Pejo Konjatić

The Influence of the Weld Width on Fracture Behaviour of the Heterogeneous Welded Joint

Since welded constructions are widely used in engineering, a certain flaws in welded joints may occur either in process of welding or in exploitation period. Easiest way to prolong working life of such welded construction is to repair welded joint to eliminate possibility of construction failure. Process of repair welding usually gives heterogeneous welded joints because during process of repair additional material is introduced into welded joint, resulting in heterogeneity from the presence of materials in welded joint point of view. Such difference in materials usually results in yield strength difference between materials, represented with mismatch ratio, and it is commonly present in welds where high strength low-alloyed (HSLA) steels were welded. Since I butt welded joints are very common in welding, a systematic investigation of such welds is performed and presented in this paper. Therefore in this investigation the influence of present material in heterogeneous weld and geometry of weld is investigated in context of fracture resistance of welded joint represented as yield load solutions in the first place. A flaw in form of crack was implemented in such heterogeneous weld and using finite element method yield load solutions for different combinations of weld geometry and material strength are obtained and presented in form of diagrams.

INVESTIGATION OF THE MIXED-MODE FRACTURE IN DELAMINATION TESTS: NUMERICAL SIMULATIONS USING COHESIVE ZONE AND PARTITIONING METHODS

Delamination (fracture) tests have been numerically investigated using various cohesive zone properties. The test utilises asymmetric and symmetric double cantilever beam specimens loaded with bending moment. Energy release rate contributions from mode I and mode II fracture are calculated using a global and local approach. Mode-mixities results are presented and analysed. The numerical partitioning results for different configurations are compared to two analytical partitioning theories, namely, after Williams and after Hutchinson and Suo. Opposite to these theories, partitioning is observed to be dependent on cohesive zone properties.

Influence of Technological Flaw Occurred during Welding of Header-Nozzle Joint Using SAW Welding Process on the Strength of Welded Joint

This paper deals with the influence of technological flaw, occurred during welding of header-nozzle joint using SAW welding process, on the strength of welded joint. Three models of welded joints geometry are modeled: model without flaw, model with assumption of flaw existence around whole length of welded joint in form of torus with 1 mm diameter (the most dangerous case) and model with largest measured flaw with 1 mm diameter and with length of 8 mm. Numerical analyses using finite element method have been conducted. From obtained results it can be concluded that technological flaw occurred during process of welding does not influence the static strength of welded joint because there is no increase in stress, which is in all three models lower than yield strength. Even in the worst case scenario, when flaw with same diameter as largest detected flaw (1 mm) would occur along whole length of weld, it is not registered stress increasing in the region of weld joint subjected to internal pressure of 102 bar. Since there is no significant stress concentrations around flaws in all three models i.e. stresses do not exceed yield strength of material, there are no plastic deformations.