Due exceptional properties such as its high-temperature resistance, mechanical characteristics, and relatively lower price, the demand for carbon fiber has been increasing over the past years. The widespread use of carbon-fiber-reinforced polymers or plastics (CFRP) has attracted many industries. However, on the other hand, the increasing demand for carbon fibers has created a waste recycling problem that must be overcome. In this context, increasing plastic waste from the new 3D printing technology has been increased, contributing to a greater need for recycling efforts. This research aims to produce a recycled composite made from different carbon fiber leftover resources to reinforce the increasing waste of Polylactic acid (PLA) as a promising solution to the growing demand for both materials. Two types of leftover carbon fiber waste from domestic industries are handled: carbon fiber waste (CF) and carbon fiber-reinforced composite (CFRP). Two strategies are adopted to produce the recycled composite material, mixing PLA waste with CF one time and with CFRP the second time. The recycled composites are tested under tensile test conditions to investigate the impact of the waste carbon reinforcement on PLA properties. Additionally, thermogravimetric analysis (TGA), X-ray diffraction (XRD), and Fourier-transformed infrared spectroscopy (FTIR) is carried out on composites to study their thermal properties.

Construction projects are often challenged by tight budgets and limited time and resources. Contractors are, therefore, looking for ways to become competitive by improving efficiency and using cost-effective materials. Using three-dimensional (3D) printing for shaping materials to produce cost-effective construction elements is becoming a feasible option to make contractors more competitive locally and globally. The process capabilities for 3D printers and related devices have been tightened in recent years with the booming of 3D printing industries and applications. Contractors are attempting to improve production skills to satisfy firm specifications and standards, while attempting to have costs within competitive ranges. The aim of this research is to investigate and test the production process capability (Cp) of 3D printers using fused deposition modeling (FDM) to manufacture 3D printed parts made from plastic waste for use in the construction of buildings with different infill structures and internal designs to reduce cost. This was accomplished by calculating the actual requirement capabilities of the 3D printers under consideration. The production capabilities and requirements of FDM printers are first examined to develop instructions and assumptions to assist in deciphering the characteristics of the 3D printers that will be used. Possible applications in construction are then presented. As an essential outcome of this study, it was noticed that the 3D printed parts made from plastic waste using FDM printers are less expensive than using traditional lightweight non-load bearing concrete hollow masonry blocks, hourdi slab hollow bocks, and concrete face bricks.

In recent years, carbon fiber has experienced a significant surge in popularity attributed to its exceptional properties, including its high-temperature resistance, mechanical strength, and cost-effectiveness. Many industries have been attracted to the prevalent use of carbon-fiber-reinforced polymers or plastics (CFRP). However, the increasing demand for carbon fiber has created a waste recycling problem that needs to be addressed. This research aimed to develop a recycled composite using PET waste as a solution to the growing demand for both materials. The recycled carbon fibers were processed chemically and mechanically to generate power for this process. Various samples were tested with different proportions of CF (10%, 20%, 30%, and 40%) to analyze their mechanical properties. The recycled composites are examined under tensile test conditions to further explore the waste carbon reinforcement’s effect on polymers’ characteristics. Scanning electron microscopy was also utilized for mechanical morphology evaluations. After analyzing the data, it was found that samples containing 20% CF had the highest elastic modulus value among all the mixes. This is attributed to the reinforcing effect of the fibers. The Elasticity Modulus of the filaments increased with the concentration of CF, reaching its peak at 20% before decreasing. This trend is also apparent in the visual representations. When compared to recycling, the Elasticity Modulus value of 20% CF filament increased by 97.5%. The precise value for CF with a 20% filament is 4719.3 MPa. Moreover, the composite samples were analyzed using SEM to characterize them, and it was discovered that the incorporation of 20% CF/PET filler produced the composition with the highest strength.

