Radial Fracture During Indentation by Acute Probes: II, Experimental Observations of Cube-corner and Vickers Indentation

Abstract

International Journal of Fracture (2005) 136:265-284Abstract. The companion article proposed a model for radial crack development at sharp contacts. The major extension of this model from previous works is the inclusion of a 'wedging' mechanism, to form a three-stress-field description of indentation crack evolution. Here, the amplitude terms of the three stress-intensity factors comprising the model are calibrated from experimental in situ and post situ inert-environment radial crack measurements on soda-lime glass. These values are scaled to predict radial crack evolution during cube corner and Vickers indentation of fused silica and soda lime glass in inert and ambient air environments. Both the conventional two-field and the proposed threefield model predictions are compared with radial crack lengths measured during indentation loadunload cycles (through the transparent materials with an in-situ apparatus). The three-field model is shown to be a great improvement over the two-field model in the description of crack evolution at cube-corner indentations, particularly with respect to the significant crack extension during loading and the attainment of a maximum crack length during unloading. The three-field model is consistent with observations of Vickers fracture in soda-lime glass and is able to reproduce the features of radial fracture evolution on the 'anomalous' glass, fused silica.

Loading rate effects on the fracture behaviour of solar control coatings during nanoindentation

“…However, when the indenter edges come into contact with the surface the stress concentration effect magnifies the local stresses and, at a critical load, cracking starts and propagates through the coating following the edge of the indenter which is in contact with it. The edge of the indenter causes a wedging effect opening the crack [11,12]. As the load increases the crack can extend, but is constrained within the impression by the substrate plastic deformation.…”

On the mechanics of fracture in monoliths and multilayers from low-velocity impact by sharp or blunt-tip projectiles

“…1 In the case of h, chipping experiments with a Vickers indenter on various ceramics revealed that h ¼ 9.3 [9]. As shown by [21], however, this coefficient is strongly (and subtly) affected by the pyramid angle f. The case of spherical chipping is more involved, and is differed to future work. The coefficients so determined are listed in Table 1.…”

Particulate solid attrition in CFB systems – An assessment for emerging technologies

“…where c is the crack length (according to Figure 9), and is an indenter constant, which for example is 0.0161 for a Berkovich indenter [44]. For such small scales, the load required to crack the material using a Vickers probe is impractical, so a cube-corner probe is often used instead, which lowers the cracking load threshold [89]. While hardness is traditionally assumed to be independent of load applied, care should be taken to indent the material sufficiently enough to prevent the phenomenon of the indentation size effect from providing accurate measurements of the particle [86].…”