Void Expansion Research Articles

Parameters Governing Void Formation and Expansion of Hollow Natural Rubber Latex Particles for Their Use as Bio‐based Nanocapsules

AbstractThis work reports the hollow latex (HL) particles developed from natural rubber latex particles (NRPs), known for their broad size distribution and non‐spherical shape. HL‐NRPs, prepared via the seeded emulsion polymerization in one pot, are studied as potential bio‐based nanocapsules for the first time. Effects of types of crosslinking agents and swelling agents, the addition of sodium dodecyl sulfate (SDS), and monomer compositions on the void formation and expansion are systematically investigated. The combined effects of phase separation between NR core swelled with divinyl benzene (DVB) and hydrophilic poly(methyl methacrylate/acrylic acid) P(MMA/AA) shell, the entanglement of rubber chains copolymerized with MMA/DVB/AA monomers, and the osmosis from external aqueous medium promoted the void formation. While crosslinking agents affected the void formation and shell strength, SDS and type of monomers governed colloidal stability and polymerization loci as well as morphology, respectively. The ability of HL‐NRPs as nanocapsules is explored by encapsulating fluorescent dyes, i.e., hydrophilic fluorescein isothiocyanate (FITC) and lipophilic Nile red (NiR), as model cargo. From the dye release test after 24 h, the cumulative concentrations of FITC in methanol and of NiR in tetrahydrofuran are 0.17 and 0.11 µg mL−1, respectively. The results suggested that FITC is released from HL‐NRPs easier than NiR possibly due to the different encapsulation location.

Study on LBE corrosion failure of FeAl/Al2O3 coatings after ion irradiation

FeAl/Al2O3 coatings, candidate coating materials for lead-cooled fast reactors, are first irradiated to produce pre-defects and then subjected to lead-bismuth eutectic corrosion to simulate the performance in the coupled field of irradiation and corrosion. Irradiation causes voids in the outer Al2O3 layer resulting in irradiation swelling and causes lattice distortion and dislocations in the inner FeAl layer resulting in compressive strain and intercrystalline void expansion. The weakened coatings crack during corrosion and suffer from Pb, Bi, and O penetration, causing internal corrosion and oxidation. Beyond the cracked areas, the coatings demonstrate commendable corrosion resistance with minimal penetration. The irradiation-induced structural evolution and the subsequent lead-bismuth eutectic corrosion failure of the coatings are elucidated in detail.

Grain size-dependent delay of avalanches during void evolution in a nanocrystalline Ni

The effect of grain size on the underlying dynamics of void evolution in a nanocrystalline (NC) Ni was dissected. Multiscale characterizations reveal that, unlike the suppression of void nucleation by the compressive stress in coarse-grained Ni, dispersive nano- and micro-voids formed readily in NC Ni during compression. Acoustic emission measurements and molecular dynamic simulations demonstrate that the unique structural features and deformation mechanics implicitly occurring in NC metals play multifaceted roles during void evolution. Although the presence of excessive nucleation sites, such as grain boundaries and triple junctions, together with the activation of intergranular plasticity facilitate void nucleation, high interface population retards dislocation-driven void expansion, resulting in sluggish void growth and a corresponding delay of coalescence avalanches.

Evolution Characteristics of Void in the Caving Zone Using Fiber Optic Sensing.

