destructive testing pics

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  • BillC
    Senior Member
    • Oct 2005
    • 184

    #16
    There is more than one cause for "brittle" failure...

    Welding Magazine recently had a very interesting set of articles from Omer Blodgett (Blodgett's Basics) regarding ductility.

    American Machinist is a center for ideas and insights on technologies for machining, cutting, tooling, forming, manufacturing materials, robotics, quality, and shop operations.


    Try reading the articles and see what you think...

    Regards,
    Bill
    "The more I learn about welding the more I find there is to learn..."

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    • Powerstrokinit
      Senior Member
      • Aug 2006
      • 183

      #17
      I am kinda guessing at this, but I think the center tube deforms and flattens out causing a stress riser at the edge that leads into the HAZ were it starts to brittle crack. It looks like it gets no plastic deformation at the crack.

      Does this sound reasonable, or am I off my rocker on this one?

      Tobin
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      • eric75
        Member
        • Sep 2004
        • 70

        #18
        I think geometry is playing a big part in this. The weld is right in the middle of a huge stress riser. The spot where the crack began is under perhaps 50 times more stress than 1/4" lower on the tube. (OK, these are made up numbers; you calculate the stress and let me know if I am in the right ballpark)

        The test results described in the above commentary certainly are appropriate for standard tensile and bending tests. Those tests have been designed to minimize the effect of the stress concentration factor. The metal should break away from the weld. The failure modes in a "well-designed" real part should be necking or buckling, but not brittle fracture. This test however stacks the deck for the weld or the HAZ to fail because of the higher stress... Good test.

        From the angle and surface of the fracture, it looks a little bit brittle. Even with bits of toe included, I would say the crack started where the HAZ borders the weld. I am interested to know if this broke in one sudden pop, or did it slowly rip as you moved the ram down?

        I would like to see someone prove me wrong, but I don't think an ideal specimen would fail in a different place when put through this test.

        Although I am not qualified with enough welding experience to offer constructive criticism of the weld quality or technique, it appears that the advice offered above is correct. The HAZ looks a little big, the bead looks a little small. Moving faster (and even hotter to allow you to move faster) will put less total heat into the part. (Heat accumulates over time sent welding)

        If my opinions seem off base, let me know. I am only thinking about this to refresh my memory of what I learned in class three years ago. I real job is designing stuff that doesn't require near this much thought.

        (when I refer to "above commentary" I mean the discussion that a good weld should never break in the HAZ)

        Comment

        • dandimand
          Senior Member
          • Oct 2005
          • 485

          #19
          for the most part i would say as long as there is no undercut your welds look fine its the way your doing the destructive testing that is causing the failure . every chassis build cept one welds pretty much the same way you do only one that puts in a big weld is the one that builds the dragsters in washington perhaps for a reason but they are big and ugly welds . dont beat yourself up on this I think your doing fine. moly always cracks in the haz nature of the beast but if the chassis is designed properly then even in a crash for the most part no one tube will see this kind of stress. your welds pretty much look the same as every other guy out there doing this type of work . we normally just use 70s-2 good fit up is key as to not overheat and change the structure of the tubing to much that is the most common failure i see of this sort looks like the weld is burnt i guess . yours dont look that way .
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          • KB Fabrications
            Senior Member
            • Jan 2006
            • 1632

            #20
            Originally posted by SNAFU
            just out of curiosity, I welded some scrap 4130 tubing and put it in a hydraulic press to see what the breaking point was, and where it would break...



            interesting results, thought I would share...
            I have tried to refrain from entering this thread but as it goes along, I have some thoughts. First, it seems that the original poster just welded up a random part and put it in the hydraulic press to see how it would fail. There is nothing wrong with that but it really doesn't address anything more than the particular way he choose to go about this. This part is not something that is in, or going into, production but something he just decided to do on the fly. It failed and just by looking at the pics a number of conclusions can, and have been, reached. If this was a "real" part, who's to say that as it stands it wouldn't pass muster? He claims he tested it to 10 tons but without knowing all the conditions first hand it's a little hard to make a determination from the pics alone. I have seen welds that looked much worse and that had much worse looking HAZ's put into product that never failed. Doesn't make it right, it's just what I have seen.

            To me, just from the pics, the weld looks too hot. The color of the bead should not be dulled/muted like that but rather should have a somewhat clean/golden/rainbow look like the pic I have posted. Granted the material I was welding is thicker but I welded bicycles for years and never let the joint look the way the original pictures looked.

