Indentation crack length method

Determined by the post-indentation crack length method, equation (5.41). 

The standard unfortunately also included a Vickers indentation crack length method as an alternative to estimate fracture resistance. The measured property in that instance is deemed as indentation fracture resistance and not a genuine fracture toughness. 

The advent of the Vickers indentation crack length techniques in the mid to late 1970 s was a major distraction. It was not until 1991 that a concerted effort to refine and standardize technically rigorous fracture toughness test methods was resumed in ASTM Committee C-28, Advanced Ceramics. Work on the reference material began at National Institute of Standards and Technology (NIST) in May 1997 shortly after the ASTM Provisional Standard PS 070-97 was approved in April 1997. 

There are several techniques by which K f. can be measured. The two most common methods entail measuring the fracture stress for a given geometry and known initial crack length and measuring the lengths of cracks emanating from hardness indentations. 

Indentation strength in bending was widely used to characterize the crack propagation resistance with increasing crack length. In this method a controlled crack is formed by Vickers indenter and... 

The indentation strength (IS) method induces Vickers indentations into flexure strength bars with smooth surfaces. The critical stress intensity at fracture is measured, and calculated. It is not necessary to measure crack lengths, but results are dependent on the indenter load. 

Indentation testing as a method of measuring fracture toughness of SiC-whisker reinforced AI2O3 composites was evaluated. Polishing was found to influence the measured significantly. The different equations that exist to correlate the crack length with were critically... 

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 ... 

Figure 3a. Crack growth resistance curves from indentation strength (IS) [23] and chevron notch short bar methods [24] compared to fracture toughness values via C 1421. For the PB and SCF methods, the precrack length is plotted. For the CNB method, the crack extension to maximum load is plotted.

This method helps to avoid the often inaccurate measurement, of the length of cracks resulting from the indentation. 

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