Dislocation mechanics of point forces

Observations of both crack-tip and nanoindentation-tip emission of dislocations have led us to the conclusion that the quantification of such phenomena will soon be at hand. This will eventually lead to more precise mechanisms and solutions for brittle-ductile transition and contact wear phenomena. While the stresses are not singular at a Hertzian contact, the point forces produce stresses similar to those at a crack tip. For example at 10 nm beyond a crack-tip loaded to 1 MPa-m ^1/2 , the maximum shear stress is 4 GPa. At 10 nm below a 66 nm radius diamond indentation tip loaded to 65 μN, a resolved shear of 4 GPa results. It happens that these 65 μN indenter tip and 1 MPa-m ^1/2 (converted to G_I) crack-tip extension forces are just about those levels required for emission of dislocations. Nearly in situ transmission electron and atomic force microscopies of both the initial emission stages and distributions of dislocations at point forces have been accomplished in Fe-3wt%Si single crystals. Complementary nanoindentation studies of yield instabilities in the μN regime will be shown to reinforce the point-force concept.