**6. Conclusion**

278 Smart Actuation and Sensing Systems – Recent Advances and Future Challenges

**Figure 27.** Resistance changing at a fixed load (anisotropic MRE Gr 21.95%)

load applied leads to lower resistance of Gr-MREs.

and the external load is fixed in Fig. 29.

35

40

45

50

55

**Resistance(k Ohm)**

60

65

70

75

graphite weight fraction 20%, 21.95% & 23.81%

1

10

100

**Resistance(k Ohm)**

1000

10000

The Fig. 27 shows the change in the resistance for given external forces. Along with the raising of magnetic field intensity, the sample's resistance decreases. The higher external

0 50 100 150 200 **Intensity of magnetic field(mTesla)**

theoretical 1N experimental 1N theoretical 5N experimental 5N theoretical 10N experimental 10N

The next two figures Fig. 28 and 29 show the resistance variation between anisotropic MREs with graphite weight fraction 20%, 21.95%, and 23.81%. The magnetic field is fixed in Fig. 28

> 20% theoretical 117.8mT 20% experimental 117.8mT 21.95% theoretical 117.8mT 21.95% experimental 117.8mT 23.81% theoretical 117.8mT 23.81% experimental 117.8mT

**Figure 28.** Resistance between different sample at 117.8mT magnetic field (anisotropic MRE with

0 2 4 6 810 12 **Load(N)**

Both isotropic and anisotropic samples of graphite-based magnetorheological elastomers (Gr-MREs) with various graphite weight fractions ranging from 0% to 23.8% were fabricated in this study. The microstructural observation of these samples shows that the presence of graphite powder affects the forming of carbonyl iron chains. The sample with less graphite shows better-aligned carbonyl iron chains which influence the magnetorheology of MREs. In addition by connecting two iron chains in parallel and connecting the disconnected iron chains, the graphite contributes to the conductivity of MREs.

Steady state and dynamic tests such as strain amplitude sweep and angular frequency sweep were used to test the magnetorheology of Gr-MREs. With the help of graphite in MREs, the Storage and Loss Moduli are both changed. The steady state tests showed that the graphite can diminish the viscoelastic linear range of MREs. The dynamic tests proved that the samples with higher graphite weight fraction show higher initial Storage and Loss Moduli and lower MR effects. Additionally, the resistance of each MRE sample exhibits a decreasing trend with the graphite weight fraction.

Based on a Dipole model, a representative volume unit was presented to show the resistance of ideal anisotropic MREs. The current flowing through the ideal chain structure were derived by taking into account both the tunnel current and conductivity current. In the mathematical model, two parameters, λi and λg, were introduced to reflect the effect of the iron particles and graphite, which are both exponential functions of particle volume fractions. The exponential parameters were identified and then used to reconstruct modelling predictions. The comparison between experimental results with modelling predictions indicate that the proposed mathematical model can well investigate the sensing capabilities of the graphite based MRE elastomers.
