Fine Fragments Research Articles

Peridynamic‐based modeling of elastoplasticity and fracture dynamics

AbstractThis paper introduces a particle‐based framework for simulating the behavior of elastoplastic materials and the formation of fractures, grounded in Peridynamic theory. Traditional approaches, such as the Finite Element Method (FEM) and Smoothed Particle Hydrodynamics (SPH), to modeling elastic materials have primarily relied on discretization techniques and continuous constitutive model. However, accurately capturing fracture and crack development in elastoplastic materials poses significant challenges for these conventional models. Our approach integrates a Peridynamic‐based elastic model with a density constraint, enhancing stability and realism. We adopt the Von Mises yield criterion and a bond stretch criterion to simulate plastic deformation and fracture formation, respectively. The proposed method stabilizes the elastic model through a density‐based position constraint, while plasticity is modeled using the Von Mises yield criterion within the bond of particle paris. Fracturing and the generation of fine fragments are facilitated by the fracture criterion and the application of complementarity operations to the inter‐particle connections. Our experimental results demonstrate the efficacy of our framework in realistically depicting a wide range of material behaviors, including elasticity, plasticity, and fracturing, across various scenarios.

What kind of corrosion products are “black spots”? —Effects of reduced sulfur compounds on corrosion of bronze artefacts

While deterioration due to the generation of “black spots” is reported, consensus on the specific corrosion products comprising black spots and underlying deterioration mechanisms is lacking. This study investigated the deterioration of copper objects by analysing the black spots that appeared on them and proposes environmental conditions to suppress the appearance of black spots. Bronze artefacts excavated from a marine archaeological site, on which black spots were generated, were closely observed, and investigated. First, X-ray fluorescence and micro-X-ray diffraction analyses were performed on a bronze artefact, from which the black spots were removed, to determine the composition of the artefact. Second, to investigate the composition of the black spots, fine structure analysis of the black spots on the fine fragments of the bronze artefacts was conducted using scanning and transmission electron microscopy, energy dispersive X-ray spectroscopy, and electron diffraction (ED) analysis. The results indicate that the black spots were partially composed of metallic copper and a fine particle mixture of Cu2S and CuSO4. These results imply that the transformation of copper sulfide to metallic copper may have played an important role in the initiation and propagation of black spots. In this study, ED analysis was performed on the microscopic area of the black spots; no amorphous phases were detected, and all observed phases were identified as crystalline materials. To determine the sources of gas-phase sulfur compounds that cause black spots, H2S and carbonyl sulfide (COS) emissions from a spherical clay artefact (a cannon ball with gunpowder excavated from an underwater archaeological site) which was exhibited in the same showcase with the bronze artefacts were analysed via gas chromatography. The concentrations of H2S and COS were 0.462 and 8.636 ppb, respectively; these are significantly higher than those in the lower troposphere. These results indicate that deterioration by black spots occurred because of H2S and COS, which were emitted from the spherical clay artefact excavated from an underwater archaeological site in the exhibition case. In addition, it was confirmed that the inclusion of deoxygenating and dehumidifying agents (RP-AN) in the plastic bag in which the spherical clay artefact was inserted resulted in a significant decrease in the concentration of H2S and COS.

A Study on the Interception using Fine Fragments and Particles to Hypersonic Vehicles

This paper describes the interception using fine fragments and particles to hypersonic vehicles which have a vulnerability in thermal and pressure during glide-phase flight. This interception concept is based on the fast relative velocity and the flight vulnerability of hypersonic vehicles. For the density calculation of fragmentation and particle in interception, error analysis of end-phase was performed including radar, intercept missile and target maneuvering errors. In relation to the vulnerability and error analysis, the penetration characteristics of fine fragments in high temperature were analyzed. Presented the interception in glide-phase could be applied to the concept of horizontal multi-layer defense to hypersonic vehicles.

