9.4 Integrität von Schweißverbindungen
Filtern
Dokumenttyp
- Vortrag (32)
- Zeitschriftenartikel (14)
- Posterpräsentation (5)
- Beitrag zu einem Tagungsband (4)
Schlagworte
- Residual stress (55) (entfernen)
Organisationseinheit der BAM
- 9 Komponentensicherheit (55)
- 9.4 Integrität von Schweißverbindungen (55)
- 8 Zerstörungsfreie Prüfung (25)
- 8.5 Röntgenbildgebung (25)
- 9.2 Versuchsanlagen und Prüftechnik (19)
- 5 Werkstofftechnik (10)
- 5.1 Mikrostruktur Design und Degradation (6)
- 5.0 Abteilungsleitung und andere (5)
- 9.3 Schweißtechnische Fertigungsverfahren (4)
- 8.0 Abteilungsleitung und andere (3)
Paper des Monats
- ja (1)
Low Transformation Temperature (LTT) welding consumables represent an innovative approach to realize compressive residual stress in weld and HAZ. LTT welding consumables use the volume-expanding martensitic phase transformation near room temperature to generate compressive residual stress during cooling. This article focusses on the weld geometry of LTT welding consumables and their influence on residual stress reduction. For this purpose, LTT layers were additionally applied to the front sides of conventionally welded longitudinal stiffeners. By varying parameters such as offset and welding speed, different weld geometries could be realized. These were analyzed for geometric parameters, chemical composition and residual stress using X-ray diffraction and fatigue testing. While the chemical composition was only slightly influenced by parameters changes, a clear influence was observed regarding to weld geometry and residual stress. The conventionally weld was characterized by tensile residual stress of ≈350 MPa at the weld toe, the additional LTT weld bead exhibits compressive and tensile residual stress of ≈-150MPa to ≈+150MPa depending to the parameter variation.
Laser Powder Bed Fusion (PBF-LB/M) is a layer wise metal additive manufacturing (AM) technology, which enables significant advancements of component design, leading to potential efficiency and performance improvements. However, the thermal cycles inherent to the process comprising large localized thermal gradients and repeated melting and solidification cycles leads to the generation of high magnitude residual stresses. These residual stresses can be detrimental both during manufacturing of components and in subsequent application. Therefore, a deep understanding of the influence of process parameters on the residual stresses are crucial for efficient manufacturing and safe application. The experimental characterization of these residual stresses is therefore crucial and can provide a reliable baseline for simulations of both the process and applications.
Diffraction-based methods for residual stress analysis using penetrating neutrons and high energy X-rays enable non-destructive spatially resolved characterization of both surface and bulk residual stresses. However, the unique microstructural features inherent to the process can challenge some of our assumptions when using these methods. These challenges include the determination of a stress-free reference, the use of correct elastic constants (both SCEC and DEC) and the influence of surface roughness, texture, and porosity on residual stresses.
This presentation will detail recent insights and recommendations for the characterization of residual stresses in a range of PBF-LB/M metallic alloys (Fe, Ni, Al and Ti)
The determination of residual stress in additively manufactured materials is a challenge, even after decades from the establishment of the basics of residual stress analysis. This is due to the peculiar microstructure of such materials. In fact, researchers have discovered that conventional methods for the determination of RS in materials do not properly work for AM materials. In this tutorial, the basics of RS analysis will be explained, together with the basics of AM manufacturing techniques. The microstructure of the peculiar materials (AM) dealt with here will be elucidated. Successively, the necessary modifications to the conventional approaches to RS analysis will be explained and case studies will be displayed, for the attendant to touch with hands the peculiarities of the approaches. Finally, a few experimental and theoretical tips will be given on dos and don’ts for a correct determination of RS in AM materials.
Residual stress formation during repeated gouging and repair welding cycles of high-strength steels
(2024)
The construction of foundation and erection structures for wind power plants requires the use of modern, sustainable and resource-efficient high-strength fine-grained structural steels. Weld defects due to the welding process are unacceptable. To overcome this issue, local thermal gouging followed by re-welding is a common and cost-effective method. The high shrinkage restraint of the gouge by the surrounding structure can cause crack initiation when design and re-weld induced residual stresses are superimposed. This risk is intensified by the progressive degradation of the microstructure and mechanical properties of high-strength steels during the weld repair process.
This investigation focuses on high-strength steels S500MLO for offshore applications and S960QL for mobile crane applications. The reduction and development of residual stresses caused by local thermal gouging and re-welding was investigated. Digital Image Correlated (DIC) stress-strain analysis was performed during preheating, welding and cooling. The results of the global DIC analysis and local longitudinal and transverse residual stresses of the weld determined by X-ray diffraction were found to be in good agreement. Furthermore, different stress levels were identified during gouging and welding. Repeated repair cycles led to an increase of longitudinal and transverse residual stresses in the weld metal as well as a hardness increase in the heat affected zone.
Influence of machining on residual stresses in additive manufactured high-strength steel components
(2024)
This study focuses on the effect of machining on the residual stresses and distortion of WAAM specimens. Defined specimens were welded fully automatically with a special WAAM solid wire (yield strength >820 MPa) with different geometric designs. The residual stresses state before and after cutting of the AM structure from the substrate plate were analyzed by means of X-ray diffraction on the specimen surface and complementary by 3d deformation analyses using photogrammetry. The results reveal significant influences of the geometry on the relaxation and redistribution of residual stresses.
This article focuses on the selective placement of additional LTT layers to generate compressive residual stresses in fatigue-critical areas of conventional weld joints. This enables an economical solution without effecting the integrity of welded joints. For this, longitudinal stiffeners made of high-strength steel were gas metal arc welded using conventional welding consumable in the first layer. Afterwards, a chromium-nickel alloyed LTT welding consumable was deposit on front sides of the stiffeners. By varying the welding parameters, different weld geometries of the LTT filler metal could be analyzed. The effects of additional LTT layers were investigated with regards to residual stresses, microstructure and strength. X-ray residual stresses measurements show that the residual stresses at the failure critical weld toe are significantly reduced by using additional LTT layers. While the conventional weld is characterized by tensile residual stresses, compressive residual stresses can be detected at the LTT weld. The level of residual stresses is influenced by the geometry of the LTT layer. Additional LTT layers with a high offset to the conventional weld generate more compressive residual stress in the HAZ than with a low offset. Therefore, the weld geometry has a considerable impact on the residual stress profile.