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1 – 10 of 149
Article
Publication date: 19 August 2014

Mohammed Morovat, Michael Engelhardt, Todd Helwig and Eric Taleff

This paper presents highlights of on-going research, which aims at developing analytical, computational and experimental predictions of the phenomenon of creep buckling in steel…

Abstract

This paper presents highlights of on-going research, which aims at developing analytical, computational and experimental predictions of the phenomenon of creep buckling in steel columns subjected to fire. Analytical solutions using the concept of time-dependent tangent modulus are developed to model time-dependent buckling behavior of steel columns at elevated temperatures. Results from computational creep buckling studies using Abaqus are also presented, and compared with analytical predictions. Material creep data on ASTM A992M steel is also presented and compared to existing creep models for structural steel. Both analytical and computational methods utilize material creep models for structural steel developed by Harmathy, by Fields and Fields, and by the authors. Predictions from this study are also compared against those from Eurocode 3 and the AISC Specification. Results of this work show that neglecting creep effects can lead to erroneous and potentially unsafe predictions of the strength of steel columns subjected to fire.

Details

Journal of Structural Fire Engineering, vol. 5 no. 3
Type: Research Article
ISSN: 2040-2317

Keywords

Article
Publication date: 1 November 1996

C. Kropik and H.A. Mang

Contains a report on three‐dimensional finite element (FE) analyses of deformations and stresses resulting from the excavation of shallow underground railway tunnels. Multisurface…

Abstract

Contains a report on three‐dimensional finite element (FE) analyses of deformations and stresses resulting from the excavation of shallow underground railway tunnels. Multisurface elasto‐viscoplastic material models are employed for consideration of the mechanical behaviour of the soil and the shotcrete shell supporting the excavation. Both are formulated within the framework of closest point projection algorithms. For soil a cap model is used, consisting of a curved failure surface, a tension cut‐off and an elliptical cap. The latter allows consideration of the evolution of plastic strains even for the limiting case of a purely volumetric stress state. The movement of the cap is governed by a hardening law, describing the relation between the hydrostatic pressure and void ratio. The shotcrete model is a rotating crack model, taking ageing of the maturing concrete into account. It consists of a strain‐hardening Drucker‐Prager cone and three Rankine (crack) surfaces. Demonstrates the usefulness of the cap model to predict the mechanical behaviour of the soil by means of tests on remoulded, saturated clay. The model parameters of the clayey silt of Vienna, where the analysed tunnel is located, are fit to standard test results. The parameters of the shotcrete model are fit to test results published in the literature. Compares the analysis of a single‐track tunnel with the results of field measurements from sliding micrometers. Furthermore, the stresses in the shotcrete lining are examined. In view of the inhomogeneity of the material and of unavoidable deficiencies of the measurements it is fair to say that the mechanical effects resulting from the excavation of tunnels are modelled reasonably well.

Details

Engineering Computations, vol. 13 no. 7
Type: Research Article
ISSN: 0264-4401

Keywords

Article
Publication date: 18 November 2013

Mica Grujicic, Jennifer Snipes, Subrahmanian Ramaswami, Rohan Galgalikar, James Runt and James Tarter

Polyurea is an elastomeric two-phase co-polymer consisting of nanometer-sized discrete hard (i.e. high glass transition temperature) domains distributed randomly within a soft…

Abstract

Purpose

Polyurea is an elastomeric two-phase co-polymer consisting of nanometer-sized discrete hard (i.e. high glass transition temperature) domains distributed randomly within a soft (i.e. low glass transition temperature) matrix. A number of experimental investigations reported in the open literature clearly demonstrated that the use of polyurea external coatings and/or internal linings can significantly increase blast survivability and ballistic penetration resistance of target structures, such as vehicles, buildings and field/laboratory test-plates. When designing blast/ballistic-threat survivable polyurea-coated structures, advanced computational methods and tools are being increasingly utilized. A critical aspect of this computational approach is the availability of physically based, high-fidelity polyurea material models. The paper aims to discuss these issues.

Design/methodology/approach

In the present work, an attempt is made to develop a material model for polyurea which will include the effects of soft-matrix chain-segment molecular weight and the extent and morphology of hard-domain nano-segregation. Since these aspects of polyurea microstructure can be controlled through the selection of polyurea chemistry and synthesis conditions, and the present material model enables the prediction of polyurea blast-mitigation capacity and ballistic resistance, the model offers the potential for the “material-by-design” approach.

