Change search
Refine search result
12 1 - 50 of 58
CiteExportLink to result list
Permanent link
Cite
Citation style
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf
Rows per page
  • 5
  • 10
  • 20
  • 50
  • 100
  • 250
Sort
  • Standard (Relevance)
  • Author A-Ö
  • Author Ö-A
  • Title A-Ö
  • Title Ö-A
  • Publication type A-Ö
  • Publication type Ö-A
  • Issued (Oldest first)
  • Issued (Newest first)
  • Created (Oldest first)
  • Created (Newest first)
  • Last updated (Oldest first)
  • Last updated (Newest first)
  • Disputation date (earliest first)
  • Disputation date (latest first)
  • Standard (Relevance)
  • Author A-Ö
  • Author Ö-A
  • Title A-Ö
  • Title Ö-A
  • Publication type A-Ö
  • Publication type Ö-A
  • Issued (Oldest first)
  • Issued (Newest first)
  • Created (Oldest first)
  • Created (Newest first)
  • Last updated (Oldest first)
  • Last updated (Newest first)
  • Disputation date (earliest first)
  • Disputation date (latest first)
Select
The maximal number of hits you can export is 250. When you want to export more records please use the Create feeds function.
  • 1.
    Andreasson, Eskil
    et al.
    Blekinge Institute of Technology, School of Engineering, Department of Mechanical Engineering.
    Kao-Walter, Sharon
    Blekinge Institute of Technology, School of Engineering, Department of Mechanical Engineering.
    Ståhle, Per
    Micro-mechanisms of a laminated packaging material during fracture2014In: Engineering Fracture Mechanics, ISSN 0013-7944, E-ISSN 1873-7315, Vol. 127Article in journal (Refereed)
    Abstract [en]

    The micro-mechanisms of fracture in a laminate composed of an aluminium foil and a polymer film are considered in this study. The laminates as well as the individual layers, with and without premade centre-cracks, were tensile tested. Visual inspection of the broken cross-sections shows that failure occurs through localised plasticity. This leads to a decreasing and eventually vanishing cross-section ahead of the crack tip for both the laminate and their single constituent layers. Experimental results are examined and analysed using a slip-line theory to derive the work of failure. An accurate prediction was made for the aluminium foil and for the laminate but not for the freestanding polymer film. The reason seems to be that the polymer material switches to non-localised plastic deformation with significant strain-hardening.

  • 2.
    Andreasson, Eskil
    et al.
    Blekinge Institute of Technology, School of Engineering, Department of Mechanical Engineering.
    Mehmood, Nasir
    Blekinge Institute of Technology, School of Engineering, Department of Mechanical Engineering.
    Kao-Walter, Sharon
    Blekinge Institute of Technology, School of Engineering, Department of Mechanical Engineering.
    Trouser tear tests of two thin polymer films2013Conference paper (Refereed)
    Abstract [en]

    Trouser tear testing has been concerned in this research work. A polypropylene film and a low density polyethylene film used in the packaging industry are considered. The experimental trouser tear tests showed different results for both materials when they were subjected to load in different material directions. Therefore the hypothesis was verified, that the in-plane material orientation/alignment induced during manufacturing, hence creating anisotropic in-plane mechanical properties, also affects the tearing behavior. A brittle-like failure was shown in the polypropylene film while the low density polyethylene presented a highly ductile behavior. The two polymer films can be classified as one low-extensible and one high-extensible material according to the test method utilized. Material parameters in the principal material directions i.e. manufacturing direction and cross direction were extracted from the experimental tests for further numerical studies. Scanning electron microscope was used for micromechanical and fractographical analysis of the crack tip and crack surfaces created during the tests. The methods discussed will help classify different groups of materials and can be used as a predictive tool for the crack initiation and crack propagation path in packaging material, especially thin polymer films.

  • 3.
    Andreasson, Eskil
    et al.
    Blekinge Institute of Technology, School of Engineering, Department of Mechanical Engineering.
    Mehmood, Nasir
    Blekinge Institute of Technology, School of Engineering, Department of Mechanical Engineering.
    Mao, Tan
    Blekinge Institute of Technology, School of Engineering, Department of Mechanical Engineering.
    Kao-Walter, Sharon
    Blekinge Institute of Technology, School of Engineering, Department of Mechanical Engineering.
    Experimental and Numerical fracture of cracks emanating from different types of flaws in thin polymer films2013Conference paper (Refereed)
    Abstract [en]

    Fracture mechanical Mode I tensile testing has been performed on an oriented polyproplyne film used in packaging industry. Physical Tensile testing for the continuum material has been performed to observe the material strength and to extract continuum material properties for numerical analysis. Fracture mechanical testing of different shaped notches is performed to observe the failure initiation in the material. A brittle-like failure was shown in the polypropylene film while the low density polyethylene presented a highly ductile behavior. A finite element method (FEM) strategy has been successfully developed to perform numerical analysis of polymer films. The developed FEM model gives an accurate and approximate method to compare and analyze the experimental and numerical results. The obtained results have shown a very fine similarity under theoretical, experimental and numerical analysis. Depending on crack geometry different shape crack effects showed the transferability of localized stresses at different points around the crack. Fracture surface and fracture process is analyzed using scanning electron microscope (SEM). Brittle failure with small deformation and presence of small voids and their coalescence has also been shown in SEM micrographs for LDPE material. The methods discussed will help classify different groups of materials and can be used as a predictive tool for the crack initiation and crack propagation path in packaging material, especially thin polymer films.

  • 4. Bjerkén, Christina
    et al.
    Kao-Walter, Sharon
    Ståhle, Per
    Fracture Mechanisms of a Thin Elastic Plastic Laminate2006Conference paper (Refereed)
    Abstract [en]

    The fracture toughness of a polymer-metal laminate composite is obtained by mechanical testing of a specimen containing a pre-crack. The laminate is a material used for packaging. It consists of a thin aluminium foil and a polymer coating. A centre cracked panel test geometry is used. Each of the layers forming the laminate is also tested separately. The result is compared with the measured fracture strength of the individual layers. It is observed that the load carrying capacity increases dramatically for the laminate. At the strain when peak load is reached for the laminate only aluminium is expected to carry any substantial load because of the low stiffness of the LDPE. However, the strength of the laminate is almost twice the strength of the aluminium foil. The reason seems to be that the aluminium forces the polymer to absorb large quantities of energy at small nominal strain. The toughness compares well with the accumulated toughness of all involved layers. Possible fracture of the interface between the layers is discussed.

