## 3 Results
### SEM Analysis  
SEM is essential for post-impact analysis because its sub-micrometer resolution and large depth of field reveal key failure features such as fiber/matrix debonding, matrix fracture morphology, nanofiber bridging, and thermoplastic flow. These microstructural insights help validate the toughening and self-healing mechanisms inferred from the graphs, thereby linking the observed effects of reinforcements to the measured improvements in impact strength and thermal recovery. For untreated virgin specimens (Figure 8a), the fracture surface is dominated by epoxy facets and extensive flat fiber imprints. Long split cracks run parallel to the fiber bundles, and fiber pull-out is evident. These features confirm brittle matrix cleavage combined with abrupt interlaminar delamination. Thermal exposure of the treated virgin specimens (Figure 8b) leaves the macro-morphology essentially unchanged; large planar facets and straight delamination planes persist, indicating that the neat epoxy network lacks sufficient mobility at 150 \({}^{\circ}\)C to reflow or blunt existing cracks. This observation aligns with the negligible thermal recovery identified in the previous graphs. For nanofiber-interlayered specimens (Figure 9a), a dense, web-like nanofiber mat is clearly discernible between the glass fiber layers. Numerous short fibers bridge the fracture gap, while the epoxy displays rough river patterns, which are characteristic signatures of crack deflection at the mat interface [52]. Following thermal treatment (Figure 9b), the nanofiber mat remains intact, and the damage mechanisms are still visible. Matrix cracks and fiber fractures are observed, and fiber pull-out debris accumulates along the interleaf region. Some delaminations appear in both untreated and treated specimens, particularly at the epoxy-nanofiber interface. Considering that neither the nanofiber mat nor the epoxy matrix melts at 150 \({}^{\circ}\)C, a similar fracture morphology is expected to persist in the treated samples. For PE-modified specimens (Figure 10a), the matrix contains numerous rough, ductile ligaments surrounding partially debonded fibers. Rounded micro-voids, typical of PE domains pulled from the epoxy matrix, are dispersed throughout. Extended fiber pull-out is also present, corroborating the oscillations observed in the force-time graphs. After thermal exposure at 150 \({}^{\circ}\)C for 30 min, the treated specimens (Figure 10b) display a fracture surface coated with a continuous, filmy layer bridging adjacent fiber bundles. Smeared resin strings and rounded PE blisters appear between piles, demonstrating that molten PE has migrated and partially filled micro-cracks. This observation rationalizes the \(\sim\)25% increase in peak force (P2T) and the dual-peak profile seen in the force-time curves, where initial stiffening was followed by a delayed global maximum. The untreated specimen (Figure 11a) reveals a nanofiber mat that remains largely intact but is bordered by multiple delamination steps propagating both above and below the mat. The fracture path skirts the nanofiber layer rather than penetrating it, confirming the mat's crack-deflection role; however, the presence of several delaminated plies indicates that the matrix-mat interface is only partially effective in capturing delaminations. Localized fiber  
Figure 8: Virgin (**a**) untreated and (**b**) treated specimens (red arrows: matrix cracks, cyan arrows: delaminations). Figure 9: Nanofiber-interlayered (**a**) untreated and (**b**) treated specimens (red arrows: matrix cracks, cyan arrows: delaminations, white arrow: nanofiber mat). cracks originate where axial glass filaments intersect the nanofiber mat, suggesting that load transfer across this interface was still stress-concentrating under the first impact. After thermal treatment (Figure 10(b)), distinct changes in damage morphology are observed.