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Shipsha, A., Hallström, S. & Burman, M. (2019). Effect of stacking sequence and bundle waviness in quasi-isotropic NCF composites subjected to compression. Composites Part B: Engineering
Open this publication in new window or tab >>Effect of stacking sequence and bundle waviness in quasi-isotropic NCF composites subjected to compression
2019 (English)In: Composites Part B: Engineering, ISSN 1359-8368, E-ISSN 1879-1069, ISSN 1359-8368Article in journal (Refereed) Accepted
Abstract [en]

The current study is focused on the compressive strength of composite materials containing non-crimp fabric (NCF) reinforcement, and how ply stacking sequence and fibre waviness influence onset and growth of damage in such materials. Experiments reveal significant effects from stacking sequence, both on the compressive strength as such, and on the underlying failure mechanisms. The fibre waviness also has a strong influence on the strength. Fibre kinking is seen before ultimate failure for all configurations but some of them also show local delamination prior to kinking. A finite element simulation methodology is developed and used for the studied cases. It handles local variations of fibre orientations by corresponding re-orientation of stiffness matrices at element level. The simulations provide good predictions of intra- and inter-laminar failure considering both in- plane and out-of-plane fibre bundle waviness. The model is further used in a parametric study of the influence from bundle waviness on the compressive strength.

Keywords
Fabrics/textiles, Strength, Finite element analysis (FEA), Mechanical testing
National Category
Composite Science and Engineering
Research subject
Aerospace Engineering
Identifiers
urn:nbn:se:kth:diva-262037 (URN)10.1016/j.compositesb.2019.107423 (DOI)2-s2.0-85072574900 (Scopus ID)
Note

QC 20191016

Available from: 2019-10-14 Created: 2019-10-14 Last updated: 2019-10-16Bibliographically approved
Stig, F. & Hallström, S. (2019). Effects of Crimp and Textile Architecture on the Stiffness and Strength Composites with 3D Reinforcement. Advances in Materials Science and Engineering, Article ID 8439530.
Open this publication in new window or tab >>Effects of Crimp and Textile Architecture on the Stiffness and Strength Composites with 3D Reinforcement
2019 (English)In: Advances in Materials Science and Engineering, ISSN 1687-8434, E-ISSN 1687-8442, article id 8439530Article in journal (Refereed) Published
Abstract [en]

The aim of this study is to experimentally determine how the weave architecture and yarn crimp affect the measured tensile stiffness and strength of composites containing 3D textile reinforcement. It is shown that both the stiffness and strength decrease nonlinearly with increasing 3D crimp. The ultimate strength of specimens containing nominally straight yarns and specimens containing crimped yarns can differ more than a factor of 3, and the stress causing onset of damage can be affected even more. Adding nominally straight stuffer yarns into a 3D-woven reinforcement significantly increases the fibre volume fraction, the stiffness, and the strength of the composite. However, since the stuffer yarns are virtually straight and thus stiffer than the warp yarns, they attract the load and reach their strength at relatively lower strain than the warp yarns. The reinforcement architecture varies between the surfaces and the interior of the studied textiles, which has corresponding influence on the local stiffness. The onset of failure is predicted satisfactorily accurate with relatively simple estimations. The ultimate strength is a result of extensive damage progression and thus more dubious to predict.

Place, publisher, year, edition, pages
HINDAWI LTD, 2019
National Category
Materials Engineering
Identifiers
urn:nbn:se:kth:diva-248111 (URN)10.1155/2019/8439530 (DOI)000460863300001 ()2-s2.0-85062791938 (Scopus ID)
Note

QC 20180426

Available from: 2019-04-26 Created: 2019-04-26 Last updated: 2019-04-26Bibliographically approved
Rajput, M. 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, 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, ISSN 1099-6362, 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.

Keywords
Non-crimp fabric, drop-weight rig, low-velocity impact, fractography, barely visible impact damage, X-ray micro-tomography, foam core
National Category
Aerospace Engineering
Research subject
Aerospace Engineering
Identifiers
urn:nbn:se:kth:diva-262026 (URN)10.1177/1099636219837133 (DOI)
Projects
Vinnova NFFP6 DAMTISS
Funder
Vinnova, 2013-01132
Note

QC 20191024

Available from: 2019-10-14 Created: 2019-10-14 Last updated: 2019-10-24Bibliographically approved
Stig, F. & Hallström, S. (2019). Extended framework for geometric modelling of textile architectures. Composite structures
Open this publication in new window or tab >>Extended framework for geometric modelling of textile architectures
2019 (English)In: Composite structures, ISSN 0263-8223, E-ISSN 1879-1085, ISSN ISSN 0263-8223Article in journal (Refereed) Submitted
Abstract [en]

