Develop paragraphs by definition when you want to set working generalizations that will help control the meaning and scope of important terms. Defining is an effective way of controlling the scope of terms. In the following paragraph, an extended definition is used as part of the introduction to a research article. The intention here is both to establish the terms of the discourse and to establish the importance of the subject. By exploring the meaning of the term bimetals, the writer creates a shared concept that focuses the discussion that follows. Note the use of other devices, such as functional description and enumeration.
Bimetallic ComponentsBimetals are components made up of two separate metallic units, each occupying a distinct position in the component. Bimetal rods or wires (also called clad metal, duo- or dual-metal) are made of dissimilar metals. The rod core, a cylindrical body made of one metal, is surrounded by a concentric, cylindrical sleeve of another metal. Some fibrous metals may also be regarded as bimetallic; for example, rods made by unidirectional solidification of some eutectic compositions contain a metallic (or nonmetallic) compound of fibrous filaments embedded in an almost pure metallic matrix. The structure of a present-day Nb-Sn superconducting core can be even more complex. It is multimetallic--containing more than two dissimilar metals. The two elements of a bimetallic product are usually intimately interlocked, so that they function in unison.
Bimetal rods or wire stems make it possible to combine properties of dissimilar metals. For example:
- Aluminum-clad steel wire combines the strength of steel with the electrical conductivity and corrosion resistivity of aluminum.
- Superconductor core clad with copper sleeve combines superconductivity at cryogenic temperatures with assurance against failure when a local temporary rise in resistance or temperature occurs.
Although the number of desired bimetallic combinations for practical use is virtually unlimited, manufacturing difficulties restrict the number of bimetallic combinations actually in use.
--Based on B. Avitzur et al., "Criterion for the Prevention of Core Fracture during Extrusion of Bimetal Rods," Journal of Engineering for Industry