Factorial design, processing, characterization and microstructure analysis of PIP-based C/SiC composites

Abstract

Polymer impregnation and pyrolysis (PIP) process-based C/SiC composites are fabricated using the in-house synthesized methyl-polycarbosilane (PCS). Two-level factorial design matrix is employed to carry out experiments to study the effect of four factors on flexural strength of the composite. Total sixteen sets of composite samples are fabricated. Response table, normal probability plot, ANOVA and regression analysis are carried out to determine the statistical significant factors. Composite density ($\rho$), fibre volume fraction ($V_{\mathrm{f}}$) and pyrolysis temperature (T) are found to be statistically significant, while softening point (SP) of the PCS and interaction of these four factors are found insignificant. Higher levels of the density and $V_{\mathrm{f} }$ have shown positive effect, while the pyrolysis temperature has negative effect on the flexural strength of the composites. Flexural strength was found to be in the range of 374–592 MPa depending on the process parameters. The mechanical behaviour of the composites at different process conditions was explained with the help of their microstructures.

Appendices

Appendix 1

Procedure for estimating fibre volume fraction in the composite sample

Required number tows of 6K carbon fibre are wound to get composite of length (L, length of the each composite sample is fixed to 250 mm), width (W, width of the composite samples varied between 5 and 10 mm) and thickness (t, thickness of the composite sample was 0.9–1.7 mm). Typical scheme of UD composite is shown as figure 10. Fibre volume fraction in the composite samples was estimated using the following formula:

$$\begin{aligned} {V}_\mathrm{f} =\frac{{n{*} {Wt}_{1}} /{\rho }_\mathrm{carbon \,fiber}}{{L {*} W {*} t}} \end{aligned}$$

where

• n = number of carbon fibre tows wound in the graphite fixture slot and number of tows present in composite sample,

• ${Wt}_{1}$ = average weight of a single carbon fibre tow of 250 mm length (g),

• ${\rho }_\mathrm{carbon\, fiber}$ = the density of carbon fibre in g $\hbox {cm}^{-3}$, as per the supplier and manufacturer, density of the T300 carbon fibres is 1.76 g $\hbox {cm}^{-3}$,

• L = length of the composite (kept fixed,equal to 250 mm),

• W = width of the composite,

• t = thickness of the composite.

The following steps were followed to estimate the fibre volume fraction.

• Step 1: Average weight of a single 6K carbon fibre tow of 250 mm length was determined. A long tow of 25 m length was cut and weighed on a digital balance with least count of 10 mg. The weight of 25 m long tow was divided by 100 to get weight of a 250 mm long tow. The weight of 250 mm long, 6 K carbon fibre tow $({ Wt}_{1}$) was found to be 0.088 g.

• Step 2: Dimensions of the composite samples was measured using the digital vernier calipers.

• Step 3: Using the above formula, the following typical calculations were made to estimate $V_{\mathrm{f}}$ in the final composite samples of length 250 mm. Some typical estimated values are given in the below table.

n	N * ${Wt}_{1 }$(g)	Fibre volume ($\hbox {cm}^{3}$)	W(cm)	t (cm)	$V_{\mathrm{f}}$
9	0.792	0.45	0.5	0.09	0.4
17	1.496	0.85	0.5	0.17	0.4
18	1.584	0.90	1.0	0.09	0.4
27	2.376	1.35	1.0	0.09	0.6
34	2.992	1.70	1.0	0.17	0.4
51	4.488	2.55	1.0	0.17	0.6