Developments in Ceramic Materials Research

196
M. A. Sheik
HITCO composite architecture comprises of a laminate with 10-12 laminae of 8-harness
satin weave of Carbon-Carbon fabric stacked up to form the final composite laminate with
Graphite matrix. The schematic with a single lamina considered as the Unit Cell in Figure 22
has been the starting point for modelling, with various other feature details that have been
closely examined being mentioned during the course of RVE Unit Cell modelling.
This RVE Unit Cell model has been formed with due correlation with the two
micrographs showing the weave formation from the top and the side edges captured, as
shown sketched in Figure 22.
The sketch also shows schematically how simultaneously these features are to be
captured in modelling. It is evident from the edge micrograph in Figure 20(b) that a single
lamina can not be isolated from the laminate stack due to the present nesting of the weave,
overlapping and encroachment of the top and bottom laminae on to the middle laminae,
resulting in a very compact intertwined fibre tow structure. As a start the nesting factor, more
geometrically random than repeated, has been ignored in modelling in order to avoid double
complexity with the weave.
Figure 22 shows the schematic view of the Unit Cell that is created with the help of
micrographs of the HITCO CMC composite sections through the XY and XZ planes shown in
Figure 20(a) and 20(b) respectively, coupled with the generic architecture details of the 8
harness satin weave. Bright areas in Figure 20(a) denote Carbon fibre tow of the warp and
dark areas denote segments of the Carbon fill fibre bundles in the composite. From within
these features a 3D Unit Cell is identified, which on replicating itself across in three spatial
directions produces the macro-structure of the CMC. A brief but specific outline of the
modelling undertaken with ABAQUS/CAE is given here.
Standard modelling procedure in ABAQUS/CAE has been sequentially detailed earlier
for the DLR-XT Unit Cell. It was built using 4 quarter parts that assemble together to form
the Unit Cell with fibre tows and matrix together. In contrast, the HITCO Unit Cell has been
created as a single part since this RVE is the smallest unique geometric entity that cannot be
further simplified or divided. For HITCO, first the fibre tows, warp and fill, are separately
created and then the matrix region is ‘filled’ around it in the cuboidal envelope of the 3D Unit
Cell outline.
Figure 22. Schematic drawing of the 8 harness satin weave material single lamina.