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.
KeywordsFracture Toughness Crack Length Silicon Nitride Indentation Load Stable Crack Growth
Unable to display preview. Download preview PDF.
- 1.J.B. Wachtman, Mechanical Properties of Ceramics, John Wiley & Sons Inc., New York (1996).Google Scholar
- 7.V.M. Sglavo, R. Dal Maschio, Controlled indentation-induced cracks for the determination of fracture toughness in alumina, Fracture Mechanics of Ceramics, 11, 233 - 243 (1996).Google Scholar
- 14.A.M. El Aslabi, G. Kleist, R.W. Steinbrech, H. Nickel, Evaluation of indentation fracture toughness of Si3N4 using crack profile measurements, Fortschrittsberichte der DKG, 6, 133 - 149 (1991).Google Scholar
- 17.J. Kiibler, Fracture toughness of ceramics using the SENVB method: first results of a joint VAMAS/ESIS round robin, Ceram. Eng. Sci. Proc.,to be published.Google Scholar