Natural cellulose based material are promising materials because of their excellent mechanical strength/weight performance. Crystalline cellulose can be as strong as steel with a yield modulus around 110-220 GPa. Moreover it is an abundant natural material which is a great answer to the needs in sustainable and biodegradable material. Currently, many efforts are being taken to estimate the properties of nano-cellulosic composites from those of their constituents, mainly by means of analytical methods such as Halpin-Tsai or Hashin. These methods provide good predictions of the overall stiffness; however, they are limited to elastic behaviour and to a uniform distribution of the particles in the composite.
In this paper, we present a modelling approach that is more versatile and that enables to also consider particle agglomeration and non-elastic behaviour such as particle debonding and fracture. A representative volume element (RVE) of the nano-cellulosic composites is examined by means of the finite element method for this purpose. An estimate of the stiffness in a certain direction can be determined by submitting the RVE to a uniform displacement and by evaluating the resulting average traction in this direction. An axisymmetric RVE is studied, consisting of a single, cylindrical particle, representing the cellulose reinforcement, and the surrounding matrix. Moreover, a third phase, commonly denoted as interphase, is considered in between the particle and the matrix. The characteristics of this phase are known to lie between the ones of the particle and the matrix. Because of the nano-size of the particles, the volume fraction of the interphase can become higher than the one of the particles, underlining the importance of this phase for the mechanical behaviour of the composite.
The model allows to study the influence of the composite characteristics, such as volume fraction and aspect ratio of the fibres and the mechanical properties of fibres and matrix, on the overall composite behaviour. Emphasis is placed on the interphase in order to get a better understanding of its effect on the overall behaviour. In the future, stress concentration and debonding will also be investigated to determinate weak points of such a nano-cellulosic composites. The model will be validated by comparing model predictions with experimental data from literature and possibly own tests.
Keywords: FEM, Nano-cellulosic composites, inclusion, interphase, overall stiffness
Authors
Caudoux R.
Department of Infrastructure and Environment, Glasgow University
De Borst K.
Department of Infrastructure and Environment, Glasgow University
Rahimi S.
Department of Infrastructure and Environment, Glasgow University
Login to download the PDF