Effect of void size and Mg contents on plastic deformation behaviors of Al-Mg alloy with pre-existing void: Molecular dynamics study

The plastic deformation properties of cylindrical pre-void Aluminum-Magnesium (Al-Mg) alloy under uniaxial tension are explored using molecular dynamics simulations with embedded atom method (EAM) potential. The factors of Mg content, void size, and temperature are considered. The results show that the void fraction decreases with increasing Mg in the plastic deformation, and it is almost independent of Mg content when Mg is beyond 5%. Both Mg contents and stacking faults around the void affect the void growth. These phenomena are explained by the dislocation density of the sample and stacking faults distribution around the void. The variation trends of yield stress caused by void size are in good agreement with Lubarda model. Moreover, temperature effects are explored, the yield stress and Young's modulus obviously decrease with temperature. Our results may enrich and facilitate the understanding of the plastic mechanism of Al-Mg with defects or other alloys.

Active Galactic Nuclei Abundance in Cosmic Voids

The abundance of active galactic nuclei (AGN) in cosmic voids is relatively unexplored in the literature, but can potentially provide new constraints on the environmental dependence of AGN activity and the AGN-host coevolution. We investigated AGN fractions in one of the largest samples of optically selected cosmic voids from Sloan Digital Sky Survey Data Release 12 for redshift range 0.2–0.7 for moderately bright and bright AGN. We separated inner and outer void regions based on the void size, given by its effective void radius. We classified galaxies at a distance <0.6 R eff as inner void members and galaxies in the interval 0.6 < R/R eff < 1.3 as outer void galaxies. We found higher average fractions in the inner voids (4.9 ± 0.7)% than for their outer counterparts (3.1 ± 0.1)% at z > 0.42, which clearly indicates an environmental dependence. This conclusion was confirmed upon further separating the data in narrower void-centric distance bins and measured a significant decrease in AGN activity from inner to outer voids for z > 0.42. At low redshifts (z < 0.42), we find very weak dependence on the environment for the inner and outer regions for two out of three bins. We argue that the higher fraction in low-density regions close to void centers relative to their outer counterparts observed in the two higher-redshift bins suggests that more efficient galaxy interactions may occur at a one-to-one level in voids that may be suppressed in denser environments due to higher velocity dispersions. It could also indicate less prominent ram pressure stripping in voids or some intrinsic host or void environment properties.

Quantifying the size and healing of volumetric muscle wounds using 3D Slicer on CT scans in a canine model

Volumetric soft tissue and muscle wounds can arise from trauma or necrotizing soft tissue infection. Quantifying the size of these wounds can be challenging, as they often have irregular borders and contours. 3-dimensional Computed Tomography (3dCT) has been used to characterize the volume of numerous tissue structures, but these use cases invariably involve structures for which clear anatomic borders exist. This is not the case for volumetric soft tissue or muscle wounds, where the volume of the wound being assessed, which is actually a void representing the absence of tissue, does not contain an explicit border at the superficial surface. We present a method that allows quantification of the void size of volumetric muscle wounds from CT scans processed using the software package 3D Slicer and uses sequential time series scans to chart the progression of healing in such wounds. The development of a means to quantify wound size and healing rate is a necessary capability in order to assess the efficacy of potential therapeutic interventions aimed at enhancing healing of such wounds.

Finite element simulation and multi-factor stress prediction model for cement concrete pavement considering void under slab

Uneven support as result of voids beneath concrete slabs can lead to high tensile stresses at the corner of the slab and eventually cause many forms of damage, such as cracking or faulting. Three-dimensional (3D) finite element models of the concrete pavement with void are presented. The accuracy of the model is verified by two methods. The analysis shows that the impact of void size and void depth at the slab corner on the slab stress are similar, which result in the change of the position of the maximum tensile stress. The maximum tensile stresses do not increase with the increase of the void size for relatively small void size. The maximum tensile stress increases rapidly with the enlargement in the void size when the size≥0.4m. The increments of maximum tensile stress can reach 183.7% when the void size are 1.0m. The increase of slab thickness can effectively reduce maximum tensile stress. A function is established to calculate the maximum tensile stress of the concrete slab. The function takes into account the void size and the slab thickness. The reliability of the function was verified by comparing the error between the calculated and simulated results.

Finite element analysis to determine the role of porosity in dynamic localization and fragmentation: Application to porous microstructures obtained from additively manufactured materials

In this paper, we have performed a microstructurally-informed finite element analysis on the effect of porosity on the formation of multiple necks and fragments in ductile thin rings subjected to dynamic expansion. For that purpose, we have characterized by X-ray tomography the porous microstructure of 4 different additively manufactured materials (aluminium alloy AlSi10Mg, stainless steel 316L, titanium alloy Ti6Al4V and Inconel 718L) with initial void volume fractions ranging from 0.0007 % to 2 %, and pore sizes varying between 6 micrometers 110 micrometers. Three-dimensional analysis of the tomograms has revealed that the voids generally have nearly spherical shape and quite homogeneous spatial distribution in the bulk of the four materials tested. The pore size distributions quantified from the tomograms have been characterized using a Log-normal statistical function, which has been used in conjunction with a Force Biased Algorithm that replicates the experimentally observed random spatial distribution of the voids, to generate ring expansion finite element models in ABAQUS/Explicit which include actual porous microstructures representative of the materials tested. We have modeled the materials behavior using von Mises plasticity, and we have carried out finite element calculations for both elastic perfectly-plastic materials, and materials which show strain hardening, strain rate hardening and temperature softening effects. Moreover, we have assumed that fracture occurs when a critical value of effective plastic strain is reached. The finite element calculations have been performed for expansion velocities ranging from 50 m/s to 500 m/s. A key point of this investigation is that we have established individualized correlations between the main features of the porous microstructure (i.e. initial void volume fraction, average void size and maximum void size) and the number of necks and fragments formed in the calculations. In addition, we have brought out the effect of the porous microstrucure and inertia on the distributions of neck and fragment sizes. To the authors' knowledge, this is the first paper ever considering actual porous microstructures to investigate the role of material defects in multiple localization and dynamic fragmentation of ductile metallic materials.