## 3 Results and Discussions  
### Mechanical Test Results  
The bonding characteristics of the JLS and SLS specimens were tested by applying tensile load under displacement-controlled mode as per the ASTM D5868 standard. When the tensile load was applied, the entire load was distributed through the adhesive region. It has been reported by several researchers with solid evidences that the thickness of the adherend does not have a significant role in the distribution of load under shearing [26]. There could also be more than one peak load value, with each of them contributing to the damage characteristics or the bonding characteristics of the specimen. Figure 4 shows the load vs. time curve for the specimens. In the research work presented, more than one peak can be observed in the load vs. time curve for both specimens. It must be noted that although there are several small peaks observed in both JLS and SLS specimens in Figure 4, the initial peak load is considered as the initial rupture point and the final peak load is considered as the final rupture point. Since these mechanical results provide only a limited amount of information on the damage characteristics, the acoustic emission results have been used in the subsequent sections. Table 3 shows the mechanical characteristics of both JLS and SLS specimens. Figure 4: Load vs. time curve: **(a)** JLS Specimens; **(b)** SLS Specimens. The first major observation from the mechanical test results is the varying peak load values of the same specimen group, both in JLS and SLS. This is common when it comes to the practice of adhesive bonded specimens [27; 28; 29] because the bond quality is not only determined by the curing characteristics, the thickness of the adhesive and other mechanical characteristics, but also on the efficiency of the user who handles the adhesives. The adhesives are normally mixed using a hand mixer rather than a mechanical controller owing to its high viscosity and requirements. Thus, it is inevitable that a considerable amount of difference can be observed between the adhesive bonded specimens of the same group. This is the reason why there is a difference in both the peak loads at initial and final ruptures and they are not similar between the same specimen group (refer to Figure 4 and Table 3). Furthermore, under this view, an increase in the number of test specimens would increase the accuracy of the evaluation of the scattering but it not will reduce the latter. As indicated in the previous sections, the thickness of the adherend does not generally affect the strength of the adhesive bonded shear specimens under displacement-controlled mode. Nonetheless, the thickness of the adhesive carries the majority, if not all the load. In the SLS specimens, owing to their larger thickness than JLS specimens, higher peak loads are accounted for. The average peak load at the initial rupture in SLS specimens is 6.78 kN, while the JLS specimens have an average peak load of 4.18 kN. Similarly, at the final rupture stage, SLS specimens have an average peak load of 7.02 kN, while JLS specimens have 4.52 kN. In SLS specimens, the load is carried along the cross-sectional area of the adhesive region. However, in the JLS specimens, the shear strength of the specimen is also governed by the end curvature effect. This is explained by [PERSON] et. al. [11] in their research work. Single lap joints, when loaded, transfer most of the load in shearing. Joggled lap joints, however, transfer most of the load in peeling. This is also the reason why the joggled lap joints have lower displacement when compared to the single lap joint specimens. The joggled joints suffer lateral deflections rather than shearing, which result in inducing high peel stress on the neutral axis. This results in the crack initiating at the joggled knee of the curvature region. This will result in low peak loads, which are observed in the present research work (see Table 3 and Figure 4).