Void Dynamics Research Articles

Assessing gradient parameters for damage control in notched plates: Finite element analysis of locally functionally graded materials using the Gurson-Tvergaard-needleman (GTN) model

This study investigates functionally graded materials (FGMs) as reinforcement for notched plates prone to crack propagation. Using a novel meshing technique and the Gurson-Tvergaard-Needleman damage model within ABAQUS-Explicit, we explore how various gradation parameters affect material damage under stress. The model, incorporating Von Mises stress theory and Voce hardening law, simulates plastic flow and progressive damage from void dynamics. Validated against experimental data, our findings reveal that local gradation parameters significantly influence void damage and structural performance of notched components. This research provides crucial insights into FGMs' potential to enhance structural integrity in engineering applications involving notched structures.

Simulation and on-line monitoring using optical fiber Bragg grating sensors of temperature history during laser-assisted automated fiber placement

Automated fiber placement (AFP) in situ consolidation (ISC) of thermoplastic composite possess the potential to reduce manufacturing costs and improve manufacturing efficiency. The properties of composite manufactured by the ISC are affected by several mechanisms including polymer degradation, crystallization, intimate contact, polymer healing and void dynamics. All these mechanisms are directly affected by the temperature history. Consequently, the control and accurate measurement of temperature history during ISC are particularly important for improving the properties of composite. In this study, a simplified three-dimensional transient heat transfer model was established. The effect of tool temperature and placement speed on the temperature history and peak temperature were predicted. Simultaneously, an online temperature monitoring system was built and the optical Fiber Bragg Grating sensors (FBGS) was used to measure the temperature history. The results indicated that the predicted results of the model were consistent with the measured results, the error was below 8%. In addition, the temperature history of layers was significantly affected by the tool temperature and placement speed. The temperature of the layers decreased to near the tool temperature after cooling, and a higher tool temperature increasing its peak temperature because of the reduce of the cooling rate. On the contrary, an increase in placement speed will reduce the peak temperature of the layers.

Design strategies towards the optimal shock-tolerance of nanocrystalline Al matrix composite

Achieving high shock tolerance in structural materials is a complex topic. It requires a balance between dynamic strength and toughness, but these properties are challenging to attain simultaneously. We have examined dynamic responses of typical composite structures by merging MD and DFT simulations. The composite structure featuring SiC nanowires bridging multiple grains exhibits exceptional shock tolerance, when compared to both the matrix material (polycrystalline Al) and other composite structures with isolated intergranular or intragranular SiC nanoparticles. Our research has revealed that the structural configuration is responsible for the exceptional shock tolerance through facilitating amorphization and the significant suppression of void dynamics evolution. Nanocomposite materials, characterized by bridged and specific orientation interfaces, offer a solution to this inherent trade-off. The approach demonstrated promising generalization ability and holds enormous potential for extension to alloys field.

Electromigration-induced void evolution and failure of Cu/SiCN hybrid bonds

The realization of high interconnect densities for three-dimensional integration demands development of new wafer-to-wafer bonding approaches. Recently introduced Cu-to-Cu wafer-to-wafer hybrid bonding schemes overcome scaling limitations, but like other Cu-based interconnect structures, they are prone to electromigration. Migration and growth of voids, induced by electromigration and mechanical stress, cause Cu-to-Cu hybrid bonds to fail. A comprehensive modeling approach is required to fully understand the complex dynamics of voids with their influencing factors, such as current density, temperature, and mechanical stress. In this work, we utilize such a modeling approach to perform studies of void migration through Cu-to-Cu hybrid bonds. The calculated velocities of the evolving void surface fully correspond to the experimentally observed behavior of voids migrating from the lower pad to the upper diffusion barrier of the upper pad, where they cause electrical failure. The migration velocity of a void in the upper pad is 20% higher than the migration velocity of a void in the bottom pad. Unbalance of the normal velocity distribution at the void surface leads to the transformation of the originally ellipsoid void into a teardrop shape. The simulations provide full insight in the impact of layout geometry, material properties, and operating conditions on void dynamics. In addition, the results enable targeted adjustments of the influencing factors to inhibit void migration and growth in order to delay or to fully prevent Cu-to-Cu hybrid bond failure.

