Preparation And Properties Of Sandwich Fiber Reinforced Composites Based On 3D Printing

As one lightweight,high-strength,high-performance structure,the sandwich structure is used in aerospace,construction,military and other fields widely.Low cost,high performance and low energy consumption are the development direction of modern advanced manufacturing technology.Although sandwich structure can achieve the effect of light weight and high strength through the design of sandwich structure,its preparation process has the problems of long process chain,poor product designability and high energy consumption.As an additive manufacturing technology,3D printing can realize the manufacturing of 3D entities.It has the characteristics of flexible design and rapid molding,and can remedy the problems existing in the preparation of sandwich structure effectively.However,3D printing is limited by printing materials and has the disadvantages of poor mechanical properties of printed products.In order to solve the problem of poor mechanical properties of 3D printing,currently the most extensive approach is to add reinforced fiber into 3D printing materials to prepare fiber reinforced composites and improve the mechanical properties of the materials.This paper adopts high-performance aramid fiber as reinforcing,3D printing consumables polylactic acid（PLA）as the matrix by fused deposition modeling（FDM）3D printing preparation of fiber reinforced composite sandwich structure,and modified by phosphoric acid,silane coupling agent modification（KH-560）to improve the combination of aramid fiber and PLA matrix effect,increase mechanical properties of the material.The effects of FDM printing parameters on the mechanical properties of PLA corrugated sandwich structure prepared by pure PLA and PLA corrugated sandwich structure reinforced by fiber were studied.In addition,ultrasonic nondestructive testing technology is used to analyze the defects of 3D printing materials and study the types and uniformity of defects under various printing conditions.The main conclusions are as follows:（1）When pure PLA is printed,the effects of various printing parameters on the accumulation and mechanical properties of the sample are as follows:when the printing layer height increases,the accumulation effect of each layer gradually becomes worse,the pores between each layer gradually become larger,and the mechanical properties of the sample gradually decline;Print at higher temperatures,the mechanical properties of the specimen showed a trend of decrease after the first increase,when the print temperature is 210℃,in this paper the research scope,the mechanics properties of the sample is best;With the increase of printing speed,the accumulation effect of PLA on the surface of the sample gradually deteriorated,and the mechanical properties of the sample decreased to a certain extent.（2）After the addition of the enhancement,the printing speed had a great impact on the binding effect of the fiber and PLA matrix.With the improvement of the printing speed,the binding effect of the fiber and PLA matrix gradually became worse,and the fiber was not completely coated by the PLA matrix.On the basis of selecting the optimal printing speed(40mm·s^-1)in this study,the influence law of the printing layer height and printing speed on the mechanical properties of the sample is roughly the same as that of pure PLA printing.（3）After aramid fiber is modified,its surface morphology,macromolecular chain groups and tensile strength will all change to some extent.After modification of phosphoric acid and silane coupling agent,the morphological change of the fiber gradually intensifies as the concentration of the treating agent increases.When the concentration of the treating agent is too high（phosphoric acid:40%,silane coupling agent:20%）,the morphological change of the fiber surface has been significantly changed.With the increase of the concentration of the treatment agent,the tensile strength of aramid fiber decreases gradually.After modification of phosphoric acid and silane coupling agent,aramid fiber macromolecular chain will graft some functional groups.（4）The modified aramid fiber and PLA matrix were combined to prepare corrugated sandwich structure composites.With the increase of the modifier concentration,the mechanical properties of the sample showed a trend of increasing first and then decreasing,which was roughly the same as the effect law of fiber modification.（5）Ultrasonic nondestructive testing technology is used for nondestructive testing and analysis of 3D printing materials.When pure PLA prints,the defect types of the sample are mainly pore and loose structure.After aramid fiber is added,the defect degree of the sample increases.After aramid fiber is modified,the pore defects of the sample will decrease to a certain extent.