A Review of Wood Compression along the Grain—After the 100th Anniversary of Pleating

This study focuses on the compression of wood along the grain (also known as pleating), a modification that improves the pliability of higher-density hardwoods with a moisture content above 20%. Pleated wood can be bent into small curves in any direction. The success of the industrial pleating process in some parts of the world is influenced by many factors, such as wood species, wood quality, moisture content, compression ratio, fixation time, etc. Pleating by 20% causes the modulus of elasticity to decrease to one-third for oak and beech, and the bending ratio can be increased above ½. Bending stress decreases and the absorbed energy increases multiple times. The impact bending strength also increases significantly. The walls of cells crinkle by pleating and the microfibrils of the fibres become distorted. Many patents, articles, and books on this subject have been published since 1917, and this review attempts to introduce and, where necessary, critically analyse them.