchment was found to be 411 t km−2 year−1 which has increased from 327 t km−2 year−1 in around three decades due to rise in temperature causing increase in discharge and proportion of debris-covered glacierized area.

9

Thermal convection in a ferromagnetic fluid layer with magnetic field dependent viscosity: a correction applied

Prakash J., Kumar R., Kumari K.

Studia Geotechnica et Mechanica

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2017

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Vol. 39, nr 3

39--46

EN

The effect of magnetic field dependent (MFD) viscosity on thermal convection in a horizontal ferromagnetic fluid layer has been investigated numerically. A correction is applied to Sunil et al. [24] which is very important in order to predict the correct behavior of MFD viscosity. Linear stability analysis has been carried out for stationary convection. The MFD viscosity parameter δ as well as the measure of nonlinearity of magnetization M3, both have a stabilizing effect on the system. Numerical results are also obtained for large values of magnetic parameter M1 and predicted graphically.

10

Eigenvalue approach to nanobeam in modified couple stress thermoelastic with three-phase-lag model induced by ramp type heating

Kumar R., Devi S.

Journal of Theoretical and Applied Mechanics

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2017

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Vol. 55 nr 3

1067--1079

EN

This article deals with the study of a thermoelastic nanobeam in a modified couple stress theory subjected to ramp-type heating. The mathematical model is prepared for the nanobeam in thermoelastic three-phase-lag. The Laplace transform and the eigenvalue approach are used to find the displacement component, lateral deflection, temperature change and axial stress of the thermoelastic beam. The general algorithm of the inverse Laplace transform is developed to compute results numerically. The comparison of three-phase-lag, dual-phaselag and GN-III (1993) models are represented, and their illustration is depicted graphically. This study finds the applications in engineering, medical science, sensors, etc.

11

Effect of Hall current in thermoelastic materials with double porosity structure

Kumar R., Vohra R.

International Journal of Applied Mechanics and Engineering

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2017

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Vol. 22, no. 2

303--319

EN

The present investigation is concerned with one dimensional problem in a homogeneous, isotropic thermoelastic medium with double porosity structure in the presence of Hall currents subjected to thermomechanical sources. A state space approach has been applied to investigate the problem. As an application of the approach, normal force and thermal source have been taken to illustrate the utility of the approach. The expressions for the components of normal stress, equilibrated stress and the temperature change are obtained in the frequency domain and computed numerically. A numerical simulation is prepared for these quantities. The effect of the Hartmann number is depicted graphically on the resulting quantities for a specific model. Some particular cases of interest are also deduced from the present investigation.

12

Axisymmetric vibration for micropolar porous thermoelastic circular plate

Kumar R., Kaushal P., Sharma R.

International Journal of Applied Mechanics and Engineering

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2017

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Vol. 22, no. 3

583--600

EN

The present investigation is concerned with a two dimensional axisymmetric problem in a homogeneous isotropic micropolar porous thermoelastic circular plate by using the eigen value approach. The Laplace and Hankel transform are used to solve the problem. The expression of displacements, microrotation, volume fraction field, temperature distribution and stresses are obtained in the transformed domain subjected to thermomechanical sources. A computer algorithm is developed for numerical computations. To obtain the resulting quantities in a physical domain, a numerical inversion technique is used. The resulting quantities are depicted graphically for a specific model. Some special cases are also deduced.

13

Robust and reliable portfolio optimization formulation of a chance constrained problem

Sengupta R. N., Kumar R.

Foundations of Computing and Decision Sciences

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2017

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Vol. 42, No. 1

83--117

EN

We solve a linear chance constrained portfolio optimization problem using Robust Optimization (RO) method wherein financial script/asset loss return distributions are considered as extreme valued. The objective function is a convex combination of portfolio’s CVaR and expected value of loss return, subject to a set of randomly perturbed chance constraints with specified probability values. The robust deterministic counterpart of the model takes the form of Second Order Cone Programming (SOCP) problem. Results from extensive simulation runs show the efficacy of our proposed models, as it helps the investor to (i) utilize extensive simulation studies to draw insights into the effect of randomness in portfolio decision making process, (ii) incorporate different risk appetite scenarios to find the optimal solutions for the financial portfolio allocation problem and (iii) compare the risk and return profiles of the investments made in both deterministic as well as in uncertain and highly volatile financial markets.

