A new toughness test for ball-shaped specimens is presented. In analogy to the “Surface Crack in Flexure”-method the fracture toughness is determined by making a semi-elliptical surface crack with a Knoop indenter into the surface of the specimen. In our case the specimen is a notched ball with an indent opposite to the notch. The recently developed “Notched Ball Test” produces a well defined and almost uniaxial stress field.

The stress intensity factor of the crack in the notched ball is determined with FE methods in a parametric study in the practical range of the notch geometries, crack shapes and other parameters. The results correlate well with established calculations based on the Newman-Raju model.

The new test is regarded as a component test for bearing balls and offers new possibilities for material selection and characterisation. An experimental evaluation on several ceramic materials will be presented in a consecutive paper.

This tool is provided by ISFK to promote the use of the NBT-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/958/) and
• S. Strobl, P. Supancic, T. Lube, R. Danzer: "Toughness Measurement on Ball Specimens, Part I: Theoretical Analysis", Journal of the European Ceramic Society 32 (2012), 1163-1173, Rev., SCI, dx.doi.org/10.1016/j.jeurceramsoc.2011.12.003