Damping properties and microstructure of magnetorheological composites based on iron sand and natural rubber

Material with high damping capability is desired from the viewpoint of vibration suppression in structures. Rubber is by far the most commonly used material for damping; here damping relies on the energy absorbed due to viscous flow that occurs during deformation in this viscoelastic materials. However, enhancement of damping through rubber modification or rubber selection to increase viscous flow, not surprisingly, generally results in a reduction in stiffness and strength [1]. More recently, a new class of damping materials, magnetorheological elastomers (MREs) have been developed such that inclusion of magnetic particles in rubber enables additional damping through magnetic particle interaction and interfacial friction. Furthermore, damping and stiffness can be varied by application of an applied magnetic field during fabrication or in service. MREs can be utilised for damping, either alone or within a composite structure such as those including steel plates

Development of Elastomeric Composites from Iron Sand and Natural Rubber for Vibration Damping

Material with high damping capability is used to reduce vibration in structures. Magnetorheological elastomers (MREs) are a new group of damping materials which consist of an elastomeric matrix containing a suspension of magnetically permeable particles. Damping occurs mainly by the viscous flow of the rubber matrix and inclusion of magnetic particles in the rubber enables additional damping through magnetic particle interaction and interfacial damping. The aim of this thesis was to produce MREs based on iron sand and natural rubber that have good damping performance for potential use in vibration damping. Dynamic Mechanical Analysis (DMA) was carried out in an isothermal shearmode to measure the changes in material properties caused by vulcanization in order to assess the optimum cure time of rubber compounds to ensure the best damping performance. The results revealed that the shear storage modulus (G′), shear loss modulus (G′′) and tan δ all reflect the vulcanization process, however, tan δ gave the best representation of the level of vulcanization. Indeed, tan δ was able to be used to derive the optimum cure time for rubber compounds and showed good agreement with the results using conventional methodology. The Taguchi method was employed to investigate the effect of a number of factors, namely, iron sand content, iron sand particle size and applied magnetic field during curing on tan δ and energy dissipated during hysteresis tests. The data were then statistically analysed to predict the optimal combination of factors and experiments were then conducted for verification. It was found that the iron sand content had the greatest influence on tan δ when measured over a range of frequency (0.01-130Hz at 0.5% strain amplitude and at room temperature) as well as on the energy dissipated during the hysteresis tests. The iron sand content and magnetic field were also found to influence the width of the peak in tan δ as a function of temperature (studied over the range -100 to 50ºC at 1Hz and 0.5% strain amplitude). However, none of the factors showed significant influence on tan δ for the plateau region from 1.0-4.5% strain amplitude at 100Hz and at room temperature, which is likely to be due to breakdown of weak interactions between iron sand and rubber at low strain amplitudes and therefore, damping being dominated by the viscous flow of the rubber matrix and friction of rubber chains and iron sand. Evidence from SEM micrographs of MRE sections showed that isotropic MREs had uniform particle distribution and that alignment of magnetic particles occurred for anisotropic MREs as a consequence of an applied magnetic field. However, obvious gaps between iron sand and rubber were evident, suggesting weak interaction between iron sand andrubber. Bis-(3-triethoxysilylpropyl) tetrasulphane (TESPT) was employed for surface modification of iron sand. The amount of TESPT was varied at five levels (2, 4, 6, 8 and 10wt%) relative to iron sand content to assess the optimum amount of coupling agent for interfacial bonding and damping performance. Evidence that coupling had occurred between iron sand and TESPT was identified by Raman Spectroscopy and the grafting percentage was determined by thermogravimetric analysis. Crosslink density assessment by swelling testing provided evidence that the tetrasulphane group of TESPT formed crosslinks with the rubber chains. The results exhibited the advantages of TESPT as a coupling agent between iron sand particles and rubber and also revealed that 6% TESPT content produced the highest crosslink density. It was found that the silane coupling agent improved the amount of energy dissipated during hysteresis tests as well as tan δ over the range of frequency and strain amplitude explored. The results also revealed that with silane treated iron sand, tan δ increased with increasing magnetic field up to a saturation point at 600 mT. However, the presence of coupling agent and formation of different lengths of aligned particles did not strongly affect the peak height and width of the tan δ versus temperature curves. Tan δ and energy dissipated during hysteresis testing of isotropic and anisotropic MREs containing silane modified iron sand particles were compared with existing antivibration rubbers. The chosen antivibration rubbers for comparison contained different contents of carbon black filler (30, 50 and 70 phr) in a natural rubber matrix. Energy absorption for comparative samples was generally higher than isotropic and anisotropic MREs over the range of frequency and strain amplitude explored, as well as in hysteresis testing and this was believed to be largely due the presence of carbon black in the existing antivibration rubber formulations. Further assessment was carried out on materials that were the same as the anisotropic MREs except they had additions of carbon black. The energy absorption was generally found higher than comparative samples with the same carbon black contents, supporting the use of iron sand to improve damping. However, this trend was found to reverse at around Tg, which is considered to be due to the segmental motion of rubber chains being by far the most significant influence on energy absorption in the glass transition zone. A model was developed to include viscous flow of the rubber matrix, interfacial damping and magnetism-induced damping to give the total damping capacity of MREs. The proposed model was assessed experimentally using a series of isotropic and anisotropic MREs. Comparison between tan δ with predicted damping capacity showed that the predicted damping capacity matched the experimental trends with average percentage difference of 8.1% and 21.8% for MREs with modified iron sand and unmodified iron sand, respectively