Voiding dynamics of pelvic organ prolapse: Large scale comparative study.

To determine the voiding dynamics of the patients with pelvic organ prolapse (POP). A retrospective patient file review was performed of 877 female patients with lower urinary tract symptoms. After exclusion criteria 373 female patients were eligible for the study. Two patient groups w/wo prolapse were identified. The symptoms, patient characteristics, patterns of free urine flow, and detrusor voiding pressure curves were compared between two groups. A comparison of the urodynamic findings between the subgroups (mild/moderate, severe, and w/o prolapse) was made and shown on a scatter plot graphics of Pdet Qmax versus Qmax as well. A total of 373 patients with median age 54 (18-92), 189 (51%) had varying degrees and forms of POP while 184 (49%) did not have any prolapse (p < 0.003). Logistic regression analysis results showed that older age [p = 0.023, odds ratio (OR) = 1.01, confidence interval (CI): (1.00-1.03)], weaker pelvic floor muscle strength [p = 0.032, OR = 1.67, CI: (1.04-2.69)], more frequent symptom of hesitancy [p = 0.003 OR = 2.15 CI: (1.29-3.58)], prolonged-tailed shaped curve pattern of free urine flow [p = 0.027 OR = 1.97 CI: (1.08-3.58)], and higher Pdet Qmax (22 cmH2 O) values [p = 0.002, OR = 1.02, CI: (1.00-1.03)] were the independent different features of the patients with prolapse. Subgroup urodynamic analysis showed significantly lower free flowmetry Qmax and higher Pdet Qmax values in patients with severe prolapse. Prolonged/tailed-shaped curve pattern of free urine flow was significantly more frequent in patients with prolapse. Voiding dynamics of the patients with prolapse were significantly different from the patients' w/o prolapse. They had higher Pdet Qmax values, more frequent symptom of hesitancy, and prolonged shaped free flow curve pattern. Free flow Qmax values were lower in patients with severe prolapse.

Research on Void Dynamics during In Situ Consolidation of CF/High-Performance Thermoplastic Composite

Automated fiber placement (AFP) in situ consolidation of continuous CF/high-performance thermoplastic composite is the key technology for efficient and low-cost manufacturing of large thermoplastic composites. However, the void in the in situ composite is difficult to eliminate because of the high pressure and the short consolidation time; the void content percentage consequently is the important defect that determines the performance of the thermoplastic composite parts. In this paper, based on the two-dimensional Newtonian fluid extrusion flow model, the void dynamics model and boundary conditions were established. The changes of the void content percentage were predicted by the cyclic iteration method. It was found that the void content percentage increased gradually along the direction of the layers’ thickness. With the increasing of the laying speed, the void content percentage increased gradually. With the increasing of the pressure of the roller, the void content percentage gradually decreased. When the AFP speed was 11 m/min and the pressure of the compaction roller reached 2000 N, the void content percentage of the layers fell below 2%. It was verified by the AFP test that the measured results of the layers’ thickness were in good agreement with the predicted results of the model, and the test results of the void content percentage were basically equivalent to the predicted results at different AFP speeds, which indicates that the kinetic model established in this paper is representative to predict the void content percentage. According to the metallographic observation, it was also found that the repeated pressure of the roller was helpful to reduce the void content percentage.

Imprints of the cosmic void evolution on the baryon processes inside galaxy haloes

