The Research On Mechanical Properties Of Sandwich Composite With Wooden Skin And Honey-comb Core Subjected To Transverse Loading

Sandwich composite with wooden skin and paper honey-comb core can be used in furniture product,interior decoration,package tranportation and other civil industry etc.because of low density,convinence with product available,advantage of mechanical property,design flexible and evenness of large surface.However,it should be noted that mechanical property research of sandwich construction subjected to transverse loading has significant effect to design and application of those materials.Therefore,sandwich composite with honey-comb core was regarded as project of the thesis,and the flexural and transverse compression property was analysed systematically.The results have been listed as below.(1)The equation to calculate maximum flexural normal stress of sandwihch beam with soft core was derived based on Equivalent single beam theory.After that,three-point flexural experiment using orthogonal test method was carried out;and the results show that the effect of cell size to bending strength has very significant while other factors such as panel type and applied glue amount have little influence on it.The effect of core thickness to bending strength with "?" direction specimens has more significant than to "//" direction specimens.Furthermore,the bending strength with"?" direction specimens are higher totally than "//" ones with the same construction.On the basis of Winkler ideal elastic foundation theory,the indentation failure load for three-point quasi-static flexural test was derived by considering top skin axial stress.Then two failure modes of core shear and skin indentation were analysed systematicly by comparing theoretical model and test results and the relative error is approximate no more than ±20%.(2)Layer-wise first-order theory(LFOT)with two variables for sandwich beam was derived by virtual work principle.After comparison with Classical first-order theory(CFOT)and three-point flexural test results,it is shown that transverse displacement calculated by LFOT is more conservative than CFOT within elastic stage,and LFOT has higher accuracy than CFOT to calculate the deformation of sandwich beam with thin core.At the same loading level,the "//" direction specimens has larger deformation than "?" ones.In addition,the core shear strain and stress calculated by LFOT are generally less than CFOT because of considing surface resistance to shear force.But the difference between the two theories becomes smaller with increasing core thickness.Furthermore,the recalculation of cross-sectional stress integration by LFOT can fulfill static equilibrium with same loading condition.(3)On the foundation of LFOT,sandwich beam element with two nodes and six freedoms was set up.The numerical results show that average difference of transverse displacement between Finite element model(FEM)and LFOT is less than 10%.And the cross-sectional stress and strain calculated by FEM is similar to LFOT for thin core sandwich beam while it is close to CFOT step by step with increasing core thickness.(4)Revised first-order theory(RFOT)was derived by recalculation of cross-sectional stress and core shear modulus based on CFOT.The numerical results show that transverse displacement calculated by RFOT is similar to LFOT for thin core sandwich beam while it is close to CFOT step by step with increasing core thickness.At the same time,the transverse displacement caused by bending moment and shear force is declined accordingly,but the ratio of shear deformation to total goes upward.In addition,the shear deformation calculated by RFOT tends to value of CFOT with increasing ratio of core thickness to skin.(5)On the basis of three-point flexural test,the equation to calculate surface indentation at the loading point considering bending normal stress was given.After comparison with test results,RFOT and LFOT considering skin indentation respectively have higher accuracy than CFOT to forecast the transverse displacement of sandwich beam.(6)The compression experiment of sandwich construction was carried out using orthogonal test method.It is shown that the effect of cell size both to compression strength and core transverse modulus is very significant while other factors such as panel type,core thickness have little influence on it.In addition,the effect of applied glue amount both to compression strength and core transverse modulus has a little significant.On the basis of previous test,the equivalent buckling stress subjected to transverse loading was derived by Timoshenko stability theory.It is shown that the relative error between theoretical model and test results is approximate no more than±15%.The transverse compression strength of sandwich composite can be improved largely by increasing cell edge's thickness and reducing cell size of honey-comb.