Thermal strain

     If a bar of length L and coefficient of linear expansion α were subjected to a temperature rise of T , its length will increase by a distance αLT, as described in Chapter 20. Thus the new length of the bar will be:
                                                 
                                                            L + αLT = L(1 + αT )
     Now, as the original length of the bar was L, then the thermal strain due to a temperature rise will be:

     However, if the bar were not constrained, so that it can expand freely, there will be no thermal stress. If, however, the bar were prevented from expanding then there would be a compressive stress in the bar.