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Shahid, S., Andreasson, E., Petersson, V., Gukhool, W., Kang, Y. & Kao-Walter, S. (2023). Simplified Characterization of Anisotropic Yield Criteria for an Injection-Molded Polymer Material. Polymers, 15(23), Article ID 4520.
Open this publication in new window or tab >>Simplified Characterization of Anisotropic Yield Criteria for an Injection-Molded Polymer Material
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2023 (English)In: Polymers, E-ISSN 2073-4360, Vol. 15, no 23, article id 4520Article in journal (Refereed) Published
Abstract [en]

Injection-molded polyethylene plates exhibit highly anisotropic mechanical behavior due to, e.g., the uneven orientation of the polymer chains during the molding process and the differential cooling, especially in the thickness direction. Elastoplastic finite element modeling of these plates in particular is used with isotropic yield criteria like von Mises, trading off accuracy in favor of simpler constitutive characterization and faster solution. This article studies three different anisotropic yield criteria, namely, Hill 1948, Barlat Yld91, and Barlat Yld2004-18P, for the finite element modeling of low-density polyethylene (LDPE) at large uniaxial tensile deformation and compares the accuracy and computation time with von Mises. A simplified calibration technique is investigated to identify the constitutive parameters of the studied Barlat group yield criteria. The calibration process is simplified in the sense that only uniaxial tensile tests with digital image correlation measurements are used for the calibration of all the yield criteria studied in this article, although a standard calibration procedure for the Barlat group yield criteria requires additional material testing using more demanding test setups. It is concluded that both Barlat Yld91 and Barlat Yld2004-18P yield criteria can be calibrated with only a few tensile tests and still capture anisotropy in deformation–stress–strain at different levels of accuracy. © 2023 by the authors.

Place, publisher, year, edition, pages
MDPI, 2023
Keywords
anisotropic yield criteria, finite element model, injection molding, polyethylene, Anisotropy, Calibration, Finite element method, Image correlation, Tensile testing, Anisotropic yields, Element models, Finite element modelling (FEM), Injection moulded, Mechanical behavior, Molded polymers, Polymer materials, Von Mises, Yield criterion, Polyethylenes
National Category
Applied Mechanics
Identifiers
urn:nbn:se:bth-25820 (URN)10.3390/polym15234520 (DOI)001116663400001 ()2-s2.0-85179124252 (Scopus ID)
Funder
Vinnova, 20200125Knowledge Foundation, 20180159
Available from: 2023-12-30 Created: 2023-12-30 Last updated: 2024-01-17Bibliographically approved
Wang, X., Liu, M., Kao-Walter, S. & Hu, X. (2020). Numerical evaluation of rotordynamic coefficients for compliant foil gas seal. Applied Sciences, 10(11), Article ID 3828.
Open this publication in new window or tab >>Numerical evaluation of rotordynamic coefficients for compliant foil gas seal
2020 (English)In: Applied Sciences, E-ISSN 2076-3417, Vol. 10, no 11, article id 3828Article in journal (Refereed) Published
Abstract [en]

Compliant foil gas seal is one of the advanced cylindrical gas seal technologies and can be commonly used in the secondary flow system of an aero-engine. It can enhance the dynamic stability of the aero-engine by meeting the steady requirements of the aero-engine seal system. To evaluate the performance of compliant foil gas seal, the steady performance of the gas seal is firstly analyzed to predict the sealing efficiency and obtain the pressure distribution of the gas seal in the compressible flow field. Then, the effects of the operating parameters on the rotordynamic coefficients are analyzed using the finite differential method. It can be used to predict the operation performance of the aero-engine and prepare for the optimization and test rig of compliant foil gas seal on the T-shaped groove. © 2020 by the authors.

Place, publisher, year, edition, pages
MDPI AG, 2020
Keywords
Compliant foil gas seal, Numerical evaluation, Rotordynamic coefficients
National Category
Fluid Mechanics and Acoustics Aerospace Engineering
Identifiers
urn:nbn:se:bth-20016 (URN)10.3390/app10113828 (DOI)000543385900165 ()2-s2.0-85086085074 (Scopus ID)
Note

Open access

The current research has been supported by the China Scholarship Council (grant no. 201708740009).

Available from: 2020-06-29 Created: 2020-06-29 Last updated: 2020-09-07Bibliographically approved
Shahmardani, M., Ståhle, P., Islam, M. S. S. & Kao-Walter, S. (2020). Numerical simulation of buckling and post-buckling behavior of a central notched thin aluminum foil with nonlinearity in consideration. Metals, 10(5), Article ID 582.
Open this publication in new window or tab >>Numerical simulation of buckling and post-buckling behavior of a central notched thin aluminum foil with nonlinearity in consideration
2020 (English)In: Metals, ISSN 2075-4701, Vol. 10, no 5, article id 582Article in journal (Refereed) Published
Abstract [en]

In thin notched sheets under tensile loading, wrinkling appears on the sheet surface, specifically around the cracked area. This is due to local buckling and compression stresses near the crack surfaces. This study aims to numerically study the buckling behavior of a thin sheet with a central crack under tension. A numerical model of a notched sheet under tensile loading is developed using the finite element method, which considers both material and geometrical nonlinearity. To overcome the convergence problem caused by the small thickness-to-length/width ratio and to stimulate the buckling, an imperfection is defined as a small perturbation in the numerical model. Both elastic and elasto-plastic behavior are applied, and the influence of them is studied on the critical buckling stress and the post-buckling behavior of the notched sheet. Numerical results for both elastic and elasto-plastic behavior reflect that very small perturbations need more energy for the activation of buckling mode, and a higher buckling mode is predominant. The influences of different parameters, including Poisson’s ratio, yield limit, crack length-to-sheet-width ratio, and the sheet aspect ratio are also evaluated with a focus on the critical buckling stress and the buckling mode shape. With increase in Poisson’s ratio. First, the critical buckling stress reduces and then remains constant. A higher yield limit results in increases in the critical buckling stress, and no change in the buckling mode shape while adopting various crack length-to-sheet-width ratios, and the sheet aspect ratio changes the buckling mode shape.

Place, publisher, year, edition, pages
MDPI, 2020
Keywords
buckling behavior; thin metal sheet; central crack; wrinkling; perturbation; buckling mode shape
National Category
Applied Mechanics
Identifiers
urn:nbn:se:bth-19443 (URN)10.3390/met10050582 (DOI)000540220000030 ()
Funder
Knowledge Foundation
Note

Open access

Available from: 2020-05-11 Created: 2020-05-11 Last updated: 2021-06-09Bibliographically approved
Ståhle, P., Shahmardani, M. & Kao-Walter, S. (2020). On buckling and fracture of thin elastic-plastic foils. In: Iacoviello, F Sedmak, A Marsavina, L Blackman, B Ferro, GA Shlyannikov, V Stahle, P Zhang, Z Moreira, PMGP Bozic, Z BanksSills, L (Ed.), 1ST VIRTUAL EUROPEAN CONFERENCE ON FRACTURE - VECF1: . Paper presented at 1st European-Structural-Integrity-Society (ESIS) Virtual European Conference on Fracture (ECF), JUN 29-JUL 01, 2020, ELECTR NETWORK (pp. 2065-2071). ELSEVIER
Open this publication in new window or tab >>On buckling and fracture of thin elastic-plastic foils
2020 (English)In: 1ST VIRTUAL EUROPEAN CONFERENCE ON FRACTURE - VECF1 / [ed] Iacoviello, F Sedmak, A Marsavina, L Blackman, B Ferro, GA Shlyannikov, V Stahle, P Zhang, Z Moreira, PMGP Bozic, Z BanksSills, L, ELSEVIER , 2020, p. 2065-2071Conference paper, Published paper (Refereed)
Abstract [en]

