And the partial differentiation of specific energy by components of strain OU L=Ox 08y OU -=O aa aa 二 OUAOUa0 ar II. Strain energy Since the components of stress and components of strain and then the specific energy U are all the function of coordinates, the strain energy U. of the whole elastic body is Substituting the three kinds of expressing forms of specific energy yields three kinds of integrating forms of strain energy 1111 xy xy z x z x yz yz U U U       =   =   =   1 1 1 , , z z y y x x U U U       =   =   =   1 1 1 , , And the partial differentiation of specific energy by components of strain II. Strain energy Since the components of stress and components of strain and then the specific energy are all the function of coordinates, the strain energy . of the whole elastic body is: U1 U  U = U dxdydz 1 2 1 Substituting the three kinds of expressing forms of specific energy yields three kinds of integrating forms ofstrain energy