            The HAZ looks too big as has already been stated but that doesn't mean the weld wouldn't hold for a given application. The bead itself doesn't look horrible by any means but IMHO it could have been done better by putting more thought into controlling the weld parameters.

            KB
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            Comment

            • Tex
              Senior Member
              • Dec 2006
              • 147

              #21
              Great pictures. I just have a couple questions. (Aerometalworker, you too) What is the proper testing method for 4130 tubing welds? This kind-of goes back to a previous post about TIG vs. O/F welding of 4130. I thought the welds looked pretty decent and if they hadn't been stuck in a press, who knows if it was good or bad? AMW, isn't there some type of fatigue test for this? I appreciate pictures of stuff being broken, though.
              Matt Adams A&P, IA
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              • Aerometalworker
                Senior Member
                • Dec 2005
                • 831

                #22
                Originally posted by Tex View Post
                Great pictures. I just have a couple questions. (Aerometalworker, you too) What is the proper testing method for 4130 tubing welds? This kind-of goes back to a previous post about TIG vs. O/F welding of 4130. I thought the welds looked pretty decent and if they hadn't been stuck in a press, who knows if it was good or bad? AMW, isn't there some type of fatigue test for this? I appreciate pictures of stuff being broken, though.
                Tex,
                Unfortunately there is no "standard" for testing aircraft tubing cluster welds by the governing body. The AWS may but that doesnt apply. Most institutions do a scarfed joint in something like 3/4" .035 with the inner tube and rosettes per AC 43.13. Without the inner tube the weld tube will stretch and deform a good bit, before it finally tears, at some distance from the edge of the weld. Hard welds will snap with a "bang" without any deformation. Fatigue is a whole other story, with its own testing. Hard, small welds done with Tig and not properly treated have caused fatal failures in the past, in production aircraft. Im sorry but I dont aggree with the "low heat input" way of welding this material. Ive seen many failures due to hard welds, and none due to soft. I even had a "Welding Engineer" at another company inform me that MIG was the best way to weld 4130 due to "Low heat Imput". I hope to God that man never gets to work on an aerospace vehicle.

                -Aaron
                "Better Metalworking Through Research"

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                • Aerometalworker
                  Senior Member
                  • Dec 2005
                  • 831

                  #23
                  Originally posted by Tex View Post
                  Great pictures. I just have a couple questions. (Aerometalworker, you too) What is the proper testing method for 4130 tubing welds? This kind-of goes back to a previous post about TIG vs. O/F welding of 4130. I thought the welds looked pretty decent and if they hadn't been stuck in a press, who knows if it was good or bad? AMW, isn't there some type of fatigue test for this? I appreciate pictures of stuff being broken, though.
                  Tex,
                  Unfortunately there is no "standard" for testing aircraft tubing cluster welds by the governing body. The AWS may but that doesnt apply. Most institutions do a scarfed joint in something like 3/4" .035 with the inner tube and rosettes per AC 43.13. Without the inner tube the weld tube will stretch and deform a good bit, before it finally tears, at some distance from the edge of the weld. Hard welds will snap with a "bang" without any deformation. Fatigue is a whole other story, with its own testing. Hard, small welds done with Tig and not properly treated have caused fatal failures in the past, in production aircraft. Im sorry but I dont aggree with the "low heat input" way of welding this material. Ive seen many failures due to hard welds, and none due to soft. I even had a "Welding Engineer" at another company inform me that MIG was the best way to weld 4130 due to "Low heat Imput". I hope to God that man never gets to work on an aerospace vehicle.

                  -Aaron
                  "Better Metalworking Through Research"

                  Miller Dynasty 300DX
                  Miller Dynasty 200DX
                  Miller Spectrum 375 extreme
                  Miller Millermatic Passport

                  Miller Spot Welder
                  Motor-Guard stud welder

                  Smith, Meco, Oxweld , Cronatron, Harris, Victor, National, Prest-o-weld, Prest-o-lite, Marquette, Century Aircraft, Craftsman, Goss, Uniweld, Purox, Linde, Eutectic, and Dillon welding torches from 1909 to Present. (58 total)

                  Comment

                  • OldSparks
                    Senior Member
                    • Oct 2005
                    • 220

                    #24
                    Originally posted by Aerometalworker View Post
                    My hints as others, would be to increase the fillet size, ramp the temperatures more slowly. If you welding 5 seconds after you hit the current, your putting in way too much localized heat, shoot for 15-30 seconds.

