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van Dijk, Nico P.
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Publications (10 of 21) Show all publications
van Dijk, N. P., Wu, D., Persson, C. & Isaksson, P. (2019). A global digital volume correlation algorithm based on higher-order finite elements: Implementation and evaluation. International Journal of Solids and Structures, 168, 211-227
Open this publication in new window or tab >>A global digital volume correlation algorithm based on higher-order finite elements: Implementation and evaluation
2019 (English)In: International Journal of Solids and Structures, ISSN 0020-7683, E-ISSN 1879-2146, Vol. 168, p. 211-227Article in journal (Refereed) Published
Abstract [en]

We propose a DVC technique that is based on higher-order finite-element discretization of the displacement field and a global optimization procedure. We use curvature penalization to suppress non-physical fluctuations of the displacement field and resulting erroneous strain concentrations. The performance of the proposed method is compared to the commercial code Avizo using trabecular bone images and found to perform slightly better in most cases. In addition, we stress that the performance of a DVC method needs to be evaluated using double scans (zero strain), virtual deformation (imposed deformation) and real deformation. Double scans give insight into the presence of noise and artifacts whereas virtual deformation benchmarks allows evaluation of the performance without noise and artifacts. Investigation of the performance for actual deformed heterogeneous materials is needed for evaluation with noise, artifacts and non-zero strains. We show that both decreasing the resolution of the displacement field (increasing subvolume size) as well as (increasing) curvature penalization (regularization) have a similar effect on the performance of evaluated DVC methods: Decreasing the detrimental effect of noise, artifacts and interpolation errors, but also decreasing the sensitivity of a DVC method to displacement peaks, discontinuities and strain concentrations. The needed amount of regularization is a trade-off between accuracy and precision of the estimated strain fields and their resolution. The obtainable accuracy and precision of the estimated displacement fields are influenced by interpolation errors in the DVC procedure and the relative amount of detail, noise and artifacts in the images. Errors in the displacement field are typically magnified during the strain calculation. Based on the tests and subvolume sizes (16-50 voxels) in this study, the expected order of magnitude of the accuracy and precision is 0.1 micro-voxels and 1 milli-voxels for the displacements and 0.1 and 1 milli-strains of the strain fields. 

Place, publisher, year, edition, pages
PERGAMON-ELSEVIER SCIENCE LTD, 2019
Keywords
Digital volume correlation, Accuracy, Precision, Benchmarks, Evaluation, Trabecular bone
National Category
Applied Mechanics
Identifiers
urn:nbn:se:uu:diva-387714 (URN)10.1016/j.ijsolstr.2019.03.024 (DOI)000469906300017 ()
Funder
Swedish Research Council, 2016-04608Göran Gustafsson Foundation for promotion of scientific research at Uppala University and Royal Institute of Technology
Available from: 2019-06-26 Created: 2019-06-26 Last updated: 2019-08-12Bibliographically approved
Espadas-Escalante, J. J., van Dijk, N. P. & Isaksson, P. (2019). A phase-field model for strength and fracture analyses of fiber-reinforced composites. Composites Science And Technology, 174, 58-67
Open this publication in new window or tab >>A phase-field model for strength and fracture analyses of fiber-reinforced composites
2019 (English)In: Composites Science And Technology, ISSN 0266-3538, E-ISSN 1879-1050, Vol. 174, p. 58-67Article in journal (Refereed) Published
Abstract [en]

A phase-field model for brittle fracture is proposed and evaluated for strength and fracture analyses of composites. In addition to the elastic properties, this approach makes use of only the fracture toughness and the strength of the material. The capability of the method is shown in analyses of composites at two scales. In laminates, strengths of notched laminates are estimated, including hole size effects. In a lamina, cracks developed in both transverse tension and compression are analyzed and compared to other numerical methods in the literature. The effects of a spectral and a hydrostatic-deviatoric decomposition of the strain energy density, two variants often used in phase-field formulations, are studied. It is shown that the choice of the decomposition affects the fracture development. Results are compared to experiments and simulations in the literature showing the capabilities of the phase-field approach.

