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Microscopic close-up of mild steel sheet metal. Sheet metal is metal formed into thin, flat pieces, usually by an industrial process. Thicknesses can vary significantly; extremely thin sheets are considered foil or leaf, and pieces thicker than 6 mm (0.25 in) are considered plate, such as plate steel, a class of structural steel.
The typical test uses a 10 mm (0.39 in) diameter steel ball as an indenter with a 3,000 kgf (29.42 kN; 6,614 lbf) force. For softer materials, a smaller force is used; for harder materials, a tungsten carbide ball is substituted for the steel ball. The indentation is measured and hardness calculated as:
Regular ferrous alloys are the most common due to price and availability. Common sizes of corrugated material can range from a very thin 30 gauge (0.012 inches, 0.3 mm) to a relatively thick 6 gauge (0.1943 inches, 5 mm). Thicker or thinner gauges may also be produced.
MIL-DTL-46100E specifies a steel of identical hardness. [3] MIL-DTL-32332 specifies ultra-hard steel, with Brinell hardness in excess of 570. [3] A Chinese publication lists 30MnCrNiMo "685" steel as the material used in Chinese rolled armor plates, with a Brinell Hardness of HBW 444-514 (thin) / 429-495 (thick).
In addition to the descriptive steel grade naming system indicated above, within EN 10027-2 is defined a system for creating unique steel grade numbers. While less descriptive and intuitive than the grand names they are easier to tabulate and use in data processing applications.
The material thicknesses for such thin-walled steel members usually range from 0.0147 in. (0.373 mm) to about ¼ in. (6.35 mm). Steel plates and bars as thick as 1 in. (25.4 mm) can also be cold-formed successfully into structural shapes (AISI, 2007b). [3]
Gusset plates are used to connect beams and columns together or to connect truss members. They can be either the only way of connecting the beam and columns or they can be used with bolts and welds. Gusset plates are therefore used in most metal weight-bearing structures, but the material and size of the gusset plate varies based on the structure.
The backing plate was vital; it would usually be 0.25-inch (6.4 mm) thick mild steel. Since this was from what vital parts of a ship's superstructure were made, it was possible to cast plastic armour in situ between existing plates and temporary wooden shuttering, usually to a thickness of 4 inches (100 mm). Where this was not possible ...