## 5 Conclusions  
In this paper, the mechanical characteristics of epoxy-based carbon composites with damping materials has been studied after prolonged environmental aging. Low velocity impact resistance was analyzed to assess the freeze-thaw aging treatment effects on multilayered composites. Two different damping materials were used, Kraibon HHZ9578/99 and Kraibon SUT9609/24, and lamination processes and lay-up stack were maintained constant as T300/EP, taken as reference material. The impact tests were performed according the ASTM D7136 standard and effect of damping insertion, velocity, moisture and combination of them, are studied. SEM analysis were conducted to evaluate interfaces between composite and damping layer. The following conclusions can be drawn:  
* It is possible to compare ASTM D5229 and IEC 60068 thermal cycle since diffusion is a thermal activated process. Diffusion during freeze phase could be taken as negligible; so just phase with enough thermal energy could be considered for time process evaluation.
* Activation energy of diffusional process was calculated and a maximal diffusion coefficient at infinite temperature is obtained; diffusion profile at different temperatures is now possible to plot in order to evaluate the saturation absorption time for these composites. Quite similar coefficient of diffusivity for all types of samples ensure the adoption of damping materials as functional layers do not influence the characteristics of sandwich structures after aging.
* The interface of Kraibon SUT appears continuous and well adherent with the faced layers, proving an excellent wettability. This is probably related to the lower modulus of elasticity and greater elongation at break than HHZ. This feature could be one of the key reasons for the greater energy absorption of the composite damped with SUT. As a result of aging there are no substantial variations in the structure, which maintains excellent adhesion. In contrast, HHZ shows discontinuity and porosity within the damping layer. These defects have been found in the untreated sample and are therefore not attributed to treatment in temperature and humidity. Certainly, bad interfacial adhesion and porosities are considered as preferential channels for diffusion.  
As a result of the previous work, questions remain open on the chemical variations of the interface after aging or on the effect of the variation of stacking sequence, lay-up on the absorption of humidity and how this can influence the impact resistance. Further studies will be needed in the future.  
Conceptualization, E.V., L.S. and M.C.; methodology, E.V., L.S. and M.C.; validation, E.V. and L.S.; formal analysis, E.V.; investigation, E.V.; resources, M.C.; data curation, L.S.; writing--original draft preparation, E.V.; writing--review and editing, E.V., L.S. and M.C.; visualization, M.C.; supervision, M.C.; project administration, M.C.; funding acquisition, M.C. All authors have read and agreed to the published version of the manuscript.  
This research received no external funding.  
Not applicable.  
The data presented in this study are available on request from the corresponding author.  
The authors wish to acknowledge: Gummiwerk KRAIBURG GmbH for the supply of damping materials \"KRAIBON\" SUT9609/24-HHZ 9578/99\", G.Angeloni(r) S.r.l. for the supply of CFRP material and SFC COMPOSITI S.r.l. for the production of damped composite panels and Ing. [PERSON] for the collaboration during the project.  
The authors declare no conflict of interest.