Study On The Characteristics Of Embedded Sensors Based On Piezoelectric Materials

Under the impetus of the 14 th Five-Year Plan,civil infrastructure has experienced rapid development,with structures such as bridges,highways,and tunnels becoming increasingly large-scale,complex,and intelligent.However,due to harsh service environments,frequent natural disasters,and complex operating conditions,many engineering structures are subjected to long-term dynamic and complex loading,resulting in internal damage and even structural failure.In this context,how to efficiently and accurately monitor and evaluate the internal stress changes and health status of structures has become a hot research topic in the academic community.In this paper,firstly,we designed and fabricated a three-directional normal stress sensor based on lead magnesium niobate-lead titanate(PMN-PT)piezoelectric material,and conducted basic performance tests as well as calibration experiments under reciprocating and impact loading modes.Secondly,the sensor was encapsulated into "smart aggregate" form and embedded into the interior of reinforced concrete beams,achieving real-time monitoring of multi-axis complex stresses inside the engineering structure under dynamic loading.Finally,the experimental results were compared with finite element analysis to verify the effectiveness of the sensor.The main contributions of this paper are as follows :(1)A three-directional normal stress piezoelectric smart aggregate sensor that can be embedded into reinforced concrete structures was designed and fabricated using PMNPT material.The insulation,waterproofing effectiveness,and electrical performance of the sensor were tested using a multimeter.In addition,the stability of the output signal and frequency response characteristics of the sensor were studied using an MTS-810electro-hydraulic servo universal testing machine(2)The three-directional cross-sensitivity matrix of the sensor and the potential and stress distribution under different monitoring surfaces of the sensor was obtained through COMSOL simulation.Comparing the simulation results with experimental data showed that the sensor has similar sensing performance between different monitoring surfaces.Furthermore,the three-dimensional interlayer cross-interference of the sensor can be deemed negligible.(3)The sensing characteristics of the piezoelectric smart aggregate in reciprocating and impact loading modes were studied using an MTS universal testing machine and a drop hammer impact system,and the sensitivity was calibrated.The experiments showed that the performance of the sensors in both loading modes was highly stable,and the sensitivities were the same under both loading modes.The sensitivity coefficient obtained from the experiments was slightly smaller than the simulated value.(4)The three sensors were fabricated and embedded into a reinforced concrete beam,and a LETRY hydraulic servo universal testing machine was used to conduct dynamic reciprocal loading stress monitoring tests on the beam.Furthermore,the feasibility of using piezoelectric smart aggregate sensors for monitoring complex multiaxial stresses inside the structure was verified by comparing and validating with COMSOL simulation.The results showed that the sensors embedded in the beam could effectively monitor the actual stress changes inside the beam,and the average error of voltage and stress output of the three sensors inside the beam were within a controllable range,proving the accuracy and reliability of the designed sensors.They can be widely used to monitor actual complex stress changes inside large structures.