Thermal Expansion Coefficient of a Material

Thermal expansion coefficient of a material, a dimensionless number, is a physical property that quantifies how much the material changes in size when its temperature changes.  Most materials expand when heated and contract when cooled because the atoms or molecules within the material vibrate more vigorously at higher temperatures, increasing their average spacing.  The thermal expansion coefficient expresses the amount of dimensional change per unit length, area, or volume for each degree of temperature change. In engineering and science, the most commonly used value is the linear thermal expansion coefficient, which describes the change in length of a material per unit original length per degree of temperature change.  

Mathematically, the linear thermal expansion coefficient relates the change in length of a material to its original length and the temperature change.  A material with a high thermal expansion coefficient experiences a larger dimensional change for a given temperature variation, while a material with a low coefficient experiences a smaller change.  The coefficient is typically expressed in units of reciprocal temperature, such as per degree Celsius (°C⁻¹) or per kelvin (K⁻¹).

The thermal expansion coefficient is an important parameter in the design of structures, machines, pipelines, bridges, buildings, electronic devices, and other engineered systems.  Differences in thermal expansion between connected materials can generate stresses, deformation, or failure if not properly accommodated.  For this reason, engineers use thermal expansion coefficients to predict dimensional changes caused by temperature variations and to ensure that components remain functional and safe throughout their operating temperature range.