Moisture-dependent elastic and plastic properties of pine wood and bamboo cell wall layers measured by nanoindentation

Abstract A more systematic, multiscale characterization of the mechanical properties of lignocellulosic materials, such as wood and bamboo, is needed so that manufacturers can better tailor their properties for specific end-uses. Nanoindentation was used to assess the mesoscale elastic modulus ( <m:math xmlns:m="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <m:msubsup> <m:mi>E</m:mi> <m:mi>S</m:mi> <m:mrow> <m:mi>N</m:mi> <m:mi>I</m:mi> </m:mrow> </m:msubsup> </m:math> ${E}_{S}^{NI}$ ) and Meyer’s hardness ( H ) of secondary cell wall layers (SCWL) in Moso bamboo, and S 2 SCWL and compound corner middle lamella (CCML) in loblolly pine. The anisotropic SCWL was tested in both longitudinal and transverse directions. The effects of moisture content (MC) were studied by testing specimens conditioned between 1 % and 92 % relative humidity (RH). Both pine and bamboo SCWL exhibited many of the same features in their MC- and orientation-dependent <m:math xmlns:m="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <m:msubsup> <m:mi>E</m:mi> <m:mi>S</m:mi> <m:mrow> <m:mi>N</m:mi> <m:mi>I</m:mi> </m:mrow> </m:msubsup> </m:math> ${E}_{S}^{NI}$ and H results, which suggested that the features were general characteristics of SCWL from different plants. A new transition in plasticity was observed around 2–4 % MC in which the SCWL transverse H had a sudden 20 % decrease. For comparison to literature plasticity S 2 SCWL uniaxial compression flow stress ( σ ) measurements made using micropillar compression testing, a H -derived uniaxial compression flow stress ( σ H ) was calculated using established methods. The σ H compared well to the literature σ , which supported that both H and σ can be used to similarly study plastic deformation mechanisms.