The interaction of simultaneous fracture and buckling constitutes problems at manufacturing and handling of thin foils. Buckling occurs as an additional event that complicates the prediction of the critical load that may lead to fracture. For most sufficiently thin foils the plastic slip occurs through the foil thickness which leads to reduction of the cross section width until the foil fails. The process leads to a necking type of deformation which confines itself to a narrow region that extends ahead of the crack tip. The width of the region is close to the foil thickness. At failure the width of the necking region is twice the foil thickness. In the present investigation the crack is assumed to be small compared to the foil geometry and the foil is assumed to be small compared with the crack length. Because of the latter the necking type of plastic region is modelled as a cohesive zone. Since the fracture toughness is not involved in the failure the only two relevant length parameters are crack length and foil thickness. The material model is defined by the elastic modulus, Poisson's ratio and yield stress. The remote load at buckling and at failure is determined and given on dimensionless form, which leaves Poisson's ratio and the ratio of buckling stress versus failure stress as the only free parameters. Two scales of yielding, the load at the ASTM-limit for linear fracture mechanics and twice that load, including the purely elastic result are investigated. Poisson's ratio is varied in the interval from -0.9 to 0.5 for the elastic case and from -0.6 to 0.5 for the plastic cases. The lower theoretical limit -1 for Poisson's ratio was not obtained because of numerical difficulties. The results rules out the possibility of failure before buckling for any reasonable construction material. (C) 2020 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd4.0) Peer-review under responsibility of the European Structural Integrity Society (ESIS) ExCo

Place, publisher, year, edition, pages
ELSEVIER, 2020
Series
Procedia Structural Integrity, ISSN 2452-3216 ; 28
Keywords
Thin foil, Metal, Buckling, Necking, Fracture, Elastic-Plastic, Cohesive zone
National Category
Mechanical Engineering
Identifiers
urn:nbn:se:bth-21371 (URN)10.1016/j.prostr.2020.11.030 (DOI)000632387500233 ()
Conference
1st European-Structural-Integrity-Society (ESIS) Virtual European Conference on Fracture (ECF), JUN 29-JUL 01, 2020, ELECTR NETWORK
Note

open access

Available from: 2021-04-29 Created: 2021-04-29 Last updated: 2022-05-25Bibliographically approved
Kang, Y., Liu, M., Kao-Walter, S., Liu, J. & Cen, Q. (2019). Numerical Analysis of Pressure Distribution in a Brush Seal Based on a 2-D Staggered Tube Banks Model. Intelligent Automation and Soft Computing, 25(2), 405-411
Open this publication in new window or tab >>Numerical Analysis of Pressure Distribution in a Brush Seal Based on a 2-D Staggered Tube Banks Model
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2019 (English)In: Intelligent Automation and Soft Computing, ISSN 1079-8587, E-ISSN 2326-005X, Vol. 25, no 2, p. 405-411Article in journal (Refereed) Published
Abstract [en]

A two-dimensional model of staggered tube banks of the bristle pack with different pitch ratios was solved by computational fluid dynamics (CFD). The pressure distribution along the gap centerlines and bristle surfaces were studied for different upstream pressure from 0.2 to 0.6MPa and models. The results show that the pressure is exponentially rather than strictly linearly decreasing distributed inside the bristle pack. The pressure distribution is symmetry about the circle's horizontal line. The most obvious pressure drop occurred from about 60 degrees to 90 degrees. There is no stationary state reached between the kinetic energy and the static pressure when the upstream is larger than 0.3MPa.

Place, publisher, year, edition, pages
TSI PRESS, 2019
Keywords
Brush seal, Computational Fluid Dynamics (CFD), Pressure distribution, Staggered tube banks
National Category
Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:bth-18608 (URN)10.31209/2019.100000102 (DOI)000475551300019 ()
Available from: 2019-09-10 Created: 2019-09-10 Last updated: 2019-11-14Bibliographically approved
Reheman, W., Ståhle, P. & Kao-Walter, S. (2019). On instabilities of growing bi-material interfaces. In: Procedia Structural Integrity, ICIS2019: . Paper presented at 3rd International Conference on Structural Integrity, ICSI 2019, 2-5 September 2019, Funchal, Madeira, Portugal (pp. 850-856). Elsevier, 17
Open this publication in new window or tab >>On instabilities of growing bi-material interfaces
2019 (English)In: Procedia Structural Integrity, ICIS2019, Elsevier, 2019, Vol. 17, p. 850-856Conference paper, Published paper (Refereed)
Abstract [en]

This study concerns with the evolution of morphological patterns that often arise on the interface of bi-material, so called metal-precipitate phase, due to the instability of the interfaces. The instability leads to growth or retraction of small perturbation, which may determine the formation of a variety of morphological patterns initially arising on surfaces of growing precipitates at small length scales. To better understand the cause of different patterns on the bi-material interfaces, an analytical study of the stability of the precipitate-matrix interface is performed. First, a wavy interface perturbation is used to examine the spontaneous variations that occur at the precipitate-matrix interface. Then, the analysis utilises Cerruti?s solution to compute the perturbed stress field surrounding the interface. It is shown that a virtually flat interface subjected to tension is in general unstable. The amplitude of sinusoidal perturbations decays for short wave lengths and grow for longer wave lengths. Both a critical wave length for which the perturbation amplitude is unaffected and a specific ditto which obtain maximum perturbation growth rate are derived

