Design and evaluation of a linear damper working with MR shear thickening fluids

Magnetorheological (MR) materials and shear thickening fluids are both smart material and their combination could offer both MR and ST effects. This study looks at the properties and behaviour of magnetorheological shear thickening fluid (MRSTF) in particular whilst applied as a semi-active energy absorber. A device with two forms of varying vibration control has been created and measured. The result shows that this MRSTF filled damper showed both MR and properties

Sensing and Rheological Capabilities of MR Elastomers

Magnetorheological elastomers (MREs) are smart materials where polarized particles are suspended in a non-magnetic solid or gel-like matrix. Two kinds of MREs, namely anisotropic and isotropic, are fabricated either under a magnetic field or without a field [1,2]. In anisotropic MREs, polarised particles are arranged in chains within a polymer media such as silicon rubber or natural rubber. The shear modulus of MRE can be controlled by the external magnetic field, which has led to many applications, such as tuned vibration absorbers, dampers and sensor

Study of PDMS based magnetorheological elastomers

The fabrication of conventional magnetorheological elastomers (MRE) is usually taken more than 1 day because the conventional matrixes such as natural rubber and silicone rubber need long curing time to become solid state. This study presents a rapid method for fabricating MRE within 90 minutes by using poly(dimethylsiloxane) (PDMS) as the matrix thanks to the rapid curing of PDMS in high temperature. A total of four PDMS based MRE samples were fabricated. Their mechanical and rheological properties under both steady-state and dynamic loading conditions were tested with a parallel-plate rheometer. Additionally, the microstructures of the PDMS based MREs were also observed by SEM and compared with the silicone rubber based MRE

Study of shear thickening/stiffened materials and their applications

This thesis focused on the properties of shear thickening/stiffened materials and their applications. The fabrication of shear thickening fluid (STF) made from ethylene glycol and fumed silica was studied and its properties were measured with a rheometer under state steady and dynamic test conditions. The temperature effect on shear thickening fluid was also investigated and a numerical function was proposed to express the relationship between the temperature, viscosity, and concentration of fumed silica. Adding fumed silica to a currently used commercial electrolyte resulted in a shear thickening electrolyte with a higher ionic conductivity than the commercial electrolyte. Furthermore, the batteries using this shear thickening electrolyte provided extra mechanical protection than those batteries containing commercial electrolyte. The magnetorheological shear thickening fluids (MRSTFs) can be gained by combining the magnetorheological fluid (MRF) and shear thickening fluid. This new MRSTFs were tested and revealed both a magnetorheological effect and shear thickening properties. Moreover, the damper filled with MRSTF had unique properties coming from both magnetorheological fluid and shear thickening fluid. Shear stiffened elastomers (SSEs) made of silicone rubber and silicone oil were fabricated and observed by scanning electron microscope (SEM). A cluster structure was observed and the sample with a higher concentration of silicone oil had longer clusters of silicone rubber. The rheology of shear stiffened elastomers was measured with a rheometer and it showed that the sample with a higher concentration of silicone oil had a longer linear range and a lower shear modulus. During the dynamic frequency sweep tests when the shear strain amplitude was above a critical value, the shear stiffened elastomer sample was seen to change from solid to liquid and then from liquid to solid, which was the onset of shear stiffened

Study of magnetorheology and sensing capabilities of graphite based MR elastomers

This study focuses on the magnetorheology and sensing capabilities of graphite based MR Elastomers (Gr MREs). By introducing graphite to conventional MREs, the Gr MREs with various graphite weight fraction are derived. Both steady state tests 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 samples with higher graphite weight fraction show higher initial storage and loss moduli and lower MR effects. Also the microstructures of isotropic and anisotropic Gr MREs are observed. We can see that the carbonyl iron particles array in chains in the anisotropic MREs and the graphite powders disperse in matrix randomly. Graphite powders contribute to the magnetorheology of MREs such as increasing the initial mechanical properties and diminishing the MR effect. Also the graphite powders connect different carbonyl iron chains parallelly, which helps to reduce the total resistance of MREs. The conductivity of Gr MREs is affected by three factors. The first is the weight fraction of graphite in the Gr MRE samples; the more weight fraction of graphite is, the more conductive Gr MRE sample is. The external force applied on the samples is another factor. Increasing external force can cause the electrical resistance decrease. The other cause affecting sample conductivity is the intensity of magnetic field. When the intensity rises, the resistance of samples goes down. This paper introduces the Gr MREs’ fabrication process, analyzes the relationship between the resistance of Gr MREs, the external force and the intensity of magnetic field and shows the data gotten from the experiments

