Fig. 2: SEM analysis of the crack initiation and propagation in GRE composite leading to the fiber-resin interface separation after repeated freeze–thaw cycling.
From: Freeze–thaw recycling for fiber–resin separation in retired wind blades
a Longitudinal view of the fiber-resin interface before freeze–thaw cycling, showing pre-existing voids and micro-cracks near the interface (indicated by red arrows). b Transversal view of the GRE composite, detailing the dimensions of pre-existing cracks. c Longitudinal view after freeze–thaw treatment, revealing widened and extended cracks at the fiber-resin boundary. d Transversal view showing further crack expansion, with inset magnifying the increased crack width. e Initial state of voids and micro-cracks near the fiber-resin boundary, with epoxy connected to glass fiber marked in yellow and unconnected epoxy in purple, forming complete circles, indicating an intact interface. f Early-stage crack formation in epoxy resin during freeze–thaw cycling. g Inset (triangle) shows micro-crack initiation in epoxy voids near the interface, with newly formed cracks highlighted in red. Crack propagation is demonstrated by half-split circles connected by new cracks, showing a chain reaction as water connects neighboring voids, creating pathways for further penetration. h, i Glass fiber surface showing remaining epoxy resin in an oval shape due to repeated pressure at the boundary. The triangle shows the enlarged area. j Final image showing complete separation of fiber and resin after freeze–thaw treatment.