Place, publisher, year, edition, pages
Elsevier, 2019
Series
Procedia, ISSN 2452-3216
National Category
Mechanical Engineering
Identifiers
urn:nbn:se:bth-18710 (URN)10.1016/j.prostr.2019.08.113 (DOI)000505162900112 ()
Conference
3rd International Conference on Structural Integrity, ICSI 2019, 2-5 September 2019, Funchal, Madeira, Portugal
Funder
ÅForsk (Ångpanneföreningen's Foundation for Research and Development), 18-489
Note

open access

Available from: 2019-09-27 Created: 2019-09-27 Last updated: 2020-01-23Bibliographically approved
Kang, Y., Liu, M., Hu, X., Kao-Walter, S. & Zhang, B. (2019). Theoretical and numerical investigation into brush seal hysteresis without pressure differential. Advanced Composites Letters, 28, Article ID UNSP 0963693519885386.
Open this publication in new window or tab >>Theoretical and numerical investigation into brush seal hysteresis without pressure differential
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2019 (English)In: Advanced Composites Letters, ISSN 0963-6935, Vol. 28, article id UNSP 0963693519885386Article in journal (Refereed) Published
Abstract [en]

Brush seal is a novel type contact seal, and it is well-known due to its excellent performance. However, there are many intrinsic drawbacks, such as hysteresis, which need to be solved. This article focused on modeling hysteresis in both numerical way and analytic way without pressure differential. The numerical simulation was solved by the finite element method. General contact method was used to model the inter-bristle contact, bristle-rotor contact, and bristle-backplate contact. Bristle deformation caused by both vertical and axial tip force was used to validate the numerical model together with reaction force. An analytic model in respect of the strain energy was created. The influence of structure parameters on the hysteresis ratio, with the emphasis on the derivation of hysteresis ratio formula for brush seals, was also presented. Both numerical model and analytic model presented that cant angle is the most influential factor. The aim of the article is to provide a useful theoretical and numerical method to analyze and predict the hysteresis. This work contributes the basis for future hysteresis investigation with pressure differential.

Place, publisher, year, edition, pages
SAGE PUBLICATIONS LTD, 2019
Keywords
brush seal, hysteresis, ABAQUS, strain energy, general contact
National Category
Tribology (Interacting Surfaces including Friction, Lubrication and Wear)
Identifiers
urn:nbn:se:bth-19024 (URN)10.1177/0963693519885386 (DOI)000500013300001 ()
Note

open access

Available from: 2019-12-18 Created: 2019-12-18 Last updated: 2024-01-04Bibliographically approved
Islam, M. S., Kao-Walter, S. & Andreasson, E. (2019). Trouser tear testing of thin anisotropic polymer films and laminates. International Journal of Fracture, 219(2), 187-201
Open this publication in new window or tab >>Trouser tear testing of thin anisotropic polymer films and laminates
2019 (English)In: International Journal of Fracture, ISSN 0376-9429, E-ISSN 1573-2673, Vol. 219, no 2, p. 187-201Article in journal (Refereed) Published
Abstract [en]

This research has investigated the essential work of fracture (EWF) from trouser tear test of polyethylene terephthalate (PET), low-density polyethylene (LDPE) films and their corresponding laminate using a convenient cyclic tear test method. Propagation of tear crack in these thermoplastics deflects from the initial crack path due to the material anisotropy. An improvement to a two-zone tear model for determining tear EWF was proposed for LDPE-like materials. Energy dissipation due to non-uniform bending of the trouser-legs was determined to be significant in EWF calculation of tearing and this was therefore considered in this study. To measure the tear EWF in laminates, contribution from delamination energy dissipation was accounted for.

