BEAMS
Consider a beam in pure bending. The flexure formula gives the normal stress σ_x=My/I
. Using Eq.( 5.1. ), The strain energy density is U_0= M^2 y^2/〖2EI〗^2 . After carrying this into Eq. ( 5.7 ) and noting that M^2/〖2EI〗^2 is a function of x alone, We obtain