Issue 38

N.O. Larrosa et alii, Frattura ed Integrità Strutturale, 38 (2016) 266-272; DOI: 10.3221/IGF-ESIS.38.36 269 Fig. 2 shows the FE models. Due to symmetric conditions of loading and geometry a quarter of C(T) and SE(T) specimens were modelled, to improve computational efficiency. One half of the pipe was modelled in order to be able to apply pure bending. In [6], it was shown that element size in the defect section affects the results for the damage accumulation process; therefore, this value must be determined by comparison with experimental results. For API X65, the element size is 0.15mm [6]. The material constants to apply the fracture criterion of Eq. (3) for API X65, based on the defined element size are  =3.29,  = -1.54 and γ =0.01. The damage model is implemented within C3D8 hexahedron solid elements using the ABAQUS UHARD and USDFLD user-defined subroutines [20] coded in FORTRAN 90. The total numbers of elements/nodes in the FE models are from 23,366/26,016, 82,520/88,929 and 117,595/130,416 for the SE(T) specimen, C(T) specimen and the pipe, respectively. (a) (b) (c) Figure 1 : Schematic illustration of fracture toughness specimens showing the dimensions: (a) C(T) specimen; (b) SE(T) specimen; (c) Pipe with surface circumferential crack. (a) (b) (c) Figure 2 . Finite element models: (a) C(T) specimen; (b) SE(T) specimen; (c) Pipe with surface circumferential crack.