## 3 Results and Discussion  
### Load and Instrumental Signal Behavior in the Bending Tests  
Figure 4 shows the typical development of the average curves of load and instrumental signal in the two-point bending tests relative to the displacement of the loading nose. The average and the variation coefficients of the generic parameters for each sensor, such as the maximum instrumental signal (V\({}_{\text{smax}}\)), the instrumental signal at the beginning of the test (V\({}_{\text{so}}\)), the instrumental signal at maximum load (V\({}_{\text{s}}\) (P\({}_{\text{max}}\))), the maximum load (P\({}_{\text{max}}\)), and the displacement when the loading nose touches the strain gauge (DP\({}_{\text{o}}\)) are determined and presented in Table 2.  
Figure 4: Generic parameters of the average load and instrumental signal curves from the bending tests. Figure 3: Relationship between instrumental signal and load P.  
Different mean \(\text{DP}_{\text{o}}\) and \(\text{V}_{\text{so}}\) values were observed for each sensor and throughout the test repetitions, which can be attributed to experimental errors. These errors occurred due to difficulties in determining the moment when the surface of the strain gauge was touched by the loading nose and due to the initial settling of the measuring system of the strain gauge. Consequently, new uncertainties that have a significant impact on the behavior of the instrumental signal are posed in the estimation of \(\text{V}_{\text{so}}\) (see Table 3). Furthermore, the value for the maximum load (\(\text{P}_{\text{max}}\)) was consistent for each strain gauge in all of the repetitions (see Table 2). However, the magnitude of \(\text{P}_{\text{max}}\) differed significantly for each strain gauge, which is attributed to the position of the embedment and an inverse relationship between load and position of the loading nose [18]. Then, \(\text{P}_{\text{max}}\) diminished as the embedment moved away from the central axis of the sensing area of the strain gauge. Hence, when the distance of \(\text{x}_{\text{o}}\) increases, a lower total applied load is required to maintain the maximum bending moment constant in the area of embedment. Therefore, due to the dimensions of the tested material, new uncertainties concerning the measuring of \(\text{x}_{\text{o}}\) are introduced. In Table 2, the average values of the generic parameters are different for each sensor due to the characteristics of the tests presented in Table 1. This is attributed to the position of the embedment in the sensing area of the strain gauge and to the absence of a calibration process to adjust the display of the data acquisition system to zero. The repeatability of the tests was determined due to the low value of the coefficients of variation (CV) observed for the instrumental signal (less than 1%) and the load (less than 7%), which validated the measuring systems. Thus, there is no influence of the measuring systems on the trends shown in the tests for each sensor, which implies that the variations or differences between them were only due to experimental errors. The average performance of the load and the instrumental signal for each sensor in the two-point bending tests is shown in Figure 5a,b, respectively. In Figure 5, the displacement value considered as small-displacement limit (SDL) is shown by a vertical dashed line [29].