Projects / Programmes
Determination of dynamic fracture toughness of welded structures
| Code |
Science |
Field |
Subfield |
| 2.10.06 |
Engineering sciences and technologies |
Manufacturing technologies and systems |
Welding |
| Code |
Science |
Field |
| T150 |
Technological sciences |
Material technology |
Strength mismatching, undermatched welds, soft root layer, fracture toughness, CTOD test, constraint effect, local brittle zones, crack driving force, finite element method, static loading, dynamic loading
Researchers (3)
| no. |
Code |
Name and surname |
Research area |
Role |
Period |
No. of publicationsNo. of publications |
| 1. |
14030 |
PhD Ivan Gubenšek |
Mechanics |
Researcher |
2002 - 2004 |
438 |
| 2. |
16164 |
PhD Aleš Lesnika |
Mechanics |
Researcher |
2002 - 2004 |
210 |
| 3. |
08488 |
PhD Zdravko Praunseis |
Energy engineering |
Head |
2002 - 2004 |
341 |
Organisations (1)
Abstract
From point of view of high strength low alloyed (HSLA) steels weldability it is more economical to produce undermatched welded joint with soft root layer. Such weld joint has expressive strength mismatching. The soft root layer was made by softer (lower yield strength) electrodes in order to prevent cold cracking and to enable lower preheat temperatures.
One should pay attention to the level of strength mismatching which should be sufficient to provide high enough toughness of soft root layer by using chosen weld consumable (wire, electrode) and welding procedure. High toughness of soft root layer is necessary in order to enable local plastic deformation and to prevent brittle fracture of welded construction under static and dynamic loading. It is of utmost importance not to exclude the possibility of plane crack (hydrogen cracking, lack of fusion, etc) and local brittle zone appearance in HSLA steel welded joints, which can cause failure in heat affected zone (HAZ) and also in weld metal (WM).
The aim of this investigation is to find out regarding to fracture - mechanical testing a proper consumable for soft root layer built up which, together with other regions (weld filler metal - filler passes) have enabled high toughness of welded joint and reliable exploitation of welded structure at static and dynamic overloading (for example eartquake). Soft root layer was exposed to strong root weld metal alloying from the base material, which can affected for a change of soft root layer mechanichal and toughness properties after welding. The differences in mechanical properties among different weld regions affect the strain distribution around the crack tip during fracture toughness tests and consequently influence the CTOD fracture toughness values. This thesis demonstrates that both strength and toughness control the fracture behaviour of such complex weldments.
Therefore, a detail research of mismatcing influence on weld joint fracture behaviour during crack (defect) propagation from undermatched to overmatched microstructure and in oposite way should be done. In this purpose the experimental and numericalapproach with 3D weld joint modeling will be used.
The results of the experimental investigation was to determine if the applied welding procedure without preheating for undermatched welded joint with soft root layer is appropriate for commercially available HSLA steel weldability improvement in regard to the achieved fracture toughness of the soft root layer. The HSLA steels usually require preheating if matching or overmatching weld consumable is used (anyhow, it is hard to get satisfactory toughness for higher strengths), which is not only expensive (about 30 % of whole welded construction cost), but also needs a carefully designed and strictly followed welding procedure.
Expected outcome of the proposed research is also determination of the transferable criterion of the ductile crack initiation and propagation in the application to the evaluation of structural integrity of welded structures.
