Stress fracture toughness, defined

Fracture Properties Fracture toughness defines the stress distribution in the body just before fraciure and is given by... 

Fracture Toughness. The fracture criterion was defined by a critical value of the crack tip stress intensity, known as the fracture toughness. Ceramics often fail ia pure tension, designated mode I, and Kj replaces ia equation 6. Thus die appHed tensile stress at which fracture... 

Fracture toughness is the resistance to propagation of cracks through a material and is usually quantified by the stress intensity factor, K, defined as... 

Secondly, Irwin 6) found that the stress field around a sharp crack in a linear elastic material could be uniquely defined by a parameter named the stress-intensity factor, K and stated that fracture occurs when the value of K, exceeds some critical value, K C. Thus, K, is a stress field parameter independent of the material whereas Klc, often referred to as the fracture toughness, is a measure of a material property. Again the subscript I is used to denote the tensile-opening mode. 

Thus, these two concepts are equivalent. In the classical failure context, fracture depends on some critical combination of stress at the crack tip and the tip radius, neither of which are precisely defined (or definable) or accessible to measurement. For experimental accuracy and practical apphcation, it is more appropriate to use the accessible quantities o and a to determine the fracture toughness of the material. It is to be recognized that the quantities involving a a and a represent the crackdriving force, and 2y, in the Griffith sense, represents the material s resistance to crack growth, or its fracture toughness. 

In principle then, a fracture toughness parameter has been defined in terms of linear elastic analysis of a cracked body involving the strain energy release rate G, or the stress intensity factor K. For thick sections, the fracture toughness is defined as Gic, and for thinner sections, as Gc or R (referred only to mode 1 loading here). This value is to be measured in the laboratory and applied to design. The validity of... 

The lower hmit of integration (at or ai) is usually defined on the basis of nondestructive inspection (NDl) capabilities, or on prior inspection the upper limit is defined by fracture toughness or a predetermined allowable crack size that is consistent with inspection requirements (a/ or 2)- Equations (7.5) and (7.6) may be rewritten in terms of the stress intensity factor K ... 

The fracture toughness, a term defined by Irwin (1956, 1960) to characterize brittleness, provides a measure of the conditions required for catastrophic crack propagation in a material (see Section 1.6). One fracture toughness parameter is the surface fracture energy y, defined as one-half G, the critical strain energy release rate above which catastrophic failure occurs. In turn G is related to another convenient toughness parameter, the critical stress intensity factor a measure of the stress field at the crack tip. For fracture of an isotropic material in a plane strain modet (Baer, 1964, p. 946) ... 

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