Developments in Ceramic Materials Research

Modeling of Thermal Transport in Ceramics Matrix Composites 205
The heat flux concentration is 25% greater than the in-plane heat flux (light green)
indicating that sudden change in flow direction has been dictated by fibre tow undulations and
this is how the heat is expected to flow through the composite fabric across the dominant heat
flow x-direction. An overall flow contour summary is given in Figure 32 and Figure 33 for inplane
and through-thickness heat flow scenarios respectively for the full composite RVE Unit
Cell (except in Figures 32(e) and 33(e) where matrix is removed). The arrows depict the
prevailing heat flux direction in each case.
It is imperative that the final results obtained bare similarity to the experimental data and
this has been shown in Table 8 with limited input information for the FE analysis as far as
constituent material properties are concerned. The input values taken for the modified matrix
region was calculated from Equation 14 using rule of mixtures as the matrix and air in voids
and cracks, comprising the bulk porosity, do have isotropic thermal conductivity. Hence an
input value of k = 18.72 has been used based on the values of k and k mp
m p given in Table 9.
Table 8. Values of Thermal Conductivity of the Constituent Materials
Material k (W m -1 K -1 ) Volume Fraction (%)
Carbon Fibre Transverse 7
50
Carbon Fibre Longitudinal 70
Carbon Matrix 28 39
Air (porosity) 0.001 11
Table 9. FE analyses compared with Manufacturer’s Thermal Conductivity Data
(W.m -1 K -1 )
Experimental Data Numerical Analysis (Steady-State)
In-plane 28 25.656 (+ 8%)
Through-Thickness 8 9.79 (- 22%)
5. COMPUTATIONAL ASPECTS
It has been highlighted earlier that with the increase in the geometric complexity of the
CMCs, the requirement of the computing resources has risen. This has been reiterated by the
current modelling effort with 8-harness satin weave geometry, apart from the modelling
challenge of the HITCO materials’ fibre tow weave pattern which alone has been massive
enough. It can be reckoned that with the multiplication of the Unit Cell (each containing
around a Million elements) across the lamina and then the laminate, demand for
computational power increases drastically. Special arrangement is therefore required for
conducting analysis of such large FE models.
Earlier DLR-XT Unit Cell had been managed within a single-CPU desktop machine
operating on Windows XP with 80 Gigabytes storage space and 512 Megabytes physical
memory. It has also been observed how the machine had been swapping its hard disk for need
of fast storage; as much as 1.8 Gigabytes at times, almost 4 times the physical memory. In
that case, the element count had not exceeded 200,000 whereas in the present case this figure