JEC COMPOSITES MAGAZINE - Issue #82 - July 2013 - 60

3D fabrics
Comparison of calculated properties in warp and weft directions indicates that the failure strain, which is dominated by the
brittle fibres, is similar in both directions. For the strength in
both fabric directions, the Fweft/Fwarp ratio would be expected to be 1.03, reflecting the ratio of fibre volume fractions for 7
layers in weft direction and 6 layers in warp direction, if all yarns
were perfectly straight. The actual ratio, Fweft/Fwarp = 0.76, is
similar to the ratio of fibre volume fractions, Vfweft/Vfwarp =
0.74, for 5 layers in weft direction and 6 layers in warp direction.
This implies that the two crimped surface layers in weft direction do not significantly affect the composite strength.

Conclusions
A systematic approach was presented to assess the effect of local
geometrical variations on composites processing and mechanical properties. The motivation was to highlight the geometrical
features essential for accurate modelling of 3D woven composites and quantify the relationship between geometry and
performance. For the example of a 3D orthogonal weave reinforcement, the geometry of the composites was characterised
in detail by μ-CT image analysis. The geometrical models were
generated in TexGen in a semi-automated manner with local
geometrical refinements. Based on these models, CFD simulation of impregnating flow and static mechanical analysis were
carried out for prediction of in-plane permeability and in-plane
tensile properties, respectively. With inclusion of local variations in geometrical modelling, the predictions of permeability
improved significantly compared with the experimental data.
The prediction of mechanical strength also revealed different
failure mechanisms in warp and weft directions, as there are
local geometrical differences in crimp, binder configuration and
yarn cross-sectional shapes. n
Fig. 8: Comparison of experimental and simulated stress-strain curves of
the orthogonal reinforced composites, Vf = 55 %; A: tensile load in warp
direction; B: tensile load in weft direction

More information:
www.nottingham.ac.uk/engineering-rg/materialsmechanicsandstructures/pcrg/polymercompositesresearchgroup.aspx
Contact:
Andreas.Endruweit@nottingham.ac.uk
Acknowledgements
This work was supported by the Engineering and Physical Sciences
Research Council [grant number: EP/IO33513/1], through the EPSRC
Centre for Innovative Manufacturing in Composites.

Fig. 9: SEM images of fracture surfaces under tension in warp (left) and
weft (right) direction

tensile strength can be attributed mainly to the realistic models
with a high level of geometrical detail. As pointed out by
Mouritz [1], local fibre misalignment because of the presence
of the binder may give rise to local axial shear stresses and may
cause plastic strain resulting in irreversible matrix deformation.
Further studies are required to investigate in more detail the
relation between composite strength at the unit cell scale and
fabric architecture.

60 jec composites magazine / No82 July 2013

References
[1] Mouritz, A.P., Three-dimensional (3D) fibre reinforcements for composites, in Composite reinforcements for optimum performance, P. Boisse,
Editor 2011, Woodhead Publishing: UK. p. 157-199.
[2] Long, A.C. and L.P. Brown, Modelling the geometry of textile reinforcements for composites: TexGen, in Composite reinforcements for
optimum performance. P. Boisse, Editor 2011, Woodhead Publishing Ltd.
[4] Weisstein, E.W., «Superellipse.» From MathWorld--A Wolfram Web
Resource. http://mathworld.wolfram.com/Superellipse.html
[4] Gebart, B.R., Permeability of Unidirectional Reinforcements for RTM.
Journal of Composite Materials, 1992. 26(8): p. 1100-1133.
[5] Endruweit, A., P. McGregor, A.C. Long, and M.S. Johnson, Influence of
the fabric architecture on the variations in experimentally determined
in-plane permeability values. Composites Science and Technology,
2006. 66(11-12): p. 1778-1792.
[6] Maurin, R., P. Davies, N. Baral, and C. Baley, Transverse Properties
of Carbon Fibres by Nano-Indentation and Micro-mechanics. Applied
Composite Materials, 2008. 15(2): p. 61-73.
[7] Ruijter, W., Analysis of mechanical properties of woven textile composite as functions of textile geometry, PhD dissertation, 2008, School
of M3, University of Nottingham: Nottingham, United Kingdom.

http://www.nottingham.ac.uk/engineering-rg/materialsmechanicsandstructures/pcrg/polymercompositesresearchgroup.aspx http://mathworld.wolfram.com/Superellipse.html

JEC COMPOSITES MAGAZINE - Issue #82 - July 2013

Table of Contents for the Digital Edition of JEC COMPOSITES MAGAZINE - Issue #82 - July 2013