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Mehmood, Nasir
Publications (8 of 8) Show all publications
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: 2019-06-14Bibliographically approved
Zhang, D., Mao, K., Islam, M. S. S., Andreasson, E., Mehmood, N. & Kao-Walter, S. (2015). Powerful Modelling Techniques in Abaqus to Simulate Necking and Delamination of Laminated Composites.
Open this publication in new window or tab >>Powerful Modelling Techniques in Abaqus to Simulate Necking and Delamination of Laminated Composites
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2015 (English)Other (Other academic)
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 delamination can significantly impact the loading capacity of the laminated material. However, the influence mechanisms of the defects are still unclear, and no appropriate research tool is available. Therefore, the FEM model based on already available techniques in ABAQUS is developed in this work. The aim with the model is to create a robust numerical analysis tool for further research work.

In the modeling process, possibility of necking in substrates and interfacial delamination between material layers is considered. The constitutive material behaviour is elastic-plastic complemented with progressive damage, based on Hooke’s Law, the J2 yield criterion, isotropic hardening, associated flow-rule and ductile damage model are formulated to demonstrate necking behavior of substrates. In ABAQUS, three modeling techniques, namely VCCT, Cohesive Element, and XFEM, have been used to 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 modeling techniques. The special modelling skills for respective modeling techniques, element type, meshing technique of each model, are also introduced. The comparison with the theoretical results shows necking in substrates and interfacial delamination are also achieved in all three models as expected. Deformation results of the simulation are very close to that of the theoretical analysis. Technique features of VCCT, Cohesive Element and XFEM in modelling of interfacial delamination are analyzed and concluded. These three FEM models can all be utilized according to the requirements of subsequent research.

Publisher
p. 21
Keywords
Laminated Composites, Necking, Delamination, ABAQUS, Ductile Damage, VCCT, Cohesive Element, XFEM
National Category
Applied Mechanics
Identifiers
urn:nbn:se:bth-11631 (URN)
Projects
KKS profile MD3S
Note

This is a  presentation in SIMULIA 2015 Regional User Meeting, Copenhagen, Denmark, 12th October 2015

Available from: 2016-02-12 Created: 2016-02-12 Last updated: 2016-02-12Bibliographically approved
Islam, M. S. S., Zhang, D., Mehmood, N. & Kao-Walter, S. (2015). Study of Shear Dominant Delamination in Thin Brittle-High Ductile Interface. In: National Agency for Finite Element Methods and Standards (NAFEMS): . Paper presented at NORDIC Seminar: Simulating Composite Materials and Structures, Stockholm.
Open this publication in new window or tab >>Study of Shear Dominant Delamination in Thin Brittle-High Ductile Interface
2015 (English)In: National Agency for Finite Element Methods and Standards (NAFEMS), 2015Conference paper, Oral presentation with published abstract (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.

Keywords
Shear Dlamination, Thin Packaging Material, Composites, Cohesive Zone Modelling, Finite Element Simulation, Tensile Testing
National Category
Applied Mechanics
Identifiers
urn:nbn:se:bth-11607 (URN)
Conference
NORDIC Seminar: Simulating Composite Materials and Structures, Stockholm
Available from: 2016-02-04 Created: 2016-02-04 Last updated: 2016-02-05Bibliographically approved
Andreasson, E., Mehmood, N. & Mao, T. (2014). An Experimental, Numerical and SEM Study of Fracture in a Thin Polymer Film. In: MATERIALS STRUCTURE & MICROMECHANICS OF FRACTURE VII: . Paper presented at 7th International Conference on Materials Structure and Micromechanics of Fracture, MSMF, Brno (pp. 225-+). Trans Tech Publications Inc., 592-593
Open this publication in new window or tab >>An Experimental, Numerical and SEM Study of Fracture in a Thin Polymer Film
2014 (English)In: MATERIALS STRUCTURE & MICROMECHANICS OF FRACTURE VII, Trans Tech Publications Inc., 2014, Vol. 592-593, p. 225-+-Conference paper, Published paper (Refereed)
Abstract [en]

