To elucidate the mechanism of wood sandwich compression, the response of wood compressing yield stress to hygrothermal conditions was investigated in this study with respect to preheating temperature (30–210 °C) and moisture content (MC, 0–100 %). An associated functional model was developed to predict wood yield stress based on the measured MC and temperature in wood. A 1 % increase in wood MC or a 10 °C increase of temperature led to a decrease in wood yield stress exceeding 0.1 MPa. Significant variations in yield stress, exceeding 0.8 MPa, were observed between high MC layer(s) and the remaining layer(s) along the wood thickness when there was an MC variation over 5 %. Preheating the wood with by heating platens accelerated water/moisture migration in wood, resulting in relatively low yield stress in the wood interior areas where water/moisture had migrated. This study demonstrated that the comparatively low yield stress of some wood areas was responsible for sandwich compression. When mechanically compressed, only the wood layer(s) with lower yield stress was compressed, leading to sandwich compression, regardless of whether the mechanical force was applied tangentially or radially.

中文翻译：

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从屈服应力角度阐明木材夹层压缩的机理

为了阐明木材夹层压缩的机理，本研究调查了木材压缩屈服应力对湿热条件的响应，包括预热温度 (30–210 °C) 和水分含量 (MC, 0–100 %)。开发了一个相关的功能模型，以根据木材中测得的 MC 和温度来预测木材屈服应力。木材 MC 增加 1% 或温度增加 10 °C 会导致木材屈服应力降低超过 0.1 MPa。当 MC 变化超过 5% 时，在高 MC 层和沿木材厚度的剩余层之间观察到屈服应力的显着变化，超过 0.8 MPa。通过加热压板预热木材加速木材中的水/水分迁移，导致水分/水分迁移的木材内部区域的屈服应力相对较低。这项研究表明，一些木材区域相对较低的屈服应力是造成夹层压缩的原因。当机械压缩时，只有具有较低屈服应力的木层被压缩，导致夹层压缩，无论机械力是切向还是径向施加。