Failure modes of strain gauges

[Bellis]

I am trying to determine some failure modes of strain gauges and the means of accomplishing some of them. Things like loose leads, debonding, physical damage, thermal effects, doing things that cause saturation.

I am looking for ideas of what other failure modes are and ways to accomplish them, like how do i cause debonding, things like that, any recommendations are appreciated. Thanks.

 

[berkeman]

One way to induce some of those failures (and even emulate the real world) would be to have a cyclic bending of the gauge through some angle, and take it to failure. Like, make a small test bed where you can mount a gauge and the wires, and strain relieve whatever you don't want to fail, and then have a little motor arrangement to cycle some bending. If you want the gauge material to fail first, be sure to strain relieve/support the wires, etc. If you want the wires to fail first, don't strain relieve them.

Kind of like a little shaker/bender table arrangement.

 

[Bellis]

One way to induce some of those failures (and even emulate the real world) would be to have a cyclic bending of the gauge through some angle, and take it to failure. Like, make a small test bed where you can mount a gauge and the wires, and strain relieve whatever you don't want to fail, and then have a little motor arrangement to cycle some bending. If you want the gauge material to fail first, be sure to strain relieve/support the wires, etc. If you want the wires to fail first, don't strain relieve them.

Kind of like a little shaker/bender table arrangement.

Ah, well I do in fact have the shaker table arrangement set up, I guess my question relates more to how to go about inducing failure and types of failure I might want to be away of.

 

[berkeman]

Interesting -- I googled strain gauge failure mechanisms, and got lots of hits. Unfortunately, they were mainly on using strain gauges in studying the failure mechanisms of structures and materials (Doh!). I didn't try quoting the search string to try to get a better hit list, so you might try that.

I did see something interesting on one of the pages:

http://www.davidson.com.au/products/strain/mg/technology/technotes/pcindex.pdf

They talk about a failure mechanism where too high of a voltage and power were used with the gauge, causing thermal issues.

 

[berkeman]

I tried quoting the whole google search string, but that was too specific and garnered zero hits. However, "strain gauge failure" produced a good hit list, which should provide you with more ideas:

http://www.google.com/search?hl=en&q="strain+gauge+failure"&btnG=Search

 

[Bellis]

Great, I appreciate the advice

 

[FredGarvin]

Strain gauges fail for the most common sense reasons.

- Over strain
- Over temp
- Over current
- Incorrect bonding
- Physical impact
- Environmental wear (salt spray, corrosive environment etc...)
- Improper gauge selection (while not a physical failure, it is a failure mode)

 

[Astronuc]

With respect to - Over strain - match the strain gauge with the expected strain. Know the elastic range, i.e. strain to yield strength, which is usually a design criterion, or a fraction thereof.

If one is straining to failure, that could be 10% to 60% depending on the metallurgical state of the material and any critical flaws that may be present.