ABSTRACT Cosmic voids provide a unique environment to study galaxy formation and evolution. In this paper, we analyse a set of hydrodynamic zoom-in simulations of voids, to analyse in detail their inner structures. These voids were identified in a cosmological simulation and classified according to their surrounding dynamics at very large scales: whether they are in expansion or contraction at their outskirts. We study how these environments and the dynamics of voids impact the baryonic processes inside haloes and their mechanisms of formation and evolution. We find an underabundance of processed gas within the voids that can be associated with the lack of massive haloes. By studying the dynamical phase-space diagram of haloes and the halo-particle correlation function, we find that haloes inside of contracting voids are slightly affected by the presence of bigger structures, in comparison to haloes in the inner regions of expanding voids. This fact is consistent when you see dark matter or gas particles. We show that the halo assembly depends on the void dynamical state: haloes in expanding voids assemble slowly than those in contracting voids and in the general universe. This difference in the assembly impacts the baryonic evolution of haloes. Overall the redshift range analysed that haloes in voids have less baryon content than haloes in the general universe and particularly at z = 0 less stellar content. Our results suggest that the large-scale void environment modulate the baryonic process occurring inside haloes according to the void dynamical state.

Self‐Healing of Crystal Voids in Double Perovskite Nanocrystals Is Related to Surface Passivation

AbstractDouble perovskites are considered for future photovoltaic and electro‐optic applications as a toxic‐free alternative to lead halide perovskites. Alas, due to the lower efficiency of lead‐free devices, material properties need to improve to compete. In this work, the self‐healing and annealing of crystal voids is reported. Experiments are conducted on nanocrystals and in situ a transmission electron microscopy (TEM) microscope. The setup enables creation of crystal voids and to monitor their dynamics in real time. Void trajectories and velocities are calculated for TEM videos. An inaccessible, protected volume for migration near the nanocrystal outer surface is discovered, confining the migration of voids to inner crystal parts. Once surface passivation in the form of organic ligands is removed, void dynamics changes, to enable annealing of the voids and self‐healing of the crystal. It is determined that surface ligand protection against void migration is extending several atomic layers below the crystal surface. Modeling based on these results predict equilibrium positions for the voids, which are discovered in the data. The study suggests that tuning of organic ligand density influences structural stability and crystal defect tolerance in double perovskites. Engineering surfaces with inherent self‐healing properties may increase efficiencies in future devices based on these materials.

Redshift-space effects in voids and their impact on cosmological tests – II. The void-galaxy cross-correlation function

ABSTRACT This is the second part of a thorough investigation of the redshift-space effects that affect void properties and the impact they have on cosmological tests. Here, we focus on the void-galaxy cross-correlation function, specifically, on the projected versions that we developed in a previous work. The pillar of the analysis is the one-to-one relationship between real and redshift-space voids above the shot-noise level identified with a spherical void finder. Under this mapping, void properties are affected by three effects: (i) a systematic expansion as a consequence of the distortions induced by galaxy dynamics, (ii) the Alcock–Paczynski volume effect, which manifests as an overall expansion or contraction depending on the fiducial cosmology, and (iii) a systematic off-centring along the line of sight as a consequence of the distortions induced by void dynamics. We found that correlations are also affected by an additional source of distortions: the ellipticity of voids. This is the first time that distortions due to the off-centring and ellipticity effects are detected and quantified. With a simplified test, we verified that the Gaussian streaming model is still robust provided all these effects are taken into account, laying the foundations for improvements in current models in order to obtain unbiased cosmological constraints from spectroscopic surveys. Besides this practical importance, this analysis also encodes key information about the structure and dynamics of the Universe at the largest scales. Furthermore, some of the effects constitute cosmological probes by themselves, as is the case of the void ellipticity.

Identification of Cellular Voids in the Human Otic Capsule.

The otic capsule consists of dense highly mineralized compact bone. Inner ear osteoprotegerin (OPG) effectively inhibits perilabyrinthine remodeling and otic capsular bone turnover is very low compared to other bone. Consequently, degenerative changes like dead osteocytes and microcracks accumulate around the inner ear. Osteocytes are connected via canaliculi and need a certain connectivity to sustain life. Consequently, stochastic osteocyte apoptosis may disrupt the osteocytic network in unsustainable patterns leading to widespread cell death. When studying bulk-stained undecalcified human temporal bone, large clusters of dead osteocytes have been observed. Such "cellular voids" may disrupt the perilabyrinthine OPG mediated remodeling inhibition possibly leading to local remodeling. In the common ear disease otosclerosis pathological bone remodeling foci are found exclusively in the otic capsule. We believe the pathogenesis of otosclerosis is linked to the unique bony dynamics of perilabyrinthine bone and cellular voids may represent a starting point for otosclerotic remodeling. This study aims to identify and characterize cellular voids of the human otic capsule. This would allow future cellular void quantification and comparison of void and otosclerotic distribution to further elucidate the yet unknown pathogenesis of otosclerosis.

