Crack-tip Shielding by Dislocations and Fracture Toughness in NaCl Crystals

Fracture Toughness of the Fe–Zn Intermetallic Compounds Measured by Bend Testing of Chevron-Notched Single-Crystal Microbeams

“…The stress intensity factor near the crack tip, so-called local stress intensity factor K I local , can be considered to be the sum of the contribution from an external tensile stress (K I ) and that from dislocations emitted from the crack tip (k D ): 44,45) The k D value is usually negative in sign because the stress field of the dislocations emitted from the crack tip is compressive to mitigate the tensile stress concentration around the crack induced by the external stress. 45) Thus, the magnitude of the fracture toughness is determined by the crystal bonding strength (first term) as well as the ability of stress relaxation by dislocations (second term).…”

Crack tip shielding observed with high-resolution transmission electron microscopy

“…These findings indicate that there is a direct relationship between dislocations and the BDT. Figure 1 (a) shows a contour map of the stress component normal to the crack plane, σ yy , around a crack tip, with a pair of pure edge dislocations in front of the crack tip without any stress applied [ 3 , 4 ]. The contour map was obtained by calculating the stress field based on the elastic theory derived by Thomson, with the dislocation configuration as shown in Fig.…”

“…1 (b). In this configuration, two dislocations are located ±45° from the crack line and 100 μm away from the crack tip [ 4 ]. The extra half-planes of these dislocations were both at the crack side with respect to their slip planes, as shown in Fig.…”

The condition for the cyclic plastic deformation of the crack tip: the influence of dislocation obstacles

“…The advantage of this deformation mechanism is that no further dislocation sources are necessary. This emission of dislocation was observed during the in-situ deformation in a transmission electron microscope [1] to [3] by etch pit technique [4,5] and by photoelastic techniques I- 6,7]. The conditions for such an emission have been first discussed by Rice and Thomson [8] and later by others [3], 1,9] to [12].…”