PSI - Issue 5

Zuheir Barsoum et al. / Procedia Structural Integrity 5 (2017) 1401–1408 Zuheir Barsoum / Structural Integrity Procedia 00 (2017) 000 – 000

1407

7

5.2. Butt welds

Fig 7 shows the load carrying capacity estimations for full and- partially penetrated butt welded joints in S700 and S960. FEA and experiments are in good agreement with each other and the standards are conservative for the most cases. As the weld metal penetration increases, in case of over-matching joints, the estimation by Eurocode 3 tends towards less conservative estimations. When the weld metal penetration reaches full penetration, the base plate strength limits the strength of the joint. In such cases the standards recommend use of the strength of the lower strength section in the joint in calculating the capacity. One reason for the conservatism of the standards is the use of safety factors. AWS D1.1 is more conservative as it allows the use of higher safety factors. In case of S700 partially penetrated joints, the maximum load carrying capacity is 70% of the fully penetrated joints. In case of S960 matched partially penetrated joints, the loss in load carrying capacity is 30% and in case of under-matched joints, 57% of the base plate strength could be achieved.

Fig 7. Load carrying capacity for butt welds (a) S700 full (b) S700 partial (c) S960 full (d) S960 partial penetration.

6. Conclusions The most important geometrical parameters of welds are the weld root and toe, flank angle at the weld toe and the depth of penetration at the weld root. The most important mechanical parameters of the welded joint are strength of base material, filler material and HAZ. Along with these parameters the static strength is influenced by the width of the weld metal and HAZ. This zone is created due to microstructural changes occurring because of welding process in the base material near by the weld metal. In high strength steel welds this effect is more prominent than the mild steel welded joints, usually a decrease in strength is observed in HAZ as compared to the base material. Among the geometrical parameters weld metal penetration is an important parameter which influence the static strength significantly. It is observed that the static strength of the joint increases with an increase in weld metal penetration. This effect is more significant in joints with under-matching filler material, moderate in joints with matching filler material and comparatively less in joints with over-matching filler material. It is also observed that with the increase of the yield strength of the steel the static strength increase provided similar weld metal penetration is achieved and similar strength filler material is used in the joint. As the load increases the correlation factor, β w , decreases. Higher correlation factors result in conservative estimations and lower β w results in less conservative but more economical estimations. The use of β w = 1.0 was found appropriate for under-matching welds in S700 MC. β w = 1.0 was also found appropriate for welds in S960 which ensured 20% safety to the maximum load carrying capacity of the joint.