## Materials and Methods  
### Materials  
For preparing the specimens, a prepreg fabric laminate with ER450 epoxy matrix (SAATI CIT CC206 ER450 43%) was used. The carbon fiber configuration is stitched with layers of fibers overlapping one other. The nominal ply thickness is 0.244 mm. The composite laminates for both JLS and SLS specimens (Figure 1) were cured by the autoclave method. Other details such as number of plies and geometry of the adherend can be found in Tables 1 and 2, respectively. The specimens were prepared by following the ASTM D5868-Standard Test Method for Lap Shear Adhesion for Fiber-Reinforced Plastic (FRP) Bonding [25]. The adhesive used for this study has a shear strength of 25 MPa and a peel strength of 65 MPa. The thickness of the adhesive coated and the area of the adhesive coated are also provided in Tables 1 and 2.  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline  & \multicolumn{4}{c}{**Flat Adhered**} \\ \hline
**Length (mm)** & **Width (mm)** & **Thickness (mm)** & **No. of Plies** & **Stacking sequence** \\ \(101.6\pm 0.12\) & 26.09 \(\pm\) 0.07 & 2.0 \(\pm\) 0.04 & 8 & [+45/\(-\)45]\({}_{\text{J}}\)/\(-\)45/+45 \\ \hline \multicolumn{4}{c}{**Curved Adhered**} \\ \hline
**Length (mm)** & **Width (mm)** & **Thickness (mm)** & **No. of Plies** & **Stacking sequence** \\ \(101.6\pm 0.17\) & 26.09 \(\pm\) 0.05 & 1.5 \(\pm\) 0.02 & 6 & [+45/\(+\)45/\(-\)45]\({}_{\text{S}}\) \\ \hline \multicolumn{4}{c}{**Overlapping Region (Adhesive)**} \\ \hline
**Length (mm)** & **Width (mm)** & **Thickness (mm)** & **Thickness (mm)** \\ \(26\pm 0.21\) & & 26.09 \(\pm\) 0.06 & 3.67 \(\pm\) 0.05 \\ \hline \hline \end{tabular}
\end{table}
Table 1: JLS specimens’ geometry and characteristics.  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline  & \multicolumn{4}{c}{**Upper Adhered**} \\ \hline
**Length (mm)** & **Width (mm)** & **Thickness (mm)** & **No. of Plies** & **Stacking sequence** \\ \(101.6\pm 0.11\) & 25.33 \(\pm\) 0.12 & 1.3 \(\pm\) 0.05 & 5 & +45/\(+\)45/\(-\)45/\(+\)45 \\ \hline \multicolumn{4}{c}{**Lower Adhered**} \\ \hline
**Length (mm)** & **Width (mm)** & **Thickness (mm)** & **No. of Plies** & **Stacking sequence** \\ \(101.6\pm 0.09\) & 25.33 \(\pm\) 0.14 & 6.4 \(\pm\) 0.12 & 26 & +45/[+45/\(-\)45]\({}_{\text{J}}\)/\(+\)45 \\ \hline \multicolumn{4}{c}{**Overlapping Region (Adhesive)**} \\ \hline
**Length (mm)** & **Width (mm)** & **Thickness (mm)** & **Thickness (mm)** \\ \(26\pm 0.12\) & & 25.33 \(\pm\) 0.25 & 8.5 \(\pm\) 0.11 \\ \hline \hline \end{tabular}
\end{table}
Table 2: SLS specimens’ geometry and characteristics.  
Figure 1: Single-lap shear (SLS) (**a**) and joggled-lap shear (JLS) (**b**) specimens’ nominal dimensions.  
The adhesive was cured at temperature of 65 \({}^{\circ}\)C for 1 hour, then the specimens were tested after 5 days. Three specimens in each type have been studied. The JLS and SLS bonded laminates are provided in Figure 2.  
The reason behind using large variation in thickness between the upper adherend and lower adherend in the SLS specimens (Figure 1a) is to simulate the configuration of the composites used in aerospace structures. SLS configuration, in particular, represents the bonding between the flange of the lower spar of the fuselage and the front bulkhead. JLS configuration (Figure 1b) represents the bonding between the fuselage and the half-wing. Although there is no standard procedure that has been followed for setting the thickness and number of plies, the test procedures were carried out carefully as per the ASTM D5868 standards. Moreover, it has been indicated by many researchers that the thickness of the adherend does not play a significant role in load distribution under displacement-controlled testing conditions [26]. The entire load is distributed through the thickness of the adhesive, which is the crucial factor in this research work.