Search results

1 – 10 of over 45000
To view the access options for this content please click here
Article
Publication date: 6 August 2020

Niu-Jing Ma, Li-Xiong Gu, Long Piao and Xing-Zhi Zhang

Stiffened plates have been widely used in civil, marine, aerospace engineering. As a kind of thin-walled structure operating in complex environment, stiffened plates…

Abstract

Purpose

Stiffened plates have been widely used in civil, marine, aerospace engineering. As a kind of thin-walled structure operating in complex environment, stiffened plates mostly undergo a variety of dynamic loads, which may sometimes result in large-amplitude vibration. Additionally, initial stresses and geometric imperfections are widespread in this type of structure. Furthermore, it is universally known that initial stresses and geometric imperfections may affect mechanical behavior of structures severely, particularly in dynamic analysis. Thus, the purpose of this paper is to study the stress variation rule of a stiffened plate during large-amplitude vibration considering initial stresses and geometric imperfections.

Design/methodology/approach

The initial stresses are represented in the form of initial bending moments applying to the stiffened plate, while the initial geometric imperfections are considered by means of trigonometric series, and they are assumed existing in the plate along the z-direction exclusively. Then, the dynamic equilibrium equations of the stiffened plate are established using Lagrange’s equation as well as aforementioned conditions. The nonlinear differential equations of motion are simplified as a two-degree-of-freedom system by considering 1:2 and 1:3 internal resonances, respectively, and the multiscale method is applied to solve the equations.

Findings

The influence of initial stresses on the plate, stresses during internal resonance is remarkable, while that is moderate for initial geometric imperfections. (Upon considering the existence of initial stresses or geometric imperfections, the stresses of motivated modes are less than the primary mode for both and internal resonances). The influence of bidirectional initial stresses on the plate’s stresses during internal resonance is more remarkable than that of unidirectional initial stresses. The coupled vibration in 1%3A2 internal resonance is fiercer than that in internal resonance.

Originality/value

Stiffened plates are widely used in engineering structures. However, as a type of thin-walled structure, stiffened plates vibrate with large amplitude in most cases owning to their complicated operation circumstance. In addition, stiffened plates usually contain initial stresses and geometric imperfections, which may result in the variation of their mechanical behavior, especially dynamical behavior. Based on the above consideration, this paper studies the nonlinear dynamical behavior of stiffened plates with initial stresses and geometrical imperfections under different internal resonances, which is the originality of this work. Furthermore, the research findings can provide references for engineering design and application.

Details

Engineering Computations, vol. 38 no. 2
Type: Research Article
ISSN: 0264-4401

Keywords

To view the access options for this content please click here
Article
Publication date: 28 October 2014

Abderrazzak El Boukili

The purpose of this paper is to provide a new three dimension physically based model to calculate the initial stress in silicon germanium (SiGe) film due to thermal…

Abstract

Purpose

The purpose of this paper is to provide a new three dimension physically based model to calculate the initial stress in silicon germanium (SiGe) film due to thermal mismatch after deposition. We should note that there are many other sources of initial stress in SiGe films or in the substrate. Here, the author is focussing only on how to model the initial stress arising from thermal mismatch in SiGe film. The author uses this initial stress to calculate numerically the resulting extrinsic stress distribution in a nanoscale PMOS transistor. This extrinsic stress is used by industrials and manufacturers as Intel or IBM to boost the performances of the nanoscale PMOS and NMOS transistors. It is now admitted that compressive stress enhances the mobility of holes and tensile stress enhances the mobility of electrons in the channel.

Design/methodology/approach

During thermal processing, thin film materials like polysilicon, silicon nitride, silicon dioxide, or SiGe expand or contract at different rates compared to the silicon substrate according to their thermal expansion coefficients. The author defines the thermal expansion coefficient as the rate of change of strain with respect to temperature.

