Study on active regulation of interlaminar fracture toughness of carbon fiber composites via recovery characteristics of electrothermally activated shape memory alloys

Interlaminar delamination remains a major limitation of CFRP laminates, while most existing toughening approaches provide passive resistance that cannot be externally regulated after fabrication. The electrothermal use of embedded shape memory alloy (SMA) wires offers a potential route for active regulation, but the associated specimen-scale crack-closing response and its numerical representation remain insufficiently quantified. In this study, Mode I delamination of CFRP laminates containing naturally embedded, non-pre-strained NiTi wires was investigated using double cantilever beam tests with synchronized electrical, thermal and full-field deformation measurements. Two laminate thicknesses and two NiTi wire diameters were examined, with electrically loaded CFRP and unactivated SMA-CFRP specimens used as reference configurations. R-curve measurements and –ICTOD relations were combined with a J-integral-based inverse procedure to characterize the effective crack-closing response. Electrothermal activation increased the apparent Mode I delamination resistance and extended the crack-growth range required to reach the steady response. For the 4 mm series, the steady-state resistance increased from 880.00 to 1296.00 J/m 2 and the characteristic bridging-zone length from 53.96 to 71.25 mm; for the 3 mm series, the corresponding values increased from 851.67 to 1301.67 J/m 2 and from 51.53 to 77.32 mm. The activated SMA-CFRP specimens operated at terminal powers of approximately 2–7 W, compared with 48–50 W for the high-current electrically heated CFRP condition. A thermo-mechanical SMA model reproduced part of the activation-related structural response, while an equivalent three-stage cohesive zone model represented the remaining post-peak resistance. These results establish an experimental and numerical framework for externally controlled electrothermal regulation of delamination resistance in SMA-CFRP laminates.