Hetero‐blast from a structural reactive material cylinder under explosive loading

AbstractA structural reactive material (SRM) cylinder is considered here as a limiting case of a dense metallic energetic system in which a mixture of metal particles is consolidated to the theoretical maximum density excluding porosity, to possess both high energy density and mechanical strength. Dynamic fragmentation and free‐field explosion of a 103 mm inner diameter SRM cylinder charge is experimentally studied, with a wall thickness varying in a range of metal‐to‐explosive mass ratio M/C=1.3 to 4.0. Under explosive loading, the SRM cylinder produces a designated fragment size distribution divided into two groups: fine fragments with sizes on the order of 102 μm and below, and coarse fragments with sizes on the order ranging between 100‐101 mm. Prompt detonation shock‐induced reaction (DSIR) of the expanding cloud of high‐concentration fine fragments supplements the energy to enhance the primary blast as it propagates, while the coarse fragments form a high‐speed, high‐concentration metal momentum flux crossing the fireball and blast front to contribute to the total impulse loading to a nearby structure. Rapid impact‐induced reaction (IIR) of the secondary fragments from high‐speed coarse SRM fragments further enhances the reflected blast loading or generates a high interior explosion pressure as fragments perforate into the structure. The above distinctive characteristics of a unique hetero‐blast are coupled effectively in the near‐field range.

A numerical investigation of thermal stress induced cracking pattern in the solidifying nuclear fuel droplet during MFCI

During Molten Fuel Coolant Interaction (MFCI) occurring in a Sodium-cooled Fast Reactor (SFR) following a severe accident, the corium jet breaks up into coarse droplets due to hydrodynamic instabilities and fine flaked debris are generated due to the thermal stress cracking occurring on the solidifying droplet. In particular mixed oxide core debris quenched by liquid sodium are more prone to thermal stress cracking because of the excellent heat transport properties of liquid sodium, which leads to a large temperature gradient across the crust of the ceramic fuel. In this paper, thermal stress initiated cracking of solid crust of the nuclear fuel droplet is studied using Fracture Bifurcation Theory (FBT) and Minimum Potential Energy Principle (MPEP). FBT is able to predict the minimum crack length needed for crack propagation or catastrophic failure depending on the computed KI values. On the other hand, MPEP can predict the periodic and hierarchical cracking pattern that can develop on the core debris. This helps in the prediction of number of cracks and the crack length that can develop on the solid crust. Parametric studies have been carried out by varying MOX droplet sizes, crust thickness and cooling conditions and calculating KI by semi-analytical means and comparing it with KIC. The analysis revealed that solidifying droplets with radius equal to or more than 2 mm are susceptible to thermal stress initiated crack growth and catastrophic breakage even if a few tens of micron size initial crack develops on its surface. Then a particular case of 2 mm radius core debris is considered and its cracking pattern is studied by applying MPEP. This optimal crack configuration is obtained by minimizing potential energy for a given range of crack length and spacing. The analysis has been carried out with ANSYS APDL code which calculates the strain energy for a given initial crack length and spacing. The 2D computational model is validated with a similar study carried out for Alumina disc quenched in water and the results are in good agreement. The minimum fine fragment size predicted by the analysis for mixed oxide debris is a flake like debris with equivalent radius of 41 µm when approximated to be a sphere. The particle size correlates well with the fine debris sizes reported in literature of MFCI experiments.

Heterogeneities of grain boundary contact for simulation of laboratory-scale mechanical behavior of granitic rocks

From a practical point of view, grain structure heterogeneities are key parameters that control the rock response and still remains a challenge to incorporate in a quantitative manner. One of the less discussed topics in the context of the grain-based model (GBM) in the particle flow code (PFC) is the contact heterogeneities and the appropriate contact model to mimic the grain boundary behavior. Generally, the smooth joint (SJ) model and linear parallel bond (LPB) model are used to simulate the grain boundary behavior. However, the literature does not document the suitability of different models for specific problems. Another challenge in implementing GBM in PFC is that only a single bonding parameter is used at the grain boundaries. The aim of this study is to investigate the responses of a laboratory-scale specimen with SJ and LPB models, considering grain boundary heterogeneous and homogeneous contact parameters. Uniaxial and biaxial compression tests are performed to calibrate the response of Creighton granite. The stress–strain curves, volumetric dilation, inter-crack (crack in the grain boundary), and intra-crack (crack within the grain) development, and failure patterns associated with different contact models are examined. It was found that both the SJ and LPB models can reproduce the pre-peak behavior observed for a granitic rock type. However, the LPB model is unable to reproduce the post-peak behavior. Due to the large interlocking effect originating from the balls in contact and the ball size in the LPB model, local dilation is induced at the grain boundaries. This overestimates the volumetric dilation and residual shear strength. The LPB model tends to result in discontinuous inter-cracks and stress localization in the rock specimen, resulting in fine fragments at the rock surface during failure.

