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  • Charpy V-Notch tests, and the meaning ...

    There seems to be a lot of misunderstandings here, and most people have absolutely no idea ......

    Essentially, a Charpy test measures the "toughness" of a weld.

    Proceedure for the test, do the weld, cut the sample to specified size, put a notch in the weld. Bring it to the temperature you want to test at, clamp it in the apparatus.

    A pendulum is used, again, standard, weight and arc. Bring it up to height, release it, it strikes the sample. The sample will always break, that's not important. What is important is how far the pendulum swings up afterwards, doing the measurements and arithmetic one can determine exactly how much energy it took to break the sample, measured in ft./lbs.

    Not the same as a tensile test. 70,000 PSI pull is still 70,000 pounds pull, the charpy test measures the resistance to cracking and failure, and the ability to take stresses, from a sudden impact.

    Generally, a more ductile weld will absorb more energy, before giving way, than a more brittle weld material.

    As I understand it, ALL T-8 wires need to have charpy tests, ALL Low-hydrogen rods need charpy tests, to meet AWS specs. For the most part, also ALL dual-shield wires (gas-shielded, flux cored) also require charpy tests. NO T-11 wires need to have charpy tests, nor GS or G wires. In fact, it's just not done, if a T-11 wire could have a charpy test, it will become a T-8 wire, right???

    This started becoming really important here in California, only after the Northridge earthquake. Far too many buildings, were severely damaged, or just fell down, due to the use of T-11 wires. They are still used many places across the country, just not where seismic rules are in place.

    Understand, I am far from an expert at any of this, I am not an engineer, if anybody has any better explanations, please post up.
    Obviously, I'm just a hack-artist, you shouldn't be listening to anything I say .....

  • #2
    Izod, Charpy V-Notch

    JS: That's a good description of the test(s). The Izod test strikes the sample of the notch side, where as, the Charpy test strikes it on the back side of the key hole, or v-notch.

    Impact strength (or absorption of energy) is actually a volumetric property, modulous of resilience is expressed in in.,-lb/in3, or simply lbs/in2 psi.

    When impact loading exceeds the elastic limit (or yield strength) of the material, it calls for toughness in the material, rather than resilience.

    Toughness is the ability of the material to resist fracture under impact loading.

    As JS mentioned, the testing machine indicates the amount of energy in ft-lb required to fracture the specimen. This is the measure of notch impact strength.

    Tests are performed at varying temperatures, as some steels exhibit considerale loss of strength at low temperatures.

    Based on sample size, and all things being relative, various formulas (which I don't have on my keyboard) are used to calculate modulus of elasticity, yield strength, yield strain, modulus of resilience.

    Good work JS

    Dave
    Last edited by davedarragh; 11-18-2009, 03:37 PM.
    "Bonne journe'e mes amis"

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    • #3
      [QUOTE=JSFAB;213666]


      This started becoming really important here in California, only after the Northridge earthquake. Far too many buildings, were severely damaged, or just fell down, due to the use of T-11 wires.
      QUOTE]



      There were many individual welds that failed but there were no structures that collapsed because of those isolated weld failures.
      The cause was pegged on three things: connection design, the wires used and really shoddy welding.

      JTMcC.
      Some days you eat the bear. And some days the bear eats you.

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      • #4
        CalTrans California's transportation Dept. Was forced to grind out and reweld all welds on the rebar on seismic retrofitted bridges. All due to poor craftsmanship.

        And thanks for the explaination.
        The reason I asked Is one I haven't done enough wire feed welding to know one wire from the next. And two Selecting a wire for this job I found wires that meet impact requirements and wires that are not required to meet impact requirements. And I wanted to know what the difference was.
        Now I Know.
        Thanks JS, JT, and Dave.
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        • #5
          Originally posted by kcstott View Post
          CalTrans California's transportation Dept. Was forced to grind out and reweld all welds on the rebar on seismic retrofitted bridges. All due to poor craftsmanship.

          And thanks for the explaination.
          The reason I asked Is one I haven't done enough wire feed welding to know one wire from the next. And two Selecting a wire for this job I found wires that meet impact requirements and wires that are not required to meet impact requirements. And I wanted to know what the difference was.
          Now I Know.
          Thanks JS, JT, and Dave.
          Looks like your 12VS is going to get a workout UltraCore 71C is some sweet wire. It runs on 100% CO2. The wire itself is black, and perforated, no snips needed. The 15# spool fits in the feeder, because the spool has a recess for the retainer. It's certified FEMA 353 and AWS D1.8 Seismic.

