Characteristics of Brittle Fracture under General Combined Modes(Welding Mechanics, Strength & Design)

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In the previous papers, the brittle fracture initiation characteristics of plates with an inclined crack under bi-axial tension were studied. This condition led to the brittle fracture under the combination of opening (Mode I) and sliding (Mode II) modes. In this paper, brittle fracture under all possible combination of opening, sliding and tearing (Mode III) modes is investigated both theoretically and experimentally. Using specimens of PMMA (Polymethylmethacrylate), fracture tests under pure Mode II, pure Mode III, the combination of Modes I and III, and that of Modes I, II and III are carried out. Then the test results are compared with those predicted by the fracture criteria which are represented in terms of: (1) maximum tangential stress, [^σθ]_<max>, (2) maximum energy release rate at the propagation of a small kinked crack, [G^k(γ)]_<max>, and (3) maximum energy release rate at the initiation of a small kinked crack, [G(γ)]_<max>. The following conclusions are drawn from the results of the investigation. (1) The measured fracture stresses under an arbitrary combination of the crack surface displacement modes are in good agreement with those predicted by [G^k(γ)]_<max> or [G(γ)]_<max> criterion. These energy release rates are expressed in the closed forms, and can be applied to any crack under any combination of the lodes. (2) Although [^σθ]_<max> criterion may be used for fracture under any combined modes including Mode III, this is not effective except for the combinations of Modes I and II. (3) The interaction curves of brittle fracture strength under any arbitrary combenations of Modes I, II, and III are obtained based on [G^k(γ)]_<max> and [G(γ)]_<max> criteria.


  • Transactions of JWRI

    Transactions of JWRI 9(2), 237-246, 1980-12

    Osaka University


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