Vickers diamond-tipped

The hardness of a material typically represents its ability to resist indentation. Macroscopic hardness is usually measured by pressing a diamond tip (of known area A) into a solid, with a given load (force). The hardness //, often called Vicker s or Knoop hardness (which differ by the diamond tip geometry), is defined as // = W//4, where W is the load and A is the indented area. This is a destructive test The permanent indentation caused by the diamond is produced by breaking bonds and displacing atoms. A typical indentation profile is shown in Figure 8.1, and the Vicker s and Knoop hardnesses of several materials are listed in Tables 8.1 and 8.2. 

Several methods have been developed for hardness testing. Those most often used are Brinell, Rockwell, Vickers, Tukon, Sclerscope, and the files test. The first four are based on indentation tests and the fifth on the rebound height of a diamond-tipped metallic hammer. The file test establishes the characteristics of how well a file takes a bite on the material. 

The loading of a diamond-tipped Vickers indenter into most ceramic and glass materials results in the formation of cracks from the corners of the indentation (Figure 14.22). Anstis et al. [22] developed a method to correlate the length of these cracks with the fracture toughness of the material ... 

Tests such as Vickers, Knoop, and Brinell use an indentation technique that impinges a hard tip (e.g., diamond) into the sample with a known load (Figure 2.35a). After a designated period of time, the load is removed, and the indentation area is measured. The hardness, H, is defined as the maximum load, L, divided by the residual indentation area, (Eq. 11). The coefficient, F, varies depending on which indentation method is used. This value (14.229 for Knoop and 1.854 for Vickers)... 

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