The fictitious material concept

There are many ductile materials for which the strain-hardening and the strain-to-failure are simultaneously significant. Because of the significant strain-hardening, no valid K-based fracture toughness (K-Ic or k(c)) is obtained from the standard test methods. Hence, the equivalent material concept (EMC) seems to be null in predicting the failure load of notched ductile components. On the other hand, due to the large strain-to-failure, a very large value of the strain energy density is computed for the ductile material until the ultimate point, leading to a very large value of the tensile strength of the equivalent material. As a result, extremely large failure loads are predicted by the Modified EMC (MEMC) for notched ductile members, which are not consistent with the experimental results at all. Consequently, for such ductile materials, both EMC and MEMC are null. To overcome this major limitation, the Fictitious Material Concept (FMC) is proposed in the present study, by which virtual values of K-c and Young's modulus are defined and computed for the real ductile material, and utilized for predicting the failure loads of notched ductile members. For this purpose, first, fracture of AISI 304 stainless steel, which is a ductile material with significant strain-hardening, high elastic modulus, and large strain-to-failure, containing blunt Vnotches is studied both theoretically and experimentally under pure mode I and mixed mode I/II loading conditions. The specimens with different notch inclination angles, notch angles, and notch tip radii are prepared and tested under displacement-control remote tension and their failure loads are recorded experimentally. Then, by linking FMC to the maximum tangential stress (MTS) and mean stress (MS) brittle fracture criteria, the test results are theoretically predicted. It is revealed that both FMC-MTS and FMC-MS combined models can predict the experimental results well.