The Modified Void Nucleation and Growth Model (MNAG) for Damage Evolution in BCC Ta

Abstract

A void coalescence term was proposed as an addition to the original void nucleation and growth (NAG) model to accurately describe void evolution under dynamic loading. The new model, termed as modified void nucleation and growth model (MNAG model), incorporated analytic equations to explicitly account for the evolution of the void number density and the void volume fraction (damage) during void nucleation, growth, as well as the coalescence stage. The parameters in the MNAG model were fitted to molecular dynamics (MD) shock data for single-crystal and nanocrystalline Ta, and the corresponding nucleation, growth, and coalescence rates were extracted. The results suggested that void nucleation, growth, and coalescence rates were dependent on the orientation as well as grain size. Compared to other models, such as NAG, Cocks–Ashby, Tepla, and Tonks, which were only able to reproduce early or later stage damage evolution, the MNAG model was able to reproduce all stages associated with nucleation, growth, and coalescence. The MNAG model could provide the basis for hydrodynamic simulations to improve the fidelity of the damage nucleation and evolution in 3-D microstructures.

In situ measurement of damage evolution in shocked magnesium as a function of microstructure

“…However, it may also be due, in part, to the void growth rate not being constant across the damage plane or throughout time. This is an important observation to make, as many currently used damage models implement a single void growth rate function for all voids across a sample ( 28 , 29 , 31 ). While these calculations do require assumptions of negligible tilt and void layering, as discussed above, this estimate is the first time such a rate has been experimentally quantified.…”

“…Many analytical void damage models have been developed that attempt to predict spall strength and void evolution over time ( 5 , 27 ). Models have incorporated effects such as void nucleation and growth ( 28 ), rate dependency ( 29 , 30 ), and void coalescence ( 31 ), to name a few, with varied degrees of success in predicting experimental data.…”

“…This is particularly relevant to the gas gun impact experiments shown herein (with strain rates ≲10 5 s −1 ) and is important because it has been shown that strain rate has a notable effect on total damage in materials ( 35 ). Deficiencies in current analytical strain-equivalent damage models ( 5 , 27 – 29 , 31 ) for nucleation and growth include assumptions and simplifications of the initial positioning of void nucleation sites, void growth rates, and void shapes. This lack of understanding is, in part, related to the absence of direct, real-time quantitative measurements of void nucleation and early-stage growth.…”

Fracture Mechanics—Theory, Modeling and Applications

“…In [3], Chen et al proposed the modified void nucleation and growth model (MNAG model) in which the original void nucleation and growth model (NAG model) was extended by added a term to account for the void coalescence. The MNAG model was parameterized with molecular dynamics (MD) shock data of single crystal and nanocrystalline Ta.…”

Machine Learning Based Approach to Predict Ductile Damage Model Parameters for Polycrystalline Metals

“…Currently, ductile damage in materials is represented using various models such as TEPLA, TONKS, MNAG etc. [1][2][3][4]. However, these models need to be parameterized using experimental velocity-time and porosity position data.…”