Observations and analysis of samples from scanning electron microscopic (SEM) micrographs has been concerned in this work. The samples originate from fractured mechanical mode I tensile testing of a thin polymer film made of polypropylene used in the packaging industry. Three different shapes of the crack; elliptical, circular and flat, were used to investigate the decrease in load carrying capacity. The fracture surfaces looked similar in all studied cases. Brittle-like material fracture process was observed both by SEM micrographs and the experimental mechanical results. A finite element model was created in Abaqus as a complementary tool to increase the understanding of the mechanical behaviour of the material. The numerical material models were calibrated and the results from the simulations were comparable to the experimental results.

Place, publisher, year, edition, pages
Trans Tech Publications Inc., 2014
Series
Key Engineering Materials
Keywords
Abaqus, brittle, fracture mechanics, fracture surface, polypropylene, SEM.
National Category
Applied Mechanics
Identifiers
urn:nbn:se:bth-6548 (URN)10.4028/www.scientific.net/KEM.592-593.225 (DOI)000336694400049 ()oai:bth.se:forskinfoBD53420BE255CBCAC1257BEC0041C660 (Local ID)9783037859346 (ISBN)oai:bth.se:forskinfoBD53420BE255CBCAC1257BEC0041C660 (Archive number)oai:bth.se:forskinfoBD53420BE255CBCAC1257BEC0041C660 (OAI)
Conference
7th International Conference on Materials Structure and Micromechanics of Fracture, MSMF, Brno
Available from: 2014-11-20 Created: 2013-09-20 Last updated: 2017-06-16Bibliographically approved
Mehmood, N., Andreasson, E. & Kao-Walter, S. (2014). SEM observations of a metal foil laminated with a polymer film. In: Zhang, Z Skallerud, B Thaulow, C Ostby, E He, J (Ed.), 20TH EUROPEAN CONFERENCE ON FRACTURE: . Paper presented at 20th European Conference on Fracture (ECF), JUN 30-JUL 04, 2014, Norwegian Univ Sci Technol, Trondheim, NORWAY (pp. 1435-1440). ELSEVIER SCIENCE BV
Open this publication in new window or tab >>SEM observations of a metal foil laminated with a polymer film
2014 (English)In: 20TH EUROPEAN CONFERENCE ON FRACTURE / [ed] Zhang, Z Skallerud, B Thaulow, C Ostby, E He, J, ELSEVIER SCIENCE BV , 2014, p. 1435-1440Conference paper, Published 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.

Place, publisher, year, edition, pages
ELSEVIER SCIENCE BV, 2014
Series
Procedia Materials Science, ISSN 2211-8128 ; 3
Keywords
Adhesion, metal, micro-mechanisms, polymer, strain localization
National Category
Other Mechanical Engineering
Identifiers
urn:nbn:se:bth-14581 (URN)10.1016/j.mspro.2014.06.232 (DOI)000398274600227 ()
Conference
20th European Conference on Fracture (ECF), JUN 30-JUL 04, 2014, Norwegian Univ Sci Technol, Trondheim, NORWAY
Available from: 2017-06-19 Created: 2017-06-19 Last updated: 2017-06-19Bibliographically approved
Islam, M. S. S., Kao-Walter, S., Jian, L. & Mehmood, N. (2014). Study of Shear Property of HDPE by Experiment and Simulation. In: : . Paper presented at World Conference on Fracture and Damage Mechanics, Kottayam, India. International and Interuniversity Centre for Nanoscience and Nanotechnology (IIUCNN)
Open this publication in new window or tab >>Study of Shear Property of HDPE by Experiment and Simulation
2014 (English)Conference paper, Oral presentation only (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.

