# Mechanical Properties Assessment of Low-Content Capsule-Based Self-Healing Structural Composites
## 4 Concluding Remarks  
In this study, the mechanical properties of low-content capsule-based CFRPs were investigated. The investigation was focused at determining the influence of capsules integration within a composite by measuring the knock down effect. Furthermore, the self-healing efficiency of the developed materials was evaluated. The interlaminar fracture toughness (G\({}_{\text{IIC}}\)) did not have a significant decrease (\(-14\%\)) compared to the reference composite. Towards the same direction, flexural strength and modulus where slightly decreased, \(5\%\) and \(6\%\), respectively, with regards to the neat material. As far as the self-healing efficiency is concerned, G\({}_{\text{IIC}}\) recovered up to \(84\%\). Flexural strength healing efficiency reached the \(16\%\) and \(14\%\) while flexural modulus \(14\%\) and \(30\%\) compared to the unhealed and the reference material, respectively.  
It is worth mentioning that the assessment of healing presented in the current study, is with a couple of alternations to the standard protocol recommended by ASTM D7264/D6264M-07. In order to avoid the catastrophic failure of composites, which is the fiber breakage, an unloading and reloading  
Figure 14: Cumulative AE hits vs. load for a representative modified specimen under 3 PB conditions. Depiction of felicity effect and load values used for the calculation of felicity ratio.  
cycle was applied. This protocol is closer in real applications where loadings are not constant, and by no means fiber breakage is acceptable.  
Furthermore, the self-healing functionality is supposed to be targeted in specific areas which are susceptible in damage. For this reason, UF capsules were not dispersed to all composite layers in the case of 3-point bending, which resulted in a notable healing efficiency by ensuring simultaneously a controlled and low knock down effect  
The healing efficiency rates mostly demonstrate the good adhesion between the polymer matrix and the encapsulate healing system combined with the highly reactive character of the scandium triflate.  
The acoustic emission recordings were utilized to support the experimental process by ensuring the damage mechanism of matrix microcracking.  
It is conceivable that the low integrated content of capsules when combined with a proper catalyst can provide recovery without significantly compromising the initial mechanical performance. With further developments, the capsule-based composites have the potential for being incorporated into a variety of applications to provide the desired multifunctionality.  
Conceptualization, V.K., S.T. and A.P.; methodology, S.T., X.T. and D.B.; validation, S.T., V.K. and A.P.; formal analysis, M.K., X.T. and D.B.; investigation, M.K., X.T. and D.B.; resources, M.K., X.T. and D.B.; writing--original draft preparation, X.T., M.K. and D.G.B.; writing--review and editing, S.T.; visualization, X.T., M.K. and D.B.; supervision, V.K. and A.P.; project administration, V.K. and A.P.; funding acquisition, V.K. and A.P. All authors have read and agreed to the published version of the manuscript. This research received no external funding. The authors declare no conflict of interest.