Experimental proof of squeeze damping capacity of imbibed soft porous layers subjected to impact

During last decade a series of theoretical studies revealed the high pressures generated in highly porous soft materials imbibed with fluids and subjected to compression, with possible application to impact damping. The mechanism, named eXPoroHydroDynamic (XPHD) Lubrication, combines the resistance to flow inside the porous matrix with its variable (decreasing) permeability during compression. Early experimental results obtained on falling ball and pendulum tests, at low velocity (V<6m/s), were promising. This paper reports preliminary experimental results obtained at medium impact velocity and high energy, for circular, flat contact surface, performed on a gas gun test rig. Specimens ("damping cells") made by encapsulation of a porous material and glycerine have been tested in various impacted structures. It is shown that the maximum contact force is reduced up to 50% when the impacted structure includes the proposed specimens. Visual inspection of impacted specimens clearly shows that for medium velocity the impact was supported by high squeezing pressure generated inside the porous layer. The experiments have also shown that the presence of a bullet-proof vest does not change significantly the impact force variation. Comparison with the XPHD model for disc configuration shows satisfactory agreement for velocity V < 17m/s.