          Dave
          "Bonne journe'e mes amis"

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          • #6
            Yeah I about to charge the company a rental rate
            The LWS here supplies to fab shops mostly. Not iron workers so getting a dual shield wire is a day or two out.
            Miller Syncrowave 200 W/Radiator 1A & water cooled torch
            Millermatic 252 on the wish list
            Bridgeport Mill W/ 2 axis CNC control
            South bend lathe 10LX40
            K.O. Lee surface grinder 6X18
            Over 20 years as a Machinist Toolmaker
            A TWO CAR garage full of tools and a fridge full of beer
            Auto shades are for rookies
            www.KLStottlemyer.com

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            • #7
              Originally posted by JSFAB View Post
              There seems to be a lot of misunderstandings here, and most people have absolutely no idea ......

              Essentially, a Charpy test measures the "toughness" of a weld.

              ...
              A long time ago I worked in a metallurgical r&d lab ... that's how
              I remember it...
              The only thing I'd alter is that the Charpy test is not
              limited to just welds.

              Thanks for posting it

              frank

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              • #8
                Originally posted by JSFAB View Post
                if anybody has any better explanations, please post up.







                Caution!
                These are "my" views based only on “my” experiences in “my” little bitty world.

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                • #9
                  Charpy Impact

                  This topic is a mystery to a lot of people.

                  Charpy's are just impact toughness at a relative temperature -usually cold temperatures.

                  The test can be run at different temperatures - as cold as like -60F.
                  Probably not that low for Califrornia seismic requirements but used in other industries like Natural Gas & Military Shipyard work. Your building code will probably reference testing at one of the temperatures listed in ASTM.

                  A lot of structural steel, plate, filler wire, welding rods do come prequalified with Charpy tests (You can ask for them when you order your steel or welding rod - It's on the Material Test Reports MTR's from the steel mills). If it doesn't arrive prequilified it can be tested. Rolling direction of the plate is critical when conducting and or qualifying your Plate and/or Welding Procedure Specification WPS.

                  The problem comes in the companies Weld Procedures Specifications WPS. For doing this work you are supposed to use qualified procedures (Some companies buy these from AWS or they come up with there own). This is where things go wrong welding interpasss temperatures are not usually followed and it destroys the Charpy properties of both the filler and the base metals. The problem is more common to wire due to the fact that it is highly efficient thus heat input can be easily exceeded. How many times have you seen a FCAW weld wider than 10x filler diam? Almost always.

                  Companies and Supervisors don't need to understand the physics behind the test that's not important. They need to understand the proper use of the companies Weld Procedures Specifications and why the limits are set on the welding parameters. The final and most important issue is training welders - this is difficult because production has always been the priority not quality.
                  Bobcat 225
                  The rest is bright RED "Tig & GMAW"
                  Just got a new Hypertherm 30

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                  • #10
                    Originally posted by Hillbilly69 View Post
                    ............................The problem is more common to wire due to the fact that it is highly efficient thus heat input can be easily exceeded. How many times have you seen a FCAW weld wider than 10x filler diam? Almost always. ...........
                    Just a question,,,, is this ten times the wires listed diameter which includes the filled core??

                    Thanks in advance.
                    Last edited by Sandy; 11-21-2009, 02:13 PM.

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                    • #11
                      I'm glad I started this topic, and I'm glad a few guys that know more about it chimed in.

                      Hey, Sonora, how about the Reader's Digest version?????
                      Obviously, I'm just a hack-artist, you shouldn't be listening to anything I say .....

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                      • #12
                        Welding Parameters

                        FCAW weld width is typically 10x outside diameter of the wire. It will be on a properly completed WPS. So common 0.045" and 0.052" wire gives you a 1/2" final FCAW weld width if you stay within the WPS. The manufacturer of the wire sometimes has limits aswell.

                        IMO it's got more to do with heat input into the base metal than the ability the filler in making a clean weld.
                        Bobcat 225
                        The rest is bright RED "Tig & GMAW"
                        Just got a new Hypertherm 30

                        Comment


                        • #13
                          Originally posted by Hillbilly69 View Post
                          FCAW weld width is typically 10x outside diameter of the wire. It will be on a properly completed WPS. So common 0.045" and 0.052" wire gives you a 1/2" final FCAW weld width if you stay within the WPS. The manufacturer of the wire sometimes has limits aswell.

                          IMO it's got more to do with heat input into the base metal than the ability the filler in making a clean weld.
                          Hey thanks, you've helped me here. I was just looking for something I could use personally as a general guideline for what is more or less acceptable and what might be considered excessive.

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                          • #14
                            Yes, how much is excessive?
                            Attached Files

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                            • #15
                              Slightly off-topic here but you're looking for general guidlines, I thought I would throw a few more out there:

                              For FCAW 10x wire dia. is max weave

                              For SMAW use about 5-6x electrode dia.

                              For any application, do not exceed 2x parent material thickness-- a lot of structural welds are actually only 75% of material thickness

                              ie. when joining 2- 1/2" plates in a fillet weld, don't exceed 3/8" in the throat of the weld.

                              If the joint dictates making a weldment that will be considerably larger than the thickness of the parent metal, it's likely a good idea to run stringers rather than a large weave to limit heat input on the parent metal.

                              Cheers,

                              WH
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