ABSTRACT. The influence of exploitation period and temperature on the fatigue crack growth parameters in different regions of a welded joint is analysed for new and exploited low-alloyed Cr-Mo steel A-387 Gr. B. The parent metal is a part of a reactor mantle which was exploited for over 40 years, and recently replaced with new material. Fatigue crack growth parameters, threshold value K th , coefficient C and exponent m, have been determined, both at room and exploitation temperature. Based on testing results, fatigue crack growth resistance in different regions of welded joint is analysed in order to justify the selected welding procedure specification.

Original scientific paper Machines aimed for different purposes must be designed taking into account specific shape, type of load and materials they are made of. Nowadays different design solutions can easily be examined by using the finite element method. In this paper an example is given of examining a machine with closed supporting structure, made of iron-concrete, dynamically loaded composite material.Keywords: composite material iron-concrete; dynamic loading; finite element method; supporting structure Analiza noseće konstrukcije alatnog stroja od kompozitnog materijala metodom konačnih elemenata Izvorni znanstveni članak Strojevi različite namjene moraju biti projektirani uzimajući u obzir specifičan oblik, vrstu opterećenja i materijal od kojeg su izrađeni. Različita projektna rješenja danas se mogu lako provjeriti primjenom metode konačnih

Analysis of fracture toughness of high-strength low alloyed steel, Nionikral-70, welded joint constituencies, subjected to variable load is given in this paper, using two parameters. Crack initiation resistance is determined by testing of endurance limit and by designing of Wöhler curves. Crack propagation resistance is determined by testing of crack growth rate, and accordingly determination of Paris equation parameters. Analysis of fracture toughness is given based on testing results, comparing obtained values for base metal, weld metal and heat affected zone.

The problem of fracture toughness, KIc, determination at a crack tip localized in a welded joint is placed in principle because fracture mechanics assumes homogenous material, not only around the crack tip but on a distance from it, in order to maintain valid theoretical assumptions and importance of the fracture toughness as the property measured by some of the fracture mechanics methods. Welded joint, as an integral part of a structure, represents inhomogeneity by microstructure and mechanical properties, often by geometrical form, and by the stress field as well, which are affected by various factors as well as residual stresses after welding [1]. However, these general difficulties did not disenable experimental determination of the fracture toughness under plane strain, KIc, in certain critical areas of a welded joint, or welded joint as a whole, but rather there are difficulties in interpreting the meaning of the measured values. Specimens for the fracture mechanics parameters determination are specimens with cracks, and cracks appears in welded joints as the most critical defects.

In this paper is determined dependence on the motive power of the cutting speed for exploitative area efficiency on tool machine life and cross section chips for a universal machine tool for processing by scraping. These dependences were used to determine the main features of the optimal and maximal motive power machine. On the basis of this, analysed of the increase in motive power machine for characteristical cases in order to adapt the exploitation characteristics on the new requirements for the purpose of improve productivity.Using the previous analysis, it was determined the best solution from the aspect a rational design of the machine, while simultaneously provided the utilization of the main features on the basis of increase in rpm using increased tool life. In order to better presentation of problems, analysed in the appropriate diagrams PV and VD.On the characteristic example of manufacturing practices, at the end of this paper, is given the overview of improvements exploitation characteristics of a universal lathe appropriate calculations from the aspect of adjustment the characteristics on the new requirements, with the expectation that the reconstruction of the machine will be the lowest.