Fracture transitions in iron: Strain rate and environmental effects

Abstract

Abstract

Review Article: Case studies in future trends of computational and experimental nanomechanics

“…The amount of plastic energy dissipation depends upon stress field interactions between the crack tip and the emitted dislocations based upon the applied stress tensor, r ij . This stress field problem can then be related to G IC through the applied strain rate, _ e. Considering the interdependence of plasticity and fracture, the dislocation activation parameters V*, s*, H 0 can be combined to describe the dislocation velocity, v, as done in Hintsala et al 204 to dictate the shielding of the crack tip by dislocations. The dislocation activation parameters will depend upon the temperature, T, and the presence of impurities.…”

“…This requires understanding of how confining pressure, 205 radiation enhanced dislocation glide (REDG), 206 impurities, 207 state of stress, 208 and length scale 209 affect dislocation nucleation and mobility. The REDG effect 204 is important since most studies of length scale effects at submicron sizes are accomplished in either SEM or TEM. Maeda et al 206 observed from TEM experiments on SiC a roughly linear increase in dislocation velocities with increasing electron beam intensity, though the velocity depends on dislocation length and dislocation character.…”

Linking Nanoscales and Dislocation Shielding to the Ductile–Brittle Transition of Silicon

“…One possibility that could include all the variables outlined in the previous section is an approach we had proposed previously [17,28] which included s*V*, similar to what has been used for thermally activated creep mechanisms: [29] …”

“…[16] It has become generally accepted that this allows dislocation shielding to provide an increase in the fracture toughness. [6,[17][18][19] However, an accurate model for predicting the DBT has not yet been achieved due to many complicating variables which require extensive data to evaluate. To give some sense of the problem, a number of variables known to affect dislocation nucleation and mobility in silicon are:…”

“…Length-scale effects. [6,[17][18][19][20] The required data to evaluate each of these variables do not yet exist, which will become a task of increasing importance as nanotechnology continues to mature. Thermal and stress assistance are generally well-understood in terms of the energetic competition between plasticity and fracture at the bulk scale, but coupling with length-scale effects requires further study.…”