Preperation of Modified Epoxy-based Thermosetting Composite and Its 3D Printing Method
Supervisor:shang jian zhong wang zhuo
Thermosetting epoxy resin composites are lightweight,chemically stable with good mechanical properties.As a result,they are gradually replacing metallic materials and widely used in aerospace vehicles and other fields.In this thesis,3D printing technology of this sort of materials,which are strengthened and toughened synergistically with multi-scale reinforcements,was studied.According to nozzle height,extrusion rate,extrusion speed and nozzle moving speed parameters of the printing process,the printing process was optimized and a principle prototype 3D printer was developed.In order to solve the 3D printing problems of thermosetting composite materials,the material preparation and the printing process were studied.The main work and innovation of this thesis are as follows:(1)According to the performance and printable requirements of the thermosetting composites used in military unmanned aerial vehicles and fighters,the type and content of the additives including the matrix materials,curing agents,diluents,thickeners and reinforcements are determined.The component design and preparation process of the thermosetting composite matrix which can be used for extrusion 3D printing were studied,and the testing and analysis methods of its mechanical properties,thermal properties and rheological performance were determined.(2)Ball milling and liquid phase oxidation-ultrasonic cooperative process were adotped to obtain the surface modified carbon fibers.The optimal process parameters were determind.And the surface morphology and wettability of carbon fibers were studied before and after surface modification.The influence rule of the average length and contents of carbon fibers on the mechanical performance of the composites were studied.A modified rule of mixtures,which can predict the elastic modulus of the composites in a large range,was proposed.Finally,the minimum average length and the optimal contents of carbon fibers were determined.(3)The multi-scale filler synergistic modification technique is proposed to enhance the strength and toughness of the composites.By adding the micron-scale and nano-scale fillers to the composite matrix and optimizing the content,surface treatment process and dispersion method of the fillers,the comprehensive performance of the polymer can be improved without losing other properties,especially its fracture toughness.A modified Halpin-Tsai model was proposed to predict the elastic modulus of the composites.The strengthening and toughening mechanism of epoxy composites by multi-scale fillers were discussed.In addition,the influence of multi-scale fillers on the viscous-temperature properties and rheological performance of epoxy-based composites was analyzed,and the corresponding parameters in the rheological model were determined to predict the printing process window.(4)The rheological performance of epoxy-based composites were designed through adding the thickeners.The composite was transformed from a Newtonian fluid to a non-Newtonian fluid.The rheological performance of epoxy-based composites under different compositional conditions is different.By analyzing the storage shear modulus,loss shear modulus and yield shear stress,the rheological properties of the composites which are suitable for extruded 3D printing were determined.(5)An efficient layered algorithm for STL model was proposed.The triangular facets in STL model were sorted and eliminated,and the facets that intersected with the layered cut plane were extracted rapidly.Finally,the stratified tangent plane was intersected with each facet.Compared to commercial softwares,the proposed algorithm was about 1.5 times faster.The prototype of pneumatic extruded 3D printer was set up.The influence of the nozzle height,extrusion rate,extrusion speed and nozzle speed on the printing results was analyzed.The calculation method for the critical nozzle height of multi-layer printing was presented,and the compensation factor was chosen.