Change search
ReferencesLink to record
Permanent link

Direct link
Analysis of the compressive response of Nano Fibrillar Cellulose foams
KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.).
KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.).ORCID iD: 0000-0003-3611-2250
2015 (English)In: Mechanics of materials (Print), ISSN 0167-6636, Vol. 80, no Part A, 13-26 p.Article in journal (Refereed) Published
Abstract [en]

Nano Fibrillar Cellulose (NFC) is fast emerging as a biomaterial with promising applications, one of which is cellular foam. The inner structure of the foam can take various shapes and hierarchical micro-structures depending on the manufacturing parameters. The compressive response of foams developed from these materials is currently a primary criterion for the material development. In this work, we focus on the connection between the non-linear part of the response and the inner structure of the material. We study the effect of internal contact and its contribution to gradual stiffening in the energy absorbing region and accelerated stiffening in the densification region of the large strain compressive response. We use the finite element method in this study and discuss the applicability and efficiency of different modelling techniques by considering well defined geometries and available experimental data. The relative contribution of internal contact is singled out and mapped onto the overall compressive response of the material. The effect of initial non-straightness of the cell walls is studied through superposing differing percentages of the buckling modes on the initial geometry. The initial non-straightness is seen to have a significant effect for only strains up to 1%. The secant modulus measured at slightly higher strains of 4%, demonstrates lesser effect from the non-straightness of cell walls. The simulations capture the compressive response well into the densification regime and there is an order of magnitude agreement in between simulations and experiments. We observed that internal contact is crucial for capturing the trend of compressive response.

Place, publisher, year, edition, pages
2015. Vol. 80, no Part A, 13-26 p.
Keyword [en]
NFC foams, Internal contact, Voronoi structures, Foam densification, Effect of foam porosity
National Category
Materials Engineering
URN: urn:nbn:se:kth:diva-159620DOI: 10.1016/j.mechmat.2014.09.006ISI: 000347493100002ScopusID: 2-s2.0-84908214965OAI: diva2:787162
Swedish Research Council

QC 20150209

Available from: 2015-02-09 Created: 2015-02-05 Last updated: 2015-05-21Bibliographically approved
In thesis
1. Non-linear mechanics of nanocellulose foams
Open this publication in new window or tab >>Non-linear mechanics of nanocellulose foams
2015 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

There has been a growing interest in nano-fibrillar cellulose (NFC), which has been fuelled not merely by the advantages it presents in terms of strength to weight ratio and biodegradability, but also owing to the recent advances in production techniques. NFC foam is essentially a hierarchical structure, wherein nanofibrils account for the smallest scale, with the pores/cell walls forming the meso scale. A complete scanning of the mechanical property space would require understanding of the contribution of each of these scales in these foams. We aim to understand these scale relationships, eventually allowing for the possibility of tailoring material properties at scales of interest.

In paper A, we look at the applicability of two-dimensional random Voronoi structures in capturing the large-strain compressive response of these foams. We introduce internal contact, into the interiors of the cell walls, with the aim of capturing the densification regime. We then study the scaling effects associated with such a model, and, subsequently single out the contribution of internal contact on the overall compressive response. While it is seen that internal contact in random structures allow for capturing the densification regime, the model only provides an order of magnitude agreement with experimental data.

In paper B, we characterize the NFC foam based on both uni-axial and bi-axial experiments. One of the aims is to ascertain if there are effects of directionality to the stress-strain response. For the two considered porosities, we do not find any evidence for directionality in the response. We then proceed to make the assumption of isotropy, and adopt the well-known Ogden-Roxburgh “pseudo-elastic” model - originally proposed for incompressible rubber like materials - for the particular case of highly compressible foams. The model allows to capture the damage observed in unloading and also the significant residual strains.

Abstract [sv]

Det finns ett växande intresse för nanofibrillar cellulosa (NFC), inte bara på grund av goda egenskaper som hög styrka i förhållande till vikt samt nedbrytbarhet, utan även beroende på framsteg inom produktionstekniken. NFC-skum är i huvudsak en hierarkisk struktur, där nanofibriller representerar den minsta skalan och porer/cellväggar representerar meso-skalan. En fullständig karaktärisering av skummets mekaniska egenskaper kräver förståelse för bidraget från var och en av dessa skalor. Vårt mål är att förstå hur skalorna relaterar till varandra vilket öppnar för möjligheten att skräddarsy materialegenskaper för skalor av intresse.

I artikel A undersöker vi förmågan hos tvådimensionella slumpmässiga Voronoi strukturer att fånga spännings-töjningsbeteendet i tryck för dessa skum. I syfte att fånga förtätningseffekter hos spännings-töjningsbeteendet introducerar vi intern kontakt i det inre av cellväggarna. Vi studerar sedan skalningseffekterna associerade med en sådan modell, och isolerar bidraget från intern kontakt på skummets övergripande beteende i tryck. Även om det framgår att modellering av intern kontakt för slumpmässiga strukturer gör det möjligt att fånga förtätningsbeteendet ger modellen endast överensstämmelse inom en storleksordning mot experimentell data.

I artikel B karaktäriserar vi NFC skum med hjälp av enaxliga och biaxiella prov. Ett av syftena är att undersöka huruvida det finns ett riktningsberoende hos spännings-töjningsbeteendet. För de två undersökta porositeterna finner vi inga bevis för riktningskänslighet hos spännings-töjningsbeteendet. Vi fortsätter sedan med att göra ett antagande om isotropi och tillämpar den välkända pseudo-elastiska Ogden-Roxburgh modellen, från början utvecklad för inkompressibla gummiliknande material, för de starkt kompressibla skummen. Modellen gör det möjligt att fånga de skador och restspänningar som uppstår vid avlastning.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2015. 23 p.
TRITA-HFL. Report / Royal Institute of Technology, Solid Mechanics, ISSN 1654-1472 ; 0574
National Category
Other Mechanical Engineering
Research subject
Solid Mechanics
urn:nbn:se:kth:diva-166878 (URN)978-91-7595-563-6 (ISBN)
2015-05-28, Seminarierummet Hållfasthetslära, Teknikringen 8D, KTH, Stockholm, 13:00 (English)

QC 20150521

Available from: 2015-05-21 Created: 2015-05-21 Last updated: 2015-05-28Bibliographically approved

Open Access in DiVA

No full text

Other links

Publisher's full textScopus

Search in DiVA

By author/editor
Srinivasa, PrashanthKulachenko, Artem
By organisation
Solid Mechanics (Dept.)
In the same journal
Mechanics of materials (Print)
Materials Engineering

Search outside of DiVA

GoogleGoogle Scholar
The number of downloads is the sum of all downloads of full texts. It may include eg previous versions that are now no longer available

Altmetric score

Total: 66 hits
ReferencesLink to record
Permanent link

Direct link