Experimental observations and micromechanical modeling of successive-damaging phenomenon in wood cells’ tensile behavior

Single wood cells have complex tensile behavior. To gain insight into this complex functionality, the behavior of single wood tracheids was studied under controlled cyclic tensile loading. The cyclic tensile stress–strain curves show that beyond the yield point the tracheid undergoes permanent deformations and its rigidity increases. As in plasticity elastic (or visco-elastic) unloading takes place and energy is dissipated by permanent deformation. Consequently, single tracheids show a load-history dependent behavior. To understand the intervening mechanism in the process of elasto-plastic response of a wood tracheid, a micromechanical based model was developed. This model permits us to describe the influence of non-uniformity of microfibril angle (MFA) and other defects on the wood cell rigidity and to discuss different scenarios, which may occur during the tensile test. Successive damage of the hemicelluloses and lignin matrix and reduction of MFA as mainly responsible for elasto-plastic response of a wood cell were suggested. It should be noted that this paper is part of the research work which has been reported previously (Navi et al. in Wood Sci Technol 29:411–429, 1995; 36:447–462, 2002; Sedighi-Gilani et al. in Wood Sci Technol 39:419–430, 2005).