An Impact Test for Use with Cermets

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Abstract
Several specimens of a commercially produced nickel‐bonded titanium carbide cermet were tested in eight laboratories at room temperature and at 1800°F. by an increment‐type impact test in which the specimens were held as a cantilever in a vise and were subjected to repeated blows of increasing intensity at their free ends. The inconsistent results obtained were attributed to differences in (1) vise jaw insert material and design, (2) vise gripping pressure, or (3) the stress condition of the specimen at elevated temperatures as contrasted with that at room temperature. A different increment‐type impact test was developed and was used for evaluating the low‐velocity impact behavior of cermets as a function of temperature. In this test the specimens were supported at their ends and were subjected to impact loading at their midpoints by a freely falling hammer. Hot tests were conducted on specimens heated by means of their electrical resistance. The test was modified, by the addition of a miniature muffle furnace, for testing electrical insulators at elevated temperatures. It was established that increment impact tests, when used with metal‐bonded cermets, are subject to a repeated‐blow effect; i.e., low‐energy blows contribute not only to recoverable elastic deformation but also to some permanent damage. In spite of this complication, the new test has been tentatively accepted for use by several cermet research laboratories.
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