Three dimensional (3D) textiles are finding their way into fibre reinforced composite applications, and for good reasons; they can eliminate the hazard of delamination and enable complex reinforcement shapes. There is, therefore, a need for engineering methods to simulate these advanced textile structures during the product development phase. This is many times challenging since the textile architecture is truly 3D and not built by layers as in conventional laminated composites. The overall approach is similar as in a method previously presented by the authors, but some steps are changed that enable modelling of textiles containing strongly curved yarns with very good geometric representation. That is essential for reliable simulations of all parts of the 3D reinforced composite materials, which could then be performed at close to authentic meso level resolution. The resulting textile geometries are very similar to the real materials they represent, both in terms of variation of yarn cross section area and shape along the length of the yarns. This is demonstrated by comparison of details between the real materials and their numerical counterparts.

Keywords
3D weave; 3D reinforcement; 3D textile; composite materials; geometric model; crimp
National Category
Composite Science and Engineering
Identifiers
urn:nbn:se:kth:diva-262060 (URN)
Available from: 2019-10-14 Created: 2019-10-14 Last updated: 2019-10-14
Khokar, N., Hallström, S. & Winberg, F. (2019). Increasing energy absorption and reliability of beams by improved architecture and web-flange junctions. In: Advanced Materials for Defense: 1st World Conference on Advanced Materials for Defense (AUXDEFENSE 2018). Paper presented at 1st World Conference on Advanced Materials for Defense, AUXDEFENSE 2018, Lisbon, Portugal, 3-4 September 2018 (pp. 114-119). Baech: Trans Tech Publications Ltd
Open this publication in new window or tab >>Increasing energy absorption and reliability of beams by improved architecture and web-flange junctions
2019 (English)In: Advanced Materials for Defense: 1st World Conference on Advanced Materials for Defense (AUXDEFENSE 2018), Baech: Trans Tech Publications Ltd , 2019, p. 114-119Conference paper, Published paper (Refereed)
Abstract [en]

Lightweight and strong composite material beams are increasingly sought to quickly, easily, and cost-effectively transport and setup a variety of constructions such as bridges, cabins/stores/shelters, vehicles etc. For structural beams produced as conventional laminated composite materials, their weak areas tend to occur at intersections such as web-flange junctions due to absence of fibres bridging the interconnections. This drawback can however be overcome with development of profiled 3D textile reinforcements having combination architectures and constituent web-flange parts inherently mutually interconnected through fibre interlacement. In addition to general strength improvement, beams containing such novel reinforcement architectures also show increased energy absorption capability due to the mutual web-flange integration at the junctions. An 'I' and a 'flanged-triangle' cross-section beams were produced by a novel non-conventional weaving method, using carbon fibres as reinforcement, and their energy absorption capabilities were tested. These beams respectively absorbed over 50% and 300% more energy per weight in bending, compared to metal counterparts. This paper presents some relevant aspects of these innovative beams.

Place, publisher, year, edition, pages
Baech: Trans Tech Publications Ltd, 2019
Series
Key Engineering Materials, ISSN 1662-9795 ; 812
Keywords
Combination-architecture, Energy absorption, Profiled beam, Web-flange junction, Architecture, Glass ceramics, Laminated composites, Network security, Reinforcement, Weaving, 3D textiles, Conventional weaving, Energy absorption capability, Strength improvements, Structural beams, Web-flange junctions, Flanges
National Category
Composite Science and Engineering
Identifiers
urn:nbn:se:kth:diva-262436 (URN)10.4028/www.scientific.net/KEM.812.114 (DOI)2-s2.0-85071597447 (Scopus ID)9783035713664 (ISBN)9783035733662 (ISBN)
Conference
1st World Conference on Advanced Materials for Defense, AUXDEFENSE 2018, Lisbon, Portugal, 3-4 September 2018
Note

QC 20191104

Available from: 2019-11-04 Created: 2019-11-04 Last updated: 2019-11-04Bibliographically approved
Khokar, N., Hallström, S. & Winberg, F. (2019). Increasing energy absorption and reliability of beams by improved web-flange junctions. Paper presented at AuxDefense conference, Lisbon, Portugal, 2018. Key Engineering Materials
Open this publication in new window or tab >>Increasing energy absorption and reliability of beams by improved web-flange junctions
2019 (English)In: Key Engineering Materials, ISSN 1013-9826, E-ISSN 1662-9795, ISSN 1013-9826Article in journal (Refereed) Accepted
Abstract [en]

