The Ball-on-Three-Balls strength test for discs and plates: Extending and simplifying stress evaluation

The Ball-on-Three-Balls-test has proven to be an accurate and easy-to-use option for strength testing. However, the maximum stress must be calculated based on Finite-Element-Analysis results. For this purpose, a fitted function was already provided. This function is based on results which were generated under the assumption of punctiform load introduction. Deviations from these conditions occur through an increase in contact-area between the loading ball and the specimen, large specimen deformations, friction, or plastic deformation of the balls. These non-linear effects are investigated by Finite-Element-Analysis for a wide range of specimens. It is shown that the maximum stress is sensitive to the area of contact between the loading ball and the specimen. Furthermore, thin specimens are subject to large deformations, which significantly decrease the maximum stress. Therefore, a revised fitted function is derived. For specimens with exceptional geometries, non-linear effects are considered with correction factors added to the new fitted function.

Automated summary

The Ball-on-Three-Balls test is an accurate and easy-to-use option for strength testing, but the maximum stress needs to be calculated based on Finite-Element-Analysis results. A fitted function has been provided based on results generated under the assumption of punctiform load introduction. Non-linear effects caused by an increase in contact area, specimen deformations, friction, or plastic deformation of the balls are investigated using Finite-Element-Analysis. Thin specimens experience large deformations, decreasing the maximum stress. Therefore, a revised fitted function is derived, with correction factors added for specimens with exceptional geometries.