Design And Mechanical Properties Of Structure With Negative Stiffness Based On Curved Beam

Negative stiffness(NS)porous structure is a novel light multifunctional structure which has attracted wide attention at home and abroad in recent years.Owing to its special mechanical properties,such as negative stiffness,multi-stability,repeatability,etc.,it has great potential to be used in energy absorption,vibration control,phase transformation meta-material,expandable structure and noise isolation.At present,the previously reported NS structures have some shortcomings,such as low mechanical properties,low energy absorption efficiency,single structural form.Most of the researchs only focus on the static mechanical properties of the structure.Moreover,some important problems,such as dynamic response,high cycle performance,have not been fully studied.In order to overcome the problems of negative stiffness structure in the previous research status,two negative stiffness structures based on curved beams are designed and fabricated,and establish a complete theory,experiment and simulation system to characterize and evaluate the properties of these structures:1.Metal negative stiffness structure: The traditional negative stiffness structure is mainly subjected to elastic deformation.Therefore,elastomers and plastics are the main materials used in the negative stiffness structure at present.The mechanical properties of these materials are generally low,which greatly limits the practical application of negative stiffness structure.In this paper,a reusable metal structure,which can dissipate energy through plastic deformation and exhibit NS behavior through inelastic instability,is presented firstly.Mechanical properties of this structure are investigated with a combination of compression tests and simulations.Using experimentally verified numerical model,the influence of geometric parameters on energy absorption is revealed.Numerical results show that the compressive strength and specific energy absorption increase as the parameter ratio,t/L and h/L increases.The energy absorption efficiency increases with increasing t/L,but decrease with the increasing ratio,h/L.Repeatability of the structure is then investigated through cyclic compression and impact of structural dimensions on repeatability is preliminarily studied.Besides,annealing treatment is conducted to try to improve repeatability.Finally,based on the interlocking assembly method,a 3D NS structure is proposed and fabricated.Obtained results show that the specific energy absorption of the presented structure is more than most traditional NS structures and its energy absorption efficiency is high.Simultaneously,the property of the structure is repeatable and the repeatability of the structure declines with the increase of structure dimensions.Moreover,repeatability can be improved a lot through annealing treatment,but the mechanical performance deteriorates.2.Composite negative stiffness structure: Although metal negative stiffness structure has certain reusability,its reusable times can not meet the needs of engineering.In this paper,a composite negative stiffness structure composed of two material systems is presented and researched.The design concept of composite materials is used for the design of negative stiffness structures.There are different stress distribution characteristics in different regions of the negative stiffness structure during deformation.A two-material system combining soft material and hard material is used to construct a negative stiffness structure to achieve high-order recyclability and improve structural performance.The specimen of the structure was fabricated by combination of Selective Laser Sintering(SLS)technology and Fused Deposition Modeling(FDM)technology.A complete experimental and simulation system was established to characterize and evaluate the properties of the structure and to compare the energy absorption capacity of the composite NS structure with the single material NS structure of equivalent relative volume.The repeatability of the structure was verified by quasi-static cycle of loading and unloading.Besides,the dynamic characteristics of the structure are obtained by vibration test.Finally,the cushion performance of the structure was studied by the impact experiments.Experimental results of the impact tests show that the structure exhibits good cushion performance by thresholding the magnitude of acceleration response and completely reusable.Therefore,the structure can find usefulness in a number of unique applications requiring recoverable shock isolation,such as bumpers,helmets and other personal protection devices.