The objective of the NIST Charpy Machine Verification Program is to evaluate the performance of impact test machines used worldwide to qualify structural steels. We offer our customers standard reference materials (SRMs) that enable certification of their impact machines to a traceable measurement system. The indirect verification of machine performance increases the accuracy of impact data, which improves predictions of the reliability of bridges, buildings, railroads and other infrastructure, as well as the safety of products manufactured from structural steels such as oil and gas pipelines, heavy trucks, mining equipment, power plants and wind turbines. If you have comments or questions, please email Enrico Lucon at enrico.lucon [at] nist.gov
The videos presented here reflect the way Charpy impact tests are performed in the Charpy Laboratory at NIST in Boulder, Colorado.
The ASTM E23 standard (Section 5) states that “Safety precautions should be taken to protect personnel from the swinging pendulum, flying broken specimens, and hazards associated with specimen warming and cooling media.”
Safety precautions that address these hazards are implemented in the NIST Charpy Laboratory and include the following:
The safety precautions employed in the NIST Charpy Laboratory are briefly described here to foster understanding. It is understood that Charpy machine facilities at other institutions may implement different or additional safety precautions.
This video describes different ways to assess and measure possible damage and wear in the Charpy machine (anvils, striker, supports, etc.), through casting parts by means of a molding compound, impacting a special aluminum block or directly measuring parts that are off the machine.
This video describes the NIST process for qualifying lots of reference Charpy specimens, later to be sold to customers for the indirect verification of their impact machines in accordance with the ASTM E23 and/or the ISO 148-2 standards.
This video illustrates how NIST evaluates the test results returned by a customer, providing advice and recommendations based on the examination of the tested specimens. Successful verification of the Charpy machine is provided by an official NIST letter, certifying compliance with ASTM E23 and/or ISO 148-2. NIST also offers customers the possibility of comparing their results with other labs through our Proficiency Test website (https://charpy.nist.gov/PT/).
This video describes the operations that need to be carried out on a Charpy machine before indirect verification testing is conducted. These include checking the machine bolts, examining anvils and striker for wear and damage, verifying clearances for shrouds if applicable, checking the analog scale of the machine if applicable, and determining the friction losses for the machine.
This video explains how to purchase NIST reference specimens for the indirect verification of Charpy machines though the website https://www.nist.gov/srm. The distinction between NIST-Verification and Self-Verification specimens is explained. Additional Charpy reference specimens that can be purchased include dynamic force verification specimens, miniaturized verification specimens, and Charpy specimens for the self-verification of machines equipped with 2mm-strikers.
This video illustrates how NIST examines indirect verification Charpy specimens tested by customers, in order to determine whether their machine might exhibit damage or excessive wear. Typical circumstances that can be detected by examining broken specimens include: worn anvils, subsize wear, damaged anvils, chipped anvils, sharp anvils, off-center specimen, off-center striker, bent pendulum. All these situations can affect Charpy energy measurements, and cause a machine to fail verification.
This video indicates best practices for testing Charpy specimens at temperatures different than ambient temperature (specifically, testing NIST verification specimens at -40 °C). ASTM E23 prescribes that transfer time of the specimen from the cooling medium to the impact position be limited to 5 seconds or less.
For more than 100 years, scientists have tested the impact resistance of metals used in construction by employing an apparatus called a Charpy machine. This device has a long, weighted arm that swings like a pendulum. When the arm is released, it strikes a metal sample. Researchers measure the energy it took to break the sample in two.
A Charpy test determines the impact toughness of metal samples by striking them with a swinging mass. The traditional test method requires measuring the difference between the height of the striker before and after impact. An instrumented striker, on the other hand, has force sensors on the striker's edge, allowing scientists to record the force on the sample through impact. This helps researchers to more precisely determine the impact toughness and ductility of various metals.