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The dynamical behaviour of the laser beam fusion cutting process of metals is investigated. Integral methods such as the variational formulation are applied to the partial differential equations for the free boundary problem and a finite dimensional approximation of the dynamical system is obtained. The model describes the shape of the evolving cutting kerf and the melt flow. The analysis is aimed at revealing the characteristic features of the resultant cut, for example, ripple formation and adherent dross. The formation of the ripples in the upper part of the cut, where no resolidified material is detectable, is discussed in detail. A comparison with numerical simulations and experiments is made.

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The paper analyses the influence of the strain rate on the behaviour of unalloyed steels with Re 210 – 550 MPa in the deformation process. It presents and analyses the results of the influence of the strain rate ranging from 10-3 to 2.5.102 s-1 on the yield point, the tensile strength, the elongation and the reduction of area. It analyses the non-homogeneity of development of plastic deformation from both the macroscopic and microscopic points of view, as well as the influence of the strain rate on the development of plastic deformation. Since the intensity of the influence of the strain rate on the properties of materials depends on their internal structure, the tested steels are divided into three groups based on their yield point and yield point to tensile strength ratio.