Tolerance Design Method For Negative Poisson's Ratio Metamaterial Performance

Metamaterial is an emerging material that is arranged with artificial configuration as functional units.It can realize new features that are not available in the natural world.It is widely used in aerospace,automotive,optics and other fields.Metamaterials come in many forms,but their main structural characteristics are easily derived from the arrangement of specific unit cells.As a kind of metamaterial,negative Poisson's ratio metamaterial has good mechanical properties,and has the characteristics of energy absorption and heat insulation.Facing various needs,we can design the metamaterial configuration by means of topology optimization,etc.However,the tolerance constraints required during the processing of metamaterials are not traditionally used to ensure interchangeability and assembly requirements,but when the structure size of the material is within the tolerance range,it can ensure that the required performance meets the design requirements.To this end,the precision design process of metamaterials is studied by taking the precision design of negative Poisson's ratio functional structure for performance accuracy as an example.Facing the demand for the precise manufacturing of periodic negative Poisson's ratio functional structure performance,this paper starts with obtaining the response relationship between the macroscopic performance of the structure and the tolerance,and proposes two dimensional tolerance design methods for performance accuracy.The effect of structural properties is studied.The main work includes the following aspects:First,in the introduction,the research status of metamaterials and negative Poisson's ratio structures is reviewed,the current development process of precision design is summarized,the problems to be solved by this topic are drawn from it,and the research significance is expounded.Secondly,two methods are used to derive the relationship between performance and dimensional parameters through the unit cell axial mechanical compression model,build a simulation model to establish the performance and tolerance design function,and obtain the response relationship between the macroscopic target performance of the structure and the dimensional tolerance.The effectiveness of the two methods is proved by examples.Among them,the method of deriving the mechanical model is simple,but there will be deviations from the simulation model verification,and the correction coefficient needs to be added.The method of constructing simulation models requires parameterization to establish iteratively calculated periodic negative Poisson's ratio structural simulation models including performance tolerance,which requires a large amount of calculation.Next,a dimensional tolerance design method for negative Poisson's ratio structure performance accuracy using sequential quadratic programming(SQP)and proxy model is proposed.The sequential quadratic programming method needs to specify the appropriate objective function and constraint conditions for tolerance design.The proxy model method needs to specify the model type and sampling method to construct the proxy model to guide the tolerance value allocation.It is verified by examples that both methods can achieve performance-oriented precision design under the premise of ensuring qualified performance.Finally,the influence degree of shape and position tolerance on performance accuracy is studied.By setting the form and position of periodic structure shape and position tolerance reasonably,the periodic star-shaped negative Poisson's ratio structure including straightness tolerance and cell center position tolerance is parametrically established Simulation model.Study the influence of different grades of geometric tolerances on the performance of negative Poisson's ratio structure equivalent elastic modulus: the larger the geometric tolerance value is,the lower the mean value of the elastic modulus of the star structure;Lower than the original value;the impact of the same level of geometric tolerance on performance is lower than the dimensional tolerance.The simulation results show that all the tolerance design results are qualified.