14

Reflection and Refraction of Plane HarmonicWaves at an Interface Between Elastic Solid and Magneto-thermoelastic Diffusion Solid with Voids

Kumar R., Kansal T.

Computational Methods in Science and Technology

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2017

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Vol. 23, No. 1

43--56

EN

The problem of the reflection and refraction phenomenon due to longitudinal and transverse waves incident obliquely at a plane interface between uniform elastic solid half-space and magneto-thermoelastic diffusive solid half-space with voids has been studied. It is found that the amplitude ratios of various reflected and refracted waves are functions of the angle of incidence and frequency of the incident wave. The amplitude ratios and energy ratios have been computed numerically for a particular model. The variations of energy ratios with angle of incidence are shown graphically.

15

Thermal Decomposition and Kinetics Studies of AN, KDN and Their Mixtures with and without Catalysts

Kumar P., Joshi P. C., Kumar R.

Central European Journal of Energetic Materials

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2017

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Vol. 14, no. 1

184--200

EN

Potassium dinitramide (KDN) was incorporated in ammonium nitrate (AN) crystals in AN/KDN ratio of 90/10, 75/25 and 50/50 by a co-crystallization method. These mixtures were subjected to thermal decompositional studies (DSC-TG) using a Simultaneous Thermal Analyzer (STA). The catalysts used for the present studies were: i) cupric(II) oxide (CuO) and, ii) copper-cobalt based metal oxide (Cu-Co*). For all catalytic samples, 2% by weight percent of catalyst was added to the total weight of the samples. Thermal decomposition studies were carried out for all the oxidizer samples prepared. Thermal decompositional studies were carried out at three different heating rates, i.e. 3 K/min, 5 K/min and 10 K/min, and the kinetic parameters were computed using the model free Flynn-Wall-Ozawa equation. It has been observed that 50% KDN addition resulted in complete suppression of endothermicity indicating total supression of the phase changes of AN in this temperature range. Further, it was noticed that CuO acts as a better phase stabilizer for AN as compared to Cu-Co*. However, Cu-Co* considerably increased the net exothermic decompositional heat release (J/g) of AN.

16

The onset of convection in a rotating multicomponent fluid layer

Prakash J., Singh V., Kumar R., Kumari K.

Journal of Theoretical and Applied Mechanics

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2016

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Vol. 54 nr 2

477--488

EN

The onset of convective instability is analysed in a rotating multicomponent fluid layer in which density depends on n stratifying agents (one of them is heat) having different diffusivities. Two problems have been analysed mathematically. In the first problem, a sufficient condition is derived for the validity of the principle of the exchange of stabilities. Further, when the complement of this condition holds good, oscillatory motions of neutral or growing amplitude can exist, and thus it is important to derive upper bounds for the complex growth rate of such motions when at least one of the bounding surfaces is rigid so that exact solutions of the problem in closed form are not obtainable. Thus, as the second problem, bounds for the complex growth rates are also obtained. Above results are uniformly valid for quite general nature of the bounding surfaces.

17

Low-Power High-Speed Double Gate 1-bit Full Adder Cell

Kumar R., Roy S., Bhunia C. T.

