A new strength test for ceramic spheres (balls) is presented. A long narrow notch is cut in the equatorial plane of the ball and the ball is then loaded in compression perpendicular to the notch. This causes tensile stresses in the outer surface region of the ball opposite to the notch, which are analysed carefully with ?nite element (FE) methods. The tensile stress amplitude depends on the bending moment in the notch ligament – given by the applied force – and on details of the notch geometry. The stress state in the highly stressed surface is almost uniaxial showing only a slight in?uence of Poisson’s ratio. Numerical solutions for balls with quite different notch geometries are given. The link below takes you to an applet which allows the calculation of all these data for a wide range of geometries.
Strength tests have been performed on commercial silicon nitride balls of 5 mm diameter. Two sets of specimens having notches of different length have been tested. Although the typical fracture loads in both sets of data are quite different, the tensile strengths are closely similar. This indicates the validity of the data evaluations. Experimental details are discussed and an analysis of the experimental uncertainties on the test results is made. For balls with 5 mm the uncertainties are estimated to be less than ± 3% (of the measured value). For balls having a diameter of 10 mm or more the uncertainties are less than ± 1%.
This tool is provided by ISFK to promote the use of the NBT-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/959/) and
- P. Supancic, R. Danzer, S. Witschnig, E. Polaczek, R. Morrell: "A New Test to Determine the Tensile Strength of Brittle Balls - The Notched Ball Test", Journal of the European Ceramic Society29 (2009), 2447-2459, http://dx.doi.org/10.1016/j.jeurceramsoc.2009.02.018
More information, references and application examples
P. Supancic, R. Danzer, S. Witschnig, E. Polaczek, R. Morrell: "A New Test to Determine the Tensile Strength of Brittle Balls - The Notched Ball Test", Journal of the European Ceramic Society 29 (2009), 2447-2459, doi:10.1016/j.jeurceramsoc.2010.11.031
P. Supancic, R. Danzer, Z. Wang, S. Witschnig, O. Schöppl: "The Notched Ball Test - A New Strength Test for Ceramic Spheres", in: Dongliang Jiang, Yuping Zeng, Mrityunjay Singh, J. G. Heinrich (Eds.), Ceramic Materials and Components for Energy and Environmental Applications, 2010, 327-335