ENERGYMETHOD 8 11-1 GENERAL EXPRESSIONS OF THE STRAIN ENERGY 、 Principle of energy Strain energy stored in the elastic body is equal to the work done by external forces, that is U=wr Method to analyze and calculate displacements deformations and internal forces of deformable bodies by this kind of relation is called energy method 2, Calculation of the strain energy of rods 1). Calculation of the strain energy of rods in tension or compression n(x)dx or U N2( Ni Li Density of the u 丿2EA 2E:A Strain energy: 2§11–1 GENERAL EXPRESSIONS OF THE STRAIN ENERGY 1、Principle of energy： 2、Calculation of the strain energy of rods： 1). Calculation of the strain energy of rods in tension or compression：  = L x EA N x U d 2 ( ) 2 = = n i i i i i E A N L U 1 2 2  2 1 u = Strain energy stored in the elastic body is equal to the work done by external forces，that is: U=W Method to analyze and calculate displacements 、deformations and internal forces of deformable bodies by this kind of relation is called energy method. or Density of the strain energy: