How did the Proving Ring Come About?
At the end of World War I, the Brinell Hardness Test, then the predominant test for testing the hardness of metals, was in disrepute because of disagreements in the results from different laboratories. The American Society for Steel Treating, one predecessor of today's American Society for Testing and Materials (ASTM) and the American Society for Metals asked the National Bureau of Standards (NBS), the predecessor of the National Institute of Standards and Technology (NIST), to look into the matter.
The task was assigned to the Engineering Mechanics Section, headed by H. L. Whittemore who in turn assigned the project to S. N. Petrenko, an engineer in the section.
The early success of Petrenko with his deadweight machine led to the construction of a better machine, one with cast iron weights and a better loading technique. While materials could now be tested in the laboratory, a challenge remained as to how to transfer the accuracy and constancy of the test with deadweight loads to material testing machines used in the field. Petrenko reasoned that this transfer could be accomplished by a simple metal ring equipped with a means of measuring its deflection under load. Whittemore in turn suggested the vibrating reed and micrometer screw. Thus was born the Whittmore-Petrenko Proving Ring, later known simply as the Proving Ring.
Devices combining the ideas of Petrenko and Whittemore were built in the National Bureau of Standards shops in the early 1920's. On September 14, 1926 Whittemore and Petrenko filed a patent , number 1648375, with the Patent Office. The patent was granted on November 8, 1927. Whittemore and Petrenko filed a second patent, number 1927478, on August 29, 1929 to reflect improvements in the design of the proving ring. This patent was granted on September 19, 1933.
The business depression of the 1930's combined with the difficulties involved in manufacturing proving rings discouraged commercial production of the ring. Whittemore was at a loss to get them into service until he finally prevailed upon a distant relative, W.S. Morehouse, who had a small machine shop in York, PA to begin commercial production. The Morehouse Instrument Company still produces proving rings today.