It will take me a bit to catch up on this thread but if I remember correctly the strain gauges have to mate to the material which you are wanting to measure the deflection and the expansion is limited to say between 8% and 10% of the material. They resemble like a compressed spring and as the spring like architecture, actually parallel in theory, is expanded it changes the resistance seeing the geometry of the metal has changed and the electron lattice has been modified. When a voltage is applied to a conductor the electrons tend to wad up, with respect to their steady state position, toward one end.
Kind Regards,
Raimey
rse
