Critical role of reducing interfacial friction in compressive creep characterisation of pinewood

Compressive creep tests (CCTs) are widely used in viscoelastic characterisation of wood. However, the prevalent use of dry friction conditions in wood CCTs often introduces considerable uncertainties into the acquired creep data. To address this critical issue, this study proposes a simple yet more accurate CCT-based strategy for viscoelastic characterisation of wood. In this strategy, oil-lubricated conditions are first designed to reduce interfacial friction in CCTs, followed by optimally fitting of the obtained creep data using multi-element (generalised) viscoelastic models. To validate this strategy, comparative CCTs of typical pinewood samples under both oil-lubricated and dry-friction conditions are conducted, and numerical simulations of the CCTs are further performed. The results indicate that: (i) the axial deformation of pinewood in dry-friction CCTs can be significantly underestimated (by up to 28.45%), leading to unrealistic creep data and viscoelastic parameters. (ii) Viscoelastic parameters calibrated from lubricated CCTs can achieve the desired creep prediction accuracy (97.09%), demonstrating a 19.28% improvement over those from unlubricated CCTs. The findings of this study highlight the critical role of reducing interfacial friction in CCTs of the pinewood, with broader implications for the accurate characterisation and prediction of the creep behavior in various woods and timber structures.