13th International Conference on Fracture June 16–21, 2013, Beijing, China -2- moisture content variations. In addition, numerical modeling has been used in order to model the alteration of mechanical properties of wood during drying phase or to study the shape of sawn timber subjected to moisture variation. Simultaneously, several authors have coupling numerical and experimental techniques to analyze the shrinkage . Among them, Kowalski et al. [6] have shown the efficiency of the analytical approach for the identification of fracture process in dried wood based on acoustic emission technique; Kowalski et al. have also presented a model of drying providing the evaluation of moisture content distribution in wood during the drying rate periods, with the moisture content at the body surface reaches the fiber saturation point (FSP). In this work, the radial and tangential strains (inducing crack process) due to the natural drying of a green wood slice are investigated by analytical, experimental and numerical methods. The first part of the paper recalls the experimental setup composed of a green wood slice in Douglas, a high-sensitivity balance and a video camera. The device is based on the mark tracking method composed of an acquisition system date recording the displacement of targets posted on the wood slice during the drying phase. Simultaneously, the sample is placed on an electronically balance providing the weight measure versus time. The second part details the analysis of experimental results; in this case, the evolution of moisture content versus time is posted in order to obtain the PSF. The radial and transversal strains are computed according to an analytical approach based on a mathematical model coming from cylindrical strain calculations. In the last part, this analytical method is coupling with the swelling-shrinkage tensor taking into account an orthotropic configuration. The finite element calculation is limited, in this paper, at an elastic behavior integrating a mechano-sorptive effect. Also the actual numerical model predicts the cracking due to the transversal shrinkage. 2. Experimental setup The experimental protocol is based on a green wood slice in Douglas fir with a thickness of 30mm just peeled. Sample is initially conditioned in water in order to assure its saturation. As shown in Figure 1, the preparation of the specimen consists of drawing black marks according to a polar reference centered at the sample heart. In a second step, the sample is placed in the experimental chamber in which the temperature of 22°C and a relative humidity of 33%RH are maintained constant. The sample is placed on a precision balance in order to measure the masse evolution during the drying process. In the same time, black marks allow performing a marking tracking protocol in order to record displacements of these marks using the videometric technology [18]. Versus time, sample mass, displacements and the crack evolution are simultaneously recorded until the mass stability corresponding to the moisture content balance. In order to evaluate the average value of moisture content, samples are placed in a 103°C environment by using an oven. Figure 1. Experimental sample and device
RkJQdWJsaXNoZXIy MjM0NDE=