Wood moisture and temperature dependent impact-induced fracture toughness-brittle transition

As an engineering structural material, wood is increasingly demanded for its remarkable advantages. When exposed to shallow and deep cryogenic temperature environment environments, its mechanical properties deviate from those at normal temperature due to temperature-humidity effects. However, current research has paid little attention to the service failure risk caused by brittle fracture of wood in engineering applications, especially when subjected to unexpected impact stress in cold region. To fill this gap, the impact toughness (A_w) of Populus ussuriensis and Larix gmelinii wood under three humidity conditions was examined across a wide temperature range (-196 °C to 60 °C) to investigate their tough-brittle transition (TBT) characteristics. Results show that the impact fracture morphology of wood gradually presented brittle fracture characteristics with decreasing temperature, and higher moisture content (MC) accentuated these brittle characteristics. The A_w of both wood species decreased with temperature, with two inflection points around 0 °C and in the range of − 60 °C to − 40 °C. The temperature range of − 40 °C to − 60 °C was a critical zone where fracture properties of wood shift from toughness to brittleness, increasing the risk of brittle-fracture. A strong linear relationship existed between temperature and A_w for each MC level (R² ≥ 0.89). Additionally, a multivariate nonlinear model of A_w based on temperature and MC was developed with a high goodness of fit (R² ≥ 0.96). These findings lay a foundation for predicting brittle-fracture risks in wooden components and offer deeper insights into their mechanical behavior in cold-climate engineering applications.