Punch tip effects in diffusional impression creep

The effect of a surface cavity on the diffusional creep of a half space by impression of a punch whose end fits the cavity was studied analytically and numerically and compared with the normal case of the same punch of a flat end pushed into a flat surface without the cavity. A straight punch with a half cylindrical tip pushed into a half cylindrical groove of the same size as the tip produces the same impression velocity as the normal case. However, for a cylindrical punch with a semi-spherical tip pushed into a semi-spherical hole of the same size as the tip, the impression velocity is 4/π faster than the normal case. By using the finite element method (ABAQUS program), a cylindrical punch with a flat end pushed into a cylindrical cavity of the same size as the punch was also studied. If the depth of the cavity is 1.5 times the punch radius, the impression velocity is only about 5% smaller than the normal case provided that the lateral contact area is a free surface. If the lateral contact area is impermeable to vacancies, the impression velocity is about 28% smaller.