was pseudoplastic (Fig.7.7d).It has also been observed that matrices with domain textures, which mainly develop in pitch containing aliphatic hydrogen,have a higher propensity to form intramatrix and interface cracks(Figueiras et al.,1995). The presence of primary QI particles in coal-tar pitches restricts the development of mesophase during pyrolysis,producing matrices with a smaller size of optical texture,a lower amount of cracks and stronger fiber-matrix bonding(Figueiras et al.,1998).Figure 7.8 illustrates how the QI affects the mechanical properties and failure mechanism of the material.For an undensified composite prepared from a pitch with 11 wt%of QI(Fig.7.8a) the flexural strength is higher than for a composite prepared from a free QI pitch(Fig.7.8b). The increase in the strength of the composites containing QI is accompanied by a change in the mode of failure.Composite from QI free pitch shows a classical multiple fracture mode (a) 500 CC-11 400 (edW) 40μm 300 200 100 0 4 Strain (x10-3mm.mm-1) (b) 500 CC-o 400 10um 300 200 100 0 0 2 3 4 5 6 Strain (x10-3mm.mm-1) Figure 7.8 Stress-strain curves and fracture surfaces for(a)composite from a pitch with 11 wt%of QI and (b)composite from a QI free pitch. 2003 Taylor Franciswas pseudoplastic (Fig. 7.7d). It has also been observed that matrices with domain textures, which mainly develop in pitch containing aliphatic hydrogen, have a higher propensity to form intramatrix and interface cracks (Figueiras et al., 1995). The presence of primary QI particles in coal-tar pitches restricts the development of mesophase during pyrolysis, producing matrices with a smaller size of optical texture, a lower amount of cracks and stronger fiber–matrix bonding (Figueiras et al., 1998). Figure 7.8 illustrates how the QI affects the mechanical properties and failure mechanism of the material. For an undensified composite prepared from a pitch with 11 wt % of QI (Fig. 7.8a) the flexural strength is higher than for a composite prepared from a free QI pitch (Fig. 7.8b). The increase in the strength of the composites containing QI is accompanied by a change in the mode of failure. Composite from QI free pitch shows a classical multiple fracture mode Figure 7.8 Stress–strain curves and fracture surfaces for (a) composite from a pitch with 11 wt % of QI and (b) composite from a QI free pitch. 40 mm CC-11 10 mm CC-0 40 mm CC-11 Stress (MPa) 40 µm CC-11 10 mm CC-0 Stress (MPa) 10 µ CC-0 Strain (× 10–3 mm.mm–1) 0 100 200 300 400 500 0123456 Strain (× 10–3 mm.mm–1) 0 100 200 300 400 500 01 23 4 56 (a) (b) © 2003 Taylor & Francis