  • 5.
    Chen, Hao
    et al.
    Kunming University of Science & Technology, CHN.
    Li, Xuechao
    Kunming University of Science & Technology, CHN.
    Wan, Rundong
    Kunming University of Science & Technology, CHN.
    Kao-Walter, Sharon
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mechanical Engineering. Fac. of Mech. & El. Eng., Shanghai Second Polytechnic Univ., 201209 Shanghai, China.
    Lei, Ying
    Anhui University of Technology, CHN.
    A DFT study of the electronic structures and optical properties of (Cr, C) co-doped rutile TiO22018In: Chemical Physics, ISSN 0301-0104, E-ISSN 1873-4421, Vol. 501, p. 60-67Article in journal (Refereed)
    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.

  • 6.
    Chen, Hao
    et al.
    Kunming University of Science & Technology, CHI.
    Li, Xuechao
    Kunming University of Science & Technology, CHI.
    Wan, Rundong
    Kunming University of Science & Technology, CHI.
    Kao-Walter, Sharon
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mechanical Engineering.
    Lei, Ying
    Anhui University of Technology, CHI.
    Leng, Chongyan
    Kunming University of Science & Technology, CHI.
    A DFT study on modification mechanism of (N,S) interstitial co-doped rutile TiO22018In: Chemical Physics Letters, ISSN 0009-2614, E-ISSN 1873-4448, Vol. 695, p. 8-18Article in journal (Refereed)
    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

  • 7. Chen, S.H.
    et al.
    Wang, Tzuchiang
    Kao-Walter, Sharon
    A crack perpendicular to a bimaterial interface an interface in finite solid2003In: International Journal of Solids and Structures, ISSN 0020-7683 , Vol. 40, no 11, p. 2731-55Article in journal (Refereed)
    Abstract [en]

    The dislocation simulation method is used in this paper to derive the basic equations for a crack perpendicular to the bimaterial interface in a finite solid. The complete solutions to the problem, including the T stress and the stress intensity factors are obtained. The stress field characteristics are investigated in detail. It is found that when the crack is within a weaker material, the stress intensity factor is smaller than that in a homogeneous material and it decreases when the distance between the crack tip and interface decreases. When the crack is within a stiffer material, the stress intensity factor is larger than that in a homogeneous material and it increases when the distance between the crack tip and interface decreases. In both cases, the stress intensity factor will increase when the ratio of the size of a sample to the crack length decreases. A comparison of stress intensity factors between a finite problem and an infinite problem has been given also. The stress distribution ahead of the crack tip, which is near the interface, is shown in details and the T stress effect is considered.

  • 8. Chen, S.H.
    et al.
    Wang, Tzuchiang
    Kao-Walter, Sharon
    Finite boundary effects in problem of a crack perpendicular to and terminating at a bimaterial interface2005In: Acta Mechanica Sinica, ISSN 0567-7718 (p)1614-3116(online), Vol. 21, no 1, p. 56-64Article in journal (Refereed)
    Abstract [en]

    The problem of a crack perpendicular to and terminating at an interface in bimaterial structure with finite boundaries is investigated. The dislocation simulation method and boundary collocation approach are used to derive and solve the basic equations.Two kinds of loading form are considered when the crack lies in a softer or a stiffer material, one is an ideal loading and the other one fits to the practical experiment loading. Complete solutions of the stress field including the T stress are obtained as well as the stress intensity factors. Influences of T stress on the stress field ahead of the crack tip are studied. Finite boundary effects on the stress intensity factors are emphasized. Comparisons with the probled presented by Chen et al. (int. J. Solids and Structure, 2003,40, 2731-2755) are discussed also.

  • 9.
    Islam, Md. Shafiqul Islam
    et al.
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mechanical Engineering.
    Zhang, Defeng
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mechanical Engineering.
    Mehmood, Nasir
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mechanical Engineering.
    Kao-Walter, Sharon
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mechanical Engineering.
    Study of Shear Dominant Delamination in Thin Brittle-High Ductile Interface2015In: National Agency for Finite Element Methods and Standards (NAFEMS), 2015Conference paper (Other (popular science, discussion, etc.))
    Abstract [en]

    Thin laminates of Aluminum (Al) and Low Density Polyethylene (LDPE) is an essential constituent 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 behaviour of this composite. However, measuring the shear delamination is challenging as conventional test methods have limitations when the substrates are very thin. This study explains a method that uses uniaxial tensile testing on the pre-cracked specimen of this composite to find energy dissipation due to shear delamination and successfully use it in Finite Element Simulation in Abaqus. The delamination was observed in a narrow strip region close to fracture surfaces and measured with special visualization aid. Similar response was found in FEM simulation. Scanning Electron Microscopic (SEM) study of delaminated interface confirms the domination of shearing. In a cohesive zone modelling in Finite Element Simulation software, the shear delamination energy was used as input parameter along with an arbitrary bi-linear cohesive law. The substrates’ constitutive response was modelled considering non linear plasticity and softening. Finally proposed delamination energy separation method was validated with comparison between the physical tests and FEM simulations.

  • 10.
    Islam, Md Shafiqul
    et al.
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mechanical Engineering. Blekinge Institute of Technology.
    Kao-Walter, Sharon
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mechanical Engineering.
    Andreasson, Eskil
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mechanical Engineering.
    Trouser tear testing of thin anisotropic polymer films and laminates2019In: International Journal of Fracture, ISSN 0376-9429, E-ISSN 1573-2673Article in journal (Refereed)
    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.

