mechanics Mechanics () is the area of physics concerned with the relationships between force, matter, and motion among Physical object, physical objects. Forces applied to objects may result in Displacement (vector), displacements, which are changes of ...

and

physics Physics is the scientific study of matter, its Elementary particle, fundamental constituents, its motion and behavior through space and time, and the related entities of energy and force. "Physical science is that department of knowledge whi ...

, shock is a sudden

acceleration In mechanics, acceleration is the Rate (mathematics), rate of change of the velocity of an object with respect to time. Acceleration is one of several components of kinematics, the study of motion. Accelerations are Euclidean vector, vector ...

caused, for example, by

impact Impact may refer to: * Impact (mechanics), a large force or mechanical shock over a short period of time * Impact, Texas, a town in Taylor County, Texas, US Science and technology * Impact crater, a meteor crater caused by an impact event * Imp ...

, drop, kick,

earthquake An earthquakealso called a quake, tremor, or tembloris the shaking of the Earth's surface resulting from a sudden release of energy in the lithosphere that creates seismic waves. Earthquakes can range in intensity, from those so weak they ...

, or

explosion An explosion is a rapid expansion in volume of a given amount of matter associated with an extreme outward release of energy, usually with the generation of high temperatures and release of high-pressure gases. Explosions may also be generated ...

. Shock is a transient physical excitation. Shock describes matter subject to extreme rates of force with respect to time. Shock is a vector that has units of an acceleration (rate of change of velocity). The unit ''g'' (or ''g'') represents multiples of the

standard acceleration of gravity The standard acceleration of gravity or standard acceleration of free fall, often called simply standard gravity and denoted by or , is the nominal gravitational acceleration of an object in a vacuum near the surface of the Earth. It is a constant ...

and is conventionally used. A shock pulse can be characterised by its peak acceleration, the duration, and the shape of the shock pulse (half sine, triangular, trapezoidal, etc.). The

shock response spectrum A Shock Response Spectrum (SRS)Acronym
Acronym is a graphical representation of a

shock absorber A shock absorber or damper is a mechanical or hydraulics, hydraulic device designed to absorb and Damping ratio, damp shock (mechanics), shock impulses. It does this by converting the kinetic energy of the shock into another form of energy (typic ...

*Measuring the shock absorbing ability of package

cushioning Package cushioning is used to protect items during shipment. Vibration and impact shock during shipment and loading/unloading are controlled by cushioning to reduce the chance of product damage. Cushioning is usually inside a shipping container ...

*Measure the ability of an athletic helmet to protect people *Measure the effectiveness of

shock mount A shock mount or isolation mount is a mechanical fastener that connects two parts elastically to provide shock (mechanics), shock and vibration isolation. Isolation mounts allow equipment to be securely mounted to a foundation and/or frame and, ...

s *Determining the ability of structures to resist seismic shock: earthquakes, etc. *Determining whether personal protective fabric attenuates or amplifies shocks *Verifying that a Naval ship and its equipment can survive explosive shocks Shocks are usually measured by

accelerometer An accelerometer is a device that measures the proper acceleration of an object. Proper acceleration is the acceleration (the rate of change (mathematics), rate of change of velocity) of the object relative to an observer who is in free fall (tha ...

s but other

transducer A transducer is a device that Energy transformation, converts energy from one form to another. Usually a transducer converts a signal in one form of energy to a signal in another. Transducers are often employed at the boundaries of automation, M ...

s and high speed imaging are also used. A wide variety of laboratory

instrumentation Instrumentation is a collective term for measuring instruments, used for indicating, measuring, and recording physical quantities. It is also a field of study about the art and science about making measurement instruments, involving the related ...

is available; stand-alone

shock data logger A shock data logger or vibration data logger is a measurement instrument that is capable of autonomously recording shocks or vibrations over a defined period of time. Digital data is usually in the form of acceleration and time. The shock and vib ...

s are also used. Field shocks are highly variable and often have very uneven shapes. Even laboratory controlled shocks often have uneven shapes and include short duration spikes; Noise can be reduced by appropriate digital or analog filtering. Governing

test method A test method is a method for a test in science or engineering, such as a physical test, chemical test, or statistical test. It is a specified procedure that produces a test result. To ensure accurate and relevant results, a test method should b ...

s and specifications provide detail about the conduct of shock tests. Proper placement of measuring instruments is critical. Fragile items and packaged goods respond with variation to uniform laboratory shocks; Replicate testing is often called for. For example,

MIL-STD-810 MIL-STD-810, U.S. Department of Defense Test Method Standard, Environmental Engineering Considerations and Laboratory Tests, is a United States Military Standard that specifies environmental tests to determine whether equipment is suitably desig ...

G Method 516.6 indicates: ''at least three times in both directions along each of three orthogonal axes".

Shock testing

Shock testing typically falls into two categories, classical shock testing and pyroshock or ballistic shock testing. Classical shock testing consists of the following shock impulses: half

sine In mathematics, sine and cosine are trigonometric functions of an angle. The sine and cosine of an acute angle are defined in the context of a right triangle: for the specified angle, its sine is the ratio of the length of the side opposite th ...

, haversine,

sawtooth wave The sawtooth wave (or saw wave) is a kind of non-sinusoidal waveform. It is so named based on its resemblance to the teeth of a plain-toothed saw with a zero rake angle. A single sawtooth, or an intermittently triggered sawtooth, is called a ...

, and

trapezoid In geometry, a trapezoid () in North American English, or trapezium () in British English, is a quadrilateral that has at least one pair of parallel sides. The parallel sides are called the ''bases'' of the trapezoid. The other two sides are ...

