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Publikationer (10 of 27) Visa alla publikationer
Costa, S., Bru, T., Olsson, R. & Portugal, A. (2019). Improvement and validation of a physically based model for the shear and transverse crushing of orthotropic composites. Journal of composite materials, 53(12), 1681-1691
Öppna denna publikation i ny flik eller fönster >>Improvement and validation of a physically based model for the shear and transverse crushing of orthotropic composites
2019 (Engelska)Ingår i: Journal of composite materials, ISSN 0021-9983, E-ISSN 1530-793X, Vol. 53, nr 12, s. 1681-1691Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

This paper details a complete crush model for composite materials with focus on shear dominated crushing under a three-dimensional stress state. The damage evolution laws and final failure strain conditions are based on data extracted from shear experiments. The main advantages of the current model include the following: no need to measure the fracture toughness in shear and transverse compression, mesh objectivity without the need for a regular mesh and finite element characteristic length, a pressure dependency of the nonlinear shear response, accounting for load reversal and some orthotropic effects (making the model suitable for noncrimp fabric composites). The model is validated against a range of relevant experiments, namely a through-the-thickness compression specimen and a flat crush coupon with the fibres oriented at 45° and 90° to the load. Damage growth mechanisms, orientation of the fracture plane, nonlinear evolution of Poisson's ratio and energy absorption are accurately predicted.

Nyckelord
Crushing, damage mechanics, friction, finite element analysis
Nationell ämneskategori
Teknik och teknologier
Identifikatorer
urn:nbn:se:ri:diva-36301 (URN)10.1177/0021998318807964 (DOI)
Tillgänglig från: 2018-11-15 Skapad: 2018-11-15 Senast uppdaterad: 2019-06-28Bibliografiskt granskad
Bru, T., Asp, L., Olsson, R. & Vyas, G. (2018). Biaxial transverse compression testing for a fibre reinforced polymer material. In: : . Paper presented at 18th European Conference on Composite Materials ECCM-18.
Öppna denna publikation i ny flik eller fönster >>Biaxial transverse compression testing for a fibre reinforced polymer material
2018 (Engelska)Konferensbidrag, Publicerat paper (Refereegranskat)
Abstract [en]

Unidirectional laminates have been tested under uniaxial transverse compression and under biaxialtransverse compression. Failure occurred by shear in an inclined failure plane parallel to the fibres.The transverse shear response of the material on the failure plane was evaluated from the tests. In thebiaxial tests, the failure load was considerably higher than in the uniaxial tests. For a given transverseshear strain the transverse shear stress was also higher in the case of biaxial compression. It is alsoshown that using waisted specimens instead of prismatic specimens does not seem to bring noticeablebenefits for through-thickness uniaxial compression tests. The experimental results presented here areimportant input to the development and the validation of damage models of fibre reinforced polymermaterials accounting for the matrix nonlinear response in shear and compression.

Nyckelord
Polymer matrix composites, biaxial testing
Nationell ämneskategori
Teknik och teknologier
Identifikatorer
urn:nbn:se:ri:diva-36302 (URN)
Konferens
18th European Conference on Composite Materials ECCM-18
Tillgänglig från: 2018-11-15 Skapad: 2018-11-15 Senast uppdaterad: 2019-06-28Bibliografiskt granskad
Farajzadeh Khosroshahi, S., Olsson, R., Wysocki, M., Zaccariotto, M. & Galvanetto, U. (2018). Response of a helmet liner under biaxial loading. Polymer testing, 72, 110-114
Öppna denna publikation i ny flik eller fönster >>Response of a helmet liner under biaxial loading
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2018 (Engelska)Ingår i: Polymer testing, ISSN 0142-9418, E-ISSN 1873-2348, Vol. 72, s. 110-114Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

Helmets are the most effective protective item for motorcyclists. The liner of the helmet is the part of the helmet which dissipates most of the impact energy and mitigates the risk of head injuries. It has been proposed that the helmet test standards should include assessment of the helmets for oblique impacts that is not currently addressed in the standards. A conventional uniaxial compression test method is still used for characterization of the helmet liner material. However, compressive tests of EPS foams provide reliable results for normal loading on EPS, but do not provide a realistic result for oblique impacts. Therefore, we carried out experimental tests to measure the response of EPS foams, which are commonly used for helmet liners, under biaxial loading. The result of our experiments show that the shear response of EPS foams is a function of axial compression, and increasing the axial strain leads to increased shear stiffness, and thus higher levels of shear stress. We also showed that including shear-stiffening of EPS in the FE assessment of helmets may change the headform rotational acceleration by 25%. Therefore, such behavior of EPS foams should be included in FE analysis of helmets in the case of oblique impacts for a more realistic assessment of their performance.

Nyckelord
Biaxial mechanical response, EPS, Helmet, Oblique impact, Compression testing, Safety devices, Shear stress, Compressive tests, Experimental test, Mechanical response, Reliable results, Rotational acceleration, Uni-axial compression tests, Accident prevention
Nationell ämneskategori
Naturvetenskap
Identifikatorer
urn:nbn:se:ri:diva-35573 (URN)10.1016/j.polymertesting.2018.10.012 (DOI)2-s2.0-85054874584 (Scopus ID)
Anmärkning

 Funding details: FP7-PEOPLE-2013-ITN-608092, REA, Research Executive Agency; Funding text: The research leading to these results has received funding from the People Programme (Marie Sklodowska Curie Actions) of the European Union’s Seventh Framework FP7/2007-2013/under REA grant agreement n° [ FP7-PEOPLE-2013-ITN-608092 ] and from the ECCELLENZA programme of the CARIPARO foundation under the REDIPhE project.

Tillgänglig från: 2018-11-08 Skapad: 2018-11-08 Senast uppdaterad: 2019-06-28Bibliografiskt granskad
Costa, S., Portugal, A., Olsson, R., Vyas, G. & Bru, T. (2018). Validation of a novel model for the compressive response of FRP: numerical simulation. In: : . Paper presented at 21st International Conference on Composite Materials ICCM-21.
Öppna denna publikation i ny flik eller fönster >>Validation of a novel model for the compressive response of FRP: numerical simulation
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2018 (Engelska)Konferensbidrag, Publicerat paper (Refereegranskat)
Abstract [en]

A progressive damage model for matrix compression is complemented with matrix tension in a physically based manner. The interaction of damage mechanisms undergoes a preliminary validation using single elements. The crushing response is validated with two different flat specimens with the fibres oriented transversely and at 45 degrees to the load. The model combines friction with damage to model the shear response accurately, which is necessary for reliable crush simulations. The behaviour in tension is history dependent, i.e. the model accounts for the stiffness reduction and strength to carry load in tension when previously damaged occurs in compression.The validation is performed against different tests showing the reliability of the model for different fibre orientation, specimen geometry and multiaxial loading scenarios. The crush response is well captured as well as the geometry and location of the different damage mechanisms.

Nyckelord
Crushing, Damage modes, Friction, Damage mechanics
Nationell ämneskategori
Teknik och teknologier
Identifikatorer
urn:nbn:se:ri:diva-36298 (URN)2-s2.0-85053166997 (Scopus ID)
Konferens
21st International Conference on Composite Materials ICCM-21
Tillgänglig från: 2018-11-15 Skapad: 2018-11-15 Senast uppdaterad: 2019-08-15Bibliografiskt granskad
Bru, T., Waldenström, P., Gutkin, R., Olsson, R. & Vyas, G. M. (2017). Development of a test method for evaluating the crushing behaviour of unidirectional laminates. Journal of composite materials, 51(29), 4041-4051
Öppna denna publikation i ny flik eller fönster >>Development of a test method for evaluating the crushing behaviour of unidirectional laminates
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2017 (Engelska)Ingår i: Journal of composite materials, ISSN 0021-9983, E-ISSN 1530-793X, Vol. 51, nr 29, s. 4041-4051Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

