## 5 Mechanical Properties of the Natural Fibers Reinforced Epoxy Composites
### Tensile Behaviour  
The tensile behaviour of a material represents its ability to stretch under pulling force without failure. The natural fibers' tensile strength and modulus of elasticity increase with the cellulose content [104]. [PERSON] et al. [94] studied the behaviour of banana fiber-reinforced epoxy (wt.% (0-20%)) composites. The study found improvement in the mechanical properties such as tensile strength, impact strength, and flexural strength with the increase in banana fiber up to 15 wt.%, after which it decreased. Another study [76] with banana fiber-reinforced epoxy composites also found that as the banana fiber wt.% reinforcement increased, the tensile strength and hardness of the composites increased up to a certain wt.% reinforcement. Initially, the increment in the fiber and epoxy matrix adhesion leads to an increment in the tensile strength of the NFRCs as it can bear load because of increased matrix bonding by covering the complete surface area of fiber [38; 105]. The decrease in the mechanical properties of the NFRC after a certain wt.% reinforcement is due to the increase in porosity caused by poor adhesive bonding between fiber and epoxy. [PERSON] et al. [68] presented the experimental study using different natural fibers' (Prosopis Juliflora, Abutilon Indicum, and Tapsi) reinforcement. The tensile and flexural strength of the NFRCs increased as the fiber loading increased, but after further increments (>20 wt.%) of fiber, the strengths decreased. [PERSON] et al. [92] showed an increment in the tensile strength of the fabricated composites as the coir fiber length increased. Fiber orientation also plays an important role in regard to tensile strength. A study with different fiber loadings (30, 40, and 50 wt.%) and orientations (0\({}^{\circ}\), 30\({}^{\circ}\), 45\({}^{\circ}\), and 60\({}^{\circ}\) \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
** Composites (wt\%/wt\%)** & **Tensile Strength (MPa)** & **Flexural Strength (MPa)** & **Impact Strength (J/m)** & **Impact Energy (kJ/m\({}^{2}\))** & **Hardness** & **Ref.** \\ \hline Banana + sisal/epoxy (8/92), & & & & & & \\
5 mm fiber length & 9.48 & 28.43 & 2.15 & - & - & [102] \\ \hline Banana + sisal/epoxy (12/88), & & & & & & \\
5 mm fiber length & 16.39 & 26.15 & 2.37 & - & - & [102] \\ \hline Banana + sisal/epoxy (16/84), & & & & & & \\
5 mm fiber length & 12.74 & 37.56 & 2.62 & - & - & [102] \\ \hline Banana & + sisal/epoxy (8/92), & & & & & \\
10 mm fiber length & 8.54 & 22.22 & 5.21 & - & - & [102] \\ \hline Banana & + sisal/epoxy (12/88), & & & & & \\
5 mm fiber length, & 15.52 & 31.4 & 8.33 & - & - & [102] \\ \hline Banana & + sisal/epoxy (16/84), & & & & & \\
5 mm fiber length, & 10.3 & 25.56 & 11.56 & - & - & [102] \\ \hline Luffa + groundnut-epoxy (40/60) & 20 & 53 & - & 1.1 & - & [103] \\ \hline Hemp/epoxy (9/91) & 69.85 & 10.15 & - & 5.7 & 50.1 HV & [18] \\ \hline Nettle/epoxy (9/91) & 66.9 & 16 & - & 6.7 & 52.0 HV & [18] \\ \hline Hemp + nettle/Epoxy (18/82) & 71.72 & 14.21 & - & 6.2 & 59.1 HV & [18] \\ \hline Prosopis Juliflora/epoxy (20/80) & 72 & 254 & 74 & - & - & [68] \\ \hline Abutilon Indicum/epoxy (20/80) & 67 & 216 & 92 & - & - & [68] \\ \hline Tapsi/epoxy (20/80) & 49 & 225 & 45 & - & - & [68] \\ \hline \hline \end{tabular}
\end{table} 
Table 4: _Cont._was conducted by [PERSON] et al. [70]. They found that the tensile strength increased when the fiber loading was increased from 30 to 40 wt.% due to the better matrix and fiber adhesion. However, the further increment in the fiber loading (50 wt.%) lowered the tensile strength due to increased voids resulting from the improper matrix and fiber adhesion. [PERSON] et al. [95] investigated the effect of fiber loading in pine fiber epoxy composite. They found that the tensile strength increased up to 10 wt.% fiber loading and decreased afterwards. This was attributed to poor adhesion of fiber and matrix with the high-fiber content. The chemical treatment of the fiber also leads to improvement in the tensile properties of the composites.