22 Brittle
Generally speaking, metals are not brittle when compared to a rock or other materials (Zinc is an exception). Metals do not break easily because of their metallic bonds. However, if improperly heat treated a steel can become relatively brittle and crack. Pig iron is also more brittle than any other form of iron or steel.
Brittle materials may be cast or thermoformed.
In the photograph above, the specimen failed by brittle failure, as seen from the lack of plastic deformation. Note that nodular graphite cast irons are usually ductile, so this specimen is not representative for this class of alloys.
A material is brittle if, when subjected to stress, it fractures with little elastic deformation and without significant plastic deformation. Brittle materials absorb relatively little energy prior to fracture, even those of high strength. Breaking is often accompanied by a sharp snapping sound.
When used in materials science, the term brittle is generally applied to materials that fail when there is little or no plastic deformation before failure. One proof is to match the broken halves, which should fit exactly since no plastic deformation has occurred.
Some metals show brittle characteristics due to their slip systems. The more slip systems a metal has, the less brittle it is, because plastic deformation can occur along many of these slip systems. Conversely, with fewer slip systems, less plastic deformation can occur, and the metal will be more brittle. For example, HCP (hexagonal close packed) metals have few active slip systems, and are typically brittle.
Videos
Watch this video How and When Metals Fail by Cornell University, June 19, 2013.
Derived from Brittleness – Wikipedia accessed and available 5 March 2024, and The Virtual Machine Shop (2011), (http://www.jjjtrain.com/vms/eng_metallurgy/eng_metallurgy_07.html) retrieved from the Wayback Machine 15 January 2024.