Findings

Several numerical experiments have been used for different temperatures ranging from 30 to 1,000°C. These experiments did show that the temperature affects strongly the extrinsic stress in the channel of a 45 nm PMOS transistor. On the other hand, the author has compared the extrinsic stress due to lattice mismatch with the extrinsic stress due to thermal mismatch. The author found that these two types of stress have the same order (see the numerical results on Figures 4 and 12). And, these are great findings for semiconductor industry.

Practical implications

Front-end process induced extrinsic stress is used by manufacturers of nanoscale transistors as the new scaling vector for the 90 nm node technology and below. The extrinsic stress has the advantage of improving the performances of PMOSFETs and NMOSFETs transistors by enhancing mobility. This mobility enhancement fundamentally results from alteration of electronic band structure of silicon due to extrinsic stress. Then, the results are of great importance to manufacturers and industrials. The evidence is that these results show that the extrinsic stress in the channel depends also on the thermal mismatch between materials and not only on the material mismatch.

Originality/value

The model the author is proposing to calculate the initial stress due to thermal mismatch is novel and original. The author validated the values of the initial stress with those obtained by experiments in Al-Bayati et al. (2005). Using the uniaxial stress generation technique of Intel (see Figure 2). Al-Bayati et al. (2005) found experimentally that for 17 percent germanium concentration, a compressive initial stress of 1.4 GPa is generated inside the SiGe layer.

Details

COMPEL: The International Journal for Computation and Mathematics in Electrical and Electronic Engineering, vol. 33 no. 6
Type: Research Article
ISSN: 0332-1649

Keywords

To view the access options for this content please click here
Article
Publication date: 20 December 2018

Shalini Saha, Amares Chattopadhyay and Abhishek Kumar Singh

The purpose of this paper is to develop a numerical (finite-difference) model exploring phase and group velocities of SH-wave propagation in initially stressed

Abstract

Purpose

The purpose of this paper is to develop a numerical (finite-difference) model exploring phase and group velocities of SH-wave propagation in initially stressed transversely isotropic poroelastic multi-layered composite structures and initially stressed viscoelastic-dry-sandy multi-layered composite structures in two distinct cases.

Design/methodology/approach

With the aid of relevant constitutive relations, the non-vanishing equations of motions for the propagation SH-wave in the considered composite structures have been derived. Haskell matrix method and finite-difference scheme are adopted to deduce velocity equation for both the cases. Stability analysis for the adopted finite-difference scheme has been carried out and the expressions for phase as well as group velocity in terms of dispersion-parameter and stability-ratio have been deduced.

Findings

Velocity equations are derived for the propagation of SH-wave in both the composite structures. The obtained results are matched with the classical results for the case of double and triple-layered composite structure along with comparative analysis. Stability analysis have been carried out to develop expressions of phase as well as group velocity in terms of dispersion-parameter and stability-ratio. The effect of wavenumber, dispersion parameter along with initial-stress, porosity, sandiness, viscoelasticity, stability ratio, associated with the said composite structures on phase, damped and group velocities of SH-wave has been unveiled.

Originality/value

To the best of authors’ knowledge, numerical modelling and analysis of propagation characteristics of SH-wave in multi-layered initially stressed composite structures composed of transversely isotropic poroelastic materials and viscoelastic-dry-sandy materials remain unattempted inspite of its importance and relevance in many branches of science and engineering.

Details

Engineering Computations, vol. 36 no. 1
Type: Research Article
ISSN: 0264-4401

Keywords

To view the access options for this content please click here
Article
Publication date: 8 August 2016

Samia M Said

The dual-phase-lag (DPL) model and Lord-Shulman theory with one relaxation time are applied to study the effect of the gravity field, the magnetic field, and the…

Abstract

Purpose

The dual-phase-lag (DPL) model and Lord-Shulman theory with one relaxation time are applied to study the effect of the gravity field, the magnetic field, and the hydrostatic initial stress on the wave propagation in a two-temperature generalized thermoelastic problem for a medium with an internal heat source that is moving with a constant speed. The paper aims to discuss this issue.

