Study On The Deformation Failure And Aging Mechanisms For Continuous Fiber Reinforced Composites Fabricated By Fused Deposition Modeling

Fused filament fabrication was a promising technique for the fabrication of complex composites parts filled with continuous fibers.In order to ensure the long-term durability and safe application of continuous fiber reinforced composites,it was of great importance to evaluate the effect of aging on their mechanical performances.In this paper,failure and aging mechanisms for continuous glass fiber reinforced composites fabricated by fused deposition modeling(FDM CGFRCs)were studied.Experimental and numerical modelling of mechanical properties for FDM CGFRCs were analyzed.This paper comprised several sections as following:Firstly,the relationships between structure of FDM CGFRCs and their mechanical properties and aging resistance were studied.Three types of specimens were prepared:specimens without continuous fiber reinforced(uRCs),specimens reinforced with concentrated stacking of continuous glass fiber layers and with separated stacking of continuous glass fiber layers.The flexural properties of FDM CGFRCs under different hygrothermal aging time were studied.Macro-micro failure mechanisms were analyzed.Additionally,the Fickian model was used to understand moisture absorption and diffusion responses of FDM CGFRCs.The results showed that flexural modulus and flexural strength were significantly improved by continuous fibers.Compared with specimens reinforced with concentrated stacking of continuous glass fiber layers,specimens reinforced with separated ones had higher flexural modulus and strength.Moisture absorption of FDM CGFRCs was higher than that of uRCs.After 30 days of aging,flexural modulus and strength for uRCs increased due to due to the recrystallization of PA6,while those for FDM CGFRCs decreased due to weakened interlayer bonding.Moreover,the problem of delamination was more and more serious with increasing aging time.Then,the failure and ageing mechanisms of Matrix/Matrix interlayer interface(M/M),Matrix/continuous glass fiber interlayer interface(M/G)and of continuous glass fiber/continuous glass fiber interlayer interface(G/G)were studied.Floating roller peel test was used.The results showed that bonding strength for unaged M/M was the highest of three kinds of interlayer interfaces,while for unaged G/G was the lowest.After 30 days of aging,retention of bonding strength for M/M was the highest,while for M/G was the lowest.The main failure modes of unaged M/M were PA6 plastic deformation and ductile fracture,while of M/G and G/G were continuous glass fiber/PA6 debonding.After 30 days of ageing,the fracture transferred from plasticity to brittleness.Additionally,the bonding of continuous glass fiber/PA6 weakened.Finally,finite element model was used to simulate mechanical responses and failure behaviors of FDM CGFRCs.Hash in criteria was applied to the damage prediction of FDM CGFRCs.Cohesive elements were used to simulate the delamination behaviors.Moreover,stacking sequence of continuous glass fiber layers was optimized in order to improve the mechanical properties and durability for FDM CGFRCs.The results showed that load bearing capacity of FDM CGFRCs could be improved when continuous fiber layers were deposited at the compression and tensile side of specimens.Higher stiffness and durability of FDM CGFRCs could be obtained when 15 layers of continuous fiber were stacked on the compression side and 15 layers were stacked on the tensile side.