Multiphysics mechanism analysis and prediction of wrinkle defects in automated fiber placement of thermoplastic prepregs

Wrinkle defects frequently arise during automated fiber placement of thermoplastic composites due to inadequate process design, with prepreg buckling instability as a defining feature. In this paper, a defect prediction framework integrating multiple deformation mechanisms was constructed to simulate wrinkle formation during automated fiber placement. A hypoelastic constitutive model was developed to capture the mechanical response of unidirectional thermoplastic prepreg. The formation mechanisms of wrinkles under varying temperatures and steering radii were investigated, and the predictive capability of the model was validated experimentally. Wrinkle defects were attributed to mechanical instabilities driven by the interplay of deformation mechanisms, evolving through a dynamic process of shear compensation followed by buckling instability. Experimental and simulation results demonstrated that, as the temperature increased, in-plane shear deformation became the dominant mechanism, dissipating part of the compressive strain energy and thereby mitigating axial buckling. Wrinkle formation was fundamentally driven by axial compression induced by placement trajectory curvature. With reduced steering radii, bending progressively became the prevailing mechanism, while interlaminar bonding was insufficient to restrict fiber motion or accommodate it through shear. The localized accumulation of compressive strain energy subsequently triggered prepreg buckling, resulting in the formation of wrinkle defects.