Place, publisher, year, edition, pages
Springer Netherlands, 2019
Keywords
Trouser tear test, Essential work of fracture, Flexible laminate, Crack path deviation, Delamination
National Category
Mechanical Engineering Applied Mechanics
Identifiers
urn:nbn:se:bth-18780 (URN)10.1007/s10704-019-00389-3 (DOI)000492415800003 ()
Note

open access

Available from: 2019-10-22 Created: 2019-10-22 Last updated: 2021-01-14Bibliographically approved
Chen, H., Li, X., Wan, R., Kao-Walter, S. & Lei, Y. (2018). A DFT study of the electronic structures and optical properties of (Cr, C) co-doped rutile TiO2. Chemical Physics, 501, 60-67
Open this publication in new window or tab >>A DFT study of the electronic structures and optical properties of (Cr, C) co-doped rutile TiO2
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2018 (English)In: Chemical Physics, ISSN 0301-0104, E-ISSN 1873-4421, Vol. 501, p. 60-67Article in journal (Refereed) Published
Abstract [en]

To get an effective doping model of rutile TiO2, we systematically study geometrical parameters, density of states, electron densities, dielectric functions, optical absorption spectra for the pure, C mono-doping, Cr mono-doping and (Cr,C) co-doping rutile TiO2, using density functional calculations. We find that a C doped system presents higher stability under Ti-rich condition, while Cr doped and (Cr,C) co-doped systems are more stable under O-rich condition. For (Cr,C) co-doping situation, the imaginary part of the dielectric function reflects the higher energy absorption efficiency for incident photons. Moreover, co-doping system exhibits much bigger red-shift of optical absorption edge compared with Cr/C single doping systems, because of the great reduction of the direct band gap. The calculated optical absorption spectra show that the (Cr,C) co-doping rutile TiO2 has higher photocatalytic activity in the visible light region.

Place, publisher, year, edition, pages
Elsevier, 2018
Keywords
rutile TiO2; co-doping; impurity states; band gap; photocatalytic activity
National Category
Materials Chemistry
Identifiers
urn:nbn:se:bth-15729 (URN)10.1016/j.chemphys.2017.11.021 (DOI)000426452900008 ()2-s2.0-85037833826 (Scopus ID)
Projects
Structural Mechanics Research Lab
Available from: 2018-01-09 Created: 2018-01-09 Last updated: 2020-10-06Bibliographically approved
Chen, H., Li, X., Wan, R., Kao-Walter, S., Lei, Y. & Leng, C. (2018). A DFT study on modification mechanism of (N,S) interstitial co-doped rutile TiO2. Chemical Physics Letters, 695, 8-18
Open this publication in new window or tab >>A DFT study on modification mechanism of (N,S) interstitial co-doped rutile TiO2
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2018 (English)In: Chemical Physics Letters, ISSN 0009-2614, E-ISSN 1873-4448, Vol. 695, p. 8-18Article in journal (Refereed) Published
Abstract [en]

To obtain a more efficient (N,S) co-doping scheme, we systematically analyze the geometrical parameters, density of states, charge densities, relative dielectric functions and UV–Vis absorption spectra for pure, N/S substitution/interstitial doped and (N,S) substitution/interstitial co-doped TiO2 by using density functional calculations. Compared with (N,S) substitution co-doping, (N,S) interstitial co-doping TiO2 exhibits a more obvious red-shift of absorption edge, because of the band gap is further reduced. Furthermore, there are shallow impurity levels coupling with the top of valence band. The calculated UV–Vis absorption spectra illustrate that (N,S) interstitial co-doping TiO2 has much higher photocatalytic activity in the visible light region. © 2018

Place, publisher, year, edition, pages
Elsevier B.V., 2018
Keywords
Band gap, Co-doping, Impurity states, Photocatalytic activity, Rutile TiO2, Electromagnetic wave absorption, Energy gap, Geometry, High-k dielectric, Oxide minerals, Photocatalysis, Titanium dioxide, Impurity state, Modification mechanism, Photocatalytic activities, Relative dielectric, Shallow impurities, Visible light region, Titanium compounds
National Category
Other Mechanical Engineering
Identifiers
urn:nbn:se:bth-15918 (URN)10.1016/j.cplett.2018.01.044 (DOI)000427386500002 ()2-s2.0-85041647576 (Scopus ID)
Available from: 2018-02-22 Created: 2018-02-22 Last updated: 2018-04-06Bibliographically approved
Organisations
Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0002-9468-9421

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