Watertown Arsenal Charpy bar standards

The historical source of calibrated standard Charpy bars, now superseded by NIST. Tom notes Watertown Arsenal is "a mall now."

Every now and then, the shipyard would get a report from Sparrows Point that this particular plate had 30 foot-pounds of toughness. A really good steel. A really good steel could stop the hammer at 264 foot-pounds. When I was developing my steel, I used to stop the hammer on a regular basis. If you stop the hammer, you have to recalibrate with about $2,000 worth of Charpy bars. You used to buy them from Watertown Arsenal, which is a mall now out here in Watertown, Massachusetts. Now you buy them from NIST, the National Institute of Standards and Technology — they sell standard Charpy bars, supposed to be calibrated. So the steel could be 264, or 5, or 15, or 20, or 30.

Origin story of Charpy bar calibration — Army arsenal at Watertown (now Watertown Mall) calibrated impact bars from ~1900 because Army was interested in steel impact properties. NIST took over after Mansfield Amendment (~1972).

A Charpy bar is a little notched impact bar — a piece of steel that you hit with a calibrated hammer. When they started doing that around 1900 or so, those were calibrated over at Watertown Arsenal, which is now Watertown Mall. It used to be an Army arsenal, and they did that for years because the Army was interested in steel and the impact properties of steel.