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  1. #1
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    Nothing Lasts Forever

    I posted this on my blog but also want to share it here.



    Yes, my frame broke. This is the first time I have had a frame that I built break. It is sad but did not fail catastrophically plus I was not hurt so I don't really see it as a bad thing. It's life and we grow from our experiences.

    What do you guys think? Are there things that I should look for in terms of understanding and learning from this?

    Hopefully we can have a good discussion.
    Mark Farnsworth, Raleigh, NC
    http://farnsworthbikes.com

  2. #2
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    Yikes! glad you are OK.

    I'm not really a TIG guy, but it seems like probably Inconsistent welding? Maybe where the crack started was over heated and more brittle?

  3. #3
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    What to look for?

    It was one of my better welds but I won't claim it is perfect.

    One thing I am looking for is a discussion of what to look for. I am reviewing the material that I can find such as the following:
    Welding defect - Wikipedia, the free encyclopedia

    When pushed to the limit anything will fail. The question is how should a frame fail and what should I be looking for.

    In my case, the crack went across the tube rather than following the line of the weld.


    The following example from google shows a case where a crack followed the edge of the weld.


    The key question is what should I be looking for and what would the signs be of a weld defect vs. simply too much stress?
    Last edited by febikes; 02-05-2014 at 04:43 AM.
    Mark Farnsworth, Raleigh, NC
    http://farnsworthbikes.com

  4. #4
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    Well the fact that your weld didn't break would imply that it was not an imperfection in the weld itself.

    I'm in engineering school right now and I actually had a lecture on fatigue and stress concentrations today, funny enough.

    The concentration could be caused by a manufacturing flaw, impurity in the steel, a dent, a bad weld (cold or undercut), a hardened section of material (HAZ), maybe a stray file mark... a lot of different things. A frame experiences cyclical loading in its life and a ton of it too. When metal is stressed it cold works - so it gets "stronger" but becomes more brittle. when an area is more brittle than the surrounding material, it works beyond the yield strength faster and in a positive feedback loop sort of way it quickly leads to failure of that area and causes things like cracks and failure.

    If it were my bike, I would probably do a TON of practice joints think a lot about heat control, and cut each one open to look at the penetration.

    That picture is of a Ti frame. I know when Ti was first coming on the scene a lot of frames failed like that because the welds were contaminated.

  5. #5
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    Did you stop/start at the centerline of the frame (ie at the middle/bottom of the downtube)? That will often create a stress riser that will crack the tube. Don't ask how I learned this...

    -Walt
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  6. #6
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    Not sure if starts/stops are the root cause

    Thanks Walt,

    In terms of welding I have gotten better on every frame that I built and continue to do practice joints. I am still improving but based on my very limited knowledge I am not sure that I see any weld fault in this case. In particular it does make me feel good that the crack did not follow the line of the weld.

    I used back purge, NOVA 969 tubing, 045 wire, 70 amps, and the pulse feature of my Miller 150 STH. The crack did form near a stop/start area but I am not sure that was the cause. Are there specific things I should be looking for in the broken weld?

    No part of the actual welds cracked. It is clear that the crack started just past the weld on the downtube. The crack did not follow the edge of the weld.

    As luck will have it I was having problems with my digital camera when I built this frame so I don't have good records of the welding.

    I can't stress enough how much this frame has seen in terms of riding, past crashes, and general abuse. Just before this happened I had gone into a ditch at speed. In addition, after the crack formed I heard it creaking and kept riding because it was cold and dark. I knew something was wrong but ignored it.

    It is possible that this is a case of "Underbead_cracking". If so, what are things I should be looking for to be sure?
    Welding defect - Wikipedia, the free encyclopedia

    Would adding a gusset be a good idea?

    It is also possible that the frame was correctly built, if this is the case, what should I look for to be sure?
    Mark Farnsworth, Raleigh, NC
    http://farnsworthbikes.com

  7. #7
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    Quote Originally Posted by febikes View Post
    In particular it does make me feel good that the crack did not follow the line of the weld.
    NO!

    I am no engineer or metalurgist at all, but I have a bit of experience with metal of all sorts and in many applications. I would walk right back from this statement of yours, and actually flip it right on its head. Look at it 180* from there. 1) It is clear in this case that the weld was a "decent one," in so far as it was not the point of failure. Unless they are pretty atrocious, welds themselves are rarely the problem in general steel welding. 2) It is clear to me that the initiation point was right at the base of the HT junction, in the root of the weld, in the DT itself. There may have been any of the attributes present that Adarn mentioned to begin this chain of events, and I do believe it was a chain, not one distinct issue. The fact that the crack did not follow the weld suggests that the tube was not crystallized or otherwise overheated to any great degree, as if the weld had drastically overheated the tube at the root throughout the HAZ, it would have broken there all the way around. The fact that the path of least resistance traveled up through the tube beyond the HAZ should make you feel good where your welding is concerned, in my opinion.

