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Kao-Walter, Sharon
Publications (10 of 55) Show all publications
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
Engineering and Technology
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: 2018-03-23Bibliographically 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
Pilthammar, J., Sigvant, M. & Kao-Walter, S. (2018). Introduction of elastic die deformations in sheet metal forming simulations. International Journal of Solids and Structures, 151(S1), 76-90
Open this publication in new window or tab >>Introduction of elastic die deformations in sheet metal forming simulations
2018 (English)In: International Journal of Solids and Structures, ISSN 0020-7683, E-ISSN 1879-2146, Vol. 151, no S1, p. 76-90Article in journal (Refereed) Published
Abstract [en]

Simulations of sheet metal forming (SMF) with finite element models (FE-models) for stamped parts in the car industry are useful for detecting and solving forming problems. However, there are several issues that are challenging to analyze. Virtual tryout and analyzes of stamping dies in running production are two important cases where many of these challenging issues are present. Elastic deformations of dies and press lines and a physically based friction model is often missing when these types of cases are analyzed. To address this, this research aims to develop a method wherein the results of two separate FE-models are combined to enable SMF simulations with the inclusion of elastic tool and press deformations. The two FE-models are one SMF model with two-dimensional (2D) rigid tool surfaces and one structural model of the die and press. The structural model can predict surface shapes and pressure distributions for a loaded stamping die. It can also visualize relatively large and unexpected deformations of the die structure. The recommended method of transferring the deformations from the structural model to the 2D surfaces is through an FE technique called submodeling. The subsequent SMF simulations show that the method for calculating and using the deformed surfaces together with the TriboForm friction model yields a result that matches measured draw-in and strains. It is verified that the ability to virtually deform a die and include the resulting geometry in forming simulations is of high importance. It can be used for the virtual tryout and optimization of new dies or analyses of existing dies in running production. It is suggested that future research focus on a more efficient and automated workflow. More experimental data and simulations are also needed to verify the assumptions made for the simulation models. This will enable the method to be adopted in a reliable way for standard SMF simulations. © 2017.

Place, publisher, year, edition, pages
Elsevier Ltd, 2018
Keywords
Elastic tooling, Friction, Sheet metal forming, Structural analysis, Surface compensation, Automotive industry, Computer supported cooperative work, Deformation, Dies, Metal forming, Presses (machine tools), Sheet metal, Stamping, Tribology, Automated workflow, Forming simulations, Friction modeling, Physically based, Research focus, Structural modeling, Two Dimensional (2 D), Finite element method
National Category
Materials Engineering
Identifiers
urn:nbn:se:bth-14475 (URN)10.1016/j.ijsolstr.2017.05.009 (DOI)000447577700007 ()2-s2.0-85019444887 (Scopus ID)
Note

The authors are grateful for the financial support from Volvo Cars and wishes to thank Tata Steel, AutoForm Engineering, and TriboForm Engineering for valuable cooperation and support. The authors also wish to express their appreciation of their management team at Volvo Cars and Mats Walter, Head of Mechanical Engineering Department at Blekinge Institute of Technology, for enabling an eminent cooperation.

Available from: 2017-06-13 Created: 2017-06-13 Last updated: 2018-11-01Bibliographically approved
Kang, Y., Liu, M., Kao-Walter, S., Reheman, W. & Liu, J. (2018). Predicting aerodynamic resistance of brush seals using computational fluid dynamics and a 2-D tube banks model. Tribology International, 126, 9-15
Open this publication in new window or tab >>Predicting aerodynamic resistance of brush seals using computational fluid dynamics and a 2-D tube banks model
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2018 (English)In: Tribology International, ISSN 0301-679X, E-ISSN 1879-2464, Vol. 126, p. 9-15Article in journal (Refereed) Published
Abstract [en]

Aerodynamic resistance of a brush seal was mainly studied. The velocity distribution along three specified lines was presented. By considering the pressure differential, Reynolds number and Euler number (Eu) were modified. The effect of geometric arrangements and pressure differentials on Eu and leakage were analyzed. Two correlations were fitted based on the numerical results. The results reveal the velocity distribution is almost flat, asymmetric along the specified lines. The velocity increases and decreases almost linearly at centerlines. Eu decreases gradually less with the increase of pressure differential and trends towards a fixed value. A larger Eu indicates stronger resistance but not necessarily less leakage. Finally, two fitted correlations are developed and one is exponential to the row number fits better. © 2018 Elsevier Ltd