Findings

The model is validated by comparing its predictions with the corresponding experimental data.

Originality/value

The work clearly demonstrated that, in order to maximize shock-mitigation effects offered by polyurea, chemistry and processing/synthesis route of this material should be optimized.

Details

Multidiscipline Modeling in Materials and Structures, vol. 9 no. 4
Type: Research Article
ISSN: 1573-6105

Keywords

Article
Publication date: 1 February 2016

Dimitrios A. Dragatogiannis, Elias P. Koumoulos, Ioannis A Kartsonakis and Costas A. Charitidis

The study of nanoindentation as a reliable method to extract creep properties as well as for fundamental understanding of deformation mechanisms at small length scales is an open…

Abstract

Purpose

The study of nanoindentation as a reliable method to extract creep properties as well as for fundamental understanding of deformation mechanisms at small length scales is an open interesting field. The observed creep behavior is attributed to time-dependent plastic deformation based on loading rates. There is a lot of work in the field of nanoindentation in order to understand the dynamic effects on nanomechanical properties. The paper aims to discuss these issues.

Design/methodology/approach

The deformation mechanism is investigated under two experimental approaches (high and low loading rates, respectively) during nanoindentation. The effect of loading rate in the nanomechanical properties, during nanoindentation creep of zinc layer on hot dip galvanized (HDG) steel, is discussed through nanoindentation.

Findings

Analysis of this research effort is emphasized on nanoindentation stress exponent, a critical parameter for the life time and reliability of nano/micro-materials and systems. The corrosion resistance was studied by electrochemical impedance spectroscopy (EIS) and localized EIS.

Originality/value

The study of nanoindentation as a reliable method to extract creep properties as well as for fundamental understanding of deformation mechanisms at small length scales is an open interesting field. The observed creep behavior is attributed to time-dependent plastic deformation based on loading rates. The deformation mechanism is investigated under two experimental approaches (high and low loading rates, respectively) during nanoindentation. The effect of loading rate in the nanomechanical properties, during nanoindentation creep of zinc layer on HDGsteel, is discussed through nanoindentation. Analysis of this research effort is emphasized on nanoindentation stress exponent, a critical parameter for the life time and reliability of nano/micro- materials and systems. The corrosion resistance was studied by EIS and localized EIS.

Details

International Journal of Structural Integrity, vol. 7 no. 1
Type: Research Article
ISSN: 1757-9864

Keywords

Article
Publication date: 11 November 2021

Dragan D. Milašinović, Aleksandar Landović and Danica Goleš

The purpose of this paper is to contribute to the solution of the fatigue damage problem of reinforced concrete frames in bending.

Abstract

Purpose

The purpose of this paper is to contribute to the solution of the fatigue damage problem of reinforced concrete frames in bending.

Design/methodology/approach

The problem of fatigue damage is formulated based on the rheological–dynamical analogy, including a scalar damage variable to address the reduction of stiffness in strain softening. The modal analysis is used by the finite element method for the determination of modal parameters and resonance stability of the selected frame cross-section. The objectivity of the presented method is verified by numerical examples, predicting the ductility in bending of the frame whose basic mechanical properties were obtained by non-destructive testing systems.

Findings

The modal analysis in the frame of the finite element method is suitable for the determination of modal parameters and resonance stability of the selected frame cross-section. It is recommended that the modulus of elasticity be determined by non-destructive methods, e.g. from the acoustic response.

Originality/value

The paper presents a novel method of solving the ductility in bending taking into account both the creep coefficient and the aging coefficient. The rheological-dynamical analogy (RDA) method uses the resonant method to find material properties. The characterization of the structural damping via the damping ratio is original and effective.

Details

Engineering Computations, vol. 39 no. 4
Type: Research Article
ISSN: 0264-4401

Keywords

Article
Publication date: 28 August 2007

Gordon Geißler, Michael Kaliske, Michael Nase and Wolfgang Grellmann

The purpose of this paper is to evaluate current simulation capabilities for thin film delamination on the basis of real test data as well as a contribution to its extension in…

1505

Abstract

Purpose

The purpose of this paper is to evaluate current simulation capabilities for thin film delamination on the basis of real test data as well as a contribution to its extension in order to partly substitute experimental investigations.