  • 11.
    Islam, Md. Shafiqul
    et al.
    Blekinge Institute of Technology, School of Engineering, Department of Mechanical Engineering.
    Kao-Walter, Sharon
    Blekinge Institute of Technology, School of Engineering, Department of Mechanical Engineering.
    Chen, Xin
    Blekinge Institute of Technology, School of Engineering, Department of Mechanical Engineering.
    Deng, Hong Yu
    Blekinge Institute of Technology, School of Engineering, Department of Mechanical Engineering.
    Innovation for and by the People with Disabilities: A Case Study in Improvement of the Manual Wheelchair2013Conference paper (Refereed)
    Abstract [en]

    This paper focuses on information-driven engineering, where information is gathered by means of innovation for people and by the people. This case study was carried out on innovation of a manual wheelchair. Through active participation of person with disability (direct users) and their carers (indirect user), knowledge awareness of the early design was increased. Computer aided engineering tools were used for the development of virtual prototype (VP) and after further feedback from direct and indirect users design was adjusted. Additionally, Physical prototype was built to practically demonstrate the new features to users and finally the prototype was readjusted to bridge user requirement even more. This innovation process identifies additional improvement aspects and contributes beyond fundamental personal needs and increases well being.

  • 12.
    Islam, Md. Shafiqul
    et al.
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mechanical Engineering.
    Kao-Walter, Sharon
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mechanical Engineering.
    Jian, Li
    Mehmood, Nasir
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mechanical Engineering.
    Study of Shear Property of HDPE by Experiment and Simulation2014Conference paper (Refereed)
    Abstract [en]

    The aim of this work is to evaluate the effect of different specimen dimension and crack length on the mechanical properties of HDPE (High Density Polyethylene) which is often used in the packaging industry. In the experimental part, two main specimens are chosen. One is dog-bone shaped tensile specimen for finding the tensile material properties. The other one is modified shear specimen for studying the shear damage. A corresponding numerical simulation is done by applying a commercial Finite Element Analysis (FEA) program ABAQUS. In addition, the microscopic analysis was performed to observe the fracture surface of specimen after the test with scanning electron microscope (SEM). A series of experiments and simulation were processed and results show that fracture initiation and propagation behavior in the shear specimen is sensitive to the size of the pre-crack (notch) and shear strain at failure.

  • 13.
    Islam, Md. Shafiqul
    et al.
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mechanical Engineering.
    Kao-Walter, Sharon
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mechanical Engineering. Shanghai Second Polytechnic Univ., Faculty of Mech. & El. Eng., 201209, Shanghai, China.
    Yang, Geng
    Kungliga Tekniska högskolan, SWE.
    Study of Ligament Length Effect on Mode Mix of a Modified In-Plane Shear Test Specimen2016In: Materials Performance and Characterization, E-ISSN 2165-3992, ISSN 2165-3992, Vol. 5, no 3, p. 249-259Article in journal (Refereed)
    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.

  • 14.
    Islam, Md. Shafiqul
    et al.
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mechanical Engineering.
    Zhang, Defeng
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mechanical Engineering.
    Mehmood, Nasir
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mechanical Engineering.
    Kao-Walter, Sharon
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mechanical Engineering.
    Study of Shear Dominant Delamination in Thin Brittle-High Ductile Interface2016In: 21ST EUROPEAN CONFERENCE ON FRACTURE, (ECF21) / [ed] Francesco Iacoviello, Elsevier, 2016, Vol. 2, p. 152-157Conference 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.

  • 15.
    Islam, Shafiqul
    et al.
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mechanical Engineering.
    Kao-Walter, Sharon
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mechanical Engineering.
    Yang, Geng
    Measuring Shear Fracture Toughness with a Modified Shear Test Specimen2015Conference paper (Refereed)
    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 and often need special arrangements. 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 than optimized by using Finite Element Analysis (FEA) to find the geometry and the size of the pre-crack to avoid the mixed mode loading and minimize effect of normal stresses. For the specimen in discussion, an upper and lower limit of useable ligament length can be found. Finally, a method for determining the fracture toughness was discussed according to essential work of fracture.

  • 16.
    Islam, Shafiqul
    et al.
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mechanical Engineering.
    Khan, Abdullah
    Kao-Walter, Sharon
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mechanical Engineering.
    Jian, Li
    A Study of Shear Stress Intensity Factor of PP and HDPE by a Modified Experimental Method together with FEM2013In: International Journal of Mechanical, Aerospace, Industrial and Mechatronics Engineering, ISSN 2010-376X, Vol. 7, no 11Article in journal (Refereed)
    Abstract [en]

    Shear testing is one of the most complex testing areas where available methods and specimen geometries are different from each other. Therefore, a modified shear test specimen (MSTS) combining the simple uniaxial test with a zone of interest (ZOI) is tested which gives almost the pure shear. In this study, material parameters of polypropylene (PP) and high density polyethylene (HDPE) are first measured by tensile tests with a dogbone shaped specimen. These parameters are then used as an input for the finite element analysis. Secondly, a specially designed specimen (MSTS) is used to perform the shear stress tests in a tensile testing machine to get the results in terms of forces and extension, crack initiation etc. Scanning Electron Microscopy (SEM) is also performed on the shear fracture surface to find material behavior. These experiments are then simulated by finite element method and compared with the experimental results in order to confirm the simulation model. Shear stress state is inspected to find the usability of the proposed shear specimen. Finally, a geometry correction factor can be established for these two materials in this specific loading and geometry with notch using Linear Elastic Fracture Mechanics (LEFM). By these results, strain energy of shear failure and stress intensity factor (SIF) of shear of these two polymers are discussed in the special application of the screw cap opening of the medical or food packages with a temper evidence safety solution.

  • 17.
    Kang, Yachi
    et al.
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mechanical Engineering.
    Liu, Meihong
    Kunming Univ, CHN.
    Kao-Walter, Sharon
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mechanical Engineering.
    Liu, Jinbin
    Kunming Univ, CHN.
    Cen, Qihong
    Kunming Univ, CHN.
    Numerical Analysis of Pressure Distribution in a Brush Seal Based on a 2-D Staggered Tube Banks Model2019In: Intelligent Automation and Soft Computing, ISSN 1079-8587, E-ISSN 2326-005X, Vol. 25, no 2, p. 405-411Article in journal (Refereed)
    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.

