Springback Behavior and Viscoelastic Mechanism of <scp>CCF</scp> / <scp>PEKK</scp> Composite U‐Shaped Beams Formed by Hot‐Press Molding

ABSTRACT The springback deformation of thermoplastic composite components during the molding and unloading process essentially originates from the release of residual elastic strain caused by incomplete viscoelastic relaxation of the material during the high‐temperature molding stage. This paper takes the continuous carbon fiber reinforced polyetherketoneketone (CCF/PEKK) composite U‐shaped beam as a typical research object. Starting from the engineering scale response of the material's viscoelastic state, the intrinsic control mechanism of the molding conditions on the springback behavior is explored. Results indicate that molding temperature plays a dominant role in regulating the springback angle, primarily by affecting the storage modulus and the characteristic stress relaxation timescale of the material; when the material relaxation time is significantly smaller than the process time scale, the sensitivity of the springback response to the holding time is significantly weakened. Based on the equivalent viscoelastic response description, a quantitative relationship between the springback angle and the material storage modulus was established, and the pressure and time correction terms were introduced to construct a springback prediction model. The model prediction results are in good agreement with the experimental data, and the prediction error is controlled within ±10%. The research results show that the springback behavior of thermoplastic composites can be reasonably explained under the unified framework of the material's viscoelastic state and geometric constraints, providing a mechanical understanding of the molding springback problem with physical constraints.