Design/methodology/approach

The exact expressions of the considered variables are obtained by using normal mode analysis.

Findings

Numerical results for the field quantities are given in the physical domain and illustrated graphically in the absence and presence of the gravity field as well as the magnetic field. Comparisons are made between the results of the two different models with and without temperature dependent properties and for two different values of the hydrostatic initial stress. A comparison is also made between the results of the two different models for two different values of the time.

Originality/value

In the present work, the author shall formulate a two-temperature generalized magneto-thermoelastic problem for a medium with temperature dependent properties and with an internal heat source that is moving with a constant speed under the influence of a gravity field and a hydrostatic initial stress. Normal mode analysis is used to obtain the exact expressions for the displacement components, thermodynamic temperature, conductive temperature, and stress components. A comparison is carried out between the considered variables as calculated from the generalized thermoelasticity based on the DPL model and the L-S theory in the absence and presence of a magnetic field as well as a gravity field. Comparisons are also made between the results of the two theories with and without temperature dependent properties and for two different values of hydrostatic initial stress. A comparison is also made between the results of the two different models for two different values of the time.

Details

Multidiscipline Modeling in Materials and Structures, vol. 12 no. 2
Type: Research Article
ISSN: 1573-6105

Keywords

To view the access options for this content please click here
Article
Publication date: 1 June 1954

John H. Argyris

FAILURE of panels under static compression, or for that matter under any loads, involves a vast array of problems ranging from properties of material to initial

Abstract

FAILURE of panels under static compression, or for that matter under any loads, involves a vast array of problems ranging from properties of material to initial instability and post‐buckling phenomena as occurring in various types of panels. It is not intended here to do justice to all these aspects of the subject but to select a single—but at the same time very important—topic, develop its analysis as fully as possible, and present the results in a readily applicable form. The structure investigated is the single skin stiffened panel under compression and the mode of failure considered, denoted by flexural cum torsional failure, involves predominantly flexure and torsion of the stringer with a wavelength of greater order of magnitude than stringer height and pitch. By torsional deformation of the stringer we understand a rotation of its undistorted cross‐section about a longitudinal axis R in the plane of the plate, the position of which will be selected later on (see FIG. 1b). The panel may, of course, also fail in a local mode of stringer and plate with a short wave‐length of the order of magnitude of stringer height and pitch, but the analysis of this case is not included here (see, however, Argyris and Dunne). Note that a local mode of deformation of a stringer formed by straight walls is commonly defined as a distortion of the cross‐section in which the longitudinal edges where two adjacent walls meet remain straight (see FIG. 1c).

Details

Aircraft Engineering and Aerospace Technology, vol. 26 no. 6
Type: Research Article
ISSN: 0002-2667

To view the access options for this content please click here
Article
Publication date: 6 April 2020

Sunita Deswal, Devender Sheoran and Kapil Kumar Kalkal

The purpose of this paper is to establish a model of two-dimensional half-space problem of linear, isotropic, homogeneous, initially stressed, rotating thermoelastic…

Abstract

Purpose

The purpose of this paper is to establish a model of two-dimensional half-space problem of linear, isotropic, homogeneous, initially stressed, rotating thermoelastic medium with microtemperatures. The expressions for different physical variables such as displacement distribution, stress distribution, temperature field and microtemperatures are obtained in the physical domain.

Design/methodology/approach

Normal mode analysis technique is adopted to procure the exact solution of the problem.

Findings

Numerical computations have been carried out with the help of MATLAB programming, and the results are illustrated graphically. Comparisons are made to show the effects of rotation, time and microtemperatures on the resulting quantities. The graphical results indicate that the effects of rotation, microtemperatures and time are very pronounced on the field variables.

