Quality Characterization And Regulation Of Prepreg Tow Steering Based On Automatic Placement Process

Automatic placement is the key technology for prefabrication of advanced composite components,and curve placement is a widely used technique in the fabrication of large curvature components.Based on the automatic curve placement test bench,the causes and geometric characteristics of wrinkle defects in prepreg tow steering were studied firstly.The quality evaluation index was established based on the physical conformity of effective fit length,etc.Then,the influence law and mechanism of the automatic placement process parameters on the quality of the tow steering were explored.Finally,the finite element modeling and simulation of the automatic curve placement was carried out to explore the stress distribution of the tow steering.The specific research contents of the thesis are as follows:The first chapter briefly introduces the automatic placement technology of composite materials,focusing on the research status of prepreg curve placement,prepreg tow steering quality evaluation,prepreg placement modeling,etc.The research background and research significance of this paper was summarized the research framework was built.In the second chapter,the mathematical model of the steering force of the prepreg tow was established.The parameters which influence prepreg tow steering were calculated.The cosine function was used to characterize the geometric characteristics of the wrinkle curvature,and the effect of the wrinkle size on the strength was explored by means of a three-point bending test.It was found that defects(such as wrinkles)generated during the deposition process lead to wrinkle defects in the cured fiber.It was further found that the bending properties of the laminate decreased as the wrinkles increased.In the third chapter,the prepreg automatic curve placement test device was designed and improved.An evaluation system that combines the effective fitting length ratio,wrinkle angle and radius of curvature ratio to describe the quality of prepreg tow steering was established.The curve placement test under different process parameters was completed.The results shown that the overall quality increased first and then decreased with the increase of temperature,decreased with the increase of the lay-up velocity,increased first and then decreases with the increase of lay-up tension,increased first and then decreases with the increase of lay-up pressure.The supplementary design completed the orthogonal test of the curve placement,and the temperature,velocity and tension have the most significant influence on the quality of the tow turn-laying.In the fourth chapter,prepreg 90° peeling test were completed.Compared with the results of the third chapter test,it shown that the quality was positively correlated with the tack of the prepreg,and the radius of curvature ratio was inversely related to the stiffness.Appropriate process parameter intervals were obtained based on the test.The friction coefficient between the pressure roller and the prepreg surface and the influence of the profiled pressure roller on the placement quality were studied.It was found that the moderately improved friction coefficient and the elliptical pressure roller are beneficial to improve the quality of the prepreg tow steering.In the fifth chapter,the finite element model of prepreg dynamic curve placement was established.The bond relationship between prepreg and mold in the model was characterized by Cohesive Zone Model(CZM).The parameters were obtained by probe test.The parameters of the prepreg material were obtained by tensile,off-axis stretching,and compression tests.The simulation results of the model shown that the prepreg is subjected to tensile stress on the outer side of the curve placement,the inner compressive stress and the initial end stress are concentrated.Compared with the curve placement test at different temperatures the degree of coincidence was good.The sixth chapter summarized the research content and innovation points of this paper,expounded the research results of each chapter of the thesis,and made a prospect for the shortcomings of the existing research,and put forward the content that needs further research.The above research results provided a theoretical basis for the regulation of the quality of the prepreg tow steering during the automatic placement,and it has great significance in providing data support for improving the quality of the prepreg tow steering through the process parameters.