form chain-like structures when the external magnetic field is applied, resulting in an increase of the apparent viscosity(粘性) of the fluid
(Fig. 1 and 2).
Where G is the complex material modulus. This model is also a good approximation for MR devices. However, the actual behaviour is more complicated and includes stiction(静摩擦) and hysteresis(磁滞现象) such such as shown in Fig. 3.d
• Dynamic Yield Strength – provides high yield strength in the presence of a magnetic field and very low yield strength in the absence of a magnetic field; allows for a wide range of controllability.
地势
MRF-122EG Magneto-Rheological Fluid
Features and Benefits
• Fast Response Time – responds instantly and reversibly to changes in a magnetic field.
• Hard Settling Resistant – provides high resistance to hard settling; easily redispersed(重分散).
• Non-Abrasive(零磨损)– formulated to not abrade(损伤) the devices in which the MR fluid is used.
Fig. 1 : Chain-like structures formation in the MR fluid under an externally applied magnetic field (from LORD corporation)
Fig. 2: Chains formation in a drop of MR fluid (from ISC Fraunhofer)
当外加磁场施加于铁磁质时，其原子的偶极子按照外加场自行排列。 即使当外加场被撤离，部分排列仍保持：此时，该材料被磁化。在该材 料中，磁场强度（H）和磁感应强度（B）之间的关系是非线性的。如 果在增强场强条件下，此二者关系将呈曲线上升到某点，到达此点后， 即使场强H继续增加，磁感应强度B也不再增加。该情况被称为磁饱和 （magnetic saturation）。
The rheological behaviour of MR fluids is often represented as a Bingham plastic model with a variable yield strength depending on the applied magnetic field H (Fig. 3a and 3b). The flow is governed by the equation:
• Temperature Resistant – performs consistently throughout a broad temperature range, meeting the requirements of demanding applications such as automotive shock absorbers.
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What are magneto rheological fluids?
Magnetorheological fluids belong to the group of so called
controllable fluids. This means that they exhibit a significant change in their rheological behaviour when an external magnetic field(外部磁 场) is applied to them. They are indeed composed of micron-sized magnetic particles(微米级磁粒), located inside a liquid carrier, that
where is the shear stress, is the shear strain and is the viscosity of the fluid. The operating range is the shaded area in Fig. 3c. Below the yield stress (at strains of the order of 10-3), the MR fluid behaves viscoelastically:
Fig. 3 : (a) and (b) Bingham plastic model, (c) Operating range, (d) Hysteretic behaviour in MR fluid devices
磁滞现象 Hysteresis
磁滞现象在铁磁性材料中是被广泛认知的。是指在磁化和去磁过程 中，铁磁质的磁化强度不仅依赖于外磁场强度，还依赖于原先磁化强度 的现象。