    While the HAZ was clearly the point where the failure began, I'm not at all sure that welding itself was the issue, based on this somewhat slim evidence here. I would surmise that based on the length of the HT, the number of miles, and perhaps hard ones at that, the point at where it began, and that this exact point represents the weakest piece of material in the area, that it was a simple fatigue failure from too many stress cycles. If any of the physical points that Adarn raised were contributors is hard to say, but they certainly were not alone, and in my opinion not the lead cause.

    It is always interesting in such cases to very closely scrutinize the edge of the tube for clues. Quite often you can clearly see the evidence of a slow and steady failure, where it had seemed to you that it failed suddenly. The point at where the crack began is often corroded slightly, rust in this case, having been open and exposed for some time prior to it being noticed. Even if the failure point is not corroded, it might often appear darker or dirtier than the rest. This area can often also appear to be polished variously smoother than the rest of the tube edge if it is a spot that sees bending or twisting loads. The creaking you heard being the sign of this friction. The rest of the edge would appear more jagged as if it had been ripped clean away, suddenly.

    This is arguably the point of greatest stress in any frame, and the number of solutions out there to combat this potential is legion. I might imagine that not only might your frames be sporting one of these reinforcements in the future, but that we will all be watching our head tubes more closely!
    Most people ply the Well Trodden Path. A few seek a different way, and leave a Trail behind.
    - John Hajny, a.k.a. TrailMaker

  8. #8
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    Though the picture is not a good one it looks to me that the crack didn't start at the weld but some where else you can tell by rusted portion being the oldest and the area close to the weld is shiny being the last piece to fail. I could be wrong we need a better pic
    PAYASO 36er.....Live the Circus

  9. #9
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    Glad your OK and thanks for shairing!

    It looks like a toe crack to me which is a welding defect. The bottom of the down tube can give bad torch angle which can do a few things.. undercut the tube, bad penetration or by sticking the electrode out to far not shield the weld properly. I like to slow down in this area and come at it more from the side. I also like to add more filler in this area just as long the toes fuse in I think it helps blend the joint better.

  10. #10
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    Fatigue crack initiated at the edge of the weld. Could be a bad joint, or just the 'weakest link'. Once you have the crack it will propagate where the stress is highest, which means with this joint geometry it will travel away from the weld and across the tube at some point.

    This is a common failure, especially on a 29er with a shortish head tube and big miles.

  11. #11
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    Quote Originally Posted by DEFCON4130 View Post
    It looks like a toe crack to me which is a welding defect. The bottom of the down tube can give bad torch angle which can do a few things.. undercut the tube, bad penetration or by sticking the electrode out to far not shield the weld properly. I like to slow down in this area and come at it more from the side. I also like to add more filler in this area just as long the toes fuse in I think it helps blend the joint better.
    After reading about a toe crack, I am inclined to agree with this although I am still not 100% sure. I will be doing a lot of practice welds this year.
    Welding defect - Wikipedia, the free encyclopedia

    Quote Originally Posted by TrailMaker View Post
    The fact that the crack did not follow the weld suggests that the tube was not crystallized or otherwise overheated to any great degree, as if the weld had drastically overheated the tube at the root throughout the HAZ, it would have broken there all the way around. The fact that the path of least resistance traveled up through the tube beyond the HAZ should make you feel good where your welding is concerned, in my opinion.
    Thanks, although I am still pretty nervous about it. I guess my concern is not that it failed but rather I want to be sure it was a "good death" where the failure does not indicate any HAZ issues.

    Is the theoretically perfect failure occur at the butt transition zone or is failure at the toe of the weld considered normal?

    Quote Originally Posted by TrailMaker View Post
    This is arguably the point of greatest stress in any frame, and the number of solutions out there to combat this potential is legion. I might imagine that not only might your frames be sporting one of these reinforcements in the future, but that we will all be watching our head tubes more closely!
    Thanks, I am thinking about moving up to 171 down tubes and adding a small gusset on future builds in addition to doing a lot of practice for smoother welds.
    Mark Farnsworth, Raleigh, NC
    http://farnsworthbikes.com

  12. #12
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    It looks to me, and I will admit that the pictures do not show the failure line well, that the metal in the weld is the cleanest which would tell me that it was probably the last to break in the line of failure while the opposite end of the tube is quite dark which could mean it's been open for a while or it could mean that you hit the dirt when things went south.

    You said you stuffed the thing into a ditch before this failure, that's your problem among others. Your frame was going to fail because you caused damage. Even with a standard cyclical failure there isn't much you can do apart from normal caution and the use of best practices during welding. Metal which is cyclically loaded will fail, full stop. Metal which is loaded beyond the yield strength has failed and altered the strength of the material. If you put those two things together you get a failure which is what happened here.