  • 18.
    Kang, Yuchi
    et al.
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mechanical Engineering.
    Liu, Meihong
    Kunming University of Science and Technology, CHI.
    Kao-Walter, Sharon
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mechanical Engineering.
    Reheman, Wureguli
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mechanical Engineering.
    Liu, Jinbin
    Kunming University of Science and Technology, CHI.
    Predicting aerodynamic resistance of brush seals using computational fluid dynamics and a 2-D tube banks model2018In: Tribology International, ISSN 0301-679X, E-ISSN 1879-2464, Vol. 126, p. 9-15Article in journal (Refereed)
    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

  • 19. Kao-Walter, Sharon
    A Visit to M.V. Lomonosov Moscow State University (June 2002)2002Other (Other academic)
  • 20. Kao-Walter, Sharon
    Mechanical and Fracture Properties of Thin Al-foil2001Report (Other academic)
    Abstract [en]

    Mechanical and fracture behaviour of thin Aluminium foil (with a thickness of 6-9 mm) was studied. Tensile tests and fracture toughness tests of different material thickness and different specimen size have been performed. Results influence by the size of specimen has been discussed.

  • 21. Kao-Walter, Sharon
    On the Fracture of Thin Laminates2004Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    This thesis concerns mechanical and fracture properties of a thin aluminium foil and polymer laminate that is widely used as packaging material. The possibility of controlling the path of the growing crack propagation by adjustment of the adhesion level and the property of the polymer layer is investigated. First, the fracture process of the aluminium foil is investigated experimentally. It is found that fracture occurs at a much lower load than what is suggested by standard handbook fracture toughness. Observations in a scanning electron microscope with a tensile stage show that small-scale stable crack growth occurs before the stress intensity factor reaches its maximum. An examination using an optical profilometric method shows almost no plastic deformation except for in a small necking region at the crack tip. However, accurate predictions of the maximum load are obtained using a strip yield model with a geometric correction. Secondly, the mechanical and fracture properties of the laminate are studied. A theory for the mechanics of the composite material is used to evaluate a series of experiments. Each of the layers forming the laminate is first tested separately. The results are analysed and compared with the test results of the entire laminate with varied adhesion. The results show that tensile strength and strain at peak stress of the laminate, with or without a crack, increase when the adhesion of the adhesive increases. It is also found that a much larger amount of energy is consumed in the laminated material at tension compare with the single layers. Possible explanations for the much higher toughness of the laminate are discussed. Finally, the behaviour of a crack in one of the layers, perpendicular to the bimaterial interface in a finite solid, is studied by formulating a dislocation superposition method. The stress field is investigated in detail and a so-called T stress effect is considered. Furthermore, the crack tip driving forces are computed numerically. The results show that the analytical methods for an asymptotically small crack extension can also be applied for a fairly large amount of crack growth. By comparing the crack tip driving force of the crack deflected into the interface with that of the crack penetrating into the polymer layer, it is shown how the path of the crack can be controlled by selecting a proper adhesion level of the interface for different material combinations of the laminate.

  • 22.
    Kao-Walter, Sharon
    et al.
    Blekinge Institute of Technology, School of Engineering, Department of Mechanical Engineering.
    Andreasson, Eskil
    Blekinge Institute of Technology, School of Engineering, Department of Mechanical Engineering.
    Ståhle, Per
    Micro-mechanism of Thin and Laminated Packaging Material during Fracture2012Conference paper (Refereed)
    Abstract [en]

    Fracture path of a polymer coated and uncoated aluminium foil (about 6-7 um) is followed in a Scanning Electron Microscope. The crack length and applied load were measured during crack initiation and growth. The specimens’ cross section were then studied using the optical profilometric method to exam the deformed surface. For the uncoated Al-foil, no fracture surface can be observed. Fracture seems to occur through so-called necking. This behaviour was successfully modelled by a modified strip yield model. It leads to a conclusion that the crack tip is preceded a substantial plastic zone as compared with the crack length. The result was then compared to a polymer coated Al-foil. Further more, similar experimental works were performed on a polymer coated and uncoated Polypropylene. The results were discussed and compared to the cases with Al-foil layer.

  • 23. Kao-Walter, Sharon
    et al.
    Dahlström, J.
    Karlsson, T.
    Magnusson, A.
    A study of the relation between mechanical properties and adhesion level in a laminated packaging material2004In: Mechanics of composite materials, ISSN 0191-5665, E-ISSN 1573-8922, Vol. 40, no 1, p. 29-36Article in journal (Refereed)
    Abstract [en]

    The mechanical properties of a laminate consisting of aluminum-foil, adhesive, and polymer layers were studied in relation to the adhesion level. A special application for liquid-food packaging materials was considered. In experiments, laminates with and without adhesive layers were tested. Tensile tests were first run for every layer of the laminate, and the data obtained were then used in analyzing the results of tensile tests on the entire laminate, as well as in theoretical and finite-element calculations. Relations between different mechanical properties (such as Young's modulus, the peak stress, and the strain at the peak stress) and the adhesion level were analyzed. It was found that the tensile strength and the strain at the peak stress increased with adhesion level. Only slight differences in Young's modulus were observed at different adhesion levels.

  • 24.
    Kao-Walter, Sharon
    et al.
    Blekinge Institute of Technology, School of Engineering, Department of Mechanical Engineering.
    Hu, Min
    Walter, Mats
    Blekinge Institute of Technology, School of Engineering, Department of Mechanical Engineering.
    Leon, Armando
    A Comparison of 2-zone and 3-zone Models in Tearing based on Essential Work of Fracture2009Conference paper (Refereed)
    Abstract [en]

    Two different models (2-zone and 3-zone) for describing the deformation and fracture behavior of tearing ligament was compared and discussed based on the experimental results made by Kim et al. The models are based on the Essential Work of Fracture approach for predicting the specific total work of fracture along the tear path across plastic zones. The experiment and analysis were based on 2-leg trousers tear specimen. The materials chosen in this work were PET (0.508 mm). The results showed that the accuracy of 3-zone model was higher than 2-zone model. It was found that this difference is because the 2-zone model did not consider the plastic deformation caused by loading prior to tearing. Also a finite element model was created to simulate the behavior around the crack tip.

