Two parameter characterization of semi-circular cracks in anisotropic plastic materials

In this paper, the J-Q two-parameter characterization of Hill-anisotropic elastic–plastic crack-front fields are examined for surface cracked plates under uniaxial tensile loadings. A method for two-parameter characterization crack-front field in anisotropic plastic materials is presented. Extensive three-dimensional elastic–plastic finite element analyses were performed for semi-circular surface cracks in a finite thickness plate, under remote uniaxial tension loading conditions. Surface cracks with relative depths a/t = 0.2, 0.6 were investigated. The loading levels spanned from small-scale to large-scale yielding. Different crack orientations with respect to the material coordinate directions were also considered. In topological planes perpendicular to the crack front, the crack-front stress fields were obtained. In order to facilitate the determination of Q-factors, modified boundary layer analyses were also conducted. The modified boundary layer analyses were adapted to account for plastic anisotropy. The J-Q two-parameter approach was then used in characterizing the elastic–plastic crack-front stress fields along these 3D crack fronts. Complete distributions of the J-integral and Q-factors for a wide range of loading conditions were obtained. The results indicate that the J–Q characterization is applicable to Hill-anisotropic plastic materials and provides good estimate for the crack-front constraint loss experienced under large-scale yielding. It was also observed that the isotropic and anisotropic J–Q parameters can significantly diverge, especially, when crack planes are misaligned with respect to the material coordinate system. This highlights the importance of the consideration of plastic anisotropy when performing constraint-based fracture mechanics analyses.