. Pyroshock and ballistic shock tests are specialized and are not considered classical shocks. Classical shocks can be performed on Electro Dynamic (ED) Shakers, Free Fall Drop Tower or Pneumatic Shock Machines. A classical shock impulse is created when the shock machine table changes direction abruptly. This abrupt change in direction causes a rapid velocity change which creates the shock impulse. Testing the effects of shock are sometimes conducted on end-use applications: for example, automobile

crash test A crash test is a form of destructive testing usually performed in order to ensure safe design standards in crashworthiness and crash compatibility for various modes of transportation (see automobile safety) or related systems and compon ...

s. Use of proper

s and

Verification and validation Verification and validation (also abbreviated as V&V) are independent procedures that are used together for checking that a product, service, or system meets requirements and specification (technical standard), specifications and that it fulf ...

protocols are important for all phases of testing and evaluation.

Effects of shock

Mechanical shock has the potential for damaging an item (e.g., an entire

light bulb Electric light is an artificial light source powered by electricity. Electric Light may also refer to: * Light fixture, a decorative enclosure for an electric light source * ''Electric Light'' (album), a 2018 album by James Bay * Electric Light ( ...

) or an element of the item (e.g. a filament in an

Incandescent light bulb An incandescent light bulb, also known as an incandescent lamp or incandescent light globe, is an electric light that produces illumination by Joule heating a #Filament, filament until it incandescence, glows. The filament is enclosed in a ...

): * A

brittle A material is brittle if, when subjected to stress, it fractures with little elastic deformation and without significant plastic deformation. Brittle materials absorb relatively little energy prior to fracture, even those of high strength. ...

or fragile item can fracture. For example, two crystal wine glasses may shatter when impacted against each other. A

shear pin A shear pin is a mechanical detail designed to allow a specific outcome to occur once a predetermined force is applied. It can either function as a safeguard designed to break to protect other parts, or as a conditional operator that will not al ...

in an engine is designed to fracture with a specific magnitude of shock. Note that a soft

ductile Ductility refers to the ability of a material to sustain significant plastic deformation before fracture. Plastic deformation is the permanent distortion of a material under applied stress, as opposed to elastic deformation, which is reversi ...

material may sometimes exhibit brittle failure during shock due to time-temperature superposition. * A

malleable Ductility refers to the ability of a material to sustain significant plastic deformation before fracture. Plastic deformation is the permanent distortion of a material under applied stress, as opposed to elastic deformation, which is reversi ...

item can be bent by a shock. For example, a copper pitcher may bend when dropped on the floor. * Some items may appear to be not damaged by a single shock but will experience

fatigue Fatigue is a state of tiredness (which is not sleepiness), exhaustion or loss of energy. It is a signs and symptoms, symptom of any of various diseases; it is not a disease in itself. Fatigue (in the medical sense) is sometimes associated wit ...

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 Reliability, reliable, or unreliable may refer to: Science, technology, and mathematics Computing * Data reliability (disambiguation), a property of some disk arrays in computer storage * Reliability (computer networking), a category used to des ...

is reduced. * A shock may cause an item to become out of adjustment. For example, when a precision scientific instrument is subjected to a moderate shock, good

metrology Metrology is the scientific study of measurement. It establishes a common understanding of Unit of measurement, units, crucial in linking human activities. Modern metrology has its roots in the French Revolution's political motivation to stan ...

practice may be to have it re

calibrate In measurement technology and metrology, calibration is the comparison of measurement values delivered by a device under test with those of a calibration standard of known accuracy. Such a standard could be another measurement device of known ...

d before further use. * Some materials such as primary high

explosive An explosive (or explosive material) is a reactive substance that contains a great amount of potential energy that can produce an explosion if released suddenly, usually accompanied by the production of light, heat, sound, and pressure. An ex ...

s may

detonate Detonation () is a type of combustion involving a supersonic exothermic front accelerating through a medium that eventually drives a shock front propagating directly in front of it. Detonations propagate supersonically through shock waves wit ...

with mechanical shock or impact. * When

glass bottles Common uses for bottles made from glass include food condiments, soda, liquor, cosmetics, pickling and preservatives; they are occasionally also notably used for Message in a bottle, the informal distribution of notes. A glass bottle can vary in ...

of liquid are dropped or subjected to shock, the

water hammer Hydraulic shock ( colloquial: water hammer; fluid hammer) is a pressure surge or wave caused when a fluid in motion is forced to stop or change direction suddenly: a momentum change. It is usually observed in a liquid but gases can also be aff ...

effect may cause

hydrodynamic In physics, physical chemistry and engineering, fluid dynamics is a subdiscipline of fluid mechanics that describes the flow of fluids – liquids and gases. It has several subdisciplines, including (the study of air and other gases in moti ...

glass breakage.

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 In materials science and metallurgy, toughness is the ability of a material to absorb energy and plastically deform without fracturing.shock absorber A shock absorber or damper is a mechanical or hydraulics, hydraulic device designed to absorb and Damping ratio, damp shock (mechanics), shock impulses. It does this by converting the kinetic energy of the shock into another form of energy (typic ...

s, or cushions to control the shock transmitted to the item.

Cushioning Package cushioning is used to protect items during shipment. Vibration and impact shock during shipment and loading/unloading are controlled by cushioning to reduce the chance of product damage. Cushioning is usually inside a shipping container ...

reduces the peak acceleration by extending the duration of the shock. * Plan for failures: accept certain losses. Have redundant systems available, etc.

Notes

External links

*Response to mechanical shock, Department of Energy

* Shock Response Spectrum, a primer

* A Study in the Application of SRS

Mechanics Packaging Fracture mechanics Acceleration

Shock testing

Effects of shock

Considerations

See also

Notes

Further reading

External links