  • 25. Kao-Walter, Sharon
    et al.
    Huang, Yayu
    From Friendship Provinces to University Teacher/Student Exchange2009Conference paper (Other (popular science, discussion, etc.))
    Abstract [en]

    The establishment of the province friendship between Blekinge (Sweden) and Yunnan (China) has lead to a coperation agreement between two local Universities: Blekinge Institute of Technology and Kunming University of Science and Technology. It leads to the development of the cooperation of two provices in the fields of culture, business and education.

  • 26. Kao-Walter, Sharon
    et al.
    Levin, M.L.
    Petronyuk, J.S.
    Walter, Mats
    Acoustic imaging internal microstructure of a packaging material2008Conference paper (Refereed)
    Abstract [en]

    Microstructure of a paper-based packaging material was studied by acoustic microscopy method. The laminate structure of the packaging material contains paperboard, polymer and aluminium, which are widely used for aseptic liquid food package. The method has also been used to detect delaminations inside the material. The results show the possibility to study the micro structural features of paperboard, polymer and aluminium foil layered materials by applying the high-resolution ultrasonic acoustic microscopy. The potential for visualization defects in the body of this kind of materials is discussed in order to further develop the Non-Destructive Testing (NDT) method in food packaging industries.

  • 27. Kao-Walter, Sharon
    et al.
    Mfoumou, Etienne
    Laksman, Efraim
    Stress Relaxation of a Paper Sheet under Cyclic Load: An Experimental and Theoretical Model2010In: Materials Sciences and Applications, ISSN 2153-117X, E-ISSN 2153-1188, Vol. 1, no 6, p. 317-322Article in journal (Refereed)
    Abstract [en]

    Mechanical experiments have been performed to study the dynamic stress relaxation of a paper sheet material mainly used in food packaging industry. The material was cyclically tensile-loaded with a strain range between 2.4% and 4%. The time period for each cycle was 400 seconds. It was found that stress will decrease when the number of cycles increases in the case of upper load and vice versa in the case of lower load. At the same time, the stress to strain curves followed the same pattern as the one from the previous cycle. The stress relaxation behavior of each cycle has been analyzed and the dynamic relaxation modulus was derived. An improved model is proposed to describe the dynamic relaxation behavior of the paper sheet. This model shows a very good fit to the experimental results and trends of prediction are observed. Furthermore, the physical description of this model and the variation by the cycles is discussed.

  • 28.
    Kao-Walter, Sharon
    et al.
    Blekinge Institute of Technology, School of Engineering, Department of Mechanical Engineering.
    Mfoumou, Etienne
    Blekinge Institute of Technology, School of Engineering, Department of Mechanical Engineering.
    Ndikontar, Maurice
    Mechanical Properties and Life-Cycle Sustainability Aspects of Natural Fibre2012In: Advanced Materials Research, TRANS TECH PUBLICATIONS LTD , 2012, Vol. 347-353, no Part 1-7, p. 1887-1893Conference paper (Refereed)
    Abstract [en]

    In order to understand the basic definition of the natural material, references of recently published articles were studied. From these articles, the definition of different terms like renewable material, recyclable material, biodegradable material, sustainable material and finally natural material were collected. Furthermore, a classification of natural fibre was drawn. One of these natural fibres - the coconut was chosen for a more detail analysis in mechanical point of view. An integrated method to analyse the sustainability of the coconut fibre as one of the blend components in building construction will be suggested. Finally, several uses of the fibre are reviewed.

  • 29. Kao-Walter, Sharon
    et al.
    Ståhle, Per
    Fracture Behavior of an Ultra Thin Al-foil- Measuring and Modelling of the Fracture Process2001Conference paper (Refereed)
  • 30. Kao-Walter, Sharon
    et al.
    Ståhle, Per
    Chen, S.H.
    A Finite Element Analysis of a Crack Penetrating or Deflecting into an Interface in a Thin Laminate2006In: Key Engineering Materials, ISSN 1013-9826, E-ISSN 1662-9795, Vol. 312, p. 173-178Article in journal (Refereed)
    Abstract [en]

    The crack tip driving force of a crack growing from a pre-crack that is perpendicular to and terminating at an interface between two materials is investigated using a linear fracture mechanics theory. The analysis is performed both for a crack penetrating the interface, growing straight ahead, and for a crack deflecting into the interface. The results from finite element calculations are compared with asymptotic solutions for infinitesimally small crack extensions. The solution is found to be accurate even for fairly large amounts of crack growth. Further, by comparing the crack tip driving force of the deflected crack with that of the penetrating crack, it is shown how to control the path of the crack by choosing the adhesion of the interface relative to the material toughness.

  • 31. Kao-Walter, Sharon
    et al.
    Ståhle, Per
    Hägglund, Rickard
    Fracture toughness of a laminated composite2003In: Fracture of Polymers, Composites and Adhesives II, Elsevier , 2003, p. 355-364Chapter in book (Other academic)
    Abstract [en]

    The fracture toughness of a polymer-metal laminate composite is obtained by mechanical testing of a specimen containing a pre-crack. The result is compared with a calculated fracture toughness based on the measured fracture toughness of the individual layers. The laminate is a material used for packaging. It consists of a thin aluminium foil and a polymer coating. A centred crack panel test geometry is used. Each of the layers forming the laminate is also tested separately. It is observed that the load carrying capacity increases dramatically. At the strain when peak load is reached for the laminate only aluminium is expected to carry any substantial load because of the low stiffness of the LDPE. However, the strength of the laminate is almost twice the strength of the aluminium foil. The reason seems to be that the aluminium forces the polymer to absorb large quantities of energy at small deformation. The result is compared with the accumulated toughness of all involved layers. A more elaborate model is proposed in the light of non-linear material behaviour and development of a fracture process zone at the crack tip. Possible fracture of the interface between the layers is discussed.

