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Alfredsson, K. Svante
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Publications (10 of 22) Show all publications
Svensson, D., Alfredsson, K. S., Stigh, U. & Jansson, N. E. (2016). Measurement of cohesive law for kink-band formation in unidirectional composite. Engineering Fracture Mechanics, 151, 1-10
Open this publication in new window or tab >>Measurement of cohesive law for kink-band formation in unidirectional composite
2016 (English)In: Engineering Fracture Mechanics, ISSN 0013-7944, E-ISSN 1873-7315, Vol. 151, p. 1-10Article in journal (Refereed) Published
Abstract [en]

Kink-band formation is an important mechanism limiting the compressive strength of high strength composites. A cohesive zone model is used to model the material in a unidirectional carbon fibre composite that forms the kink-band. Equilibrium of configurational forces is used to design and evaluate the experiments. Microscopic studies show that a kink-band is formed with the height of about 200 μm. The corresponding cohesive law has a peak stress of about 1.5 GPa, a compression at failure of about 50 μm and a fracture energy of about 25 kJ/m2.

Place, publisher, year, edition, pages
Elsevier, 2016
Keywords
Composites, Configurational forces, DIC-measurement, Kink-band formation, Cohesive zone modelling
National Category
Applied Mechanics
Research subject
Technology; Mechanics of Materials
Identifiers
urn:nbn:se:his:diva-11717 (URN)10.1016/j.engfracmech.2015.10.040 (DOI)000368922000001 ()2-s2.0-84947934411 (Scopus ID)
Projects
NFFP FiKomINFINIT MDC
Funder
Knowledge Foundation, 20130305VINNOVA, NFFP 013223
Available from: 2015-11-27 Created: 2015-11-27 Last updated: 2019-01-22Bibliographically approved
Svensson, D., Alfredsson, K. S. & Stigh, U. (2016). On the ability of coupled mixed mode cohesive laws to conform to LEFM for cracks in homogeneous orthotropic solids. Engineering Fracture Mechanics, 163, 426-448
Open this publication in new window or tab >>On the ability of coupled mixed mode cohesive laws to conform to LEFM for cracks in homogeneous orthotropic solids
2016 (English)In: Engineering Fracture Mechanics, ISSN 0013-7944, E-ISSN 1873-7315, Vol. 163, p. 426-448Article in journal (Refereed) Published
Abstract [en]

The ability of coupled cohesive laws to conform to the predictions of linear elastic fracturemechanics (LEFM) in the case of small-scale-yielding (SSY) is explored. The study is concerned with cracks in homogeneous orthotropic solids and the results apply also for the case of isotropy. Both potential based and non-potential based cohesive laws are considered. It is shown that the initial stiffnesses of the cohesive law must be matched to the elastic moduli of the orthotropic solid in order to achieve a constant ratio of the cohesive stress components ahead of the crack tip. A simple condition for this is provided. For non potential based laws an additional apparently sufficient condition on the non-linear part of the cohesive law is identified: The traction vector must not change direction if the directionof the separation vector is constant. Fulfillment of this condition provides a uniform local mode mix in the cohesive zone with a value equal to the global mode mix. It is demonstrated that potential based cohesive laws display a varying local mode mix at the crack tip for cases with a mode dependent work of separation. This is identified as acomplicating feature in terms of calibrating the parameters of a cohesive law to experimental data.

