Issue 31

J. Xavier et alii, Frattura ed Integrità Strutturale, 31 (2015) 13-22; DOI: 10.3221/IGF-ESIS.31.02 21 Specimens 1 A 2 A p I,0 w I u w I c w Iu  Logistic Exponential (N/mm) (N/mm) (-) (mm) (mm) (mm) (MPa) (MPa) 1 0.001 0.32 1.51 0.014 0.005 0.14 9.19 9.81 2 0.002 0.23 1.60 0.019 0.008 0.14 7.20 7.45 3 0.023 0.26 3.15 0.019 0.016 0.08 10.5 8.00 4 0.005 0.25 2.48 0.026 0.019 0.13 6.95 6.01 5 0.013 0.26 2.14 0.027 0.017 0.15 6.15 5.69 6 0.004 0.26 1.82 0.016 0.008 0.12 10.2 10.0 7 0.005 0.18 2.37 0.015 0.010 0.08 8.28 7.35 8 0.009 0.25 1.86 0.033 0.018 0.18 4.58 4.38 9 0.013 0.27 2.64 0.038 0.028 0.16 5.33 4.38 10 0.004 0.23 2.24 0.024 0.014 0.13 6.70 6.06 Mean 0.008 0.25 2.18 0.023 0.014 0.13 7.51 6.93 Coefficient of variation C.V.(%) 87.2 13.8 23.1 34.3 47.2 22.9 26.6 28.5 Table 4 : Parameters of the logistic function ( 1 A , 2 A , p and I,0 w ), and characteristic values of maximum stress ( Iu  ) and relative displacements ( I u w , I c w , see Fig. 2) determined by the Irwin-Kies equation. C ONCLUSIONS he resistance curves in mode I of P. pinaster were determined by applying the CBBM and Irwin-Kies equations to the DCB fracture test. Initial and critical strain energy release rates in mode I were then determined. By combining these strain energy release rate values, determined from both CBBM and Irwin-Kies equations, with CTOD in mode I provided by DIC, characteristic R –curves and cohesive laws in mode I for P. pinaster were evaluated by the direct method. Results were consistent with literature values. Moreover, the proposed procedure was validated by finite element simulations using a cohesive zone model with a bilinear softening law that was adjusted to the experimental ones. The good agreement observed between numerical and experimental results demonstrates the adequacy of the proposed procedure in the determination of the wood cohesive law under mode I fracture. A CKNOWLEDGEMENT his work is supported by European Union Funds (FEDER/COMPETE - Operational Competitiveness Programme) and by national funds (FCT - Portuguese Foundation for Science and Technology) under the project FCOMP-01-0124-287 FEDER-022692. The authors would like to acknowledge the support of FCT under the project PTDC/EME-PME/114443/2009 and Ciência 2008 program. R EFERENCES [1] Satyanarayana, K., Arizaga, G.G.C., Wypych, F., Biodegradable composites based on lignocellulosic fibers – An overview, Prog Polym Sci, 34 (2009) 982–1021. [2] Xavier, J., Belini, U., Pierron, F., Morais, J., Lousada, J., Tomazello, M., Characterisation of the bending stiffness components of MDF panels from full-field slope measurements, Wood Sci Technol, 47 (2013) 423–441 [3] FAO, State of the World's Forests 2009 Report. Part 2 - Adapting for the future. UN Food and Agriculture Organization (2009). T T