13th International Conference on Fracture June 16–21, 2013, Beijing, China -2- method, Stress Intensity Factor (SIF) is defined by introducing a mixed-mode separation algorithm. For isotropic as for orthotropic configurations, stress distribution into the crack tip domain is assumed to be unaffected by elastic properties [5-7]. By aggregating the results of CRDF yielded by experimental DIC and SIF, as given by a numerical FEM, the prediction of an accurate energy release rate can be proposed. Fracture mode separation is also analyzed by establishing mode I and mode II energy release rates for mixed-mode loading conditions as well as plane configurations. 2. Experimental material and methods The experimental evaluation of has been performed for several mixed-mode ratios. As shown in Figure 1, the experimental set-up involves an electromechanical press fitted with an LVDT displacement transducer and a load cell. The specimen geometry is a single-edge notched sample made from Polyvinyl Chloride (PVC) for the isotropic case and Douglas fir in the orthotropic case. The specimen dimensions are 3 208 144 10mm 创 for the PVC specimen and 3 210 150 10mm 创 with a notch length equal to 75mm. The various mixed-mode loading configurations are applied thanks to Arcan fixtures that allow imposing a number of different mixed-mode ratios defined by the angle between force direction and crack orientation. The test is run under a displacement control with an imposed velocity of the cross-head equal to 0.1 mm/s. 1 3 4 2 Mode I Mode II x1 x2 1 – Specimen 2 –Arcan fixtures 3 –Electromechanical press 4 – CCD camera Figure 1. Experimental setup Concerning measurement devices, the displacement field evolution is recorded on the specimen surface using an 8-bit CCD camera (1392 1040pixel ´ ). The image capture is performed at a rate of 1 frame per second and synchronized with the electromechanical press data (force and displacement). According to the DIC principle, a black-and-white speckled pattern is projected onto the specimen surface [10, 11]. The principle of this full-field method is based on a comparison between two images acquired during the test, one before deformation and the other after. The displacement field can then be obtained by comparing the reference image with the deformed image [10, 11]. The displacement fields, as presented in the present paper, are limited to 2D measurements. 3D effects are neglected (out-of-plane of crack lips or shear buckling induced by the specimen thickness), and plane stress state has been assumed.
RkJQdWJsaXNoZXIy MjM0NDE=