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Fracture and Delamination in Packaging Materials: A Study of Experimental Methods and Simulation Techniques
Blekinge Institute of Technology, Faculty of Engineering, Department of Mechanical Engineering. Blekinge Institute of Technology. (MD3S)ORCID iD: 0000-0002-1162-7023
2019 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Packages are the means of preservation, distribution and convenience of use for food, medicine and other consumer products. The introduction of a new package-opening technique for a better opening experience requires additional prototype development and physical testing. In order for the design process to be more rapid and robust, finite element (FE) simulations are widely used in packaging industries to compliment and reduce the amount of physical testing.

The goal of this work is to develop some building blocks for complete package-opening FE-simulation. To begin with, the study focuses on mechanical testing of packaging materials’ fracture and delamination; especially shear fracture. Use of tools like digital image correlation (DIC) and scanning electron microscope (SEM) greatly aided to the strain measuring technique and observation of fractured and delaminated surfaces respectively.

A modified shear test specimen for polymer sheet testing was developed and its geometry was optimized by FE-simulation. A geometry correction factor of shear fracture toughness for the proposed specimen was derived based on linear elastic fracture mechanics (LEFM). It was found that the specimen ligament length should vary between twice the thickness and half the ligament width of the modified shear specimen to measure the essential work of fracture.

Thin-flexible laminate of low-density polyethylene (LDPE) and aluminium (Al) is another key packaging material addressed in this study. The continuum and fracture testing of individual layers provided the base information and input for FE-modelling. The FE-simulation material parameters were calibrated from the physical test response through inverse analysis. Identification process of the laminate interface fracture energy (Gc) from peel tests was studied experimentally and theoretically. A successful FE-simulation optimization framework using artificial neural network and genetic algorithm was developed for the calibration of Gc. To address the challenge in quantifying shear Gc of laminate with very thin substrates, a convenient test technique was proposed. In a separate case, the tearing response of LDPE/PET (polyethylene terephthalate) laminate was studied to examine crack propagation, crack path deviation and delamination of the laminate in mode III fracture. Several tear EWF evaluation theories were proposed along with a cyclic tear test method.

Place, publisher, year, edition, pages
Karlskrona: Blekinge Tekniska Högskola, 2019. , p. 230
Series
Blekinge Institute of Technology Doctoral Dissertation Series, ISSN 1653-2090 ; 10
Keywords [en]
packaging materials and laminates, shear test specimen, essential work of fracture, finite element simulation, optimization, tearing, peel, polymers, cohesive zone modelling
National Category
Applied Mechanics
Identifiers
URN: urn:nbn:se:bth-18048ISBN: 978-91-7295-379-6 (print)OAI: oai:DiVA.org:bth-18048DiVA, id: diva2:1325159
Public defence
2019-09-20, J1650, Valhallavägen 1, 371 41 Karlskrona, Karlskrona, 09:00 (English)
Opponent
Supervisors
Available from: 2019-06-18 Created: 2019-06-14 Last updated: 2019-09-03Bibliographically approved
List of papers
1. A Study of Shear Stress Intensity Factor of PP and HDPE by a Modified Experimental Method together with FEM
Open this publication in new window or tab >>A Study of Shear Stress Intensity Factor of PP and HDPE by a Modified Experimental Method together with FEM
2013 (English)In: International Journal of Mechanical, Aerospace, Industrial and Mechatronics Engineering, ISSN 2010-376X, Vol. 7, no 11Article in journal (Refereed) Published
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.

Abstract [sv]

Shear testning är en av de mest komplexa testområden där tillgängliga metoder och prov geometrier skiljer sig från varandra. Därför en modifierad skjuvförsök exemplar (MSTS) kombinerar det enkla enaxlade test med en zon av intresse (ZOI) testas som ger nästan ren skjuvning. I denna studie är materialparametrar av polypropen (PP) och polyeten med hög densitet (HDPE) först mätt med dragprov med en hundbensformade prov. Dessa parametrar används sedan som underlag för den finita elementanalys. För det andra är en specialdesignad exemplar (MSTS) som används för att utföra de skjuvning stresstester i en dragprovmaskin för att få resultat i form av krafter och förlängning, sprickinitiering etc. Svepelektronmikroskopi (SEM) utförs också på skjuvbrott ytan för att finna material beteende. Dessa experiment sedan simuleras genom finita elementmetoden och jämföras med de experimentella resultaten i syfte att bekräfta den simuleringsmodell. Shear spänningstillstånd inspekteras för att hitta användbarheten av de föreslagna bryt provet. Slutligen kan ett geometrikorrektionsfaktor fastställas för dessa två material i detta specifika lastning och geometri med nagg använder Linear Elastic Brottmekanik (LEFM). Av dessa resultat, stam energi av skjuvbrott och spänningsintensitetsfaktor (SIF) i skjuvning av dessa två polymerer diskuteras i särskild ansökan av skruvkork öppnandet av medicinska eller matpaket med ett temperament bevis säkerhetslösning.

Place, publisher, year, edition, pages
WASET World Academy of Science, Engineering and Technology, 2013
Keywords
Shear test specimen, Stress intensity factor, Finite Element simulation, Scanning electron microscopy, Screw cap opening.
National Category
Applied Mechanics
Identifiers
urn:nbn:se:bth-6618 (URN)oai:bth.se:forskinfo600AEAF04A73F0F8C1257D58004FA9B4 (Local ID)oai:bth.se:forskinfo600AEAF04A73F0F8C1257D58004FA9B4 (Archive number)oai:bth.se:forskinfo600AEAF04A73F0F8C1257D58004FA9B4 (OAI)
Note

Open Access Journal

Available from: 2014-09-22 Created: 2014-09-19 Last updated: 2019-06-14Bibliographically approved
2. Study of Ligament Length Effect on Mode Mix of a Modified In-Plane Shear Test Specimen
Open this publication in new window or tab >>Study of Ligament Length Effect on Mode Mix of a Modified In-Plane Shear Test Specimen
2016 (English)In: Materials Performance and Characterization, E-ISSN 2165-3992, ISSN 2165-3992, Vol. 5, no 3, p. 249-259Article in journal (Refereed) Published
Abstract [en]

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

Abstract [sv]

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

Place, publisher, year, edition, pages
California, USA: ASTM International, 2016
Keywords
shear test specimen, polymers, fracture toughness, finite element simulation
National Category
Applied Mechanics
Identifiers
urn:nbn:se:bth-12998 (URN)10.1520/MPC20150058 (DOI)000406940600001 ()
Available from: 2016-09-06 Created: 2016-09-06 Last updated: 2019-06-14Bibliographically approved
3. Study of Shear Dominant Delamination in Thin Brittle-High Ductile Interface
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

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