Why did this break?

admin

I made a mount for a headlight on my motorcycle, and it broke today.  No unusual amount of stress, I noticed the headlight wobbling while on the freeway, thought it was a loose bolt and went to tighten it up today and it turns out the mount broke.  I was wondering if you guys would be able to tell me if it was my welding job that weakened it or what.  I welded it with a Lincoln flux core mig, gaslessIt had also been powder coated. Here are some pics:On the bike:  Before I added the extra bracesNow broken:
Reply:i see a target ...lol  relax and sqeeze the trigger63' Lincoln SA200 2008 miller trailblazer 302fibre-metal pipelinermiller camo BWEand all the guns and ammo a growin boy needs
Reply:looks like you have some under cut at the junction.   kinda hard to see.
Reply:Where did you get the rounds stock you used?  I have seen 1045  do the same thing after being welded.I'm a Lover, Fighter, Wild horse Rider, and a pretty good welding man......
Reply:[QUOTE=jakkyl;175283]I made a mount for a headlight on my motorcycle, and it broke today.  No unusual amount of stress, I noticed the headlight wobbling while on the freeway, thought it was a loose bolt and went to tighten it up today and it turns out the mount broke.  I was wondering if you guys would be able to tell me if it was my welding job that weakened it or what.  I welded it with a Lincoln flux core mig, gaslessIt had also been powder coated. Here are some pics:*****The rod that broke, sheared thru, due to excessive movement/vibration. Undercut welds, etc. can aggravate breakage, but this mount is flexing more than your design will tolerate.Without  being shown the entire assembly being in pics, as mounted--the rest of usare somewhat in the dark.'Think--gussets, stiffeners, strong-backs'Examine just 'how much' flex/vibration does the unit have. Consider changing your design. The weld parameters are not the root cause.Blackbird
Reply:Maybe it's the  motorcycle?Daye
Reply:As said, it's a fatigue failure, the red line shows the extent of the 'beach marks' that show how a crack grew until there was insufficient material left to withstand the forces. The crack initiated (at the surface) somewhere around the yellow linePoor welds could have accelerated the process (by providing a stress riser) but the design needs improving
Reply:Dave's right. The weld did not fail, I'm no metalurgest (however you spell that), but at first thought it looks like a flaw in the steel bar. I would try using harder steel with gussets and reinforcment.
Reply:Did you quench it in water too cool it off after you welded it?Miller Syncrowave 200Hobart Handler 140Thermal Dynamics Cutmaster 38E-Z Tube BenderPlasma Cam DHC2
Reply:welding on a degraded piece of steel can make an existing lamination (a discontinuity in the material itself like a crack or lamelar tear) in the steel become a delamination (not just a crack, but the crack opened up) thus becoming a stress riser and causing the piece as a whole to fail.I Enjoy not only welding, but Metallurgy too!  :-)Certified Welding Inspector at your service...Level II Nuclear Welding InspectorLevel II Nuclear Electrical InspectorLevel II Nuclear Civil InspectorLevel II Ultrasonic Thickness Testing TechnicianCertified Smartass,and Wise Acre
Reply:Can you folks say 'fatigue failure'?....like hotrodder does.Seeing this kind of stuff is quite the norm---if one actually operates a professional repair and fab shop. As I mentioned in prior post, without good pics of the entire assembly,as mounted----then a repair plan can be created, that will work.For a CWI to throw out laminar tearing (and can't even spell it), and others to fault the material is ludricrous, until the entire design is revealed to us....which has not happened.    In a perverse way---yes, it's the material's fault for allowing fatigue--due to a bad design.jakkyl--the original poster is looking for real world answers, it seems to me.Blackbird
Reply:Alright, so I need better material, a better design, and more welding practice ()I got the round stock from Lowes'.It sees a lot of vibration, and the headlight is only bolted onto the bracket with one bolt, the bracket is bolted to the bike with 2 bolts.What better kind of material can I use and how can i improve the design so this won't happen again at a very bad time?It needs to be roughly the height it's at now, and needs to be at least as far out as it is to clear the steering damper.Here is the bike as a wholeHere is where it bolts up underneath the lower tripleCloser on the bikethe opposite sidethis is what the mount looks like on the headlight, it's offset for some reasonEDIT: If you need more pics, let me know.
