| 1. |
- Andreasson, Eskil, et al.
(författare)
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Advancements in package opening simulations
- 2014
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Ingår i: Procedia Materials Science. - : Elsevier. - 2211-8128. ; , s. 1441-1446
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Konferensbidrag (refereegranskat)abstract
- The fracture mechanical phenomenon occurring during the opening of a beverage package is rather complex to simulate. Reliable and calibrated numerical material models describing thin layers of packaging materials are needed. Selection of appropriate constitutive models for the continuum material models and how to address the progressive damage modeling in various loading scenarios is also of great importance. The inverse modeling technique combined with video recording of the involved deformation mechanisms is utilized for identification of the material parameters. Large deformation, anisotropic non-linear material behavior, adhesion and fracture mechanics are all identified effects that are needed to be included in the virtual opening model. The results presented in this paper shows that it is possible to select material models in conjunction with continuum material damage models, adequately predicting the mechanical behavior of failure in thin laminated packaging materials. Already available techniques and functionalities in the commercial finite element software Abaqus are used. Furthermore, accurate descriptions of the included geometrical features are important. Advancements have therefore also been made within the experimental techniques utilizing a combination of microCT-scan, SEM and photoelasticity enabling extraction of geometries and additional information from ordinary experimental tests and broken specimens. Finally, comparison of the experimental opening and the virtual opening, showed a good correlation with the developed finite element modeling technique.
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| 2. |
- Andreasson, Eskil, et al.
(författare)
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An Experimental, Numerical and SEM Study of Fracture in a Thin Polymer Film
- 2014
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Ingår i: MATERIALS STRUCTURE & MICROMECHANICS OF FRACTURE VII. - : Trans Tech Publications Inc.. - 9783037859346 ; , s. 225-+-
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Konferensbidrag (refereegranskat)abstract
- 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.
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| 3. |
- Andreasson, Eskil, et al.
(författare)
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Deformation and Damage Mechanisms in Thin Ductile Polymer Films
- 2013
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Konferensbidrag (refereegranskat)abstract
- The mechanical material behavior of highly extensible or ductile polymer films used in the packaging industry has been studied in this work. The polymer material, consisting of different variants of polyethylene grades, is used as several components in the packaging material structure at Tetra Pak®. Experimental tensile tests were used to quantify the mechanical behavior and to be able to calibrate numerical constitutive material models. The studied polymer materials were able to withstand large deformations before breaking, involving both necking in the width and thickness direction of the specimen. During deformation re-orientation of polymer chains and substantial strain-hardening were also occurring. The latter effect was accounted for in the presented material modeling approach. The numerical simulations were solved in the general finite element software Abaqus version 6.13. In this work a continuum damage modeling (CDM) approach was used. CDM which are attractive in macro scale applications, thus solving our engineering problems, was chosen in this study due to the computational efficiency. A damage model consisting of two functionalities; initiation of damage and evolution of damage was suitable for modeling the ductile fracture behavior. During the numerical analysis it has been assumed that the polymer materials are isotropic, homogenous through the thickness, independent of strain rate and independent of temperature to ease the material parameters identification.
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| 4. |
- Andreasson, Eskil, et al.
(författare)
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Experimental and Numerical fracture of cracks emanating from different types of flaws in thin polymer films
- 2013
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Konferensbidrag (refereegranskat)abstract
- 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.
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| 5. |
- Andreasson, Eskil, et al.
(författare)
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Integrating Moldflow and Abaqus in the Package Simulation Workflow
- 2013
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Konferensbidrag (refereegranskat)abstract
- Tetra Pak has used numerical simulation tools for plastic injection molding (Moldflow) and structural analysis (Abaqus/Implicit and Abaqus/Explicit) for many years. Today these two simulation tools are used independently of each other without any coupling. How these two disciplines can be combined to better predict the mechanical response of a polymer component is presented in this work. The manufacturing process, in this case injection molding, creates the mechanical properties of the produced polymer part. Process settings, material selection and molding tool geometry affect the polymer flow, material orientation and rate of crystallinity. A method to build a layered finite element model in Abaqus using results from Moldflow simulations regarding crystallinity growth and molecular orientation is proposed. Relatively simple material models were utilized and assigned for each individual material layer through the thickness in the polymer part. These constitutive models were derived phenomenologically from experimental test results and could adequately capture both the microscopic and the macroscopic behavior in a more realistic way. The numerical results showed a good agreement with the experimental results, both regarding visual appearance and force/displacement response.
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| 6. |
- Andreasson, Eskil, et al.
(författare)
-
Is it possible to open beverage packages virtually? Physical tests in combination with virtual tests in Abaqus.
- 2012
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Konferensbidrag (refereegranskat)abstract
- The opening mechanism in a beverage package, where a mixed mode failure occurs, is a rather complex phenomenon. A better knowledge in respect of fracture mechanics is needed for the proactive prediction of the overall opening performance. Reliable material data used for virtual simulation of the opening mechanism is extracted by characterization and calibration of the packaging materials. Knowledge of how to choose appropriate constitutive models for the continuum material and how the damage initiates and propagates to various loading conditions is of great interest. The virtual tests, replicating the physical tests, are performed with the aid of the finite element method. Non-linear material response, anisotropic material behaviour, large deformation and fracture mechanics are identified effects that are all included in the virtual model. The results presented in this paper show possible selections of material models in conjunction with material damage models, adequately describing thin polymer films behaviour. Comparison between the physical test and the virtual test, exerted to fracture Mode I – Centre Cracked Tension, showed a good correlation for the chosen modeling technique.
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| 7. |
- Andreasson, Eskil, 1976-
(författare)
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Mechanics and Failure in Thin Material Layers : Towards Realistic Package Opening Simulations
- 2019
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The final goal of this PhD-work is an efficient and user-friendly finite element modelling strategy targeting an industrial available package opening application. In order to reach this goal, different experimental mechanical and fracture mechanical tests were continuously refined to characterize the studied materials. Furthermore, the governing deformation mechanisms and mechanical properties involved in the opening sequence were quantified with full field experimental techniques to extract the intrinsic material response. An identification process to calibrate the material model parameters with inverse modelling analysis is proposed. Constitutive models, based on the experimental results for the two continuum materials, aluminium and polymer materials, and how to address the progressive damage modelling have been concerned in this work. The results and methods considered are general and can be applied in other industries where polymer and metal material are present. This work has shown that it is possible to select constitutive material models in conjunction with continuum material damage models, adequately predicting the mechanical behaviour in thin laminated packaging materials. Finally, with a slight modification of already available techniques and functionalities in a commercial general-purpose finite element software, it was possible to build a simulation model replicating the physical behaviour of an opening device. A comparison of the results between the experimental opening and the virtual opening model showed a good correlation.The advantage with the developed modelling approach is that it is possible to modify the material composition of the laminate. Individual material layers can be altered, and the mechanical properties, thickness or geometrical shape can be changed. Furthermore, the model is flexible and a new opening design with a different geometry and load case can easily be implemented and changed in the simulation model. Therefore, this type of simulation model is prepared to simulate sustainable materials in packages and will be a useful tool for decision support early in the concept selection in technology and development projects.
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| 8. |
- Andreasson, Eskil, et al.
(författare)
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Micro-mechanisms of a laminated packaging material during fracture
- 2014
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Ingår i: Engineering Fracture Mechanics. - : Elsevier BV. - 1873-7315 .- 0013-7944. ; 127, s. 313-326
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Tidskriftsartikel (refereegranskat)abstract
- 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. (C) 2014 Elsevier Ltd. All rights reserved.
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| 9. |
- Andreasson, Eskil
(författare)
-
Realistic Package Opening Simulations : An Experimental Mechanics and Physics Based Approach
- 2015
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- A finite element modeling strategy targeting package opening simulations is the final goal with this work. The developed simulation model will be used to proactively predict the opening compatibility early in the development process of a new opening device and/or a new packaging material. To be able to create such a model, the focus is to develop a combined and integrated physical/virtual test procedure for mechanical characterization and calibration of thin packaging materials. Furthermore, the governing mechanical properties of the materials involved in the opening performance needs to be identified and quantified with experiments. Different experimental techniques complemented with video recording equipment were refined and utilized during the course of work. An automatic or semi-automatic material model parameter identification process involving video capturing of the deformation process and inverse modeling is proposed for the different packaging material layers. Both an accurate continuum model and a damage material model, used in the simulation model, were translated and extracted from the experimental test results. The results presented show that it is possible to select constitutive material models in conjunction with continuum material damage models, adequately predicting the mechanical behavior of intended failure in thin laminated packaging materials. A thorough material mechanics understanding of individual material layers evolution of microstructure and the micro mechanisms involved in the deformation process is essential for appropriate selection of numerical material models. Finally, with a slight modification of already available techniques and functionalities in the commercial finite element software AbaqusTM it was possible to build the suitable simulation model. To build a realistic simulation model an accurate description of the geometrical features is important. Therefore, advancements within the experimental visualization techniques utilizing a combination of video recording, photoelasticity and Scanning Electron Microscopy (SEM) of the micro structure have enabled extraction of geometries and additional information from ordinary standard experimental tests. Finally, a comparison of the experimental opening and the virtual opening, showed a good correlation with the developed finite element modeling technique. The advantage with the developed modeling approach is that it is possible to modify the material composition of the laminate. Individual material layers can be altered and the mechanical properties, thickness or geometrical shape can be changed. Furthermore, the model is flexible and a new opening device i.e. geometry and load case can easily be adopted in the simulation model. Therefore, this type of simulation model is a useful tool and can be used for decision support early in the concept selection of development projects.
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| 10. |
- Andreasson, Eskil, et al.