Void-dynamics in nano-wires and the role of microstructure investigated via a multi-scale physics-based model

With scaling of nano-interconnect linewidth toward a 3 nm technology node, electromigration in copper nano-interconnects is becoming a major limitation. In this context, the increase of texture polycrystallinity plays a major role and necessitates better understanding of the impact of void dynamics and its interaction with texture at operating conditions. To this end, comprehensive, yet efficient, physics-based numerical models are warranted given that electromigration experiments at low operating temperatures are not feasible. Albeit, development of such models has been a challenge since it involves large length-scale discrepancy between features, i.e., from wire dimensions (hundreds of micrometers) down to grains and voids (tens of nano-meters and below) leading to substantial computational cost. To this end, in this study an efficient multi-scale physics-based electromigration modeling approach is demonstrated, where an experimentally calibrated Korhonen-type 1D model solves electromigration at the global scale (entire interconnect), and a 2D local model simulates void dynamics considering the impact of electron wind, void surface energy, and stress gradients. The role of copper texture, i.e., grain boundaries, grain orientation and anisotropic properties is thoroughly investigated. We demonstrate that by tailoring the copper grain structure, void behavior and thus resistance evolution of nanowires can be effectively controlled. Compared to wider interconnects, in scaled nanowires, surface energy is found to play a dominant role on void morphology compared to electron wind. Strong anisotropy of diffusivity of copper's FCC lattice fosters faceted morphologies and emergence of slit morphology during void transition through the polycrystalline texture. Bamboo segments are shown to effectively pin the voids migrating toward the cathode in cases with cobalt cap. In addition, voids migrating from low diffusivity to high diffusivity regions adopt a longitudinally elongated morphology, which can be detrimental in a down-stream operation mode.

Evolution dynamics of voids in single crystal copper under triaxial loading condition

ABSTRACT An understanding of nucleation, growth and coalescence of voids is required to predict the spall fracture. We employ molecular dynamics simulations to investigate the effect of temperature on the nucleation and growth of voids in single crystal copper under triaxial loading condition. We find that the void density decreases with an increase in temperature. The nucleation rate of the voids diminishes as temperature increases for the range of 300–1250 K. The individual void volume fraction evolves with discrete jumps due to coalescence events. The overall void volume fraction at 1250 K appears earlier than that at 300 K indicating the failure of the material earlier at higher temperatures. The void dimensions evolve with discrete jumps due to coalescence of the voids. The void dimensions change with the applied temperature. The void size distribution at each applied temperature follows a polynomial function.

Effect of temperature on the evolution dynamics of voids in dynamic fracture of single crystal iron: a molecular dynamics study

ABSTRACT We employ molecular dynamics simulations to investigate the role of temperature on the evolution dynamics of the voids in single crystal iron. We simulate isotropic tension in single crystal iron at a constant strain rate with temperature in the range of 300–1200 K. We find that the number of voids is highest at 1200 K in comparison to that at 300 K indicating high nucleation events at high temperatures. The growth rate of the voids is highest at 300 K in comparison to that at 1200 K, indicating rapid growth of the voids at 300 K. The overall void volume fraction is highest at 300 K. The nucleation and growth of the voids at 1200 K occur earlier in time in comparison to that at 300 K indicating the earlier damage of the material at 1200 K. The individual void volume fraction evolves with many discrete jumps due to the coalescence of the voids. The dislocation density is highest at 300 K in comparison to that at 1200 K.

