Strain measurement and how to use strain gauges?

What is a strain gauge?

A strain gauge is an electrical resistor that measures strain on the surface of material.

The strain gauge is glued onto the surface of a structural element that is expereinces load. The gauge is wired into a Wheatstone bridge electrical circuit - which is typically found in a strain gauge amplifiers. The voltage across the Wheatstone bridge is measured and recorded as volts.

Why do we measure strain?

We measure strain:

  • to investigate structures under varying load,

  • structural testing,

  • verify analysis results

  • update numerical models and

  • use as feedback for controllers.

When analysing the stress of any structure, one may find high stress concentrations. Reducing these high values are pertinent to ensure an infinite fatigue life.

It is best to investigate high stress areas. But measuring stress is an intrusive approach, so we measure strain instead. That way, no alterations are made to the structure.

The stress value is the product of the strain and Young's modulus of the material of which the strain is measured.

How we use strain gauges?

We measure strain and record strain to determine the strain value at a particular high stress location. These are usually high strain areas found in the analysis of a structural elements and joints. As with accelerometers measuring acceleration, strain gauges measure strain.

But, strain gauges only measure what happens underneath them (the surface on which the strain gauge is pasted). The measured strain value will not correlate with the analysis results if the strain gauge is not mounted exactly over the strain area of interest, and will aslo give erroneous results if the strain is not uniform throughout the length of the strain gauge.

If you have a project that requires strain gauging, strain measurement, and analysis, please get in touch with our consultants on 01908 643433.

What work have we done that involves strain gauges and strain measurements?

We've instrumented several structural elements with strain gauges, al lto update finite element models and to use as controller feedback signals. Here are a few examples of what we've completed.

  • instrumented high strain areas of small structures to measure the strain during loading of the structure. These values were used for verifying the analysis model.

  • We have instrumented coil springs with strain gauges. We used the voltage measured across the gauges as feedback to a PID controller. (Feedback to PID controllers as the controller was driving the actuator that created the input force to the structure.

  • These are two of the most common uses of a strain gauge that we have installed. If you have any questions about strain gauges, pasting to fault finding, please get in touch on 01908 643 433.

    Get in touch if you are working with strain gauges and need help. Or if you have reviewed the recorded strain measurement data, and have unexplained behaviour, or lack of analysis correspondence. Please get in touch, as we've been doing this for over 25 years.

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