Lightweight and strong composite material beams are increasingly sought to quickly, easily, and cost-effectively transport and setup a variety of constructions such as bridges, cabins/ stores/shelters, vehicles etc. For structural beams produced as conventional laminated composite materials, their weak areas tend to occur at intersections such as web-flange junctions due to absence of fibres bridging the interconnections. This drawback can however be overcome with development of profiled 3D textile reinforcements having combination architectures and constituent web-flange parts inherently mutually interconnected through fibre interlacement. In addition to general strength improvement, beams containing such novel reinforcement architectures also show increased energy absorption capability due to the mutual web-flange integration at the junctions. An ‘I’ and a ‘flanged- triangle’ cross-section beams were produced by a novel non-conventional weaving method, using carbon fibres as reinforcement, and their energy absorption capabilities were tested. These beams respectively absorbed over 50% and 300% more energy per weight in bending, compared to metal counterparts. This paper presents some relevant aspects of these innovative beams.

National Category
Composite Science and Engineering
Identifiers
urn:nbn:se:kth:diva-262053 (URN)
Conference
AuxDefense conference, Lisbon, Portugal, 2018
Available from: 2019-10-14 Created: 2019-10-14 Last updated: 2019-10-14
Oddy, C., Eckermann, T., Ekh, M., Fagerström, M., Hallström, S. & Stig, F. (2019). Predicting damage initiation in 3D fibre-reinforced composites - the case for strain-based criteria. Composite structures
Open this publication in new window or tab >>Predicting damage initiation in 3D fibre-reinforced composites - the case for strain-based criteria
Show others...
2019 (English)In: Composite structures, ISSN 0263-8223, E-ISSN 1879-1085, ISSN 0263-8223Article in journal (Refereed) Accepted
Abstract [en]

Three dimensional (3D) fibre-reinforced composites have shown weight effi- cient strength and stiffness characteristics as well as promising energy absorp- tion capabilities. In the considered class of 3D-reinforcement, vertical and horizontal weft yarns interlace warp yarns. The through-thickness reinforce- ments suppress delamination and allow for stable and progressive damage growth in a quasi-ductile manner.

With the ultimate goal of developing a homogenised computational model to predict how the material will deform and eventually fail under loading, this work proposes candidates for failure initiation criteria. It is shown that the extension of the LaRC05 stress-based failure criteria for unidirectional lami- nated composites, to this class of 3D-reinforced composite presents a number of challenges and leads to erroneous predictions. Analysing a mesoscale rep- resentative volume element does however indicate, that loading the 3D fibre- reinforced composite produces relatively uniform strain fields. The average strain fields of each material constituent are well predicted by an equivalent homogeneous material response. Strain based criteria inspired by LaRC05 are therefore proposed. The criteria are evaluated numerically for tensile, compressive and shear tests. Results show that their predictions for the simulated load cases are qualitatively more reasonable.

Keywords
3D-fibre reinforcement, finite element modelling, damage initiation
National Category
Composite Science and Engineering
Identifiers
urn:nbn:se:kth:diva-262056 (URN)10.1016/j.compstruct.2019.111336 (DOI)2-s2.0-85072912566 (Scopus ID)
Funder
Swedish Energy Agency, 43346-1
Note

QC 20191021

Available from: 2019-10-14 Created: 2019-10-14 Last updated: 2019-10-21Bibliographically approved
Ekermann, T. & Hallström, S. (2019). Pull-off tests of CFRP T-joints with conventional and 3D reinforced fillets. Composite structures, 223
Open this publication in new window or tab >>Pull-off tests of CFRP T-joints with conventional and 3D reinforced fillets
2019 (English)In: Composite structures, ISSN 0263-8223, E-ISSN 1879-1085, Vol. 223Article in journal (Refereed) Published
Abstract [en]

A study of T-joints made of CFRP prepreg is presented where the joints contain either conventional uni-directional (UD) fillets or fillets with three-dimensional (3D) woven reinforcement in the joint cavity. Both pristine and impacted specimens are tested experimentally in a pull-off load case. The T-joints with UD fillets are stronger but also show greater spread in strength than T-joints with 3D fillets. The higher strength is attributed to the UD fillets' ability to deform transversely to their length direction and efficiently adapt to the T-joint cavity before curing. The 3D fillets do not admit the same level of transverse shape adaptability and if their cross sections do not fit the geometry of the T-joint cavity sufficiently well, local stress concentrations could emerge that reduce the strength of the T-joint. The UD fillets on the other hand are believed to be sensitive to manufacturing flaws causing the greater spread in strength. That in turn is attributed to a lack of crack-arresting capability in the UD fillet. The 3D fillets however have excellent crack-arresting properties due to their multidirectional fibre architecture. With a few exceptions the impact damages did not significantly affect the strength of the T-joints tested in this study.

