A Knoop-Indentation Method for R-Curve Determination
The stable growth of indentation cracks during a bending test offers an interesting possibility to study the R-curve behaviour of ceramics. The suitability of Knoop crack for such crack growth experiments is investigated on a silicon nitride.
For a proper evaluation of crack growth data the dependence of the geometric correction factor Y and of the residual stress parameter χ on crack length and indentation load have to be taken into account. Methods are developed to determine Y and χ and their change with indentation load and crack length. The measurement of R-curves is possible if Y — and χ — values determined by these methods are used for the evaluation of crack growth data.
For the investigated material a slightly rising R-curve was determined. Because of the low crack length to indent diagonal ratio of Knoop cracks a lower limit of c = 120 μm was introduced to the experimental range covered with Knoop cracks in this material.
KeywordsNickel Zirconia Brittle Nitride Pyramid
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