# Study of the Kinetics of Adhesive Bond Formation Using the Ultrasonic Method
## 5 Conclusions  
Based on this case study of the kinetics of adhesive bond formation, the following conclusions can be made:  
1. The kinetics of adhesive bond formation, determined non-destructively by both ultrasonic longitudinal and surface waves and confirmed by sample tear tests, has the character of an increasing curve in the initial stage of forming, in the adopted ultrasonic and mechanical measures of bond quality, with a tendency to stabilize after a certain period of time, marking the end of the bond formation.
2. The kinetics of adhesive bond formation can be non-destructively determined using ultrasonic longitudinal and surface waves. The longitudinal wave allows for a better--in terms of inspection technology--assessment of the tested adhesive joint than the surface wave. Mechanical tests of the strength of the adhesive bond together with the adhesive hardness testing confirm the significant possibilities of the non-destructive method for determining the kinetics of the adhesive bond formation.
3. The determination of the kinetics of adhesive bond formation allows for a more accurate determination of the time of formation of such a bond than before, which can be used in the planning of technological operations in the process of the construction of bodies of means of mass transport, the cyclicity of production, and the perfection of the technology for the manufacturing of these means, including non-destructive quality control of production.
4. The sensitivity of ultrasonic waves (longitudinal and surface) to changes in the adhesive bond, found during our research, reveals the potential possibility of using these waves also for the study of the degradation of such bonds and--as a consequence--for the diagnosis of this type of permanent bond.  
The nature of the penetration and reflection of the ultrasonic longitudinal wave and the outflow of the surface wave from an acoustically denser environment (metal) to an acoustically sparser environment (adhesive) also provides opportunities to study the course of crosslinking of the adhesive in its volume and the constitution of the adhesive bond in selected areas of the glued technical object, which determines the direction of our further research on the issue of the kinetics of the adhesive bond formation.  
**Author Contributions:** Conceptualization, J.K. and M.J.; methodology, J.K., M.J., and D.W.; software, K.S.; validation, J.K. and D.W.; formal analysis, M.J.; investigation, J.K.; resources, K.S. and M.N.; data curation, J.K.; writing--original draft preparation, M.J. and J.K.; writing--review and editing, J.K., D.W., and M.J.; visualization, M.J. and K.S.; supervision, M.J. and M.N.; project administration, K.S.; funding acquisition, M.N. All authors have read and agreed to the published version of the manuscript.  
**Funding:** This work was supported by the Polish National Centre for Research and Development under the grant decision no. DWP/TECHMATSTRATEG-III/136/2020.  
**Institutional Review Board Statement:** Not applicable.  
**Informed Consent Statement:** Not applicable.  
**Data Availability Statement:** The data presented in this study are available on request from the corresponding author. The data are not publicly available due to privacy.  
**Conflicts of Interest:** The authors declare no conflict of interest.