Strength and Fracture Toughness

Ciba 914C epoxy (high temp resistant) 20 0.25 5 

Source Reprinted with permission from Hancox NL, Mayer RM, Design Data for Reinforced Plastics—A Guide for Engineers and Designers, Chapman Hall, London, 118, 1994. Copyright 1994, Springer. 

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Finally, the nature of the crystalline microstmcture, ie, crystal size and morphology and the textural relationship among the crystals and glass, is the key to many mechanical and optical properties, including transparency/opacity, strength and fracture toughness, and machinabiUty. These microstmctures can be quite complex and often are distinct from conventional ceramic microstmctures (6). 

Hardness and solubiUty for other carbides make TiC an important component of siatered cemented carbides. Although the addition of TiC or WTiC2 to WC—Co alloys imparts crater wear resistance, it also reduces the transverse mpture strength and fracture toughness of these alloys. Therefore, the amount of TiC or WTiC2 added to WC—Co alloys for steel machining is kept to a minimum, typically no greater than 10 wt %. The TiC-based cermets, on the other hand, may contain 30—85 wt % TiC. 

Figure 22 Influence of fiber content on flexural strength and fracture toughness of (O) softwood-cement composites and ( ) hardwood-cement composites (air-cured) [78].

Table 14 Influence of Humidity on Flexural Strength and Fracture Toughness of Cellulose Fiber Reinforced Cements [78]...

Flexural strength and fracture toughness are clinically more significant than compressive strength. The flexural strength of a glass-ionomer cement can reach 39 MPa after 24 hours (Pearson Atkinson, 1991) which is a much higher value than that attained by any dental silicate cement. 

Table 5.16. Strength and fracture toughness of glass polyalkenoate filling materials Seed Wilson, 1980 Prosser et al., 1984 Lloyd Mitchell, 1984 Goldman, 1985 Prosser, Powis Wilson, 1986 Lloyd Adamson, 1987)...

These low values for flexural strength and fracture toughness compared with the values for composite resins and dental amalgams make the glass-ionomer cement less suitable than these materials in high-stress situations. 

Harris B., Beaumont P.W.R. and Moncunill de Ferran E. (1971). Strength and fracture toughness of carbon fiber polyester composites. J. Mater. Sci. 6, 238-251. 

Hing P. and Groves G.W. (1972). The strength and fracture toughness of poly-crystalline magnesium oxide containing metallic particles and fibers. J. Mater. Sci. 7, 427-434. 

Atkins A.G, and Mai Y.W. (1976). Effect of water and ice on strength and fracture toughness of intermittently bonded boron-epoxy composites J. Mater. Sci. II, 2297-2306. 

Mai Y.W. (1983). Controlled interfacial bonding on the strength and fracture toughness of Kevlar and carbon fiber composites. J. Mater. Sci. Lett. 2, 723 725,... 

Mechanical Properties. Mechanical properties obtained on the cured resins included tensile strength and fracture toughness. Tensile tests were run on an Instron model 1122 Universal Tester with a crosshead speed of 0.02 /minute. Tests were run on dry and saturated samples in air. Fracture toughness (K ) values have been obtained using a MTS 610 Materials Testing System at 0.02 /minute at ambient and elevated temperatures in air. The compact tensile specimens tested were 0.5 x 0.5 x 0.125 in dimension. Mechanical properties data are based on the results from four or more tests run at each condition. 

How do fibers and whiskers increase the strength and fracture toughness of a composite material First, fibers have great strength along the fiber axis because most of the chemical bonds are aligned in that direction. Second, there are several... 

Especially strength and fracture toughness are essential for structural applications. Therefore, great efforts are made to optimise all preconditions for a reproducible production of reliable Si3N4 ceramics with high strength... 

Coarser microstructure with increasing temperature, pose size increases /) formation pronounced, coarse structure, low strength and fracture toughness (KIC)... 

Ceramics with fine SiC and Si3N4 grains can also directly produced from amorphous precursors with no sintering additives, however they are not dense after crystallisation and therefore have relatively low strength and fracture toughness [213, 609-611]. 

Diglycidyl ether of ethoxylated resorcinol (DGER), a resorcinol-based epoxy monomer, can be cured with various epoxy curing agents to yield a balance of flexibility, low viscosity, and fast cure capability.12 The molecular flexibility of DGER is claimed to improve the impact strength and fracture toughness of the cured epoxy system. These flexibilized... 

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