# Deep Autoencoder Framework for Classifying Damage Mechanisms in Repaired CFRP
## 3 Results and Discussions  
### Mechanical Test Results  
The mechanical characterization of the damage modes of JLS specimens was carried out through a series of tensile tests, following the recommendations of the ASTM D5868 standard [51]. Two critical points can be identified from the mechanical results presented in Figure 5: the maximum load at initial failure, which indicates the onset of damage, and the maximum load at final failure, which represents the complete failure of the specimen. Although the three specimens share similar material characteristics, their peak load values differ significantly. This finding has been observed by several authors on the bonded specimen, such as [PERSON] et al., [PERSON] et al., [PERSON] et al., and [PERSON] et al. [52, 53, 54, 55]. This variation can be attributed to a series of factors such as overlap length, adhesive thickness, and scarf angle.  
These researchers unanimously recognized the significant impact of these factors on the performance of joined composites under static stress. [PERSON] et al. revealed that  
Figure 5: (**a**) Mechanical properties of JLS1 specimen, (**b**) Mechanical properties of JLS2 specimen, (**c**) Mechanical properties of JLS3 specimen.  
modifying joint dimensions could reduce maximum stress [54]. Meanwhile, [PERSON] et al. observed that the use of hand-mixed adhesives in CFRP composites could introduce geometric variations in the bonded areas, affecting their load-bearing capacity. They also noted the importance of surface treatment, temperature, and exposure to hostile environments, highlighting their effect on load performance [56]. [PERSON] et al. highlighted that the choice of adhesive and bonding agent, overlap length, and pretreatment methods influence joint strength [57]. [PERSON] et al. discussed that the reduced shear strength in composite structures is attributed to the uneven shear stress distribution and found less resilience to fatigue under repeated loading [58]. [PERSON] et al. explored the effect of the number of CFRP layers and bonding mode on the mechanical properties of composites [59; 60]. One of their works reported an improvement in load-bearing capacity and stiffness with an increase in the number of layers [60], while the other found that the double-sided reinforcement was effective [59]. [PERSON] et al. found that the adhesive thickness strongly affects joint strength, with thicker adhesives giving stronger joints [61]. [PERSON] et al. concluded that the shear stress in single-lap joints is mainly affected by the thickness of the adhesive [61], while the deformation, elastic modulus, and absorbed energy are influenced by the overlap length [62]. In summary, these studies demonstrate that variation in the mechanical properties in bonded composites can be attributed to the following factors: interface strength, adhesive thickness, presence of defects, and bonding method. In addition, they collectively highlight the complex interplay of these factors that could lead to the variations in the failure loads. The JLS 1 specimen withstood a considerably higher initial load than the JLS 2 and JLS 3 specimens. In particular, specimen JLS 2 showed low resistance to initial and final fracture (see Figure 5a-c).