Research on static and dynamic mechanical properties of spruce wood by three loading directions

Quasi-static and dynamic compression experiments ofspruce wood along axial, radial and tangential loading directions areimplemented by INSTRON and Hopkinson pressure bar equipments. Averagemoisture content and density of the spruce specimens are 12.72\% and413kg/m^3. Compression modulus and curves of quasi-static compressionstress versus strain are gained by static compression experiment. And therelation of dynamic stress versus strain is obtained by dynamic compressionexperiments with three strain rates. The experiment results show that thefailure modes of spruce specimens are fiber buckling and wrinkle whenloading direction is along the grain. When loading direction is along radialor tangential across to the grain, the failure modes is wood fiber slippageand delamination. Axial compression modulus is about twenty-one times asthat of radial across to the grain, and about thirty-two times as that oftangential across to the grain. Axial quasi-static compression yieldstrength is about nine times as that of radial and tangential across to thegrain. The radial and tangential quasi-static compression yield strengthsare almost equal. Dynamic compression yield strength of spruce wood issensitive to strain rate. The axial, radial and tangential dynamiccompression yield strengths increase greatly when strain rate is from500 to 1000s^ - 1. In addition, theory analytic solution tosingle wood cell failure under different direction compression is carriedout. The obtained expression shows that the mean limit loading is relativeto yield stress, cell structure dimension and wrinkle length for completewrinkle cases.