Initiation and growth of damage in a dual-phase steel observed by X-ray microtomography

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

“…13) Weck et al 6) analyzed the void growth in copper and Glidcop containing artificial array of holes oriented at an arbitrary angle to the tensile axis and demonstrated that the RT model gives good predictions for growth of quasi-spherical voids with stress triaxiality variation. Bouaziz et al 16) and Marie et al 10) proposed the modification of the RT model in order to account for mismatch between the prediction and the experimental measurement resulted from nucleation at high strain regime. The RT model was later revised by Huang 17) in order to extend the approach to low values of stress triaxiality.…”

“…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.…”

“…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.…”

“…8,9) Recently, many experimental and modeling efforts with X-ray tomography have been made to better understand and predict the void nucleation in steels as well as light metals such as aluminum alloys which can be more clearly observed due to their higher X-ray transmissivity than steels. Maire et al 10) measured the number of voids per unit volume in a dual-phase steel during in situ tensile test. The acquired quantitative data has then used to validate a model of void nucleation based on the Argon criterion.…”