Charpy Impact Testing: Minimizing Hammer Changes

A common misconception within metals Charpy testing is that the specimen being tested must have an impact energy between 10% and 80% of the hammer capacity to be a standard compliant test. This is not true for metals tested to current common international standards such as ISO 148 and ASTM E23. This misconception sometimes comes from confusion with plastics standards (see ISO 179-1), other older metals standards (see GOST 9454-78), and historical use of a low resolution dial indicator on metals pendulum systems. Due to these misunderstandings, labs often have multiple systems or hammers for testing a range of specimen energies.

With the release of Instron’s latest MPX Motorized Pendulum Impact Testing System, we wanted to remove the need to swap hammers or have multiple systems in one lab. In order to achieve this, we had to address two areas: the resolution of the device and the method for changing hammer energies (weight).

The resolution of the latest encoder has been improved fourfold compared to the previous model. This enables the MPX to achieve far better resolution than had previously been possible with dial indicators or their digital predecessors. The MPX encoder delivers a resolution of 0.023J on a 450J system, this is compared to about 1-0.5J resolution on a dial indicator. This improved resolution translates to a usable limit down to 0.6 J to ASTM E23, the dial on the other hand has between 12.5J and 25J.

Posted On March 06, 2012, 10:00

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