Models of dynamic measurement error variations of material testing machines

Crucial to material testing is to accurately know the force applied to the test specimen. In testing machines the load cell is used for this purpose. However, due to vibrations and inertia, the load cell and the test specimen experience different loads. In calibration experiments this difference has been found to depend on the test bar stiffness. The origin of this dependence is not yet completely understood. To find a plausible explanation, two models are here proposed and analyzed. One model of transversal frame vibrations has been suggested in the context of standardization. The other model of longitudinal machine vibrations has been studied recently and is here applied for a different parameter and frequency range. Both models are found to support experimental results. Qualitative models of this kind may greatly facilitate the improvement of testing machines as well as their dynamic calibration.