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.
Ascent or descent from a high temperature ground environment to high altitude cold environment.
Equipment operated non-continuously in a low temperature environment.
Aircraft flight exposure
Air delivery/airdrop
Ground transfer/air delivery - arctic
Ground transfer/air delivery - desert or tropical
Engineering design or stress screening requirements
Cracking and delaminating of finishes.
Cracking and crazing of embedded and encapsulating compounds.
Opening of thermal seals and case seams.
Leakage of filling materials.
Rupturing or cracking of hermetic seals.
Rupturing or cracking of vacuum glass to metal seals.
Change in electrical characteristics due to mechanical displacement or rupture of conductors or insulating materials.
Shattering of glass vials and optical material or equipment.
Binding or slackening of moving parts.
Cracking of solid pellets or grains in explosives.
Differential contraction or expansion rates or induced strain rates of dissimilar materials.
Deformation or fracture of components.
Leaking of sealed compartments.
Failure of chemical agent protection.
Changes in electrical and electronic components.
Electronic or mechanical failures due to rapid water or frost formation.
Excessive static electricity.
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
Test item configuration.
Test temperature extremes
Temperature rates of change or transition time.
Duration of exposure at each temperature.
Number of cycles.
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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