Addressing the issue of low filling efficiency in gangue slurry backfilling due to unclear evolution characteristics of voids in the overlying collapsed rock mass during mining, this study utilizes fiber optic sensing technology to monitor real-time strain changes within the rock mass. It proposes a void zoning method based on fiber optic sensing for mining the overlying rock and, in combination with physical model experiments, systematically investigates the dimensions, distribution, and deformation characteristics of rock mass voids. By analyzing fiber optic sensing data, the correlation between the rate of void expansion and the stress state of the rock mass is revealed. The research results demonstrate that as mining progresses, the internal voids of the rock mass gradually expand, exhibiting complex spatial distribution patterns. During the mining process, the expansion of voids within the overlying collapsed rock mass is closely related to the stress state of the rock mass. The rate of void expansion is influenced by changes in stress, making stress regulation a key factor in preventing void expansion and rock mass instability. The application of fiber optic sensing technology allows for more accurate monitoring of changes in rock mass voids, enabling precise zoning of voids in the overlying collapsed rock mass during mining. This zoning method has been validated against traditional theoretical calculations and experimental results. This research expands our understanding of the evolution characteristics of voids in overlying collapsed rock mass and provides valuable reference for backfilling engineering practices and backfilling parameter optimization.

Ductile fracture of high entropy alloys: From the design of an experimental campaign to the development of a micromechanics-based modeling framework

Cantor-type high entropy alloys form a new family of metallic alloys characterized by a combination of high strength and high fracture toughness. An experimental study on the CoCrNi alloy is first performed to determine the damage and fracture mechanisms under various stress states. A micromechanics-based ductile fracture model is identified and validated using these experimental data. The model corresponds to a hyperelastic finite strain multi-yield surface constitutive description coupled with multiple nonlocal variables. The yield surfaces consist of three distinct nonlocal solutions corresponding to three different modes of void expansion within an elastoplastic matrix: a void growth mode governed by a Gurson-based yield surface corrected for shear effects, an internal necking-driven coalescence mode governed by an extension of the Thomason yield surface based on the maximum principal stress, and a shear-driven coalescence mode governed by the maximum shear stress. This advanced formulation embedded in a large strain finite element setup captures the effects not only of the stress triaxiality but also of the Lode variable. In particular, the analysis shows that a failure model accounting for these two invariants of the stress tensor captures the fracture in high-entropy alloys over a wide range of conditions.

Evolution of Mechanical Behaviors and Microstructure of Tianjin Binhai Cohesive Soil during Freeze-Thaw Cycles

The variation of soil structure and mechanical damage caused by freeze-thaw cycles results in degradation of engineering properties and engineering geological problems, such as deformation, cracking, and even project accidents. In this study, the freeze-thaw cycle tests, unconfined compressive strength tests, scanning electron microscope (SEM) tests, and nuclear magnetic resonance (NMR) tests were carried out to find out the effects of freeze-thaw cycles on the mechanical behaviors and microstructure properties of Tianjin Binhai cohesive soil. The results show that the original structure of the cohesive soil has been destroyed after the first freeze-thaw cycle, resulting in severe loss of compressive strength by 84.2%. The axial stress-strain response showed a strain-hardening behavior transitioned to a strain-softening behavior after 15 freeze-thaw cycles. The unconfined compressive pressure, sensitivity, and void ratio showed the same corresponding reaction with the increase of freeze-thaw cycles. The effects of freezing and thawing on void ratio were weakening with the increase of consolidation pressure, since the void expansion and contraction were limited with smaller void sizes. The frost-heaving force during the freezing process increased the compaction of the soil structure, and face to face contact became the main contact formation, which led to a reduction in void ratio. This study provides technical guidance for evaluation on the mechanical properties and engineering stability of cohesive soil in seasonally frozen areas and technical support for artificial ground freezing treatment on underground construction of the west coast of Bohai Bay.

Internal structure change of porous asphalt concrete under coupled conditions of load, moisture and temperature