International Journal of Electronics and Telecommunications

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2016

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Vol. 62, No. 4

329--334

EN

In this paper, we proposed an efficient full adder circuit using 16 transistors. The proposed high-speed adder circuit is able to operate at very low voltage and maintain the proper output voltage swing and also balance the power consumption and speed. Proposed design is based on CMOS mixed threshold voltage logic (MTVL) and implemented in 180nm CMOS technology. In the proposed technique the most time-consuming and power consuming XOR gates and multiplexer are designed using MTVL scheme. The maximum average power consumed by the proposed circuit is 6.94μW at 1.8V supply voltage and frequency of 500 MHz, which is less than other conventional methods. Power, delay, and area are optimized by using pass transistor logic and verified using the SPICE simulation tool at desired broad frequency range. It is also observed that the proposed design may be successfully utilized in many cases, especially whenever the lowest power consumption and delay are aimed.

18

Reflection and transmission at the boundary surface of modified couple stress thermoelastic media

Kumar R., Kumar K.

International Journal of Applied Mechanics and Engineering

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2016

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Vol. 21, no. 1

61--81

EN

In this paper the reflection and transmission at a plane interface in modified couple stress generalized thermoelastic solid half spaces in the context of Loard-Shulman (LS) and Green-Lindsay (GL) theories in welded contact are investigated. Amplitude ratios of various reflected and transmitted waves are obtained due to incidence of a set of coupled longitudinal waves and coupled transverse waves. It is found that the amplitude ratios of various reflected and transmitted waves are functions of the angle of incidence, frequency and are affected by the couple stress properties of the media. Some special cases are deduced from the present formulation.

19

Wear characteristics and defects analysis of friction stir welded joint of aluminium alloy 6061-T6

Kumar R., Chattopadhyaya S., Hloch S., Krolczyk G., Legutko S.

Eksploatacja i Niezawodność

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2016

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Vol. 18, no. 1

128--135

EN

This paper deals with the wear characteristics and defects developed during friction stir welding at different process parameter of aluminium alloy (AA) 6061-T6 having thickness 6 mm. Four welded samples are prepared with rotational speed 500 rpm, 710 rpm, 1000 rpm and with welding speed of 25 mm/min & 40 mm/min. Welded samples and base material are put in wear condition under grinding machine for 120 s. Material removal is measure by taking the difference of weight before and after wear. Different types of defects and fracture are observed on the wear surface. These defects and fractures are analysed under field emission scanning electron microscope (FESEM). It is concluded that material removal from welded sample is less compared to base metal, hence wear resistance increases after friction stir welding.

PL

Praca dotyczy charakterystyki zużycia i uszkodzeń podczas zgrzewania tarciowego z przemieszaniem stopu aluminium (AA) 6061T6 o grubości 6 mm dla zmiennych parametrów. Cztery zgrzewane próbki były wykonane z prędkością obrotową 500 obr/min, 710 obr/min, 1000 obr/min dla prędkości zgrzewania 25 mm/min i 40 mm/min. Zgrzewane próbki i materiał bazowy były poddawane zużywaniu za pomocą szlifierki w czasie 120 s. Ubytek materiału mierzono jako różnicę wagi przed i po zużywaniu. Różne rodzaje wad i pęknięć zaobserwowano na zużytej powierzchni. Wady i pęknięcia analizowano za pomocą mikroskopu polowego (FESEM). Stwierdzono, że ubytek materiału ze zgrzewanych próbek jest mniejszy w porównaniu z ubytkiem dotyczącym materiału bazowego. Zwiększa się więc odporność na zużycie po zgrzewaniu tarciowym z przemieszaniem.

20

Some considerations of fundamental solution in micropolar thermoelastic materials with double porosity

Kumar R., Vohra R., Gorla M. G.

Archives of Mechanics

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2016

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Vol. 68, nr 4

263--284

EN

This paper is concerned with micropolar thermoelastic materials which have a double porosity structure. The system of the equations of the assumed model is based on the equations of motion, equilibrated stress equations of motion and heat conduction equation for material with double porosity. The explicit expressions for the fundamental solution of the system of equations in the case of steady vibrations are presented. The desired solutions are obtained by the use of elementary functions. Some basic properties are also established.