Reply:You don't need a better material, mild steel is fine. Weight can be saved by using tube instead of bar but we'll keep it simple for now.This is far from a complete solution but should get you started...NO sharp edges! They don't appear in nature (think skeletons, tress etc) for a very good reason- they're 'weak' pointsAt the headlight bracket end of the mount use a 'double shear' mount (your origonal was single shear) as this will give a larger area for the mounting bars- spread out the stress so to speakIdeally the mount wants triangulating with a third bar. If things are too tight to do this then gussets would help with regard to the flow of stress
Reply:The break was at the frame/engine end behind the steering damper, no? Looking at the beach marks, It looks like the failure MIGHT have started the the end of the weld on one side of the bar where a stress riser from a start was. (4th pic, first post)A couple things that might help: Starts and stops are often the weak points, especially starts, especially with wire feed. The start tends to be 'cold' (not enough heat is in the material to get good fusion into the base metal.) Start at the low stress end and back up a little at the stop so the stop isn't right at the end of the bead. If there is a bit of extra weld metal, don't worry. Blend it down with your grinder if need be. Where the pieces come together (the crotch between the bars) fill the area with weld metal (don't go nuts, just bridge between the rods with a few beads, starting on the middle piece, where there wont be much stress, then run side to side a few times making a little pad) and smooth the transition between the rods and the weld metal with a nice radius using your grinder. No sharp inside corners/grooves. Starting at the middle piece lets some heat get into the weld area, helping achieve good fusion with the rods that take the stress. This is in essence a gusset made of weld metal, as suggested by hotrodder.
Reply:This assembly is crying for a third member to triangulate it, hotrodder's right. Again.Blackbird
Reply:I'm no metallurgist either but our shop had been making parts with 1/2" round rod for a while. Must have made 1,000 or so with no problems, all welded the same way. Got one peice of rod that had a different color to it for some reason, sorta black. every peice we made with that rod broke alot like in your pictures. Not saying this is what happened to you but everyone in our shop agreed there was something wrong with the metal.I like to party!
Reply:^^^ the break was at the headlight mount, farthest from the engine, on the side closest to the camera (first pic, first post).So, double shear (red), should I make it like this |_|  or | | ?Fill in the crotch (blue)is this yellow the triangulation you were talking about hotrodder?Thanks for the advice
Reply:pardon me dave powelson I did forget one 'L' it IS spelled LAMELLAR TEAR. I know what i'm talking about thank you.I belive he's asking for what could have caused this to happen... ALL of the answers given are possibilities... dont rule out the material not knowing where it came from or how it was produced. Poor design could also be a factor but dont stab at others opinions as to why they believe it could have failed.Certified Welding Inspector at your service...Level II Nuclear Welding InspectorLevel II Nuclear Electrical InspectorLevel II Nuclear Civil InspectorLevel II Ultrasonic Thickness Testing TechnicianCertified Smartass,and Wise Acre
Reply:It looks like lamellar too many books and no application.......Yeah, yeah, I know you are a weldor too. But, are you a good one?
Reply:what kind of bike was that?
Reply:The weldment broke for two reasons.The weldment did not get full penetration. that can be seen in the photo.Vibration helped make it come undone.It was not the metal.Was the metal clean ? Free from the powder coating (polyester coating)?The better way to make this weldment is like the photo above with the round stock notched into the flat plate. Shown in RED.If you were connecting round rod, end to end (not an ideal situation) each end of the round rod being connected would have to be ground almost to a point so that the weld would fully penetrate the round bar. Just putting two round bars end to end and welding is very poor practice because the weld would not fully penetrate.Tubing would be much stronger believe it or not.Area 1 (inside area) + area 2 (outside area) = strengthSo if area 1 is zero- (solid bar) the strength is greatly reduced.Solid bar is usefull when there will be a lot of wear or abraision.Last edited by Donald Branscom; 03-26-2008 at 11:02 AM.
Reply:Originally Posted by WANNAWELDwhat kind of bike was that?
Reply:nekked bikes rock....I've got a Buell!Yeah, yeah, I know you are a weldor too. But, are you a good one?
Reply:Once again donald is wrong. Not enough meat + too much vibration = failure. If you are worried about weight rethink material choice and design.The difference between art and craft is the quality of the workmanship. I am an artist.
