Instrumented pyramidal and spherical indentation of polycrystalline graphite

Abstract

The elastoplastic surface deformation of a polycrystalline graphite was studied by examining the indenter's geometry dependence of load P versus penetration depth h relation (P-h relation) in instrumented pyramidal/spherical indentation tests. The tetrahedral pyramid indenters included inclined face angles ␤ of 10.0°, 22.0°(Vickers pyramid), and 40.0°. The tip radius of spherical indenters used were 32 m, 200 m, 794 m, 1.59 mm, and 6.35 mm. The true hardness H as a measure for plasticity was singled out of the elastoplastic loading parameter k 1 in the quadratic expression of P ‫ס‬ k 1 h 2 and then quantitatively related to the yield stress Y that was determined from the mean contact pressure for spherical indentation at the onset of plastic yielding. The size effect of Y, decreasing with the increase in the tip radius of spherical indenter, is discussed using the model of geometrically necessary dislocations in terms of the material length scales for a plastic field with strain gradient.

Properties of Slip‐Cast and Pressureless‐Sintered ZrB2–SiC Composites

“…Both hardness and Young's modulus are in line with the literature data on materials of similar composition 11–13 . However, standard deviation of hardness is quite high because of the presence of not homogeneously dispersed phases such as B 4 C (36 GPa), h‐BN (∼280 MPa), and graphite (300 MPa) 24–27 …”

Evaluation of Sinking-In and Cracking Behavior of Soda-Lime Glass under Varying Angle of Trigonal Pyramid Indenter

“…The in situ Meyer hardness of soda-lime glass increases with increasing the face angle of indenter. This is in line with the results of previous report (Sakai and Nakano, 2004), where Meyer hardness of the materials, which include ductile metals, ceramics, glass, and organic polymer, increases with increasing the face angle of indenter. As discussed later, the Meyer hardness is not only a material parameter but depends on the indenter geometries.…”

Application of Modified Optical Indentation Microscopy as New <i>In Situ</i> Indentation Method

“…Sakai et al pointed out that the yield stress estimated from the indentation tests depends on the radius of the spherical indenter, and is generally higher than that estimated from the compression tests. 26) As mentioned above, the superelastic deformation occurred at approximately P = 15 N. According to eq. (4), the applied load P of 15 N in this test is corresponding to the indentation stress • i of 1145 MPa, and this • i is consistent with the yield stresses estimated from the indentation test.…”