The mechanical and physical properties such as elastic modulus(E)and coefficient of thermal expansion( CTE)of fibers are strongly orientation dependent, and usually exhibit significant disf- erences in magnitude along the fiber axis and transverse to it. The high-temperature strength of some commercial silicon carbide fibers is compared in Figure 6. 4. It can be noted that the fiber tains high strength to fairly high temperatures; for example, NLP 101 fiber retains a strength of 500 MPa at 1300C, which is comparable to the room-temperature tensile strength of some high-strength, low-alloy steels In addition to the synthetic fibers and whiskers, numerous low-cost, discontinuous fillers ave been used in composites to conserve precious matrix materials at little expense to their engineering properties. These fillers include mica, sand, clay, talc, rice husk ash, fly ash, natural fibers(e.g, lingo-cellulosic fibers), recycled glass, and many others, including environmentally conscious biomorphic ceramics based on silicon carbide and silicon dioxide obtained from pyrolysis of natural wood. These various fillers and reinforcements permit a range of composite microstructures to be created that have a wide range of strength, stiffness, wear resistance, and other characteristics. Figure 6-5 shows the porous structure of pyrolyzed wood that has been used as a preform for impregnation with molten metals to create ceramic- or metal-matrix composites Interface Interfaces in composites are regions of finite dimensions at the boundary between the fiber and the matrix where compositional and structural discontinuities can occur over distances varying from an atomic monolayer to over five orders of magnitude in thickness. Composite fabrication processes create interfaces between inherently dissimilar materials(e. g, ceramic fibers and a 0200400600800100012001400 FIGURE 6-4 High-temperature strength of some SiC fibers plotted as applied stress versus test mperature.(B S. Mitchell, An Introduction to Materials Engineering and Science for Chemical Materials Engineers, Wiley Interscience, Hoboken, N), 2004) 06 MATERIALS PROCESSING AND MANUFACTURING SCIENCEThe mechanical and physical properties such as elastic modulus (E) and coefficient of thermal expansion (CTE) of fibers are strongly orientation dependent, and usually exhibit significant disf￾ferences in magnitude along the fiber axis and transverse to it. The high-temperature strength of some commercial silicon carbide fibers is compared in Figure 6.4. It can be noted that the fiber retains high strength to fairly high temperatures; for example, NLP 101 fiber retains a strength of 500 MPa at 1300~ which is comparable to the room-temperature tensile strength of some high-strength, low-alloy steels. In addition to the synthetic fibers and whiskers, numerous low-cost, discontinuous fillers have been used in composites to conserve precious matrix materials at little expense to their engineering properties. These fillers include mica, sand, clay, talc, rice husk ash, fly ash, natural fibers (e.g., lingo-cellulosic fibers), recycled glass, and many others, including environmentally conscious biomorphic ceramics based on silicon carbide and silicon dioxide obtained from pyrolysis of natural wood. These various fillers and reinforcements permit a range of composite microstructures to be created that have a wide range of strength, stiffness, wear resistance, and other characteristics. Figure 6-5 shows the porous structure of pyrolyzed wood that has been used as a preform for impregnation with molten metals to create ceramic- or metal-matrix composites. Interface Interfaces in composites are regions of finite dimensions at the boundary between the fiber and the matrix where compositional and structural discontinuities can occur over distances varying from an atomic monolayer to over five orders of magnitude in thickness. Composite fabrication processes create interfaces between inherently dissimilar materials (e.g., ceramic fibers and 1"6I9 1.4 r"- 1.2 13.. (.9 "6" 1 (/) (/) m 0.8 (/) "o a. 0.6 Q. < 0.4 ~ i 0 o NLP 101 9 NLM 102 9 N LM 202 I 200 I I I I I I 400 600 800 1000 1200 1400 Temperature (~ FIGURE 6-4 High-temperature strength of some SiC fibers plotted as applied stress versus test temperature. (B. S. Mitchell, An Introduction to Materials Engineering and Science for Chemical and Materials Engineers, Wiley Interscience, Hoboken, NJ, 2004). 406 MATERIALS PROCESSING AND MANUFACTURING SCIENCE