A strain gauge (also spelled strain gage) is a device used to measure strain on an object. Invented by Edward E. Simmons and Arthur C. Ruge in 1938, the most common type of strain gauge consists of an insulating flexible backing which supports a metallic foil pattern. The gauge is attached to the object by a suitable adhesive, such as cyanoacrylate.^[1] As the object is deformed, the foil is deformed, causing its electrical resistance to change. This resistance change, usually measured using a Wheatstone bridge, is related to the strain by the quantity known as the gauge factor.

History[edit]

Edward E. Simmons and Professor Arthur C. Ruge independently invented the strain gauge.

Simmons was involved in a research project by Dätwyler and Clark at Caltech between 1936 and 1938. They researched the stress-strain behavior of metals under shock loads. Simmon came up with an original way to measure the force introduced into the sample by equipping a dynamometer with fine resistance wires.

Arthur C. Ruge, a professor at MIT, on the other hand, conducted research in seismology. He tried to analyze the behavior of a model water tank installed on a vibration table.  He was not able to utilize the standard optical strain measurement methods of his time due to the small scale and low strains in his model. Professor Ruge (and his assistant J. Hanns Meier) had the epiphany of measuring the resistance change in metallic wires caused by strain cemented on the thin walls of the water tank model.

The development of the strain gauge was essentially just a byproduct of other research projects. Edward E. Simmons and Professor Arthur C. Ruge developed a widely used and useful measurement tool due to the lack of an alternative at their times. Arthur C. Ruge realized the commercial utility of the strain gauge. His employer at MIT waived all claims on the right of the invention, as they did not predict the economic and large-scale usage potential. This prediction turned out to be false. The strain gauge applications were quickly gaining traction as they served to indirectly detect all other quantities that induce strain. Additionally, they were simple to install by the scientists, did not cause any obstruction or property changes to the observed object and thus falsifying the measurement results. Probably the last and most important property was the ease of transmission of the electrical output signal.^[2]