More fundamental test methods are needed to assist the development of physically based and truly predictive simulation tools for composite materials under crash conditions. In this paper, a unidirectional flat specimen that can be used to validate the predicted behaviour from a simulation to the physical behaviour in the experiment is developed. A systematic experimental investigation is conducted to evaluate the influence of the trigger geometry on the crushing response by selecting two trigger types and different trigger angles. For longitudinal crushing, the traditional bevel trigger leads to out-of-plane failure by splaying with a limited amount of in-plane fracture, while the proposed trigger achieves a high amount of compressive fragmentation failure. For transverse crushing, the symmetry of the proposed new trigger improves the specimen stability during the crushing process. It is also observed that the weft threads of the unidirectional fabric reinforcement used for the tests have a strong influence on the longitudinal crushing response. The boundary conditions of the test and the information on the specimen failure gleaned from video recordings and microscopic inspections are discussed in order to facilitate a future correlation with modelling results. © 2017, © The Author(s) 2017.

Nyckelord
Crushing, fractography, mechanical testing, non-crimp fabric composite, Fracture, Fracture mechanics, Video recording, Experimental investigations, Flat specimen, Non-crimp fabric composites, Out-of-plane failures, Physically based, Predictive simulations, Trigger angle, Unidirectional fabrics
Nationell ämneskategori
Naturvetenskap
Identifikatorer
urn:nbn:se:ri:diva-33053 (URN)10.1177/0021998317697811 (DOI)2-s2.0-85037057642 (Scopus ID)
Tillgänglig från: 2018-01-11 Skapad: 2018-01-11 Senast uppdaterad: 2019-06-28Bibliografiskt granskad
McElroy, M., Jackson, W., Olsson, R., Hellström, P., Tsampas, S. & Pankow, M. (2017). Interaction of delaminations and matrix cracks in a CFRP plate, Part I: A test method for model validation. Composites. Part A, Applied science and manufacturing, 103, 314-326
Öppna denna publikation i ny flik eller fönster >>Interaction of delaminations and matrix cracks in a CFRP plate, Part I: A test method for model validation
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2017 (Engelska)Ingår i: Composites. Part A, Applied science and manufacturing, ISSN 1359-835X, E-ISSN 1878-5840, Vol. 103, s. 314-326Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

Isolating and observing the damage mechanisms associated with low-velocity impact in composites using traditional experiments can be challenging, due to damage process complexity and high strain rates. In this work, a new test method is presented that provides a means to study, in detail, the interaction of common impact damage mechanisms, namely delamination, matrix cracking, and delamination-migration, in a context less challenging than a real impact event. Carbon fiber reinforced polymer specimens containing a thin insert in one region were loaded in a biaxial-bending state of deformation. As a result, three-dimensional damage processes, involving delaminations at no more than three different interfaces that interact with one another via transverse matrix cracks, were observed and documented using ultrasonic testing and X-ray computed tomography. The data generated by the test is intended for use in numerical model validation. Simulations of this test are included in Part II of this paper.

Nyckelord
A. Laminates, B. Delamination, B. Transverse cracking, D. Mechanical testing, Carbon, Carbon fiber reinforced plastics, Computerized tomography, Cracks, Failure (mechanical), Fiber reinforced plastics, Laminates, Mechanical testing, Strain rate, Ultrasonic testing, Carbon fiber reinforced polymer, Damage mechanism, High strain rates, Low velocity impact, Model validation, Transverse cracking, Transverse matrix cracks, X-ray computed tomography, Delamination
Nationell ämneskategori
Naturvetenskap
Identifikatorer
urn:nbn:se:ri:diva-33052 (URN)10.1016/j.compositesa.2017.09.011 (DOI)2-s2.0-85030465676 (Scopus ID)
Anmärkning

