Experimental characterization of the delamination of plywood panels for CEIBA and BIRCH species

To characterize the delamination's propagation of Ceiba and Birch plywood panels, we used the energy approach which considers that the propagation of the crack is a phenomenon of energy dissipation. To determine this parameter, we considered various experimental tests. Then, we realised a comparative study between the delamination behavior of these two wood species . These tests include the DCB test for pure mode I delamination, the ELS test for pure mode II, and the MMF test for the mixed I + II mode. For each of the specimens, a thin film of Teflon was inserted in the middle plane, thus creating a pre-delaminated zone which will serve to initiate the delamination. The width of the insert varies according to the type of the specimens. The DCB test consists in propagating a crack within a bonded joint under stress and in measuring the resistance of this joint to the propagation of this crack. The purpose of the ELS test is to characterize shear delamination of composite materials. This test is characterized by its stability of the delamination propagation when compared to the three-point bending test. The sound side of the specimen is embedded while the side containing the artificial defect is loaded in the direction of thickness. To characterize delamination in mixed mode I and II, we chose the MMF test which is very practical to deploy because it uses the same assembly and the same test specimen as those of the ELS test. The loading is modified in order to impose a bending in a single lip of the delaminated part of the specimen. In this configuration, the specimen undergoes both a Mode I load and a Mode II load. The energy restitution rates in Mode I () and Mode II () can be determined using the modified beam theory. For each test, a typical force-displacement response (P-d) curve will be presented. From these experimental results, the rate of critical energy restitution (Gc) can be determined by the experimental complacency method after carrying out the characterization tests of the test specimens. Once these values are known, it will then be possible to predict and anticipate the delamination of the plywood. The delamination length is measured by visual observation using a video camera which allows the delamination to be tracked from the beginning to the end of the propagation, the beginning of the propagation being defined as a small propagation of about 1 mm from a pre-cracking. To conclude, several delamination propagation criteria will be evaluated in order to choose the criterion that models better the delamination failure response for both Ceiba and Birch