The paper presents the results of years of research in developing the technology of relaxation of residual stress and strain on welded joints of large dimensions of structures. The effects of the development of two technologies vibrational relaxation are presented. The first method was developed in the mid-‘80s for the aircraft industry “Soko” in Mostar and is based on the stabilization of the structure of tools for assembly of passenger and military aircraft. This method has been used in recent years to relax assembly welds on the bridge structure and bridge cranes. For each specific design, developed through a process of simulation technology is relaxation, which is the implementation monitored continuously with adequate instruments for detecting vibration and stress analysis. Development of new methods based on research on the parameters of which vibrational relaxation process is realized in the phase of welding and cooling time of the structure. Comparative analysis of the results of implemented technology identical welded structures point to the advantage of the new method. Specifically during the vibration is much shorter, because the gradient of stress is better, and the risk of material fatigue is minimal. The homogeneity of the weld and fracture energy of the weld and base metal heat affected zone is increased quality of new technology for relaxation, which significantly increases the stability of the realized structures.

Numerous are examples of failure and damages of welded joints, despite strict codes regarding the quality. The primary causes are defects in welded structures that arise during production or in service. For safe service of structures produced of high strength steel by welding, properties of welded joints have to be determined. For welded joint constituents (parent metal PM, weld metal WM, heat-affected-zone HAZ) these properties are determined: hardness, impact energy and its parts for crack initiation and propagation, and fracture mechanics parameters, fracture toughness, KIc, and critical J integral, JIc,. These parameters can help in evaluation of welded joint safety, and thus of the entire welded structure. Kljucne reci • zavareni spoj • tvrdoca • energija udara • mehanika loma