Fatigue/Fracture: Fillet Welds vs PJP Welds

[NS4U]

Can someone explain or point me to a reference that exaplains why fillet welds provide better fatigure and fracture resistance than PJP welds?

I understand why PJP welds are frowned upon- becuase the root of the weld can essentially be considered as a crack initiation point. BUT- I see a very similar condition at the root of fillet welds. So what is it about fillet welds that make them better than PJP welds for fatigue and fracture resitance? Thanks.

 

[gtaw]

That's a good question. If you are working with AWS D1.1 the allowable stresses for the PJP groove welds are for all practical purposes the same as those of fillet welds.

What is different for the fillet weld is the severe notch like stress riser present at the toes of the fillet welds. Fatigue cracks usually initiate at the toes of the fillet weld, whereas the PJP groove welds may have a higher tendency to initiate fatigue cracks in the root of the weld. I would assume that the nature or the orientation of the stress would also play a part in where the crack initiates first.


Best regards - Al