(författare)
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Simulation of thin aluminium-foil in the packaging industry
- 2017
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Ingår i: AIP Conference Proceedings. - : American Institute of Physics Inc.. - 0094-243X. - 9780735415805
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Konferensbidrag (refereegranskat)abstract
- This work present an approach of how to account for the anisotropic mechanical material behaviour in the simulation models of the thin aluminium foil layer (≈10 μm) used in the Packaging Industry. Furthermore, the experimental results from uniaxial tensile tests are parameterised into an analytical expression and the slope of the hardening subsequently extended way beyond the experimental data points. This in order to accommodate the locally high stresses present in the experiments at the neck formation. An analytical expression, denominated Ramberg-Osgood, is used to describe the non-linear mechanical behaviour. Moreover it is possible with a direct method to translate the experimental uniaxial tensile test results into useful numerical material model parameters in Abaqus™. In addition to this the extended material behaviour including the plastic flow i.e. hardening, valid after onset of localisation, the described procedure can also capture the microscopic events, i.e. geometrical thinning, ongoing in the deformation of the aluminium foil. This method has earlier successfully been applied by Petri Mäkelä for paperboard material [1]. The engineering sound and parameterised description of the mechanical material behaviour facilitates an efficient categorisation of different aluminium foil alloys and aid the identification of the correct anisotropic (RD/TD/45°) mechanical material behaviour derived from the physical testing. © 2017 Author(s).
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| 11. |
- Andreasson, Eskil, et al.
(författare)
-
Trouser tear tests of two thin polymer films
- 2013
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Konferensbidrag (refereegranskat)abstract
- 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.
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| 12. |
- Björn, Linnea, 1994, et al.
(författare)
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Scanning Small-Angle X-ray Scattering of Injection-Molded Polymers: Anisotropic Structure and Mechanical Properties of Low-Density Polyethylene
- 2023
-
Ingår i: ACS Applied Polymer Materials. - 2637-6105. ; 5:8, s. 6429-6440
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Tidskriftsartikel (refereegranskat)abstract
- Injection molding is known to create a layered anisotropicmorphologyacross the sample thickness due to varying shear and cooling ratesduring the manufacturing process. In this study, scanning small-angleX-ray scattering was used to visualize and quantify the distributionof hierarchical structures present in injection-molded parts of low-densitypolyethylene (LDPE) with varying viscosities. By combining scatteringdata with results from injection molding simulations and tensile testing,we find that oriented shish-kebab structures, as well as elongatedspherulite structures consisting of semicrystalline ellipsoids, contributeto high ultimate tensile strength along the flow direction. Furthermore,we show that a higher degree of orientation is found close to theinjection gate and in LDPE with higher viscosity, consequently fromelevated shear and cooling rates present during the injection moldingprocess.
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| 13. |
- Islam, Md. Shafiqul, 1984-, et al.
(författare)
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The Effects of Stress Triaxiality on the Neck Initiation and Fracture of High-density Polyethylene (HDPE)
- 2022
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Ingår i: Procedia Structural Integrity. - : Elsevier. - 9781713870302 ; , s. 745-754
-
Konferensbidrag (refereegranskat)abstract
- This study analyses the tensile mechanical behaviour and deformation of neck i.e localization initiation, propagation and fracture of injection-moulded polymer composed of high-density polyethylene (HDPE) as a function of initial stress triaxiality. Three different specimen geometries namely i) Simple tension, ii) Plane strain and iii) Shear specimens were punched from injection-moulded HDPE plates and tested experimentally in uniaxial tension to introduce different stress triaxialities. These specimen geometries used are standard for the material characterization of sheet metals. However, for plate polymer materials such specimen geometries have not comprehensively been studied earlier. Standard shear specimen geometry has been further optimized in this work using finite element models to restrict unwanted out-of-plane deformations arising at large deformation. The digital image correlation (DIC) technique is used to acquire the full field deformation and in particular the localized strains in the neck region of the specimens. Based on the major-minor strain paths from DIC-measurements stress triaxiality has been calculated. It is challenging to follow the stochastic pattern at larger local strain in DIC and hence the strain at failure has been measured using orthogonal grid lines on the specimen surface. Finally, strains at neck-initiation and failure at three different stress triaxialities are reported for injection-moulded HDPE in two material orientations. It is observed that within the elastic limit the stress triaxialities obtained from the experimental tests were close to the ideal values found in the literature and neck-initiation strain is strongly dependent on the stress triaxiality. However, as neck initiates and propagates, the triaxialities for all geometries shift closer to the measured value in a simple tension specimen i.e. 0.33 limiting the effect of the initial triaxiality on failure strain.
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| 14. |
- Islam, Md Shafiqul, 1984-, et al.
(författare)
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Trouser tear testing of thin anisotropic polymer films and laminates
- 2019
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Ingår i: International Journal of Fracture. - : Springer Netherlands. - 0376-9429 .- 1573-2673. ; 219:2, s. 187-201
-
Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 15. |
- Kao-Walter, Sharon, et al.
(författare)
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Micro-mechanism of Thin and Laminated Packaging Material during Fracture
- 2012
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Konferensbidrag (refereegranskat)abstract
- 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.
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| 16. |
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| 17. |
- Kroon, Martin, et al.