Place, publisher, year, edition, pages
Elsevier Ltd, 2018
Keywords
Aerodynamic resistance, Brush seal, Euler number, Reynolds number
National Category
Other Mechanical Engineering
Identifiers
urn:nbn:se:bth-16219 (URN)10.1016/j.triboint.2018.04.023 (DOI)000437075900002 ()2-s2.0-85046798940 (Scopus ID)
Available from: 2018-05-24 Created: 2018-05-24 Last updated: 2018-08-21Bibliographically approved
Reheman, W., Ståhle, P., Andreasson, E. & Kao-Walter, S. (2017). NUMERICAL ANALYSIS OF ANISOTROPIC STIFFNESS OF THIN AL FOIL IN MULTIPLE MATERIAL DIRECTIONS BASED ON EXPERIMENTS. In: Jan Høgsberg and Niels L. Pedersen (Ed.), NSCM30 - the 30th Nordic Seminar on Computational Mechanics: Proceedings. Paper presented at 30th Nordic Seminar on Computational Mechanics (NSCM30), Copenhagen (pp. 175-178).
Open this publication in new window or tab >>NUMERICAL ANALYSIS OF ANISOTROPIC STIFFNESS OF THIN AL FOIL IN MULTIPLE MATERIAL DIRECTIONS BASED ON EXPERIMENTS
2017 (English)In: NSCM30 - the 30th Nordic Seminar on Computational Mechanics: Proceedings / [ed] Jan Høgsberg and Niels L. Pedersen, 2017, p. 175-178Conference paper, Published paper (Refereed)
Keywords
Thin foil, Aluminium alloy, Anisotropy, Symmetry plane, Young's modulus
National Category
Other Mechanical Engineering
Identifiers
urn:nbn:se:bth-16371 (URN)
Conference
30th Nordic Seminar on Computational Mechanics (NSCM30), Copenhagen
Available from: 2018-06-08 Created: 2018-06-08 Last updated: 2018-06-19Bibliographically approved
Zhang, T., Xu, W., Islam, S., Wu, X. & Kao-Walter, S. (2016). Handy Wheel Chair to help Disabled People Get into the Car. In: PROCEEDINGS OF THE 2015 INTERNATIONAL SYMPOSIUM ON MATERIAL, ENERGY AND ENVIRONMENT ENGINEERING (ISM3E 2015): . Paper presented at International Symposium on Material, Energy and Environment Engineering (ISM3E), Changsha, China. Atlantis Press
Open this publication in new window or tab >>Handy Wheel Chair to help Disabled People Get into the Car
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2016 (English)In: PROCEEDINGS OF THE 2015 INTERNATIONAL SYMPOSIUM ON MATERIAL, ENERGY AND ENVIRONMENT ENGINEERING (ISM3E 2015), Atlantis Press , 2016, , p. 3Conference paper, Published paper (Refereed)
Abstract [en]

A wheelchair with a gear system was designed and analysed in order to find a good solution for people with wheelchair to move into the car. This gear system has been designed to be installed in the car and the whole wheelchair can be moved into the car automatically even with the people on it. The three dimensional design have been done in a CAD commercial program with this the solid mechanics analysis was also performed. Volvo XC 60 and V60 as well as a foldable wheelchair have been chosen in this work.

