![]() ![]() You are starting to form a plastic hinge, but if you unload the beam, much of its deflection (Δ) will spring back, but not all of the deflection. If you continue the loading the locations (the planes) of the yielding fibers move inward toward the N.A. fibers just start to yield, that’s L1 (load 1). The beam is loaded until the top and bot. We’ve all seen this problem in our early engineering courses, so it may be a slightly simpler example, but the thinking is the same for a cold bent pipe, just a bit more complicated because of shape geometry, etc. bending moment at the center of the beam. Let’s also start out with a simple rectangular beam section, in simple bending, a simple max. At the same time dig out your Engineering Mechanics, Advanced Strength of Materials and Theory of Elasticity text books and start reviewing them on these topics. Try this thinking on for size, and see if it fits your needs or understanding of your problem. We didn’t have nearly as nice a set-up as shown in the video, but what they are doing is the same process as we were studying and learning. I’ve never used the system you linked and haven’t studied the subject in some years. hole out of the part and measures the strain change around that hole to determine the residual stress. I am aware of the drilling and strain gage method of assessing residual stress, and it pretty much seems to be the standard method today. And, in fact, if you could measure accurately enough the bend angle in the pipe would change from cutting out the coupon, because you have disrupted the equilibrium stress conditions (the residual stresses) after the bending process. To answer your basic question., you can’t remove a coupon from the pipe without changing the residual stress in it and in the pipe around the coupon hole. RE: Residual Stress in (Shop) Cold Bends auzie5 (Mechanical) Should I maybe consider pulling some longitudinal samples as well to check if any residual stresses are impacting longitudinal properties? However, tensile tests are typically from transverse coupons to qualify the bend procedure. Thus if I passed my mechancial tests on the test bend I would not need to worry about residual stresses. I have always thought that if there are residual stresses left in the bend, they would impact the results of my test bend mechanical test results. Unless for sour service, I cannot remember an instance when I post bend heat treated a cold bend (even for much tighter bend radii). Is the general statement that, "cold bends have more residual stress left in them than induction bends" accurate? I would assume that depending on the quenching rate, induction bends can have residual stresses left in them as well.įor cold bends, I have always just completed my mechanical testing on my test bend to qualify the cold bend procedure without giving any serious thought to residual stresses existing in the finished bend. I do admit that the idea of residual stresses left in a finished cold bend is a bit confusing to me at the moment. As soon as they hear 20" they immediately conclude it must be fabricated using the induction bending process before I've even had a chance to detail the bend radius (example: 25D). I tend to run into people who prefer induction bends over cold bends as a rule. Thanks for the input racookpe1978 and LittleInch. RE: Residual Stress in (Shop) Cold Bends weldstan (Materials) 28 Jan 16 18:26 However, I am unclear if I can remove a coupon from the finished bend to perform ASTM E837-13 tests or if I would be required to mount the Restan MTS3000 on the finished bend since removed a coupon may relieve some of the residual stress in the steel after the bending process. As one of my checks, I would like to demonstrate the bending process has not introduced unacceptable levels of residual stress into the finished bend. 448 line pipe to a 25D bend radius and 30 degree bend angle using a hydraulic ram bending machine. I am in the process of cold bending some NPS 20 x 12.5mmWT, CSA Z245.1 Gr. However, I am uncertain about the effects on the residual stress in the pipe if I remove a coupon from the test bend for testing in the Restan MTS3000 instrument. Since we complete destructive testing on a test bend before moving into production, I liked the idea of following ASTM E837-13 to determine residual stress by the hole-drilling strain gage method. As I was looking for an instrument to measure the residual stress left in the pipe after bending I came across a product (Restan MTS3000 – see video demonstration: ). I am currently exploring bending large bore steel line pipe using a hydraulic ram bending machine. My question is: Does removing a coupon from a test bend relieve the residual stress in that coupon? Or can I remove a small coupon from the test bend and still accurately measure the residual stress introduced into the steel during the cold bending process? ![]()
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