Materials Science Glossary - U

ultimate (tensile) strength. See tensile strength.

ultra-high-molecular-weight polyethylene (UHMWPE). A polyethylene polymer that has an extremely high

molecular weight. Distinctive characteristics of this material include high impact and abrasion resistance and a low coefficient of friction.

unit cell. The basic structural unit of a crystal structure. It is generally defined in terms of atom (or ion) volume.

unsaturated. Describes carbon atoms that participate in double or triple covalent bonds and, therefore, do not bond to a maximum of four other atoms.

upper critical temperature. For a steel alloy, the minimum temperature above which, under equilibrium conditions, only austenite is present.