Place, publisher, year, edition, pages
Atlantis Press, 2016. p. 3
Series
AER-Advances in Engineering Research, ISSN 2352-5401
Keywords
Wheel Chair, Access to car, Foldable
National Category
Other Mechanical Engineering
Identifiers
urn:nbn:se:bth-11513 (URN)10.2991/ism3e-15.2015.141 (DOI)000388447400141 ()978-94-6252-141-4 (ISBN)
Conference
International Symposium on Material, Energy and Environment Engineering (ISM3E), Changsha, China
Note

open access

Available from: 2016-01-26 Created: 2016-01-26 Last updated: 2018-01-16Bibliographically approved
Pilthammar, J., Sigvant, M. & Kao-Walter, S. (2016). Including die and press deformations in sheet metal forming simulations. In: Cardoso, RPR Yoon, JW Dick, RE Neto, ES DeSa, JMAC Adetoro, OB (Ed.), NUMISHEET 2016: 10TH INTERNATIONAL CONFERENCE AND WORKSHOP ON NUMERICAL SIMULATION OF 3D SHEET METAL FORMING PROCESSES, PTS A AND B. Paper presented at 10th International Conference and Workshop on Numerical Simulation of 3D Sheet Metal Forming Processes, SEP 04-09, 2016, Bristol, ENGLAND. IOP PUBLISHING LTD, Article ID UNSP 032036.
Open this publication in new window or tab >>Including die and press deformations in sheet metal forming simulations
2016 (English)In: NUMISHEET 2016: 10TH INTERNATIONAL CONFERENCE AND WORKSHOP ON NUMERICAL SIMULATION OF 3D SHEET METAL FORMING PROCESSES, PTS A AND B / [ed] Cardoso, RPR Yoon, JW Dick, RE Neto, ES DeSa, JMAC Adetoro, OB, IOP PUBLISHING LTD , 2016, article id UNSP 032036Conference paper, Published paper (Refereed)
Abstract [en]

Structural analysis, in Abaqus, of a stamping die and subsequent morphing of the tool surfaces in AutoForm were performed to improve a sheet metal forming simulation. First, the tool surfaces of the XC90 rear door inner were scanned. They were not matching when the die was unloaded and could therefore not give any satisfying results in sheet metal forming simulations. Scanned surface geometries were then added to a structural FE-model of the complete stamping die and some influential parts of the production press. The structural FE-model was analysed with Abaqus to obtain the structural deformations of the die. The calculated surface shapes were then transferred to AutoForm where a forming simulation was performed. Results from the different sheet metal forming simulations were compared to measured draw in curves and showed a substantial increase in accuracy and ability to analyse dies in running production when the morphed surfaces were used.

Place, publisher, year, edition, pages
IOP PUBLISHING LTD, 2016
Series
Journal of Physics Conference Series, ISSN 1742-6588 ; 734
National Category
Other Mechanical Engineering
Identifiers
urn:nbn:se:bth-14668 (URN)10.1088/1742-6596/734/3/032036 (DOI)000402734500041 ()
Conference
10th International Conference and Workshop on Numerical Simulation of 3D Sheet Metal Forming Processes, SEP 04-09, 2016, Bristol, ENGLAND
Available from: 2017-06-22 Created: 2017-06-22 Last updated: 2017-06-22Bibliographically approved
Zhang, D., Mao, K., Islam, M. S. S., Andreasson, E. & Kao-Walter, S. (2016). Powerful Modelling Techniques in ABAQUS to Simulate Failure of Laminated composites. Karlskrona: Blekinge Tekniska Högskola
Open this publication in new window or tab >>Powerful Modelling Techniques in ABAQUS to Simulate Failure of Laminated composites
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2016 (English)Report (Refereed) [Artistic work]
Abstract [en]

In this study, laminated composites consisting of LDPE (Low Density Polyethylene), Al-foil (Aluminum foil)and an adhesive interface layer is focused. The defects like necking in LDPE, Al-foil layer and interfacial delaminationcan significantly impact the loading capacity of the laminated material. However, the influence mechanisms of thedefects are still unclear, and no appropriate research tool is available. Therefore, the FEM model based on alreadyavailable techniques in ABAQUS is developed in this work. The aim with the model is to create a robust numericalanalysis tool for further research work.In the modelling process, possibility of necking in substrates and interfacial delamination between material layers isconsidered. A coupled elasto-plasticity damage constitutive model, based on Hooke’s Law, the J2 yield criterion,isotropic hardening, associated flow-rule and ductile damage model, is formulated to demonstrate necking behaviorof substrates. In ABAQUS, three modelling techniques, namely VCCT, Cohesive Element, and XFEM, have been usedto simulate interfacial delamination. The simulation results are compared with the theoretical results.A uniaxial tension test consisting of a two material laminate is simulated by using these three modelling techniques.The special modelling skills for respective modelling techniques, element type, meshing technique of each model, arealso introduced. The comparison with the theoretical results shows necking in substrates and interfacial delaminationare also achieved in all three models as expected. Deformation results of the simulation are very close to that of thetheoretical analysis. Technique features of VCCT, Cohesive Element and XFEM in modelling of interfacialdelamination are analyzed and concluded. These three FEM models can all be utilized according to the requirementsof subsequent research.