  • 32. Kao-Walter, Sharon
    et al.
    Tryding, Johan
    Fracture mechanics of materials: From steel to packaging material2007Conference paper (Refereed)
    Abstract [en]

    The application of fracture mechanics started during the 20th century. By natural reason, most of the early research has been related to e.g. construction and defence industries. The fracture mechanics theories have been developed based on materials used by these industries, e.g. metals, plastic, concrete and soil materials. Later, along with the development of composite materials (and now even nano-materials), fracture mechanics theory was extended to include the fracture behaviour in composite materials. Nowadays, packaging industries utilize the fracture theories to enhance the package quality and cut the costs. Paper based packages for liquid food in ambient climate have been built up by the combination of paper, plastic and aluminium-foil. Research in this area has been done by the authors. It is found that many fracture related problems that occurs in the making of liquid food packages can be analyzed by the theory of fracture mechanics. However, it is the authors experience that to fully understand the interaction of the materials leading to fracture in the package laminate, further research in fracture of laminate is needed.

  • 33. Kao-Walter, Sharon
    et al.
    Walter, Mats
    Dasari, A
    Leon, Armando
    Tearing and Delaminating of a Polymer Laminate2011In: Key Engineering Materials, ISSN 1013-9826 , Vol. 465 , p. 169-174Article in journal (Refereed)
    Abstract [en]

    The fracture behaviour of laminated materials was studied in this work. The materials used in this work were low-density polyethylene (LDPE) laminated on polyethylene (PET). The thickness of the LDPE was 27 μm and the PET was 100 μm. Experiments were performed by using a 2-leg trousers specimen to analyse the tearing behaviour of the laminate in relation to the delamination. A clear delamination zone was observed during the crack propagation by tearing. Furthermore, a finite element calculation was performed to simulate the behavior around the crack tip during the tearing. A correlation between adhesion and crack propagation was discussed. Finally, the theory of Essential Work of Fracture (EWF) was used for predicting the specific total work of fracture along the tear path across the plastic zones.

  • 34. Kao-Walter, Sharon
    et al.
    Walter, Mats
    Muhammadi, A.B.
    Tensile and Tearing Fracture Behaviour of Food Packaging Laminate2007Conference paper (Other academic)
    Abstract [en]

    Fracture behaviour of laminated food packaging materials is studied. The materials used in this work were the single layer of Aluminium foil (Al-foil), Low density polyethylene (LDPE) and the lamination of these single layers. Experiments were performed by applying the centred crack specimen as well as the 2-leg trousers specimen. It was observed that the load carrying capacity increased for the tensile and decreased for the tearing specimen when the two layers are laminated together. It was also found that in the case of tearing the crack growth was not only initiated by shear stress but also by normal stress. A modified strip yield model and the essential work of fracture theory were used to analyze the deformation and the fracture behaviour. The initial crack growth of the single layers and the laminate during the tensile and tearing were compared and investigated.

  • 35.
    Kao-Walter, Sharon
    et al.
    Blekinge Institute of Technology, School of Engineering, Department of Mechanical Engineering.
    You, Zhong
    Jiang, Xun
    Katangoori, Rahul Reddy
    Blekinge Institute of Technology, School of Engineering, Department of Mechanical Engineering.
    Stress and Stability Analysis of a Building Column with a Pre-folded Origami Pattern2012Conference paper (Refereed)
    Abstract [en]

    A tubular structure by applying the pre-folded origami pattern has been developed at the department of Engineering Science, University of Oxford (see Figure 1). Most of the application is in vehicles. For further application possibility in the fields of Building, bridge, Subway or underground structure, stress and stability analysis were performed. Different cases were calculated by theory of instability and Finite Element Method. Different design solutions were introduced and their strength and stability properties were compared by loading the structure with a compression force on the top of the column. The objective of this work is to find a good solution in safety, sustainability and economy point of view. Failure risk due to the eventually pre-crack in structure will also be discussed by the theory of fracture mechanics.

  • 36.
    Katangoori, Rahul Reddy
    et al.
    Blekinge Institute of Technology, School of Engineering, Department of Mechanical Engineering.
    Kao-Walter, Sharon
    Blekinge Institute of Technology, School of Engineering, Department of Mechanical Engineering.
    You, Zhong
    Conceptual study on an origami patterns of type I tapered square tub with and without a crack2013In: Applied Mechanics and Materials, Trans Tech Publications, Switzerland , 2013, Vol. 275-277, p. 184-188Conference paper (Refereed)
    Abstract [en]

    Thin-walled tubes with origami patterns are popular design for the energy observing devices. However, less study has been done when they subjected to cracks. In this work, the origami square tube with different height to wall thickness ratio are first studied to investigate the collapse modes and deformation mode. Further more, stress concentration areas are identified by numerical simulations. Finally, horizontal and vertical crack was implemented in one of the side in order to study the effect on the deformation mode.

  • 37.
    Leon, Armando
    et al.
    Blekinge Institute of Technology, School of Engineering, Department of Mechanical Engineering.
    Ahlin, Kjell
    Blekinge Institute of Technology, School of Engineering, Department of Mechanical Engineering.
    Kao-Walter, Sharon
    Blekinge Institute of Technology, School of Engineering, Department of Mechanical Engineering.
    On Determining Instability Conditions for Stay Cables Subjected to Parametric Resonance2009Conference paper (Other academic)
    Abstract [en]

    Parametric Resonance Vibration in cables of cable-stayed bridges is mainly studied when the excitation frequency is close to or twice the cable natural frequency. It is, however, important to consider other cases for this frequency relationship, since among other factors, cable-parametric resonance vibrations are strongly depending on the displacement amplitude at the cable supports. Consequently, the present research work is focused on determining, by experimental and numerical analysis, the instability conditions for stay cables subjected to parametric resonance within a wide range of frequency ratios. This is accomplished, by finding the minimum displacement required at the cable supports in order to induce non-linear vibration of considerable amplitude at the cable. Once the cable characteristics (geometry, material properties, inherent damping and initial tensile preload) are known, the instability conditions are identified and expressed in a simplified and practical way in a diagram. Numerical results are compared to those obtained by experimental analysis carried out on a simplified scaled model (1:200) of the Öresund Bridge. A good agreement between numerical and experimental results is found.

