Characterization and modeling of void nucleation by interface decohesion in dual phase steels

In Situ Observation of Void Nucleation and Growth in a Steel using X-ray Tomography

“…Landron et al 12) obtained similar results and identified ε N0 as the strain with the first occurrence of nucleation for the smooth and the notched samples of the dual-phase steels. They revealed two different nucleation regimes at low and high strains and proposed the empirical equation modified the Argon criterion by using the local stress triaxiality for interface decohesion in the dual phase.…”

“…A considerable number of voids nucleated at that regime could be coalesced into the neighboring void clusters in a short period of time as soon as they nucleated, then it might be failed to acquire all of them at the specified interval of the tomography scan. The predicting model for nucleation based on the Argon criterion 11) was considered to verify its validation with this experimental result and could be described by an exponential expression of the following form: 10,12,13) (8) where, A is a constant equal to 9 000 mm -3 in this study and ε N is a critical value of the strain from which nucleation starts to occur. ε N0 is the critical strain when a pure shear is applied and a value of 0.94 seems to allow a good fit for the evolution of N measured in this study.…”

“…This model has been demonstrated good agreement on various types of steels and extended by subsequent studies to take into account the shape change of voids in tensile and transverse directions using a finite number of voids in different types of steels such as austenitic, ferritic and martensitic matrices. 9,18) Most studies mentioned above are limited to the inclusion-free or unconsidered, 10,12,13,18) the homogeneous 9) and the model materials embedding artificial damages 6,7,19,20) for easy estimation. Concerning the complexity of damage evolution leading to a ductile fracture, the artificial voids have been employed in many studies to simplify the analysis of damage evolution.…”

“…It is often used in the tomographic study as a first-order estimation of the triaxiality regardless of the specimen geometries, e.g., cylindrical bars, 5,8,12,18) flat ones, 6,7,9,10,13,19,20) even at notched ones. 5,8,13,18,20) The Bridgman formula, however, is only valid for an axisymmetric geometry.…”

“…Beyond ε = 0.44, however, the gap between two predictions and the experimental results was widened with increasing strain, thus the predicted values were almost double of the experimental result at a point just before fracture. Even though considering the other prediction modified by Landron et al, 12) it is easily expected that this mismatch could still be remained due to its limited validation. Thus these predictions could be valid only for the very beginning of the deformation (ε/ε N < 1) at which no void coalescence occurs.…”