Place, publisher, year, edition, pages
Elsevier, 2016
Keywords
Composites, Cohesive zone modelling, Finite element analysis, Delamination, Mixed mode fracture
National Category
Applied Mechanics
Research subject
Technology; Mechanics of Materials
Identifiers
urn:nbn:se:his:diva-12855 (URN)10.1016/j.engfracmech.2016.05.018 (DOI)000383309500027 ()2-s2.0-84989957760 (Scopus ID)
Projects
MDC
Funder
Knowledge Foundation
Available from: 2016-08-31 Created: 2016-08-31 Last updated: 2019-01-22Bibliographically approved
Alfredsson, K. S., Biel, A. & Salimi, S. (2015). Shear testing of thick adhesive layers using the ENF-specimen. International Journal of Adhesion and Adhesives, 62, 130-138
Open this publication in new window or tab >>Shear testing of thick adhesive layers using the ENF-specimen
2015 (English)In: International Journal of Adhesion and Adhesives, ISSN 0143-7496, E-ISSN 1879-0127, Vol. 62, p. 130-138Article in journal (Refereed) Published
Place, publisher, year, edition, pages
Elsevier, 2015
National Category
Applied Mechanics
Research subject
Technology; Mechanics of Materials
Identifiers
urn:nbn:se:his:diva-11337 (URN)10.1016/j.ijadhadh.2015.07.008 (DOI)000361401900018 ()2-s2.0-84938939472 (Scopus ID)
Available from: 2015-08-12 Created: 2015-08-12 Last updated: 2019-01-22Bibliographically approved
Biel, A., Alfredsson, K. S. & Carlberger, T. (2014). Adhesive Tapes; Cohesive Laws for a Soft Layer. Paper presented at 20th European Conference on Fracture,NTNU Trondheim, Norway,30/6-4/7 2014. Procedia Materials Science, 3, 1389-1393
Open this publication in new window or tab >>Adhesive Tapes; Cohesive Laws for a Soft Layer
2014 (English)In: Procedia Materials Science, ISSN 2211-8128, Vol. 3, p. 1389-1393Article in journal (Refereed) Published
Abstract [en]

For adhesive tapes, the strain before fracture often exceeds 500%. Although the maximum stresses are quite modest the high strains to fracture result in impressive fracture energy. Due to hydrostatic stress the fracture process often starts by nucleation of microscopic cracks inside the layer. The final crack path is usually close to one of the adherends.

Repeated experiments are performed both with DCB-specimens and butt-joints. The used adhesive tape is an acrylic foam tape with a thickness of 1.1 mm and a width of 19 mm. The geometry of the specimen is adapted to the properties of the soft layer. For the DCB-specimen this implies that the length of the specimen is about 1 m. The evaluated cohesive laws from the DCB- specimens give a fracture energy of 2 kN/m and a maximum stress about 0.5 MPa. For the butt-joints, the evaluated cohesive law corresponds well to the results from the DCB-experiments. However, the strain to fracture is slightly smaller. The stress in these specimens is distributed over a larger area and a nucleated crack rapidly crosses the load bearing area and fails the joint prematurely. For both kinds of experiments the evaluated cohesive laws show a small linear part. After this part there is an almost linear strain-hardening phase until fracture.

Place, publisher, year, edition, pages
Amsterdam: Elsevier, 2014
Keywords
Pressure-sensitive adhesive (PSA), Adhesive tape, Cohesive law, Double Cantilever Beam (DCB)
National Category
Engineering and Technology Applied Mechanics
Research subject
Technology; Mechanics of Materials
Identifiers
urn:nbn:se:his:diva-9672 (URN)10.1016/j.mspro.2014.06.224 (DOI)000398274600219 ()
Conference
20th European Conference on Fracture,NTNU Trondheim, Norway,30/6-4/7 2014
Available from: 2014-07-13 Created: 2014-07-13 Last updated: 2019-03-04Bibliographically approved
Svensson, D., Alfredsson, K. S., Biel, A. & Stigh, U. (2014). Measurement of cohesive laws for interlaminar failure of CFRP. Composites Science And Technology, 100, 53-62
Open this publication in new window or tab >>Measurement of cohesive laws for interlaminar failure of CFRP
2014 (English)In: Composites Science And Technology, ISSN 0266-3538, E-ISSN 1879-1050, Vol. 100, p. 53-62Article in journal (Refereed) Published
Place, publisher, year, edition, pages
Elsevier, 2014
Keywords
Polymer–matrix composites (PMCs), Delamination, Finite element analysis (FEA), Digital image correlation (DIC)
National Category
Applied Mechanics
Research subject
Technology; Mechanics of Materials
Identifiers
urn:nbn:se:his:diva-9559 (URN)10.1016/j.compscitech.2014.05.031 (DOI)000340222400008 ()2-s2.0-84902333949 (Scopus ID)
Projects
Keks och Effekt
Available from: 2014-06-23 Created: 2014-06-23 Last updated: 2019-01-22Bibliographically approved
Svensson, D., Alfredsson, K. S., Stigh, U. & Jansson, N. E. (2013). An experimental method to determine the critical energy release rate associated with longitudinal compressive failure in CFRP. In: Proceeding of the 19th international conference on composite materials (ICCM 19): . Paper presented at 19th International Conference on Composite Materials, July 28-August 2, 2013, Montréal, Canada.
Open this publication in new window or tab >>An experimental method to determine the critical energy release rate associated with longitudinal compressive failure in CFRP
2013 (English)In: Proceeding of the 19th international conference on composite materials (ICCM 19), 2013Conference paper, Published paper (Refereed)
Abstract [en]

