Liquid to liquid thermal shock testing applies thermal shocks to test samples by alternately immersing them in a high- and low-temperature liquid medium. Very high thermal ramp rates can be achieved with this method; much more so than air to air thermal shock methods.
The machine used for this protocol has a high-temperature reservoir and low-temperature reservoir with a mechanical arm and specimen basket. The arm is programmed to move at desired intervals, transferring the basket from hot to cold sections, subjecting the unit(s) under test to thermal shock. The movement of the specimen basket between chambers is usually done within 10 seconds. This time can also be adjusted, as required by the testing protocol. Size of the basket is 6”x6”x6”, and special fixturing is available to accommodate odd-shaped items.
Different liquids can be utilized depending on the application. Anything from water, silicone oil, or inert liquids developed for thermal shock testing, with high electrical resistance and low surface tension may be used. A temperature range in excess of -65 to +150°C is achievable with this system.
Temperature shock testing can help determine physical, chemical and operation problems of a product. In the field, sudden temperature changes can occur, for example, during transport from an air-conditioned room indoors to a high temperature desert outdoors.
The expansion and contraction caused by the temperature variation generate stress from differences in the expansion rates of parts made of different bonded materials. Repeated stress causes accumulated fatigue, leading to cracks and rupturing. Some examples of physical problems are shattering, binding or cracking of either the surface or internal components. This equipment is compliant to widely-used standards such as MIL-STD-810F, MIL-STD-202, MIL-DTL-38999, TIA/EIA-455-71 and others.