Combining geomechanical and hydrogeological modeling for drainage analysis in Block Caving mine development

Underground caving operations are naturally affected by mud and water inflows. These inflows occur mainly because caving operations are connected to a surface or a previous mining area through a broken subsidence zone where there is potential to accumulate water. Additionally, the surface/groundwater can mix with fine fragments within the broken column, which can generate a sudden mud rush through the drawpoints. A key mitigation measure for this hazard is drainage of the surrounding rock mass. However, an effective mine drainage system can be designed only if the physical behavior of groundwater flow is known. This work proposes a methodology that couples a geomechanical model designed in FLAC3D© with a hydrogeological model developed in FEFLOW©. The geomechanical model determines the spatial and temporal distribution of the stress field and induced strain due to caving. The spatial and temporal distribution of the hydraulic conductivity is analytically defined as a function of the induced strains. Then, the hydrogeological model is linked with the geomechanical model to simulate patterns of groundwater flow through the rock mass during cave propagation. Finally, a drainage chart is presented based on the hydrogeological simulation considering different caving stages and different system recharge due to surface inflows.

Compressive Behavior of Concrete Subjected to High Rate of Loading Using SHPB

Concrete is the most widely used construction material for strategic structures which are subjected to high rate of loading (impact and blast loading). Hence, the study of the concrete material becomes essential day by day for the structural engineers for the analysis and design of the concrete structures for safety and security purposes. This paper focuses on investigating the dynamic compressive response of the standard concrete (M35) and high-strength concrete (M60) under impact loading by using the newly developed split Hopkinson pressure bar setup (SHPB) apparatus. First, the calibration of SHPB performed at a 4.90[Formula: see text]ms[Formula: see text] impact velocity generates almost similar incident and transmission trapezoidal profile waves with minor reflection showing accuracy. Second, the dynamic compression tests were performed on the standard concrete (SC) and high-strength concrete (HSC) specimens of 29.5[Formula: see text]mm in diameter and [Formula: see text][Formula: see text]mm in length with an aspect ratio of about 1([Formula: see text]) and a comparative study of strain rate effect and quasi-static compressive strength on the material properties has been investigated. The dynamic compression behavior of SC and HSC thus studied under varying strain rates has been presented in terms of the compressive strength, dynamic increase factor, stress–strain relationship, material failure, and fragmentation. Compressive strength increments of 114% and 41% were observed in SC and HSC as the loading condition changed from quasi-static to dynamic. In addition, the HSC described the [Formula: see text]% and [Formula: see text]% higher compressive strength corresponding to 290[Formula: see text]s[Formula: see text] and 131[Formula: see text]s[Formula: see text] strain rate as compared to SC describing that the HSC is more sensitive to the strain rate. The dynamic mechanical properties increased with an increase in the strain rate, and the DIFs were found to vary in the range of 1.42–2.14 and 1.07–1.41 for SC and HSC, respectively. The critical strain and ultimate strain were also found to be sensitive to strain rate and increased with increase in strain rate for both grades of concrete. Moreover, strain rates exert a noteworthy influence on fragmentation, leading to an increase in the percentage weight of fine fragments and a decrease in the percentage weight of large fragments as the strain rate increases. Additionally, there is an overall increase in the quantity of fragments for both SC and HSC specimens under these conditions. The flaky, elongated, angular, and irregular shape fragments were observed but their quantity and size varied significantly with strain rate.

