Multiscale micromechanical modeling of the elastic properties of the S2 layer in archaeological wood cell walls

Predicting the elastic properties of archaeological wood is challenging because chemically driven degradation, including constituent loss and compositional change, is coupled across scales with microstructural evolution such as porosity development and moisture variation. This study develops a parameterized multiscale composition–structure–property framework for the secondary-wall S2 layer based on Voigt–Reuss mixing relations. Constituent-loss coefficients are introduced to translate chemical analyses of archaeological Chinese fir into a micromechanical model of the S2 layer, and molecular dynamics simulations are used to provide the moisture-dependent elastic and shear moduli of crystalline cellulose, amorphous cellulose, hemicellulose, and lignin as constitutive inputs. The model predicts the effective elastic properties of the S2 layer in both modern and archaeological Chinese fir, showing good consistency with nanoindentation-derived apparent stiffness measurements within the defined validation scope. The results suggest that stiffness reduction in archaeological wood is governed by the coupled effects of constituent degradation, moisture-induced matrix softening, and porosity development. The proposed framework provides a quantitative basis for relating chemical composition and microstructural change to the effective mechanical response of degraded wood cell walls, and may support the mechanical assessment and conservation of archaeological wood.