Funding details: Langley Research Center

Tillgänglig från: 2018-01-11 Skapad: 2018-01-11 Senast uppdaterad: 2019-06-28Bibliografiskt granskad
Costa, S., Gutkin, R. & Olsson, R. (2017). Mesh objective implementation of a fibre kinking model for damage growth with friction. Composite structures, 168, 384-391
Öppna denna publikation i ny flik eller fönster >>Mesh objective implementation of a fibre kinking model for damage growth with friction
2017 (Engelska)Ingår i: Composite structures, ISSN 0263-8223, E-ISSN 1879-1085, Vol. 168, s. 384-391Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

A newly developed physically based model for the longitudinal response of laminated fibre-reinforced composites during compressive damage growth is implemented in a Finite Element (FE) software. It is a mesoscale model able to capture the physics of kink-band formation by shear instability, the influence of the matrix in supporting the fibres and the rotation of the fibres during compression, resulting in more abrupt failure for smaller misalignments. The fibre kinking response is obtained by solving simultaneously for stress equilibrium and strain compatibility in an FE framework. Strain softening creates pathological sensitivity when the mesh is refined. To make the model mesh objective, a methodology based on scaling the strain with the kink-band width is developed. The FE implementation of the current model is detailed with focus on mesh objectivity, and generalized to irregular meshes. The results show that the current model can be used to predict the whole kinking response in a 3D framework and thus account for the correct energy dissipation.

Nyckelord
Crushing, Damage mechanics, Fibre kinking, Friction, Mesh objectivity, Energy dissipation, Fiber reinforced plastics, Fibers, Laminated composites, Mesh generation, Fibre reinforced composites, Kink band formations, Longitudinal response, Meso-scale modeling, Physically based modeling, Strain compatibility, Finite element method
Nationell ämneskategori
Naturvetenskap
Identifikatorer
urn:nbn:se:ri:diva-29316 (URN)10.1016/j.compstruct.2017.02.057 (DOI)2-s2.0-85013781749 (Scopus ID)
Tillgänglig från: 2017-05-12 Skapad: 2017-05-12 Senast uppdaterad: 2019-06-28Bibliografiskt granskad
Bru, T., Olsson, R., Gutkin, R. & Vyas, G. M. (2017). Use of the Iosipescu test for the identification of shear damage evolution laws of an orthotropic composite. Composite structures, 174, 319-328
Öppna denna publikation i ny flik eller fönster >>Use of the Iosipescu test for the identification of shear damage evolution laws of an orthotropic composite
2017 (Engelska)Ingår i: Composite structures, ISSN 0263-8223, E-ISSN 1879-1085, Vol. 174, s. 319-328Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

The experimental evaluation of the shear response of fibre-reinforced plies is a requirement for accurate material models predicting progressive damage. In the first part of the paper, the quality of the Iosipescu shear test is investigated with full-field strain measurements and finite element analyses. In the second part, the in-plane and through-thickness shear response of an orthotropic carbon/epoxy uni-weave non-crimp fabric composite are compared, and the stress–strain curves used as input for two continuum damage mechanics models. Both models were able to predict accurately the nonlinear shear behaviour of the material. The model parameters and the damage evolution laws could easily be extracted from cyclic Iosipescu tests.

Nyckelord
Continuum damage mechanics CDM, Fabrics/textiles, Finite element analysis (FEA), Shear testing, Thermosetting resin, Carbon, Continuum damage mechanics, Damage detection, Elasticity, Thermosets, Continuum damage mechanics model, Experimental evaluation, Full-field strain measurement, Non-crimp fabric composites, Orthotropic composites, Through-thickness shears, Finite element method
Nationell ämneskategori
Naturvetenskap
Identifikatorer
urn:nbn:se:ri:diva-30816 (URN)10.1016/j.compstruct.2017.04.068 (DOI)2-s2.0-85018974882 (Scopus ID)
Anmärkning

 Funding details: 34181-1/2, Energimyndigheten; Funding text: The funding for this research from the Swedish Energy Agency (Energimyndigheten), project number 34181-1/2, is gratefully acknowledged.