  • 38. Li, JIan
    et al.
    Kao-Walter, Sharon
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mechanical Engineering.
    The friction and wear properties of Polypropylene composite filled with carbon fiber and Polyamide 62014In: Journal of Thermoplastic Composite Materials, ISSN 0892-7057, E-ISSN 1530-7980, Vol. 27, no 8, p. 1037-1044Article in journal (Refereed)
    Abstract [en]

    Carbon fiber composites were prepared in order to study the influence of fillers (polyamide 6; PA6) on the tensile and tribological properties of polypropylene (PP) composites. Tensile fracture mechanism was discussed based on the tensile testresults. Tribological tests were conducted on a Mobile Remote Handler-3 (MRH-3) friction and wear tester using a block-on-ring arrangement. It was observed that the carbon fiber (CF) played a main role in the tensile-resistant and wear-resistant properties of the CF/PP composites. The tensile properties were ruled by the fiber–matrix adhesion. Moreover, the excellent tribological performance of the CF/PA6/PP composite is consistent with the worn surface morphology shown.

  • 39.
    Mehmood, Nasir
    et al.
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mechanical Engineering.
    Andreasson, Eskil
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mechanical Engineering.
    Kao-Walter, Sharon
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mechanical Engineering. Blekinge Inst Technol, Dept Mech Engn, SE-37179 Karlskrona, Sweden.;Shanghai Second Polytech Univ, Fac Mech & El Engn, Shanghai 201209, Peoples R China..
    SEM observations of a metal foil laminated with a polymer film2014In: 20TH EUROPEAN CONFERENCE ON FRACTURE / [ed] Zhang, Z Skallerud, B Thaulow, C Ostby, E He, J, ELSEVIER SCIENCE BV , 2014, p. 1435-1440Conference paper (Refereed)
    Abstract [en]

    A thin metal foil laminated on a polymer film usually fracture at higher strains than its corresponding freestanding material layer. On the contrary the polymer film can be observed to fracture at smaller nominal strains when laminated. This is due to the strain localization induced by the created localised neck and plastic deformation in the metal foil. A significant reduction of the "gauge length" of the polymer film is observed locally. This scenario prevails if the adhesion is sufficiently high to prevent delamination to grow between the layers. The newly created gauge length is in the order of two times a metal foil thickness if the adhesion is very strong, leading to local high stress and low strains measured globally. However, this effect is not due to the brittleness of the material or shift of mechanical properties during lamination. During stretching, large deformations are observed in the moderately ductile and strain-hardening polymer film. Tensile failure (boundary conditions and geometrical effects) of polymer laminates has been observed to be governed by two mechanisms demonstrated in Fig. 1. below. In the first case, the polymer film forms a neck and is deformed locally where the metal foil has fractured and ruptures at a small strain (I). In the second case, the delamination is grown and the polymer deforms and delocalizes the strain to a substantial larger area (II). In some cases the laminated material creates multiple necks and the metal film ruptures at several positions and thus deforms at larger strains. All these observations have experimentally been demonstrated by using scanning electron microscopic (SEM) micrographs.

  • 40. Mfoumou, Etienne
    et al.
    Hedberg, Claes
    Kao-Walter, Sharon
    Static Versus Low Frequency Dynamic Elastic Modulus Measurement of Thin Films2006In: Electronical Journal of Technical Acoustics, ISSN 1819-2408, E-ISSN 1819-2408, no 17Article in journal (Refereed)
    Abstract [en]

    A new experimental technique for evaluating Young’s (or elastic) modulus of a vibrating thin film from a dynamic measurement is presented. The technique utilizes bending resonance from a remote acoustic excitation to determine Young’s modulus. Equations relating the natural frequencies to the mechanical properties are obtained, and Young’s modulus is subsequently determined. Young’s modulus values from dynamic test are compared with those (static) obtained by a standard tensile test, and consistent results are obtained. The proposed technique is relatively simple and could be used to determine Young’s modulus of a wide variety of sheet materials initially having no bending stiffness. It can also be used for determining other mechanical properties, such as compliance methods in connections with fracture mechanical testing, fatigue and damage measurements. This work emphasizes the feasibility of a damage assessment of components in-service by evaluating changes in the material characteristics.

  • 41. Mfoumou, Etienne
    et al.
    Hedberg, Claes
    Kao-Walter, Sharon
    Vibration-Based Damage Detection and Evaluation of Sheet Materials using a Remote Acoustic Excitation2008In: Acoustical Physics, ISSN 1063-7710 (print) 1562-6865 (online) , Vol. 54, no 1, p. 127-134Article in journal (Refereed)
    Abstract [en]

    A simple method of damage severity assessment on sheet materials is suggested and proved by theory and experiment. The investigated defect types are in forms of added mass and crack. The method is based on the frequency shift measurement of a material vibrating as a membrane subjected to static tension and irradiated by an acoustic wave. It is shown both theoretically and experimentally that the natural frequency of the damaged membrane is shifted relative to its position in the ideal material. A local increase in thickness (or addition of mass) shifts the natural frequency down, while a crack shifts the frequency up. The method can be considered as acoustic weighting through the frequency shift. The sensitivity of this method can be high because frequency measurement is one of the most accurate measurements in physics and metrology.

  • 42. Mfoumou, Etienne
    et al.
    Hedberg, Claes
    Blekinge Institute of Technology, School of Engineering, Department of Mechanical Engineering.
    Kao-Walter, Sharon
    Blekinge Institute of Technology, School of Engineering, Department of Mechanical Engineering.
    Narayanswamy, S.
    A New Method of Acoustical Remote Evaluation of Defective Structures and Material Characterization2007Conference paper (Refereed)
    Abstract [en]

    The feasibility of a remote monitoring of structures for a progressive damage assessment as well as material characterization using a simple and inexpensive experimental setup is discussed. The method is based on a remote acoustic excitation of transverse vibrations on a membrane using an ordinary broadband low frequency loudspeaker, and the measurement of the response using a Laser Doppler Vibrometer (LDV). Theoretical modeling is also developed to correlate the experimental results obtained, and this yields a new method for Non Destructive Testing (NDT) of sheet-like materials. The function generator provides an input voltage of a sine signal to the loudspeaker, and laser detection of the surface vibrational response of the sample is accomplished with the laser vibrometer.

