If the thickness of the sample is insufficient, measuring devices will show a harder result than the material actually has. This is due to the reduction in stress over the material thickness, which can be clearly seen in Figure 3 of the DIK. The tension is reduced from the needle in the direction of the contact surface in a ratio of approx. 1:10.
So that the substrate does not influence the measurement result, we therefore recommend selecting the minimum sample thickness depending on the hardness according to the ratio shown in the graphic (Fig. 4).
Fig. 3: Stress reduction in the material during an indentation. Source: Master’s thesis Marvin Ludwig, Leibnitz University Hannover and the DIK – German Institute for Rubber Technology e. V
Fig. 4: In order not to falsify the result, we recommend that you select the minimum thickness of the sample depending on its hardness.