Originality/value

In the present work, we have investigated the effects of rotation, time and microtemperature in an initially stressed thermoelastic medium. Although various investigations do exist to observe the disturbances in a thermoelastic medium under the effects of different parameters, the work in its present form, i.e. the disturbances in a thermoelastic medium in the presence of angular velocity, initial stress and microtemperature have not been studied till now. The present work is useful and valuable for analysis of problems involving coupled thermal shock, rotation parameter, microtemperatures and elastic deformation.

Details

Multidiscipline Modeling in Materials and Structures, vol. 16 no. 6
Type: Research Article
ISSN: 1573-6105

Keywords

To view the access options for this content please click here
Article
Publication date: 2 March 2020

Mohammed Y. Fattah and Basma A. Dawood

This study aims to predict the volume changes and collapse potential (CP) associated with the changes in soil suction by using the pressure cell and the effect of initial

Abstract

Purpose

This study aims to predict the volume changes and collapse potential (CP) associated with the changes in soil suction by using the pressure cell and the effect of initial load on soil suction. Three types of gypseous soils have been experimented in this study, sandy gypseous soil from different parts of Iraq. A series of collapse tests were carried out using the oedometer device [single oedometer test (SOT) and double oedometer test (DOT)]. In addition, large-scale model with soil dimensions 700 × 700 × 600 mm was used to show the effect of water content changes in different relations (collapse with time, stress with time, suction with time, etc.).

Design/methodology/approach

A series of collapse tests were carried out using the oedometer device (SOT and DOT). In addition, a large-scale model with soil dimensions 700 × 700 × 600 mm was used to show the effect of water content changes in different relations (collapse with time, stress with time, suction with time, etc.).

Findings

The CP increases with the increasing of the void ratio for each soil. For each soil, the CP decreased when the initial degree of saturation increased. Kerbala soil with gypsum content (30%) revealed collapse value higher than Tikrit soil with gypsum content (55%) under the same initial conditions of water content and density, this is because the higher the Cu value of Kerbala soil is, the more well-graded the soil will be. Upon wetting, the smaller particles or fractions of the well-graded soil tend to fill in the existing voids, resulting in a lower void ratio as compared to the poorly graded one. Consequently, soils with high Cu value tend to collapse more than poorly graded ones. The compressibility of the soil is low when loaded under unsaturated condition, the CP for samples tested in the DOTs under stress level 800 kPa are greater than those obtained from collapse test at a stress level of 200 kPa.

Originality/value

The initial value of suction for all soils increases with initial water content decreases.

Details

World Journal of Engineering, vol. 17 no. 2
Type: Research Article
ISSN: 1708-5284

Keywords

To view the access options for this content please click here
Article
Publication date: 21 February 2020

Changsheng Wang, Xiao Han, Caixia Yang, Xiangkui Zhang and Wenbin Hou

Numerous finite elements are proposed based on analytical solutions. However, it is difficult to find the solutions for complicated governing equations. This paper aims to…

Abstract

Purpose

Numerous finite elements are proposed based on analytical solutions. However, it is difficult to find the solutions for complicated governing equations. This paper aims to present a novel formulation in the framework of assumed stress quasi-conforming method for the static and free vibration analysis of anisotropic and symmetric laminated plates.

Design/methodology/approach

Firstly, an initial stress approximation ruled by 17 parameters, which satisfies the equilibrium equations is derived to improve the performance of the constructed element. Then the stress matrix is treated as the weighted function to weaken the strain-displacement equations. Finally, the Timoshenko’s laminated composite beam functions are adopted as boundary string-net functions for strain integration.

Findings

Several numerical examples are presented to show the performance of the new element, and the results obtained are compared with other available ones. Numerical results have proved that the new element is free from shear locking and possesses high accuracy for the analysis of anisotropic and symmetric laminated plates.

