Issue 31

J. Lopes et alii, Frattura ed Integrità Strutturale, 31 (2015) 67-79; DOI: 10.3221/IGF-ESIS.31.06 72 VCCT Cohesive elements  Requires nodal variables and topological information ahead and behind the crack front  Requires remeshing for crack propagation  Requires initial delamination  Predicts propagation of existing delamination  Does not need an onset delamination  Predicts delamination initiation and propagation  Requires a refined mesh  Requires complex input parameters  Computationally expensive Table 2 : Summary of main features of VCCT and cohesive elements techniques Finite element model ABAQUS finite element code was used in all the numerical analysis in this work. Two models were built. The reference beam with monolithic CFRP, and the hybrid beam with CFRP and the steel layer. The main feature of these models is the use of zero thickness cohesive elements. The geometrical model took advantage of the symmetries in the three-point bending test. Only one half of the beam’s length was modelled applying a proper boundary condition in the mid span. The model has a unit width with appropriate symmetry boundary conditions on both faces parallel to the lengthwise direction of the beam (x-direction). The negligible Poisson effect in the y-direction allows this simplification. Fig. 5 shows the actual beam of 20mm x 10mm (represented in transparency) and the finite element geometric model 5mm x 1mm. Figure 5 : Short beam (in translucent grey) and geometrical model of the beam (in solid grey) for finite element simulation. The reference beam was modelled with one layer of zero thickness cohesive elements in the neutral fibre and the hybrid beam was modelled with zero thickness cohesive elements in the interface between the CFRP and the steel. The models have 8 elements per thickness in the CFRP and 40 elements across length with a bias ratio of 4, i.e. 40 th element in mid-span is 4 times smaller than the 1 st element in the extreme of the beam. The largest element has 0.460mm in length and the smaller element has 0.115 mm in length. The FEM model of the reference beam has:  640 cubic 8 node C3D8R elements with reduced integration: 320 elements for each half thickness.  40 COH3D8 zero thickness cohesive elements in the neutral fibre.  1478 nodes.  5400 DOF’s. The FEM model of the hybrid beam has:  680 cubic 8 node C3D8R elements with reduced integration: 320 elements for each half thickness plus 40 elements in the steel layer.  80 COH3D8 zero thickness cohesive elements: 40 elements on each CFRP/Steel interface  1640 nodes.  5892 DOF’s. Fig. 6 shows the FEM model of the hybrid beam in ABAQUS: