Real-time Monitoring Technology Of Liquid Composite Molding Process Based On Piezoelectric Sensor Network

As an advanced composite material production technology that can be applied to the manufacture of large-scale engineering structures,the Liquid Composite Molding(LCM)process has many advantages such as rapid molding,low cost,and mass production.LCM process has become a research hotspot in the industry and academia.However,because of lacking the real-time maturely monitoring methods of LCM process,it is very difficult to guarantee the quality and consistency of the composite material products.At present,the dielectric sensor-based methods are often used to monitor the process of glass fiber composite materials,however the accuracy of these methods are not high.Many scholars in academia have proposed a variety of real-time monitoring methods,such as fiber optics,thermals,and ultrasonic.However,these methods have relatively strict application conditions and high costs.They are still in the laboratory verification stage and can't be used in industrial production immediately.This paper adopts a method combining numerical simulation and experimental verification.Firstly,the numerical simulation of the LCM process is performed to understand the basic laws of the LCM process.Then,a piezoelectric sensing network method is adopted,and several Pb-based lead Zirconium Titanate(PZT)sensors are installed on the mold(inside or outside)to monitor the LCM process in three ways of pressure method,electromechanical impedance,and wave propagation.Therefore,several physical parameters such as the pressure,the flow front and curing degree of resin can be online monitored from point to surface,from the local to the whole.Finally,a series of experiments are conducted to verify the feasibility of the proposed methods.The main work of this thesis can be summarized as follows:(1)Two important processes(the resin flow process and the coupling process between temperature and curing degree)during LCM was researched in a way of simulation.Firstly,DSC experiments were performed on the epoxy resin to obtain corresponding kinetic parameters of the model.Then the PAM-RTM FEM software was used to simulate the resin-filled fiber material to obtain the resin flow front and the specific flow process.Then,a subroutine of above kinetic parameters model was compiled by Fortran and integrated into the Abaqus FEM software to perform a coupled calculation of the temperature field and curing degree field during the curing process and the optimal curing way and the corresponding curing temperature were obtained through numerical simulation.(2)A resin flow front monitoring method based on pressure method and Lamb wave method was proposed to realize the point-to-face flow front evaluation of large-scale composite structures.By filtering and smoothing the pressure signal,it can be proved that the pressure method has higher accuracy in point monitoring.Based on the characteristics of different modes Lamb waves,three features such as A0 phase,A0 amplitude and S0 phase are extracted to indices the characterize and predict the resin flow front.The feasibility of the proposed method are verified by using several experiments.It can be included that the Lamb wave method can be used to monitor the resin flow front in a large scale mold.Although the accuracy is not as good as that of the pressure method,the position of the flow front can be predicted through the comparative analysis of Lamb waves on different paths.(3)A resin curing monitoring method based on the combination of impedance analysis and Lamb wave was proposed to achieve a comprehensive evaluation of the degree of cure from the local to the whole in the LCM process.The resonant and anti-resonant frequencies obtained by the impedance analysis are processed in a way of the normalized integral.A one-to-one mapping relationship is built by comparing the normalized integral data with the simulation results.It is found that the impedance analysis method can perform local quantitative monitoring on key areas in the molding process.The variation of So amplitude and wave velocity can be used to reflect the curing feature in different stages of the curing process and the end characteristics.The experimental results illustrate that the degree of solidification of the composite liquid forming process can be evaluated qualitatively by analyzing Lamb wave amplitude changes of different paths.