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The effect of niobium and vanadium additions (0.5 mass% and 2 mass%) on the as-cast microstructure and properties of hypoeutectic white cast iron containing 19 mass% Cr and 2.9 mass% C, has been examined. NbC carbides present in the structure of tested Fe-Cr-CNb alloys, due to their characteristic morphology, show higher wear resistance and toughness than M7C3 carbides. Increasing amount of this type of carbides, caused by the increase of niobium in the alloy, contributes to the improvement of wear resistance and dynamic fracture toughness. The alloy containing 2% Nb gives the best compromise between wear resistance and fracture toughness. This alloy shows about 23% greater dynamic fracture toughness and about 25% greater abrasion wear resistance than the basic Fe-Cr-C alloy. Besides, the secondary carbides which precipitate in the matrix regions of the tested Fe-Cr-C-V white irons also influence the abrasion behaviour and fracture toughness. The alloy containing 0.5% V has approximately the same fracture toughness but lower wear resistance than alloy with 2% Nb.

Experimental results indicate that vanadium affects the solidification process in high chromium iron. Vanadium is distributed between eutectic M 7 C 3 carbide and the matrix, but its content in carbide is considerably higher. Also, this element forms vanadium carbide. TEM observation reveals that vanadium carbide present in examined Fe-Cr-C-V alloys is being of M 6 C 5 type. DTA analysis found that with increasing vanadium content in tested alloys, liquidus temperature is decreasing, while eutectic temperature is increasing, i.e. the solidification temperature interval reduces. The narrowing of the solidification temperature interval and the formation of larger amount of vanadium carbides, as a result of the increase in the vanadium content of the alloy, will favour the appearance of a finer structure. In addition, the phases volume fraction will change, i.e. the primary -phase fraction will decrease and the amount of M 7 C 3 carbide will increase.

A new notion of joint, defined in terms of the state of motor (active or locked) and type of the elastic or rigid element, gear and/or link that follows after the motor, is introduced. Special attention is paid to the motion of the flexible links in the robotic configuration. The paper deals with the relationship between the equation of elastic line equilibrium, the "Euler-Bernoulli approach" (EBA), and equation of motion at the point of elastic line tip, the "Lumped-mass approach" (LMA). The Euler-Bernoulli equations (which have for a long time been used in the literature) should be expanded according to the requirements of the motion complexity of elastic robotic systems. The Euler-Bernoulli equation (based on the known laws of dynamics) should be supplemented with all the forces that are participating in the formation of the elasticity moment of the considered mode. This yields the difference in the structure of Euler-Bernoulli equations for each mode. The stiffness matrix is a full matrix. Mathematical model of the actuators also comprises coupling between elasticity forces. Particular integral of Daniel Bernoulli should be supplemented with the stationary character of elastic deformation of any point of the considered mode, caused by the present forces. General form of the elastic line is a direct outcome of the system motion dynamics, and cannot be described by one scalar equation but by three equations for position and three equations for orientation of every point on that elastic line. The choice of reference trajectory is analyzed. Simulation results are shown for a selected robotic example involving the simultaneous presence of elasticity of the gear and of the link (two modes), as well as the environment force dynamics.

This paper presents a theoretical background and an example of extending an elastic line equation from several aspects. Navier equation (based on the known laws of dynamics) should be supplemented with all the forces that are participating in the formation of the bending moment of the considered mode. We analyze the system in which the action of coupling forces (inertial, Coriolis', and elasticity forces) exists between the present modes. This yields the difference in the structure of Navier equations for each mode. It is shown that Daniel Bernoulli's particular integral is just one component of the total elastic deformation of the tip of any mode to which we have to add a component of the elastic deformation of a stationary regime. The essential relationship between "Lumped-mass approach" (LMA) and "Euler-Bernoulli Equations" (EBE) approaches is proved.