5.3.4 Wear Testing by Nanoindentation During each nano wear test, one cycle is defined as a pass and return of the indenter over the track, so the total distance covered for one wear test was 0.050 m. Speed of the tip during wear tests was 50 μm/s. Total of 10 wear tests for each sample were performed under the two normal loads of 20 and 50 mN. The wear in a track is characterized as the area between the initial profile and the residual profile of the wear track. In the same way, the averages of the wear track deformation are shown in Fig. 5.8. As expected the applied load has a significant effect on the wear track deformation values. However, wear track deformation values seem insensitive to the graphene content inside the composites. This situation can be explained by the anisotropy over the matrix. At the beginning nano indenter sweeps the surface to determine the initial profile of the wear track. Then, wear is done under different loadings. In Fig. 5.9, the difference in the depth is given as a comparison under a loading of 50 mN. Fluctuations on the graph are commented as the different hardness values of different elements of the composition. 5.3.5 Damage Analysis by Means of Scratch Test and 3D Optical Roughness Meter After realizing two different group of macro scratch tests, three dimensional damages were obtained by 3D optical surface scanner. The results are presented in the Figs. 5.10, 5.11, and 5.12. In Table 5.4 the volume and surface of the damage trace after scratch calculated from roughness test results are given. It is difficult to find a relation of worn volume and surface regarding the graphene contents of the compositions. In reality, because of the high shear stress at the interfaces the interfacial shear stress should probably be the main reason for damage of the matrix and reinforced filler interfaces [25]. When the indenter is slipping, tangential tensile stress is caused on the surface behind the indenter, while in front of the indenter the tangential stress is compressive. 5.3.6 Bending Testing by Means of three Point Bending Three-point bending test were conducted for each different type of composites. In tensile test, failed areas do not stay included in the specimen gauge length. Therefore, the bend test is more appropriate with our composites. Also, non-linear evolution of the curves is a consequence of the anisotropy of the inner structure. Fig. 5.6 Creep Compliance curves for specimens ERG III-III under 20 and 50 mN load 52 A.B. Irez et al.
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