In the actual working environment, the pore water pressure generated by wheel loading may accelerate the damage accumulation to the internal structure of porous asphalt concrete (PAC), resulting in the performance deterioration. In this study, a modified immersion wheel tracking test was developed by incorporating the image processing and analysis method to capture the internal structure change of the PAC at the different loading time. The varying temperatures and moisture conditions were also considered to evaluate the effect of the coupled condition. According to average rutting depth rate, the loading process was divided into three stages of condensation, transition and stabilization. The change of mesoscopic indices corresponding to each stage were analyzed. Based on void area change under wheel loading, it has been found that the rising temperature may worsen failure development and moisture damage may promote the condensation of the specimen. In comparison to a single-layer specimen, a strong constraint of the bottom layer inside a two-layer specimen on the top layer may limit void expansion. The change of aggregate skeleton was evaluated based on contact length. The loss of contact length could be due to filling failure, rheological failure and over-compaction failure. Because of the negative effect of increased temperature and moisture on asphalt mortar, wheel loading may cause more extensive skeleton degradation, leading in more contact length loss. The findings of this study reveal important information about the rutting resistance deterioration of PAC from a mesoscopic viewpoint.

Microcellular foaming of poly(lactic acid) branched with food‐grade chain extenders

AbstractThis study evaluated the effectiveness and efficiency of two food‐grade multifunctional epoxies chain extenders (CE) in branching PLA and improving its foamability. Both CE grades were effective in branching PLA causing increased end mixing torque, shear, elongational viscosities, molecular weight but decreased crystallinity of poly(lactic acid) (PLA) with CE content, due to chain entanglements. CE with low epoxy equivalent weight (EEW) was more efficient than the counterpart with high EEW due to its high reactivity. Neat PLA foams showed poor cell morphology with areas without nucleated cells and had a low expansion, owing to its low elongational viscosity. By contrast, there was a considerable change in the morphology of the PLA foam structure caused by its branching. Chain‐extended PLA foams had uniform cell morphology with a high void fraction (up to ~85%) and expansion ratio (an eightfold expansion over unfoamed PLA) due to their high elongational viscosities, suggesting that melt properties of branched PLA were appropriate for optimum cell growth and stabilization during foaming. Overall, CE with low EEW was the most effective grade and 0.25% the optimum content that provided appropriate melt viscosity to produce PLA foams with a homogeneous structure, fine cells, high void fraction, high volume expansion ratio, and cell‐population density.

Effect of anisotropy on the ductile fracture in metal reinforcements of brittle matrix composites

Mechanisms of ductile failure in brittle matrix composites with metal reinforcements are investigated using a mechanistic approach to incorporate material anisotropy. Rapid void expansion with increasing remote strain and at nearly constant remote strain (cavitation) is modeled. Fracture energy, total energy absorbed, and cavitation limit is obtained as a function of material anisotropy. It is observed that for initial void volume fraction less than or equal to 10-4 cavitation phenomenon is seen. The critical stress at cavitation is found to increase with decreasing void size until it reaches the cavitation limit. Further, it is observed that the ductile fracture of metal reinforcements in the brittle matrix composite is sensitive to the material anisotropy.

On the interaction of a solute atmosphere with a circular void in two-dimensional elasticity: A statistical mechanics approach

Solid solutions are of critical importance to many technological applications. While continuum frameworks have been developed and invoked in the past for studying behavior of solid solutions, recent studies point to the importance of image stresses in finite systems, and in particular, suggest that the homogenized self-stress field of the solutes, which enter the chemical potential in the prevalent continuum models, should be excluded in a correct treatment. The present work is concerned with the study of a solute atmosphere in the vicinity of a void in two-dimensional elasticity wherein the solute atmosphere is treated as a distribution of solute rods extended indefinitely normal to the plane of analysis. A statistical mechanics framework is adopted based on the Gibbs canonical ensemble, and the well-established path-independent integrals of solid mechanics are used for examining configurational forces on the void induced by the presence of a solute atmosphere. Numerical Monte Carlo simulations fully accounting for the interaction energy between the solute rods are used for calculation of the ensemble averages of the energy release rates associated with void translation and expansion, and semi-analytical solutions are further developed in the limit of dilute solute concentrations and large temperatures. Effect of interaction between the stress fields of a solute atmosphere and an external loading on the configurational forces is also investigated through both numerical and analytical calculations. It is shown that the interaction between the image stress field of a given concentration of solute rods and the stress field of an equi-biaxial loading results in an added contribution to the energy release rate of void expansion which does not fade away even when the solid dimensions grow indefinitely. Numerical simulations are further used to examine the effect of loading-induced solute redistribution on the energetic driving force for void expansion.

