The Research On Rheological Properties Of Two Kinds Of Bamboo-based Engineering Composite Materials

Bamboo-based engineering composite materials is a kind of tabular material that glue bamboo by adhesive and a series of mechanical and chemical processing under a certain temperature and pressure.In recent years,the proportion of bamboo industrialization in China has increased year by year,and the application has become more and more common in the field of engineering,the requirements for the properties of bamboo-based engineering composite materials are also demanding higher and higher.At present,the bamboo-based engineering composite materials mainly include laminated bamboo,bamboo plywood,glue laminated bamboo,reconsolidated bamboo and bamboo composite materials,etc.Creep is the important evaluation indicator to determine whether one material could be use for engineering or not.In the paper,the test material is glue laminated bamboo(GLB)and reconsolidated bamboo(RB),which are two kinds of bamboo-based engineering composite materials.Firstly,the experiments of bending and compressive mechanical properties test of reconsolidated bamboo and glued laminated bamboo are introduced.Then,the flexural short-term creep tests of GLB and RB were done under different loads at room temperature.The experimental curves were also fitted and analyzed by Burgers rheological model,and obtain its allowable stress.According to the rheological theory,the relaxation curve was calculated from the creep curves.(1)The flexural modulus,flexural strength,compressive modulus and compressive strength of RB and GLB are obtained.And the different failure modes is analyzed.The experimental results show that the mechanical properties of reconsolidated bamboo are better than glued laminated bamboo.Reconsolidated bamboo takes on brittle failure,and glued laminated bamboo takes on ductility failure.The mechanical properties of bamboo are related to the material character of bamboo and the properties of glued interface.(2)The creep deformation of GLB and RB can be described by three stages as elastic stage,viscoelastic stage and plastic stage.The creep curves of GLB and RB under different load at room temperature abide by the similar rule,and increase with the increase of load.The allowable stress of GLB and RB were obtained as the 14.67%and 18.93%of the maximum load.(3)The deciding coefficient R2 between the simulated curves of Burgers rheological model parameters solved by Origin software and the test curves are above 0.9994,the error between the calculated data of Burgers rheological model and the test data are below 1%,which revealed that Burgers rheological model can be used to simulated the primary creep and the secondary creep.(4)To introduce a parameter x based on Burgers rheological model can commendably solve the problem that its creep curves too linear.The deciding coefficient R2 between the simulated curve of improved rheological model and the test curves are above 0.999,in most cases,it is more accurate than Burgers rheological model.(5)The equivalence relation between creep test and relaxation experiment is discussed.According the equivalence principle,the stress relaxation curves can be deduced from its creep curves.