| Thermoplastic composites have been widely used in aerospace and other fields for their excellent characteristics such as high strength,low cost,recyclabe,and high production efficiency.However,when the automatic fiber placement(AFP)is used for the molding of thermoplastic composites,the fast lay-up speed and short application time during the AFP process lead to low crystallinity and high porosity and resin-rich areas between layers,resulting in the performance of thermoplastic AFP components is lower than traditional autoclave molding process,which seriously restricts the further promotion of thermoplastic materials.Carbon nanotubes have excellent mechanical properties,and it is important to research how to use carbon nanotubes to enhance the interlayer properties to improve the manufacturing process of thermoplastic composites in China.Firstly,this thesis investigates the effect of process parameters on the interlayer properties of thermoplastic AFP components.The hot air temperature,lay-up pressure and lay-up speed were selected as the experimental factors,and nine groups orthogonal experiment was conducted.The interlaminar shear strength,bending strength,porosity and crystallinity were measured.A fitting model was developed through the mean value analysis and the response surface analysis.The response surface method was used to find out the optimal process parameters,and the accuracy of the model was verified by experiments.Secondly,a finite element simulation model was established was established.The process of AFP was analyzed and the finite element model of single prepreg was established by ABAQUS.The influence of the process parameters on the stress state at the nip point was analyzed,and the boundary conditions were provided for the subsequent microscopic interface molecular dynamics model.Besides,the microscopic interfacial model containing carbon nanotubes between the layup layers was established using molecular dynamics method.The validity of the model was verified by calculating the mechanical properties of the model.The influence of the distribution of carbon nanotubes in the PEEK matrix on the interfacial binding energy was calculated.Based on the temperature and stress fields calculated in the finite element simulation,which were used as the boundary conditions of the microscopic interface model,the effects of process parameters on the microscopic properties such as viscosity,carbon nanotube diffusion coefficient,and bonding energy between carbon nanotubes and resin were analyzed.Finally,the AFP experiments of carbon nanopaper reinforced thermoplastic composites were carried out.Carbon nanopaper/PET composite film was made by mechanical stripping of carbon nanopaper by using PET tape.The thermoplastic AFP component containing carbon nanopaper was prepared by embedding carbon nanopaper/PET composite into the interlayers.The effect of the embedded position of carbon nanopaper on the enhancement effect was analyzed.The results showed that the existence of carbon nanopaper could improve the performance of the automatic filament laying component by 22.6%.The experiments of carbon nanopaper reinforced filament laying were carried out under different parameters,and the interlaminar shear strength was measured.The distribution of carbon nanotubes in the samples was observed under scanning electron microscope.The relationship between interlaminar shear strength,uniformity of carbon nanotubes,process parameters,stress state and micro interface characteristics of carbon nanotubes was analyzed by grey correlation method.The results show that the shear strength between layers has a great correlation with the temperature,pressure and the bonding energy of micro interface.In the experiment of carbon nanotubes reinforced automatic fibre placement,higher heating temperature,lower wire laying speed and higher wire laying pressure should be chosed,and a large interface bonding energy between CNTs and matrix on micro scale should be ensured. |
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