时间：2011-03-11 23:18来源：蓝天飞行翻译 作者：航空 点击：次
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shear section. A necked-down section of an engine-driven pump shaft designed to shear if the pump should seize. When the shear section breaks, the drive can continue to turn without causing further damage to the pump or the engine. shear strength (sheet metal construction). The strength of a riveted joint in a sheet metal structure in which the rivets shear before the metal tears at the rivet holes. A properly designed riveted joint will fail in shear. The rivets will shear before the metal tears at the rivet holes. shear stress. A type of stress that tries to slide an object apart. sheave. A grooved wheel used as a pulley. A sheave can be used to change the direction a cable must be pulled to move a weight and it can also be used to increase the force applied to a weight. If a sheave is attached to a weight, the amount of force needed to lift the weight is only one half the weight. But the cable will have to be pulled twice the distance the weight is lifted. sheet metal. Metal that has been rolled into sheets whose thickness is less than 0.25 inch. Metal whose thickness is greater than 0.25 inch is called metal plate. sheet metal layout. The drawing or pattern used to cut a piece of sheet metal. The layout includes marks to locate all of the bend tangent lines and the center marks for all of the holes to be drilled. shelf life. The normal length of time an object or material can be expected to keep its usable characteristics if it is stored and not used. Many products, such as batteries, rubber seals, shock cord, and certain types of finishing materials, have a date stamped on them. This date relates to the shelf life. If these products are not used by the date stamped on them, there is a possibility that they will not function as they should. shell (atomic structure). The outer structure of an atom formed by electrons having the same energy level as they spin around the nucleus. The K shell is nearest the nucleus. The L shell is next and, depending on the number of electrons, an atom can also have M, N, O, P, and Q shells. shell-type transformer. A type of electrical transformer encased in a steel shell. The shell completely surrounds the winding and keeps magnetic lines of flux from radiating out from the transformer. SHF (Superhigh Frequency). Electromagnetic energy with a frequency between 3 and 30 gigahertz (3 · 109 and 30 · 109 hertz). The SHF band is used for weather and doppler radar. shielded-arc welding. A form of arc welding in which the arc and the metal being welded are shielded, or covered, with an inert gas or with melted flux that keeps air away from the molten metal in the weld. shielded conductor (electrical conductor). Insulated electrical wire enclosed in a conducting braid, usually made of tinned copper. The braid is grounded so any electromagnetic radiation picked up by the braid is carried to ground. This prevents interference with the signal being carried in the conductor. |
