Study On Anti-symmetric Bistable Structures Under Hygrothermal Environment And Effect Of Initial Imperfections

Anti-symmetric cylindrical shells as a novel kind of bistable composite structure are manufactured from the carbon-fiber or glass-fiber reinforced epoxy resin composites.As morphing and deployable structures,bistable composite structures are featured by their two stable configurations and capable of deforming from one stable state to the other under an external loading.The two stable configurations can be maintained without a continuous power supply.Owing to the advantages of favorable great stiffness,light-weight and deformability,it has attracted an increasing attention in the field of smart morphing structures and energy harvesting,etc.However,the application based on bistable composite structures inevitably affected by the variation of the ambient environment(i.e.temperature and moisture,etc)is restricted.It also can be found that the initial imperfections may influence the bistable characteristics of bistable composite structures.For the present studies,anti-symmetric cylindrical shells still need to be improved.In this paper,the theoretical analysis,finite element and experiment methodology are combined to study the effects of temperature and moisture on the bistable characteristics of anti-symmetric cylindrical shells.Besides,the bistable characteristics of anti-symmetric cylindrical shells with the initial imperfections are studied by finite element method.Research works are presented as follows:1.Based on the classical lamination theory and considering the effects of temperature and moisture,the theoretical model of bistable composite structures under the effects of temperature and moisture has been derived.The first stable twisting curvature,the second stable curvature and twisting curvature are predicted by the theoretical model using the minimum potential energy theory.At last,this paper presents one method to active control the twisting curvatures of bistable composite structures with the effects of temperature and moisture.The feasibility of this method is validated in theory.2.To reach different temperature and moisture,anti-symmetric cylindrical shells are immersed in the water bath with different working temperature for different time and mechanically loaded by the testing machine with temperature box later.Furthermore,the shapes of anti-symmetric cylindrical shells with different temperature and moisture are tested by measuring equipments.The load-displacement curves,the curvatures and twisting curvatures with different temperature and moisture are obtained from the experiment.Further,another similar experiment studying the effect of moisture obtains the load-displacement curves in the snap-through process and the different shapes of anti-symmetric cylindrical shells with different moisture content.3.The snap-through processes of anti-symmetric cylindrical shells with different temperature and moisture are simulated by the finite element software ABAQUS.The load-displacement curves in the snap-through process,the curvatures and twisting curvatures in two stable states with different temperature and moisture are obtained by finite element simulation.The FE results agree very well with therotical results,but there are still some deviations in contrast with the experimental results.4.Considering resin rich imperfection,thickness imperfection and layer angle imperfection,the snap-through processes of anti-symmetric cylindrical shells with different initial imperfections are simulated by the finite element software ABAQUS.The FE results show that the curvatures and twisting curvatures may be influenced by the three different initial imperfections in the second stable state,and snap loads in different ways.The finite element methods and theoretical analysis are employed to study some special initial imperfections,and the results of them agree very well.