# Indentation Measurement in Thin Plates under Bending Using 3D Digital Image Correlation
## 3 Results and Discussion
Results show how the specimen with less stiffness experiences a higher bending deformation. From this information, it is possible to extract the involved energy to generate the contact damage and bending deformation at the specimen. The same conclusions could be obtained from the energy point of view. As shown in Figure 8, the area under the curve is higher for thicker specimens, which means that more energy has been used to create the contact damage. Once the information related to the contact model and bending experienced by the specimen was obtained, an energy analysis was performed, as Figure 4 shows. Table 3 summarizes the values of applied, absorbed and recovered energy for contact experiments with different specimen thicknesses. These values were obtained by quantifying the areas under the experimental plot measurements, as explained in Figure 4. As shown in Table 3, the total applied energy increases as the thickness increases, due to higher stiffness being involved. Similarly, both elastic energy and absorbed energy to generate permanent damage in contact increases as the thickness increases, while the bending energy (elastic and plastic) is consequently reduced as the thickness increases. It supports the assertion of higher thicknesses leading to higher contact damage. As the supporting structure was designed for high loads, the absorbed energy in the system remains below 2% for all cases, although a slight increase is shown when the specimen stiffness increases. Figure 9: (**a**) Normalized contact load as a function of the indentation/thickness ratio for different specimen thicknesses, (**b**) normalized contact load as a function of the maximum deflection/thickness ratio for different specimen thicknesses. To perform a comparison between experiments with different specimen thicknesses, Figure 10a shows the evolution of the applied energy due to contact normalized by the total applied energy versus the normalized load for three different thicknesses. As expected, the absorbed energy by contact increases for any thickness as the load increases. For the analysed and equally spaced thicknesses, the gap between curves tends to be also equally spaced. Nevertheless, this trend will disappear for very high thicknesses, in which most energy will be dissipated in the contact as permanent damage. It can be observed in Figure 10, where the plastic energy increases faster than the elastic energy as thickness increases. It could be explained taking into account that thicker specimens enhance the indentation-induced damage, while thin plates absorbed most of energy as bending. Consequently, the total applied bending energy tends to be lower as thickness increases, as is shown in Figure 10b. The rate of applied energy in contact increases as the thickness increases, whereas the rate of bending energy is going lower. To sum up, stiffness increases the contact forces at the ball contact point, which lead to deeper indentations, higher applied energy at contact, and lower applied energy for bending energy. All of these effects are enhanced as thickness increases. Figure 11 shows the percentage of applied energy due to contact and bending as a function of the specimen thickness. It is observed, that values of applied energy due to contact increases when specimen thickness increases linearly. In addition, for thicker specimens the percentage of applied energy due to bending decreases, also linearly. Figure 10: (**a**) Normalized evolution of the applied energy due to contact versus normalized load for different specimen thicknesses. (**b**) Normalized evolution of the applied energy due to bending versus normalized load for different specimen thicknesses.