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This article details the experimental and numerical results on the energy absorption performance of square tubular profile with circular discontinuities drilled at lengthwise in the structure. A straight profile pattern was utilized to compare the absorption of energy between the ones with discontinuities under quasi-static loads. The collapse mode and energy absorption conditions were modified by circular holes. The holes were drilled symmetrically in two walls and located in three different positions along of profile length. The results showed a better performance on energy absorption for the circular discontinuities located in middle height. With respect to a profile without holes, a maximum increase of 7% in energy absorption capacity was obtained experimentally. Also, the numerical simulation confirmed that the implementation of circular discontinuities can reduce the peak load (P max ) by 10%. A present analysis has been conducted to compare numerical results obtained by means of the finite element method with the experimental data captured by using the testing machine. Finally the discrete model of the tube with and without geometrical discontinuities presents very good agreements with the experimental results.

The paper presents a theory of vibratory locomotion, a prototype, and the results of experiments on mini robot, which moves as a result of inertial excitation provided by two electric motors. The robot is equipped with elastic bristles which are in contact with the supporting surface. Vibration of the robot generates the friction force which can push the robot forward or backward. The paper presents a novel model of interaction between the bristles and the supporting surface. The friction force (its magnitude and sense) is defined as a function of the robot velocity and the robot's vibrations. The analysis is done for a constant coefficient of friction and a smooth surface. Depending on the motors' speed, one may obtain a rectilinear or a curvilinear motion, without jumping or losing contact with the substrate. The results of the simulation show which way the robot moves, its mean velocity of locomotion, change of the slipping velocity of the bristles and its influence on the normal and the friction force. A prototype was built and experiments were performed with it.

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