ANALYSIS OF SCHEMES OF LOAD APPLICATIONS FOR MODELING THE STRENGTH OF WELD SEAMS WITH THE ACCOUNT OF MUTUAL INFLUENCE OF VARIOUS DEFECTS

Abstract

The main objective of this research is to study the stress concentration in welded joints of structures subjected to simultaneous action of intensive force and temperature factors. Plate structures are considered. It is assumed that in the welds connecting the plates, there may be cracks, pores and other defects. Three calculation schemes characterizing the force and temperature effects on the plate structure have been studied. Analysis of the stress intensity factors for the three proposed calculation schemes showed that the results differ from 0.5% to 2%. An approach based on the finite element method for determining a stress-strained state in the weld with pores and an inclusion is developed. The method makes it possible to estimate mutual influence of the inclusion on the origin and crack opening in the pore. This method will make it also possible to made recommendation on increasing the period of operation of the welded seams. The special feature of the studies is in creating different loads by time, by the depth of the plates, by the length of the plates and welded seams. Different temperatures are considered. The different types of finite elements are used for modeling the zone of pores. In this paper, we investigate the mutual effect of pores, inclusions, and cracks using various schemes of applying loads to the plates making up the box. For each model, calculations were made for three calculation schemes. Calculation scheme 1 provides maximum values of pressure and temperature over the entire surface of the box. Calculation scheme 2 supposes that the pressure varies both in height and width of the plate during time, the maximal temperature is applied over the entire surface. Calculation scheme 3 supposes that the temperature varies both in height and width of the plate at each moment of time, and the pressure is maximal across the entire plate. The maximum stresses are calculated in the welded seam with pores and inclusion. The comparison of results obtained by the three proposed calculation schemes is accomplished. The maximal stresses in inclusions are slightly influenced and are independent of the finite elements choice. But the maximal stresses near pores are different for different type of elements. Although the difference is not drastic it is testified about necessarily of additional research concern with the choice of the appropriate finite element for welded seam cracking analysis. The classical solid element requires essentially more computational efforts. The mutual influence of defects such as pores, inclusions, cracks on the crack propagation in the welded seam is significant with decreasing the minimum distance between the defects. As shown by calculation, the design scheme 1 gives the largest values of stresses and displacements.