                    I dont understand the love affair with tiny fillets on tubing clusters nowdays......since when does function follow form?

                    -Aaron
                    Although this isn't a priority with me, I like to soak up as much information as possible. I agree that the weld should be convex and that there are some signs of undercut or 'washdown'. As for travel speed, it seems a lot of past suggestions are to turn up the heat and travel faster. Just to clarify, if I'm reading this right, your hint is the opposite. Are you saying to adjust the heat input so that it takes 15-30 seconds to form a puddle before proceeding? Is this with the thought that the slower movement would result in slower cooling.

                    Comment

                    • trstek
                      Senior Member
                      • May 2007
                      • 485

                      #25
                      In the past after welding 4130 we heated it with a torch and let it cool normally. That was the advice I was given to normalize the metal and welds. Is this correct procedure? (non aircraft application)

                      Thanks,
                      Tom

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                      • BillC
                        Senior Member
                        • Oct 2005
                        • 184

                        #26
                        Originally posted by trstek View Post
                        In the past after welding 4130 we heated it with a torch and let it cool normally. That was the advice I was given to normalize the metal and welds. Is this correct procedure? (non aircraft application)
                        Tom,

                        How hot did you heat it after welding? Did it glow?

                        Regards,
                        Bill
                        "The more I learn about welding the more I find there is to learn..."

                        Comment

                        • Aerometalworker
                          Senior Member
                          • Dec 2005
                          • 831

                          #27
                          Originally posted by OldSparks View Post
                          Although this isn't a priority with me, I like to soak up as much information as possible. I agree that the weld should be convex and that there are some signs of undercut or 'washdown'. As for travel speed, it seems a lot of past suggestions are to turn up the heat and travel faster. Just to clarify, if I'm reading this right, your hint is the opposite. Are you saying to adjust the heat input so that it takes 15-30 seconds to form a puddle before proceeding? Is this with the thought that the slower movement would result in slower cooling.

                          Yes you are reading that correctly. In fact some of the aircraft manufacturers are limiting the amperage of the machines to force it. Rapid cooling especially is the enemy of 4130, plain and simple, do all you can to avoid it. The old trick of torch annealing the material ( Im not going to start this argument ) after Tig welding was as simple as raising the welded area to a dull red, keep it there for a minute, and slowly let it cool. Does it make the joint softer? you bet! There is no magic about 4130....just treat it like an air hardening tool steel of sorts.

                          -Aaron
                          "Better Metalworking Through Research"

                          Miller Dynasty 300DX
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                          Miller Millermatic Passport

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                          Smith, Meco, Oxweld , Cronatron, Harris, Victor, National, Prest-o-weld, Prest-o-lite, Marquette, Century Aircraft, Craftsman, Goss, Uniweld, Purox, Linde, Eutectic, and Dillon welding torches from 1909 to Present. (58 total)

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                          • trstek
                            Senior Member
                            • May 2007
                            • 485

                            #28
                            We just would heat it up, not cherry, just get it hot and let it cool.

                            I take it getting it cherry red is bad?

                            Thanks,
                            Tom

                            Comment

                            • phaxtris
                              Senior Member
                              • Mar 2007
                              • 330

                              #29
                              ive kind of stayed away from this thread aswell, but from the looks of things that would be in the area i would expect the tubing to fail, espeically with that joint configuration

                              and of course the tubing is going to be more likely to fail in the heat affected zone, especially without heat treatment, i would imagine had the weld been done a little cooler the fracture *might* have been a little further out, but you guys are forgetting this is a destructive test, the aim of the test is to find out how it fails, it is going to fail no matter what

                              i would also like to note, look at the other piece where the tubing has torn lengthwise, its not going to tear the weld apart, it should tear in the area it tore

                              i think the joint configuration plays a huge role in the outcome of this test as well as how the force was applied, the area at the base of the welded tubes is definatly seeing a lot more than 10t of force

                              destructive tests generally have an aim, 5t, 7t, 10t, etc, i would imagine if this test had some form of criteria that would have passed (where in reality would they have a tube that size be required to hold 10t of force)
                              mm210
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                              • trstek
                                Senior Member
                                • May 2007
                                • 485

                                #30
                                with respect, some of you guys said you stayed away from this thread (and I expect there are more)...

                                this is one of the best threads on this board. It talks about welding. The purpose is for people to have opinions and voice them. The readers have the task of sifting through the opinions and forming their own opinions.

                                Its called collaborating in my world...

                                Thanks to everyone who voiced their opinions...

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