Mode I fracture analysis of the double edge cracked Brazilian disk using a weight function method

Abstract

The true mode II fracture can be achieved by the double-edge cracked Brazilian disc (DCBD) under compression load. The methods to calculate stress intensity factors (SIFs) for the DCBD specimen, however, are only numerical methods at present. The analytical solutions of the mode I and II SIFs in the DCBD specimen under compression are obtained using the weight function method. The compression load is considered as the non-uniformly distributed pressure, including parabolic, quartic polynomial, elliptical, cosinoidal, and semi-periodical cosinoidal pressures. Compared with the numerical methods, the SIFs for the DCBD specimen can be calculated with high accuracy and efficiency by the analytical solutions. The calculation results show that the distribution form of pressure has a great influence on SIFs for the large contact angle and short crack. The normalized mode I and II SIFs in the DCBD specimen under compression are constantly negative for any loading angle, contact angle, and crack length. The effect of contact angle on mode I and II SIFs can be ignored when the relative crack length α ≥ 0.6. The true mode II fracture tends to occur in the DCBD specimen for the small loading angle and long crack conditions. The experiments are carried out by using sandstone DCBD specimens. The true mode II fracture toughness of the sandstone material used in this paper is 0.9383–0.9387 MPa m1/2.