(författare)
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Anisotropic Elastic-Viscoplastic Properties at Finite Strains of Injection-Moulded Low-Density Polyethylene
- 2018
-
Ingår i: Experimental mechanics. - : Springer New York LLC. - 0014-4851 .- 1741-2765. ; 58:1, s. 75-86
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Tidskriftsartikel (refereegranskat)abstract
- Injection-moulding is one of the most common manufacturing processes used for polymers. In many applications, the mechanical properties of the product is of great importance. Injection-moulding of thin-walled polymer products tends to leave the polymer structure in a state where the mechanical properties are anisotropic, due to alignment of polymer chains along the melt flow direction. The anisotropic elastic-viscoplastic properties of low-density polyethylene, that has undergone an injection-moulding process, are therefore examined in the present work. Test specimens were punched out from injection-moulded plates and tested in uniaxial tension. Three in-plane material directions were investigated. Because of the small thickness of the plates, only the in-plane properties could be determined. Tensile tests with both monotonic and cyclic loading were performed, and the local strains on the surface of the test specimens were measured using image analysis. True stress vs. true strain diagrams were constructed, and the material response was evaluated using an elastic-viscoplasticity law. The components of the anisotropic compliance matrix were determined together with the direction-specific plastic hardening parameters. © 2017 The Author(s)
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| 18. |
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| 19. |
- Kroon, Martin, et al.
(författare)
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Assessment of fracture energy of polyethylene
- 2017
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Konferensbidrag (refereegranskat)abstract
- Semi-crystalline polymers, such as polyethylene, nylon, and PET, are widely used in engineering applications, and the fracture mechanics properties of these materials are therefore of great interest. One big challenge of these materials is that they are strongly rate-dependent, which makes it difficult to identify a rate-independent surface energy which can be considered as a material property. Instead dissipation processes at the advancing crack tip have to be lumped into an effective (and rate-dependent) work of fracture. In the present paper we assess a possible experimental strategy for determining the effective work of fracture for soft polymers.
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| 20. |
- Kroon, Martin, et al.
(författare)
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Experimental and numerical assessment of the work of fracture in injection-moulded low-density polyethylene
- 2018
-
Ingår i: Engineering Fracture Mechanics. - : Elsevier BV. - 1873-7315 .- 0013-7944. ; 192, s. 1-11
-
Tidskriftsartikel (refereegranskat)abstract
- The fracture mechanics properties of injection-moulded low-density polyethylene (LDPE) sheets were investigated both experimentally and numerically. The total work of fracture was determined experimentally, by means of fracture mechanics testing of sheets of injection-moulded LDPE with side cracks of different lengths. A multi-specimen method, proposed by Kim and Joe (1987), was employed. The total work of fracture was estimated to 13 kJ/m2. The experiments were simulated numerically using the finite element method. Crack growth was enabled by inclusion of a cohesive zone, and the constitutive response of this zone was governed by a traction-separation law. The local (or essential) work of fracture was estimated through numerical analyses, where the initiation of crack growth was simulated and the outcome was compared to the experimental results. The local (i.e. essential) work of fracture was estimated to 1.7 kJ/m2, which is consistent with previous experimental measurements for the material in question. The total work of fracture, retrieved from the present experiments, agreed well with the far field values of the J-integral in the numerical analyses.
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| 21. |
- Kroon, Martin, Professor, 1974-, et al.
(författare)
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Experimental and theoretical study of stress relaxation in high-density polyethylene
- 2024
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Ingår i: Acta Mechanica. - : Springer. - 0001-5970 .- 1619-6937. ; 235:4, s. 2455-2477
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Tidskriftsartikel (refereegranskat)abstract
- Stress relaxation of high-density polyethylene is addressed both experimentally and theoretically. Two types of stress relaxation testing are carried out: uniaxial tensile testing at constant test specimen length and compression testing of a 3D structure producing inhomogeneous deformation fields and relaxation. A constitutive model for isotropic, semi-crystalline polymers is also proposed. The model has the ability to model stress relaxation at different time scales. The developed model was implemented as a user subroutine in Abaqus (UMAT). The implicit integration scheme including an algorithmic tangent modulus is described in detail. The material model is calibrated by use of the uniaxial tensile tests, and the model is then validated by simulating the compression tests of the 3D structure. The model is able to describe the uniaxial tension tests well, and the comparison between the simulations and experimental testing of the 3D structure shows very good agreement. © 2024, The Author(s).
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| 22. |
- Kroon, Martin, 1974-, et al.
(författare)
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Modeling of damage and crack growth in semi-crystalline polymers
- 2017
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Ingår i: Proceedings of NSCM 30: The 30th Nordic Seminar on Computational Mechanics, 25-27 October, 2017. - : DTU Mechanical Engineering. ; , s. 108-108
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Konferensbidrag (refereegranskat)abstract
- t. Crack growth in semi-crystalline polymers, represented by polyethylene, is considered. The material considered comes in plates that had been created through an injection-molding process. Hence, the material was taken to be orthotropic. Material directions were identified as MD: molding direction, CD: transverse direction, TD: thickness direction. Uniaxial tensile testing was performed in order to establish the direction-specific elastic-plastic behaviour of the polymer. In addition, the fracture mechanics properties of the material was determined by performing fracture mechanics testing on plates with side cracks of different lengths. The fracture mechanics tests were filmed using a video camera. Based on this information, the force vs. load-line displacement could be established for the fracture mechanics tests, in which also the current length of the crack was indicated, since crack growth took place. In parallel to the experimental testing, an anisotropic plasticity model for finite strains was developed, which accounts for orthotropic elasticity and orthotropic plastic yielding and hardening. That plasticity model was implemented as a user subroutine in Abaqus. The crack growth experiments were then simulated using Abaqus, using the implemented plasticity model in combination with a damage model. Different types of crack initiation and growth criteria were explored, and the force-displacement-crack length data from the experiments could be well reproduced. Furthermore, the direction-specific work of fracture had been established from the experiments and these energies could be compared to the values of the J-integral from the simulations for the different crack lengths.
