Study On Vibration Isolation Mechanism Of Adjustable Quasi-Zero Stiffness Bionic Structure Based On Shape Memory Materials

Vibration adversely affects precision instruments,mechanical equipment,aerospace equipment and vehicle systems.Low-frequency(below 100 Hz),largeamplitude vibrations are difficult to isolate effectively using traditional viscoelastic materials such as rubber springs.In recent years,inspired by the mechanism of biological vibration isolation,researchers have worked to develop nonlinear quasi-zerostiffness vibration isolators with high static and low dynamic stiffness to achieve high static load capacity and good isolation of low-frequency vibrations.Current quasi-zero stiffness isolators consist of a combination of positive and negative stiffness and are only effective at small displacements and specific loads.The stiffness of such structures is not adjustable and cannot be applied to changing operating environments.Organisms have evolved efficient low frequency vibration isolation solutions to maintain motion stability and protect the body from impact.For example,the arched structure of the human foot absorbs energy and reduces shock,and the multi-layered skeletal-muscular structure of a bird’s neck reduces the transmission of external forces and maintains head stability.Unlike conventional non-linear vibration isolators,bio-isolated systems have tunable performance and are able to withstand large loads while exhibiting high static and low dynamic stiffness characteristics,allowing them to adapt to complex and dynamically changing environments.Therefore,by understanding and using the theoretical mechanisms of vibration isolation construction by biological vibration isolation systems,research and development of bionic vibration isolators provide new ideas for low-frequency vibration isolation.In this paper,based on the principle of biological vibration isolation for structural design,a bionic vibration isolation structure with adjustable performance was fabricated by 3D/4D printing process using shape memory materials(PLA,polyurethane,NiTi alloy and polymer-NiTi alloy composites).The effects of material properties,structural characteristics and processing technology on the static mechanical properties and dynamic vibration isolation performance of the vibration isolation structure were investigated,and the mechanism of each experimental influencing factor was analysed,so as to establish the static and dynamic theoretical models of the biomimetic quasi-zero stiffness structure.The specific research contents are as follows:(1)Based on the inspiration that biological organisms modulate their mechanical properties by changing their morphology,we have designed and 4D printed a vibration isolation structure made of shape memory polyurethane material consisting of horizontal and vertical Bessel curve beam structures.The role of force,stiffness and deformation under different structural parameters will be theoretically analysed.The experimental and simulation analyses of the vibration isolation structure show that the structure can be adjusted to present mechanical properties of positive,quasi-zero and negative stiffness by adjusting the temporary shape.Therefore,the stiffness and vibration isolation properties can be adjusted by reprogramming the temporary shape.(2)Based on the multi-material 4D printing technology,a quasi-zero stiffness vibration isolation structure of polyurethane(TPU)/poly(lactic acid)(PLA)composites with reconfigured geometries was designed and prepared,which can achieve the adjustment of material stiffness,damping and vibration isolation properties.In the composite structure,PLA is used as a hard phase material to provide load carrying capacity and TPU is used as a soft phase material to provide damping performance.The vibration isolation and damping performance of the quasi-zero stiffness vibration isolation structure was investigated under different structural parameters.The shape memory polymers were programmed by 4D printing process to reconfigure the geometry of the quasi-zero stiffness vibration isolation structure so that the stiffness and vibration isolation performance of the vibration isolation structure are tunable.(3)The one-way and two-way shape memory alloy vibration isolating structures are designed and prepared using NiTi shape memory alloy with customisable and adjustable stiffness and vibration isolating performance,respectively.The one-way shape memory alloy vibration isolation structure consists of vertical and horizontal beams,and the structural mechanical analysis is carried out to establish the static and dynamic theoretical models.Research on the heat treatment process(time and temperature)on the phase transition characteristics of NiTi alloy beams and the vibration isolation performance of vibration isolation structures.By controlling the temperature of the alloy beam,the stiffness and vibration isolation performance of the vibration isolation structure can be adjusted.The bidirectional shape memory NiTi alloy vibration isolation structure consists of vertical and horizontal springs that are articulated.The bidirectional shape memory alloy springs were fabricated by using alloy wires,and the effects of the training method and the number of training sessions on the bidirectional shape memory characteristics of the springs were investigated.The temperature of the horizontal and vertical alloy springs was adjusted separately to change their respective spring shapes,so that the vibration isolation structure showed different stiffnesses,and then the vibration isolation performance and load capacity could be adjusted.(4)Based on the inspiration that organisms modulate their mechanical properties by changing their stiffness,quasi-zero stiffness vibration isolation structures with adjustable damping,stiffness and cushioning properties are designed and fabricated using NiTi alloys and polyurethane composites.The 3D printing process of the composites will be optimised and shape memory composites will be prepared.The effects of process parameters on the damping and stiffness properties of the composites are investigated,i.e.the modulus of the NiTi alloy increases and damping decreases with increasing temperature,while the modulus of the polyurethane decreases and damping increases and vice versa.Based on this characteristic,the vibration isolation and damping properties of composite structures can be adjusted by controlling the temperature to meet the requirements of different service conditions.In addition,the mechanical properties of variable modulus composite vibration isolation structures are theoretically analysed and the static theoretical mechanical model and dynamic vibration isolation model are established.