Research On Viscoelastic Behaviour Of Bistable Composite Laminated Structures

The bistable composite laminated structure is a kind of composite structure with two stable configurations,there is a significant geometric difference between these two configurations.Each stable configuration has a certain ability of bearing load,and these two configurations can mutual be converted with the proper external load,while it can maintain its configuration without external energy or load.Because of these specialties,the bistable composite laminated structure has a broad development prospect in aerospace field,in which lightweight and multi-functionalization are very important.However,application in the field of aeronautics and astronautics means experiencing a variety of extreme environment,including high temperature,low temperature,long time loading and so on,this situation will have a great impact on the performance of the bistable composite laminated structure.At present,the study of temperature influence on bistable composite laminated structure is generally studied on the basis of the elastic model,which only considers the elastic behavior of the material without regard to the viscoelastic characteristics.The carbon fiber reinforced polymer matrix composite,which is the widely used in the composite laminated structure,is a typical viscoelastic material;its mechanical properties are sensitive to the change of temperature and loading time.Therefore,the viscoelastic model of the bistable composite laminated structures is developed and the bistable behavior of the bistable composite structure under the influence of temperature and loading time is studied by theoretical analysis,experimental investigation and numerical simulation.The main research works are listed below:1.The glass-transition temperature,linear viscoelastic region and relaxation modulus are acquired by using the Dynamic Mechanical Analysis(DMA).According to the time temperature equivalence principle,the short-term relaxation modulus curves under different temperatures are transformed into a single long-term relaxation modulus curve under a reference temperature.On the basis of the theory of homogenization in microcosmic mechanics and finite element simulation,the single crystal cell model of carbon fiber reinforced epoxy resin matrix composites is built.Therefore the viscoelastic properties of carbon fiber reinforced epoxy matrix composites are calculated basing on the viscoelastic material properties of the epoxy resin and the elastic material properties of carbon fiber.2.Based on the linear viscoelastic theory and classical laminated theory(CLT),a viscoelastic theoretical model of the bistable composite laminated structure is developed by using minimum potential energy theory.The influence of loading time and temperature on the curvatures of the bistable structure in the second stable state is predicted analytically on the basis of the viscoelastic properties of carbon fiber reinforced epoxy matrix composites.3.By using the tensile testing machine with temperature chamber,the stable state transition experience of the bistable composite laminated structure are conducted under different temperatures,relaxation positions and relaxation times.The load-displacement curve of snap-through process and the curvature in the second stable state are studied.Meanwhile,the scanning electron microscope(SEM)images are acquired to observe the microscopic changes of the bistable composite laminated structure under different temperature.4.According to the experiment process of the bistable composite laminated structure,a viscoelastic finite element model is built by using a finite element software ABAQUS and its user subroutine UMAT.The bistable composite laminated structure’s load-displacement curves and its curvatures in the second stable state are acquired by conducting simulations of the snap-through process of the structure under different temperatures and relaxation times.