    It is less important that you identify the exact point of failure and more important that you take this as a lesson in dialing in your technique. I don't think that anyone can point to any specific place where you went wrong, especially without a lab doing failure analysis on that tube, so I don't think there is anything you need to change before you build again in particular. All the comments above are best practice sorts of comments about controlling your HAZ, preventing undercutting, getting good penetration, and so on; these are fantastic points. Your problem isn't that you necessarily messed something up, your problem is that you broke a frame which saw its fair share of use. This exposed some questions which needed to be asked about the techniques you employ whether or not they apply to you or what you did.

    Sometimes we need to experience a failure to remind us of all the stuff we could have been doing better even if what we've been doing has been functional. We can all get better, right?
    Don't you hate it when a sentence doesn't end the way you think it octopus?

  13. #13
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    Quote Originally Posted by zebrahum View Post
    It looks to me, and I will admit that the pictures do not show the failure line well, that the metal in the weld is the cleanest which would tell me that it was probably the last to break in the line of failure
    In this case it's the opposite - the joint cycles between tension and compression and the oldest part of the crack will polish.

    I've literally seen pallets of frames with this exact same failure in varying levels of destruction. The solution was to make sure stop/starts were never near the bottom of the tube, and switching to a heavier-duty down tube.

  14. #14
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    Quote Originally Posted by zebrahum View Post
    It is less important that you identify the exact point of failure and more important that you take this as a lesson in dialing in your technique. I don't think that anyone can point to any specific place where you went wrong, especially without a lab doing failure analysis on that tube, so I don't think there is anything you need to change before you build again in particular.
    Thanks! it's great to have this sort of support on the forum. I am going to really work this year to get every aspect of my welding and process 100% and am not really worried about the next build.

    Right now, I am thinking about the various gusset designs and will be planning on doing one on the next bike. It seems most if not all of the big brands like Niner, Surly, Voodoo, Salsa, etc use gussets so I will be designing something similar for my next frame.
    Mark Farnsworth, Raleigh, NC
    http://farnsworthbikes.com

  15. #15
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    Quote Originally Posted by dr.welby View Post
    In this case it's the opposite - the joint cycles between tension and compression and the oldest part of the crack will polish.

    I've literally seen pallets of frames with this exact same failure in varying levels of destruction. The solution was to make sure stop/starts were never near the bottom of the tube, and switching to a heavier-duty down tube.
    I am sure the crack did not exist prior to the start of the ride. The bike was in good shape and while it looks dirty please remember that it was raining that night and the day before. I am sure that it was not cracked on Sunday and after going in the ditch I immediately heard the creaking sound. Between the ditch and the point where the tube became a full break was around five or ten minutes. After the downtube broke I was able to ride a little bit as the top tube was bending/tearing. The reason the entire thing came apart was that it was cold so I tried to ride even when I knew it was tearing then tried to push then carry the bike until the top tube snapped fully.
    Mark Farnsworth, Raleigh, NC
    http://farnsworthbikes.com

  16. #16
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    Quote Originally Posted by dr.welby View Post
    In this case it's the opposite - the joint cycles between tension and compression and the oldest part of the crack will polish.

    I've literally seen pallets of frames with this exact same failure in varying levels of destruction. The solution was to make sure stop/starts were never near the bottom of the tube, and switching to a heavier-duty down tube.
    Certainly an interesting viewpoint, not sure I'm 100% in agreement though. That's ok, we're trying to diagnose metal failure from not great pictures in an unknown environment of both what happened at failure and what has happened to the frame since failure. Freshly broken metal can be pretty reactive so who knows what the corrosion pattern would look like in this exact case and who knows if the picture is actually showing what I said it was showing? I'm no tube failure expert, that much I can assure you.

    For the start/stop point, would you recommend that the start/stop be moved to the top if you were welding a top tube instead of a downtube? Or a seat cluster? Is the idea to prevent the start/stop point from being in a location loaded in compression?
    Don't you hate it when a sentence doesn't end the way you think it octopus?

  17. #17
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    Quote Originally Posted by zebrahum View Post
    Certainly an interesting viewpoint...
    Let me expand my viewpoint then - I have never, ever, seen any tube crack on the inside-facing portion of a tube without some point of initiation like a braze-on.

    You're essentially arguing that the portion of the failure that is at an obvious stress riser failed only after a failure in a portion of unadulterated tube. That seems unlikely, barring better photos.

  18. #18
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    Quote Originally Posted by dr.welby View Post
    You're essentially arguing that the portion of the failure that is at an obvious stress riser failed only after a failure in a portion of unadulterated tube. That seems unlikely, barring better photos.
    I will try to get some better photos.

