On the Vickers Indentation Fracture Toughness Test

Abstract

The Vickers indentation fracture toughness test, or VIF, is addressed by considering its origins and the numerous equations that have been applied along with the technique to estimate the fracture resistance, or the K Ic of ceramics. Initiation and propagation of cracks during the VIF test are described and contrasted with the pre-cracking and crack growth for internationally standardized fracture toughness tests. It is concluded that the VIF test technique is fundamentally different than standard fracture toughness tests. The VIF test has a complex three-dimensional crack system with substantial deformation residual stresses and damage around the cracks. The VIF test relates to an illdefined crack arrest condition as opposed to the rapid crack propagation of the standardized fracture toughness tests.Previously published fracture toughness results employing the VIF technique are reviewed. These reveal serious discrepancies in reported VIF fracture toughness values. Finally, recent fracture resistance measurements by the VIF technique for the Standard Reference Material SRM 2100 are presented. These are compared with standardized test results for the same material. It is concluded that the VIF technique is not reliable as a fracture toughness test for ceramics or for other brittle materials. What the VIF actually measures in terms of fracture resistance cannot be readily defined. It is recommended that the VIF technique no longer be acceptable for the fracture toughness testing of ceramic materials.

Towards engineering isotropic behaviour of mechanical properties in thermally sprayed ceramic coatings

“…During Vickers indentation measurements on the cross-section, with one of the diagonals of the indenter aligned parallel to the substrate surface, four major cracks with similar lengths tended to be observed originating at or near the corners of Vickers indentation impressions. This behaviour, which is typical of that observed in bulk ceramics [14], is shown in Fig. 1.…”

Mechanical Properties of an Fe‐Based SAM2×5‐630 Metallic Glass Matrix Composite with Tungsten Particle Additions

“…For the SAM2Â5-630 (Figure 3a), there are obvious radial cracks extending from the corners of the indent, which are characteristic of a brittle material and the basis for estimating indentation fracture toughness based on the crack lengths. [11,17,28] The radial cracks that are generated by indenting a brittle material are generated by tensile stress during the unloading process and therefore should not affect the hardness measurements. In addition to intragranular radial cracks, intergranular lateral cracks are observed after indenting SAM2Â5/2%W (Figure 3b), which represents a change in the fracture mechanism due to the tungsten dispersed at SAM2Â5 particle boundaries.…”

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

“…From the size of indentation imprint and from the length of indentation-induced crack, hardness and fracture toughness can be obtained for brittle material like glass (Lawn, 1993;Green, 1998;Fischer-Cripps, 2007). However, indentation cracking methods for evaluating fracture toughness (Kc) are open to question due to, for example, a lack of a definite solution for the stress intensity factor at the crack tip (Quinn and Bradt, 2007). In addition, glassy materials exhibit permanent densification, which sometimes reduces the residual stress for cracking and results in the value much different from the fracture toughness (KIc) measured by a self-consistent method (Rouxel, 2015).…”