  • 43. Mfoumou, Etienne
    et al.
    Kao-Walter, Sharon
    Fracture Toughness Testing of Non Standard Specimens2004Report (Other academic)
    Abstract [en]

    The fracture behavior of the main layers used in food packaging material is studied. Investigations include aluminium foil (9μm), paper board (100 μm) and Low Density Polyethylene (27 μm). The plane stress fracture toughness of each layer is derived based on a centered crack panel. Different crack sizes have been tested. A compromise (crack length) was found, at which Strip Yield Model as well as Linear Elastic Fracture Mechanics allow the validation of experimental results. Meanwhile, accurate results are obtained using the Strip Yield Model with a geometric correction. The result is also used to evaluate crack initiation from a notch when all three layers are laminated.

  • 44. Mfoumou, Etienne
    et al.
    Kao-Walter, Sharon
    Hedberg, Claes
    Fracture Mechanism and Acoustic Damage Analysis of Thin Materials2005Conference paper (Refereed)
    Abstract [en]

    The fracture behavior of paper board (100 μm) used in food packaging material is studied. The plane stress fracture toughness is measured based on a centered crack panel. Different crack sizes have been tested. A compromise (crack length) was found, at which Strip Yield Model as well as Linear Elastic Fracture Mechanics allow the validation of experimental results. Meanwhile, accurate results are obtained using the Strip Yield Model with a geometric correction. Besides, detection of damage in food packaging material is an interesting feature in quality control of the product. Therefore the material is investigated using an acoustic method. The method consists of a vibration-based damage assessment and leads to a first level differentiation between damaged and non-damaged specimens. The fracture behavior of paper board (100 μm) used in food packaging material is studied. The plane stress fracture toughness is measured based on a centered crack panel. Different crack sizes have been tested. A compromise (crack length) was found, at which Strip Yield Model as well as Linear Elastic Fracture Mechanics allow the validation of experimental results. Meanwhile, accurate results are obtained using the Strip Yield Model with a geometric correction. Besides, detection of damage in food packaging material is an interesting feature in quality control of the product. Therefore the material is investigated using an acoustic method. The method consists of a vibration-based damage assessment and leads to a first level differentiation between damaged and non-damaged specimens.

  • 45. Mfoumou, Etienne
    et al.
    Kao-Walter, Sharon
    Hedberg, Claes
    Remote Acoustic Monitoring of Thin Laminates2007Conference paper (Refereed)
    Abstract [en]

    Understanding the change in material properties in time is necessary for in-service diagnosis of structures and prevention of accidents. Therefore, a new experimental technique for evaluating Young’s (or elastic) modulus of a vibrating thin sheet from a dynamic measurement is presented. The technique utilizes bending resonance from a remote acoustic excitation. Equations relating the natural frequencies to the mechanical properties are obtained, and Young’s modulus is subsequently determined experimentally using the implemented dynamic measurement method. Young’s modulus values from the dynamic test are then compared with those (static) obtained by a standard tensile test and those obtained by the theory of laminated materials. The proposed technique appears relatively simple and is applied in this paper to laminates initially having no (or negligible) bending stiffness, and used in packaging industries. This work emphasizes the feasibility of a remote condition monitoring of components in-service by evaluating changes in the material properties.

  • 46. Mfoumou, Etienne
    et al.
    Rudenko, Oleg
    Hedberg, Claes
    Kao-Walter, Sharon
    Acoustical measurement accompanying tensile test: new modality for non-destructive testing and characterization of sheet materials2006Conference paper (Refereed)
    Abstract [en]

    A series of uniaxial tensile tests was performed for sheet materials like paperboard, polyethylene and packing layered composites. These sheets can be considered as membranes. In parallel with a tensile test, the natural frequency was measured through an acoustical excitation. Firstly, it was shown both theoretically and experimentally that, at a given load, the frequency is sensitive to the local deviation in the standard thickness or to the presence of cracks inside the material. It means that this acoustic measurement can be used as one of the methods of damage assessment, or nondestructive testing in general. Secondly, the resonance frequency shift was continuously monitored for increasing strain on polyethylene and paperboard, and the curves obtained were compared to the stress-strain curves for material characterization. They were not the same and showed a non-monotonic stiffness variation for the polyethylene. It was shown that the resonance frequency shift measurement can successfully replace the stress-strain curve for material characterization under tensile test. During a long time under load an irreversible plastic deformation of the sample takes place, and the frequency shift can also serve as a new method for evaluating the residual strain of the material.

  • 47.
    Pilthammar, Johan
    et al.
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mechanical Engineering.
    Sigvant, Mats
    Volvo Cars, SWE.
    Kao-Walter, Sharon
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mechanical Engineering.
    Including die and press deformations in sheet metal forming simulations2016In: 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 (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.

  • 48.
    Pilthammar, Johan
    et al.
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mechanical Engineering.
    Sigvant, Mats
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mechanical Engineering.
    Kao-Walter, Sharon
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mechanical Engineering.
    Introduction of elastic die deformations in sheet metal forming simulations2018In: International Journal of Solids and Structures, ISSN 0020-7683, E-ISSN 1879-2146, Vol. 151, no S1, p. 76-90Article in journal (Refereed)
    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.

  • 49.
    Reheman, Wureguli
    et al.
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mechanical Engineering.
    Ståhle, Per
    Lunds universitet, SWE.
    Andreasson, Eskil
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mechanical Engineering.
    Kao-Walter, Sharon
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mechanical Engineering.
    NUMERICAL ANALYSIS OF ANISOTROPIC STIFFNESS OF THIN AL FOIL IN MULTIPLE MATERIAL DIRECTIONS BASED ON EXPERIMENTS2017In: NSCM30 - the 30th Nordic Seminar on Computational Mechanics: Proceedings / [ed] Jan Høgsberg and Niels L. Pedersen, 2017, p. 175-178Conference paper (Refereed)
  • 50.
    Reheman, Wureguli
    et al.
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mechanical Engineering.
    Ståhle, Per
    Divison of soild mechancis, LTH, SWE.
    Kao-Walter, Sharon
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mechanical Engineering.
    On instabilities of growing bi-material interfaces2019In: Procedia Structural Integrity, ICIS2019, Elsevier, 2019, Vol. 17, p. 850-856Conference 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

12 1 - 50 of 58
CiteExportLink to result list
Permanent link
Cite
Citation style
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf