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Publications (10 of 32) Show all publications
Rajput, M. S., Burman, M., Forsberg, F. & Hallström, S. (2019). Experimental and numerical study of the response to various impact energy levels for composite sandwich plates with different face thicknesses. Journal of Sandwich Structures and Materials, 21(5), 1654-1682
Open this publication in new window or tab >>Experimental and numerical study of the response to various impact energy levels for composite sandwich plates with different face thicknesses
2019 (English)In: Journal of Sandwich Structures and Materials, ISSN 1099-6362, E-ISSN 1530-7972, Vol. 21, no 5, p. 1654-1682Article in journal (Refereed) Published
Abstract [en]

Composite sandwich structures find wide application in the aerospace sector thanks to their lightweight characteristics. However, composite structures are highly susceptible to low-velocity impact damage and therefore thorough characterization of the impact response and damage process for the used material configurations is necessary. The present study investigates the effect of face-sheet thickness on the impact response and damage mechanisms, experimentally and numerically. A uni-directional, non-crimp fabric is used as reinforcement in the face-sheets, and a closed cell Rohacell 200 Hero polymer foam is used as core material. Low-velocity impact tests are performed in a novel instrumented drop-weight rig that is able to capture the true impact response. A range of impact energies are initially utilized in order to identify when low level damage (LLD), barely visible impact damage (BVID) and visible impact damage (VID) occur. A thorough fractography investigation is performed to characterize the impact damage using both destructive and non-destructive testing. The damage from the impacts in terms of dent depth, peak contact force, deflection and absorbed energy is measured. The results show bilinear responses in dent depth vs. impact energy and absorbed energy vs. impact energy. It is found than the BVID energy works well as an indication for the onset of excessive damage. Fractography reveals that there is a failure mode shift between the LLD and the VID energy levels, and that delaminations predominantly grow along the fiber direction and rotate in a spiral pattern through the thickness, following the laminate ply orientations. Finally, a progressive damage finite element model is developed to simulate both the impact response and the delamination extent, incorporating both intra-laminar and inter-laminar damage modes. The simulation shows good agreement with the experiments.

Place, publisher, year, edition, pages
Sage Publications, 2019
Keywords
Non-crimp fabric, drop-weight rig, low-velocity impact, fractography, barely visible impact damage, X-ray micro-tomography, foam core
National Category
Applied Mechanics
Research subject
Experimental Mechanics
Identifiers
urn:nbn:se:ltu:diva-73586 (URN)10.1177/1099636219837133 (DOI)000470764900003 ()
Note

Validerad;2019;Nivå 2;2019-07-01 (johcin)

Available from: 2019-04-11 Created: 2019-04-11 Last updated: 2019-07-01Bibliographically approved
Neikter, M., Forsberg, F., Pederson, R., Antti, M.-L., Åkerfeldt, P., Larsson, S., . . . Puyoo, G. (2018). Defect characterization of electron beam melted Ti-6Al-4V and Alloy 718 with X-ray microtomography. Aeronautics and Aerospace Open Access Journal, 2(3), 139-145
Open this publication in new window or tab >>Defect characterization of electron beam melted Ti-6Al-4V and Alloy 718 with X-ray microtomography
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2018 (English)In: Aeronautics and Aerospace Open Access Journal, ISSN 2576-4500, Vol. 2, no 3, p. 139-145Article in journal (Refereed) Published
Abstract [en]

Electron beam melting (EBM) is emerging as a promising manufacturing process where metallic components are manufactured from three-dimensional (3D) computer aided design models by melting layers onto layers. There are several advantages with this manufacturing process such as near net shaping, reduced lead times and the possibility to decrease weight by topology optimization, aspects that are of interest for the aerospace industry. In this work two alloys, Ti-6Al-4V and Alloy 718, widely used within the aerospace industry were investigated with X-ray microtomography (XMT), to characterize defects such as lack of fusion (LOF) and inclusions. It was furthermore possible to view the macrostructure with XMT, which was compared to macrostructure images obtained by light optical microscopy (LOM). XMT proved to be a useful tool for defect characterization and both LOF and un-melted powder could be found in the two investigated samples. In the EBM built Ti-6Al-4V sample high density inclusions, believed to be composed of tungsten, were found. One of the high-density inclusions was found to be hollow, which indicate that the inclusion stems from the powder manufacturing process and not related with the EBM process. By performing defect analyses with the XMT software it was also possible to quantify the amount of LOF and un-melted powder in vol%. From the XMT-data meshes were produced so that finite element method (FEM) simulations could be performed. From these FEM simulations the significant impact of defects on the material properties was evident, as the defects led to high stress concentrations. It could moreover, with FEM, be shown that the as-built surface roughness of EBM material is of importance as high surface roughness led to increased stress concentrations.

Place, publisher, year, edition, pages
MedCrave Group, 2018
Keywords
X-ray tomography, Ti-6Al-4V, Alloy 718, defects and electron beam melting
National Category
Metallurgy and Metallic Materials Other Materials Engineering Fluid Mechanics and Acoustics Applied Mechanics
Research subject
Engineering Materials; Solid Mechanics; Experimental Mechanics
Identifiers
urn:nbn:se:ltu:diva-68924 (URN)10.15406/aaoaj.2018.02.00044 (DOI)
Available from: 2018-05-28 Created: 2018-05-28 Last updated: 2018-11-08Bibliographically approved
Berglund, L., Forsberg, F., Jonoobi, M. & Oksman, K. (2018). Promoted hydrogel formation of lignin-containing arabinoxylan aerogel using cellulose nanofibers as a functional biomaterial. RSC Advances, 8(67), 38219-38228
Open this publication in new window or tab >>Promoted hydrogel formation of lignin-containing arabinoxylan aerogel using cellulose nanofibers as a functional biomaterial
2018 (English)In: RSC Advances, ISSN 2046-2069, E-ISSN 2046-2069, Vol. 8, no 67, p. 38219-38228Article in journal (Refereed) Published
Abstract [en]

In this work, three-dimensional (3D) aerogels and hydrogels based on lignin-containing arabinoxylan (AX) and cellulose nanofibers (CNF) were prepared. The effects of the CNF and the crosslinking with citric acid (CA) of various contents (1, 3, 5 wt%) were evaluated. All the aerogels possessed highly porous (above 98%) and lightweight structures. The AX-CNF hydrogel with a CA content of 1 wt% revealed a favorable network structure with respect to the swelling ratio; nanofiber addition resulted in a five-fold increase in the degree of swelling (68 g of water per g). The compressive properties were improved when the higher CA content (5 wt%) was used; when combined with CNF, there was a seven-fold enhancement in the compressive strength. The AX-CNF hydrogels were prepared using a green and straightforward method that utilizes sustainable resources efficiently. Therefore, such natural hydrogels could find application potential, for example in the field of soft tissue engineering.

Place, publisher, year, edition, pages
Royal Society of Chemistry, 2018
National Category
Bio Materials Applied Mechanics
Research subject
Wood and Bionanocomposites; Experimental Mechanics
Identifiers
urn:nbn:se:ltu:diva-71733 (URN)10.1039/C8RA08166B (DOI)000451075500012 ()2-s2.0-85057291251 (Scopus ID)
Note

Validerad;2018;Nivå 2;2018-11-23 (johcin)

Available from: 2018-11-23 Created: 2018-11-23 Last updated: 2019-09-19Bibliographically approved
Neikter, M., Forsberg, F., Lycksam, H., Pederson, R. & Antti, M.-L. (2017). Microstructure and Defects in Additive Manufactured Titanium: a Comparison Between Microtomography and Optical Microscopy. In: : . Paper presented at 3rd International Conference on Tomography of Materials and Structures, Lund, Sweden, 26-30 June 2017.
Open this publication in new window or tab >>Microstructure and Defects in Additive Manufactured Titanium: a Comparison Between Microtomography and Optical Microscopy
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2017 (English)Conference paper, Oral presentation with published abstract (Other academic)
Abstract [en]

The aim of this work has been to compare two different analysing methods;x-ray microtomography and light optical microscopy, when it comes to defects and microstructure of additively manufactured Ti-6Al-4V. The results showthat both techniqueshave theirpros and cons:microtomography is the preferred choicefor defect detectionby analysing the full 3D sample volume, while light optical microscopy is better for analysing finer details in 2D.

