Strain gages, sometimes called strain gauges, are tools used to measure the amount of strain that an object has.
In 1938, Arthur Ruge and Edward Simmons invented what would later become the most common type of strain gaging tools. Their device had an insulating flexible backing that supported a metallic foil pattern. In order to measure the strain on an object, you attach it to an object with an adhesive. As the strain deforms the object, so too does the foil become deformed. This in turn causes the foil’s electrical resistance to change, which is most commonly measured with a Wheatstone bridge.
Strain gaging tools utilize electrical conductance’s physical property, as well as its dependence on the conductor’s geometry. If strain stretches an electrical conductor within the limits of its elasticity — stretches it so that it doesn’t deform permanently or even break — the electrical conductor will get longer and narrower, making it more electrically resistant.
That’s not all. If a conductor is compressed, it’ll broaden and shorten. So long as the compression doesn’t force it to buckle, its electrical resistance from end-to-end will decrease, rather than increase.
Using the strain gaging tool’s measured electrical resistance, it’s possible to infer the amount of stress that’s being induced upon the object.
Nowadays, a typical strain gaging tool forms a zig-zag pattern of parallel lines using a thin conductive strip. If any amount of stress is applied in the direction of the parallel lines’ orientation, a multiplicatively larger strain measurement is created. Consequently, there’s a multiplicatively larger change in resistance, allowing the tool’s user to observe more than he or she could with a single straight-line conductive wire.
In short, strain gaging tools can measure the amount of strain on an object using the as it becomes stretched or compressed. If you have any questions about regular or custom strain gaging tools, feel free to share in the comments.