The behavior of certain metals and alloys, most notably those with body-centered cubic structures, in which they exhibit a pronounced decrease in ability to absorb energy without fracturing below a certain temperature (ie., the ductile-to-brittle transition temperature) or above a certain strain rate. The ductile-to-brittle transition temperature is especially important in considering the material’s ability to absorb impact, as measured by the Charpy (or related) tests.