Reply:looks to me like you need a brace coming down from upper triple clamp to support the weight.  Bring the support down and attach it to the flat part of the bracket that the headlight bolts to. Try to keep it as straight as possible.The headlight had to wobble all over the place before it broke.mm135HTP Invertig 201 With water cooler9" Southbend LatheLots of hand tools.Originally Posted by Jolly RogerOnce again donald is wrong. Not enough meat + too much vibration = failure. If you are worried about weight rethink material choice and design.
Reply:this failure appears to be caused by undercut that was stressed. no way it has anything to do with a lamination. the bar would be split open at the lamination if that were the case. Do laminations occur in round bar?
Reply:laminations can occur anywhere in any material...  not just in certain kinds  hahaCertified Welding Inspector at your service...Level II Nuclear Welding InspectorLevel II Nuclear Electrical InspectorLevel II Nuclear Civil InspectorLevel II Ultrasonic Thickness Testing TechnicianCertified Smartass,and Wise Acre
Reply:Lynn, the pics Jakkyl posted show well defined beach marks- text book example of fatigue failure. Lamellar tearing looks completely different.Jakkyl, i would make the double shear mount this way l_l  and by triangulation i mean add a third bar, something like the red line would suffice... but obviously the headstock's in the way making life more difficult. If there is a path through to the upper triple clamp (as already suggested) then use it. If not then you'll have to fabricate a bracket that uses the existing mounting bolts on the lower clamp- something like the yellow scribble. All of the tubes/bars attach to that plate which then bolts up to the bottom of the triple clamp
Reply:Did Suzuki design that? It looks like 'about' a pair of 1/2" solid rods to mount the headlight. Has anyone picked up, in one hand, a headlight that size? I don't see any way that a pair of solid 1/2" rods (or 5/8) will handle the job, for any length of time. IMHO, you need another connection at the top of the light to stop the vibration. At any given RPM, even an inline 4, has a vibration that will kill 1/2" solid rods. If one or the other rods don't break, the piece between them will.Last edited by Craig in Denver; 03-27-2008 at 11:21 PM.9-11-2001......We Will Never ForgetRetired desk jockey. Hobby weldor with a little training. Craftsman O/A---Flat, Vert, Ovhd, Horz. Miller Syncrowave 250
Reply:It broke cause it was a bad part, fix it. Teasing ya!The clean break follows the point of origin. Hard to see in these photos, but it looks like a cold edge or a dimple in the toe edge of that weld right there. Send it to a lab for full forensics. Teasing ya, again!Might need a rubber dampner.Last edited by tanglediver; 03-28-2008 at 02:29 AM.City of L.A. Structural; Manual & Semi-Automatic;"Surely there is a mine for silver, and a place where gold is refined. Iron is taken from the earth, and copper is smelted from ore."Job 28:1,2Lincoln, Miller, Victor & ISV BibleDanny
Reply:Don't want to sound like an ***. But from the looks of your welds, I would suggest going to the dealer or a bike salvage yard and buy a factory bracket. It might even be mounted with a rubber or nylon shoulder washers so the brackets mounting flange has some sort of vibration dampener between the two mounting surfaces.Also, you mentioned flux core wire with no gas. That will work, but it's always better to have the gas flowing whether your running flux core or not, especially if your not an experienced welder. Get some gas flowing out of the nozzle and your welds will probably improve immediately.One other solution might be,only ride your bike during daylight hours,,,,,Here's an actual statement which was made by a nosy customer, right after I noticed him pick up a metal part, only to fling it into a wall at incredible speed: No, no,,,, it wasn't hot,,,, it just didn't take me long to look at it! You wouldn't happen to have any ice I can put on this blister would you?
Reply:wow if people would have actually READ what i was posting there wouldn't be so many questions as to what i meant.i didn't mean that it failed because of a lamellar tear, i used that as an example as a flaw that can occur in the base metal itself.i didn't mean it failed because of the base metal either, he was asking for reasons that it could have failed... good lord.Certified Welding Inspector at your service...Level II Nuclear Welding InspectorLevel II Nuclear Electrical InspectorLevel II Nuclear Civil InspectorLevel II Ultrasonic Thickness Testing TechnicianCertified Smartass,and Wise Acre
Reply:Also, you mentioned flux core wire with no gas. That will work, but it's always better to have the gas flowing whether your running flux core or not, especially if your not an experienced welder. Get some gas flowing out of the nozzle and your welds will probably improve immediately.
