Strength and Fracture

When semiconductor compounds are formed, the covalent bond is provided by p electrons. In this case the atom of element A (Ga, In) supplies one electron and atom of element (As, Sb) supplies three electrons. 

The less energy gap for the semiconductor compounds the less is bulk modulus and the larger mean-square amplitude. 

The bulk modulus decreases and mean-square vibration amplitude increases when going from GaP to InSb. The band gap Eg decreases at the same time. We see that the strength of the interatomic bonding reduces with increasing the sum Ha + Hs, where Ha and wb are the principal quantum numbers of the outer shells for the a and elements, respectively. The sum jia + ub equals for C, Si, and Ge to 4, 6, and 8, respectively. It changes from 7 for the semiconductor GaP to 9 for InSb. 

Fracture is one possible failure mode of materials under mechanical load. It occurs when a crack grows, eventually entirely through a machine component, causing it to fail. In brittle fracture the crack is sharp, and its geometry causes a concentration of stress at the tip. In a continuum description of the soUd and in the limit 

Griffith set up an energy balance equation, comparing the amount of elastic energy released by crack extension with the amount of surface energy needed to generate the newly exposed crack surface. The Griffith criterion for britde fracture is expressed as 

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Using flaw visuahzation system data the strength and fracture mechanics estimations are carried out in accordance with defect assessment regulatory procedure M-02-91 [5]. Recently, the additions had been included in the procedure, concerning interpretation of expert flaw visualization sysf em data, computer modelling, residual stresses, in-site properties of metal, methods of fracture analysis. 

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. 

Liu Y-N, Li M, Gu Y, ZhangX, Zhao J, Li Q, et al. The interfacial strength and fracture characteristics of ethanol and polymer modified carbon nanotube fibers in their epoxy composites. Carbon. 2013 Feb 52(0) 550-8. 

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]. 

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. 

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