7 th EUROMECH Solid Mechanics Conference J. Ambrosio et.al. (eds.) Lisbon, Portugal, 7–11 September 2009 FEM SIMULATION OF CRACK GROWTH IN GLULAM BY USING A 3D ORTHOTROPIC–VISCOELASTIC MODEL AND COHESIVE ELEMENTS Giuseppe Zagari 1 , Stefania Fortino 2 and Gerhard Dill–Langer 2 1 University of Calabria Via P. Bucci, Cubo 39/b - 87036 Arcavacata di Rende (CS) - Italy e-mail: gzagari@unical.it 2 VTT - Technical Research Centre of Finland P.O.Box 1000, FIN - 02044 VTT stefania.fortino@vtt.fi e-mail: stefania.fortino@vtt.fi 3 MPA University of Stuttgart, Otto-Graf-Institut (FMPA) Abteilung Holzbau, Pfaffenwaldring 4b - 70569 Stuttgart - Germany e-mail: gerhard.dill-langer@mpa.uni-stuttgart.de Keywords: Glued laminated timber, Viscoelastic creep models, Mode I wood fracture, Crack growth, Cohesive elements, Generalized J integral, FEM, Abaqus code. Abstract. This paper presents a three–dimensional orthotropic–viscoelastic model for the anal- ysis of cracked wood structures under short–term loading or sustained loads in the presence of constant values of temperature and moisture content. Kelvin–type elemental deformations are used for describing the viscoelastic creep and the whole constitutive model is implemented into the Umat user subroutine of Abaqus FEM code. The crack growth simulation under short– term loading is done by using a suitable exponential damage law and the cohesive elements of Abaqus in the fracture process zone. The optimal parameters for the damage law are determined through a parametric study involving a certain number of nonlinear analyses for monotonically proportional loads scaled with respect to the experimental fracture energy of the specimen. The proposed computational approach is validated by analyzing glued laminated (glulam) spec- imens under opening mode and the numerical load–displacement curves are compared with both literature results and experimental data obtained in the context of the present research. For long–term fracture tests under sustained loads and constant moisture content, a criterion of crack initiation based on a viscoelastic integral parameter is also introduced. Both the pro- posed constitutive model and the computational approach can be further extended to cases of crack propagation in presence of variable humidity conditions. 1