Tillgänglig från: 2017-09-06 Skapad: 2017-09-06 Senast uppdaterad: 2019-06-28Bibliografiskt granskad
Bru, T., Portugal, A., Olsson, R., Vyas, G. & Costas, S. (2017). Validation of a novel model for the compressive response of FRP:experiments with different fibre orientations. In: : . Paper presented at 21st International Conference on Composite Materials Xi’an, 20-25th August 2017.
Öppna denna publikation i ny flik eller fönster >>Validation of a novel model for the compressive response of FRP:experiments with different fibre orientations
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2017 (Engelska)Konferensbidrag, Publicerat paper (Refereegranskat)
Abstract [en]

Crush tests have been performed on flat unidirectional non-crimp fabric (NCF) coupons with differentfibre orientations as part of the validation of a ply-based damage model for crash. The fibre off-axisangle with respect to the crushing direction ranged from 0º to 90°. The results of the tests indicate thatthe crush stress remains unchanged for off-axis angles between 0° and 15°. The failure mode in thesespecimens was out-of-plane kinking. For 20° and 25° off-axis angles the crush stress dropped 20% andevidence of out-of-plane kinking were harder to find. For 45° off-axis angle a network of matrixcracks develops in the specimen and for 90° off-axis angle a brittle shear failure is observed. It issuggested that the out-of-plane kinking is promoted because of the natural waviness of NCF materialsand that the high in-plane shear stress generated from 20-25° off-axis loading results in a transitionfrom out-of-plane kinking to in-plane kinking. These hypotheses need, however, to be verified by anextended failure analysis of the crush specimens.

Nyckelord
Crushing, Mechanical testing, Fibre kinking, Fractography, Non-crimp fabric
Nationell ämneskategori
Teknik och teknologier
Identifikatorer
urn:nbn:se:ri:diva-36300 (URN)2-s2.0-85053103484 (Scopus ID)
Konferens
21st International Conference on Composite Materials Xi’an, 20-25th August 2017
Tillgänglig från: 2018-11-15 Skapad: 2018-11-15 Senast uppdaterad: 2019-08-14Bibliografiskt granskad
Grauers, L., Olsson, R. & Gutkin, R. (2014). Energy absorption and damage mechanisms in progressive crushing of corrugated NCF laminates: Fractographic analysis (ed.). Composite structures, 110(1), 110-117
Öppna denna publikation i ny flik eller fönster >>Energy absorption and damage mechanisms in progressive crushing of corrugated NCF laminates: Fractographic analysis
2014 (Engelska)Ingår i: Composite structures, ISSN 0263-8223, E-ISSN 1879-1085, Vol. 110, nr 1, s. 110-117Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

To develop reliable and physically based models for the crash behaviour of composite laminates, a thorough understanding of the failure mechanisms is crucial. Compression tests of corrugated Non-Crimp Fabric (NCF) laminates, made of carbon fibre unidirectional (UD) fabric with a [0/90]3S stacking sequence and epoxy, have been performed to study the energy absorbing damage mechanisms. Samples from the specimens have been studied with optical microscopy and Scanning Electron Microscopy (SEM) to identify the mechanisms involved in the crushing process. The specimens tested fail partly in bending and partly in pure compression with a mode I delamination separating these two regions. In the region failing in pure compression, the main damage mechanisms are kink band formation and matrix cracking of transverse bundles, whereas in the part failing in bending mixed mode delaminations, intralaminar shear fracture of axial bundles and kink band formation through parts of bundles are identified. © 2013 Elsevier Ltd.

Nyckelord
Crush, Fabrics/textiles, Fractography, Fracture, Fracture mechanics
Nationell ämneskategori
Materialteknik
Identifikatorer
urn:nbn:se:ri:diva-13148 (URN)10.1016/j.compstruct.2013.11.001 (DOI)
Tillgänglig från: 2016-09-22 Skapad: 2016-09-22 Senast uppdaterad: 2019-06-28Bibliografiskt granskad
Identifikatorer
ORCID-id: ORCID iD iconorcid.org/0000-0002-2627-3280

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