Influence of Microstructure and Specimen Size on Cleavage Fracture Below and At General Yield

ABSTRACT The paper describes investigations made on ferritic and baintic microstructures, to study cleavage fracture occurring below and at general yield. The microscopic cleavage fracture stress σ f * was determined with double-edge notched tensile (DENT) specimens of varying size in combination with 3-dimensional finite element computations, which were regarded as necessary due to the significant amount of plasticity at general yield. In contrast to the general assumption that σ f * is no function of temperature, a considerable temperature dependence of σ f * was found, also after taking a critical distance x C into account, according to the Ritchie, Knott and Rice (RKR) model. It is discussed, if a temperature dependence of σ f * might be regarded as physically reasonable. An explanation for this behaviour could be found in terms of the thermal activation of dislocation motion, which is needed to produce the critical conditions for failure.