Study On Mechanical Performances Of Sandwich Panels Under Bending And Axial Loads

Sandwich panel is composed of two relatively high strength faces and a relatively thick and light insulated core.It is being extensively used in many energy-efficient buildings for its many favorable properties such as high load-bearing capacity at low weight,excellent thermal insulation,rapid erection.This thesis investigates the mechanical performances of building sandwich panels with organic foam core when subjected to uniformly distributed load,axial load and bending moment.Based mainly on mechanical principles,the corresponding calculation formulae are derived theoretically.The experimental method and finite element(FE)method are used for comparison with the theoretical method.The results of these studies can provide referential basis for the design and application of sandwich panels.The main research contents of this subject are as follows:(1)Considering the effect of shear deformation,the exact formulae for calculating deformation and load bearing capacity of thick faced sandwich panels subjected to uniformly distributed load are derived from the force-deformation relationships of differential equations.The corresponding exact formulae for hinged-hinged sandwich panel and fixed-fixed one are derived respectively.Based on these formulae,the bending moment partition coefficient and shear partition coefficient are given for simplified calculation of bending moment and shear force in face part and sandwich part.The calculation of thin faced sandwich panels can be regarded as a special case of thick-faced sandwich panels.The theoretical formulae for wrinkling bearing capacity are analyzed based on the principle of minimum potential energy.Two groups of full-scale sandwich panels are tested by vacuum chamber loading method,including the sandwich panel composed of two steel(ST)faces and a phenolic foam(PF)and the sandwich panel composed of two fiber-reinforced calcium silicate(CS)faces and a polyurethane(PU)foam core material.The results show that the maximum deformations of two groups of specimens firstly exceed the limiting deformation and then they are failed finally.Thin-faced PF sandwich panels are failed due to the wrinkling of thin-face and thick faced ST-PF sandwich panels are failed due to the local buckling of flange of thick face.The CS-PU sandwich panels are failed due to the stress of CS face arriving at the ultimate strength.The corresponding FE simulation analyses are performed by the FE software.The the results of tests and FE analyses are used to verify the accuracy of the results of theoretical formulae.(2)Considering the effect of shear deformation on buckling performances,the buckling formulae of axially loaded sandwich panels with hinged-hinged and fixed-fixed constraint condition are theoretically derived.With an effective length factor,both buckling formulae are unified into the same form.The buc kling performances of CS-PU sandwich panels subjected to axial loads are tested.The FE analyses including eigenvalue analyses and geometrical nonlinear analyses are performed.Comparing the results of theoretical calculation,test and FE method,a good agreement is obtained and this illustrates the accuracy of the buckling formulae.The results of parametric analyses illustrate that increasing the core shear modulus can obviously increase global buckling loads of short sandwich panels and this influence becomes less important with the increasing length.(3)Considering the second order effect,the mechanical performances of sandwich panels under the combined action of transverse uniformly distributed load and axial load are analyzed.The theoretical accurate formulae for calculating deformation and internal force of sandwich panels with hinged-hinged and fixed-fixed constraint condition are derived.The amplification factor is obtained by using the approximate method that the total deformation is divided into bending deformation and shear deformation.The study show that this factor depends on the ratio of axial load to buckling load.The results of the accurate formulae are compared with the results of the approximate formulae using amplification factor,and the errors are very small.The FE analyses are used to verify the accuracy of theoretical formulae.(4)The mechanical performances of sandwich panels with initial deformation are theoretically analyzed,considering the effect of core shear deformation and the second order effect.The theoretical formulae for calculating deformation and internal force of sandwich panels under the combined action of uniformly distributed load,bending moment and axial load are derived.The amplification factor of axially loaded sandwich panels with initial geometric imperfection is obtained.The eccentric compressive load is equivalent to the combined action of bending moment and axial load.FE analyses are performed in these loading conditions.These theoretical calculation results are compared with FE results and the errors are small,which show that the theoretical calculation formulae are proved to be correct.