## 4 Conclusions  
In this study, functional particles such as piezoelectric (PZT) ceramic and shape memory alloy (SMA) particles have been incorporated in composite laminates to accelerate the loss of vibration energy. PZT ceramic particles and SMA particles are mixed with epoxy resin and rolled into a film shape before they are interleaved between prepreg plies for better distribution of the particles. In this study, 20 \(\upmu\)m thickness epoxy resins film with well-dispersed particles was produced to improve particle dispersion inside composite materials. The loss factor (tan \(\delta\)) was measured with various particle loadings to verify the effectiveness of interleaving in the vibration damping of laminate specimens. Therefore, dispersed particles used in this study increased the vibration damping capacity without reducing the mechanical properties.  
Through SEM and EPMA, the degree of dispersion of particles inside the composite material was evaluated, and it was observed that the particles were well distributed between the composite interplies. However, in the case of the 25 g/m\({}^{2}\) specimen, PZT particles were found to form aggregates between the composite interplies. This confirmed that applying more than 25 g/m\({}^{2}\) of particles to a thin mixture film of 20 \(\upmu\)m thickness would lead to a decrease in dispersion.  
Mixture films were produced, where the content of PZT and SMA particles varied from 0 g/m\({}^{2}\) to 25 g/m\({}^{2}\) in an increment of 5 g/m\({}^{2}\), to verify the vibration damping performance according to the content of the particles. To evaluate the vibration damping of the manufactured composite specimens, the loss factor was measured using DMA. It was recognized that there was an optimal particle content to improve vibration damping performance.  
In order to verify the vibration damping effect when PZT and SMA particles are applied at the same time, a film containing 10 g/m\({}^{2}\) particles content of each material was produced. In this case, the loss factor was improved in all frequency ranges. In addition, when PZT and SMA are applied simultaneously, PZT is expected to enhance the vibration damping performance of SMA.  
The flexural modulus was measured to confirm whether the introduction of interleaves between composite plies affects the mechanical properties of the material. Little change  
Figure 10: Flexural modulus of the CFRP specimens with (**a**) PZT- and SMA-particle-dispersed mixture films for different particle loadings and (**b**) PZT-, SMA-, and PZT 10 g/m\({}^{2}\) loading/SMA 10 g/m\({}^{2}\) loading mixed-particle-dispersed mixture films.  
in flexural modulus with the content of the particles was observed. Therefore, dispersed particles used in this study increased the vibration damping capacity without reducing the mechanical properties.  
This study demonstrates an effective way to improve the vibration damping of synthetic laminates through interleaving of particle/resin mixed films. We propose optimal conditions to improve the vibration damping capability of the composite by attempting various particles and particle loads.  
Conceptualization, J.-M.J. and W.-L.L.; validation, J.-M.J., D.-S.L., S.-N.M. and W.-I.L.; formal analysis, J.-M.J. and D.-S.L.; investigation, J.-M.J. and S.-H.K.; resources, S.-M.K.; data curation, J.-M.J. and D.-S.L.; writing--original draft preparation, J.-M.J.; writing--review and editing, J.-M.J.; visualization, D.-S.L.; supervision, S.-M.K.; project administration, W.-I.L.; funding acquisition, S.-M.K. All authors have read and agreed to the published version of the manuscript.  
This work was supported by the research program (NRF-2020M3D1A2102467) funded by National Research Foundation of Korea.  
Not applicable.  
The authors declare no conflict of interest.