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| 23. |
- Kroon, Martin, 1974-, et al.
(författare)
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Modelling of Damage and Crack Growth in Semi-crystalline Polymers
- 2018
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Ingår i: Presented at International Conference on Plasticity, Damage and Fracture 2018, Puerto Rico. - : Neat press. - 9780991165452
-
Konferensbidrag (refereegranskat)abstract
- Crack growth in semi-crystalline polymers, represented by polyethylene, is considered. The material considered comes in plates that had been created through an injection-molding process. Hence, the material was taken to be orthotropic. Material direction were identified as MD: molding direction, CD: transverse direction, TD: thickness direction. Uniaxial tensile testing was performed in order to establish the direction-specific elastic-plastic behaviour of the polymer. In addition, the fracture mechanics properties of the material was determined by performing fracture mechanics testing on plates with side cracks of different lengths. The fracture mechanics tests were filmed using a video camera. Based on this information, the force vs. load-line displacement could be established for the fracture mechanics tests, in which also the current length of the crack was indicated, since crack growth took place. In parallel to the experimental testing, an anisotropic plasticity model for finite strains was developed, which accounts for orthotropic elasticity and orthotropic plastic yielding and hardening. That plasticity model was implemented as a user subrouting in Abaqus. The crack growth experiments were then simulated using Abaqus, using the implemented plasticity model in combination with a damage model. Different types of crack initiation and growth criteria were explored, and the force-displacement-crack length data from the experiments could be well reproduced. Furthermore, the direction-specific work of fracture had been established from the experiments and these energies could be compared to the values of the J-integral from the simulations for the different crack lengths.
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| 24. |
- Kroon, Martin, Professor, 1974-, et al.
(författare)
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Numerical and experimental analysis of inelastic and rate-dependent buckling of thin injection-moulded high-density polyethylene structure
- 2024
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Ingår i: International Journal of Solids and Structures. - : Elsevier. - 0020-7683 .- 1879-2146. ; 290
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Tidskriftsartikel (refereegranskat)abstract
- Semi-crystalline polymers is an important group of materials that is used in a vast array of products. In this study, the rate-dependent properties of high-density polyethylene (HDPE) are investigated, both experimentally and theoretically. Experimental compression testing of a three-dimensional HDPE structure is performed and analysed numerically by use of the finite element method. In addition, an Eulerian constitutive material model for isotropic, semi-crystalline polymers is proposed. The model is able to account for such essential phenomena as strain-rate dependence, work hardening, pressure-dependence of inelastic deformations, and damage. The proposed material model was implemented in Abaqus as a VUMAT, which is an explicit implementation. The material model was calibrated by use of uniaxial tensile tests performed on HDPE dog-bone shaped samples, and the model was further explored by applying the VUMAT implementation to the compression tests of the HDPE structure. The simulation model was able to reproduce the experimental results well, both the uniaxial tests and the compression tests. In particular, the friction present in the compression tests seems to play an important role in determining the buckling mode of the structure.
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| 25. |
- Mehmood, Nasir, et al.
(författare)
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SEM observations of a metal foil laminated with a polymer film
- 2014
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Ingår i: 20TH EUROPEAN CONFERENCE ON FRACTURE. - : ELSEVIER SCIENCE BV. ; , s. 1435-1440
-
Konferensbidrag (refereegranskat)abstract
- 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.
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| 26. |
- Moberg, Christina, et al.
(författare)
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De unga gör helt rätt när de stämmer staten
- 2022
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Ingår i: Aftonbladet. - 1103-9000.
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Tidskriftsartikel (populärvet., debatt m.m.)abstract
- 1 620 forskare och lärare i forskarvärlden: Vi ställer oss bakom Auroras klimatkrav
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| 27. |
- Olsson, Pär A T, 1981-, et al.
(författare)
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Ab initio investigation of monoclinic phase stability and martensitic transformation in crystalline polyethylene
- 2018
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Ingår i: Physical Review Materials. - : American Physical Society. - 2475-9953. ; 2:7, s. 7-13
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Tidskriftsartikel (refereegranskat)abstract
- We study the phase stability and martensitic transformation of orthorhombic and monoclimic polyethylene by means of density functional theory using the nonempirical consistent-exchange vdW-DF-cx functional [Phys. Rev. B 89, 035412 (2014)]. The results show that the orthorhombic phase is the most stable of the two. Owing to the occurrence of soft librational phonon modes, the monoclimic phase is predicted not to be stable at zero pressure and temperature, but becomes stable when subjected to compressive transverse deformations that pin the chains and prevent them from wiggling freely. This theoretical characterization, or prediction, is consistent with the fact that the monoclimic phase is only observed experimentally when the material is subjected to mechanical loading. Also, the estimated threshold energy for the combination of lattice deformation associated with the T1 and T2 transformation paths (between the orthorhombic and monoclimic phases) and chain shuffling is found to be sufficiently low for thermally activated back transformations to occur. Thus, our prediction is that the crystalline part can transform back from the monoclimc to the orthorhombic phase upon unloading and/or annealing, which is consistent with experimental observations. Finally, we observe how a combination of such phase transformations can lead to a fold-plane reorientation from {110} to {100} type in a single orthorhombic crystal.
