During the frontal crash the longerons absorb most energy of all vehicles construction elements. In order to analyse the energy absorbing capabilities of longerons under axial compression loading and to evaluate the influence of longerons geometrical characteristics and materials degradation on the vehicles safety experimental investigations and numerical calculations were performed. To assess the crashworthiness of longerons the main objective was to study the behaviour of thin-walled structural elements under axial loading conditions using the Finite Element (FE) model. The numerical FE models were created using the computer code LS-DYNA. Two models of longerons were investigated with different sections shape and for each of them materials with the four different mechanical characteristics were applied. Validation of created FE model was performed according to the experimental investigation and the results were obtained of validated FE models of vehicles crash analysis [I].The results of analyses show that the value of absorbed energy by the longerons of new vehides exceeds the value of the oldest cars. The degradation of structures in the old cars has the significant influence on the absorbed energy.

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Scientists recently focus on concrete's hardening early age and its influence to solidity of a structure. Because of complex physical-chemical processes and developed strains, stresses appear in concrete and after they exceed tensile strength of concrete-develops cracks. In practice it is noted that a structure often cracks prior to commencement of exploitation. Therefore this article analyzes the influence of stresses caused by autogenous shrinkage over solidity of structure. The importance of stresses caused by concrete shrinkage significantly increases in places where a cross-section shifts. The stress concentration area develops at these points. One of the stress concentration areas is around the formwork's transverse brace and stresses due to autogeneous shrinkage are solved. To define stresses, analytical and finite element methods are used. The stresses concentration area is calculated more precisely using the finite elements method, the results obtained are exhaustive and it allows to get a clearer picture of stresses.

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This work analyses the material fracture problem due to mixed-mode: dynamic opening and in-plane shear cases. Fracture criterions are analysed and new regularities are established, that mixed-mode fracture can be determined using critical characteristics of fracture and toughness: shear modulus and Poison's ratio.Stress intensity factor dependence curves are determined due opening and in-plane shear cases with different angle of initial crack trajectory. The opening and inplane shear fracture influence ratio is set.

When material yielding occurs, the stress intensity factor, K, no longer correctly characterizes the magnitude of the stress field around the crack tip. For significant amounts of yielding, the J-integral approach is applied as an advanced tool. In practice, for many engineering applications, the non-linear plasticity effects are of importance and therefore material behavior beyond yield needs an accurate description for input to tools for assessment. This work presents J-integral values of two different steel grades (1006 and 4340) using a newly developed analytical approach for the correction factors ηpl, which takes into account the elastic–plastic properties of the material. The evaluation approach is based on absorbed energies in a Charpy-sized specimen during the elastic and plastic deformation phases. Values of these energy terms were obtained via numerical simulation of 1006 and 4340 steel Charpy-sized specimens loaded in three-point-bending. This work highlights the effect of materials plastic properties on the J-integral. Different steel grades show different amounts of plasticity defined by the strain-hardening exponent and the strain-hardening constant and these influence the fracture parameters. Application of the plastic correction factor ηpl to Charpy-sized specimens, considering the respective plastic properties of the materials, leads to values of ηpl equal to 2.286 for 1006 steel and 2.621 for 4340 steel.