Stress/strain testing for dummies ..

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After spending the last 4 or 5 hours going nowhere, I'd sure appreciate any thoughts. Several weeks ago I exhausted all the threads on 6010 and/or 6011 root and 7018 cap passes, weaving, whipping, keyhole, and puddle v. slag distinctions, Then I started thinking how easy it is to miss something basic.So, using 1/8" X 2" flat bar, I butt-welded two pieces (3/32" rod, 90-110 amps), then bend it in a vise to check integrity, etc. I always understood that you bend the piece so that the side away from the welded surface opens up. Long story short, I was expecting/hoping the piece would bend 180 degrees and be solid steel, just like tje 5g certification on You-tube.After just about every imaginable combination of rod angle, speed, amps, whipping/weaving/stringer, and rods (6010, 6011, and 7018, even 6013), all but two of them broke down the middle of the weld bead at 90 degrees of bend, some even before. Whether I moved faster or lingered enough to get a keyhole to open up, the weld always showed half-penetration or less. The weld-side looked good otherwise, stack of dimes, good tie in at the toe, fairly flat profile.To allay further misery, I tried to rationalize that perhaps stock 1/8" to 1/4" thick doesn't act the same as a 5g cert, where that coupon bent completely in half at the weld and the back side looked like solid metal. I really don't have much more than 1/4" pieces to practice on.Hope someone can follow the story line here and spot some cardinal violation. I could be wrong, but practicing another 4 hours probably won't break new ground. It's always either half-penetration or burn though after an inch of so and a messy finish. There's no one around here I can show it to or talk with, so even the most obvious or basic observation may hold the key.Thanks for any experience or anectdote you may be able to resurrect.
Reply:Pictures tell many words. Are both pieces clean within 2" of the weldzone? Do you hit the joint with a torch to dry it off and bring up the temperature? Is there a way to use run-off tabs? Are your Lo-Hy rods fresh or kept in a rod oven? Are you using high quality rods? Where is your work clamp connected and how clean is the metal it attaches to? Do you clean after every pass and maintain correct inter-pass temperatures? How much practice should it take? Last edited by tanglediver; 01-21-2011 at 09:42 PM.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:Were they full pen welds that were grinded smooth like the test? If you just butt weld flat bar together and try and bend it, its gonna break unless you did a proper root and fill.
Reply:The 5g is an open root weld and what your doing from what you describe is not. You need to leave a gap that way you can get a full pen weld.
Reply:Thanks for the benefit of your thinking. I'm going over each point and isolating the effect. What's standing out initially, and I thought it might be a false assumption on my part, is that my 1/8" flat bar didn't have to be so carefully "formated" (cleaned, beveled, root gap) as the 5g coupons that appear to be about 1" thick. I was thinking it should be easy to just burn through 1/8" or even 1/4" by turning up the amps and whipping the 6010 to just barely burn through to the other side, even in flat position. As Jay suggests, leaving a root gap (I'll start with same as rod diameter) may yield more improvement than anything else. Steve's "proper root and fill" w/ intermediate grinding down strikes me as a good method to confirm how much penetration each pass accomplished. I'm going back out and apply just one or two solutions at a time to unravel the confusion, and even though it may be overrationalization on my part, I'm placing great stock in Steve's comment, "If you just butt weld flat bar together and try and bend it, it's gonna break ..". For now until I get this worked out, I'll assume a flush joint w/ no gap or bevel would break no matter who welded it. I don't have a camera or I'd attach pictures. Can't tell you all how much I appreciate the content and comments.
Reply:What grade steel are you using? Bend tests are conducted at specific radii depending on the steel tensile / yield strength. Hot rolled is used for structural steel. Cold rolled is generally not permitted.
Reply:are you cooling your test coupons in water??daye
Reply:Find a hand in your area that can look over your procedure and tell / show you where the errors are.Getting this solves through books and the interweb is asking a lot.Your questions lack a basic understanding of welding. Look up the difference between PJP and CJP
Reply:Go buy a camera. You can take pictures of all kinds of things, including welds!
Reply:Bend tests are done on a specified radius.  The weld metal is always stronger than the parent metal.  As a result the yield strength is different.  Even if you welded the joint from one side then ground it out on the back side before doing another weld on your strap there still is the possibility that the piece will fracture if you simply bend it in a vice rather than against a radiused piece.  There are so many unknowns.  One welding instructor I know just puts an arc track across a piece about the size you used as an example.  He then bends it for the class.  If he is lucky the thing fractures.  In other cases the class can see cracks developing at the arc track marks.  The object of the lesson is to point out how heat can affect the base metal.....   and of course not to leave any tracks on your material.
Reply:tigmusky and weldinglifer, 'preciate those thoughts. Earlier posts explaining the re-grinding and gap/bevels are also dead-on. The 1/8" flat bar was more anecdotal. As most of you already intuit, a larger purpose is served in this format - that of validating fundamentals that prevail only so long as they go unchallenged; i.e., the facially flawless MIG welds that fail when dropped on a cement floor. So, the tips and thoughts will apply across the board, to other thickness, grades of steel, joint prep, etc and your cumulative efforts have been truly invaluable.Notwithstanding my lack of "basic understanding of welding" as Fat Bastard so graciously puts it, I'm pretty sure at this point I can advance the learning curve and ultimately meet his expectations.Just to close the loop, tignusky triggered a thought and I went back and waited for the coupons to cool off before testing. Just about all of them bent to 180 degrees, no cracks, no failure. Pretty simple, but easy to miss when you work alone, I guess. Also, when trying for max penetration without blowing through, the 6010's were popping, sticking, and losing the arc constantly, so while scraping up some 7018 and even 6013's, I ran across another box of 6010's and tried them. Ran smooth and controlled way better overall. Must have just had a bad batch in the beginning. The other concepts you kindly shared, I'll extrapolate along the way. Many thanks to each of you for making the time to shate the wealth - sometimes options are limited and ya do what ya can.