Place, publisher, year, edition, pages
Elsevier, 2019
Keywords
Computational mechanics, Strength, Fracture, Finite element analysis (FEA)
National Category
Composite Science and Engineering
Identifiers
urn:nbn:se:uu:diva-368254 (URN)10.1016/j.compscitech.2018.10.031 (DOI)000469407500008 ()
Available from: 2018-12-03 Created: 2018-12-03 Last updated: 2019-07-05Bibliographically approved
Vorobyev, A., van Dijk, N. P. & Gamstedt, E. K. (2019). Orthotropic creep in polyethylene glycol impregnated archaeological oak from the Vasa ship. Mechanics of time-dependant materials, 23(1), 35-52
Open this publication in new window or tab >>Orthotropic creep in polyethylene glycol impregnated archaeological oak from the Vasa ship
2019 (English)In: Mechanics of time-dependant materials, ISSN 1385-2000, E-ISSN 1573-2738, Vol. 23, no 1, p. 35-52Article in journal (Refereed) Published
Abstract [en]

Creep in archaeological oak samples and planks from the Vasa ship impregnated with polyethylene glycol (PEG) has been studied in museum-like climate. Creep studies of duration up to three years have been performed in nearly constant relative humidity and temperature of the controlled museum climate. Cubic samples were subjected to compressive creep tests in all orthotropic directions. Additionally, the creep behaviour of planks with and without PEG and of recent oak was tested in four-point bending. The experimental results have been summarised and also compared with reference results from recent oak wood. The effect of variable ambient conditions on creep and mass changes is discussed. The experimental results of creep in the longitudinal direction showed deformations even for the low stresses. There is relatively much more scatter in creep behaviour, and not all samples showed linear viscoelastic response. The creep in radial and tangential directions of the cubes and the plank samples showed a strong dependency on the ambient conditions. Some samples showed expansion for decreasing moisture content, possibly caused by the thermal expansion of the PEG component. For the planks, increasing creep deformation was observed induced by changing ambient conditions. Such behaviour may be related to e.g. oscillations in ambient conditions and presence of PEG in the wood cell wall and cell lumen. The behaviour of PEG archaeological wood depends on the level of deterioration that occurred over centuries. However, although the findings presented here apply to this specific case, they provide a unique view on such wood.

Keywords
Time dependent, Creep, Vasa ship, Cubic samples, Wood, Climate, Polyethylene glycol
National Category
Applied Mechanics
Identifiers
urn:nbn:se:uu:diva-367284 (URN)10.1007/s11043-018-9382-3 (DOI)000460024200003 ()
Funder
Swedish Research CouncilSwedish Research Council FormasVinnova
Available from: 2018-11-29 Created: 2018-11-29 Last updated: 2019-03-25Bibliographically approved
van Dijk, N. P., Wu, D., Persson, C. & Isaksson, P. (2018). Digital Volume Correlation using Quartic FEM Interpolation and Global Optimization. In: : . Paper presented at 6th European Conference on Computational Mechanics (ECCM 6), 11-15 June, Glasgow, UK. Glasgow, UK
Open this publication in new window or tab >>Digital Volume Correlation using Quartic FEM Interpolation and Global Optimization
2018 (English)Conference paper, Oral presentation with published abstract (Refereed)
Abstract [en]

Estimating deformation fields at the microscale of trabecular bone remains challenging because of 1) the complex porous structure, and 2) the large subdomains necessary for reasonable accuracy.

In this contribution we present a novel Digital Volume Correlation method (DVC) based on a displacements-field interpolation with quartic finite elements, also called 27-node bricks, and a global optimization procedure. This particular choice of interpolation provides for increased freedom of the displacement field in each subvolume and is convenient for overlapping subvolumes for robust solutions.

The global optimization maximizes the normalized correlation for all subvolumes using the nodal degrees of freedom of the displacement interpolation as design variables and a spline interpolation of the grayscale values. A good starting point for the global optimization procedure is obtained using an initial FFT-based DVC step. This procedure can be executed without any regularization yielding decent results. The results can be improved by adding curvature penalization, similar to the work of Barber and Hose [1].

The approach has been tested on a number of different benchmark problems using bone samples. For duplicate scans, the accuracy and precision of the proposed DVC technique is comparable to ShIRT-FE as reported by Palanca et al. [2]. Tests on scans of human trabecular bone, taken at the Paul Scherrer Institut, including imposed and actual deformation are ongoing. In Figure 1, the results of such a test is shown using an imposed Gaussian displacement field.

Place, publisher, year, edition, pages
Glasgow, UK: , 2018
Keywords
DVC, FEM interpolation, Global optimization, Trabecular bone
National Category
Applied Mechanics
Identifiers
urn:nbn:se:uu:diva-367370 (URN)
Conference
6th European Conference on Computational Mechanics (ECCM 6), 11-15 June, Glasgow, UK
Note

REFERENCES

[1] Barber, D. and Hose, D. (2005). Automatic segmentation of medical images using image registration: diagnostic and simulation applications. J Med Eng Technol, 29(2):53–63.

[2] Palanca, M., Tozzi, G., Cristofolini, L., Viceconti, M., and Dall’Ara, E. (2015). Threedimensional local measurements of bone strain and displacement: comparison of three digital volume correlation approaches. J Biomech Eng, 137(7):071006.

Available from: 2018-11-30 Created: 2018-11-30 Last updated: 2018-12-10Bibliographically approved
Huo, J., van Dijk, N. P. & Gamstedt, E. K. (2018). Elastic properties of rhombic mesh structures based on computational homogenisation. Engineering structures, 172, 66-75
Open this publication in new window or tab >>Elastic properties of rhombic mesh structures based on computational homogenisation
2018 (English)In: Engineering structures, ISSN 0141-0296, E-ISSN 1873-7323, Vol. 172, p. 66-75Article in journal (Refereed) Published
Abstract [en]

Flat mesh structures are used in a wide variety of applications. In particular, meshes with a rhombic unit cell are frequently employed due to their simplicity and relative ease of manufacture. This paper studies the in-plane elastic properties of such a structure as a function of the geometrical parameters by means of homogenisation techniques. We compare predicted elastic in-plane properties (i) including only bending mode of the struts, cf. Gibson-Ashby model, (ii) including both bending and stretching modes of the struts, obtained by homogenisation using beam elements and (iii) by homogenisation using beam-spring elements accounting additionally for strut joint deformation, and (iv) numerical results of elastic properties obtained by homogenisation using solid elements. The expressions of the predicted elastic properties are presented in analytical form. The homogenised elastic properties accounting for both bending and stretching matches very well with those from the model including only bending. The axial deformation of struts thus has negligible impact on the overall elastic behaviour. The complex deformation in the strut joint was also captured in the homogenised using beam-spring elements, and the results agree better with the solid element results. It is concluded that a finite-element-based homogenisation approach could serve as a straightforward analytical method to obtain elastic properties of mesh structures. This approach automatically includes all deformation mechanisms as opposed to the classical unit cell analyses of bending beams.

Place, publisher, year, edition, pages
ELSEVIER SCI LTD, 2018
Keywords
Two-dimensional mesh structure, Analytical approach, Homogenisation, Effective elastic properties
National Category
Applied Mechanics
Identifiers
urn:nbn:se:uu:diva-363207 (URN)10.1016/j.engstruct.2018.06.012 (DOI)000445440300006 ()
Available from: 2018-10-17 Created: 2018-10-17 Last updated: 2018-10-17Bibliographically approved
Vorobyev, A., Garnier, F., van Dijk, N. P., Hagman, O. & Gamstedt, E. K. (2018). Evaluation of displacements by means of 3D laser scanning in a mechanically loaded replica of a hull section of the Vasa ship.. Digital Applications in Archaeology and Cultural Heritage, 11, Article ID e00085.
Open this publication in new window or tab >>Evaluation of displacements by means of 3D laser scanning in a mechanically loaded replica of a hull section of the Vasa ship.
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2018 (English)In: Digital Applications in Archaeology and Cultural Heritage, ISSN 2212-0548, Vol. 11, article id e00085Article in journal (Refereed) Published
Abstract [en]

For a development of full-scale finite-element models of large objects in cultural heritage, it can be useful to mechanically test replicas of key parts to identify structural properties which would otherwise not be available. This paper presents full scale tests on a replica of a section of the hull of the 17th century warship Vasa in three load configurations. We focus on determining a displacement of the loaded replica from 3D laser measurements. Two measures were found useful: (i) 3D displacements at well-defined intersections of the wooden replica, and (ii) normal displacements of larger surfaces. Wood surfaces were preferred to steel parts of the rig since the latter showed more scatter in displacement values in their point clouds caused by their reflective properties. The measurements were verified with draw-wire sensors. Some of these sensors were attached to the steel rig supporting the replica and, therefore, measured relative displacements. The scanning data was also useful to quantify the absolute movement of the steel rig supporting the replica, which improved the precision of the measurements of replica deformation. Finally, it is discussed how the replica test results can be used in a model of the entire museum ship.

Keywords
3D laser scanning, Structural analysis, Vasa, Wood, Shear
National Category
Applied Mechanics
Identifiers
urn:nbn:se:uu:diva-367281 (URN)10.1016/j.daach.2018.e00085 (DOI)
Available from: 2018-11-29 Created: 2018-11-29 Last updated: 2019-01-30Bibliographically approved
Espadas-Escalante, J. J., van Dijk, N. P. & Isaksson, P. (2018). The effect of free-edges and layer shifting on intralaminar and interlaminar stresses in woven composites. Composite structures, 185, 212-220
Open this publication in new window or tab >>The effect of free-edges and layer shifting on intralaminar and interlaminar stresses in woven composites
2018 (English)In: Composite structures, ISSN 0263-8223, E-ISSN 1879-1085, Vol. 185, p. 212-220Article in journal (Refereed) Published
Abstract [en]

The free-edge effects and relative layer shifting in the interlaminar and intralaminar stresses of plain woven composite laminates under uniaxial extension is investigated numerically using a finite element approach. A computational framework of the free-edge problem for periodic structures with finite width is applied to woven laminates. First, two-layered laminates with three different shifting configurations are studied considering repeating unit cells simulating finite and infinite width. For each configuration, two different widths are considered by trimming the model at different locations in order to investigate different free-edge effects. Then, two four-layered laminates with no shifting and a maximum shifting configuration are analyzed to illustrate the effect of neighboring layers in the stresses. For each shifting configuration, different delamination mechanisms are expected. When considering more layers, it is found that the stacking configuration affects the state of stress and the free-edge effects depending on the shifting. In general, a different behavior than that of unidirectional tape laminates is found, since the interlaminar and intralaminar stresses can be higher than those generated at the free-edges. Particularly, for the maximum shifting configuration results are in agreement with experimental results in the literature where no debonding between yarns was observed at the free-edges.

Keywords
Woven composites, Finite element method, Intralaminar stresses, Interlaminar stresses, Free-edge effects, Multiscale modeling
National Category
Applied Mechanics
Identifiers
urn:nbn:se:uu:diva-341485 (URN)10.1016/j.compstruct.2017.11.014 (DOI)000418961000018 ()
Available from: 2018-02-28 Created: 2018-02-28 Last updated: 2019-07-05Bibliographically approved
Afshar, R., Alavyoon, N., Ahlgren, A., van Dijk, N. P., Vorobyev, A. & Gamstedt, K. (2017). A full-scale finite-element model of the Vasa ship. In: Proceedings of ECCOMAS Thematic Conference CompWood 2017: Computational Methods in Wood Mechanics. Paper presented at ECCOMAS Thematic Conference CompWood 2017: Computational Methods in Wood Mechanics-from Material Properties to Timber Structure, June 7-9, 2017, Vienna, Austria.
Open this publication in new window or tab >>A full-scale finite-element model of the Vasa ship
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2017 (English)In: Proceedings of ECCOMAS Thematic Conference CompWood 2017: Computational Methods in Wood Mechanics, 2017Conference paper, Oral presentation with published abstract (Refereed)
Abstract [en]

A full-scale model of the 17th century Vasa shipwreck has been developed to assess its current and future structural stability as well as design an improved support structure. A wireframe model, consisting of only lines, points and curves to describe the geometry of the ship, has been provided by the Vasa museum. It has been developed based on geodetic measurements using a total station. From this wireframe model, a three-dimensional (3D) model comprising solid bodies for solid-like parts (i.e. hull and keel), surfaces for the shell-like components (deck planks) and lines for beam-like constituents (deck beams) has been developed in Creo Parametric 3D software. This geometric model has been imported in finite-element software, Ansys, for further development of the stiffeners (knees, riders, stanchions, masts, etc.), adjustment of the correct location of deck beams and, finally, structural analyses of the entire ship (Figure 1). The procedure for selection of the different types of elements in the finite-element (FE) model, the definition of orthotropic material properties for the timber structure and preliminary results are discussed in this paper. Experiences drawn from this engineering project may also be useful in development of finite element models for structural assessment of other complex wooden structures in cultural heritage.

National Category
Applied Mechanics
Identifiers
urn:nbn:se:uu:diva-332819 (URN)
Conference
ECCOMAS Thematic Conference CompWood 2017: Computational Methods in Wood Mechanics-from Material Properties to Timber Structure, June 7-9, 2017, Vienna, Austria
Available from: 2017-11-02 Created: 2017-11-02 Last updated: 2017-11-14Bibliographically approved
Espadas-Escalante, J. J., van Dijk, N. P. & Isaksson, P. (2017). A study on the influence of boundary conditions in computational homogenization of periodic structures with application to woven composites. Composite structures, 160, 529-537
Open this publication in new window or tab >>A study on the influence of boundary conditions in computational homogenization of periodic structures with application to woven composites
2017 (English)In: Composite structures, ISSN 0263-8223, E-ISSN 1879-1085, Vol. 160, p. 529-537Article in journal (Refereed) Published
Abstract [en]

The influence of boundary conditions (BCs) in the estimation of elastic properties of periodic structures is investigated using computational homogenization with special focus on planar structures. Uniform displacement, uniform traction, periodic, in-plane periodic and a proposed mix of periodic and traction BCs are used. First, the effect of the BCs is demonstrated in structures with one-, two- and three-dimensional periodicity. Mixed BCs are shown to most accurately represent the behavior of layered structures with a small number of repeating unit cells. Then, BCs are imposed on a twill woven composite architecture. Special attention is devoted to investigate the sensitivity of the estimated properties with respect to the BCs and to show differences when considering a single lamina or a laminate. High sensitivity of the in-plane extensional modulus and Poisson's ratio with respect to the type of BCs is found. Moreover, it is shown that the mix of BCs and in-plane periodic BCs are capable to represent an experimental strain field.

Keywords
Computational homogenization, Mixed boundary conditions, Heterogeneous structures, Elastic properties, Woven composites, Finite element method
National Category
Composite Science and Engineering
Identifiers
urn:nbn:se:uu:diva-359307 (URN)10.1016/j.compstruct.2016.10.082 (DOI)000390470300044 ()
Available from: 2018-08-31 Created: 2018-08-31 Last updated: 2019-07-05Bibliographically approved
Afshar, R., van Dijk, N., Bjurhager, I. & Gamstedt, E. K. (2017). Comparison of experimental testing and finite element modelling of a replica of a section of the Vasa warship to identify the behaviour of structural joints. Engineering structures, 147, 62-76
Open this publication in new window or tab >>Comparison of experimental testing and finite element modelling of a replica of a section of the Vasa warship to identify the behaviour of structural joints
2017 (English)In: Engineering structures, ISSN 0141-0296, E-ISSN 1873-7323, Vol. 147, p. 62-76Article in journal (Refereed) Published
Abstract [en]

Modelling in design of new support systems necessitates the joint stiffness of the existing wooden structures. In valuable structures, e.g. in cultural heritage, or structures with inaccessible joints, these stiffness values must be estimated, e.g. by testing joints in tailored replicas of the original parts. Although a simplified structure, the replica, can call for finite element (FE) modelling to capture the stiffness parameters. The first step in such a process is to compare FE predictions with experimental tests, for validation purposes. The reasons for unavoidable differences in load-displacement behaviour between model predictions and experimental test should be identified, and then possibly remedied by an improved model. Underlying causes like the complex shape of joints, geometrical uncertainties, contact mechanisms and material nonlinearity are generally too computationally expensive to be included in a full-scale model. It is therefore convenient to collect such effects in the contact penalty stiffness in the joint contact areas where stresses are high, which influences the resulting joint stiffness. A procedure for this is here illustrated for the case of the 17th century Vasa shipwreck A replica of a section of the ship has been constructed, and its joints were tested in bending-compression, in-plane shear and rotation. The FE simulations showed stiffer behaviour than the experimental results. Therefore, a normal penalty stiffness in contact surfaces of the joint were introduced, and used as a calibration parameter to account for the simplifying assumptions or indeliberate imprecision in the model, e.g. concerning boundary conditions, material properties and geometrical detail. The difference between numerical predictions and experimental results could then be significantly reduced, with a suitable normal penalty stiffness value. Once an acceptable finite element model has been obtained, it is shown how this can be used to identify stiffness values for joints in the physical structure with compensation for degradation of material properties due to aging and conservation treatment.

Place, publisher, year, edition, pages
ELSEVIER SCI LTD, 2017
National Category
Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-330536 (URN)10.1016/j.engstruct.2017.05.051 (DOI)000408073500005 ()
Funder
Swedish Research CouncilVINNOVASwedish Research Council Formas
Available from: 2017-10-04 Created: 2017-10-04 Last updated: 2017-10-04
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