Fracture in thermoplastics is fundamentally a multiscale process, where nanometre-scale polymer chain movement drives micrometre-scale mechanics. Because neither traditional experiments nor conventional simulation methods can access these dimensions simultaneously, it remains an enigma how these fracture processes are linked across the scales. In the end, a critical challenge remains: Bridging the atomic (nanometre) and microscopic length scales to fully connect molecular architecture to global failure properties. While numerous multiscale simulation techniques are being developed to reduce or even close this gap, their validation is hindered by a severe lack of suitable, high-fidelity benchmark data spanning both the nano- and micro-regimes. To provide this crucial data, we developed a novel framework that successfully upscales an established coarse-grained molecular dynamics (MD) model of a generic thermoplastic. This approach enables simulations covering multiple micrometres of material using up to 30 million coarse-grained superatoms, significantly exceeding previous MD limits. We systematically investigate the influence of boundary conditions, pre-crack length, and key chain properties (chain length, chain entanglement and bending stiffness) on crack propagation. Our analysis reveals two major findings essential for multiscale modelling: first, crack propagation in thermoplastics is not governed by a minimal pre-crack length, but is primarily sensitive to the interplay between boundary conditions and simulation domain size. Second, we can identify and characterise an inactive zone - an obstacle region - that forms immediately between the crack tip and the developing polymer fibrils. This zone, whose existence was previously only hinted at, must be overcome for sustained crack growth, representing a key nanoscale mechanism. These micrometre scale MD simulations offer multiscale insights into failure of thermoplastics and provide the robust, high-resolution benchmark data necessary for the confident development and validation of next-generation multiscale modelling techniques for thermoplastics.
Richter et al. (Thu,) studied this question.