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| 28. |
- Olsson, Pär A T, 1981-, et al.
(författare)
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All-atomic and coarse-grained molecular dynamics investigation of deformation in semi-crystalline lamellar polyethylene
- 2018
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Ingår i: Polymer. - : Elsevier Ltd. - 0032-3861 .- 1873-2291. ; 153, s. 305-316
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Tidskriftsartikel (refereegranskat)abstract
- In the present work we have performed classical molecular dynamics modelling to investigate the effects of different types of force-fields on the stress-strain and yielding behaviours in semi-crystalline lamellar stacked linear polyethylene. To this end, specifically the all-atomic optimized potential for liquid simulations (OPLS-AA) and the coarse-grained united-atom (UA) force-fields are used to simulate the yielding and tensile behaviour for the lamellar separation mode. Despite that the considered samples and their topologies are identical for both approaches, the results show that they predict widely different stress-strain and yielding behaviours. For all UA simulations we obtain oscillating stress-strain curves accompanied by repetitive chain transport to the amorphous region, along with substantial chain slip and crystal reorientation. For the OPLS-AA modelling primarily cavitation formation is observed, with small amounts of chain slip to reorient the crystal such that the chains align in the tensile direction. This force-field dependence is rooted in the lack of explicit H-H and C-H repulsion in the UA approach, which gives rise to underestimated ideal critical resolved shear stress. The computed critical resolved shear stress for the OPLS-AA approach is in good agreement with density functional theory calculations and the yielding mechanisms resemble those of the lamellar separation mode. The disparate energy and shear stress barriers for chain slip of the different models can be interpreted as differently predicted intrinsic activation rates for the mechanism, which ultimately are responsible for the observed diverse responses of the two modelling approaches. © 2018 Elsevier Ltd
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| 29. |
- Olsson, Pär, et al.
(författare)
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Ab initio and classical atomistic modelling of structure and defects in crystalline orthorhombic polyethylene : Twin boundaries, slip interfaces, and nature of barriers
- 2017
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Ingår i: Polymer. - : Elsevier Ltd. - 0032-3861 .- 1873-2291. ; 121, s. 234-246
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Tidskriftsartikel (refereegranskat)abstract
- We study the stability of twin boundaries and slip in crystalline orthorhombic polyethylene by means of density functional theory (DFT), using a nonempirical, truly nonlocal density function, and by means of classical molecular dynamics (MD). The results show that, in accordance with experimental observations, there is a clear preference to chain slip over transverse slip for all considered slip planes. The activation energy for pure chain slip lies in the range 10–20 mJ/m2 while that for transverse slip corresponds to 40–280 mJ/m2. For the (11¯0)-slip plane the energy landscape is non-convex with multiple potential energy minima, indicating the presence of stable stacking faults. This suggests that dissociation of perfect dislocations into partials may occur. For the two low-energy twin boundaries considered in this work, {110} and {310}, we find that the former is more stable than the latter, with ground state energies corresponding to 8.9 and 28 mJ/m2, respectively. We have also evaluated how well the empirical MD simulations with the all-atom optimized potential for liquid MD simulations (OPLS-AA) and the coarse-grained united atom (UA) potential concur with the DFT results. It is found that an all-atom potential is necessary to partially capture the γ-surface energy landscapes obtained from the DFT calculations. The OPLS-AA predicts chain slip activation energies comparable with DFT data, while the transverse slip energy thresholds are low in comparison, which is attributed to weak close ranged monomer repulsion. Finally, we find that the H-H interaction dominates the slip activation. While not explicitly represented in the UA potential, its key role is revealed by correlating the DFT energy landscape with changes in the electron distributions and by MD simulations in which components of the OPLS-AA intermolecular potential are selectively silenced. © 2017 Elsevier Ltd
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| 30. |
- Pilthammar, Johan, et al.
