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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streamlined body. A body whose shape is such that fluid moving over it flows in smooth lines with no turbulence. A fish is an excellent example of a streamlined body. The fish can move through the water with a minimum of opposition. Fluid flowing around a flat plate or circular object has a turbulent area behind it. This turbulence causes drag. There is a minimum area of turbulence in the flow of fluid behind a streamlined body. streamline flow. The flow of a fluid in which there is no turbulence. All particles of the fluid move in continuous smooth lines. strength. The ability of a material to resist distortion or deformation caused by an external force acting on it. Strength is the ability of a material to resist stresses that try to break it. stress. A force within an object that tries to prevent any outside force changing its shape. stress corrosion. A form of intergranular corrosion that forms in metals that are subject to a continuous tensile stress. The tensile stress separates the metal along the internal grain boundaries, and the corrosion acts at the apex of the cracks that form. stressed-skin structure. A type of aircraft structure that has a minimum of internal structure and carries all, or most, of the stresses in its outside skin. An egg shell is a perfect example of a natural stressed-skin. All of the stresses acting on an egg are carried in its shell. stress relieve (steel heat treatment). A type of heat treatment of steel. When steel parts are forged, machined, or welded, stresses are often locked in them that cause the parts to warp or break. These stresses can be relieved by heating the part until it is red-hot and then allowing it to cool slowly in still air to room temperature. This type of stress relieving is called normalizing. stress riser. A location on a structure where the cross-sectional area of the part changes drastically. Stresses concentrated at such locations are likely to cause failure. A scratch, gouge, or tool mark in the surface of a highly stressed part can change the area enough to concentrate the stresses, and it becomes a stress riser. stringer (aircraft structure). A part of an aircraft fuselage structure used to give the fuselage its shape and, in some types of structure, to provide a small portion of the fuselage strength. Formers give the fuselage its cross-sectional shape, and stringers, which are channels or angles of sheet metal or metal extrusions, fill in the shape between the formers. Stringers in a semimonocoque fuselage are covered with sheet metal, and in a truss-type fuselage, with fabric. stroboscope. A special light that flashes with a brilliant, short-duration flash. A variable-frequency oscillator controls the stroboscope so it flashes at any required interval. Stroboscopes are used to study the motion of rotating or vibrating bodies. The stroboscope is shone on the object, and the frequency of the flashes is adjusted until the object appears to stand still or move in slow motion. |
