Study On The Thermal/Piezoelectric Properties Of Copolymer Piezoelectric Composite Using For Intelligent Traffic Senors

Nowadays intelligent traffic sensors play an important role in realizing the detection of traffic parameters in ITS(intelligent traffic system),among which piezoelectric traffic sensors become an ideal choice for their advantages such as high reliability,simple layout and less damage to the road surface.However,currently,piezoelectric traffic sensors are generally faced with bottleneck problems such as low accuracy and poor thermal stability,which restrict their development and application.The polymer based piezoelectric composite proposed in this paper is a unique composite material with high-thermal and high-piezoelectric properties,which possess the advantages of simple preparation process,good flexibility and low price.Basing this piezoelectric composite it is expected to develop high-performance piezoelectric traffic sensors for ITS.In this thesis,the piezoelectric composites were prepared by adding high thermal conductivity filler CNTs and high voltage electrical filler PZT on the polymer PVDF matrix.To reveal the mechanism of high thermal conductivity/high piezoelectric property,the effects of material parameters such as filler content/length/orientation/interface on thermal conductivity/piezoelectric properties of piezoelectric composite were investigated by means of numerical simulation and experimental research.Moreover,a kind of high thermal conductivity/high piezoelectric composite for piezoelectric traffic sensor was developed and its output characteristics were studied by finite element simulation.The main research contents and results are as follows:(1)The numerical simulation model of thermal conductivity of PVDF/CNTs composite was established by COMSOL with MATLAB,and the effects of material parameters such as CNTs content/length/orientation/interface on the thermal conductivity of piezoelectric composite that used in intelligent traffic sensors were studied.The results showed that the thermal conductivity of composites increased with the increase of CNTs content,length and orientation along Z axis.It was also showed that the thermal conductivity of the composites increased with the increase of the contact pressure p_c of the PVDF/CNTs interface,but hardly changed when the p_c value was greater than 1 MPa.(2)The numerical model of piezoelectric of PVDF/CNTs composite was built by COMSOL with MATLAB,and the effects of PZT content/length/orientation on the piezoelectric property of piezoelectric composite that used in intelligent traffic sensors were studied.The results showed that,the piezoelectric properties of composite improved with the increase of PZT content and length.When the orientation of PZT increased,the piezoelectric properties of PVDF/PZT composites along the orientation direction increased,while the piezoelectric properties in other directions decreased.It was also found that when the content,length and orientation of PZT changed,besides the piezoelectric properties of the composites,their mechanical and electrical properties would also be affected.(3)PVDF/PZT/CNTs piezoelectric composite films with different material ratios were prepared by vacuum hot pressing,and its thermal conductivity/piezoelectric properties were tested.Then the experimental results and numerical simulation results were compared,and the mechanism of high thermal conductivity/high piezoelectric composite was studied.The results showed that,when adding low content CNTs,the thermal conductivity of composite decreased due to the increase of contact thermal resistance.The measured values of thermal conductivity were most similar to those obtained in numerical simulation when p_c=1.With the increase of PZT content,the piezoelectric constant values of the composites were also increasing.However,when the PZT content continued to increase,the increase rate tended to be reduced due to the agglomeration effect of fillers.(4)A finite element model of piezoelectric traffic sensor was designed by element analysis software ANSYS,and the working process of piezoelectric traffic sensor was simulated on macro scale.Five piezoelectric composites with different material parameters were designed as sensor materials and the sensitivities of piezoelectric traffic sensors for each material under different loads were compared and analyzed.In addition,the output characteristics of each piezoelectric traffic sensor under different materials,loads and temperatures were discussed and analyzed.The results showed that,under uniform load,the voltage output of sensors based on various materials had a good linear relationship with the load and stress value.The sensitivity met the requirements of the piezoelectric traffic senor.The piezoelectric output increased with the increase of tire grounding load.When the ambient temperature was high,the piezoelectric output of the piezoelectric traffic sensor could be improved to some extent by improving the thermal conductivity of the composites,so as to improve the sensitivity and accuracy of the senor.It was also showed that material parameters such as filler content/length/orientation affected the output of piezoelectric traffic senor.The higher the content of PZT,the larger the orientation along the polarization direction and the longer the length of PZT,the higher the piezoelectric properties of the composites,and the larger the voltage output value of the piezoelectric traffic sensor.