Choosing the Right System: Assessing Env. Params & Measuring Cantilever Beam

[hunterage2000]

1). Would you always go through a selection criteria to help decide on the most appropriate one to use if you had no prior knowledge of the system?

2). Would the environmental parameters need to be assessed for any kind of system regardless of the conditions?

3) Would the dimensions of the cantilever beam need to be measured to decide on the placement of the strain gauges or would strain be distributed evenly across the beam?

 

[AlephZero]

I don't understand what you are trying to get at with (1) and (3). If you don't know anything about a system, or what its shape and dimensions are, you can't "select" or "design" anything.

You can't measure anything unless you have some idea of the results you expect. You need a model the system (which could mean anything from a simple hand calc to a detailed computer simulation) before you can decide what to measure and how to measure it.

For (2), the answer is "yes", but whether the assessment would take two seconds or two years depends on the system and the environmental conditions, so this question seems almost as vague as (1) and (3).

 

[hunterage2000]

you have answered 1 and 2 for me. For 3 I know the dimensions of the beam but I don't know if the placement of the strain gauges at some points on the beam matters or not.

 

[AlephZero]

For 3 I know the dimensions of the beam but I don't know if the placement of the strain gauges at some points on the beam matters or not.

Where you put the gauges depends on loading and the stress distribution you expect and exactly what you are trying to measure.

For example with a cantilever loaded at the tip, the bending stress is zero at the tip and a maximum at the other end. But it you put the gauges too close to the fixed end, you may be measuring the local strain caused by the way it is fixed (clamped, bolted, whatever) rather than the "global" bending stress in the beam.

If you are trying to measure Youngs modulus for the beam material, you would want to avoid the local "end effects". On the other hand if you the beam was part of a "real" engineering structure, the local stress concentration(s) at the ends might be exactly what you were trying to measure.