The sapwood and heartwood of plantation sugi wood (Cryptomeria japonica), and plantation hinoki (Chamaecyparis obtusa) wood were flat-sawn into timbers, then kiln-dried to a MC level below 12%. These timbers were further processed into specific sizes and wetted on the surfaces, preheated at 150 °C and radially compressed into sandwich compressed timbers. Density distribution, compressed layer(s) position and thickness, surface hardness were investigated. It was demonstrated that sugi and hinoki timbers were both applicable for sandwich compression. By controlling the preheating time, sugi heartwood timber, sugi sapwood timber and hinoki timber can be all sandwich compressed, which resulted in surfaces compressed timbers, interior compressed timbers and center compressed timbers. When sugi timbers were sandwich compressed, density only tremendously increased in the earlywood. The increased density of the compressed sugi earlywood was independent of compressed layer(s) position, compressing distance or annual growth width, while for hinoki timbers compression, density increased both in earlywood and latewood. Surface hardness of the uncompressed sugi sapwood was almost twice of that of the uncompressed sugi heartwood. Surface compression sharply increased the surface hardness of sugi heartwood and sugi sapwood. Interior compression and center compression also contributed to increased surface hardness for the compressed timbers, but to smaller extents. Surface hardness change due to the surface compression was consistent with the surface average density change of timbers. Compression layer(s) position exerted statistically significant effects on the surface hardness, while surface hardness of the compressed wood was almost unrelated to the original density of the used wood or average density of the sandwich compressed wood. However, bigger compressing distance led to bigger surface hardness for the surface compressed wood.

中文翻译：

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杉木（Cryptomeria japonica）和扁柏（Chamaecyparis obtusa）木材的夹层压缩：密度分布、表面硬度及其可控性

人工林杉木 (Cryptomeria japonica) 和人工林桧木 (Chamaecyparis obtusa) 的边材和心材被平锯成木材，然后窑干至 MC 水平低于 12%。这些木材被进一步加工成特定尺寸并润湿表面，在 150 °C 下预热并径向压缩成夹层压缩木材。研究了密度分布、压缩层位置和厚度、表面硬度。结果表明，杉木和丝柏木材均适用于夹层压缩。通过控制预热时间，杉木心材、杉边材和丝柏都可以进行夹层压缩，从而产生表面压缩木材、内部压缩木材和中心压缩木材。当杉木被夹心压缩时，密度仅在早材中显着增加。压缩杉早材的密度增加与压缩层位置、压缩距离或年生长宽度无关，而对于扁柏木材压缩，早材和晚材的密度增加。未压缩的杉木边材的表面硬度几乎是未压缩的杉木心材的两倍。表面压缩显着增加了杉心材和杉边材的表面硬度。内部压缩和中心压缩也有助于增加压缩木材的表面硬度，但程度较小。由于表面压缩引起的表面硬度变化与木材的表面平均密度变化一致。压缩层的位置对表面硬度产生统计上的显着影响，而压缩木材的表面硬度与所用木材的原始密度或夹层压缩木材的平均密度几乎无关。然而，更大的压缩距离导致表面压缩木材的更大表面硬度。