A test specimen for measurement of the critical energy release rate associated with longitudinal compressive failure is proposed. High strains are localized by decreasing the out-of-plane thickness towards the anticipated damage region which consists of a unidirectional (UD) laminate. Thus, the compressive fibre failure mode is isolated. Microscopic studies show that the UD-material fails in a kinking mode. A method based on a generalized form of the J-integral and full-field measurements of the strain field is developed to extract the fracture energy. The fracture energy in four experiments is measured to be 20-40 kN/m. Finite element simulations  are  performed  to  validate  the experimental results. The essential features of the response are captured by modelling the damage region with cohesive elements.

Keywords
CFRP, compressive failure, kink-band, cohesive zone model
National Category
Applied Mechanics
Research subject
Technology
Identifiers
urn:nbn:se:his:diva-8585 (URN)978-0-9696797-1-4 (ISBN)
Conference
19th International Conference on Composite Materials, July 28-August 2, 2013, Montréal, Canada
Available from: 2013-10-28 Created: 2013-10-28 Last updated: 2017-11-27Bibliographically approved
Alfredsson, K. S., Gawandi, A. A., Gillespie Jr., J. W., Carlsson, L. A. & Bogetti, T. A. (2012). Flexural analysis of discontinuous tile core sandwich structure. Composite structures, 94(5), 1524-1532
Open this publication in new window or tab >>Flexural analysis of discontinuous tile core sandwich structure
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2012 (English)In: Composite structures, ISSN 0263-8223, E-ISSN 1879-1085, Vol. 94, no 5, p. 1524-1532Article in journal (Refereed) Published
Abstract [en]

Three-point flexure loading of sandwich beams with a core consisting of discrete ceramic tiles (DTSS) is considered. The tile gaps may be bonded or unbonded (open gaps). The analysis utilizes a layer-wise beam theory approach. The general formulation for the displacements and stresses in the face sheets, face/core adhesive layer, and core is derived. Solutions for stresses and displacements of the beam constituents are obtained from finite element formulation based on analytical solution of the face sheet/tile unit cell. The approach is verified by comparison to stress results obtained from ordinary finite element analysis where each layer is modeled discretely. Effects of load introduction and support conditions on the effective flexural stiffness are examined. It is demonstrated that the face sheets experience substantial stress concentrations at the tile joint locations, especially if the gaps are unfilled. Analysis of beam compliance reveals sensitivity to details of load introduction and support conditions, especially when the span length becomes comparable to the tile length.

Place, publisher, year, edition, pages
Elsevier, 2012
Keywords
Sandwich, FEA, Compliance, Interlaminar, Stress
National Category
Engineering and Technology
Research subject
Technology
Identifiers
urn:nbn:se:his:diva-5961 (URN)10.1016/j.compstruct.2011.11.028 (DOI)000302980400005 ()2-s2.0-84858706650 (Scopus ID)
Available from: 2012-06-07 Created: 2012-06-07 Last updated: 2017-12-07Bibliographically approved
Alfredsson, K. S. & Stigh, U. (2012). Stability of beam-like fracture mechanics specimens. Engineering Fracture Mechanics, 89, 98-113
Open this publication in new window or tab >>Stability of beam-like fracture mechanics specimens
2012 (English)In: Engineering Fracture Mechanics, ISSN 0013-7944, E-ISSN 1873-7315, Vol. 89, p. 98-113Article in journal (Refereed) Published
Abstract [en]

Test specimens used to determine the interlaminar strength of composites as well as the strength of adhesive layers are known to occasionally suffer from instability. Thus, even though the experiments are performed under controlled load-point displacement, the experiments are terminated prematurely by unstable crack propagation. Often there exists a critical crack length which must be exceeded in order to obtain stable crack propagation. In this paper, a general method to assess the stability of beam-like fracture mechanics specimens is developed. Both systems subjected to a single load and the more general situation with several independent loads are treated. A simple formula is derived for the critical crack length for one-parameter loading. The only parameter necessary as input is the compliance of the un-cracked specimen. For the case of non-proportional loading, stability is determined by studying the eigenvalues of a symmetric matrix. Other findings quantified in the paper are the effect of orthotropy, the influence of a flexible interphase layer and the influence of the compliance of the loading device.

