## 3 Results and Discussions
### Key Findings  
Our study led to several notable findings pertaining to the RGB intensity values under varying axial loadings. An integral aspect of our analysis involved the use of the interquartile range, which served as a performance indicator for our testing variables. The smallest average interquartile range was observed in Case 3, with the R value's average interquartile range being 15.411; the G value's, 7.899; and the B value's, 19.280. Revisiting the experimental conditions for Case 3, epoxy B and white light were used, and the auto white balance function was not employed. This outcome, presented in Figure 20, indicated the most consistent photoelastic response across all R, G, and B values.  
Interestingly, despite employing the same adhesive and light source and foregoing the white balance function in both Cases 3 and 6, the average interquartile range differed significantly between these two scenarios. This discrepancy can be attributed to the difference in the maximum applied load in each case, with Case 3 having a maximum load of 200 N and Case 6, 500 N.  
When comparing the average interquartile range between Cases 1 to 4, which showcased variations according to the type of adhesive used, and Cases 5 to 8, the latter group demonstrated quite similar results to each other. From this observation, we inferred that the shear strength and viscosity of the adhesive appear to exert the most substantial influence on the consistency of the response in the reflective photoelastic method.  
As previously mentioned, Case 3 was evaluated to show the most consistent photoelastic response. Under this condition, epoxy B was used, and among its key material properties, its shear strength was the highest at 30 MPa, tied with epoxy C, and the viscosities of the resin and hardener were the highest at 67.5 Pa.s and 7 Pa.s, respectively.  
The viscosity of an adhesive is closely related to its adhesive performance. Generally, high viscosity is associated with high adhesive strength, but it has the drawback of slow curing and difficulty in spreading evenly on surfaces, leading to reduced usability. However, adhesives with excessively high viscosity can lead to the formation of bubbles due to the roughness of the material surface, which can actually decrease the adhesive quality [37]. Therefore, choosing an adhesive solely based on its high viscosity is not advisable.  
[PERSON] et al. [38] utilized the reflective photoelastic coating technique to analyze stone masonry walls. They mentioned that attaching the photoelastic coating uniformly to the irregular specimen surface was a challenging task, requiring a significant amount of experience and skill. They emphasized that this step was the most critical in the application of the reflection photoelasticity method.  
In summary, the study's key findings indicate the pivotal role of the adhesive's characteristics in shaping the photoelastic response. Although factors such as the light source and white balance function were explored, their impact on response consistency was notably less substantial. These insights enhance our understanding of how various experimental parameters influence the photoelastic method's output and will undoubtedly guide future investigations in this domain.  
Figure 20: Average interquartile ranges of the RGB values for the photoelastic particles according to the following cases: (**a**) R-value; (**b**) G-value; (**c**) B-value.