## 1 Introduction  
Additive Manufacturing (AM) is a rapidly growing area [1, 2]. By 2024, the market is expected to reach USD 24 billion [3]. On the other hand, composite materials offer the high directional strength of fiber reinforcement with the flexibility of an adaptable matrix [2, 4]. Technologies, such as the Markforged Two(r) printer [5], blend the best features of composites and AM [6], giving those materials load-bearing capabilities that can match that of Aluminum [7]. AM could be the technology that closes the gap between topological optimization and actual fabrication [8] because of its unique ability to manufacture many lattices and intricate geometries [9]. However, designers must have appropriate mechanical properties to implement such a flexible technique in components. Markforged(r) filed a patent in 2015 for a device that used Material Extrusion (MEX) to manufacture continuous fiber composites. A schematic of the composite MEX printing process is shown in Figure 1.  
MEX, arguably the most popular of the AM technologies [10], is a manufacturing technique in which the topology is reconstructed layer by layer from a G-code file previously converted to the Standard Template Library language. For Markforged(r) composites, this process is performed by a software in the cloud called Eiger(r) [5]. The options to create a part using the Markforged(r) technology are broad in number and range. Their impact has been documented [2; 4; 11; 12; 13]. The options are the type of continuous fiber (carbon, Kevlar, fiberglass, and high-temperature fiberglass), fiber volume fraction (\(V_{f}\)), fiber fill type (concentric and isotropic, as seen on the top of Figure 2), the pattern of matrix filling (hexagonal, triangular, square, as seen at the bottom of Figure 2, and solid fill), matrix fill density, matrix deposition angle, and fiber deposition angle. The mechanical characterization for different matrix fillings from geometry and material properties is thoroughly reviewed in [4; 11]. Markforged, the sole provider of matrix and fiber, has characterized individual mechanical properties for matrix (Nylon and Onyx(r)) and continuous fibers, as seen in Table 1. It has to be noted that Onyx(r) is a composite itself, a nylon matrix reinforced with chopped carbon fiber. Thus, it shows multiple options and ranges to configure a part. Predicting the material properties is still a challenge. The available prediction models for mechanical properties do not include all the variables [18; 19], a task that has to be performed experimentally [11; 13; 20; 21] or numerically [15; 18]. However, the existing numerical modeling requires highly skilled users, a deep understanding of the mechanical behavior \begin{table}
\begin{tabular}{l c c c} \hline \hline
**Material** & \(E\) **[GPa]** & \(\sigma\) **[MPa]** & \(\epsilon\) **\%** \\ \hline Nylon & 1.7 & 33.5 & 4.5 \\ Onyx & 1.4 & 36 & 33 \\ Standard & ASTM D638 [16] & ASTM D638 [16] & ASTM D638 [16] \\ Carbon & 60 & 800 & 1.5 \\ Fiberglass & 21 & 590 & 3.8 \\ Kevlar & 27 & 610 & 2.7 \\ Standard & ASTM D3039 [17] & ASTM D3039 [17] & ASTM D3039 [17] \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Mechanical properties as provided by Markforged [5]. E is elastic modulus, \(\sigma\) is strength, and \(\epsilon\) is strain. Figure 1: Schematic of composite MEX printing. Adapted from [6]. Figure 2: Options to configure a part for fiber layout and matrix filling, adapted from [14; 15]. of composite materials, and fairly advanced numerical modeling skills [18; 19; 22; 23; 24]. Such requirements are mainly due to the composite's nature on top of the intrinsic anisotropy of AM. In order to ease the task, the authors of [4] suggested modeling mechanical performance for this kind of composite as isotropic materials with bulk mechanical properties obtained from mechanical testing and linking them to the printing variables. Therefore, the need for a model to predict mechanical properties (strength and elasticity), including the printing variables, or at least the most representative, arises.