Design/methodology/approach

The proposed model consists of a formulation that describes the behaviour of the bulk material and an approach that introduces the film's delamination capability. An implicit finite element framework with a cohesive zone implementation is used and described in detail. The numerical results on the basis of the a priori identified material parameters are related to the experimental work. In order to capture the obvious peel speed dependency of these delamination processes, a viscoelastic cohesive formulation is introduced and compared with a pure separation rate dependent cohesive material in the second part of this contribution.

Findings

The performed numerical simulations show a good approximation of the experimental peel process. The extension in order to take time‐dependent effects into account is required for the simulation of such problems. In contrast with the pure rate‐dependent model, the presented consistent formulation of the cohesive part is able to cover the whole range of observed material phenomena.

Research limitations/implications

Owing to the absence of suitable experimental single mode investigations of the sealed layer, the used cohesive material parameters are identified in relation to the pre‐existing experimental results. Furthermore, the resultant peel force has a constant value due to the assumed homogeneous cohesive material and therefore gives only a mean approximation of the experimental values at this stage of the investigation.

Originality/value

The numerical representation of such a thin film delamination process in relation to real experimental results shows the additional capabilities and the usability of the implicit finite element method with a cohesive zone implementation in a clear and illustrative way. The first proposed cohesive extension based on a rheological model shows the capability to cover the full range of time‐dependent interface layer behaviour.

Details

Engineering Computations, vol. 24 no. 6
Type: Research Article
ISSN: 0264-4401

Keywords

Article
Publication date: 3 June 2021

Shuai Li, Zhencai Zhu, Hao Lu and Gang Shen

This paper aims to present a dynamic reliability model of scraper chains based on the fretting wear process and propose a reasonable structural optimization method.

Abstract

Purpose

This paper aims to present a dynamic reliability model of scraper chains based on the fretting wear process and propose a reasonable structural optimization method.

Design/methodology/approach

First, the dynamic tension of the scraper chain is modeled by considering the polygon effect of the scraper conveyor. Then, the numerical wear model of the scraper chain is established based on the tangential and radial fretting wear modes. The scraper chain wear process is introduced based on the diameter wear rate. Furthermore, the time-dependent reliability of scraper chains based on the fretting wear process is addressed by the third-moment saddlepoint approximation (TMSA) method. Finally, the scraper chain is optimized based on the reliability optimization design theory.

Findings

There is a correlation between the wear and the dynamic tension of the scraper conveyor. The unit sliding distance of fretting wear is affected by the dynamic tension of the scraper conveyor. The reliability estimation of the scraper chain with incomplete probability information is achieved by using the TMSA for the method needs only the first three statistical moments of the state variable. From the perspective of the chain drive system, the reliability-based optimal design of the scraper chain can effectively extend its service life and reduce its linear density.

Originality/value

The innovation of the work is that the physical model of the scraper chain wear is established based on the dynamic analysis of the scraper conveyor. And based on the physical model of wear, the time-dependent reliability and optimal design of scraper chains are carried out.

Details

Engineering Computations, vol. 38 no. 10
Type: Research Article
ISSN: 0264-4401

Keywords

Article
Publication date: 1 February 2006

Dragan D. Milasinovic

The paper deals with the rheological‐dynamical analogy in which the three‐dimensional stress‐strain relations are defined under cyclic variation of stress for Hencky’s total…

Abstract

The paper deals with the rheological‐dynamical analogy in which the three‐dimensional stress‐strain relations are defined under cyclic variation of stress for Hencky’s total strain theory. In many practical visco‐elasto‐plastic problems, like as multiaxial fatigue under loading at constant stress amplitude and constant stress ratio, the load‐carrying members are subjected to proportional loading. The classical Hencky’s theory has the advantage of mathematical convenience but its disadvantage is that the deformations predicted for the volume element are independent of the loading path. The existing formulations of the constitutive models for metals are mainly based on the Prandtl‐Reuss incremental theory of elasto‐plasticity, slip theory of plasticity or continuum damage mechanics. They have been shown capable of reproducing satisfactorily most experimental results available for metallic specimens. However, from the theoretical viewpoint little has been said about how these formulations relate to realistic predicting many different inelastic and time dependent problems of two‐ or threedimensional solids, such as fatigue, discontinuous plastic deformation etc. In this paper, fundamentally new aspect of isochronous constitutive relations for Hencky’s theory, which are dependent of the each loading path, is achieved by systematically introducing RDA concept into the continuum framework. Specific inelastic and fatigue formulation of triaxial state of stress is developed and discussed within the new theoretical tool and related to von Mises plasticity..

