Shock (mechanics)


Shock (mechanics)

A mechanical or physical shock is a sudden acceleration or deceleration caused, for example, by impact, drop, kick, earthquake, or explosion. Shock is a transient physical excitation.

Shock is usually measured by an accelerometer. This describes a shock pulse as a plot of acceleration versus time. Acceleration can be reported in units of metre per second squared. Often, for convenience, the magnitude of a shock is stated as a multiple of the standard acceleration due to free fall in the Earth's gravity, a quantity with the symbol "g" having the value 9.80665 m·s-2. Thus a shock of "20"g" is equivalent to about 196 m/s2. A shock can be characterized by the peak acceleration, the duration, and the shape of the shock pulse (half sine, triangular, trapezoidal, etc). The Shock response spectrum is a method for further evaluating a mechanical shock. It is sometimes used as a defense standard for military equipment.

Effects of Shock

Mechanical shock has the potential for damaging an item (e.g., an entire light bulb) or an element of the item (e.g. a filament in an Incandescent light bulb):
* A brittle or fragile item can fracture. For example, two crystal wine glasses may shatter when impacted against each other. A shear pin in an engine is designed to fracture with a specific magnitude of shock.
* A ductile item can be bent by a shock. For example, a copper pitcher may bend when dropped on the floor.
* Some items may not be damaged by a single shock but will experience fatigue failure with numerous repeated low-level shocks.
* A shock may result in only minor damage which may not be critical for use. However, cumulative minor damage from several shocks will eventually result in the item being unusable.
* A shock may not produce immediate apparent damage but might cause the service life of the product to be shortened: the reliability is reduced.
* A shock may cause in item to become out of adjustment. For example, when a precision scientific instrument is subjected to a moderate shock, good metrology practice may be to have it recalibrated before further use.
* Some materials such as primary high explosives may detonate with mechanical shock or impact.

Considerations

When laboratory testing, field experience, or engineering judgement indicates that an item could be damaged by mechanical shock, several courses of action might be considered:
* Reduce and control the input shock at the source.
* Modify the item to improve its toughness or support it to better handle shocks.
* Use shock absorbers or cushions to control the shock transmitted to the item. Cushioning reduces the peak acceleration by extending the duration of the shock.
* Plan for failures: accept certain losses. Have redundant systems available, employ insurance, etc.

See also

* Cushioning
* Fracture mechanics
* g-force
* Impact force
* Response spectrum
* Thermal shock
* Vibration

Further reading

* DeSilva, C. W., "Vibration and Shock Handbook", CRC, 2005, ISBN 0849315808
* Harris, C. M., and Peirsol, A. G. "Shock and Vibration Handbook", 2001, McGraw Hill, ISBN 0071370811
* ASTM D6537, Standard Practice for Instrumented Package Shock Testing for Determination of Package Performance.
* MIL-STD-810F, Environmental Test Methods and Engineering Guidelines, 2000


Wikimedia Foundation. 2010.

Look at other dictionaries:

  • Shock — may refer to:Medical conditions*Shock (circulatory), a circulatory medical emergency *Acute stress reaction, often termed shock by laypersons, a psychological condition in response to terrifying events *Post traumatic stress disorder, a long term …   Wikipedia

  • Shock wave — Bombshock redirects here. For the Transformers character, see Micromasters#Bombshock. For other uses, see shockwave. Schlieren photograph of an attached shock on a sharp nosed supersonic body. A shock wave (also called shock front or simply shock …   Wikipedia

  • mechanics — /meuh kan iks/, n. 1. (used with a sing. v.) the branch of physics that deals with the action of forces on bodies and with motion, comprised of kinetics, statics, and kinematics. 2. (used with a sing. v.) the theoretical and practical application …   Universalium

  • Shock absorber — Gas damper A shock absorber is a mechanical device designed to smooth out or damp shock impulse, and dissipate kinetic energy. It is a type of dashpot. Contents …   Wikipedia

  • Fracture mechanics — Continuum mechanics …   Wikipedia

  • Contact mechanics — Continuum mechanics …   Wikipedia

  • fluid mechanics — an applied science dealing with the basic principles of gaseous and liquid matter. Cf. fluid dynamics. [1940 45] * * * Study of the effects of forces and energy on liquids and gases. One branch of the field, hydrostatics, deals with fluids at… …   Universalium

  • solids, mechanics of — ▪ physics Introduction       science concerned with the stressing (stress), deformation (deformation and flow), and failure of solid materials and structures.       What, then, is a solid? Any material, fluid or solid, can support normal forces.… …   Universalium

  • System Shock 2 — Developer(s) Irrational Games Looking Glass Studios Publisher(s) Electronic Arts …   Wikipedia

  • Aircraft flight mechanics — In aeronautics, aircraft flight mechanics is the study of the forces that act on an aircraft in flight, and the way the aircraft responds to those forces. [Clancy, L.J. Aerodynamics . Section 14.1] Aircraft flight mechanics are relevant to… …   Wikipedia


We are using cookies for the best presentation of our site. Continuing to use this site, you agree with this.