Effect of tool–pin offset on microstructure, mechanical properties, and corrosion behavior of friction stir welded AA2024-T3 and SS304 dissimilar joints

The combination of aluminum and steel materials in hybrid structures shows promising applications in the automotive, marine, and aerospace sectors. The present study investigates how the tool–pin offset impacts the microstructural, mechanical, and electrochemical characteristics of friction stir-welded joints between dissimilar AA2024-T3 and SS304 materials. The optimum conditions were achieved at a tool rotation of 560 r/min, a traverse speed of 25 mm/min, and a tool–pin offset of 1 mm towards the Al side. Upon increasing the tool–pin offset to 1.5 mm, insufficient heat input resulted in inadequate plastic deformation and material flow, leading to the creation of flaws like voids, tunnels, and interfacial gaps. However, under optimal conditions, the joint exhibited a well-defined and serrated interface, with fine steel fragments securely embedded in the Al matrix. Additionally, thin intermetallic compounds were observed around the steel fragments within the Al matrix. This favorable combination resulted in enhanced tensile strength and increased ductility in the joint. The Vickers hardness test revealed that the stir zone exhibited the highest hardness values, primarily attributed to the ultra-refinement of grains. Furthermore, the potentiodynamic test revealed that the welded samples show improved corrosion resistance against the base material AA2024-T3, although BM-SS304 exhibited the highest corrosion resistance among all the samples, likely due to its higher chromium content.

Effect of strain rate on specific fracture energy and micro-fracture surface properties of rock specimen under dynamic uniaxial compression

Effects of strain rate on specific fracture energy and micro-fracture surface properties of rock specimen were investigated at strain rates of ∼ 60–115.0 s-1. To achieve this, rock breakage was conducted under dynamic uniaxial compression using the split Hopkinson’s pressure bar. The fracture surface area of fine fragments (<8*10-3m) were measured using gas absorption method while the fracture surface area of large fragments (>8*10-3m) were measured using close-range photogrammetry. Results reveal that fracture surface area and specific fracture energy generally increase with strain rate during rock breakage under dynamic uniaxial compression. Similarly, the total fracture surface area of broken fragments also increased with dissipated energy. Results from scanning electron microscopy showed that fracture surface roughness and macro-crack abundance also increased with strain rate. Following energy requirement for rock breakage into size specifications for engineering applications, strain rate provides a reliable parameter for estimating specific fracture energy and fracture surface area at the forementioned strain rates. Accordingly, optimizing rock breakage processes using strain rate could reduce ore loss and energy wastage associated with production of unwanted fracture surfaces during rock breakage.

Effect of microstructure and microtexture evolution of oxide layer over J82B steel on mechanical descaling properties

The oxide layer covering a high-carbon steel wire rod must be efficiently removed to form ‘a well-adhered yet easy-to-remove oxide scale’ during the mechanical descaling process. In this study, the relationship between the microstructural characteristics of the oxides and the efficiency of mechanical descaling was investigated. An electron backscatter diffraction analysis was conducted prior to bending and microscratch testing to clarify the microstructural discrepancies, namely, the phase distribution and texture orientation of the oxide constituents within the oxide scale system over the steel wire rod. The oxide scale system exhibits a double-scale layered structure, primarily consisting of FeO and Fe3O4. The low-angle and low-Σ coincident site lattice (CSL) boundaries in the Fe3O4 grains inhibit crack propagation without diffusion interactions, supporting oxide spallation in the large flake state during descaling. However, if the Fe3O4 grains were distributed along the boundary between the oxide scale and the iron substrate and had a high orientation consistency with the α-Fe grains, the grown oxide scale spalled into fine fragments, and a considerable amount of oxide scale residue firmly adhered to the descaled steel specimen. Stress relief and ion vacancy diffusion mechanisms govern the growth of Fe3O4 grains near the surface and at the interface of the matrix. These results provide guidelines for adjusting the oxide scale heterogeneity of high-carbon steels to improve their descaling performance.

Automatic 3D Postoperative Evaluation of Complex Orthopaedic Interventions.

