Fused Deposition Modeling (FDM) is one of the most widely used additive manufacturing processes for fabricating complex geometries from thermoplastic polymers. Despite its popularity, the technique faces limitations due to poor mechanical characteristics and inconsistent quality, restricting its large-scale industrial adoption. Over the past two decades, significant research has focused on incorporating composite reinforcements to overcome these challenges. Strengthening the polymer matrix with nanoparticles, short fibers, or continuous fibers has been shown to enhance mechanical, thermal, and electrical properties beyond those of the neat polymer. The performance of FDM-printed composites strongly depends on the quality of feedstock filaments and precise, error-free printing execution, making them critical to scalability. This review highlights advances in FDM-based materials tailored for industrial applications, including biomedical, tooling, construction, defense, automotive, electronics, and aerospace. Structural integrity, microstructural evolution, mechanical performance, and their correlation through modeling techniques are discussed in detail. Reported studies reveal similarities in microstructures and properties across various FDM composites, which are categorized here by reinforcement type and application. This review provides a unified framework that integrates material development, microstructural characterization, and predictive modeling to establish clear process-structure-property relationships in FDM-printed polymer composites, offering practical insights for their industrial application.
The pre-assembly of nano-silica (NS) and carbon nanotubes (CNTs) into structured hybrid modifiers offers a potential route to improve nanomaterial dispersion and interfacial activity in cementitious systems. However, the relationship between pre-assembled NS/CNTs architecture, cement hydration kinetics, and nanostructure development remains insufficiently quantified. In this study, ellipsoidal pre-assembled NS/CNTs composites were prepared through a chemical activation route and incorporated into Portland cement paste. Their effects on hydration evolution, phase assemblage, pore structure, and microstructure were investigated using isothermal calorimetry, X-ray diffraction, thermogravimetric analysis, nitrogen adsorption, scanning electron microscopy, and Krstulovi & cacute;-Dabi & cacute; kinetic modeling. Under the present mix design and test conditions, the optimized pre-assembled NS/CNTs composite shortened the induction period and increased the main hydration peak intensity by approximately 100% relative to the plain reference group, indicating enhanced heterogeneous nucleation. Thermogravimetric analysis, interpreted using the adopted dilution-correction framework, indicated an apparent CH-consumption rate of 55.5% relative to the plain reference group, which is consistent with the occurrence of a pozzolanic reaction. Nitrogen adsorption further indicated pore refinement, with total porosity reduced by 52.4% relative to the plain reference Group 5 and the most probable pore diameter shifting from the capillary-pore region toward the gel-pore region. These results support a triple synergistic mechanism involving heterogeneous nucleation, pozzolanic reaction, and multi-scale filling. The findings provide evidence supporting the hydration-regulation role of pre-assembled NS/CNTs composites and offer a mechanistic basis for designing nano-engineered cementitious materials with improved microstructural density.
