Monday, June 2, 2014

DID YOU KNOW:

Thermal Expansion Coefficient

Some products are assembled using a process known as shrink-fitting. Shrink fits use thermal expansion and contraction. One component is heated so that it expands. It is then assembled onto another component that is at room temperature. Once cooled, the first component contracts, or shrinks, and fits onto the second component. Most bearings are assembled onto their shafts using this method. For such applications, thermal expansion of the metal is an important property.

The thermal expansion coefficient, a, is expressed in per °C or per °F. We can obtain the amount of expansion undergone by a material by multiplying the original length by the expansion coefficient and temperature rise. That is,

                                                                                                               

where, DL is the amount of expansion, L is the original length and DT is  temperature rise.

In components that are constrained to move, thermal expansion can lead to thermal stresses. These stresses will add to the existing stresses caused by the external load and if the combined stresses increase beyond the yield strength of the material, failure will occur.

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