## 3 Results
### Frequency Sweep Test  
Figure 6 presents the influence of filler material on storage G' and loss G\" modulus as a function of angular frequency for the filler loading level. Measurements were performed at constant shear strains in the range of linear viscoelastic response and constant temperature of 175 \({}^{\circ}\)C. For clarity, storage and loss modulus are shown separately. It can be seen from Figure 6 that all materials exhibited frequency-dependent behaviour of the moduli. However, two distinct regions can be observed at high and low frequencies. In the range of high frequencies (above \(\approx\)100 rad/s) there is no visible difference between the response of the composite materials since the values of G' and G\" converged or were parallel in log-log scale. This indicates that the behaviour of the composites at high frequencies was dominated by the binder system (matrix) and that the contribution of filler particles was less significant. Similar findings were reported for different highly filled composites; for example, SBR rubber and carbon-black and silica particles [44], polydimethylsiloxane (PDMS) and spherical glass beads [49], polyethylene terephthalate (PET) and ferrite nanoparticles [50], and PP and ceramic powder [51]. In the low-frequency region (below \(\approx\)10 rad/s) the flattening of the G' curve and to a lesser extent also G\" curve could be observed. The flattening of the curve corresponds to frequency-independent behaviour and indicates that the particle-particle interactions become dominant at lower frequencies [21; 24; 52]. Frequency independent behaviour of filled composites has also been observed for different fillers and binder combinations [40; 44; 49; 50; 51; 53]. The comparison of the frequency behaviour of composite materials at different loading levels (Figure 6) revealed that, as in the case of amplitude sweep tests, the viscoelastic behaviour in LVR depends on the type of filler material. However, in the case of 30 vol.% filler loading, there was no difference between dynamic behaviour (G\({}^{\prime}\) and G\({}^{\prime\prime}\)) of Al and 316L material, respectively, in the whole frequency range studied. As can be seen in Figure 6a,b, the curves for those two fillers overlap entirely  
Figure 6: The influence of filler material on storage G\({}^{\prime}\) and loss G\({}^{\prime\prime}\) modulus in the frequency domain for all filler loadings: (**a**) G\({}^{\prime}\) for 30 vol.%, (**b**) G\({}^{\prime\prime}\) for 30 vol.%, (**c**) G\({}^{\prime}\) for 45 vol.%, (**d**) G\({}^{\prime\prime}\) for 30 vol.%, (**e**) G\({}^{\prime}\) for 60 vol.%, and (**f**) G\({}^{\prime\prime}\) for 60 vol.%. over the whole frequency range. Further, the composites with GB and Ti particles at 30 vol.% exhibited lower values of G\({}^{\prime}\) and G\({}^{\prime\prime}\) compared to Al and 316L. The differences became larger at low frequencies indicating weaker particle-particle interactions compared to Al and 316L particles. Moreover, at lower frequencies, the composites with GB particles exhibited slightly higher values of G\({}^{\prime}\) compared to the composites with Ti particles, which would suggest that at longer times stronger network was formed for GB material at this concentration. The behaviour of the composites at 45 vol.% loading, shown in Figure 6c,d, was at high frequencies similar to the behaviour of the composites at the lowest concentration, which suggests that in the range of short times the binder system governs the material behaviour. The results of frequency tests at low frequencies suggest that in the composites with 316L particles stronger network was formed compared to the composites with Al particles. At the highest loading level (Figure 6e,f), we observed that the composites with GB, Al, and 316L exhibited very weak frequency dependence. The G\({}^{\prime}\) curve was independent on the frequency in a wide frequency range, representing strong solid-like behaviour.