Stress degradation mechanism of coal macromolecular structure: Insights from molecular dynamics simulation and quantum chemistry calculations

•Simulations based on the Wender coal macromolecular structure model were performed.•The relaxed force constants of bonds and bond angles were obtained.•Two chemical bond breakage types were identified: tensile break and shear break.•The mechanisms of the two bond breakage types were determined.•Small gas molecules were produced during Wender coal shearing.