# Recent Advances in Additive Manufacturing of Fibre-Reinforced Materials: A Comprehensive Review
## 3 Evaluation
### Dynamic Testing
The loss modulus indicates increased energy dissipation in the glass region and decreased in the rubber region, with the nylon/GF composite reflecting better fibre/matrix bonding. The complex modulus also sharply decreases with temperature, highlighting the viscoelastic nature of the composites. Nylon/CF composite shows a higher damping factor (tan \(\delta\)), signifying greater energy  
Figure 8: (**a**) Creep behaviour for different temperatures and composite materials as strain percentage [97]; (**b**) creep behaviour for different percentages of embedded composite material [96]. dissipation due to frictional damping and indicating lower stiffness and greater flexibility at high temperatures. Tan \(\delta\) is emphasised as a more reliable indicator of viscoelasticity than loss or storage modulus due to its independence from sample shape. Furthermore, [PERSON] et al. [100] used ONYX/CF as the composite material at temperatures from 30 \({}^{\circ}\)C to 160 \({}^{\circ}\)C under a constant 1 Hz frequency for isotropic and concentric fibre patterns. The study estimates the glass transition temperature (Tg) using the first inflection point in the storage modulus vs. temperature graph. The Tg values for ONYX, isotropic, and concentric samples are 65 \({}^{\circ}\)C, 94 \({}^{\circ}\)C, and 100 \({}^{\circ}\)C, respectively. Below Tg, the molecules do not have enough energy to move, but as the temperature rises near Tg, increased molecular mobility decreases the elastic modulus. Combining short (ONYX) and continuous fibres in the composite reduces molecular motion, thus requiring higher temperatures to overcome this obstacle. The concentric fibres maintain their stiffness better than the isotropic ones due to their higher polymeric ratio. As temperature rises and the materials reach their melting point, the storage moduli of both fibre layouts drop, indicating a loss of structural integrity. The damping factor (tan \(\delta\)) graph shows ONYX has better damping below 84 \({}^{\circ}\)C, but beyond this, fibre-reinforced composites exhibit higher damping. Isothermal conditions at 30 \({}^{\circ}\)C with varying frequencies between 1 and 100 Hz reveal that continuous fibre-reinforced composites have a much higher storage modulus than ONYX, indicating higher stiffness, but the frequencies do not affect the modulus. However, ONYX has better damping properties but lower stiffness compared to the continuous fibre-reinforced samples. Finally, [PERSON] et al. [101] conducted experiments for ABS, ABS/CF, and ABS/GF materials at different temperatures and found a similar trend to the previous studies. While the temperature is increasing, the E' decreases gradually due to the implementation of fibres. For Tg from 100 \({}^{\circ}\)C to 120 \({}^{\circ}\)C, neat ABS reduced E' by 98% (1072 MPa to 17 MPa), ABS/GF showed a decrease of 96%, and ABS/CF showed a decrease of 80%. The E' of the composites had a higher value than the neat ABS, indicating again stronger fibre-to-core adhesion. Tg for the ABS/CF was the highest at 116 \({}^{\circ}\)C, followed by the ABS/GF at 108 \({}^{\circ}\)C. Loss modulus graphs showed increased energy dissipation with CF and GF reinforcement, with ABS/CF having the highest loss modulus peak (1195 MPa), indicating greater internal friction and energy dissipation. ABS/CF also demonstrated slower flow and maximum heat dissipation, requiring higher temperature and extrusion speed during printing. The tan \(\delta\) graph from DMA revealed that neat ABS had the highest peak, indicating high polymer chain mobility, while the addition of CF and GF reduced the tan \(\delta\) peak, demonstrating restricted molecular mobility due to fibre reinforcement. Another study [102] observed a notable increase in the damping factor for 3D-printed ABS reinforced with carbon nanotubes (CNTs) and CF. The loss factor was 2.5% for the ABS specimens and 3.7% for the ABS/CNT specimens, while the ABS/CF specimens exhibited the highest loss factor at 10%.