Scientists and engineers often use proving rings as a way to measure force. The devices are made using a ring of metal with a spring-like consistency. Inside the ring there is a screw attached to a dial with measurements on it and a plate that vibrates after being struck with something. The contraption in the center works to show the ring's diameter after it has been compressed or stretched, which produces a reliable force measurement that can be used for other purposes.
To use a proving ring, a person will exert force on the ring in some way—generally either pushing from both ends or pulling it apart—and then strike the plate to start vibrations. At this point, the screw is generally turned until it touches the plate and stops it from vibrating. When the vibration stops, the number on the dial will show exactly how much force was used on the ring. The metal used to make the rings is often quite thick, so any flexing will often be very slight, which facilitates the need for precise measurement tools.
Proving rings are often used to calibrate the amount of force used within various force-testing devices. Once the calibration is set, other materials are placed in the devices, and it is possible to see if they can withstand the same force that was being applied to the proving ring. In this way, scientists can determine the exact strengths of various materials.
The proving ring was invented primarily because scientists needed a precise way to test the durability of various materials. Two scientists named Herbert Lucius Whittmore and Serge Nicolas Petrenko worked together to invent the devices after World War 1, and they used them to study new materials that were being invented at that time. Engineers were often excited to try new space-age materials in their designs, but they were also skeptical.
When scientists create new materials for building or use in products, sometimes there is a concern about the tolerances of the materials. Engineers who are designing machines or architects designing buildings may need to know exactly how much weight a material can withstand before using it in a particular part of the design. If this data is not precise enough, there is the possibility of a costly or dangerous accident. The proving ring allows for a very precise and reliable definition of force tolerance for nearly any material, which can help avoid these kinds of accidents.