Abstract [sv]

Syftet med detta arbete är att utvärdera effekten av olika provdimension och spricka längden på de mekaniska egenskaperna hos HDPE (High Density Polyethylene) som ofta används inom förpackningsindustrin. I den experimentella delen, är två exemplar som valts. En är hund-ben formade drag exemplar för att hitta dragmaterialegenskaper. Den andra är modifierad skjuvning exemplar för att studera skador skjuvning. En motsvarande numerisk simulering görs genom att tillämpa en kommersiell Finite Element Analysis (FEA)-programmet ABAQUS. Vidare har den mikroskopiska analysen utförs för att observera frakturytan av provet efter testet med svepelektronmikroskop (SEM). En serie experiment och simulering bearbetades och resultaten visar att fraktur initiering och utbredningsbeteende i skjuvning provet är känslig för storleken på den pre-crack (hack) och skjuvtöjning vid brott.

Place, publisher, year, edition, pages
International and Interuniversity Centre for Nanoscience and Nanotechnology (IIUCNN), 2014
National Category
Applied Mechanics
Identifiers
urn:nbn:se:bth-6617 (URN)oai:bth.se:forskinfo09C1CFA65031D655C1257D580050C65F (Local ID)oai:bth.se:forskinfo09C1CFA65031D655C1257D580050C65F (Archive number)oai:bth.se:forskinfo09C1CFA65031D655C1257D580050C65F (OAI)
Conference
World Conference on Fracture and Damage Mechanics, Kottayam, India
Available from: 2014-09-22 Created: 2014-09-19 Last updated: 2017-03-17Bibliographically approved
Andreasson, E., Mehmood, N., Mao, T. & Kao-Walter, S. (2013). Experimental and Numerical fracture of cracks emanating from different types of flaws in thin polymer films. In: : . Paper presented at Svenska Mekanikdagarna 23. Lund: Lund University
Open this publication in new window or tab >>Experimental and Numerical fracture of cracks emanating from different types of flaws in thin polymer films
2013 (English)Conference paper, Oral presentation only (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.

Place, publisher, year, edition, pages
Lund: Lund University, 2013
Keywords
Abaqus, failure, brittle, numerical, SEM, void, crack growth, coalescence, FEM, ductile, loaclized
National Category
Applied Mechanics
Identifiers
urn:nbn:se:bth-6869 (URN)oai:bth.se:forskinfo2B59ED9C4D4450B7C1257BEC0045C589 (Local ID)oai:bth.se:forskinfo2B59ED9C4D4450B7C1257BEC0045C589 (Archive number)oai:bth.se:forskinfo2B59ED9C4D4450B7C1257BEC0045C589 (OAI)
Conference
Svenska Mekanikdagarna 23
Available from: 2013-09-25 Created: 2013-09-20 Last updated: 2017-03-10Bibliographically approved
Andreasson, E., Mehmood, N. & Kao-Walter, S. (2013). Trouser tear tests of two thin polymer films. In: : . Paper presented at 13th International Conference on Fracture. Beijing, China: ICF13
Open this publication in new window or tab >>Trouser tear tests of two thin polymer films
2013 (English)Conference paper, Published 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.

Place, publisher, year, edition, pages
Beijing, China: ICF13, 2013
Keywords
Anisotropic, thin polymer film, crack propagation, fracture mechanics, SEM
National Category
Applied Mechanics
Identifiers
urn:nbn:se:bth-6920 (URN)oai:bth.se:forskinfoD68C687BA4569814C1257BC100729FB8 (Local ID)oai:bth.se:forskinfoD68C687BA4569814C1257BC100729FB8 (Archive number)oai:bth.se:forskinfoD68C687BA4569814C1257BC100729FB8 (OAI)
Conference
13th International Conference on Fracture
Note

https://www.researchgate.net/publication/236953897_Trouser_tear_testing_of_thin_ polymer_films

Available from: 2013-08-29 Created: 2013-08-08 Last updated: 2016-04-18Bibliographically approved
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