Toughness stress-intensity factor

FRACTURE TOUGHNESS STRESS INTENSITY factor CRACK BRIDGING QUASI-BRITTLE FRACTURE STRAIN... 

This approach is useful for brittle materials such as ceramics. In it, it is assumed that the material contains flaws, which is the case for any real material. It also assumes that fracture is depended on three factors, viz., the fracture toughness, stress intensity factor, and flaw size. 

For a single-value toughness material, dT/dc = 0. Accordingly, if the applied stress intensity factor is always increasing with crack length, equation 4 is always satisfied. Thus, the condition for fracture is equation 5, where is given by the applied loading conditions. 

K,- = lG,. = fracture toughness (sometimes critical stress intensity factor). Usual units MN m ... 

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. 

Stress Intensity Factor K,5cc a fracture toughness parameter used for evaluating susceptibility to stress-corrosion cracking (the subscript I signifies a tensile mode of stressing). 

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

The term fracture toughness or toughness with a symbol, R or Gc, used throughout this chapter refers to the work dissipated in creating new fracture surfaces of a unit nominal cross-sectional area, or the critical potential energy release rate, of a composite specimen with a unit kJ/m. Fracture toughness is also often measured in terms of the critical stress intensity factor, with a unit MPay/m, based on linear elastic fracture mechanics (LEFM) principle. The various micro-failure mechanisms that make up the total specific work of fracture or fracture toughness are discussed in this section. 

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. 

Kc = Critical stress intensity factor = fracture toughness... 

Kic fracture toughness (critical stress intensity factor) ... 

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