Strain measurements
Strain gauges
Measuring changes in stresses in a structure is a common engineering need, as it enables us to verify the response of a structure to the stresses to which it is subjected. We offer a wide range of solutions:
- Gauges welded or screwed or glued to the surface of metal, concrete or glass, or embedded in concrete, or clamped or welded to a cable
- Sensor dimensions from a few millimetres to 1 metre
- Measuring technology electrical (Wheatstone bridge), vibrating string or fibre optic (usually Bragg, FBG)
- Static measurements (typically one measurement per hour, for example) or dynamic measurements (hundreds of measurements per second, to measure temporary material states)
The name ‘strain gauge’ is somewhat of a misnomer, as it measures micro-strain, which can then be converted into stress, provided that the Young’s modulus of the material is known.
Another name known in France for the same sensor is ‘vibrating string extensometer’.
It should be noted that it is possible to calculate the fatigue of certain materials on the basis of stress cycles accumulated over time, in order to estimate the residual service life. An example of an application is the monitoring of orthotropic metal slabs for bridges.
Finally, it should be remembered that the sensors only measure variations in stress relative to the day of installation. Other techniques exist for measuring historical stresses, such as the flat jack or Slotstress, the central hole method, etc.