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In-plane Compressive Response of Sandwich Panels
KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures. (Lättkonstruktioner)
2009 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The high specific bending stiffness of sandwich structures can with advantage be used in vehicles to reduce their weight and thereby potentially also their fuel consumption. However, the structure must not only meet the in-service requirements but also provide sufficient protection of the vehicle passengers in a crash situation. The in-plane compressive response of sandwich panels is investigated in this thesis, with the objective to develop a methodology capable of determining if the structural response is likely to be favourable in an energy absorption perspective. Experiments were conducted to identify possible initial failure and collapse modes. The initial failure modes of sandwich panels compressed quasi-statically in the in-plane direction were identified as global buckling, local buckling (wrinkling) and face sheet fracture. Global buckling promotes continued folding of the structure when compressed beyond failure initiation. Face sheet fracture and wrinkling can promote collapse in the form of unstable debond crack growth, stable end-crushing or ductile in-plane shear collapse. Both the unstable debond crack propagation and the stable end-crushing are related to debond crack propagation, whereas the ductile in-plane shear mode is related to microbuckling of the face sheets.

The collapse behaviour of sandwich configurations initially failing due to wrinkling or face sheet fracture was investigated, using a finite element model. The model was used to determine if the panels were likely to collapse in unstable debond propagation or in a more stable end-crushing mode, promoting high energy absorption. The collapse behaviour is mainly governed by the relation between the fracture toughness of the core and the bending stiffness and strength of the face sheets. The model was successfully used to design sandwich panels for different collapse behaviour. The proposed method could therefore be used in the design process of sandwich panels subjected to in-plane compressive loads.During a crash situation the accelerations on passengers must be kept below life threatening levels. The extreme peak loads in the structure must therefore be limited. This can be achieved by different kind of triggering features.Panels with either chamfered face sheets or with grooves on the loaded edges were investigated in this thesis. The peak load was reduced with panels incorporating either of the two triggering features. Another positive effect was that the plateau load following failure initiation was increased by the triggers. This clearly illustrates that triggers can be used to promote favourable response in sandwich panels.

Vehicles are harmful to the environment not only during in-serve use, but during their entire life-cycle. By use of renewable materials the impact on the environment can be reduced. The in-plane compressive response of bio-based sandwich panels was therefore investigated. Panels with hemp fibre laminates showed potential for high energy absorption and panels with a balsa wood core behaved particular well. The ductile in-plane shear collapse mode of these panels resulted in the highest energy absorption of all investigated sandwich configurations.

 

Place, publisher, year, edition, pages
Stockholm: KTH , 2009. , xi, 27 p.
Series
Trita-AVE, ISSN 1651-7660 ; 2009:67
Keyword [en]
Sandwich, Finite Element Analysis (FEA), Fracture, In-plane compression
National Category
Other Materials Engineering Condensed Matter Physics
Identifiers
URN: urn:nbn:se:kth:diva-11160ISBN: 978-91-7415-447-4 (print)OAI: oai:DiVA.org:kth-11160DiVA: diva2:236633
Public defence
2009-10-26, Sal F3, Lindstedtsvägen 26, Stockholm, 10:15 (English)
Opponent
Supervisors
Note
QC 20100728Available from: 2009-10-06 Created: 2009-09-23 Last updated: 2010-07-28Bibliographically approved
List of papers
1. In-plane compression of sandwich panels with debonds
Open this publication in new window or tab >>In-plane compression of sandwich panels with debonds
2010 (English)In: Composite structures, ISSN 0263-8223, E-ISSN 1879-1085, Vol. 92, no 2, 532-540 p.Article in journal (Refereed) Published
Abstract [en]

The post failure behaviour of in-plane compression loaded sandwich panels is studied by considering the structural response of such panels with symmetrically located edge debonds. A parametric finite element model is used to determine the influence of different material and geometrical properties on the failure progression, i.e. after initiation of damage. The investigated failure modes are buckling of the debonded face sheets, debond propagation and face sheet failure. The postbuckling failure mode is mainly determined by the fracture toughness of the core and the bending stiffness and strength of the face sheets. The presented approach and results can be used to determine how sandwich panels should be constituted, or not, to promote damage progression favourable for efficient energy absorption during in-plane crushing. The prolonged damage propagation is very complex as it is strongly non-linear and depends on a combination of stiffness, strength and geometry of the constituent materials.