Place, publisher, year, edition, pages
ELSEVIER SCI LTD, 2019
Keywords
3D weave, 3D textile, Damage tolerance, Impact damage, Thermal contraction, Residual stress
National Category
Applied Mechanics
Identifiers
urn:nbn:se:kth:diva-255398 (URN)10.1016/j.compstruct.2019.110893 (DOI)000473320600029 ()2-s2.0-85065800924 (Scopus ID)
Note

QC 20190814

Available from: 2019-08-14 Created: 2019-08-14 Last updated: 2019-08-14Bibliographically approved
Akbarpour, S. & Hallström, S. (2019). Reinforcement around holes in composite materials by use of patched metal inserts. Composite structures, 225, Article ID 111084.
Open this publication in new window or tab >>Reinforcement around holes in composite materials by use of patched metal inserts
2019 (English)In: Composite structures, ISSN 0263-8223, E-ISSN 1879-1085, Vol. 225, article id 111084Article in journal (Refereed) Published
Abstract [en]

Metal inserts are sometimes used to improve the load carrying capacity of bolted joints in composite materials. In this paper a new concept is introduced where inserts are built during composite manufacturing by integrating stacked metal patches at locations where holes are to be made after consolidation. Initial tests and a parameter study enable more informed design, and specimens with improved stacked inserts are then produced and tested. The specimens with inserts show up to 60% strength improvement in pin-loaded tests. In addition to the experimental work, finite element analysis is performed to investigate the stress fields and the failure mechanisms. The model indicates that the singular stresses at the multi-material corner points are governing for the strength and give indications of the failure mechanisms. Some basic analytical estimates are also presented.

Place, publisher, year, edition, pages
Elsevier, 2019
Keywords
Hybrid joint, Bearing strength, Insert, Stacked, Patch
National Category
Composite Science and Engineering
Identifiers
urn:nbn:se:kth:diva-257428 (URN)10.1016/j.compstruct.2019.111084 (DOI)000480330400044 ()2-s2.0-85067507808 (Scopus ID)
Note

QC 20190902

Available from: 2019-09-02 Created: 2019-09-02 Last updated: 2019-09-02Bibliographically approved
Horberg, E., Nyman, T., Åkermo, M. & Hallström, S. (2019). Thickness effect on spring-in of prepreg composite L-profiles - An experimental study. Composite structures, 209, 499-507
Open this publication in new window or tab >>Thickness effect on spring-in of prepreg composite L-profiles - An experimental study
2019 (English)In: Composite structures, ISSN 0263-8223, E-ISSN 1879-1085, Vol. 209, p. 499-507Article in journal (Refereed) Published
Abstract [en]

This paper presents the results and analysis of an experimental study of laminate thickness effects on the spring-in and shape distortion of thermoset composite L profiles. The primary objective is to achieve a broader understanding of how shape distortion is affected by laminate bending stiffness and part thickness of L-shaped laminates whose thickness varies between 1 and 12 mm. The larger thicknesses in particular have not received much attention in previous research. This work further aims at distinguishing the pure (geometrical) thickness effect from that of the coupled laminate bending stiffness by comparing laminates with different lay-ups. The work is performed on test specimens subjected to both a standard cure cycle and post-cure heat treatment at elevated temperatures. In parallel, finite element (FE) analysis is performed to evaluate if variation in the bending stiffness or the laminate thickness affects the predicted spring-in angle. The results clearly show spring-in dependence on laminate thickness and bending stiffness, whereas this dependence is not well predicted by the FE approaches. It is concluded that both effects exist and that shape distortions are more strongly related to bending stiffness than to laminate thickness.

Place, publisher, year, edition, pages
ELSEVIER SCI LTD, 2019
Keywords
Process simulation, Cure behaviour, Prepreg, Thermal properties
National Category
Composite Science and Engineering
Identifiers
urn:nbn:se:kth:diva-241304 (URN)10.1016/j.compstruct.2018.10.090 (DOI)000454690700043 ()2-s2.0-85056208383 (Scopus ID)
Note

QC 20190125

Available from: 2019-01-25 Created: 2019-01-25 Last updated: 2019-01-25Bibliographically approved
Organisations
Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0002-9207-3404

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