Details

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

Keywords

Article
Publication date: 3 June 2014

Rajneesh Kakar, Shikha Kakar and Kanwaljeet Kaur

This purpose of this paper is to discuss certain aspects of five-parameter viscoelastic models to study harmonic waves in the non-homogeneous polymer rods of varying density…

Abstract

Purpose

This purpose of this paper is to discuss certain aspects of five-parameter viscoelastic models to study harmonic waves in the non-homogeneous polymer rods of varying density. There are two sections of this paper, in first section, the rheological behaviour of the model is discussed numerically and then it is solved analytically with the help of Friedlander Series using Eikonal equation of optics. In another section, the applicability of the developed model is studied through harmonic wave propagation in polymer non-homogeneous rods. The authors have used linear partial differential equations for finding the dispersion equation of harmonic waves in the polymers. All the cases taken in this study are discussed analytically and numerically with MATLAB.

Design/methodology/approach

A five-parameter viscoelastic model constituting of three dash-pots D 2(η 2), D 2′(η 2′), D 3(η 3) and two springs S 1(G 1), S 2(G 2) is considered. Where, G 1, G 2 are the modulli of elasticity and η 2, η 2′, η 3 are the Newtonian viscosity coefficients of the considered model, respectively. The parameters of the model are non-homogeneous in nature, i.e. module of elasticity and viscosity coefficients are space dependent. 1D problem is formed by taking the material in the form of rod of inhomogeneous polymer material by taking one end at x=0. The co-ordinate x is measured positive in the direction of the axis of the filament.

Findings

When the density, rigidity and viscosity all are equal for the first material specimen, the sound speed is constant, i.e. non-homogeneous has no effect on speed and phase of the wave is given. So it becomes the case of semi non-homogeneous medium (a medium when characteristics are space dependent while the speed is independent of space variable). The use of five-parameter models is mostly restricted in the field of rock mechanics. Thus, these models can be used in determining the time-dependent behaviour of a polymer medium.

Originality/value

The paper is original and it is not published elsewhere.

Details

Multidiscipline Modeling in Materials and Structures, vol. 10 no. 1
Type: Research Article
ISSN: 1573-6105

Keywords

Article
Publication date: 7 September 2015

Lilan Gao, Hong Gao and Xu Chen

This review paper aims to provide a better understanding of formulation and processing of anisotropic conductive adhesive film (ACF) material and to summarize the significant…

Abstract

Purpose

This review paper aims to provide a better understanding of formulation and processing of anisotropic conductive adhesive film (ACF) material and to summarize the significant research and development work for the mechanical properties of ACF material and joints, which helps to the development and application of ACF joints with better reliability in microelectronic packaging systems.

Design/methodology/approach

The ACF material was cured at high temperature of 190°C, and the cured ACF was tested by conducting the tensile experiments with uniaxial and cyclic loads. The ACF joint was obtained with process of pre-bonding and final bonding. The impact tests and shear tests of ACF joints were completed with different aging conditions such as high temperature, thermal cycling and hygrothermal aging.

Findings

The cured ACF exhibited unique time-, temperature- and loading rate-dependent behaviors and a strong memory of loading history. Prior stress cycling with higher mean stress or stress amplitude restrained the ratcheting strain in subsequent cycling with lower mean stress or stress amplitude. The impact strength and adhesive strength of ACF joints increased with increase of bonding temperature, but they decreased with increase of environment temperature. The adhesive strength and life of ACF joints decreased with hygrothermal aging, whereas increased firstly and then decreased with thermal cycling.

Originality/value

This study is to review the recent investigations on the mechanical properties of ACF material and joints in microelectronic packaging applications.

Details

Soldering & Surface Mount Technology, vol. 27 no. 4
Type: Research Article
ISSN: 0954-0911

Keywords

1 – 10 of 149