Phase field approach for void dynamics with interface stresses at the nanoscale

In this paper, a thermodynamically consistent interface stress is derived for the solid-gas interface of nanovoids within the concept of the phase field approach and using the laws of thermodynamics. The Cahn-Hilliard (CH) equation describes the evolution of nanovoid concentration which varies between 0 for perfect solid to 1 for gas. Considering the gradient term of the nanovoid concentration in the deformed state results in an inelastic term in the stress tensor which depends only on and is along the gradient of the nanovoid concentration. Also, multiplying the free energy of mixing and the gradient energy by the ratio of mass densities in the undeformed and deformed states leads to an inelastic hydrostatic stress. The combination of the above inelastic stresses gives the correct inelastic interface stress. It is proved that for a stationary interface which does not support elastic stresses, the obtained interface stress reduces to the biaxial tension which coincides with a sharp-interface approach limit. The interface stress changes the total stress distribution and affects the elastic stress field. Thus, due to the significant effect of the elastic energy on void dynamics, it can indirectly affect the void nucleation and growth. The coupled CH and elasticity equations are solved using the finite element method and several examples of void evolution are studied consisting of thermal induced initiation and propagation of a planar void, thermal induced circular void growth, evolution of void nanostructure under biaxial compression and evolution of void nanostructure with an initially, randomly distributed void concentration. The obtained results show the significant effect of the interface stress on the total stress distribution and consequently, a different distribution of thermodynamic driving force which can affect the nanostructure evolution and deformation. The interface stress represents a promotive effect on the void growth which results in a faster void growth and a larger void concentration. Also, the results reveal a significant effect of temperature, elastic properties and sample size on the interface stress.

Role of conductivity on the electromigration-induced morphological evolution of inclusions in {110}-oriented single crystal metallic thin films

The electromigration-induced microstructural evolution of inclusions such as voids, precipitates, and homoepitaxial islands is of technological importance to the reliability, the performance of the thin film interconnects, and surface nanoengineering. In the present article, we report the results on the migration of cylindrical inclusion in the {110}-oriented single crystal of face-centered-cubic metals under the action of electromigration. To this end, we employ a phase-field model based on the Cahn-Hilliard equation with anisotropy in adatom mobility. Emphasis is laid on the role of conductivity contrast between the inclusion and the matrix, and the misorientation of the fast diffusion directions with respect to the applied electric field. Numerical simulations indicate that lower misorientations favor a steady state, while higher values render the inclusion unstable, initiating a complex cycle of splitting and coalescence. At intermediate misorientations, the inclusion undergoes a time-periodic oscillation, the amplitude and the frequency of which is strongly dependent on the values of conductivity. Furthermore, higher conductivity of the matrix relative to the inclusion promotes a transverse elongation, while the similar conductivities lead to slitlike features along the direction of the electric field. Finally, a morphological map is constructed by delineating the dependence of various migration modes on conductivity contrast and misorientation. Results presented here have important implications on void dynamics in interconnects and the fabrication of nanostructures of desired features and dimensions.

Dark Energy Survey year 1 results: the relationship between mass and light around cosmic voids

ABSTRACT What are the mass and galaxy profiles of cosmic voids? In this paper, we use two methods to extract voids in the Dark Energy Survey (DES) Year 1 redMaGiC galaxy sample to address this question. We use either 2D slices in projection, or the 3D distribution of galaxies based on photometric redshifts to identify voids. For the mass profile, we measure the tangential shear profiles of background galaxies to infer the excess surface mass density. The signal-to-noise ratio for our lensing measurement ranges between 10.7 and 14.0 for the two void samples. We infer their 3D density profiles by fitting models based on N-body simulations and find good agreement for void radii in the range 15–85 Mpc. Comparison with their galaxy profiles then allows us to test the relation between mass and light at the 10 per cent level, the most stringent test to date. We find very similar shapes for the two profiles, consistent with a linear relationship between mass and light both within and outside the void radius. We validate our analysis with the help of simulated mock catalogues and estimate the impact of photometric redshift uncertainties on the measurement. Our methodology can be used for cosmological applications, including tests of gravity with voids. This is especially promising when the lensing profiles are combined with spectroscopic measurements of void dynamics via redshift-space distortions.

