Capturing collapse response of tube
Capturing collapse response of tube
(OP)
Hi,
Would a regular strain gauge in wheatstone circuit be the best option to capture the lateral collapse of a tube under external pressure? The tube will be in a pressure pit & out of view for the duration of the test. Since we cannot visually monitor it during the test, there is no way to figure out when the collapse initiates.
Would a regular strain gauge in wheatstone circuit be the best option to capture the lateral collapse of a tube under external pressure? The tube will be in a pressure pit & out of view for the duration of the test. Since we cannot visually monitor it during the test, there is no way to figure out when the collapse initiates.





RE: Capturing collapse response of tube
RE: Capturing collapse response of tube
Another problem is that we only have one free port from the pressure chamber, & there is space to insert two wires only. So that means we can only attach one strain gage which is not sufficient to capture the stress distribution. I was wondering if there exists a ring gage that will cover the ID of the tube? That way there will be only two leads coming out of the pressure chamber.
Mike
RE: Capturing collapse response of tube
so the next question is are you expecting a global failure (like euler) or localised ? if the latter, then i'd expect one side of the tube to experience higher stresses than the other and the overall averaging would give you a lower result ... average where you aniticpate failure.
btw, can't you rig up a video feed ?
could you connect the s/gauges to a wireless xmitter (and get around you wires limitation)?
have you modelled this ?
RE: Capturing collapse response of tube
Like you said all bridges in series would give a lower stress if the failure is localized (maybe due to manufacturing defects), so I not too keen on using that option even though it will most likely be a global failure.
A video feed is not an option we can use.
The wireless transmitter seems to be the best option if it is available. Can you suggest any references?
I am in the process of modelling this, but am having some problems with the FEA model. So it is in process.
RE: Capturing collapse response of tube
Using wireless gages is a possibility, but be aware that they are not necessarily as consistent as wired gages, depending on potential interference.
RE: Capturing collapse response of tube
It is a hollow tube with sealed ends and bonding the gauge on the OD would be much more easier than bonding it on the ID
RE: Capturing collapse response of tube
I realize you only have limited space to get your wire into tube area. The gauge wires are very small (20-24 gauge).
RE: Capturing collapse response of tube
But if all you want to know is the pressure at which buckline occurs, wouldn't you simply monitor pressure vs. displacement (volume of pressurant liquid pumped into the chamber)? When the pressure vs. volume curve flattens, it's a pretty good sign that either the tube buckled, or you sprang a leak somewhere.
RE: Capturing collapse response of tube
RE: Capturing collapse response of tube
( They didn't report it at the time, because it was the inner tube of a jacketed u-tube. The outer tube suffered no damage, and nobody looked deep inside until the customer reported unusually high pressure drop. ...Ooops... )
Mike Halloran
Pembroke Pines, FL, USA
RE: Capturing collapse response of tube
Thanks for that information. You are right, I think using linear gauges looks like the sensible way to about for the test.
Monitoring the pressure drop & hearing a loud bang is normally how we do it right now, but we want to capture the failure collapse mode.
RE: Capturing collapse response of tube
RE: Capturing collapse response of tube
RE: Capturing collapse response of tube