Issue 31

J. Xavier et alii, Frattura ed Integrità Strutturale, 31 (2015) 13-22; DOI: 10.3221/IGF-ESIS.31.02 13 Determining mode I cohesive law of Pinus pinaster by coupling double cantilever beam test with digital image correlation J. Xavier Centre for the Research and Technology of Agro-Environmental and Biological Sciences, CITAB, University of Trás-os-Montes and Alto Douro, UTAD, Quinta de Prados, 5000-801 Vila Real, Portugal. INEGI, FEUP, University of Porto, Rua Dr. Roberto Frias, 4200-465 Porto, Portugal. jxavier@inegi.up.pt M. Oliveira Centre for the Research and Technology of Agro-Environmental and Biological Sciences, CITAB, University of Trás-os-Montes and Alto Douro, UTAD, Quinta de Prados, 5000-801 Vila Real, Portugal. Instituto Superior Politécnico de Viseu, Departamento de Engenharia de Madeiras, Viseu, Portugal J.J.L. Morais Centre for the Research and Technology of Agro-Environmental and Biological Sciences, CITAB, University of Trás-os-Montes and Alto Douro, UTAD, Quinta de Prados, 5000-801 Vila Real, Portugal. M.F.S.F. de Moura INEGI, FEUP, University of Porto, Rua Dr. Roberto Frias, 4200-465 Porto, Portugal. A BSTRACT . The direct identification of the cohesive law in pure mode I of Pinus pinaster is addressed. The approach couples the double cantilever beam (DCB) test with digital image correlation (DIC). Wooden beam specimens loaded in the radial-longitudinal (RL) fracture propagation system are used. The strain energy release rate in mode I ( I G ) is uniquely determined from the load-displacement ( P   ) curve by means of the compliance-based beam method (CBBM). This method relies on the concept of equivalent elastic crack length ( eq a ) and therefore does not require the monitoring of crack propagation during test. The crack tip opening displacement in mode I   I w is determined from the displacement field at the initial crack tip. The cohesive law in mode I I I ( ) w   is then identified by numerical differentiation of the I I G w  relationship. Moreover, the proposed procedure is validated by finite element analyses including cohesive zone modelling. It is concluded that the proposed data reduction scheme is adequate for assessing the cohesive law in pure mode I of P. pinaster . K EYWORDS . Wood; Mode I fracture mechanics; Double cantilever beam test; Cohesive law; Digital image correlation.