Poplar - Straw Composite Structural Materials Mechanical Properties And Design

The poplar-straw laminated plank is a kind of new structural plank, The surface of laminated plank is made of poplar veneer and the center is made of straw plank.Concentrating on its bending deflection and strength problems,the thesis presents thorough and deep investigation and analysis. First,by adopting several testing methods ,the mechanic characteristics of poplar veneer and straw plank are acquired. Second,by adopting the "principle of minimal potential energy",definite formulas are deduced respectively based on the classical plate theory CPT),First-order shear deformation theory (FSDT) and high-order shear deformation theory(HSDT).At the same time ,definite formula is deduced based on delamination shear deformation theory(DSDT). By employing these formulas ,detailed analysis of transverse shear effect on bending deflection and strength could be carried out. The analysis demonstrates:when ratio of span-height is low, transverse shear affects greatly on the bending deflection。However ,with the increasing of the ratio of span-height, the difference among those results declines.But as far as bending strength is concerned, not only the results of these theories,but also the normal stress distribution along the height have striking difference while ratio of span-height is low.Alongside the increasing of the ratio,the difference goes down correspondendtly. Based on the theoretical analysis,the finite element method(FEM) is employed to analysis the bending problems of the poplar-straw laminated beam. In order to test the correctness of theoretical analysis and results of FEM,the stress and deflection of a real structure under transverse force are tested.Besides,using correlative theory ,effectual Modulus of Elasticity is acquired. At last,the method of optimal design is employed to design the shape of cross section of poplar-straw laminated beam.