Validation of void growth models using X-ray microtomography characterization of damage in dual phase steels

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

“…The strain hardening of the matrix also could reduce the prediction of these types of models. 33) Meanwhile, there were several reports demonstrating that the evolution of R was in fair agreement with two models in case of calculating with a limited number of the relatively large voids which were only concerned with growth [8][9][10]13,18) and replacing the initial value of α by a specific constant depending on a material and T state allowed them to be more valid. 9,18) These two items seem to be valuable for making the prediction better.…”

“…Similar phenomena were observed in several previous works with different types of steels. 9,10,13,18) The average diameter was almost constant or quasi-stagnated in their works when the entire voids were taken into account. 9,10) A reduction in the equivalent diameter of the voids could be due to the nucleation of the voids in the matrix.…”

“…5,8,13,18,20) The Bridgman formula, however, is only valid for an axisymmetric geometry. It seems relatively acceptable in the case of the cylindrical specimen, and then the radius r could be measured using an external shape of the specimen with assuming that each cross section is a circle at each deformation step.…”

“…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.…”

“…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.…”