Effect of Carbon Black on the Dynamic Properties of Anisotropic Magnetorheological Elastomer

In this work, dynamic properties of magnetorheological elastomers (MREs) based on iron sand and natural rubber; with different contents of carbon black filler (30 and 50 phr) were investigated. Tan δ was measured using dynamic mechanical analysis (DMA) over a range of frequency (0.01–130 Hz) and strain amplitude (0.1%–4.5%). Tan δ was found to be higher for anisotropic MREs with additions of carbon black, with 20%–40% improvement over the whole frequency range explored and 6%–15% improvement over the strain amplitude range explored. The results exhibited the advantages of carbon black in improving the damping performance of the MREs. The morphological characteristics of the MREs were also examined with scanning electron microscop

Comparison of dynamic properties of magnetorheological elastomers with existing antivibration rubbers

Tan δ and energy dissipated during hysteresis testing of isotropic and anisotropic MREs containing silane modified iron sand particles in a natural rubber matrix were compared with existing antivibration rubbers. Tan δ was measured using dynamic mechanical analysis (DMA) over a range of frequency (0.01–130 Hz), strain amplitude (0.1–4.5%), and temperature (−100–50 °C). Energy dissipated was measured using a universal tester under cyclic tensile loading. The chosen antivibration rubbers for comparison contained different contents of carbon black filler (30, 50 and 70 phr) in a natural rubber matrix. It was found that energy absorption for comparative samples was generally higher than isotropic and anisotropic MREs over the range of frequency and strain amplitude explored, as well as in hysteresis testing and this was believed to be largely due the presence of carbon black in the formulation. Further assessment was carried out on materials that were the same as anisotropic MREs except they had additions of carbon black. The energy absorption was found higher than comparative samples with the same carbon black contents, supporting the use of iron sand to improve damping. However, trends for energy absorption at around Tg were found to reverse which is considered to be due to the segmental motion of rubber chains being by far the most significant influence on energy absorption in the glass transition zone

The effect of silane coupling agent on iron sand for use in magnetorheological elastomers Part 1: Surface chemical modification and characterization

Bis-(3-triethoxysilylpropyl) tetrasulphane (TESPT) was employed for surface modification of iron sand for use in magnetorheological elastomers (MREs). The amount of TESPT was varied at five levels (2, 4, 6, 8 and 10 wt%) relative to iron sand content to assess the optimum amount of coupling agent for interfacial bonding and damping performance. Evidence that coupling had occurred between iron sand and TESPT was identified by Raman Spectroscopy and the grafting percentage was determined by thermogravimetric analysis. Subsequently, isotropic MREs containing unmodified and modified iron sand particles and natural rubber were prepared. Crosslink density assessment by swelling testing provided evidence that the tetrasulphane group of TESPT formed crosslinks with the rubber chains. The results exhibited the advantages of TESPT as a coupling agent between iron sand particles and rubber and also revealed that 6% TESPT content produced the highest crosslink density. The effects of the amount of TESPT on dynamic mechanical properties the morphological characteristics of the MREs were also investigated

