Study On The Propagation Characteristics Of Stress Wave And Processing Optimization For Automated Fiber Placement Process

With continuous development of aerospace industry,automated fiber placement(AFP)has attracted more and more attention.Unreasonable laying parameters could result in many lying defects,which could not only reduce the mechanical properties of products,but also shorten the product life.The stress caused by the continuous construction of the process and its dynamic fluctuation are the main causes of the initiation and evolution of the defects.The stress wave can reflect the size,distribution and characteristics of the internal defects of the laminates,which provides a new idea for defect detection.This thesis studies the stress wave signal during the manufacturing process,intending to find the association of stress wave and laying parameters and further reveal the relationship mechanism between the stress wave and the internal defects,which provides data and theoretical basis for real-time detection of defects and process optimization in laying process.Firstly,the propagation law of stress wave in composite laminates was analyzed according to the high-order plate theory in this thesis.The simulation of Stress wave propagation in Simulated no defective and uniform defective laminated plates was simulated through Abaqus and the propagation characteristics of stress waves were analyzed.In order to establish the composites model with different defect rates,Fortron language was used to achieve the secondary development of Abaqus.The amplitude and propagation velocity of the stress waves in random defect rate plates were calculated through simulation.The relationship between stress wave propagation characteristics and the defect rates were analyzed by regression analysis.And the relationship between the amplitude,the velocity and the defect rate was established by polynomial fitting.By changing layout parameters,27 sets of thermodynamic coupling simulation were performed.The effects of laying pressure,laying speed and preheating temperature on the propagation characteristics of stress wave in the prepregs were studied.The gray correlation analysis method was used to analyze the correlation of laying parameters on the amplitude,variance and Manhattan distance of real-time stress wave signals.In order to verify the accuracy of the simulation results and further study the relationship between defects and stress waves,real-time stress wave acquisition experiment method in laying process was designed.The real-time stress wave signals of 27 groups of different process parameters were collected.According to the influence of the laying parameters on the stress wave,the correctness of the thermodynamic coupling simulation model was verifiedUsing the microscopic observation method,the average defect rate of each specimen was calculated by means of ultrasonic A scanning and optical microscopy.The relationship among the defect rate and the velocity and amplitude of the stress wave was analyzed by combining with the stress wave signal in the previous test.The accuracy of the simulation results of the defect rate was verified,and the initiation and expansion of the cracks inside the matrix were analyzed from the strain energy point of view.Finally,the process parameters are optimized by response surface method.