This investigation aimed to comprehensively investigate the integrity and failure characteristics of deteriorated polymeric components produced through Fused Filament Fabrication (FFF) technology. The primary focus was to examine the performance of flawed 3D-printed samples, which were purposely designed and 3D-printed to incorporate a range of crack types and geometric features that were initially designed through CAD. This study adopted two main approaches to deal with the cracks by producing the flaws through design and laser processes. These specimens were subjected to destructive testing to gain valuable insights into the FFF-printed components’ performance and failure characteristics under the tensile mode, a significant concern in engineering applications. A Finite Element Analysis (FEA) was employed on the flawed and intact specimens to compare and correlate the experimental results with the simulation results. This study reveals the tested samples’ structural response and failure mechanisms under tensile loading conditions. Exceptionally, it was found that the faulty 3D-printed parts made by the laser process demonstrated less resistance to failure due to disturbing the 3D-printed extruded filament streams. In contrast, the flaws initially produced solely by the 3D printing process showed better resistance to mechanical failure due to the crack-bridging effect. It was observed that there were reductions of 11% and 32% in the failure load of the 3D-printed cracked sample and the laser-cracked samples, respectively, in comparison with the intact one. Additionally, the stress intensity factor showed a decrease of 20% in the laser-cracked sample compared to the 3D-printed one.

In this study, a finite element model was developed, and a detailed analysis was carried out to investigate the impact of inclusions on the mechanical characteristics of a 3D-printed composite sandwich beam that could initiate when printing the layers, especially during the transition period between the dissimilar material that would affect the interfacial strength between the layers that would cause the failure of the 3D-printed beams. Several parameters that could influence the failure mechanism have been investigated. These parameters include the location, size, material properties, and interfacial location of the inclusion along the beam. Linear elastic behavior has been adopted in this finite element analysis using the ‘Ansys’ simulation tool to model and analyze the defective beams compared to the intact ones. The effects of defects related to maximum shear stress (MSS) and maximum principal stress (MAPS) were investigated. The results revealed that the midpoint of the composite is highly stressed (31.373 MPa), and the concentration of stress decreases outward as we move toward the edges of the composite to reach zero at the edges. For the intact case, the deformation was maximum at the center of the composite (4.9298 mm) and zero at both ends of the beam. The MSS was highest at the center (23.284 MPa) and decreased gradually as we approached the ends on both sides to reach 0.19388 MPa at the edges, making the shear stress distribution symmetrical. The MAPS is constant throughout the beam apart from the lower face of the beam and is maximum at the face material. The MSS is high at the endpoints where we have the support reactions, which may weaken the entire material’s mechanical properties. It was also observed that along the load L3 (applied at 2 mm from the top face of the beam), the MSS values decrease as we move away from the center, which may cause failure at the end of the beam. It was also noticed that the presence of inclusions along load L2 (applied at 2 mm from the bottom face of the beam) initially causes a sharp decrease in MAPS while moving away from the center, at 25 mm, while the MAPS increases as it approaches the end of the beam. This increase in the MAPS near the beam support might be due to the reaction of the fixed support, which tends to oppose the applied flexural load and hence increases the principal stress capability of the beam.

This study assessed the effect of slicer-made interlocking joints on 3D printed sandwich panels manufactured through fused filament fabrication (FFF) in terms of flexural properties and energy absorption. Composites were prepared with thermoplastic polyurethane (TPU) as the core material and polyamide (PA), polylactic acid (PLA), polyethylene terephthalate (PET) as skin materials for each of the three composites, respectively. In order to assess the implications of internal geometry, 3D printing was done on five infill topologies (Cross-3D, Grid, Gyroid, Line and Honeycomb) at 20% density. All samples had 20% core density and underwent three point bending testing for flexural testing. It was noted that the Grid and Gyroid cores had the best performance in terms of maximum load capacity based on stretch-dominated behavior while Cross-3D and Honeycomb had lower strengths but stable moments during the bending process. Since Cross-3D topology offered the lowest deflection, it was selected for further experiments with slicer added interlocks at the face–core interface. This study revealed the most notable improvements as gains of up to 15% in peak load, 48% in maximum deflection, and 51% in energy absorption compared with the non-interlocked designs. The PET/TPU interlocked demonstrated the best performance in terms of the energy absorption (2.45 J/mm³) and peak load (272.6 N). In contrast, the PA/TPU interlocked exhibited the best flexibility and ductility with a mid-span deformation of 21.34 mm. These results confirm that slicer-generated interlocking interfaces lead to better load capacity and energy dissipation, providing a lightweight, damage-tolerant design approach for additively manufactured sandwich beams.