Surface Crack in Flexure (SCF) – Fracture Toughness Testing
The Newman and Raju formula (NRF) for the stress intensity factor (SIF) of a semi elliptical surface crack loaded in uniaxial tension or in bending has been developed about 30 years ago using an FE- analysis for several geometric parameters and fitting an analytical equation to the data points. Since in this time computer capacity was still very limited only few geometric models and only a material with the Poisson’s ratio = 0.3 was analysed, but the SIF depends on the Poisson’s ratio.
In this paper a reassessment of the NRF is made, where all relevant geometric parameters of cracks and specimens as well as several different Poisson’s ratios are considered. Even in the intersecting investigated parameter regime, the deviations of the old NRF from the new results are up to 14 %. If the Poisson’s ratio in the range of 0-0.4 is taken into account, the deviations rises up to 21 %. Furthermore the influence of the crack-surface intersection angle is discussed.
This tool is provided by ISFK to promote the use of the SCF-KIc-test. The practical use of the test is simple, but its evaluation requires FEM-calculations which we make available here. The use of the tool is free of charge.
If you use data generated with the applet (strength, pre-factor or effective regions) for your work, please cite:
- this page (http://www.isfk.at/de/1006/)
- Strobl, S., P. Supancic, T. Lube, R. Danzer: "Surface Crack in Tension or in Bending - A Reassessment of the Newman and Raju Formula in Respect to Fracture Toughness Measurements in Brittle Materials", Journal of the European Ceramic Society32 (2012), 1491-1501, http://dx.doi.org/10.1016/j.jeurceramsoc.2012.01.011