International audienc

The thermo-visco-hydro-mechanical (TVHM) loading of Abies Alba Mills (white fir of Massif Central) is investigated in this paper. A full-field measurement technique, namely the grid method, is used in the experiments in order to observe heterogeneities and to measure strain fields in the annual growth rings. This enables the investigation of the effects of moisture content changes on the strain of latewood and earlywood during creep and recovery. The tested specimens are first conditioned to a given moisture content. Each of them is then subjected to a compression test and regularly removed in order to measure the moisture content. A positioning system is developed to ensure the consistent location of each specimen with respect to the camera. Before loading, images are taken using a CCD camera to highlight the impact of moisture conditioning. Images are also acquired during the loading steps, and between each recovery step after complete unloading. All the strain maps are determined with respect to a reference image taken either before the water conditioning of the specimen or before loading. During the experiments, strain gradients clearly appear between latewood and earlywood, highlighting the variability of the mechanical properties at the ring scale. The effect of moisture content changes on the mechanical behavior of wood at the ring scale is evidenced and discerned.