Monkey detection using deep learning for monkey-repellent

Animal intrusion has caused many issues for human beings, especially monkeys. Monkeys have caused many problems such as yield crop damage, damage to human facilities and assets and stealing food. This study aims to investigate the use of deep learning to detect monkey presence accurately and use a proper repellent system to scare them away. A deep learning algorithm is constructed with supervised learning, which includes the monkey dataset with appropriate labelling of the object of interest. The detection of the monkey comes with a bounding box with respective confidence of detection. The result is then used to evaluate the accuracy of monkey detection. The accuracy of the trained model is assessed by evaluating its performance under varying conditions of camera quality and distances. The study focuses on proving the reliability of deep learning to detect monkeys and automatically perform corresponding actions like repelling monkeys. Hence this may reduce the reliance of manpower to secure a large space and improve safety issues

Development of natural rubber foam with water as a blowing agent via microwave and convection heating methods

This study used water as the physical blowing agent as well as microwave heating (MH) and convection heating (CH) to simultaneously foam and cure natural rubber foam (NRF). Various processing methods and parameters, such as single heating and sequential heating using a mix of CH and MH; were investigated. The correlation between these processing methods as well as different water loadings was then evaluated and compared in terms of physical appearance, density, and morphology. The NRF samples produced using sequential MH and CH (SMC) heating exhibited better shape and structure than samples produced using single heating of either CH or MH only as well as sequential CH and MH (SCM) heating at all water loadings. NRF samples with water loadings of 1.5 and 2.0 phr had a density of less than 0.1 g/cm3 . The potential heating mechanism of all the heating methods explored in this study was proposed and discussed to further understand the microwave heating process. The findings of this study proved that water could be utilized as a physical blowing agent in the production of NRF products with microwave-assisted foamin

Effect of Different Pressures on Polymer Flow at a Contraction Path: A Real-Time Numerical Approach

The complexity of polymer flow through a contraction arises from the simultaneous occurrence of shear and elongational strains near the entrance of the contraction path (die). Although this phenomenon has been extensively studied, the effect of plunger motion on the flow toward the contraction path remains underexplored. This study investigated the rheological behavior of thermoplastic polymers at a contraction flow path to enhance the understanding of their flow and rheological behavior, including variations in velocity, pressure, viscosity, and shear rate under varying loads. Polypropylene (PP), a semicrystalline polymer with a low melting point, was used as the test material. The operating temperature was set to 180 °C, and the displacement of the plunger, marked with black lines at its initial and final heights, was recorded under loads of 0.3, 0.6 and 0.85 MPa. The displacement rates were analyzed using MATLAB. A dynamic mesh approach in ANSYS 19 was employed to simulate the real-time motion of the plunger, incorporating a user-defined function developed in C language to control the dynamic boundary motion. The numerical approach successfully simulated the rates of plunger displacement (speed) and predicted the viscosity of PP within the paths (barrel and die). Results indicated that the plunger speed increased with pressure. The pressure generated by the plunger created a driving force that overcame the resistance to flow within the barrel. Higher pressure from the plunger resulted in a greater driving force, which increased the flow rate of the polymer melt through the barrel. On the other side, as the polymer melt flowed from a large cross-sectional area to the contraction flow area, the velocity of the polymer molecules increased, resulting in a pressure drop in the PP melt. Polymer molecules became oriented and stretched in the flow direction upon entering the contraction area, further increasing the shear rate. Consequently, the reduced cross-sectional area in the contraction increased the flow rate, elevated the shear rate, and decreased the viscosity, facilitating polymer flow through the contraction

Dynamic Properties of Magnetorheological Elastomers Based on Iron Sand and Natural Rubber

In this study, magnetorheological elastomers (MREs) based on iron sand and natural rubber were prepared. The Taguchi method was employed to investigate the effect of a number of factors, namely, the iron sand content, iron sand particle size, and applied magnetic field during curing on the loss tangent (tan δ) and energy dissipated during cyclic loading. Tan δ was measured through dynamic mechanical analysis over a range of frequency (0.01–130 Hz), strain amplitude (0.1–4.5%), and temperature (−100 to 50°C). The energy dissipated was measured with a universal tester under cyclic tensile loading. The data were then statistically analyzed to predict the optimal combination of factors, and finally, experiments were conducted for verification. It was found that the iron sand content had the greatest influence on tan δ when measured over a range of frequency, and the energy dissipated during hysteresis tests. However, none of the factors showed a significant influence on tan δ when measured over a range of strain amplitude. Furthermore, the iron sand content and magnetic field were also found to influence the width of the peak in tan δ as a function of the temperature. The morphological characteristics of the MREs were also examined with scanning electron microscopy