This article describes original carbon fiber impregnation procedure. The aim of this research is to determine carbon fiber impregnation process influence on mechanical properties of printed composite structures. 3D printing head and carbon fiber impregnation device were designed and produced. Three different polymer materials (PLA, PC, ABS) and solvent methylene chloride (DCM) were selected and solutions of different concentrations (2–10%) were prepared. 1 and 3K carbon fiber tow were impregnated with solutions (2–10%) and tensile tests of impregnated carbon fiber tow were performed. The correlation analysis revealed a strong relation between the tensile force of impregnated carbon fiber and mass of impregnated carbon fiber tow. For 3D printing 1 and 3K carbon fiber tow impregnated with 8 and 10% solutions were selected. Tensile tests were carried out to evaluate the mechanical properties of 3D printed composite structures. The obtained results revealed the dependency between the solution concentration and tensile strength, i.e. the higher the concentrations in carbon fiber impregnated with solution, the higher the tensile strength. This tendency is strong in PLA and PC impregnated 3K carbon fiber, however when the carbon fiber impregnated with ABS solution, the change in the results was not so significant. The obtained results can be used for the future development of different 3D printed composite structures.

Carbon fibre-reinforced materials are becoming more and more popular in various fields of industries because of their lightweight and perfect mechanical properties. Additive manufacturing technologies can be used for the production of complex parts from various materials including composites. Fused deposition modelling (FDM) is an excellent technology for the production of composite structures reinforced with short or continuous carbon fibre. In this study, modified FDM technology was used for the production of composites reinforced with continuous carbon fibre. The main aim of this study is to evaluate the shear strength of 3D-printed composite structures. The influence of printing layer height and line width on shear strength was analysed. Results showed that layer height has a significant influence on shear strength, while the influence of printing line width on shear strength is slightly smaller. Reduction of layer height from 0.4 mm to 0.3 mm allows increasing shear strength by about 40 percent. Moreover, the influence of the shear area and overlap length on shear force showed linear dependency, in which the shear area is increasing the shear force increasing proportionally. Finally, the results obtained can be used for the design and development of new 3D-printed composite structures.

Additive manufacturing (AM) techniques can be applied to produce carbon-fiber-reinforced polymer (CFRP) elements. Such elements can be exposed to different environmental factors, e.g., temperature, moisture, and UV radiation, related to their operational conditions. From a variety of environmental factors, the temperature is one of the most typical. Temperature strongly influences matrix material joining together CFRP components, resulting in material strength reduction. Therefore, it is important to understand processes in the composite material caused by temperature. This experimental work investigated the thermal effects on the performances of AM CFRP composites. Specimens with unidirectional (UD) alignments of the fiber reinforcement were printed using the fused deposition modeling (FDM) technique. The printed specimens were subjected to two different thermal conditions: stable continuous at 65 °C and cyclic temperature between 50 and 70 °C. Tensile testing was performed to study the mechanical strength and Young’s modulus of AM UD-CFRPs. In order to investigate the morphological structure on the surface of AM specimens, an optical microscope, scanning electron microscope (SEM), and digital microscope were utilized. Untreated (intact) samples attained the highest average tensile strength value of 226.14 MPa and Young’s modulus of 28.65 GPa. The ultimate tensile strength of the sample group subjected to stable heat treatment decreased to 217.99 MPa, while the thermal cycling group reduced to 204.41 MPa. The Young’s modulus of the sample group subjected to stable thermal exposure was decreased to 25.39 GPa, while for the thermal cycling group, it was reduced to 20.75 GPa. The visual investigations revealed that the intact or untreated specimen group exhibited lateral damage in top failure mode (LAT), the thermally stable group underwent edge delamination in the middle (DGM) as the nominated failure mode, and the explosive breakage at gauge in the middle (XGM) failure mode occurred in the sample from the thermal cycling group. Based on morphological observations at the microscale, the delamination, fiber pull-out, and matrix cracking were the dominant damages in the 3D-printed tensile-tested specimens. The molecular chains of the polymer changed their structure into an amorphous one, and only local motions of stretching occurred when the specimens were exposed to stable heating (prolonged). In the case of thermal cycling, the strain gradients were accumulated in the matrix material, and the local stresses increased as a result of the reheating and re-cooling exposure of the polymeric composites; the molecular motion of the long-range polymer structure was reactivated several times. Micro-cracking occurred as a result of internal stresses, which led to material failure and a reduction of the mechanical properties.

Additive manufacturing is a development of fabricating 3D parts layer by layer with complex geometries and utilized in numerous engineering structural applications. Fused deposition modeling technology provides higher design flexibility with aim of low cost and simplicity of material conversion to generate the composite parts. Previous studies have mainly focused on the manufacturing and characterization of continuous carbon fiber reinforced polymer composites (CCFRPCs) structure for fully dense and solid part structures and no study has been reported for porous CCFRPC parts. In this study, CCFRPCs porous structures were manufactured using FDM technology. The porous structures were fabricated with one perimeter shell by using two different types of infill patterns (grid and triangular) at three different infill densities levels (20%, 40%, and 60%). The reasons for developing such lightweight porous composite structures with continuous carbon fiber are the reduction of mass, efficient material utilization, energy consumption, and less waste generation. This study investigated the effects on tensile and flexural properties of composite specimens under uniaxial tensile loading and flexural loading, respectively. Fracture interface of the printed porous composites were examined and explored using optical microscope after performing mechanical tests. The experimental results demonstrated that infill pattern and density levels greatly affect the mechanical properties. The specimen printed using grid infill pattern with 60% infill density exhibited highest strength level in term of mechanical test and showed maximum tensile and flexural strength of 162.9 MPa and 127.24 MPa, respectively. While triangular infill pattern with 60% infill density level revealed the maximum tensile and flexural strength of 152.62 MPa and 117.53 MPa, respectively. Hence, from the results achieved in this study showed great potential and ability to replace fully dense and solid structure by the porous structure.