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In order to investigate the stability of an impact testing machine between ordinary calibrations, impact tests have been performed on a regular basis using specimens from an isolated batch of material. A nickel based alloy, W-Nr. 1.4563, was chosen due to its ageing stability. The material was heat treated and a microstructure analysis was carried out ensuring a homogenous structure in all specimens. The specimens were then cut out in the longitudinal direction.
The machine is a 300 J C-type pendulum and usually approximately 30 specimens are tested every day. Commonly the materials are very tough, generating energy values above 80% of the machine capacity.
For the stability analysis, a set of control specimens was tested on the first day of every week and the results were recorded. Notched type A specimens (Charpy V) were used and tests were performed with an ISO striker. On the other days ordinary specimens were tested. The total number of tested specimens and especially the number of specimens generating energy values above 240 J were documented.
The deviation of energy values obtained by the control specimens between the calibrations was evaluated. By using a stability diagram the correlation between energy divergence, time and number of daily tested specimens was studied.
The results could be used as complementary guidelines, apart from the regular radius measurement of the anvils, for determining optimal intervals between calibrations for similar machines used in the high energy area.
impact testing, calibration, stability
Manager, Mechanical Metallurgy, AB Sandvik Steel, Sandviken,
Research scientist, Mechanical Metallurgy, AB Sandvik Steel, Sandviken,