An alternative way to increase the maximum yield stress is to increase the particle size distribution inside the MR-fluid. The advantage of this technique is that it allows the viscosity tobe reduced while maintaining the same particle volume fraction (Goncalves et al., 2006). Aparticular case of this technique is to use bimodal particle distributions, where two differentsize groups of particles are combined (Golden et al., 2005) (Weiss et al., 1999) (Foister, 1997).As shown in Figure 2.6, a substantial increase in yield stress can be achieved by a smallincrease in the proportion of small particles (25% in weight). This effect can be explained byan increased particle packing when chains are formed.
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