## 7 Discussion and Future Trends  
The evolution of numerical simulations in FFF has significantly advanced the understanding of material flow, thermal effects, and mechanical behavior, leading to better process control and part optimization. However, challenges remain, particularly in accurately predicting material behavior, improving real-time detection, and optimizing fiber reinforcement strategies. While computational models and experimental studies have enhanced our knowledge of extrusion stability, interlayer adhesion, and residual stress formation, gaps persist in multi-scale modeling, process standardization, and large-scale industrial implementation. One of the primary limitations in melt flow modeling is the incomplete integration of pseudoplastic and viscoelastic effects, polymer shrinkage, and multi-phase interactions in numerical simulations. Current CFD studies have refined predictions of filament shape evolution and deposition flow, but they often assume Newtonian or isothermal conditions, failing to capture non-Newtonian shear-thinning behavior in thermoplastics [51]. Future research should focus on advanced multi-phase CFD models that couple thermal, rheological, and viscoelastic properties, enabling higher-fidelity extrusion simulations that align with experimental results. Additionally, the impact of high-speed extrusion on melt behavior remains underexplored, requiring models that incorporate shear stress-induced polymer degradation and flow instabilities under rapid deposition conditions [29]. The cooling and solidification phase is another field requiring further study, particularly regarding heat transfer mechanisms, interlayer diffusion, and generated residual stresses. While previous studies have confirmed that controlled chamber environments and print bed heating reduce residual stress and warping [49], there is a lack of standardized thermal models that account for material-dependent cooling rates and anisotropic heat conduction in fiber-reinforced composites. Future studies should integrate thermo-mechanical models with in situ temperature monitoring to predict real-time stress evolution during the printing process. Additionally, research should focus on adaptive cooling strategies, such \begin{table}
\begin{tabular}{c c c c c} \hline
**Software/Criteria** & **Potentiality** & **Usability** & **Scalability** & **Accessibility** \\ \hline Abaqus & High & Very high & High & High \\ Ansys & Very high & High & Very high & High \\ \hline \end{tabular}
\end{table} 
Table 2: Software comparison based on specific criteria. as localized heat control near the extrusion zone, to prevent premature solidification and adhesion defects [41]. The thermo-mechanical behavior of FFF-printed components is significantly affected by deposition-induced residual stresses, temperature gradients, and the anisotropy arising from the layer-by-layer manufacturing process. Although coupled CFD-FEA models have improved predictions of deformation and internal stress distribution, many simulations lack material-specific calibration, particularly for biocomposites and high-performance polymers [53]. Future research should focus on multi-scale simulation frameworks that integrate real-time temperature tracking, stress relaxation mechanisms, and phase transitions to improve stress accumulation modeling. Moreover, increased efforts toward developing standardized validation protocols will be crucial to bridging the gap between simulations and experimental reality, ensuring that numerical models provide reliable predictions for industrial applications. The characterization of material properties in FFF presents additional challenges due to anisotropic behavior, microstructural defects, and complex fiber-polymer interactions. While previous studies have validated the effect of building orientation, raster angle, and layer thickness on mechanical strength, existing models often overestimate failure strength by neglecting interfacial bonding imperfections [59, 60].