Originality/value

This paper proposes a new QC element for the static and free vibration analysis of anisotropic and symmetric laminated plates. In contrast with the complicated analytical solutions of the equilibrium equations, an initial stress approximation ruled by 17 parameters is adopted here. The Timoshenkos laminated composite beam functions are introduced as boundary string-net functions for strain integration. Numerical results demonstrate the new element is free from shear locking and possesses high accuracy for the analysis of anisotropic and symmetric laminated plates.

Details

Engineering Computations, vol. 37 no. 6
Type: Research Article
ISSN: 0264-4401

Keywords

To view the access options for this content please click here
Article
Publication date: 21 August 2017

Nadi Serhan Aydın

This paper aims to introduce a model-based stress-testing methodology for Islamic finance products. The importance of stress testing was indeed clearly underlined by the…

Abstract

Purpose

This paper aims to introduce a model-based stress-testing methodology for Islamic finance products. The importance of stress testing was indeed clearly underlined by the adverse developments in the global finance industry. One of the key takeaways was the need to strengthen the coverage of the capital framework. Cognisant of this fact, Basel III encapsulates provisions to enhance the financial sector’s ability to withstand shocks arising from possible stress events, thereby reducing adverse spillovers into the real economy. Similarly, the Islamic Financial Services Board requires Islamic financial institutions to run stress tests as part of capital planning.

Design/methodology/approach

The authors perform thorough backtests on Islamic and conventional portfolios under widely used risk models, which are characterised by an underlying conditional volatility framework and distribution, to identify the most suitable risk model specification. Associated with an appropriate initial shock and estimation window size, the paper also conducts a model-based stress test to examine whether the stress losses estimated by the selected models compare favourably to the historical shocks.

Findings

The results suggest that the model-based framework, when combined with an appropriate risk model and distribution, can successfully reproduce past stress periods. The conditional empirical risk model is the most effective one in both long and short portfolio cases – particularly when combined with a long-enough estimation window. The relative performance of normal vs heavy-tailed distributions and symmetric vs asymmetric risk models, on the other hand, is highly dependent on whether the portfolio is long or short. Finally, the authors find that the Islamic portfolio is generally associated with lower historical stress losses as compared to the conventional portfolio.

Originality/value

The model-based framework eliminates some of the key problems associated with traditional scenario-based approaches and is easily adaptable to Islamic finance.

Details

International Journal of Islamic and Middle Eastern Finance and Management, vol. 10 no. 3
Type: Research Article
ISSN: 1753-8394

Keywords

To view the access options for this content please click here
Article
Publication date: 27 August 2020

Devender Sheoran, Ramesh Kumar, Sunil Kumar and Kapil Kumar Kalkal

The purpose of this paper is to study the reflection of plane waves in an initially stressed rotating thermoelastic diffusive medium with micro-concentrations and two-temperature.

Abstract

Purpose

The purpose of this paper is to study the reflection of plane waves in an initially stressed rotating thermoelastic diffusive medium with micro-concentrations and two-temperature.

Design/methodology/approach

A two-dimensional model of generalized thermoelasticity is considered. The governing equations are transformed into the non-dimensional forms using the dimensionless variables. Then, potential functions are introduced for the decoupling of the waves. Further, appropriate boundary conditions are assumed to completely solve the problem. Finally, numerical computations are performed using MATLAB.

Findings

The problem is solved analytically and it is found that there exist five coupled waves in addition to an independent micro-concentration wave in the considered medium. The amplitude ratios and energy ratios of these reflected waves have also been computed numerically for a specific material.

Originality/value

The modulus values of amplitude ratios are presented graphically to exhibit the effects of angular velocity, initial stress, two-temperature, diffusion and micro-concentration parameters. The expressions of energy ratios obtained in explicit form are also depicted graphically as functions of angle of incidence. The law of conservation of energy at the free surface during reflection phenomenon is also verified.

Details

International Journal of Numerical Methods for Heat & Fluid Flow, vol. 31 no. 4
Type: Research Article
ISSN: 0961-5539

Keywords

1 – 10 of over 45000