Fused Deposition Modeling (FDM) is an additive manufacturing technology that has emerged as a promising technique for fabricating 3D printed polymers. It has gained attention recently due to its ease of use, efficiency, low cost, and safety. However, 3D-printed FDM components lack sufficient strength compared to those made using conventional manufacturing methods. This low strength can be mainly attributed to high porosity and low sinterability of layers and then to the characteristics of the polymer used in the FDM process or the FDM process itself. Regarding polymer characteristics, there are two main types of reinforcing fibers: discontinuous (short) and continuous. Continuous-fiber reinforced composites are becoming popular in various industries due to their excellent mechanical properties. Since continuous reinforcing fibers have a more positive effect on increasing the strength of printed parts, this article focuses primarily on continuous long fibers. In addition to polymer characteristics, different mechanisms have been developed and introduced to address the issue of insufficient strength in 3D-printed FDM parts. This article comprehensively explains two main FDM mechanisms: in-situ fusion and ex-situ prepreg. It also provides relevant examples of these mechanisms using different reinforcing elements. Additionally, some other less frequently utilized mechanisms are discussed. Each mechanism has its own advantages and disadvantages, indicating that further development and modification are needed to increase the strength of 3D-printed FDM parts to be comparable to those produced using traditional methods.

This study aims to systematically experimental investigate the influence of infill-patterns (IPs) on specific mechanical responses of parts fabricated by fused deposition modeling (FDM). A poly-lactic-acid (PLA) feedstock filament is utilized in the manufacturing process. Furthermore, six types of infill-patterns (deposition angle), namely full honeycomb, rectilinear, triangular, fast honeycomb, grid, and wiggle, are designed and printed. In order to determine the mechanical properties of manufactured parts, tensile tests are carried out. The mechanical properties such as extension, stress, elongation, energy, and Young’s modulus are considered as objective functions. As a result, there is a direct correlation between mechanical properties and infill patterns. Thus, it is essential to select the best infill-pattern in terms of their applications, giving sufficient strength without overdoing time and cost. Based on the results, a triangular infill-pattern has a maximum value of ultimate tensile strength and E-module (15.4 and 534 MPa, respectively). On the other hand, the wiggle pattern is more flexible.

For the first time, the synergy of shape memory polymer (SMP) blending, 4D printing, and cold programming (CP) are investigated for improving the functionality of the shape memory effect (SME), increasing medical applications of porous structures, direct programming, and removing current limitations. Porous PLA-TPU structures with different printing patterns and applied deformation were CPed under constrained and non-constrained compression modes at room temperature and were recovered in the rubbery phase. The shape fixity and shape recovery ratios were calculated and the cross-section morphology was examined with scanning electron microscopy (SEM). The shape fixity values were in the range of 39.75%–71.27%, while almost complete shape recovery ratios (100%) were observed for all porous samples. Low shape fixity ratios can be justified due to the existence of two steps of spring-back and structure relaxation after unloading in cold programming, resulting from elastic and viscoelastic behavior. The glass transition temperature of the PLA-TPU blend was 69 °C and shifted to raw materials, indicating the possibility of some interaction between the two components. SEM images showed the uniform distribution of TPU particles and matrix-droplet morphology in the PLA-TPU blend. After printing, TPU droplets were stretched and the sea-island morphology was observed in some segments.

In this study, Acrylonitrile butadiene styrene (ABS) with three different ratios of 30%, 50%, and 70% is used to enhance the shape memory and mechanical properties of Polyethylene terephthalate glycol (PETG). Additionally, morphology, printability, and dynamic thermomechanical analysis are also examined. The thermal test results show that PETG‐ABS compounds have two transition temperatures in the range of 80 and 110 °C, which are related to the components. By changing the weight percentage of PETG from 30 to 70%, three morphologies of matrix‐droplet, sea‐island, and combination of co‐continuous and matrix‐droplet are observed. The results of the mechanical properties show an increase in strength with the increase of ABS, which can be justified due to the higher strength of ABS compared to PETG. The highest tensile strength of 32.48 MPa and 15.16% elongation is obtained for PETG‐ABS(30‐70) and PETG‐ABS(70‐30), respectively. Due to the better shape memory performance of PETG, PETG‐ABS(50‐50) and PETG‐ABS(70‐30) have complete shape recovery, and with the increase of PETG, the shape recovery rate also increased. This diversity in morphology, mechanical properties, and shape memory effect is one of the goals of this research which is well fulfilled.