Charpy Impact Testing (CVN)
Impact testing shall be carried out as defined by the latest revision of ASTM E23. CVN is short for Charpy V-notch. The V-notch is the most common, and most accepted type of notch and should be used unless otherwise noted or instructed by client. CMS uses a Satec model impact tester, which is a free swing pendulum which strikes the specimens. This model has a 300 Ft/lbs of force maximum. This machine is calibrated year, and indirectly verified by NIST. The NIST indirect verification is in accordance with ASTM E 23, and requires two set of CVN’s which are supplied by NIST to be test for High and Low range verification. Copies of certifications are available upon request.
Charpy specimens are tested in conditions (i.e., room temperature, low or high temperature) dictated by customer or specification requirements. If cooling or heating of specimen is required, fill a suitable container which has a grid to raise specimen at least 1 inch off the bottom. When specimens are immersed fluid is 1 inch over specimen. The fluid must be agitated during heating or cooling. Bring liquid to desired temperature ±2 F using any means possible. Temperature should be measured by device in middle of group of specimens. Temperature of liquid and specimens should be held for at least 5 minutes minimum. Tongs used for removing specimens from medium should be left in except when handling specimen.
After specimen reaches temperature, if heating or cooling is required, place specimen in designated groove of anvil on base of machine. The notch of specimen shall be opposite from striking face of anvil, within 5 seconds of removing from medium. The pendulum should be in the “up” position for striking and the energy indicator placed at maximum scale reading. Release the pendulum and record reading. If the specimen jams in machine, disregard results and check machine for damage.
Measuring lateral expansion, the amount of expansion, must be measured relative to the plane defined by the un-deformed portion of the side of the specimen.
Determine the shear percentage by comparing the broken surfaces to the chart provided by ASTM E23 listed as “Fracture Appearance”.
Did you know that there are several specification which calls out charpy impact testing on base materials? Learn more about specific specification and what is needed to test them.