Size effects in short fibre reinforced composites

Abstract

The present paper is concerned with the analysis of size effects in short fibre reinforced composites. The microstructure of such composites often represents the first hierarchy level of a bioinspired material. For modelling fibre cracking as well as debonding between fibre and matrix material, a fully three-dimensional cohesive zone model is applied. It is shown that this model indeed captures the size effect associated with material failure of a single fibre. Furthermore, this scaling effect strongly depends on the shape and orientation of the assumed preexisting crack. For this reason, a two-dimensional description can usually only predict the size effect qualitatively. Based on the aforementioned findings, a representative volume element (RVE) containing ceramic fibres embedded within a polymer matrix is considered. Similar to the single fibre, the RVE also shows a pronounced size effect. However, the underlying physical process is significantly more complex. More explicitly, the size effect of the RVE is a superposition of that related to the isolated fibres as well as of that induced by debonding of the fibres from the matrix material. For estimating the different effects, a perfect bond is also modelled.

On the interaction between different size effects in fibre reinforced PMMA: Towards composites with optimised fracture behaviour

“…A centre crack, as assumed in the one-dimensional model used in [4,5], usually leads to an overestimation of the flaw tolerance. Furthermore, and in contrast to the results reported in [4,5], the more realistic finite element simulations performed in [8] predicted that the fracture energy of the composite might not decrease with size, but can also increase due to a changing failure mechanism. The present investigation extends the findings reported in [8] with respect to two different aspects:…”

“…The approximations made by Gao et al (e.g., one-dimensional model, no debonding of the fibres, type of the pre-existing cracks, etc.) were partly justified in [8] through finite element simulations. In line with [4,5], it was shown in [8] that a single fibre reaches its theoretical strength, if its diameter is smaller than a certain threshold (the respective representative volume element considered in [8] is shown in Figure 1).…”

Towards bio-inspired engineering materials: Modeling and simulation of the mechanical behavior of hierarchical bovine dental structure

“…The change of failure mode leads to a sharp drop in the fracture energy, since much energy is dissipated during debonding along the fiber walls. Both strength and energy are linearly depending on the fiber length due to the stress transfer along the fiber matrix interface as has been reported in [15,16]. It must be noted that even though the stress drops almost to zero abruptly for the breaking mode, tearing the RVE completely apart happens at very high strains.…”

“…The cohesive zone model is widely used in particular for fiber reinforced composites, for fiber breaking and debonding, see e.g. [43,15,44,45].…”

“…In this work, the mechanical behavior of the representative volume element (RVE) 1 is simulated representing the microstructure of the first hierarchy level based on Scheider et al [15,16].…”