270 Mechanics of Materials §11.14 shear,must also be considered.This may be determined using the strain energy formulae derived earlier in this chapter. L M2ds For bending, UB= 2EI L For shear, Us= Q2ds 2 2AG 2G ×volume Consider,therefore,the cantilever,of solid rectangular section,shown in Fig.11.11. y D NA Beam cross-section Fg.11.11. For the element of length dx Us= x Bdy dx But QAy Ib (see $7.1) -G9(（g-ra4 %了-r) -D/2 Q2B 8GI2 dx (270 Mechanics of Materials 411.14 shear, must also be considered. This may be determined using the strain energy formulae derived earlier in this chapter. For bending, For shear, 2EI 0 L Q2ds 7’ 2AG 2G = - x volume 0 Consider, therefore, the cantilever, of solid rectangular section, shown in Fig. 11.1 1. Fig. 11.11 For the element of length dx r “2 But 7=- QAy (see 47.1) Ib 2 =Qx IB - Q (Ey.) 21 4 2 US = & (: -y2)} Bdxdy Dl2 =E {-(--y’)Ydy Q D2 2G 21 4 - D/2