15. History Note: Machining, Strain Gages, and a Pulse-Heated Kolsky Bar

A special Kolsky bar apparatus with the capability to pulse heat the sample was built at the National Institute of Standards and Technology (NIST). This Kolsky bar laboratory’s initial purpose was to measure dynamic material properties in support of machining analysis research. Machining is a high-strain, high-strain-rate, high-temperature, high-heating-rate process. Developing mathematical models to analyze machining processes presents unique challenges, including appropriate material stress-strain relationships. The NIST system can heat a sample to over 1000 C in less than a second immediately prior to a Kolsky bar impact test. Although there are many traditional Kolsky bars in operation, the ability to achieve a very rapid temperature increase by electrical resistive heating is unique. The development and construction of this laboratory involved cooperative effort of several researchers from different NIST divisions. The work benefitted from a rich history of strain measuring research at the National Bureau of Standards (NBS), now named NIST, as well as drawing on a long history of interaction with the Society for Experimental Mechanics (SEM). .