Anisotropy and ageing effect on the mechanical behaviour of 3D-printed short carbon-fibre composite parts

The effect of ageing and anisotropy in 3D-printed composites including short carbon fibres embedded in a polyamide (PA/nylon & REG;) matrix is analysed experimentally. A testing campaign including tensile and fracture toughness coupons with 100% infill is studied. The effect of anisotropy induced by the Fused Deposition Modelling (FDM) procedure, caused by the alignment of the fibres with the deposition direction (raster angle), is presented. Specifically, results showed that the Young modulus and the elastic limit values are lower for the +45/-45 infill configuration with respect to the 0/90 infill configuration. Conversely, the ultimate tensile strength, the ultimate tensile strain, and the fracture toughness values are higher for the +45/-45 infill configuration. Moreover, the crack path obtained in fracture toughness coupons always followed the raster angle. Additionally, experimental results show that the 3D-printed composite parts keep the hygrothermal properties associated to the matrix, thus an ageing effect is observed even for standard environmental conditions (room temperature, 50% relative humidity). Specifically, Young modulus, elastic limit and ultimate tensile strength values are lower for the older coupons. The ultimate tensile strain is higher for the older coupons while the fracture toughness is similar. Coupons stored in a desiccator also varied the properties but in a slightly manner.