Separate universe void bias

Voids have emerged as a novel probe of cosmology and large-scale structure. These regions of extreme underdensity are sensitive to physics beyond the standard model of cosmology, and can potentially be used as a testing ground to constrain new physics. We present the first determination of the linear void bias measured in separate universe simulations. Our methods are validated by comparing the separate universe response bias with the clustering bias of voids. We find excellent agreement between the two methods for voids identified in the halo field and the down-sampled dark matter field. For voids traced by halos, we identify two different contributions to the bias. The first is due to the bias of the underlying halo field used to identify voids, while the second we attribute to the dynamical impact of long-wavelength density perturbations on void formation and expansion. By measuring these contributions individually, we demonstrate that their sum is consistent with the total void bias. We also measure the void profiles in our simulations, and determine their separate universe response. These can be interpreted as the sensitivity of the profiles to the background density of the Universe.

Hydrogen-induced softening and hardening of Zr-based amorphous alloy: dependence on the hydrogen content and mobility

The effects of hydrogen addition on the structural and mechanical properties of Zr57Al10Cu15.4Ni12.6Nb5 amorphous metallic alloy were analysed. Structural investigation, using x-ray diffraction, revealed that hydrogen addition causes the development of large void and structural expansion. By means of nanoindentation tests, it has been shown that hydrogen addition can induce either softening or hardening of Zr-based amorphous alloys depending on the extent of the hydrogen content and mobility. The shear softening of amorphous material is due to the weakness of atomic cohesion attributed to the squeezing of ‘mobile’ hydrogen atoms. When hydrogen content grows excessive, strongly bounded ‘immobile’ atoms form a densely packed structure that restrict the local atomic movement and consequently harden the amorphous material alloy.

On the stability, microstructure, and mechanical property of powder metallurgy Al–SiC nanocomposites during similar and dissimilar laser welding

Aluminum matrix nanocomposites consolidated by powder metallurgy (P/M) have significant potential for practical applications in the aerospace and automotive industries considering their admirable strength to weight ratio and good corrosion resistance. Due to dimensional restrictions in traditional P/M manufacturing routes, similar and dissimilar joining would be essential to design complex structures, however, the stability of Al-matrix nanocomposites during joining process is a crucial issue. In this research, the stability of an Al-6 vol% (50 nm, ex-situ) SiC-2 vol% (15 nm, in situ) Al2O3 hybrid P/M nanocomposite was evaluated during laser joining in comparison to similar and dissimilar joints with commercially pure aluminum (AA1050 alloy). The processing parameters were optimized with a constant focus spot size of 200 μm, laser power of 4 kW, and travel speed of 8 m/min to achieve full-penetration joints. According to the experimental results, the similar P/M nanocomposite exhibited unstable behavior during laser welding due to the formation of porosity associated with clustering and void expansion near SiC nanoparticles. Hence, the fusion zone in both joint designs consisting of similar and dissimilar containing nanocomposite material became heterogeneous due to the presence of clusters and shrinkage micro-voids. The mechanical properties of weldments deteriorated considerably, with large fluctuations in the hardness profiles as well as low joining efficiency (<30%) and brittle fracture. Defects present in dissimilar welds were mainly located at the nanocomposite side.

