Loading...
Please wait, while we are loading the content...
Similar Documents
The Effect of Microstructure on the Dynamic Equi-Biaxial Fatigue Behaviour of Magnetorheological Elastomers
| Content Provider | Semantic Scholar |
|---|---|
| Author | Zhou, Yanfen |
| Copyright Year | 2017 |
| Abstract | Dynamic equi-biaxial fatigue behaviour of isotropic and anisotropic magnetorheological elastomers (MREs) based on a silicone rubber matrix was investigated using the bubble inflation method. Constant engineering stress amplitude was used as the control mode and samples were fatigued over different stress ranges between 0.75MPa and 1.4MPa. S-N (Wöhler) curves showing plots of stress amplitude (σa) versus cycles to failure (N) are presented. Stress-strain behaviour throughout the fatigue process is described. Elastic modulus (E*) was studied for the specific cycles measured. It was found that anisotropic MREs exhibited greater fatigue resistance than isotropic MREs for a given magnetic particle content. Stress softening and hysteresis continued throughout the tests though they were most pronounced in the first dozen cycles at the lower stress amplitudes. A limiting value of E*, below which fatigue failure is likely to take place was observed in both isotropic and anisotropic MREs, although the initial modulus was higher in anisotropic MREs. Figure 1. The equal-biaxial bubble inflation test system (a), a graph depicting the tracking of the displacement of dots at the pole of the bubble; (b) an inflated MRE sample 2.2 Fabrication of MREs Both isotropic and anisotropic MREs with a carbonyl iron content of 20vol% were produced. Firstly, silicone rubber was mixed with a catalyst at a 10:1 ratio. Then the carbonyl iron particles were incorporated into the mixture and mechanically stirred to distribute the particles evenly in the elastomer matrix. The whole mixture was degassed in a vacuum to remove entrapped air bubbles and then poured into a mould. After further degassing in the mould, the compound was kept at room temperature for 48h to allow solidification. For anisotropic MREs, the compound was cured in the presence of a magnetic field using a Halbach Array after degassing. The Halbach Array can provide a mean magnetic flux of 400mT ± 5% over the 50mm nominal diameters of the test samples. The thickness of the MRE samples fabricated was 1mm. 2.3 Microscopy observation The microstructures of the isotropic and anisotropic MREs were observed using a Scanning Electron Microscope (SEM, Zeiss Supra). Samples were coated with a fine layer of gold to make them conductive and SEM images were taken with an accelerating voltage of 5KV. 2.4 Bubble inflation testing The test samples were retained in the hydraulic bubble inflation system’s inflation orifice for cycling. Initially, quasi-static tests were carried out to determine a value of failure stress and stress-strain relationship for initial loading. This allowed the equibiaxial dynamic test parameters to be set. Thereafter, fatigue tests were conducted over a range of stress amplitudes with a minimum stress of zero. Typically, pressure was applied to test samples causing them to inflate. The vision system, utilizing two charge coupled device (CCD) cameras, recorded the movement of specific points at the pole on the surface of a sample during inflation and deflation. Stress values were simultaneously calculated from the applied pressure and bubble geometry, while strain values were calculated from the change in surface distance between specific points at the bubble pole on the bubble surface, using three dimensional position coordinates obtained from the vision system output. Throughout these tests, the dynamic test facility continually recorded dimensional changes in the bubble and corrected pressure limits to maintain constant engineering stress (σEng). The dynamic test facility was integrated with a system control programme to count the accumulated cycles. The theory for obtaining stress-strain relations is described elsewhere (Jerrams et al. 2012).Test samples were not cycled in the presence of a magnetic field in the tests described here. Figure 2. SEM image of isotropic MREs Figure 3. SEM image of anisotropic MREs, arrow shows the direction of the magnetic field 3 RESULTS AND DISCUSSION 3.1 Microstructure of isotropic and anisotropic MREs The SEM images for isotropic and anisotropic MREs are shown in Figure 2 and Figure 3 respectively. As can be seen from these figures, carbonyl iron particles were distributed randomly in isotropic MREs but they formed chain-like structures in the direction of the magnetic field in anisotropic MREs. 3.2 Quasi-static testing Quasi-static tests to failure were carried out on both isotropic and anisotropic MREs and the average strength at failure was 3.5MPa and 4.1MPa respectively. These values were used to set stress amplitudes in the subsequent fatigue tests. Figure 4 shows the stress-strain curves from a quasi-static test for isotropic and anisotropic MREs. As can be observed, the stress-strain curve of an equi-biaxial test results in a similar ‘S’ shaped configuration to that seen in typical uniaxial tensile tests on rubber compounds. Unsurprisingly, the stiffer anisotropic MREs exhibited lower extensibility. |
| File Format | PDF HTM / HTML |
| Alternate Webpage(s) | https://arrow.dit.ie/cgi/viewcontent.cgi?article=1005&context=cercon |
| Language | English |
| Access Restriction | Open |
| Content Type | Text |
| Resource Type | Article |
