Theoretical study on the dynamic compression and energy absorption of porous materials filled with magneto-rheological fluid

In this paper, the dynamic compression and energy absorption behaviours of porous materials filled with MR fluid are studied theoretically. By means of Darcy's law, Ergun's equation and energy method, the single-layer and two-layer models for the energy absorption and dynamic stress are first derived, in which the compression of the skeletal material, the inertia effect, viscous flowing of the fluid as well as the MR effect are considered. The comparisons between the theoretical results and previous experiments of porous copper specimens show that the two-layer model can predict the dynamic stress before the circumferential failure of specimen very well. Based on the theoretical models, it is found that the energy dissipated by the deformation of the skeletal material and MR effect is nearly insensitive to the strain-rate, while that by the viscous flowing and inertial effect increases linearly and quadratically with the increase of impact velocity, respectively. When the strain rate is low, the energy dissipation due to the MR effect is larger than that by viscous flowing. However, if the strain-rate is higher than a certain value, the viscous energy dissipation will be dominant. Moreover, with the same strain rate, specimens with larger radius/thickness ratio could obtain higher compression stress. To improve the controllability of the MR fluid-filled porous material, higher yield stress induced by magnetic field is preferred, and the strain-rate should be as low as possible.