Study on mechanical properties of wood under different cyclic loading protocols in compression perpendicular-to-grain

The cyclic mechanical behavior of wood in the perpendicular-to-grain direction is critical for analyzing its structural performance under repeated loading. This study experimentally evaluated Douglas fir and Larch wood under three distinct cyclic loading protocols in the radial and tangential directions. The results demonstrate that under radial perpendicular-to-grain compression, both wood species exhibit characteristic “S” or “V” shaped bending deformation, accompanied by a pronounced stress enhancement in the later loading stage, while the compressive strength under constant-amplitude monotonic cyclic compression was the lowest among all protocols. Under tangential loading, Douglas fir experiences more severe damage under both constant-amplitude multi-cyclic compression and graduated-amplitude cyclic compression. In contrast, Larch shows significant compressive deformation and primarily shear failure under all three protocols. Compared to the compressive strength under constant-amplitude monotonic cyclic compression, the tangential compressive strength under graduated-amplitude cyclic compression was 17.88% and 27.6% higher for the two wood types, respectively. Based on the findings, a skeleton constitutive model considering different cyclic loading protocols is proposed for both wood species in the radial and tangential directions. The model’s reliability is verified by comparing experimental curves and theoretical constitutive curves.