In clinical practice, image-based postoperative evaluation is still performed without state-of-the-art computer methods, as these are not sufficiently automated. In this study we propose a fully automatic 3D postoperative outcome quantification method for the relevant steps of orthopaedic interventions on the example of Periacetabular Osteotomy of Ganz (PAO). A typical orthopaedic intervention involves cutting bone, anatomy manipulation and repositioning as well as implant placement. Our method includes a segmentation based deep learning approach for detection and quantification of the cuts. Furthermore, anatomy repositioning was quantified through a multi-step registration method, which entailed a coarse alignment of the pre- and postoperative CT images followed by a fine fragment alignment of the repositioned anatomy. Implant (i.e., screw) position was identified by 3D Hough transform for line detection combined with fast voxel traversal based on ray tracing. The feasibility of our approach was investigated on 27 interventions and compared against manually performed 3D outcome evaluations. The results show that our method can accurately assess the quality and accuracy of the surgery. Our evaluation of the fragment repositioning showed a cumulative error for the coarse and fine alignment of 2.1 mm. Our evaluation of screw placement accuracy resulted in a distance error of 1.32 mm for screw head location and an angular deviation of 1.1° for screw axis. As a next step we will explore generalisation capabilities by applying the method to different interventions.

Pattern Analyses of Lunar Penetrating Radar Images at Chang'E‐3, 4, and 5 Landing Sites: A New Insight Into the Evolution of Lunar Regolith

AbstractAn “atlas” of the Lunar penetrating radar (LPR) patterns is organized and a comprehensive interpretation of the lunar subsurface layers in the areas of the Chang'E (CE) mission is proposed. There are three layers inferred by the LPR high‐frequency profiles of the CE‐3 and CE‐4. The first two layers (i.e., the fine regolith and the ejecta layer) at CE‐3 and CE‐4 sites have the same strata type but differ in internal structure and thickness. The third layer at the CE‐3 site is inferred as the paleoregolith, while at the CE‐4 site, it is inferred as the alternating layer with fine materials, ejecta, and fragments. Due to the limited penetration depth of the CE‐5 LPR, the data disclose only the fine regolith, with support from the empirical ejecta distribution model. The thicknesses, physical properties, and equivalent growth rates of lunar regolith at three landing sites are estimated and discussed in detail. The lunar regolith thicknesses inferred by the CE‐3 and CE‐5 LPR data are both approximately 1.0 m. In contrast, the thickness of the lunar regolith at the CE‐4 site is 10.0 m, which is greater than that at the other two landing sites. However, the equivalent growth rate of the regolith at the CE‐3 and CE‐5 landing sites is four times greater than that at the CE‐4 landing site. This illustrates that with the increase in lunar regolith thickness, the influence of small impact gardening events on the lunar regolith reconstruction gradually weakened, and the self‐buffering effect avoids the fast growth of lunar regolith.

Recycling of waste gypsum from αlpha-hemihydrate phosphogypsum: Based on the atmospheric hydrothermal process

Phosphogypsum (PG) is a typical solid waste in the phosphorus chemical industry, which restricts the sustainable development of the phosphorus chemical industry. From the perspective of green manufacturing in the whole life cycle, this paper puts forward the hydrothermal recycling and utilization of waste gypsum (WG) from αlpha-hemihydrate phosphogypsum (α-PGHH). It is revealed that the raw material characteristics of WG will lead to the crystal fine fragmentation of the product, which will lead to the significant deterioration of the strength and filtration performance of the hardened paste. The increase of the acidity of the reaction medium is proposed to weaken the negative effect of the crystal modifier on crystal phase transition, so as to obtain recycled αlpha-hemihydrate gypsum (α-HH) with better crystal integrity and macroscopic performance. It was proved that when the pH value was controlled at 4.5, the comprehensive properties of the product were good, and the 2 h bending strength and 3 d compressive strength were 4.1 MPa and 29.2 MPa, respectively. The preparation of recycled α-HH from WG produced by α-PGHH can be achieved through the atmospheric hydrothermal process.

Effect of Subcritical Treatment (Tempering) on Hardness and Wear of High Chromium White Cast Iron

High chromium white cast iron (HCWCI) is used in mining, crushing plants, as mill liners, and in the manufacture of grinding balls. The grinding ball is the essential element in fine fragmentation. It must have an excellent life to counter extreme wear and impact conditions that it undergoes. Hence it is important to improve its mechanical properties. This study aims to find the effect of tempering temperature on microstructure, hardness, and abrasive wear of High Chromium White Cast Iron used in the manufacture of grinding balls. In this study, the balls in high chromium white cast iron with 12 to 17% Cr, of 50mm and 70mm in diameter were austenitized at 950°C for 45 min and 55 min for the balls of 50 and 70mm then were quenched in forced air. The balls were tempered at 250°C, 400°C, and 600°C for 120 min and 180 min for both diameters 50 and 70mm respectively, and cooled in the furnace. The results showed that tempering practiced at 250°C and 400°C gives an excellent hardness than balls austenitized at 950°C. It is about 60 HRC and it drops to less than 50 HRC for the tempering at 600°C. This tempering causes a significant mass loss (short life) but tempering at 250°C and 400°C decreases this loss by up to 1.6%. The results of XRD showed the presence of the martensite and carbides type M7C3 after tempering at 250°C and a ferritic matrix after tempering at 600°C.

