What is Charpy Testing and what ASTM standards require it?
Charpy testing, or impact testing was developed in 1905 by Georges Charpy in order to determine the amount of energy absorbed by a material during fracture. It was noticed that as the temperature drops, the tensile and yield of steel increases, but the ductility drops, leading to brittle and sometimes catastrophic failures.
A standard Charpy test is performed by machining a 10mm x 10mm x 55mm test piece with a notch cut at the intended fracture point. The test sample is then brought down to the specified temperature, typically in a liquid medium. The sample is placed into the fixture, and a pendulum is set to swing and break the sample at the grooved notch. The testing machine calculates the amount of energy absorbed by the sample by measuring how high the pendulum swings after fracture. The lower the swing, the more energy was absorbed. One charpy test is actually three separate tests, with the reported result being the average of the three.
Below are some commonly tested fastener grades, and their respective charpy requirements.
|F1554 grade 55
|F1554 grade 105
|-20F or +40F
|A320 grade L7
ASTM F1554 supplemental requirement S4 is tested at +40F for use with either Grade 55 or Grade 105 and -20F for use with Grade 105 only.
Portland Bolt inventories charpy tested steel round bar in F1554 grades 55 and 105 and A320 grade L7. Special charpy testing can be performed on request.