Fatigue strength of multi string weld
Fatigue strength of multi string weld
(OP)
Hi,
I have been asked to say something useful about the fatigue strength of a novel kind of weld and how it compares to a normal fillet weld. ..and I find it tricky.
The joint is essentially a one-sided T-joint. The weld is a mix between a butt-weld and a fillet-weld. First, a partial butt-weld is created and subsequently a fillet-like-weld is drawn on top of the first one. The loading is perpendicular to the weld.
I suppose I could analyze it using the effective-notch method and get some result. But, I'm suspect that the double-layering of the weld will reduce its fatigue strength in ways that are not captured by this analysis method.
What do you think? Is the effective-notch method applicable in this case? Is it possible to say something qualitative about the weld without a thorough analysis?
Best Regards,
hpon
I have been asked to say something useful about the fatigue strength of a novel kind of weld and how it compares to a normal fillet weld. ..and I find it tricky.
The joint is essentially a one-sided T-joint. The weld is a mix between a butt-weld and a fillet-weld. First, a partial butt-weld is created and subsequently a fillet-like-weld is drawn on top of the first one. The loading is perpendicular to the weld.
I suppose I could analyze it using the effective-notch method and get some result. But, I'm suspect that the double-layering of the weld will reduce its fatigue strength in ways that are not captured by this analysis method.
What do you think? Is the effective-notch method applicable in this case? Is it possible to say something qualitative about the weld without a thorough analysis?
Best Regards,
hpon





RE: Fatigue strength of multi string weld
I believe in reading your post above what you are describing is a partial penetration butt weld with an external fillet (T-joint). Is this correct? Can you post a drawing of this novel kind of weld?
RE: Fatigue strength of multi string weld
Yes, that is exactly what it is. Perhaps the word novel is an over-statement though:)
I have attached an illustration of the weld.
/hpon
RE: Fatigue strength of multi string weld
RE: Fatigue strength of multi string weld
RE: Fatigue strength of multi string weld
Is it only the general geometry that matters? Or, does the layering of the welds cause other effects such as reduced weldability for the second weld or an increase of defects?
/hpon
RE: Fatigue strength of multi string weld
Furthermore, the loading is mostly in the vertical direction and applied on the non-welded side (see attached file in third post). Therefore, I would not be too surprised if the failure mode is a root-crack.
/hpon
RE: Fatigue strength of multi string weld
This weld will be worse than a typical fillet weld in terms of fatigue strength under your stated conditions of loading in service.
RE: Fatigue strength of multi string weld
Regards,
hpon
RE: Fatigue strength of multi string weld
RE: Fatigue strength of multi string weld
Regards,
hpon
RE: Fatigue strength of multi string weld
In your situation because of the direction of loading, I believe the partial penetration weld will result in increased susceptibility to fatigue crack initiation from the weld root. If this were just a normal fillet weld, the weld toes would be more susceptaible to fatigue crack initiation in comparison to the weld root.
RE: Fatigue strength of multi string weld
RE: Fatigue strength of multi string weld
But you putt forth the actual geometry as a weakness compared to fillet welds. Could you expand a little on how you arrive at your conclusion? I would really appreciate that.
Regards,
hpon
RE: Fatigue strength of multi string weld
The best T-joint design for fatigue service is a full penetration groove weld with reinforcing fillets on both sides with additional preparation per MikeMet.
Under the loading parameters described, the design proposed is not considered good with respect for fatigue. Essentially the unwelded side will lift under tension placing a high shear load at the root of the partial penetration groove weld.
RE: Fatigue strength of multi string weld
Earlier generations of the product used a fillet weld instead of the proposed kind. How do these two compare?
Regards,
hpon
RE: Fatigue strength of multi string weld
I would ask why are you making the proposed weld noting the additional weld preparation required? Have you had previous failures with a double fillet T-Joint?
RE: Fatigue strength of multi string weld
Regards,
hpon
RE: Fatigue strength of multi string weld
RE: Fatigue strength of multi string weld
Regards,
hpon