## 3 Results
### Prerequisites
#### 3.1.2 Compression Testing
A force-displacement curve was plotted for each strut thickness (0.8 to 1.7 mm in 0.1 mm increments) of each material. Figure 3a provides a comprehensive illustration of the pressure measurements obtained with the samples produced. It was of paramount importance to establish a correlation between the measured values, the values obtained from the saddle pressure measurement, and the material behavior. The objective was to predict the sinking behavior of the test subject on the bike saddle in relation to the thickness of the strut and the pressure exerted. A constant sinking behavior would permit the drawing of conclusions regarding the comfort of the saddle. This was achieved by converting the force exerted by the testing apparatus into pressure via the cross-sectional area of the cylindrical samples (706.86 mm\({}^{2}\)). The software utilized for the measurement of saddle pressure presents the obtained values in mbar. The maximum pressure values determined during both the initial and validation saddle pressure measurements were found to be just under 900 mbar. Accordingly, a concise illustration of the transformed pressure values in mbar is presented in Figure 3b. It can be observed that a reduction in strut thickness results in a decrease in the force required by the testing apparatus to achieve the maximum set displacement of 4 mm. Similarly, the behavior observed at the conclusion of the travel distance for strut thicknesses of 0.8 to 1.0 mm is also comparable, as can be observed in Figure 3a. It is evident that the maximum force required to achieve the maximum displacement of 4 mm increases significantly with an increase in strut thickness, particularly at 1.2 mm and above. This trend persists as the strut thickness increases further. Additionally, the distances between the maximum forces demonstrate an increase with increasing strut thickness. This indicates that the relationship between strut thickness and stiffness is not linear. However, this is to be expected, as there is no linear relationship between the hardness and stiffness of elastomeric solid parts either. Similarly, the stiffness demonstrates an exponential increase with a constant rise in hardness [37]. Figure 3: Results of the compression tests and the force to pressure conversion; (**a**) force–compression curves, (**b**) corresponding conversions for TPU 1301, based on [38]. The increasing hardness can be considered to be equivalent to the thickness of the lattice structure. It is evident that strut thicknesses of 1.5 mm to 1.7 mm exhibit comparable behavior in this region, resulting in a similar stiffness. Thus, modifying the strut thickness on the saddle pad from 1.5 mm to 1.7 mm has no impact on the sinking behavior. In general, these strut thicknesses should be avoided, as they do not yield sufficiently with a total saddle thickness of 10 mm and also exhibit slight deformation at pressure ranges between 400 mbar and 900 mbar. The greatest scope for adjustment with regard to the possible sinking depth of the test subjects was observed between 0.9 mm and 1.2 mm strut thicknesses. It is recommended that a maximum sinking depth of 4 mm be avoided, given the potential for discomfort when the penetration depth on the saddle is also subject to significant increases in the event of vibrations. Based on the aforementioned data, a strut thickness of between 1.0 mm and 1.1 mm is deemed to be the optimal range for maximum pressure values of 900 mbar. An increase in the thickness of the struts in the areas of high pressure, up to a range of 1.3 mm, may provide the potential for additional stability. The results of the compression tests indicated that strut thicknesses between 1.0 and 1.5 mm should be utilized for the bespoke saddle pads manufactured from EOS TPU material. The precise pressure values were derived from the initial pressure measurements of all three test subjects in Section 3.2, and the appropriate strut thickness was defined accordingly (Table 3).