(författare)
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Surpassing Threshold Concepts within Engineering Mechanics Interactive Computer Aided Learning (CAL) to support the learning process
- 2022
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Ingår i: Högskolepedagogisk debatt. - : Högskolan i Kristianstad. - 2000-9216. ; :2, s. 77-98
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- This paper is based on a scientific literature review and interviews with teachers and researchers active in the area of Engineering Mechanics in Swedish higher education. The paper aims to identify and highlight troublesome knowledge and threshold concepts within the field of Engineering Mechanics. Moreover, the ambition is to present ideas of how to overcome these identified threshold concepts. Recent scientific research acknowledges many benefits of introducingdigital and interactive tools, denominated Computer Aided Learning (CAL), at an early stage. Digital and interactive tools can help engineering students overcome threshold concepts. A selection of these digital tools is discussed in this paper. The study concludes that elearning is an efficient way to enhance and complement the learning process. It also makes teaching material available from anywhere, at any time. Hence, students can individually adjust their learning pace. The interviews with teachers contributed to a clearer view of how dig-ital tools can be utilized and transform learning in mechanical engineering.Master students in mechanical engineering are expected to create, operate, and understand advanced digital tools. However, on the B.Sc. level, the implementation of digital tools seems to be scarce. Instead, textbooks, exercises with pen and paper, and traditional teaching are the preferred tools for learning. Implementing digital and interactive computer tools already on a basic teaching level (B.Sc.) can assist students to understand complex theories and overcome threshold concepts.
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| 31. |
- Poddar, Satyasarathi, et al.
(författare)
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Rate-dependent tensile properties of paperboard and its plies
- 2024
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Ingår i: Nordic Pulp & Paper Research Journal. - : Walter de Gruyter GmbH. - 0283-2631 .- 2000-0669.
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Tidskriftsartikel (refereegranskat)abstract
- Tensile properties of paperboard have been characterized, and it has been shown that paper tensile properties are dependent on the strain rate. Tensile testing was done using strain rates in the range 10(-4)-3 s(-1), which corresponds to crosshead movements ranging from 1 up to 24,000 mm/min, using an electro-mechanical testing machine. Two paperboards, and its free-laid top, middle and bottom plies were characterized in MD and CD. The testing was limited by the maximum crosshead speed of the testing machine. Initially 50 mm (grip to grip) long samples were tested, but to test even higher strain rates also short samples with length of 5 mm were tested. The results showed that ultimate strength increased by 9 % per decade increasing of testing rate, and Young's modulus increased by 7 %. This shows that the previously reported rule of thumb of 10 % increase of in-plane strength per decade increase of strain rate holds. The testing here shows that this is valid also at strain rates as high as 3 s(-1). Moreover, the strain at break in CD for long tensile specimens was observed to decrease when the strain rate exceeded 0.1 s(-1), which resulted in straighter crack paths.
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| 32. |
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| 33. |
- Reheman, Wureguli, et al.
(författare)
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Numerical Analysis of the Anisotropic Stiffness of a Thin Aluminium Foil in Multiple Material directions Based on Experiments
- 2017
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Ingår i: Proceedings of NSCM 30 : The 30th Nordic Seminar on Computational Mechanics 25-27 October 2017 - The 30th Nordic Seminar on Computational Mechanics 25-27 October 2017. ; , s. 175-179
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Konferensbidrag (refereegranskat)abstract
- Numerical analysis have been performed on tensile test experiment data toevaluated the performances of a 9 microns thick aluminium foil. The identification of theanisotropic material properties is based on tensile tests performed in 11 different anglesfrom 0◦to 90◦from the rolling direction. By least square fitting and extrapolation tozero load the elastic modulus is, as opposed to the general belief, proven to be very closeto the expected bulk values for this specific material. The elastic modulus is shown tobe anisotropic with a stiffness variation of aound 15%. Minimum stiffness is obtained inaround 45◦from the rolling direction
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| 34. |
- Shahid, Sharlin, 1992-, et al.
(författare)
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Simplified Characterization of Anisotropic Yield Criteria for an Injection-Molded Polymer Material
- 2023
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Ingår i: Polymers. - : MDPI. - 2073-4360. ; 15:23
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Tidskriftsartikel (refereegranskat)abstract
- Injection-molded polyethylene plates exhibit highly anisotropic mechanical behavior due to, e.g., the uneven orientation of the polymer chains during the molding process and the differential cooling, especially in the thickness direction. Elastoplastic finite element modeling of these plates in particular is used with isotropic yield criteria like von Mises, trading off accuracy in favor of simpler constitutive characterization and faster solution. This article studies three different anisotropic yield criteria, namely, Hill 1948, Barlat Yld91, and Barlat Yld2004-18P, for the finite element modeling of low-density polyethylene (LDPE) at large uniaxial tensile deformation and compares the accuracy and computation time with von Mises. A simplified calibration technique is investigated to identify the constitutive parameters of the studied Barlat group yield criteria. The calibration process is simplified in the sense that only uniaxial tensile tests with digital image correlation measurements are used for the calibration of all the yield criteria studied in this article, although a standard calibration procedure for the Barlat group yield criteria requires additional material testing using more demanding test setups. It is concluded that both Barlat Yld91 and Barlat Yld2004-18P yield criteria can be calibrated with only a few tensile tests and still capture anisotropy in deformation–stress–strain at different levels of accuracy. © 2023 by the authors.
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| 35. |
- Sigvant, Mats, et al.
