PSI - Issue 38

Tuomas Skriko et al. / Procedia Structural Integrity 38 (2022) 393–400 Skriko et al. / Structural Integrity Procedia 00 (2021) 000 – 000

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1. Introduction Currently, the International Institute of Welding (IIW) recommendations for post-weld treatments of welded joints (Haagensen and Maddox, 2013) does not include laser dressing but generally, it has been recognized as a one remelting method. In addition, detailed guidelines and proposals for high-frequency mechanical impact treatment (Marquis and Barsoum, 2016) and TIG dressing (Yildirim, 2015) has been published, and grinding has also been studied recently (Ahola et al., 2021, Braun and Wang, 2021) but less attention has been paid to laser dressing, especially in the case of ultra-high-strength steel (UHSS) weldments. Although both TIG, plasma and laser are methods for remelting and, thus, improving the local weld toe geometry, comprehensive studies are needed to determine their similarities and possible differences in terms of the effect on enhancing fatigue strength of weld joints. The aim of the present study is to investigate the fatigue characteristics of laser-dressed fillet weld UHSS joints experimentally and numerically, and thus, add its own scientific contribution to the theme in question. Fatigue tests are carried out for the non-load-carrying cruciform joints made of S960 grade steel with the applied stress ratio ( R ) of R = 0.1 and R = 0.5. Local weld geometry and residual stress measurements were carried out to characterize the key factors in the laser-dressed UHSS joints, and the results are obtained using different global and local stress criteria to address the applicability of different approaches for the fatigue assessment of the investigated joints.

Nomenclature Symbols A

elongation

strength coefficient (Ramberg-Osgood material model)

H

current

I

impact energy from Charpy V-notch test

KV

slope parameter of S - N curve

m n P Q R

strain hardening exponent (Ramberg-Osgood material model)

power

heat input stress ratio

ultimate strength yield strength weld toe radius

R m

R p 0.2

r

temperature

T U

voltage

travel speed wire feed rate stress range tilt angle travel angle residual stress

v travel v wire

Δ σ θ tilt

θ travel

σ res

Abbreviations 2D

two dimensional three-dimensional

3D Ar

argon

CO 2 carbon dioxide CTWD contact tip to work distance ENS effective notch stress FAT fatigue class FE finite element GMAW gas metal arc welding IIW

International Institute of Welding