National Category
Metallurgy and Metallic Materials Other Materials Engineering Fluid Mechanics and Acoustics
Research subject
Engineering Materials; Fluid Mechanics
Identifiers
urn:nbn:se:ltu:diva-65063 (URN)
Conference
3rd International Conference on Tomography of Materials and Structures, Lund, Sweden, 26-30 June 2017
Available from: 2017-08-14 Created: 2017-08-14 Last updated: 2018-04-25Bibliographically approved
Åström, E., Bonomi, G., Calliari, I., Calvini, P., Checchia, P., Donzella, A., . . . Zumerle, G. (2016). Precision measurements of linear scattering density using muon tomography. Journal of Instrumentation, 11(P7010)
Open this publication in new window or tab >>Precision measurements of linear scattering density using muon tomography
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2016 (English)In: Journal of Instrumentation, ISSN 1748-0221, E-ISSN 1748-0221, Vol. 11, no P7010Article in journal (Refereed) Published
Abstract [en]

We demonstrate that muon tomography can be used to precisely measure the properties of various materials. The materials which have been considered have been extracted from an experimental blast furnace, including carbon (coke) and iron oxides, for which measurements of the linear scattering density relative to the mass density have been performed with an absolute precision of 10%. We report the procedures that are used in order to obtain such precision, and a discussion is presented to address the expected performance of the technique when applied to heavier materials. The results we obtain do not depend on the specific type of material considered and therefore they can be extended to any application

National Category
Applied Mechanics
Research subject
Experimental Mechanics
Identifiers
urn:nbn:se:ltu:diva-60427 (URN)10.1088/1748-0221/11/07/P07010 (DOI)000387763000001 ()2-s2.0-85007256310 (Scopus ID)
Note

Validerad; 2016; Nivå 2; 2016-12-02 (inah)

Available from: 2016-11-15 Created: 2016-11-15 Last updated: 2018-07-10Bibliographically approved
Joffre, T., Girlanda, O., Forsberg, F., Sahlen, F., Sjödahl, M. & Gamstedt, E. K. (2015). A 3D in-situ investigation of the deformation in compressive loading in the thickness direction of cellulose fiber mats (ed.). Paper presented at . Cellulose (London), 22(5), 2993-3001
Open this publication in new window or tab >>A 3D in-situ investigation of the deformation in compressive loading in the thickness direction of cellulose fiber mats
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2015 (English)In: Cellulose (London), ISSN 0969-0239, E-ISSN 1572-882X, Vol. 22, no 5, p. 2993-3001Article in journal (Refereed) Published
Abstract [en]

Fiber mat materials based on cellulose natural fibers combines a useful set of properties, including renewability, stiffness, strength and dielectric insulation, etc. The dominant in-plane fiber orientation ensures the in-plane performance, at the expense of reduced out-of-plane behavior, which has not been studied as extensively as the in-plane behavior. Quantitative use of X-ray micro-computed tomography and strain analyses under in-situ loading open up possibilities to identify key mechanisms responsible for deformation. In the present investigation, focus is placed on the out-of-plane deformation under compressive loading of thick, high density paper, known as pressboard. The samples were compressed in the chamber of a microtomographic scanner. 3D images were captured before and after the loading the sample. From sequential 3D images, the strain field inside the material was calculated using digital volume correlation. Two different test pieces were tested, namely unpolished and surface polished ones. The first principal strain component of the strain tensor showed a significant correlation with the density variation in the material, in particular on the top and bottom surfaces of unpolished samples. The manufacturing-induced grooves generate inhomogeneities in the microstructure of the surface, thus creating high strain concentration zones which give a sensible contribution to the overall compliance of the unpolished material. More generally, the results reveal that, on the micrometer scale, high density fiber pressboard behaves as a porous material rather than a low density fiber network.

National Category
Applied Mechanics
Research subject
Experimental Mechanics
Identifiers
urn:nbn:se:ltu:diva-13682 (URN)10.1007/s10570-015-0727-7 (DOI)000361002000011 ()2-s2.0-84941414539 (Scopus ID)cf3a80ef-5a68-44c8-aa28-3ff20395ee67 (Local ID)cf3a80ef-5a68-44c8-aa28-3ff20395ee67 (Archive number)cf3a80ef-5a68-44c8-aa28-3ff20395ee67 (OAI)
Note
Validerad; 2015; Nivå 2; 20150819 (andbra)Available from: 2016-09-29 Created: 2016-09-29 Last updated: 2018-07-10Bibliographically approved
Girlanda, O., Sahlen, F., Joffre, T., Gamstedt, E. K., Schmidt, L. E., Forsberg, F. & Sjödahl, M. (2015). Analysis of the Micromechanical Deformation in Pressboard performed by X-ray Microtomography (ed.). In: (Ed.), (Ed.), IEEE Electrical Insulation Conference (EIC): Seattle, Jun 07-10, 2015. Paper presented at IEEE Electrical Insulation Conference : 07/06/2015 - 10/06/2015 (pp. 89-92). Piscataway, NJ: IEEE Communications Society
Open this publication in new window or tab >>Analysis of the Micromechanical Deformation in Pressboard performed by X-ray Microtomography
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2015 (English)In: IEEE Electrical Insulation Conference (EIC): Seattle, Jun 07-10, 2015, Piscataway, NJ: IEEE Communications Society, 2015, p. 89-92Conference paper, Published paper (Refereed)
Abstract [en]

A large number of electrical insulation components are produced in paper-based materials. Paper combines good insulating properties with the necessary mechanical and chemical stability. Paper consists of a system of fibers binding to each other creating a strong network. The presence of large open pores allows for impregnability of the material but also causes mechanical weakness in particular in the out-of-plane direction of the material. This aspect is important for pressboard components, where the resistance to compression stress is relevant for e.g. transformer windings. It is therefore relevant to understand the mechanisms that underlay the out-of-plane deformation of pressboard. In order to get a clear picture of the deformation patterns within the material, X-ray micro-computed tomography was used. Pressboard test pieces were subjected to in-situ out-of-plane compressive loading. 3D images of the sample could be captured before, during and after the loading sequence. Image analysis allowed for the definition of strain fields. The results revealed a strong correlation between the density variation within the sample and the strain calculated from the 3D images.

Place, publisher, year, edition, pages
Piscataway, NJ: IEEE Communications Society, 2015
National Category
Applied Mechanics
Research subject
Experimental Mechanics
Identifiers
urn:nbn:se:ltu:diva-40302 (URN)f60bb21b-67e2-4712-92c6-785d03ed4ce2 (Local ID)978-1-4799-7354-5 (ISBN)f60bb21b-67e2-4712-92c6-785d03ed4ce2 (Archive number)f60bb21b-67e2-4712-92c6-785d03ed4ce2 (OAI)
Conference
IEEE Electrical Insulation Conference : 07/06/2015 - 10/06/2015
Note
Validerad; 2016; Nivå 1; 20160401 (andbra)Available from: 2016-10-03 Created: 2016-10-03 Last updated: 2018-04-25Bibliographically approved
Hellström, J. G., Forsberg, F., Lundström, T. S. & Sjödahl, M. (2014). Representative volume size when modelling flow through porous structures (ed.). Paper presented at European Fluid Mechanics Conference : 14/09/2014 - 18/09/2014. Paper presented at European Fluid Mechanics Conference : 14/09/2014 - 18/09/2014.
Open this publication in new window or tab >>Representative volume size when modelling flow through porous structures
2014 (English)Conference paper, Oral presentation only (Refereed)
National Category
Fluid Mechanics and Acoustics Applied Mechanics
Research subject
Fluid Mechanics; Experimental Mechanics
Identifiers
urn:nbn:se:ltu:diva-39836 (URN)ebb0ef2a-974f-42ca-a00e-163c8d804799 (Local ID)ebb0ef2a-974f-42ca-a00e-163c8d804799 (Archive number)ebb0ef2a-974f-42ca-a00e-163c8d804799 (OAI)
Conference
European Fluid Mechanics Conference : 14/09/2014 - 18/09/2014
Note
Godkänd; 2014; 20140923 (andbra)Available from: 2016-10-03 Created: 2016-10-03 Last updated: 2018-04-25Bibliographically approved
Bhuiyan, I. U., Mouzon, J., Forsberg, F., Forsmo, S., Sjödahl, M. & Hedlund, J. (2013). Consideration of X-ray microtomography to quantitatively determine the size distribution of bubble cavities in iron ore pellets (ed.). Paper presented at . Powder Technology, 233, 312-318
Open this publication in new window or tab >>Consideration of X-ray microtomography to quantitatively determine the size distribution of bubble cavities in iron ore pellets
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2013 (English)In: Powder Technology, ISSN 0032-5910, E-ISSN 1873-328X, Vol. 233, p. 312-318Article in journal (Refereed) Published
Abstract [en]

X-ray microtomography data of iron ore green pellets of approx. 12 mm in diameter were recorded using a commercial instrument. The reconstructed volume after thresholding represented a unique dataset consisting of a three-dimensional distribution of equiaxed objects corresponding to bubble cavities. This dataset was used to successfully validate a stereological method to determine the size distribution of spherical objects dispersed in a volume. This was achieved by investigating only a few cross-sectional images of this volume and measuring the profiles left by these objects in the cross-sectional images. Excellent agreement was observed between the size distribution of the bubble cavities obtained by directly classifying their size in the reconstructed volume and that estimated by applying the aforementioned stereological method to eight cross-sectional images of the reconstructed volume. Subsequently, we discuss the possibility of calibrating X-ray tomography data quantitatively using the size distribution of the bubble cavities as a figure of merit and the results obtained by applying the stereological method to SEM images as reference data. This was justified by considering the validity of the stereological method demonstrated by tomography, the accurate thresholding made possible by back-scattered electron imaging and the solid reproducibility of the results obtained by SEM. Using different threshold values for binarization of the X-ray microtomography data and comparing the results to those obtained by SEM, we found that X-ray microtomography can be used after proper calibration against SEM data to measure the total porosity of the bubble cavities but can only provide a rough estimate of the median diameter because of the limited resolution achieved in this study.

National Category
Chemical Process Engineering Applied Mechanics
Research subject
Chemical Technology; Experimental Mechanics
Identifiers
urn:nbn:se:ltu:diva-5590 (URN)10.1016/j.powtec.2012.09.012 (DOI)000311134200037 ()2-s2.0-84867795434 (Scopus ID)3b9114fe-ca36-477f-b8ee-002ff0f7959a (Local ID)3b9114fe-ca36-477f-b8ee-002ff0f7959a (Archive number)3b9114fe-ca36-477f-b8ee-002ff0f7959a (OAI)
Note
Validerad; 2013; 20120918 (andbra)Available from: 2016-09-29 Created: 2016-09-29 Last updated: 2018-07-10Bibliographically approved
Mooser, R., Forsberg, F., Hack, E., Székely, G. & Sennhauser, U. (2013). Estimation of affine transformations directly from tomographic projections in two and three dimensions (ed.). Paper presented at . Machine Vision and Applications, 24(2), 419-434
Open this publication in new window or tab >>Estimation of affine transformations directly from tomographic projections in two and three dimensions
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2013 (English)In: Machine Vision and Applications, ISSN 0932-8092, E-ISSN 1432-1769, Vol. 24, no 2, p. 419-434Article in journal (Refereed) Published
Abstract [en]

This paper presents a new approach to estimate two- and three-dimensional affine transformations from tomographic projections. Instead of estimating the deformation from the reconstructed data, we introduce a method which works directly in the projection domain, using parallel and fan beam projection geometries. We show that any affine deformation can be analytically compensated, and we develop an efficient multiscale estimation framework based on the normalized cross correlation. The accuracy of the approach is verified using simulated and experimental data, and we demonstrate that the new method needs less projection angles and has a much lower computational complexity as compared to approaches based on the standard reconstruction techniques.

National Category
Applied Mechanics
Research subject
Experimental Mechanics
Identifiers
urn:nbn:se:ltu:diva-3945 (URN)10.1007/s00138-011-0376-2 (DOI)000313496100013 ()2-s2.0-84872334033 (Scopus ID)1caad981-4935-434d-a4d2-65037eaa9e4e (Local ID)1caad981-4935-434d-a4d2-65037eaa9e4e (Archive number)1caad981-4935-434d-a4d2-65037eaa9e4e (OAI)
Note
Validerad; 2013; 20111028 (andbra)Available from: 2016-09-29 Created: 2016-09-29 Last updated: 2018-07-10Bibliographically approved
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Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0001-7395-3302

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