Deflection
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Deflection is a term used in physics, automotive, engineering, and weapon applications to describe four separate phenomena.
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[edit] Structural Engineering
In engineering mechanics, deflection is a term that is used to describe the degree to which a structural element is displaced under a load. The deflection of a member under a load is directly related to the slope of the deflected shape of the member under that load and can calculated by integrating the function that mathmatically describes the slope of the member under that load. Deflection can be calculated by standard formulae (will only give the deflection of common beam configurations and load cases at discrete locations), or by methods such as "Virtual Work", "Direct Integration", "Castigliano's Method", "Macaulay's Method" or the "Matrix Stiffness Method" amongst others (See Structural Analysis textbooks for procedure).
An example of the use of deflection in this context is in building construction. Architects and builders select materials for various applications. The beams used for frame work are selected on the basis of deflection, amongst other factors.
The elastic deflection f and angle of deflection φ (in radians) in the example image, a (weightless) cantilever beam, can be calculated (at the free end) using :
- fB = F·L3 / (3·E·I)
- φB = F·L2 / (2·E·I)
where
- F = force acting on the tip of the beam
- L = length of the beam (span)
- E = modulus of elasticity
- I = area moment of inertia
The deflection @ any point along the span can be calculated using the above-mentioned methods.
From this formula it follows that the span L is the most determinating factor; if the span doubles, the deflection increases 23 = 8 fold.
Building codes determine the maximum deflection, usually as a fraction of the span e.g. 1/400 or 1/600. Either the strength limit state (allowable stress) or the serviceability limit state (deflection considerations amongst others) may govern the minimum dimensions of the member required.
In electronic engineering, and more specifically cathode ray tube (CRT) technology, deflection refers to the use of electromagnetic or electrostatic fields to deflect an electron beam to provide a two-dimensional display on a screen formed by the flat face of the CRT.
The deflection must be considered for the purpose of the structure. If you are designing a steel frame to hold a glazed panel, there must be minimum deflection, as this could fracture the glass.
The deflective shape of a beam can be represented by the moment diagram, intergrated.
[edit] Automotive
Deflection as an automotive term is used as a measure of the tightness of car engine belts, which is measured using a belt gauge.
[edit] Physics
In physics deflection is the event where an object collides and bounces against a plane surface.
In such collisions involving a sphere and a plane, the collision angle formed with the surface normal (the incidental angle α) must equal the bounce angle (the accidental angle β), α = β
[edit] Weapons
Deflection is a tactic used in battle that describes "leading the target"; that is, shooting ahead of a moving target so that the target and projectile will collide. This tactic is only necessary when using slow projectiles, such as a crossbow bolt, or over long distances, such as in an aerial dogfight. During World War II, U.S. Navy pilots were taught explicitly on the concept in order to capitalize on the advantages of the Wildcat.
