# Influence of Aging Conditions on the Dynamic Stiffness of EPDM and EVA Rail Pads
## 6 Conclusions  
This study provides a detailed characterization of some of the main degradation mechanisms affecting the service life and performance of rail pads, which are essential components for ensuring the safety, comfort, and durability of railway infrastructure. Through experimental tests carried out under conditions representative of the railway environment, it has been established that the aging behavior significantly depends on both the material used (EPDM or EVA) and the geometry of the component. Additionally, the study quantitatively evaluates how specific variables, such as mechanical fatigue, ultraviolet radiation, and exposure to hydrocarbons, influence the dynamic stiffness of these components. These results allow for a more precise selection of rail pad materials and designs based on the specific operational conditions they will face in service. Furthermore, the insights gained provide the foundation for optimizing preventive maintenance strategies by enabling a more accurate understanding of track stiffness, thus contributing to reduced operating costs, minimized service disruptions, and extended component lifetimes. Future research should address the combination of different degradation agents on the same rail pad, as well as further explore the role that geometry plays in its deterioration.  
In conclusion, this study has provided a detailed characterization of how mechanical and chemical aging processes influence the dynamic stiffness of rail pads manufactured with EPDM and EVA, materials widely used in the railway industry. The results show that mechanical degradation progressively increases the dynamic stiffness of rail pads, with EVA pads being the most affected, exhibiting stiffness increases of up to 27%. On the other hand, exposure to UV radiation produced variable effects depending on exposure intensity and pad geometry, initially decreasing stiffness at lower exposures and subsequently increasing it at prolonged exposures. Additionally, hydrocarbon exposure also revealed different behaviors depending on the material type. These findings highlight the importance of considering aging mechanisms in the selection and proper maintenance of rail pads, laying the groundwork for future research on combined effects and the influence of pad geometry.  
Conceptualization, I.R., J.A.S.-A., D.F. and I.C.; methodology, I.R., J.A.S.-A., I.C. and S.D.; software, I.R., J.A.S.-A. and D.F.; validation, I.R., J.A.S.-A. and D.F.; formal analysis, I.R., J.A.S.-A. and D.F.; investigation, I.R.; data curation, I.R.; writing--original draft preparation, I.R.; writing--review and editing, I.R., J.A.S.-A., D.F. and J.C.; visualization, I.R., J.A.S.-A. and D.F. supervision, J.A.S.-A. and D.F.; project administration, D.F., I.C., J.C. and S.D.; funding acquisition, D.F., I.C., J.C. and S.D. All authors have read and agreed to the published version of the manuscript.  
This publication is part of the R&D&I project PID2021-128031 OB-I00 funded by MCIN AEI/10.13039/501100011033 and by \"ERDF A way of making Europe\".  
Not applicable.  
Data Availability Statement: Data will be made available upon request.  
This work was supported by PANDROL who provided the rail pads for the experimental study.  
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.