Place, publisher, year, edition, pages
Karlskrona: Blekinge Tekniska Högskola, 2016. p. 9
Series
Blekinge Tekniska Högskola Forskningsrapport, ISSN 1103-1581 ; 2016:01
Keywords
Laminated Composites, Necking, Delamination, ABAQUS, Ductile Damage, VCCT, Cohesive Element, XFEM
National Category
Applied Mechanics
Identifiers
urn:nbn:se:bth-11934 (URN)
Projects
KKs Profil MD3S
Funder
Knowledge Foundation
Available from: 2016-05-30 Created: 2016-05-30 Last updated: 2016-08-17Bibliographically approved
Islam, M. S. S., Kao-Walter, S. & Yang, G. (2016). Study of Ligament Length Effect on Mode Mix of a Modified In-Plane Shear Test Specimen. Materials Performance and Characterization, 5(3), 249-259
Open this publication in new window or tab >>Study of Ligament Length Effect on Mode Mix of a Modified In-Plane Shear Test Specimen
2016 (English)In: Materials Performance and Characterization, E-ISSN 2165-3992, ISSN 2165-3992, Vol. 5, no 3, p. 249-259Article in journal (Refereed) Published
Abstract [en]

Shear fracture toughness is an important material behavior that needs to be determined and considered in many industrial fields. At the same time, shear testing is one of the complex material testing areas where available methods are few, often need special arrangements, and most of the methods do not strictly satisfy the definition of pure shear. In this study, a modified shear test specimen was proposed to measure the shear fracture toughness by uniaxial loading in a tensile testing machine. High density polyethylene (HDPE) was used as test material for the experiments. The specimen was created in order to suit the most common used tensile test machine. The specimen was then optimized by using finite element analysis (FEA) to find the geometry and the size of the pre-notch to avoid the mixed mode loading and minimize effects of normal stresses. For the specimen in discussion, an upper and lower limit of usable ligament length can be found. A method for determining the fracture toughness was discussed according to the essential work of fracture. Finally, an example of a special application of the proposed specimen was presented where the variation of shear strength of controlled delamination material (CDM) was measured.

Abstract [sv]

Shear brottseghet är ett viktigt material beteende som måste bestämmas och beaktas i många industriella områden. Samtidigt, testar skjuvning en av de komplexa materialtestområden där tillgängliga metoder är få, ofta behöver specialarrangemang, och de flesta av de metoder som inte strikt uppfyller definitionen av ren skjuvning. I denna studie var en modifierad skjuvning provstycket föreslås att mäta skjuv-brottsegheten genom enaxlig belastning i en dragprovningsmaskin. Högdensitetspolyeten (HDPE) användes som testmaterial för experimenten. Provet skapades för att passa den vanligaste använda dragtestmaskin. Provet därefter optimeras med användning av finit elementanalys (FEA) för att hitta den geometrin och storleken av för-hack för att undvika den blandat läge lastning och minimera effekterna av normala påkänningar. För provet i diskussionen kan hittas en övre och undre gräns för användbar ligament längd. En metod för att bestämma brottsegheten diskuterades i enlighet med den väsentliga brottarbetet. Slutligen ett exempel på en speciell tillämpning av den föreslagna provet presenteras där variationen av skjuvhållfastheten kontrollerad delamineringsmaterial (CDM) mättes.

