## 3 Results
### Force-Displacement  
The force-displacement responses of the four laminate architectures during the first and second low-velocity impacts, including the effect of the 150 \({}^{\circ}\)C and 30 min heat treatment, were analyzed.  
The virgin composites (Figure 5a) exhibited the steepest decline in post-impact load-bearing capacity. The untreated specimens demonstrated only partial recovery by slightly retracing, whereas the thermally treated specimens failed to restore stiffness, resulting in a further rightward shift of the displacement curve. These findings corroborate the brittle, delamination-driven fracture behavior, as evidenced by the significant peak force reduction observed in the force-time analysis.  
The nanofiber-interleaved specimens (Figure 5b) displayed a multi-step retraction, where each unloading segment was interrupted by small force rebounds, corresponding to secondary peaks seen during the loading phase. These rebounds were attributed to progressive failures within the electrospun PAN mat; each time a bundle of nanofibers debonded, local compliance increased, generating a short, recoverable displacement before the next bundle was engaged. Because the mat constrains crack opening, the overall retraction remains relatively steep, suggesting that most deformation was reversible. After thermal treatment (N2T), the retraction became straighter and longer, indicating reduced interfacial friction.  
In the PE-modified specimens (Figure 5c), the unloading branch following the first peak did not drop vertically but instead curved back toward the displacement axis, forming  
Figure 5: Force-displacement graphs of (**a**) virgin, (**b**) nanofiber-layered, (**c**) PE-modified, (**d**) and hybrid specimens.  
a wide, ductile retraction. This curved behavior is indicative of localized matrix shear yielding around PE domains. Once the crack front stabilized, the softened PE/epoxy blend continued to carry load, and the laminate sprang back gradually, resulting in a broader retraction radius than that of the virgin laminate. Upon re-impact, the same specimen (P1U) exhibited an even wider retraction, consistent with permanent plasticization of the interfacial region. In contrast, the treated specimen (P2T) showed a shorter yet higher retraction arc. After re-impact, the same specimen (P1U) shows a still broader retract, consistent with permanent plasticization of the inter region. By contrast, the treated specimen (P2T) exhibits a shorter but higher retract arc which might be the evidence that molten PE has refilled micro-voids, stiffened the interface and allowed the laminate to deal with load elastically before complete unloading.  
The untreated hybrid specimens (Figure 5d) combined the ductile curvature characteristic of PE laminates with the steep recovery profile of nanofiber-reinforced laminates, producing a smooth, parabolic retraction that concluded with the smallest permanent indentation among all groups. Notably, the treated specimen (H2T) retained this parabolic shape while elevating the entire curve, suggesting that the laminate initially released load rapidly, then transitioned into a prolonged, gentle tail without intermediate rebounds. This behavior confirms that molten PE infiltrated the nanofiber network, fused delaminated regions, and restored continuous load paths. The absence of oscillations or abrupt compliance shifts throughout retraction highlights the re-establishment of cohesive load-bearing capability and explains why the hybrid laminate recovered both stiffness and energy absorption capacity following treatment. The gradual post-peak descent further supports distributed energy dissipation rather than sudden fiber pull-out.  
These findings imply that PE particles enhanced ductility and provided reversible flow, electrospun PAN nanofiber mats constrain delamination, and their synergistic integration achieves both prominent impact resistance and effective thermal self-healing.