Prediction and analysis of flexural stiffness for 3D-printed continuous fiber–reinforced composites with different matrix fill ratios and layer orders

Bending load is often encountered in engineering applications, but it is less studied for 3D-printed continuous fibre–reinforced composites (CFRC). We present the flexural properties of 3D-printed composites as a function of layer order and matrix fill ratio. We applied Classic Laminate Theory to estimate the flexural modulus and showed that the Kerner-Hashin model is suitable for taking voids into account when calculating the elastic properties of the matrix layer. Using optical microscopic analysis, we identified the main defect sources of 3D-printed CFRC structures, such as voids, fibre waviness, fragmentation and poor bonding between laminas. By performing failure analysis based on the Fibre Bundle Cell method, we found that the use of top/bottom-type reinforcement instead of alternating layering will increase the reliability of the 3D-printed composites under bending load. Furthermore, the failure process will be more gradual and cover higher load levels, which increases safety.