Mechanical Properties And Heat Treatment Mechanism Of 3D Printed Continuous CF/PA Composites

Composite materials are widely used in various fields due to its good service performance,but the traditional manufacturing limits the forming of complex structural parts.3D printing opens up a new way for the design and manufacture of high-performance complex composite structures.However,problems such as high porosity and weak interlayer adhesion limit the further application of 3D-printed composites in advanced manufacturing and high-end equipment fields.In this paper,continuous carbon fiber and short carbon fiber filled polyamide forming synergetic reinforced composites,the mechanical properties of 3D-printed composites based on FDM were studied considering heat treatment and printing parameters.The main contents are as follows:(1)The effects of heat treatment on the dimensional stability and flexural properties of continuous carbon fiber reinforced composites(CCFRCs)prepared by FDM was studied.The effect of stacking sequence on CCFRCs performance was evaluated by stacking CCF layers centrally and dispersively.The result showed that the dimensional change of CCFRCs during heat treatment was much closely related to the microstructure change than the material crystallization.Heat treatment could improve the flexural properties of CCFRCs by increasing matrix crystallinity and decreasing porosity.Besides,heat treatment delayed the crack initiation of CCFRCs,and the crack propagation rate was reduced when stacking CCF layers dispersively.(2)The peeling strength and failure behavior of CCFRC layers at different filling angles were evaluated.Combined with the microstructure changes,the strengthening mechanisms of CCFRCs mechanical properties by heat treatment were further revealed.It was found that the interlaminar peel strength of MM was the highest in CCFRCs,followed by CM and CC.When the relative angle between the peeling path and the delamination extension direction was 45°,and the continuous fiber bundles splited to form bridging phenomenon,the peel strength of CCFRCs was higher.The enhancement of interlaminar properties of composites was closely related to the microstructure changes caused by heat treatment,which reduced local pores,increased the interface contact,and made partial pores became crack arrest point due to merge and rounded.(3)The finite element model of continuous fiber reinforced composites was established by ABAQUS.The fiber/matrix layers’ damage initiation,damage propagation and the failure modes at stable delamination propagation for CCFRCs during I-peel failure were analyzed.The simulated peel strength of CCFRCs was very close to the experimental results,which verified the correctness of the model.Through the damage analysis of printed layers in different peeling stages,it was found that CCF layer played a major bearing role in CCFRCs.Similarly,the existence and distribution of CCF layer would affect the damage failure mode of adjacent matrix layers,namely,the stress distribution and damage propagation behavior of matrix layers were affected by the filling angle of CCF layers.Based on the preliminary experimental and simulation results,the CCFRCs composite was optimized and heat treated,and the printed composite with high stiffness and energy absorption effect was obtained.