Shap Analyses And Experiment Research Of Multi-steady Structures

Because of structural aesthetic and flexible demand of architecture,structure and aerospace.Multi-stable structure has been paid more and more attention by domestic and foreign scholars,and its construction form,design method and mechanics analysis have been extensively studied.based on the summary of research results at home and abroad,a kind of multi-stable structure design framework is put forward.The design method and morphological analysis process of planar and spatial multi-stable structures are introduced,and the structure of expandable bar is introduced into multi-stable structures,and the design,experiment and finite element analysis of the expandable bar are made.Based on the theory of mechanism analysis,hinged joints or expandable bars are introduced into the traditional scissors mechanisms to form multi-hinge scissors mechanisms or expandable scissors mechanisms with multiple degrees of freedom(DOF).The kinematic analy sis and position solution of several typical planar expandable mechanisms are carried out.According to the result of position solution,and based on the constraint Jacobian matrix method,the DOF of the mechanism is calculated.In the form of simple mechanism,the analytical solution is obtained by MAPLE,and to complex form,the numerical solution is obtained by MATLAB.However the method of numerical Jacobian matrix only reflects the DOF of the body in current coordinate value,so many differnet position coordinate solutions in the mechanism motion process are selected to verify the accuracy of the calculation of the DOF A basic expandable scissors mechanism under different supports is analyzed.The singular value points in the process of motion of the mechanism are found by the position analysis solution.The Jacobian matrix method is used to calculate the degree of freedom of the whole process of the mechanism,which Verifies the correctness of theoretical derivation.For complex planar scissors mechanisms,the Monte Carlo method is used to randomly sample expansion quantities of expandable bars in the allowable range of the structure,and several positon results are obtained.And then the DOF of the mechanism is obtained by using the constraint Jacobian matrix method.Based on the constraint equations of the planar scissors mechanism,the constraint equations of the spatial scissors mechanism and the expandable scissors mechanism are given.With the examples of expandable mechanism in space,the number of DOF of the different expansions is calculated by using the constrained Jacobian matrix.And the correctness of the constraint equation is verified.Based on the analysis results of the scissors mechanism,combined with several examples,the topological structure and geometrical optimization of the planar and spatial scissors mechanisms are presented.A new multi-stable structure design framework is proposed to facilitate the structural design which can approach the multi-objective morphology and realize the multi-objective interchange.Taking the planar scissors mechanism as an example,first the initial and target curves P0 and P1 arc given,this shape design method is used to optimize the mechanism.The geometric parameters and the DOF are chosen as the optimization variables.The mechanism constraints are established,and the minimum value of the constraint is solved by the fmincon function.Then the initial and target shapes of the mechanisms is determined Select the finite number of intermediate moments in the transformation path to verify the process mobility of the optimization mechanism.According to the optimization results of the existing planar scissors,the optimal design of the cy lindrical and the rotating scissors mechanism is carried out.In this paper,the design idea of the cylindrical spatial scissors mechanism is put forward,the geometrical and motion of the basic scissors unit of the rotating plane is analyzed,and a new type of spatial scissors unit is proposed,which is introduced into the spatial scissor mechanism to optimize the design.After the optimization of the planar and spatial scissors mechanism,the driving and braking mode is discussed,and the mechanism is transformed into the multi-stable structure.The ABAQUS static analysis of the multi-stable structure is carried out to verify the feasibility of the drive scheme and the rationality of the design.At the end of paper,a novel expandable bar struct is proposed,which consists of a outer side steel shell,retractable short tubes,connecting springs,stiffening plates and end connecting plates.The mechanical analysis and the finite element simulation of detail structure are carried out,and the reasonable expandable bar struct is obtained.Combined with the size of the bar in the multi-stable structure,the structure of the symmetrical expandable bar struct,the spring asymmetric expandable bar struct and the square steel asymmetric expandable bar struct are put forward.The finite element simulation and experimental study on the limit state of normal use and bearing capacity of the three structures are carried out respectively.