Fracture behavior, fibrous

Baskaran, S., and Halloran, J.W. (1993), Fibrous monolithic ceramics II, Flexural strength and fracture behavior of the silicon carbide/graphite system , J. Am. Ceram. Soc., 76(9) 2217-2224. 

Numerous studies have been made of the mechanical properties of fibrous composites these include recently published papers on impact properties by Izod (1,2, 3,4) and Charpy (5,6) and drop weight (7) tests. We reported the Charpy impact fracture behavior of various glass-polyester composites regarding the effects of temperature (8,9,10), specimen size (8), and fiber orientation (10). This paper describes the effects of the tough-brittle transition in the impact behavior of glass-polyester composites which occurs with a variation of temperature and specimen size. 

The cellular micro- and macrostructure pseudomorphs with naturally grown wood tissue show a complex mechanical behavior, which is governed hy the unique arrangement of cells. In some aspects, the fracture behavior in biomorphous ceramics is similar to that of fibrous monolithic ceramics, as well as that of laminate composite ceramics showing a noncatastrophic stress-strain behavior. A pronounced anisotropy of fracture behavior is a characteristic feature which depends on the loading conditions with respect to the orientation of the cell-packing structure [357]. 

Zimmermann, J. W, Hilmas, G. E., Fahrenholtz, W. G. (2009). Thermal shock resistance and fracture behavior of ZrB -based fibrous monolith ceramics. Journal of the American Ceramic Society, 92,161-166. doi 10.1111/j. 1551-2916.2008.02824.x. 

Figure 5 presents the results of tensile tests for the HPC/OSL blends prepared by solvent-casting and extrusion. All of the fabrication methods result in a tremendous increase in modulus up to a lignin content of ca. 15 wt.%. This can be attributed to the Tg elevation of the amorphous HPC/OSL phase leading to increasingly glassy response. Of particular interest is the tensile strength of these materials. As is shown, there is essentially no improvement in this parameter for the solvent cast blends, but a tremendous increase is observed for the injection molded blend. Qualitatively, this behavior is best modeled by the presence of oriented chains, or mesophase superstructure, dispersed in an amorphous matrix comprised of the compatible HPC/OSL component. The presence of this fibrous structure in the injection molded samples is confirmed by SEM analysis of the freeze-fracture surface (Figure 6). This structure is not present in the solvent cast blends, although evidence of globular domains remain in both of these blends appearing somewhat more coalesced in the pyridine cast material.

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