Place, publisher, year, edition, pages
Elsevier, 2012
Keywords
Stable crack growth, Unstable crack growth, J-integral, Delamination, Mixed mode fracture, Toughness testing
National Category
Mechanical Engineering
Research subject
Technology
Identifiers
urn:nbn:se:his:diva-6437 (URN)10.1016/j.engfracmech.2012.04.027 (DOI)000306535200008 ()2-s2.0-84862122861 (Scopus ID)
Available from: 2012-10-11 Created: 2012-10-04 Last updated: 2017-12-07Bibliographically approved
Alfredsson, K. S., Gawandi, A. A., Gillespie, J. W., Carlsson, L. A. & Bogetti, T. A. (2011). Stress analysis of axially and thermally loaded discontinuous tile core sandwich with and without adhesive filled core gaps. Composite structures, 93(7), 1621-1630
Open this publication in new window or tab >>Stress analysis of axially and thermally loaded discontinuous tile core sandwich with and without adhesive filled core gaps
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2011 (English)In: Composite structures, ISSN 0263-8223, E-ISSN 1879-1085, Vol. 93, no 7, p. 1621-1630Article in journal (Refereed) Published
Abstract [en]

An analytical study is performed to investigate the stress states in an axially and thermally loaded sandwich structure with a discontinuous ceramic tile core. General and simplified models are developed to determine stresses in the constituents of the sandwich structure with and without adhesive in the gaps between adjacent tiles. A general model that allows local bending of the face sheet and a simplified model which assumes uniform through-thickness stress distribution in the face sheets are developed. It is shown that the normal stress in the face sheet decreases when the gap is filled by adhesive, although the tile stress increases. The analytical model shows that normal and shear stresses at the face/core interface can be reduced by filling the gaps between tiles. Filled gaps also elevate the axial stiffness of the structure. Model results are verified by comparison to a previously developed analytical model and finite element analysis. (C) 2011 Elsevier Ltd. All rights reserved.

Place, publisher, year, edition, pages
Elsevier, 2011
Keywords
Sandwich, Adhesive, Stresses, Compliance, Interlaminar
National Category
Composite Science and Engineering
Research subject
Technology
Identifiers
urn:nbn:se:his:diva-5543 (URN)10.1016/j.compstruct.2011.01.015 (DOI)000289764300002 ()2-s2.0-79955473233 (Scopus ID)
Available from: 2012-03-09 Created: 2012-03-01 Last updated: 2017-12-07Bibliographically approved
Stigh, U., Alfredsson, S. K., Andersson, T., Biel, A., Carlberger, T. & Salomonsson, K. (2010). Some aspects of cohesive models and modelling with special application to strength of adhesive layers. International Journal of Fracture, 165(2), 149-162
Open this publication in new window or tab >>Some aspects of cohesive models and modelling with special application to strength of adhesive layers
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2010 (English)In: International Journal of Fracture, ISSN 0376-9429, E-ISSN 1573-2673, Vol. 165, no 2, p. 149-162Article in journal (Refereed) Published
Abstract [en]

An overview of recent development of cohesive modelling is given. Cohesive models are discussed in general and specifically for the modelling of adhesive layers. It is argued that most cohesive models model a material volume and not a surface. Detailed microscopic and mesomechanical studies of the fracture process of an engineering epoxy are discussed. These studies show how plasticity on the mesomechanical length scale contributes to the fracture energy in shear dominated load cases. Methods to measure cohesive laws are presented in a general setting. Conclusions and conjectures based on experimental and mesomechanical studies are presented. The influence of temperature and strain rate on the peak stress and fracture energy of cohesive laws indicates fundamentally different mechanisms responsible for these properties. Experiments and mesomechanical studies show that in-plane straining of an adhesive layer can give large contributions to the registered fracture energy. Finite element formulations including a method to incorporate this influence are discussed.

Place, publisher, year, edition, pages
Springer Netherlands, 2010
Keywords
Cohesive modelling, Measurement cohesive law, Fracture energy, Traction-separation, J-integral, Adhesive bond
National Category
Engineering and Technology
Research subject
Technology
Identifiers
urn:nbn:se:his:diva-4146 (URN)10.1007/s10704-010-9458-9 (DOI)000281680600003 ()2-s2.0-77956393829 (Scopus ID)
Available from: 2010-06-16 Created: 2010-06-16 Last updated: 2017-12-12Bibliographically approved
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