(författare)
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SMART STAMPING : IMPROVED QUALITY IN STAMPING BY MODEL DRIVEN CONTROL
- 2018
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Konferensbidrag (refereegranskat)abstract
- Sheet Metal Forming is a very complex manufacturing process with a number of non-linearities, e.g. large deformations, localisation, elastic-plastic materials, pressure and velocity dependant friction conditions and structural deficiencies in the die and press, present and interacting simultaneously. This leads to disturbances in running production that results in production waste, e.g. down time for the press line and cost for rework and scrapping of parts. These production problems are also hard to understandand solve based on experience and analytical models due to the presence of several non-linearities. An alternative is to try to solve these problems proactively before they occur. This could be done with model based control by creating a digital twin of the die-set and the press line. Therefore, a virtual production process is developed to be able to use as knowledge building and as engineering tool during development, manufacturing, issue resolution and optimization. In this paper presents the authors ideas and plans for research and other activities within the area of model based control of sheet metal forming.
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| 36. |
- Tabourot, Laurent, et al.
(författare)
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Experimental characterization and microstructure linked modeling of mechanical behavior of ultra-thin aluminum foils used in packaging
- 2018
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Ingår i: PROCEEDINGS OF 21ST INTERNATIONAL ESAFORM CONFERENCE ON MATERIAL FORMING (ESAFORM 2018). - : American Institute of Physics Inc.. - 9780735416635
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Konferensbidrag (refereegranskat)abstract
- This paper is based on the hypothesis that introducing distribution of mechanical properties is beneficial for modeling all kinds of mechanical behavior, even of ordinary metallic materials. To bring proof of its admissibility, it has to be first shown that modeling based on this assertion is able to efficiently describe standard mechanical behavior of materials. Searching for typical study case, it has been assessed that at a low scale, yield stresses could be strongly distributed in ultrathin aluminum foils used in packaging industry, offering opportunities to identifying their distribution and showing its role on the mechanical properties. Considering initially reduced modeling allow to establish a valuable connection between the hardening curve and the distribution of local yield stresses. This serves for finding initial value of distribution parameters in a more sophisticated identification procedure. With finally limited number of representative classes of local yield stresses, concretely 3 is enough, it is shown that a 3D finite element simulation involving limited numbers of elements returns realistic behavior of an ultrathin aluminum foil exerted to tensile test, in reference to experimental results. This gives way to large possibilities in modeling in order to give back complex experimental evidence. © 2018 Author(s).
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| 37. |
- Zhang, De-Feng, et al.
(författare)
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Modeling and Study of Fracture and Delamination in a Packaging Laminate
- 2016
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Ingår i: PROCEEDINGS OF THE 3RD INTERNATIONAL CONFERENCE ON MATERIAL ENGINEERING AND APPLICATION (ICMEA 2016). - : ATLANTIS PRESS. - 9789462522725 ; , s. 408-414
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Konferensbidrag (refereegranskat)abstract
- In this work, a packaging laminate consisting of LDPE (Low Density Polyethylene), Alfoil (Aluminum foil) is focused, and failure due to necking in substrates and interfacial delamination under loading are considered. A coupled elasto-plasticity damage and fracture constitutive model is combined. The proposed constitutive model is incorporated into the FEM code ABAQUS and utilized to simulate a uniaxial tension in the laminate with an interfacial pre-crack. The simulation results show deformation of the laminate agrees well with theoretical results. The new combined constitutive model is proper to study the failure due to necking and interfacial delamination in the laminate. And the interfacial delamination mode in pre-crack tip could be influenced by fracture toughness ratio of mode I, II.
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| 38. |
- Zhang, Defeng, et al.
(författare)
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Powerful Modelling Techniques in ABAQUS to Simulate Failure of Laminated composites
- 2016
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Rapport (refereegranskat)abstract
- In this study, laminated composites consisting of LDPE (Low Density Polyethylene), Al-foil (Aluminum foil)and an adhesive interface layer is focused. The defects like necking in LDPE, Al-foil layer and interfacial delaminationcan significantly impact the loading capacity of the laminated material. However, the influence mechanisms of thedefects are still unclear, and no appropriate research tool is available. Therefore, the FEM model based on alreadyavailable techniques in ABAQUS is developed in this work. The aim with the model is to create a robust numericalanalysis tool for further research work.In the modelling process, possibility of necking in substrates and interfacial delamination between material layers isconsidered. A coupled elasto-plasticity damage constitutive model, based on Hooke’s Law, the J2 yield criterion,isotropic hardening, associated flow-rule and ductile damage model, is formulated to demonstrate necking behaviorof substrates. In ABAQUS, three modelling techniques, namely VCCT, Cohesive Element, and XFEM, have been usedto simulate interfacial delamination. The simulation results are compared with the theoretical results.A uniaxial tension test consisting of a two material laminate is simulated by using these three modelling techniques.The special modelling skills for respective modelling techniques, element type, meshing technique of each model, arealso introduced. The comparison with the theoretical results shows necking in substrates and interfacial delaminationare also achieved in all three models as expected. Deformation results of the simulation are very close to that of thetheoretical analysis. Technique features of VCCT, Cohesive Element and XFEM in modelling of interfacialdelamination are analyzed and concluded. These three FEM models can all be utilized according to the requirementsof subsequent research.
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| 39. |
- Zhang, Defeng, et al.
(författare)
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Powerful Modelling Techniques in Abaqus to Simulate Necking and Delamination of Laminated Composites
- 2015
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- 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.
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