Place, publisher, year, edition, pages
Oxford, UK: Elsevier, 2010
Keyword
Sandwich; Fracture; Finite element analysis (FEA)
National Category
Composite Science and Engineering
Identifiers
urn:nbn:se:kth:diva-11155 (URN)10.1016/j.compstruct.2009.08.039 (DOI)000271561100038 ()2-s2.0-70349801487 (Scopus ID)
Note

QC 20100728

Available from: 2009-09-23 Created: 2009-09-23 Last updated: 2017-12-13Bibliographically approved
2. Energy absorption of SMC/balsa sandwich panels with geometrical triggering features
Open this publication in new window or tab >>Energy absorption of SMC/balsa sandwich panels with geometrical triggering features
2010 (English)In: Composite structures, ISSN 0263-8223, E-ISSN 1879-1085, Vol. 92, no 11, 2676-2684 p.Article in journal (Refereed) Published
Abstract [en]

The influence of triggering topologies on the peak load and energy absorption of sandwich panels loaded in in-plane compression is investigated. Sandwich panels with different geometrical triggering features are manufactured and tested experimentally. The damage initiation in panels with grooves is investigated using finite element models. As expected the investigated triggering features reduce the extreme load peaks. A less expected result is that the plateau load following peak load tends to be higher for panels with triggering features. Both results are favourable for the crash performance of panels in vehicle applications. For panels containing no or few grooves the peak load seems to be governed by principles of fracture mechanics while initial failure in panels with a higher number of grooves appears to be controlled by the average stress.

Place, publisher, year, edition, pages
Oxford, UK: Elsevier, 2010
Keyword
Sandwich; Energy absorption; Edgewise compression; Damage triggering
National Category
Applied Mechanics Composite Science and Engineering Other Materials Engineering
Identifiers
urn:nbn:se:kth:diva-11156 (URN)10.1016/j.compstruct.2010.03.018 (DOI)000279301300007 ()2-s2.0-77953356942 (Scopus ID)
Note

QC 20150729

Available from: 2009-09-23 Created: 2009-09-23 Last updated: 2017-12-13Bibliographically approved
3. Design for various collapse behaviour of sandwich panels subject to in-plane compression
Open this publication in new window or tab >>Design for various collapse behaviour of sandwich panels subject to in-plane compression
(English)Manuscript (preprint) (Other academic)
Abstract [en]

Sandwich panels were designed for different collapse behaviour when compressed in the in-plane direction, by altering the material and geometrical properties. An approach previously developed by the authors was used in the design process of the sandwich panels. Panels with CSM glass fibre face sheets of two different thicknesses and two different core materials were studied both numerically and experimentally. The collapse mode of sandwich panels is mainly dependant on the relation between the fracture toughness of the core material and the bending stiffness and strength of the face sheets. By altering properties like the fracture toughness of the core material or the face sheet thickness, the failure mode could be altered. It was shown that the adopted approach can be used in design of sandwich panels for different failure behaviour.

National Category
Composite Science and Engineering
Identifiers
urn:nbn:se:kth:diva-11157 (URN)
Note

QC 20100728

Available from: 2009-09-23 Created: 2009-09-23 Last updated: 2016-03-16Bibliographically approved
4. Energy absorption of sandwich panels containing bio-based materials
Open this publication in new window or tab >>Energy absorption of sandwich panels containing bio-based materials
2010 (English)Manuscript (preprint) (Other academic)
National Category
Applied Mechanics Composite Science and Engineering Other Materials Engineering
Identifiers
urn:nbn:se:kth:diva-11158 (URN)
Note

QC 20100728

Available from: 2009-09-23 Created: 2009-09-23 Last updated: 2016-05-16Bibliographically approved
5. Energy Absorption of Sandwich Panels Subjected to In-plane Loads
Open this publication in new window or tab >>Energy Absorption of Sandwich Panels Subjected to In-plane Loads
2006 (English)In: 8th Biennial ASME Conference on EngineeringSystems Design and Analysis, Torino, Italy, 4-7 July, 2006: Volume 3: Dynamic Systems and Controls, Symposium on Design and Analysis of Advanced Structures, and Tribology, 2006, 739-747 p.Conference paper, Published paper (Refereed)
Abstract [en]

Theenergy absorption mechanisms of sandwich panels subjected to in-plane compressionare studied. Quasi-static experiments are performed and analysed in orderto support the development of a modelling strategy for failureinitiation and propagation in sandwich panels. The test specimens consistof balsa wood cores and glass-fibre reinforced polyester faces. Duringcompression of a tested panel, the displacement field on oneouter face is measured using a digital speckle photography (DSP)equipment. The absorbed energy is related to debonding, delamination andcrushing of the face sheets and crushing of the core.At initial failure, the load drops dramatically and is thenrelatively constant during continued compression. The energy per unit lengthnecessary for propagation of the damage is considerably lower thanfor damage initiation. Assuming that the damage propagation is uniformthrough the thickness of the panels a simple model ofdamage growth is developed. Calibration of the model is howeverdubious due to the large scatter in the experimental results.The studied material shows damage mechanisms favourable for efficient energyabsorption but the behaviour is far from being optimal.

Keyword
Computer simulation; Delamination; Energy absorption; Loads (forces); Mathematical models; Structural
National Category
Composite Science and Engineering
Identifiers
urn:nbn:se:kth:diva-11152 (URN)10.1115/ESDA2006-95771 (DOI)000249558200084 ()2-s2.0-33845767479 (Scopus ID)0-7918-4250-9 (ISBN)
Conference
8th Biennial ASME Conference on Engineering Systems Design and Analysis, Torino, Italy, 2006
Note

QC 20100728

Available from: 2009-09-23 Created: 2009-09-23 Last updated: 2016-05-16Bibliographically approved

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