One of the most important devices for absorbing energy of the impact is circular tubes which absorb energy in different modes of plastic deformation. But one of the most important modes of deformation is dynamic progressive buckling caused by the axial collapse. This mode has the most energy absorption. In this study, the behavior of thin walled tubes (with caps) which have a fossa near the end edges of the tube has been investigated in numerical and experimental way. This is the contrary to the previous researches on energy absorption which used the quasi-static form. To carry out experimental tests, a drop hammer machine has been used. In the numerical part, capabilities of Abaqus have been employed. The results show that caps improve energy absorption thus more energy is absorbed in less length crushing, and the up and down fossa of the tube causes the maximum collapse force occurred with a delay. Also these absorbers have a linear behavior in absorbing energy with respect to the crushing length and the average collapse force has not been changed by increasing the hammer weight. An experiment was done to assess the collisions with the same kinetic energy to study strain rates in four collisions. It was seen that a reduction of 16.9 percent in strain rate increases 2.6 percent of the crushing length.