Metal fracture toughness

ASTM E399-90, "Plane Strain Fracture Toughness of Metallic Materials," MnnualBook ofMSTM Standards, ASTM PubHcations, Philadelphia, 1993. 

Directed Oxidation of a Molten Metal. Directed oxidation of a molten metal or the Lanxide process (45,68,91) involves the reaction of a molten metal with a gaseous oxidant, eg, A1 with O2 in air, to form a porous three-dimensional oxide that grows outward from the metal/ceramic surface. The process proceeds via capillary action as the molten metal wicks into open pore channels in the oxide scale growth. Reinforced ceramic matrix composites can be formed by positioning inert filler materials, eg, fibers, whiskers, and/or particulates, in the path of the oxide scale growth. The resultant composite is comprised of both interconnected metal and ceramic. Typically 5—30 vol % metal remains after processing. The composite product maintains many of the desirable properties of a ceramic however, the presence of the metal serves to increase the fracture toughness of the composite. 

Generally the harder the ceramic, the better its wear resistance however, other properties such as fracture toughness may play the dominant role. If a ceramic is mated with a metal hardness is the determining factor, but when a ceramic is mated with another ceramic fracture toughness appears to determine the wear rate (54). 

In metals, inelastic deformation occurs at the crack tip, yielding a plastic zone. Smith [34] has argued that the elastic stress intensity factor is adequate to describe the crack tip field condition if the inelastic zone is limited in size compared with the near crack tip field, which is then assumed to dominate the crack tip inelastic response. He suggested that the inelastic zone be 1/5 of the size of the near crack tip elastic field (a/10). This restriction is in accordance with the generally accepted limitation on the maximum size of the plastic zone allowed in a valid fracture toughness test [35,36]. For the case of crack propagation, the minimum crack size for which continuum considerations hold should be at least 50 x (r ,J. 

Plane Strain Fracture Toughness of Metallic Materials, 1982 Annual Book of ASTM Standards, Part 10, Standard No. E399. 

Figure 10.6. (a) Indentation nanohardness of silver/chromium multilayers and single films of the constituent metals, as a function of depth affected by plastic deformation, (b) Charpy impact energies, a measure of fracture toughness, of three materials, as a function of test temperature they are mild steel, ultrahigh-carbon steel and a composite of the two kinds of steel (courtesy Dr. J. Wadsworth) (Fig. 10.6(b) is from Kum et at. (1983)). 

ASTM-E 399-81 Standard test method Plane-strain fracture toughness of metallic materials... 

The major drawback of ceramics is their intrinsic brittleness. For example, most metals have a fracture toughness forty times greater than... 

ASTM El820-99 Standard Test Method for Measurement of Fracture Toughness , 1999 Annual Book of ASTM Standard Volume 3.01 Metals-Mechanical Testing Elevated and Low-Temperature Tests Metallography, American Society for Testing and Materials, 1999. 

J. O Donnell, H. Huthmann, and A. A. Tavassoli, The Fracture Toughness Behavior of Austenitic Steels and Weld Metal Including the Effects of Thermal Aging and Irradiation , Int. J. Pres. Ves. Piping, 65 (1996), 209-220. 

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. 

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