Fatigue Strength Analysis of 6061 Aluminum T-Joint Fillet Arc Weldment with respect to Various Bead Formation

다국어 초록 (Multilingual Abstract)

Portion of aluminum in car body increases because of mass reduction request due to global environmental problems. However, there is a picky prerequisite in using aluminum to car body because it has low arc weldability caused by low viscosity and surface tension. In these days, this welding problem seems almost solved thanks to the advances in welding machines and related techniques. Another important obstacle in using aluminum is that there are rare aluminum weldment fatigue assessment reports. The number of related literature that can be found in internet is just below 10. Moreover, most of them are not considering various weldment shape itself.
This research is about fatigue strength assessment of aluminum arc T-joint fillet welding. This is the last report of a series of aluminum arc welding fatigue assessment. The previous ones are for butt joint and lap joint fillet weld. Target material is 6061-T6 aluminum sheets which are widely used in automotive industry for body structure. Thickness of the sheets is 4mm and the weldments are made with T-joint fillet arc welding. Focused factors in the weldments are penetration depth, gap between the sheets and toe angle. Fatigue strengh of the weldment is assessed with these various weld shape factors.
Fatigue experiments are conducted with 5 tons fatigue test machine. SR(stress ratio) value was 0.1 and the vibration frequency was 20Hz. The maximum number of repeated loading cycle was 500,000. Various levels of tensile load applied to the specimens. Totally 5 specimens are experimented for one condition and their average fatigue strength is computed then depicted as S-N curve.
The ideal condition for higher fatigue strength is larger toe angle with full penetration. The results also shows same trend, but the effect of toe angle is not stronger than gap and penetration depth. It means that control of gap and penetration depth is more important than controlling toe angle in fatigue strength perspective. One peculiar phenomenon observed through the assessment is the effect of the pores inside the weld. Generally it is known that the pores lower the tensile strength, however it is observed that the pores almost did not affect on the fatigue strength. Several cases even showed higher fatigue strengh for higher porosity. It seems that the pores play a role of crack stop hole in general fatigue crack problem.