Reply:Originally Posted by Craig in DenverDid Suzuki design that? It looks like 'about' a pair of 1/2" solid rods to mount the headlight. Has anyone picked up, in one hand, a headlight that size? I don't see any way that a pair of solid 1/2" rods (or 5/8) will handle the job, for any length of time. IMHO, you need another connection at the top of the light to stop the vibration. At any given RPM, even an inline 4, has a vibration that will kill 1/2" solid rods. If one or the other rods don't break, the piece between them will.
Reply:No, it's not a suzuki design.  The headlight is off of an Indian Scout.  You can't go out and buy the bracket because no one makes it; Not too many people putting Indian parts on Suzuki's, ya know  .  I liked the looks of the headlight, so I needed some way to mount it and that's what I came up with.This is all good stuff, I'm still trying to figure out how to put it all together.  There is not much room down there, so my options are limited.  There's not a good path from the upper to lower triple for a top mount.  So i think I'll have to do something like hotrodder's diagram.  Also, I don't NEED to use round bar, if you guys have a better suggestion.  All I need is something that will hold the headlight there with minimal vibration that allows room for vertical adjustment. That doesn't look horrible.
Reply:Originally Posted by jakkylNo, it's not a suzuki design.  The headlight is off of an Indian Scout.  You can't go out and buy the bracket because no one makes it; Not too many people putting Indian parts on Suzuki's, ya know  .  I liked the looks of the headlight, so I needed some way to mount it and that's what I came up with.This is all good stuff, I'm still trying to figure out how to put it all together.  There is not much room down there, so my options are limited.  There's not a good path from the upper to lower triple for a top mount.  So i think I'll have to do something like hotrodder's diagram.  Also, I don't NEED to use round bar, if you guys have a better suggestion.  All I need is something that will hold the headlight there with minimal vibration that allows room for vertical adjustment. That doesn't look horrible.
Reply:It took me a while to figure out that the part that broke is not the same as the part shown in the first picture. It appears that after the first picture was taken you added what (for that lack of a better term) I will call "gusset bars" across the bend. When you added those, rather than allowing the long curves in the bars to flex and absorb stress, you concentrated all that stress on the both ends of the gusset bars.Normally that would not be that big of a deal but I think that these two pictures tell the story:Look very closely at the crater of the weld at the end of the gusset bar. It looks like you were running a little too hot especially once the workpiece heated up from earlier welds. It seems that this led to a under filled (concave) crater at the end of the weld. During solidification the surface of concave beads is under tension and very prone to crater cracks (also called star and spider cracks). I would bet that this was the origin of failure. Of course the crack propagated through the shortest cross sectional area available which was straight through the bar.I think that using proper crater filling techniques would've prevented this failure.Some have mentioned undercut. Is there undercut present? Yes. Is undercut a stress riser? Yes, but nowhere near as much of a stress riser as a crater crack. I seriously doubt that undercut played any significant role in this failure. The three real causes where under fill, crater crack, high fatigue loading.As for lamellar tearing (I know arcflashlynn didn't mean to say that it was a cause), it can occur in any rolled material. Hot rolled, cold rolled, steel and other metals that are rolled can be susceptible. Just about the only type that isn't susceptible to lamellar tearing is cast metals. That being said lamellar tearing only occurs in the direction of rolling. In round bar such as this it would not cause a failure across the rod but along the length.While the quality of the rod cannot be determined, I seriously doubt it was bad enough to play a significant role in the failure.one last note: Originally Posted by dingleballsit's always better to have the gas flowing whether your running flux core or not, especially if your not an experienced welder.
Reply:Simple fix. Start with the Headlight and build a new bike around it. LOL.
Reply:sure are a lot of theories here.the first thing i would do is take a file to one of the broken ends to determine whether it was hardened.if it's hard,then you used a high carbon material that cooled too quickly after welding. if it's soft ,then the fatigue failure may be the correct cause. the photos give the appearance of a very fine grain structure, making me think it's hard.
Reply:i'm just gunna say that you may have undercut it since you used a terrible wire.. i hate that lincoln fluxcore.. next time i suggest you find  a machine with gas and s6 wirehttp://specific.net
Reply:mmm mmm i love the look of nekkid bikes... hope you dont plan on putting any plastic back on it! As far as a fix goes i highly suggest using a rubber damper as part of the solution... those motors run smooth but they have some vibration in them for sure.