Issue 48

M. Estrada et alii, Frattura ed Integrità Strutturale, 48 (2019) 348-356; DOI: 10.3221/IGF-ESIS.48.33 352 considering the continuum strong discontinuity approach [19,20]. The developed program was tested in different simulations. R ESULTS : NUMERICAL SIMULATION OF SPECIMENS SUBJECTED TO TENSION AND SHEAR ue to the anisotropy of the bamboo culm, its characterization must be done through tests with different configurations. Among all the possibilities, some of them are tensile tests and direct shear tests. The numerical model was tested in these cases to verify the cracking patterns and to adjust some parameters of materials that are difficult to measure in the laboratory. In both tests, the numerical problem is considered as a plane stress problem with its domain discretized into triangular elements. The fiber distribution is considered uniform, so a constant volume fraction of fibers is maintained in all elements of the mesh. The shape and scale Weibull parameters to describe the softening of the fibers were computed from tensile tests of individual vascular bundles of bamboo Guadua angustifolia [27]. Parameter Value Reference Parameter Value Reference ( ) m k 0.60 ( ) f k 0.40 ( ) m E 500 MPa [28,29] ( ) f E 43 GPa [18,27] ( ) m  0.38 [28,29] ( ) f y  259 MPa [18,27] ( ) m u 0.20 N/mm [30] ( ) f G 15.6 GPa ( ) max m  5.00 MPa [30] ( ) max f  130 MPa Table 1 : Material parameters used for the numerical simulations. The exponent (m) or (f) indicates whether it is a property of the matrix or the fibers, respectively. All material parameters used for the simulations are presented in Tab. 1. The parameter ( ) f G is obtained from its relation with ( ) f E and Poisson’s ratio, and the maximum shear strength ( ) max f  is obtained from a transformation of stresses, where ( ) f y  is taken as the maximum principal stress. Figure 3 : LGB specimen subjected to tensile stress: (a) sketch of the experimental tested specimen, (b) finite element mesh of the numerical simulation, with a detail of the mesh. Tensile test Fig. 3 shows a sketch of the experimental test specimen [4,31] and the numerical specimen with its mesh. Laboratory instrumentation gives us the load P and the relative displacement  at the two central points. The domain is discretized in 1008 triangular elements, reducing the size at the central part of the specimen, where it is presumed to fail. The left border is displacement constraint, and an incremental displacement  is imposed to the nodes at the right border. Fig. 4 shows lines of equal displacement at three different load steps. Fig. 5 shows two specimens with different types of cracks. D