Investigating the electromigration limits of Cu nano-interconnects using a novel hybrid physics-based model

To predict the impact of technological variables such as materials, dimensions, interfaces, and operating conditions on Cu electromigration, in this study a hybrid modeling framework is developed by coupling a global Korhonen-type electromigration modeling module with a cellular automaton-based void dynamics module. The modeling framework is corroborated and benchmarked using experiments on Cu interconnects and is used to predict the impact of scaling on Cu electromigration induced stress evolution. The simulations shed light on the impact of dimensional scaling on stress kinetics, void nucleation, and growth phases, where the nucleation phase is found to become longer than the growth phase and voids are found to grow relatively more rapidly upon nucleation in highly scaled linewidth. In addition, the simulations predict 22% lower median time to failure and a higher variability of time to failure for downstream vs upstream electromigration modes due to the more critical impact of near via voiding in downstream cases. Lending further credence to its predictive merits, the model predicts and explains complex R-shift signatures occurring at high temperature electromigration experiments due to void dynamics.

A non-local void dynamics modeling and simulation using the Proper Generalized Decomposition

In this work we develop a void filling and void motion dynamics model using volatile pressure and squeeze flow during tape placement process. The void motion and filling are simulated using a non-local model where their presence is reflected in the global macroscale behavior. Local pressure gradients during compression do play a critical role in void dynamics, and hence the need for a non-local model. Deriving a non-local model accounting for all the void motion and dynamics entails a prohibitive number of degrees of freedom, leading to unrealistic computation times with classical solution techniques. Hence, Proper Generalized Decomposition – PGD – is used to solve the aforementioned model. In fact, PGD circumvents the curse of dimensionality by using separated representation of the space coordinates. For example, a 2D problem can be solved as a sequence of 1D problems to find the 2D solution. The non-local model solution sheds light on the fundamental of the void dynamics including their pressure variation, motion and closure mechanisms. Finally, a post treatment of the transient compression of the voids is used to derive conclusions regarding the physics of the void dynamics.

Atomic simulation of void location effect on the void growth in nickel-based single crystal

Void growth in metallic materials are strongly affected by local microstructure. The location of defect produces a great influence on the mechanical properties of material, especially if defect occurs at the interface. Considering the complex microstructure of nickel-based single crystal, the Ni, Ni3Al and Ni/Ni3Al interface model were established to analyze the expansion dynamics of void using molecular dynamics (MD) method. The expansion behavior of void shows that a/6〈1 1 2〉 Shockley partial dislocations initially nucleates on the free surface of void during the stretching of Ni and Ni3Al model. Whereas, dislocations nucleate from the interface of Ni/Ni3Al interface model. Evolution of void suggested that the plasticity deformation is dominated by movable Shockley partial dislocations and immovable Stair-rod dislocations. Void size effect analysis revealed that the larger void radius is, the smaller yield stress and Young’s modulus are. The mechanical properties of Ni/Ni3Al interface model were controlled by the interaction between void and interface.

Utility of Urodynamics in Children with Dysfunctional Voiding

This review will allow the reader to understand the rationale for urodynamic testing in a child who is neurologically intact and is suspected of having dysfunctional voiding. We will look to define criteria that will prevent the overuse and unnecessary use of this invasive test in children. The literature does not support the routine use of invasive urodynamics for children with urge syndrome but does support its use for elucidation of dysfunctional voiding abnormalities in neurologically intact children. The child with functional voiding issues presents itself with factors that are different from the child with neurogenic causes of incontinence. The role of the brain cannot be taken out of the equation in the normal sensate child and its impact can be quite significant leading to results that may not be what is actually occurring in day to day life. It is also critical that the person ordering VUD understand that there is limited value in ordering these tests for urge incontinence and frequency since the diagnosis of DO can be made for the most part from the history. Judicious use of the VUD study can be quiet valuable in allowing the user to pinpoint in complex cases the cause of the incontinence or poor voiding dynamics that are present. VUD should be a final choice in the workup of the sensate child with functional voiding problems and rarely used as a first line evaluation.