31. 如右圖所示之立方體,E = 3.6 MPa,ν = 0.4,各面承受均勻拉力0.09 MPa,試求此立方體體積應變(volumetric strain)為何?
(A) 0.005 m3 / m3 (B) 0.01 m3 / m3 (C) 0.015 m3 / m3 (D) 0.02 m3 / m3