Experimental observations of microstructural influences on the mechanics of wood cell bundles in tension

The influences of the degradation and post degradation of a cellulosic wood fiber under tensile loading on its mechanical behaviour are shown. The variation of the longitudinal Young's modulus for a small group of wood fibers of Silka Epicea during a tensile loading are investigated. Small size specimens (30 × 2 × 0.2 mm) consisting of early and late wood fibers are prepared and tested by microtesting device, large and irreversible deformation are observed and load-extension curves obtained for both fiber consist of three distinct segments. The first segment gives an overall Young's modulus of the fibers before any degradations of the wood substances. Beyond this point the specimen becomes less stiff and undergoes a large, mainly irreversible deformation under load increase. This is attributed to the degradation of the media. The further increase of the loading is followed with a steeper segment (third segment) of the load-extension curve. At the end the microfibrils totally fails.