Place, publisher, year, edition, pages
California, USA: ASTM International, 2016
Keywords
shear test specimen, polymers, fracture toughness, finite element simulation
National Category
Applied Mechanics
Identifiers
urn:nbn:se:bth-12998 (URN)10.1520/MPC20150058 (DOI)000406940600001 ()
Available from: 2016-09-06 Created: 2016-09-06 Last updated: 2018-07-09Bibliographically approved
Islam, M. S. S., Zhang, D., Mehmood, N. & Kao-Walter, S. (2016). Study of Shear Dominant Delamination in Thin Brittle-High Ductile Interface. In: Francesco Iacoviello (Ed.), 21ST EUROPEAN CONFERENCE ON FRACTURE, (ECF21): . Paper presented at 21st European Conference on Fracture, ECF21, 20-24 June 2016, Catania, Italy (pp. 152-157). Elsevier, 2
Open this publication in new window or tab >>Study of Shear Dominant Delamination in Thin Brittle-High Ductile Interface
2016 (English)In: 21ST EUROPEAN CONFERENCE ON FRACTURE, (ECF21) / [ed] Francesco Iacoviello, Elsevier, 2016, Vol. 2, p. 152-157Conference paper, Published paper (Refereed)
Abstract [en]

Thin laminates of Aluminum (Al) foil and Low Density Polyethylene (LDPE) film are essential constituents of food packages where these two substrates are bonded together with a thin layer of LDPE acting as adhesive. Noticeably, Al is a low ductile/quasi brittle material, whereas LDPE is highly ductile. The mechanism of delamination and strength of bond between the interfaces dictates the continuum and damage behavior of this composite. However, measuring the shear delamination properties is challenging as conventional test methods have limitations when the substrates are very thin and flexible. This study explains a tentative method that uses uniaxial tensile testing on the pre-cracked specimen of this composite to find energy dissipation due to shear delamination and successfully uses it in Finite Element Simulation in Abaqus. The delamination was observed in a narrow strip-like region close to fracture surfaces and measured with special visualization aid. A similar response was found in FEM simulation. Scanning Electron Microscopic (SEM) study of delaminated interface confirms the delamination to be shear in nature. In a cohesive zone modeling in Abaqus, the measured shear delamination energy was used as input parameter along with an arbitrary bi-linear cohesive law for validation of the experimental measurement.

Abstract [sv]

Tunna laminat av aluminium (Al) folie och lågdensitetspolyeten (LDPE) film är väsentliga beståndsdelar i livsmedelsförpackningar, där dessa två substrat är sammanbundna med ett tunt skikt av LDPE som fungerar som bindemedel. Märkbart är Al en låg segt / kvasi sprött material, medan LDPE är mycket formbart. Mekanismen för delaminering och styrka bindningen mellan gränssnitten dikterar kontinuum och skador beteende denna komposit. Men mäta skjuvning delamineringsegenskaper är utmanande som konventionella testmetoder har begränsningar när substraten är mycket tunn och flexibel. Denna studie förklarar en preliminär metod som använder enaxlig dragprovning på förhand spruckna exemplar av denna komposit för att hitta energiupptagning på grund av skjuvning delaminering och framgångsrikt använder den i finita elementsimulering i Abaqus. Delamineringen observerades i en smal remsliknande region nära brottytor och mättes med särskild visualisering stöd. Ett liknande svar återfanns i FEM simulering. Svepelektronmikroskop (SEM) studie av delaminerat gränssnitt bekräftar delaminering att vara skjuvning i naturen. I en sammanhängande zon modellering i Abaqus, var den uppmätta skärdelaminering energi som används som inparameter tillsammans med en godtycklig bilinjär sammanhängande lag för validering av experimentella mätningen.

Place, publisher, year, edition, pages
Elsevier, 2016
Series
Procedia Structural Integrity, ISSN 2452-3216
Keywords
Interlaminar shear delamination; thin flexible substrate; composite; cohesive zone modeling; work of fracture; tensile testing
National Category
Applied Mechanics
Identifiers
urn:nbn:se:bth-12996 (URN)10.1016/j.prostr.2016.06.020 (DOI)000387976800019 ()
Conference
21st European Conference on Fracture, ECF21, 20-24 June 2016, Catania, Italy
Note

Open access

Available from: 2016-09-06 Created: 2016-09-06 Last updated: 2017-05-26Bibliographically approved
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