Mechanical Properties and Microstructures of Highly Fe-Containing Al–Mg–Si Alloys Processed by Severe Plastic Deformation under High Pressure

In this study, A6022-based Al–Mg–Si alloys with three additional Fe contents are processed by high-pressure torsion (HPT) and high-pressure sliding (HPS). Both processes yield a similar tensile strength exceeding 400 MPa. Fe intermetallics were finely and homogeneously fragmented to an average size of ∼2 µm by the HPT process. The high tensile strength is attributed to such a fine and homogeneous fragmentation of Fe intermetallics. It is also demonstrated that the finely fragmented Fe intermetallics play an important role to maintain finer grain size even after solution treatment.

On the question of the fine fragmentation of liquid-metal droplets during steam explosions

On the question of the fine fragmentation of liquid-metal droplets during steam explosions

Ignition and combustion behavior of gel fuel particles with metal and non-metal additives

A group of elastically deformable gel fuel compositions was prepared from oil-filled cryogels with fine particles (Al, Cu, Fe, carbonaceous, inert) and without them. Fuel particles exposed to radiant heating at an oxidizer temperature of 600–1000 °C consistently ignited with dispersion that had a positive effect on the intensity of the fuel component burnout. For different fuel compositions, the ignition delay times vary from 1 to 10 s, the velocities vary from 0.3 to 1.4 m/s, and the average diameters of the burnout area vary from 7 to 15 mm. At heated air temperatures above 900 °C, the ignition delay times are quite similar. Within the whole range of source temperatures, the fuel composition with fine carbonaceous particles ignites most rapidly. The gel fuel composition with Al particles is characterized by the highest ignition delay times and lowest velocities of fine fragments.

Effect of kaolinite additive on water-soluble sodium release and particle matter formation during Zhundong coal combustion

Zhundong coal causes serious slagging problems and particle matter (PM) pollution due to its high sodium content. In this paper, sodium release and PM formation experiments were carried out in tube and laboratory dropper furnaces using three types of coal in Zhundong. The effects of kaolinite additives on sodium release and PM formation, as well as the mechanism of different types of sodium release and PM formation, were investigated. The results showed that compared with water-soluble sodium, most organic sodium was released after a series of complex complexation reactions, such that kaolinite exhibited a better adsorption effect on water-soluble sodium. Furthermore, the concentration of different types of Na in PM emitted differed as a result of different coals, which would lead to different collision frequencies between particles and kaolinite. The PM2.5 stemmed from the homogeneous condensation of volatile elements and the fragmentation of minerals in the combustion, while the PM10 originated from the coalescence of the fine fragments of fly ash. Moreover, the kaolinite additive intensified the heterogeneous condensation reaction with gaseous sodium to form larger particles, due to the reaction effect of kaolinite for water-soluble sodium of PM2.5 being stronger than organic sodium and the organic sodium of PM10 being stronger than water-soluble sodium.

Empirical Rule of Fruit Rind Fragmentation in Muskmelon Netting

The suberized netting tissue on the surface of muskmelons is a remnant of the rind fragmentation caused by the mechanical imbalance between the expanding flesh meat and the solidified epidermis during growth. The appearance of this netting pattern is an important indicator for assessing the quality of muskmelons; however, very few quantitative studies have been conducted on the geometry of the netting. This study statistically analyzed the areas of fine epidermis fragments surrounded by the net using image analysis and explored a common rule governing the probability distribution of the fragment area. We found that the fragment area distribution follows a universal law by the modified Bessel function, which is consistent with the theoretical argument for the fracture behavior of brittle materials.