Stereovision measurements on evaluating the modulus of elasticity of wood by compression tests parallel to the grain

In this work, the evaluation of the longitudinal modulus of elasticity (E-L) of maritime pine (Pinus pinaster Ait.) was investigated by means of compression tests parallel to the grain. Strain data was collected by digital image correlation (DIC) and compared with results from glued strain gauges. The DIC method provided similar results compared to the strain gauge measurements, but with reduced scatter due to higher gauge area, making the technique less sensitive to the wood heterogeneity (earlywood and latewood layers). The influence of the specimen parasitic end-effects (i.e., friction and damage) on the apparent modulus of elasticity was further investigated by testing specimens with different cross-sections and lengths. The apparent modulus of elasticity is underestimated for increasing specimen cross-sections and decreasing specimen lengths. Friction has a negligible effect on apparent modulus of elasticity, while the extension of the damaged contact zone is the governing phenomenon. (C) 2011 Elsevier Ltd. All rights reserved.