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A Study of Shear Stress Intensity Factor of PP and HDPE by a Modified Experimental Method together with FEM
Blekinge Institute of Technology, Faculty of Engineering, Department of Mechanical Engineering.
Blekinge Institute of Technology, Faculty of Engineering, Department of Mechanical Engineering.
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. Vol. 7, no 11
Keyword [en]
Shear test specimen, Stress intensity factor, Finite Element simulation, Scanning electron microscopy, Screw cap opening.
National Category
Applied Mechanics
Identifiers
URN: urn:nbn:se:bth-6618Local ID: oai:bth.se:forskinfo600AEAF04A73F0F8C1257D58004FA9B4OAI: oai:DiVA.org:bth-6618DiVA: diva2:834140
Note

Open Access Journal

Available from: 2014-09-22 Created: 2014-09-19 Last updated: 2017-03-07Bibliographically approved
In thesis
1. Shear Fracture and Delamination in Packaging Materials: A study of Experimental Methods and Simulation Techniques
Open this publication in new window or tab >>Shear Fracture and Delamination in Packaging Materials: A study of Experimental Methods and Simulation Techniques
2016 (English)Licentiate 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. Package opening is becoming complicated in many cases because of cutting cost in design and production of opening techniques. Introduction of new package opening technique, material or geometry for better opening experience, forces new design measurements which require a large number of prototype developments and physical testing. In order to achieve more rapid and accurate design, Finite Element Method (FEM) Simulations are widely used in packaging industries to compliment and reduce the number of physical testing.

The goal of this work is to develop the building blocks towards complete package opening simulation. The study focuses on testing and simulation of shear fracture and shear delamination of packaging materials. A modified shear test specimen was developed and optimized by finite element simulation. Test method was validated for High-density polyethylene (HDPE) and Polypropylene (PP). The developed method has been accepted by international standards organization ASTM. Based on linear elastic fracture mechanics, a geometry correction factor of shear fracture toughness for the proposed specimen was derived. The study concluded that, for ease of opening, HDPE is a more favorable material for screw caps than PP. When performing the experiment with the shear specimen to find essential work of fracture, the ligament length should be varied between twice of the thickness and half of the width of the specimen ligament.

Multi-layered thin laminate of Low-density polyethylene (LDPE) and aluminum (Al), also known as Al/LDPE laminate, is another key object addressed in this study. Continuum and fracture testing of individual layers provided the base information and input for numerical modeling. The propagation of an interfacial pre-crack in lamination in Al-LDPE laminate was simulated using several numerical techniques available in the commercial FEM solver ABAQUS, and it was concluded that using the combination of VCCT technique to model the interfacial delamination and coupled elasto-plastic damage constitutive for Al and LDPE substrates can describe interfacial delamination and failure due to necking. It was also concluded that the delamination mode in a pre-crack tip is influenced by the ratio of fracture energy release rate of mode I and II. To address the challenge in quantifying shear energy release rate of laminate with very thin substrate, a convenient test technique is proposed. Additionally, scanning electron microscopic study provided useful information on fractured and delaminated surfaces and provided evidence that strengthened the conclusions of this work.

The proposed test methods in this work will be crucial to measure the shear mechanical properties in bulk material and thin substrates. Laminates of Al and LDPE or similar material can be studied using the developed simulation technique which can be effectively used for decision support in early package development.

Place, publisher, year, edition, pages
Karlskrona: Blekinge Tekniska Högskola, 2016. 110 p.
Series
Blekinge Institute of Technology Licentiate Dissertation Series, ISSN 1650-2140 ; 5
Keyword
Package opening, Shear test specimen, Stress intensity factor, Finite Element simulation, Scanning electron microscopy, Polymers, Interlaminar shear delamination
National Category
Mechanical Engineering
Identifiers
urn:nbn:se:bth-13340 (URN)978-91-7295-333-8 (ISBN)
Presentation
2016-12-09, J1650, Blekinge Tekniska Högskola, 37179 Karlskrona, 10:00 (English)
Opponent
Supervisors
Projects
model driven development and decision support project (MDS3)
Available from: 2016-11-09 Created: 2016-11-07 Last updated: 2017-05-02Bibliographically approved

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