    From looking at the tube in person, what I think happened was that the crack started at the toe of the weld on the bottom of the down tube. When I looked at the crack it was more jagged at the toe of the weld where the bead creates a stress riser. The crack was smoother as it "travelled" around the tube.

    Starting and stopping beads on the sides makes sense and will be part of my process refinements.

    I am pretty sure that the crack progressed around the tube while I was riding. I heard creaking that in hindsight was progressive. It was raining so everything was wet and dirty.
    Mark Farnsworth, Raleigh, NC
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  19. #19
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    Quote Originally Posted by dr.welby View Post
    Let me expand my viewpoint then - I have never, ever, seen any tube crack on the inside-facing portion of a tube without some point of initiation like a braze-on.

    You're essentially arguing that the portion of the failure that is at an obvious stress riser failed only after a failure in a portion of unadulterated tube. That seems unlikely, barring better photos.
    I have! It was on a famous ti maker rode frame and the crack started
    About 1 1/2" north of the seat tube at the 9 o'clock position and traveled south straight thru the seat tube and seat stay and welds almost a perfectly straight line and ended in the seat stay no where near the brake bridge or cable holders just in the middle of the tubes both ends.

    I Was thinking it started from the internal butting but I would think The butting was further up the tube not 1 1/2-2" from ST
    PAYASO 36er.....Live the Circus

  20. #20
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    Dumb question: did you double check the butts? Could the crack be in the thin section? You can probably take some calipers to it now.

    I had a braced frame break in a similar place, beyond the fillet. Also not catastrophic. I, rightly or wrongly, have attributed it to cooking the tube too much (as well as being an overal badass). That was a 1.5" 9/6/9 TT Verus HT. The next bike has a 1/7/1 supertherm, and hasn't broken so far, so we'll see how it goes. Since the previous frame lasted for 4 years, I'm not holding my breath.

  21. #21
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    Hey Mark;

    It is my opinion that this was a slow failure, and that a crack existed there for some time. You would have had to specifically look for it to see it. It could have been nothing more than a hairline crack in the finish, and virtually undetectable. I've had cracks like that in frames that I knew were prone to failing in a certain spot. I had to use a magnifying glass and a bright light to see them, but there they were, looking like a simple scratch in the paint. Being in the root of a weld told me other wise, and I watched them open and spread over time until I no longer felt comfortable riding the thing. Next bike!

    It seems very unlikely to me that stuffing it into a ditch would cause a rapid failure like this. Although this may have hastened the failure, I believe it was only contributory, not causal. I've had any number of crap generic cheapo bikes as a kid that had been ridden into curbs, walls, parked cars, etc.,, forks bent back, both in the legs, crown, and steerer, DTs kinked at the HT joint, you name it. All good studies of the concept of rake and trail! None of them ever failed, and I usually rode the crap out of anything I had, as likely to be in the air as on the ground.

    Perhaps this is why we see so many bikes with a bend in the DT just aft the HT. It makes for an easier weld joint. I guess everyone has decided that it also looks good too!
    Last edited by TrailMaker; 02-06-2014 at 05:33 AM.
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  22. #22
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    Quote Originally Posted by TrailMaker View Post
    Perhaps this is why we see so many bikes with a bend in the DT just aft the HT. It makes for an easier weld joint.
    That's usually for clearance so the adjustment knobs on the tops of suspension forks don't smack into the down tube when the wheel rotates more than 90 degrees.

  23. #23
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    I took more photos...
    Failure Analysis | Farnsworth Elemental

    My camera is not really good at close up shots but looking at the way the tube failed it is clear that the weld did not actually fail. The crack started at the crotch then moved around the tube.

    Big thanks to everyone who contributed to the discussion. I feel a lot better about the failure and think my craft will ultimately improve as a result.
    Mark Farnsworth, Raleigh, NC
    http://farnsworthbikes.com

  24. #24
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    Yeah, you can see the polished/peened spots around where the crack left the edge of the weld. Then traveling up the tube up towards the 3 and 9 o'clock points you can see the characteristic scalloping (though on a thin tube it looks more sawtooth-y) of the crack propagating upwards. As the crack moves up the cross-section of the remaining tube starts to drop quickly so the crack moves faster, hence the change in texture from polished to scalloped. Finally at some point the pattern should just turn uniformly rough where the tube gave up.

  25. #25
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    It's part of learning the craft, one of those not 'if' but 'when' things. It's what you do with that experience that matters for subsequent frames. Think of all you've learned since that frame, well before this analysis/post-mortem.

    What Walt said about where you start and stop the weld is a new consideration to my ears.
    Slowly slipping to retrogrouchyness

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