## 6 Systematic Literature Review  
### General Trends in Simulation Approaches  
To provide a comprehensive overview of the current modeling approaches in FFF using PLA, a comparative analysis of relevant studies was conducted. Table 1 summarizes the characteristics of the selected studies, including materials analyzed, methodologies employed, simulation software used, key parameters, and principal findings. This synthesis offers a structured basis for understanding the modeling strategies applied in the context of FFF with PLA. A consistent feature across the studies is the reliance on numerical tools adapted to simulate thermal, mechanical, and rheological behavior during filament deposition. These include commercial platforms equipped with proprietary or customizable algorithms, such as Ansys(r), Abaqus(r), COMSOL [79], UMFPACK [80], Slic3r [58], multiscale algorithms [81], and other in-house numerical models [82]. Figure 21: Stress–strain curves of ABS–SCF composite specimens under uniaxial tensile loading for (**a**) cross-ply and (**b**) angle-ply printing strategies, comparing computational models CM-1 and CM-2 with experimental results. Adapted with permission from [76]. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**REF** & **Analysis** & \
\begin{tabular}{c} **Material** \\ **Evaluated** \\ \end{tabular} & **Software** &
\begin{tabular}{c} **Parameters** \\ **Analyzed** \\ \end{tabular} & **Results** & **Limitations and Gaps** \\ \hline
[2] & RW & - & R (Bibliometry, VOS viewer & Keywords, research & Identifies growth in AM linked to & Focused on Scopus data, lacks \\  & & & & trends, co-authorship, & Industry 4.0 (A, IoT) and 5.0 & technical depth on AM process \\ \hline
[3] & RW & Polymers & Ansys, Abaqus, COMSOL, MATLAB & Melt flow, thermal behavior, mechanical properties. & Numerical models can predict & Limited experimental validation \\  & & & & behavior, mechanical & process behavior but often rely on & and oversimplified material \\ \hline
[4] & RW & FRP & – & Applications, challenges, material systems, performance. & Reviews CFRP benefits in multiple sectors; emphasizes lightweighting and customizability. & Broad scope lacks deep technical analysis or modeling of fiber \\ \hline
[9] & RW & Natural fibers and mineral composites & R (Bibliometry, VOS viewer & Sustainability, biodegradability, fiber/matrix interaction. & Natural fillers offer eco-friendly & Lacks standardization and process control; limited \\  & & & & fiber/matrix interaction. & treatment improve properties. & mineral-reinforced AM data. \\ \hline
[17] & RW & Thermoplastics & – & Material selection, design parameters, trends. & Covers extrusion methods, hybrid processes, and polymer categories. & Lacks coverage of real-time control, multi-materials, and long-term validation. \\ \hline
[19] & RW & Thermoplastics & – & Void types, formation causes, parameter effects. & Defines four main void types: parameter tuning and post-processing reduce defects. & No real-time detection methods: predictive modeling is still limited. \\ \hline
[32] & RW & - & – & Inelastic models, flow-type parameters, rheological equations. & Discusses flow-type parameter use in CFD to improve realism for non-Newtonian polymer melts. & No direct AM application serves as a foundational theory for future simulations. \\ \hline
[36] & RW & Polymers and Composites & Ansys, COMSOL, MATLAB & Melt flow, solidification, warpage, fiber & Models capture key process stages, including melt and solidification, but lack integration. & Few fully coupled models; limited experimental validation. \\ \hline
[8] & RW & Polymers and Composites & – & Material type, printing temperature, phase change, actuation behavior. & Residual stresses affect shape recovery and structural deformation; driven by thermal gradients and anisotropic effects. & Lack of quantitative models and experimental studies on stress evolution during actuation. \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Systematic literature review.