Hydrolytic aging-induced embrittlement in short-fiber reinforced polyamide: A micromechanical approach using numerical homogenization

This work introduces a simulation framework for predicting the durability of 30 wt.% glass fiber reinforced polyamide-66 (PA66-GF30) composites under hydrolytic aging by directly coupling a chemical aging descriptor, the number-average molar mass ( M n ), with a local mechanical failure indicator at the matrix level. Unlike prior studies that correlates M n with global composite properties such as strain-at-break or maximum stress, the proposed approach targets the polyamide matrix, which is primarily affected by hydrolysis, enabling a more physical description of embrittlement. The identification of a local failure indicator was performed using FFT-based numerical homogenization on a representative three-dimensional microstructure, which was reconstructed from high-resolution micro-computed tomography ( μ CT) data. Accumulated plastic strain ( A P S ) was found as a robust, orientation-independent criterion of failure initiation that correlates linearly with the drop of the M n . The model predicts a critical M n of approximately 18 kg⋅mol -1 for full embrittlement in PA66, consistent with values of the literature. Failure modeling was validated at the macroscale using FE-based simulations of hydrolyzed injection-molded components loaded in tension mode. This modeling approach is applicable to different hygro-thermal conditions and constitutes one of the first integrated chemo-mechanical simulation methods for fiber-reinforced polyamides. This framework provides a promising route for mechanistic-based lifetime assessment of polymer-based engineering components in hydrolytic environments.