Testing Disciplines
Temperature Shock
| Temperature shock tests are intended to evaluate the effects of sudden temperature changes at the outer surfaces of material or equipment under test. It is applicable when the material or equipment is likely to experience sudden changes of air temperature in normal use or as a screening tool to reveal potential flaws in material or devices. | |
| Causes of Thermal Shock | |
Movement
between heated areas and a low temperature environment.
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Ascent or
descent from a high temperature ground environment to
high altitude cold environment.
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Equipment
operated non-continuously in a low temperature
environment.
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Aircraft
flight exposure
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Air
delivery/airdrop
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Ground
transfer/air delivery - arctic
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Ground
transfer/air delivery - desert or tropical
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Engineering
design or stress screening requirements
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| Effects | |
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Cracking
and delaminating of finishes.
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Cracking
and crazing of embedded and encapsulating compounds.
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Opening of
thermal seals and case seams.
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Leakage of
filling materials.
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Rupturing
or cracking of hermetic seals.
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Rupturing
or cracking of vacuum glass to metal seals.
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Change in
electrical characteristics due to mechanical displacement
or rupture of conductors or insulating materials.
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Shattering
of glass vials and optical material or equipment.
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Binding or
slackening of moving parts.
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Cracking of
solid pellets or grains in explosives.
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Differential
contraction or expansion rates or induced strain rates of
dissimilar materials.
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Deformation
or fracture of components.
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Leaking of
sealed compartments.
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Failure of
chemical agent protection.
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Changes in
electrical and electronic components.
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Electronic
or mechanical failures due to rapid water or frost
formation.
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Excessive
static electricity.
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| Temperature Extremes | |
| Except for stress screening, a range of temperatures that reflects the anticipated service should be used. Stress screening temperature extremes are determined by the design requirements or analysis. | |
| Test Item Configuration | |
| The configuration of the test item will affect the test results. The use of the anticipated configuration of the item during storage, shipment, or use should be considered. For stress screening or engineering evaluation the test unit is typically un-packaged. | |
| Relative Humidity | |
| For most applications, the relative humidity (RH) is not controlled. If relative humidity could have an effect on the test item then it should be considered when developing the test plan. Such a case might be cellulose, which can be porous, absorb moisture and then expand upon freezing. | |
| Rates of Change | |
| The transition time from one temperature extreme to the other is associated with the actual thermal shock in the application. For engineering evaluation or stress screening the thermal transfer should be as rapid as possible, typically one minute or less. | |
| Test Variables | |
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Test item
configuration.
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Test
temperature extremes
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Temperature
rates of change or transition time.
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Duration of
exposure at each temperature.
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Number of
cycles.
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| Apparatus | |
| The required apparatus consists of a single chamber capable of rapid rates of heating and cooling or two chambers, one for each temperature, or a two-celled temperature shock chamber. The chambers should be equipped with instrumentation capable of controlling and monitoring the test conditions. | |
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