Substituting organic manure for compound fertilizer increases yield and decreases NH3 and N2O emissions in an intensive vegetable production systems

Substituting organic manure for compound fertilizer may play an important role in regulating the nitrogen (N) cycle and consequently affecting crop yield in agroecosystems. However, how substituting different organic manures for compound fertilizer affects crop yield and ammonia (NH3) and nitrous oxide (N2O) emissions in the vegetable system during the life-cycle production (including storage and field application) remains poorly elucidated. Thus, we conducted a greenhouse experiment to investigate the effects of substituting organic manure species, i.e., stored swine manure fertilizer (SS), swine manure covered by straw (CS), stored swine fertilizer mixed with biochar (BS), and stored swine manure fertilizer with void expansion (OS) for compound fertilizer (FC) on rapeseed yield and NH3 and N2O emissions in a rapeseed-cropping system in China. The results showed that the total gaseous N losses (NH3 and N2O) were 1.6, 1.4 and 1.1 times higher in SS, CS and OS than FC, respectively. However, total gaseous N losses in BS was 0.9 times less than FC. Compared with FC, rapeseed yield and N uptake in SS and CS were decreased by 17.2–20.2% and 16.0%–28.1%, respectively, but which were increased by 7.3% and 54.1% in BS, respectively. In addition, OS decreased rapeseed yield by 17.2%, but increased N uptake by 8.5%. Therefore, the effects of substituting organic manure for compound fertilizer on rapeseed yield, N uptake, NH3 and N2O varied regarding different organic manure species. Adopting stored swine fertilizer mixed with biochar might be a sound management practice to reduce gaseous N losses and enhance N uptake and yield in intensive vegetable production systems.

Robust, highly porous hydrogels templated within emulsions stabilized using a reactive, crosslinking triblock copolymer

PolyHIPEs (PHs) are porous polymers that are typically templated within surfactant-stabilized high internal phase emulsions (HIPEs). Hydrogel PHs (HG-PHs) have exhibited potential as absorbents, adsorbents, release systems, and tissue engineering scaffolds. Recent work has shown that HG-PHs with highly temperature sensitive water uptakes could be produced using a reactive block copolymer (BC) as the sole surfactant, monomer, and crosslinker. It is not clear, however, whether these properties could be transferred to a HG-PH based on conventional hydrogel monomers and synthesized within a HIPE stabilized using a reactive BC. This work investigates HG-PHs based on acrylamide (AAm) synthesized within a HIPE stabilized by F-127-DMA, a reactive crosslinking BC based on methacrylate endcapped Pluronic F-127 (a commercial PEO-PPO-PEO triblock copolymer with poly(ethylene oxide) (PEO) endblocks and a poly(propylene oxide) (PPO) midblock). All the F-127-DMA-containing HG-PHs exhibited highly interconnected porous structures, low densities, and robust compressive behaviors with no chalkiness. The combination of F-127-DMA crosslinking and emulsion templating produced amplified and accelerated water uptakes, up to 161 g/g, associated with hydrogel-swelling-driven void expansion, and enhanced the temperature sensitivity, with the uptake decreasing by ∼50% between 5 and 60 °C, compared to reference HG-PHs and to conventional hydrogels.

The Distance and Motion of the Maffei Group

Abstract It has recently been suggested that the nearby galaxies Maffei 1 and 2 are farther in distance than previously thought, such that they no longer are members of the same galaxy group as IC 342. We reanalyze near-infrared photometry from the Hubble Space Telescope, and find a distance to Maffei 2 of 5.73 ± 0.40 Mpc. With this distance, the Maffei Group lies 2.5 Mpc behind the IC 342 Group and has a peculiar velocity toward the Local Group of −128 ± 33 km s−1. The negative peculiar velocities of both of these distinct galaxy groups are likely the manifestation of void expansion from the direction of Perseus-Pisces.

