Exoskeletons are the mechanical systems whose operation is carried out in close cooperation with the human body. In this paper, the authors describe a mathematical model of the hydraulic exoskeleton of a lower limb. The coordinates of characteristic points of the exoskeleton in the sagittal plane as a function of user height are presented. The mathematical models, kinematics, and kinetics equations were determined. The masses of the actuators and their dimensions were selected based on catalog data. The force distribution in the wearable system during the squat is shown. The proposed models allowed us to determine the trajectory of individual points of the exoskeleton and to determine the forces in hydraulic cylinders that are necessary to perform a specific displacement. The simulation results show that the joint moments depend linearly on actuator forces. The dynamics equations of the wearable system are non-linear. The inertia of the system depends on the junction variables and it proves that there are dynamic couplings between the individual axes of the exoskeleton.

No abstract

Cold-formed thin-walled beams may lose the stability in different ways. The common buckling modes which have an influence on the failure of the beam are lateral-torsional, local and distortional buckling. The strength of cold-formed members can be calculated with the Effective Width Method which is incorporated in many international and national standards. In this paper, the experimental and theoretical results calculated with the aforementioned method have been compared.

The paper presents a proposal of using an experimental phenomenological approach and energy based method to the modelling of mechanical properties of nonlinear elastic materials using examples of two selected polymers. On the basis of an experimental stress-strain relation, together with transversal deformation measurement and the geometrical interpretation of the deformation process, analytical forms of the strain energy density function and a pure volumetric part of the strain energy density function have been introduced. The volumetric part of energy has been used in the description of the material damage process interpreted as the appearance of the first plastic deformations, which is the original part of the work and continuous investigations carried out by Wegner and Kurpisz. All theoretical investigations have been illustrated using examples of PVC and PA-6.

Thin walled cold formed structures were, and still are, very popular structural elements used in mechanical engineering. Modern technology and the progress in materials engineering allow to fabricate various shapes of thin walled cold formed components. Therefore, combinations between technology possibilities, material properties, loads and engineering requirements are wide and unlimited for thin walled components. The aim of this paper is to perform an experimental study of cold formed C-channel steel beams under four-points bending loads based on the global and the local buckling phenomena. A test rig was developed with a specially designed support system to subject thin-walled steel beams to a four-point bending load, where the support and loads were applied to the shear center of the open section steel beam. It is shown that it is not possible to completely eliminate the torque load on a thin-walled beam with an open section where load and support are applied in the shear center because investigated beams weren’t ideal made. Thin walled open section beams are very sensitive for boundary conditions and geometrical accuracy. The force of gravity is also working. The presented research methodology can be improved and do test with other open section thin walled beams.