Study of magnetorheology and sensing capabilities of MR elastomers

This study focuses on the magnetorheology and sensing capability of graphite based Magnetorheological Elastomers (Gr MREs). By introducing graphite (Gr) to conventional MREs, the Gr MREs are derived. The anisotropic sample with 20% graphite weight fraction was selected to be compared with anisotropic conventional MREs. The microstructures of anisotropic Gr MREs and conventional MREs were observed. Both steady state tests and dynamic tests were conducted to study rheological properties of the samples. For dynamic tests, the effects of strain amplitude, and frequency on both storage modulus and loss modulus were measured. For sensing capability, the resistance of selected Gr MREs under different magnetic fields and external loadings is measured with a multi-meter. Either higher magnetic field or more external loading results in the resistance increment. Based on an ideal assumption of perfect chain structure, a mathematical model was proposed to investigate the relationship between the MRE resistance with the external loadings. In this model, the current flowing through the chain structure consists of both tunnel current and conductivity current, both of which depends on external loadings. The modelling parameters were identified and reconstructed from comparison with experimental results. The comparison indicates that both experimental results and modelling prediction agree favourably well

Comparison of rheological behaviors with fumed silica-based shear thickening fluids

Shear thickening fluids (STFs) of differing compositions were fabricated and characterised in order to observe the effect of varying chemical and material properties on the resultant rheological behavior. Steady shear tests showed that for a given carrier fluid and particle size exists an optimum weight fraction which exhibits optimal shear thickening performance. Testing also showed that increasing particle size resulted in increased shear thickening performance and its onset whilst altering the carrier fluid chemistry has a significant effect on the thickening performance. An explanation is provided connecting the effect of varying particle size, carrier fluid chemistry and weight fraction to the resultant rheological behavior of the STFs. Two STFs were chosen for further testing due to their improved but contrasting rheological behaviors. Both STFs displayed a relationship between steady and dynamic shear conditions via the Modified Cox-Merz rule at high strain amplitudes (γ0 ≥ 500%). Understanding the effects of particle and liquid polymer chemistry on the shear thickening effect will assist in \u27tailoring\u27 STFs for certain potential or existing applications

Sensing capabilities of graphite based MR elastomers

This paper presents both experimental and theoretical investigations of the sensing capabilities of graphite based magnetorheological elastomers (MREs). In this study, eight MRE samples with varying graphite weight fractions were fabricated and their resistance under different magnetic fields and external loadings were measured with a multi-meter. With an increment of graphite weight fraction, the resistance of MRE sample decreases steadily. Higher magnetic fields result in a resistance increase. Based on an ideal assumption of a perfect chain structure, a mathematical model was developed to investigate the relationship between the MRE resistance with external loading. In this model, the current flowing through the chain structure consists of both a tunnel current and a conductivity current, both of which depend on external loadings. The modelling parameters have been identified and reconstructed from comparison with experimental results. The comparison indicates that both experimental results and modelling predictions agree favourably well

Viscoelastic properties of MR elastomers under harmonic loading

This paper presents both experimental and modeling studies of viscoelastic properties of MR elastomers under harmonic loadings. Magnetorheological elastomer (MRE) samples were fabricated by mixing carbonyl iron power, silicone oil, and silicone rubber and cured under a magnetic field. Its steady-state and dynamic properties were measured by using a parallel-plate rheometer. Various sinusoidal loadings, with different strain amplitude and frequencies, were applied to study the stress responses. The stress–strain results demonstrated that MR elastomers behave as linear visocoelastic properties. Microstructures of MRE samples were observed with a scanning electron microscope. A four-parameter linear viscoelatic model was proposed to predict MRE performances. The four parameters under various working conditions (magnetic field, strain amplitude, and frequency) were identified with the MATLAB optimization algorithm. The comparisons between the experimental results and the model predictions demonstrate that the four-parameter viscoelastic model can predict MRE performances very well. In addition, dynamic properties of MRE performances were alternatively represented with equivalent stiffness and damping coefficients