Microphase-Separated Macroporous Polymers from an Emulsion-Templated Reactive Triblock Copolymer

A polyHIPE (PH) is a macroporous polymer synthesized within a high internal phase emulsion (HIPE). The high-porosity, highly interconnected, open-cell structures and the PH-swelling-driven void expansion mechanism have made PH systems of interest for liquid absorption. Usually, only hydrophobic liquids or only hydrophilic liquids are considered for absorption applications. Here, PHs that are based solely on a reactive triblock copolymer (consisting of methacrylate-terminated poly(ethylene oxide) (PEO) end blocks and a poly(propylene oxide) midblock) were synthesized within oil-in-water HIPEs that are bereft of conventional monomers, cross-linking comonomers, and surfactants. The PH walls consisted of microphase-separated structures with crystalline PEO domains, a microstructure that is difficult to achieve in PHs. These PHs absorbed both hydrophobic liquids and hydrophilic liquids, with the PH-swelling-driven void expansion amplifying the absorption. For water absorption, the PH structure enhanced the tem...

Investigation on fracture behavior and mechanisms of DGEBF toughened by CTBN

Carboxyl-terminated butadiene-co-acrylonitrile (CTBN) was used as the toughener to improve the mechanical performance and fracture toughness of diglycidyl ether of bisphenol F (DGEBF) by prereacted approach. The results show that the chemical bonding interface was formed between DGEBF and CTBN particles in the prepolymerization reaction process, which remarkably enhances the fracture toughness of the composites. Based on the qualitative and quantitative analyses, it shows the main toughening mechanisms are the plastic shear banding effect resulted from the plastic deformation of the EP matrix and the plastic void expansion because of the debonding of CTBN particles from the EP matrix.

Positron annihilation exploration of voids in zinc zirconium borate glass ceramics entrenched with ZnZrO3 perovskite crystal phases

Origin of atomic-deficient free-volume structure in ZnO–ZrO2–B2O3 glass ceramic versus ZrO2 concentration was explored by positron annihilation lifetime spectroscopy (PAL) technique. XRD and SEM studies, on the titled samples indicated that the samples consist of tetragonal ZnZrO3 perovskite crystal phases. The IR spectroscopic studies suggested that Zr4+ ions prevailingly occupy octahedral positrons and play crucial role in formation of positron trapping holes in the samples. The PAL studies using 0.1MBq 22Na positron source indicated a significant variation in the positron annihilation life time with increasing ZrO2 for both positron- and positronium (Ps) trapping channels. The intensity of the longest positron annihilation component I3 is decreased from 4.45 to 3.07%, whereas o-Ps decay lifetime τ3 is enhanced from 1.18 to 1.34ns with increase of ZrO2 from 0 to 5.0mol%. These results suggested that the glass ceramic CZ5 contains the maximum free space or void expansion and void agglomeration.

Nanoscale morphology and optical property evolution of Pt nanostructures on GaN (0 0 0 1) by the systematic control of annealing temperature and duration with various Pt thickness

By the controlled fabrication of Pt nanostructures, various surface morphology dependent electronic, catalytic and optical properties can be exploited for a wide range of applications. In this paper, the evolution of Pt nanostructures on GaN (0 0 0 1) by the solid-state dewetting of Pt thin films is investigated. Controlling the annealing temperature, time and film thickness allows us to fabricate distinct size, density and configurations of Pt nanostructures. For 10 nm Pt thickness, tiny voids and Pt hillocks up to 550 °C, extensive void expansion and Pt nanostructure evolution between 600 °C–750 °C and finally Pt nanostructures assisted nanoholes penetration on GaN surface above 800 °C are demonstrated. Furthermore, comparatively elongated Pt nanostructures and NHs are resulted with 20 nm Pt thickness and voids growth and connected Pt nanostructure are formed by annealing duration control. The transformation of Pt films to nanostructures is governed by the surface diffusion, Rayleigh instability, Volmer–Weber growth and energy minimization mechanism whereas NHs penetration is commenced by the decomposition of GaN, Pt–Ga alloying and nitrogen desorption at high temperature. In addition, the optical characteristic of Pt nanostructures on GaN (0 0 0 1) by reflectance, photoluminescence (PL) and Raman spectroscopy demonstrate the surface morphology dependent spectral response.