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In the present study, weight functions (WFs) of a subsurface crack were derived by proposing a new general form for approximate one‐dimensional WF. The WFs coefficients were considered as a function of crack length to depth ratio and were obtained using reference stress intensity factors (SIFs) of 16 cracks under uniform, linear, and parabolic normal and shearing loadings. The verification was performed by comparison of the straight and coupled SIFs calculated by WF and finite element modelling under some complicated loadings. In conclusion, the WFs can be simply and effectively employed for evaluating the cracks under any complex stress distributions. [ABSTRACT FROM AUTHOR]

Elliptical subsurface cracks are one of the probable types of cracks that occur in engineering structures. Due to the non-symmetrical geometry with respect to the crack surface, coupling of the fracture modes occurs in an elliptical subsurface crack and so, the crack under normal loading will experience all fracture modes. Mode III caused by the coupling effect under normal loading is negligible whereas mode II is significant. In this paper, mixed mode two dimensional weight functions of the elliptical subsurface cracks parallel to the surface are derived for aspect ratios of α=0.2, 0.4, 0.6, 0.8, 1.0 and ratios of crack depth to crack length of β=0.05, 0.06, 0.08, 0.1, 0.14, 0.2, 0.3, 0.5, 1.0. Mixed mode stress intensity factors under uniform normal loading are used as reference stress intensity factors. By curve fitting on the calculated weight functions coefficients, the derived weight functions are able to be used for any α and β. To verify the weight functions, the stress intensity factors of all points of the crack front are calculated under linear, elliptic paraboloid and trigonometric paraboloid stress distributions and compared to the finite element results. Comparison of the results shows high accuracy with mean relative error less than 7%. Using derived weight functions, mixed mode stress intensity factors of the subsurface elliptical crack can be determined for any α and β and under any normal stress distributions. [ABSTRACT FROM AUTHOR]