# Recent Advances in Additive Manufacturing of Fibre-Reinforced Materials: A Comprehensive Review
## 3 Evaluation
### Quasi-Static Mechanical Testing
#### 3.1.2 Bending Testing  
Bending testing evaluates the flexural strength and stiffness of mechanical components. In bending tests, the specimen is placed on two supports, and a load is applied at the centre or multiple points along its length until it bends or fractures. The most common testing apparatus are the three- and four-point bending tests, as shown in Figure 3c,d and Figure 4. Each method provides different results, so this review focused mainly on results from the three-point bending apparatus. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Study** & **Technology** & **Materials** & \
\begin{tabular}{c} **Ultimate Tensile** \\ **Strength (MPa)** \\ \end{tabular} &
\begin{tabular}{c} **Tensile Modulus** \\ **(GPa)** \\ \end{tabular} & **Standard** \\ \hline Krajangsawasodi & Prepre extrusion & ABS & \(24\pm 1\) & \(2.1\pm 0.2\) & ASTM D-638 \\
[62] & Prepre extrusion & ABS-CF & \(70\pm 4\) & \(8.91\pm 1\) & ASTM D-638 \\ \hline [PERSON] [60] & Prepre co-extrusion & ABS & \(23.4\pm 1.4\) & \(1.37\pm 0.08\) & ASTM D-638 \\  & Prepre co-extrusion & ABS-BASALT & \(120.82\pm 3.75\) & \(5.83\pm 0.23\) & ASTM D-638 \\ \hline [PERSON] [65] & Prepre extrusion & ONYX & \(29.9\) & \(0.818\) & ASTM D3039 \\  & Prepre extrusion & ONYX-CF & \(434\) & \(92.9\) & ASTM D3039 \\  & Prepre extrusion & ONYX-CF & \(484\) & \(104\) & ASTM D3039 \\ \[PERSON] [66] & Prepre extrusion & ONYX-CF & \(90\pm 8.06\) & \(1.42\pm 0.12\) & ASTM D-638 \\ \[PERSON] [60] & Prepre co-extrusion & PA & \(28.48\pm 0.71\) & \(1.07\pm 0.1\) & ASTM D-638 \\  & Prepre co-extrusion & PA-BASALT & \(144\pm 5.24\) & \(5.34\pm 0.15\) & ASTM D-638 \\ \[PERSON] [PERSON] [63] & Prepre co-extrusion & PA-CF & \(169.9\pm 0.32\) & \(13.1\pm 0.35\) & ISO 527-2:2012 \\ \hline [PERSON] [64] & Prepre extrusion & PA & \(30.9\pm 0.9\) & \(0.41\pm 0.28\) & ASTM D3039 \\  & Prepre extrusion & PA-CF & \(436.7\pm 6.2\) & \(51.7\pm 0.6\) & ASTM D3039 \\  & Prepre extrusion & PA-Kevlar & \(305.2\pm 36.2\) & \(25.5\pm 0.7\) & ASTM D3039 \\  & Prepre extrusion & PA-GF & \(381.2\pm 28.1\) & \(19.6\pm 0.6\) & ASTM D3039 \\ \hline [PERSON] [59] & In situ impregnation & PA-CF & \(189\) & \(11.7\) & - \\ \hline [PERSON] [67] & Prepre co-extrusion & PETG & \(30.7\pm 1\) & \(1.4\pm 0.3\) & ASTM D-638 \\  & Prepre co-extrusion & PETG-CF & \(270\pm 20\) & \(2.55\pm 0.5\) & ASTM D-638 \\ \hline Heidari-Rarani & Prepre extrusion & PLA & \(45\pm 1.8\) & \(2.69\pm 0.18\) & ASTM D-638 \\
[58] & Prepre extrusion & PLA-CF & \(61.4\pm 2.1\) & \(8.28\pm 0.56\) & ASTM D3039 \\ \hline An [59] & In situ impregnation & PLA-CF & \(252\) & \(12.8\) & - \\ \hline Z. [PERSON] [68] & In situ impregnation & PLA-CF & \(481\pm 56\) & \(39\pm 5\) & ASTM D3039 \\  & In situ impregnation & PLA-CF & \(650\pm 99\) & \(61\pm 2.5\) & ASTM D3039 \\ \hline An [59] & In situ impregnation & PU-CF & \(311\) & \(11.1\) & - \\ \hline Saenz-Castillo [69] & In situ consolidation & PEEK-CF & \(1847\pm 81\) & \(136\pm 6\) & EN 2561, type A \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Tensile properties of composites for different technologies. In the reviewed literature, a similar dynamic of increase as there is in tensile strength is also present in the flexural strength. In prepreg extrusion, the output data from [PERSON] et al. 's [58] specimens showed that pure PLA has a 72.76 MPa flexural strength and 2.87 GPa flexural modulus, while the implementation of CF increased the values by 110% for flexural strength and 300% for modulus. This is probably because the fibres were at 90\({}^{\circ}\) of the building axis, and this did not give any significant strength amplification. Instead, if the fibres were laid on the 0\({}^{\circ}\) axis, then the flexural strength would probably be higher. [PERSON] et al. [71] also tested specimens with a PLA/CF compound but for different Vr of 22%, 33%, and 40% of fibres and found that with a higher Vr, the flexural strength and modulus increases. Furthermore, the results from [PERSON] et al.