Size and shape effects of wood compression energy absorption characteristics

Objective The research aimed to investigate the influence of specimen size and shape on wood compression energy absorption characteristics and guide the scientific test and evaluation of wood compression energy absorption properties.

Method Through a quasi-static large deformation compression test, the compressive response and energy absorption characteristics of Populus tomentosa, Chinese fir, paulownia and balsa wood under the different cross-sectional dimensions (20 mm × 20 mm, 50 mm × 50 mm), different cross-sectional shapes (20 mm round and 20 mm × 20 mm square) were investigated, and analyzed by t-test.

Result (1) The stress-strain curve of wood under compression was unaffected by specimen size and shape, following a “three-stage” pattern. (2) The size effect of wood compressive crushing strength along grain was significant, and the crushing strength decreased with the increase of specimen size. The crushing strength along the grain of paulownia and balsa wood decreased from 30.94 and 14.56 MPa for small-sized specimens to 26.06 and 13.37 MPa for large-sized specimens, and the size effect coefficients were 0.84 and 0.92, respectively. The transverse compressive strength, the failure mode and compressive energy absorption performance of wood along grain and cross grain were all not affected by specimen size. (3) The compressive crushing strength along the grain of wood had a significant shape effect. The compressive strength of four kinds wood along the grain of round specimens was smaller than that of square specimens, and the shape effect coefficient ranged from 0.88 to 0.93. The specimen shape effect of wood compression failure mode and energy absorption performance was related to tree species characteristics. The failure mode and energy absorption performance of Chinese fir, paulownia and balsa wood were not influenced by the specimen shape. The energy absorption performance of the round specimens of Populus tomentosa wood was significantly greater than those of the square specimens, which had an obvious shape effect. (4) The compressive strength of wood increased with an increase in wood density and compressive strength, with a more apparent size and shape effect.

Conclusion The energy absorption characteristics of low-density wood have no size and shape effects, so it is recommended to use small-size square specimens with easy sampling, simple processing, fewer consumables and low cost for compression energy absorption evaluation.