Investigation On Anisotropy Of Fiber Reinforced Polymer Composites In 3D Printing

3D printing technology was one of the hot research topics in manufacturing industry.Due to the limitations of 3D printing materials and printing processes,the mechanical properties of 3D printing products are low,which limits the application of 3D printing products.When the 3D printed material was reinforced with fibers,it was found that the fibers were oriented by shear force during the 3D printing process,leading to the composite materials of 3D printing were anisotropic.In this paper,carbon fiber reinforced polylactic acid composites were prepared by fused deposition method,and carbon nanotube and whisker reinforced photosensitive resin composite materials were prepared by photocuring molding method to study the fiber orientation mechanism and the anisotropy of the composites in the two 3D printing methods.The main research contents are as follows:(1)Carbon fiber/polylactic acid composite samples with three built orientations(X,Y,Z)were prepared by fused deposition 3D printing technology and the mechanical properties and tribological properties of the composites were studied.The results showed that the tensile strength,impact strength and elongation at break of the three built oriented samples all showed the trend of X sample>Z sample>Y sample,and the sliding friction coefficient in three directions showed the trend of X direction <Y direction<Z direction.According to the analysis,the orientation of the carbon fibers in the printing direction and the interface bonding force of the fuse were the main factors for the anisotropy of the composite.(2)The effects of different printing parameters of fused deposition 3D printer on the mechanical properties of three built oriented samples were investigated,as well as the effects of heat treatment and microwave treatment on the mechanical properties of 3D printed samples.The results showed that with the increase of the printing temperature,the tensile strength and impact strength of the X sample did not change significantly,and the tensile strength and impact strength of the Y sample and Z sample increased first and then decreased.With the increase of thickness,the tensile strength and impact strength of the X sample and Z sample gradually decreased,and the tensile strength and impact strength of the Y sample gradually increased.With the increase of printing speed,the tensile strength and impact strength of X sample did not change significantly.The tensile strength and impact strength of Y sample increased first and then decreased,and the tensile strength and impact strength of Z sample increased gradually.The tensile strength of the Xsample and Y samples was improved after heat treatment and microwave treatment.According to the analysis,the density,interface bonding force and oxidation degree of the fuse surface were the main factors affecting the mechanical properties of the composite in three directions.(3)Two kinds of horizontally and vertically built oriend carbon nanotubes and potassium titanate whisker reinforced photosteensitive resin composite samples were prepared by photocuring 3D printing technology,and the photocuring speed,mechanical properties and tribological properties of the composites were investigated.The results showed that the tensile strength,impact strength and hardness of the horizontally constructed oriented sample were all larger than those of the vertically oriented orientation,and the frictional coefficient and the wear rate of the horizontal plane were both smaller than the vertical plane.According to the analysis,unlike fused deposition 3D printing,uncured homogeneous small molecules in photocured 3D printing had a certain penetration and good bonding ability with the formed surface.The bonding strength between the layers after curing is not much different from that of the resin body.Orientation of carbon nanotubes and whiskers parallel to the horizontal plane was a major factor leading to anisotropy of the composite.