The difference of creep compliance for wood cell wall CML and secondary S2layer by nanoindentation

Wood is generally considered a linear orthotropic viscoelastic. The creep of cell wall under long-term load is important for the deformation and destruction of wood. The aim of this study was to investigate the difference of creep compliance between compound middle lamella (CML) and secondary S(2)layers by nanoindentation creep testing. The results indicated that the creep compliance of cell wall under compression along grain increased with the maximum load and loading rate increasing. Furthermore, the creep compliances and creep compliance percentages of the CML layer were more than that of the secondary S(2)layer, and the viscoelastic behavior of the CML layer also was more sensitive to MC compared with the S(2)layer. Finally, the Burgers' model was appropriate for predicting the viscoelastic behavior of wood cell walls. The parameters of Burgers' model dropped markedly with increased MC. These parameters in the CML layer also were lower than those of S(2)layer. The differences of creep properties between the CML and S(2)layers can prove that the slippage failure of cell wall under compression along grain occurs in the S(2)layer.