| Bionic flexible strain sensors with slit structural units are widely used in the fields of wearable devices,electronic skin,human-computer interaction and medical detection.However,the bionic flexible strain sensors have defects such as large structural deformation failure,passive fitting,single function and non-adjustable,which seriously limit the further development of related sensors.Exploring the design and preparation of flexible strain sensors with structural safety design,adaptive active deformation,adjustable sensing function and multifunctional sensing fusion is an important way to expand the applications of strain sensors.Helical structure,as a multifunctional integrated bionic structural element,is widely used for the synergistic optimisation of strong and tough properties and intelligent deformation.In this paper,based on the unique process characteristics of fused deposition moulding,combined with the design of bionic spiral structure,the design and preparation of mechanics-safe,adaptive deformation,functionally adjustable bionic flexible strain sensors is achieved.The specific research content of this paper mainly includes the following four aspects:(1)To meet the structural safety design requirements of flexible strain sensors,bionic samples with spiral structure characteristics were designed and prepared based on FDM printing process.The effects of interlayer angle,filling rate and gradient design of the bionic spiral structure on the tensile and three-point bending properties of the structure were investigated,and the intrinsic relationship between the gradient of filling rate and the gradient distribution of the spiral angle on the mechanical properties of the samples was revealed.In addition,combined with the melt shear-induced mechanism of FDM process,single-stage and multi-stage bionic helical structures were prepared by using poly(lactic acid)(PLA)material and carbon fibre-reinforced PLA material(C/PLA),respectively,to explore the influence of the layer design on the mechanical properties of the structure,and to obtain the mechanically relevant structural parameters,which provide a theoretical basis for the structural safety design and preparation of the strong strain sensors.(2)To meet the demand of strain sensors to adaptively and actively fit complex surfaces,based on the shape memory polymer stress-induced 4D deformation strategy,combined with the design of the bionic spiral structure,the adaptive and active deformation is achieved under the induction of thermal excitation.In this paper,we use a combination of finite element simulation and experimental methods to study the effects of interlayer angle,filling rate,aspect ratio and printing parameters on the adaptive deformation mode and deformation degree of the helical structure,to reveal the influence of structural and process parameters on the adaptive deformation of the structure,and to establish the intrinsic relationship between structure-process-function.Combined with the hierarchical structural design,it also explores the influence of hierarchical design on the adaptive active deformation of structure.Finally,through the demonstration of complex structural adaptation,the intelligent programmable characteristics of the spiral structure are proved.(3)In order to improve the complexity of the adaptive deformation of the structure,an adaptive multimodal bilayer deformation strategy for a bilayer structure is constructed.On the basis of the stress-induced 4D deformation of the helical structure,the bilayer structure model is designed through the external strain layer,and the thermal induction realises the bidirectional deformation of the smart structure.In this paper,we study the effects of the pre-strain of the external strain layer,the filling angle of the helical structure,the interlayer turning angle,the thickness and the aspect ratio of the sample on the bidirectional adaptive deformation mode and the degree of deformation,to reveal the influence of the pre-strain of the external layer and the structural parameters on the bidirectional deformation law,and to construct a mechanism of bidirectional deformation of a bilayer structure,and finite element simulation verifies the feasibility and validity of multimodal complex deformation for the design of the bilayer structure.(4)An intelligent programming mechanism for the sensing characteristics of flexible strain sensors is constructed to meet the demand for adjustable sensing characteristics of strain sensors.Based on the unique process characteristics of FDM,a bionic gap structure is constructed,and combined with the intelligent deformation strategy of the bilayer structure,a bionic flexible strain sensor with programmable sensing characteristics is designed and prepared.The influence of the gap structure parameters on the sensing characteristics of the bilayer structure before deformation is investigated,and the influence of the structural parameters of the bionic sensing gap unit on its adjustable sensing characteristics is revealed to optimise the FDM filling rate.The effect of microstructure adjustment of the slit sensing unit on its sensitivity under multi-modal conditions in 4D deformation is investigated,and the mapping relationship between the deformed structure-sensing function is analysed.In addition,the proposed proposed bionic strain sensor combines the actuation and sensing functions to achieve the deformation self-detection and position self-awareness functions.(5)In order to improve the flexibility and convenience of the sensor,a wireless adaptive intelligent strain sensor is designed by integrating wireless sensing technology on the basis of the bionic strain sensor,and the sensor is demonstrated in the fields of wearability,health monitoring,human body movement recognition,vibration detection and wind speed detection,etc.,which verifies the validity of the advantageous functions such as the bionic adaptive sensor’s complex curved surface adaptive fit,the sensing characteristics can be programmable,and the reliability is high. |
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