Large Cracks Research Articles

Silica Nanoparticles Modified by Biphenyl Groups for Crack-Free Coating on Synthetic Paper.

Water-based acrylic emulsions are a crucial component of water-based ink. Preventing visible cracks in emulsion coating during drying is a great challenge due to the high polarity and high surface tension of water. Herein, we propose that the cracking resistance of the coating can be enhanced through the incorporation of hydrophobic silica nanoparticles. The hydrophobic silica nanoparticles were fabricated by the modification of biphenyl groups to the surface of silica nanoparticles through postcoating using dimethoxydiphenylsilane. The presence of phenyl groups on the surface of biphenyl-modified silica nanoparticles (BPSNs) was confirmed by the Raman spectrum, Sears number, and zeta potential measurements. The formation of large cracks was significantly reduced by the incorporation of BPSN into water-based acrylic emulsion coatings. BPSN strengthens the forces of attraction between the resin particles in coatings, enabling the coating to resist the stresses caused by drying. This work provides a simple method to obtain crack-free coatings of water-based acrylic emulsion on a nonabsorbent substrate, offering a promising strategy for the printing industry to broaden the application of water-based ink.

Fracture and Fatigue Crack Growth Behaviour of A516 Gr 60 Steel Welded Joints

The facture and fatigue behaviour of welded joints made of A516 Gr 60 was analysed, bearing in mind their susceptibility to cracking, especially in the case of components which had been in service for a long time period. With respect to fracture, the fracture toughness was determined for all three zones of a welded joint, the base metal (BM), heat-affected zone (HAZ) and weld metal (WM), by applying a standard procedure to evaluate KIc via based on JIc values (ASTM E1820). With respect to fatigue, the fatigue crack growth rates were determined according to the Paris law by the standard procedure (ASTM E647) to evaluate the behaviour of different welded joint zones under amplitude loading. The results obtained for A516 Gr. 60 structural steel showed why it is widely used in the case of static loads, since the minimum value of fracture toughness (185 MPa√m) provides relatively large critical crack lengths, whereas its behaviour under amplitude loading indicated a need for further improvement in WM and HAZ, since the crack growth rate reached values as high as 4.58 × 10−4 mm/cycle. In addition, risk-based analysis was applied to assess the structural integrity of a pressure vessel, including comparison with the high-strength low-alloy (HSLA) steel NIOVAL 50, proving once again its superior behaviour under static loading.

Ultrasonic cavitation finishing of 316 L stainless steel using different abrasive particles: A combined SPH simulation and experimental study

Ultrasonic cavitation and its driving effect on abrasive particles have been studied and applied to the surface finishing of 316 L stainless steel. To explore the influence of abrasive characteristic parameters on the surface finishing process, a cavitation-driven single abrasive impact model was established by coupling the smoothed particle hydrodynamics (SPH) method with the finite element method (FEM). The changes in the workpiece surface and the wear of abrasive particles after the impact were analysed, the effects of the abrasive particle size, material and shape were discussed, and the effectiveness of the model was verified through ultrasonic finishing experiments. SiC abrasive particles possessing irregular shape and Al2O3 abrasive particles possessing irregular and spherical shapes were used for comparison. Both simulation and experimental results indicate that the abrasive particle with a high hardness and a spherical shape has better material removal capability. However, the spherical abrasive particles tended to occur large cracks and split into small pieces, which accelerated the wear of the abrasives. In this work, the best finishing result was obtained by using irregularly shaped SiC abrasive particles, and the surface roughness Ra was improved by 12.87 %. This study provides a comprehensive understanding of the material removal process using cavitation-driven abrasives and examines the influence of key characteristics of abrasive particles. These insights are significant for advancing the application and enhancement of this technology in metal surface treatment.

Large Scale Pavement Crack Evaluation Through a Novel Spatial Machine Learning Approach Considering Geocomplexity

Large Scale Pavement Crack Evaluation Through a Novel Spatial Machine Learning Approach Considering Geocomplexity

Bending Properties of Finger-Jointed Bamboo Scrimber Composite Beams

The finger-joint technique is an effective and economical method for producing bamboo scrimber composites for structural engineering and construction applications. This study investigates the failure modes and mechanical strength of finger-jointed bamboo scrimber specimens and composite beams loaded parallel and perpendicular to the finger profile orientation. Results indicate that the primary failure mode in finger-jointed bamboo scrimber specimens is damage to the finger-joint area. In V-type composite beams, primary failure was observed as the separation of laminated boards and finger joints, while in H-type beams, large cracks formed and expanded alongside finger joint damage. No statistically significant difference was observed in the modulus of elasticity (MOE) and modulus of rupture (MOR) between the two types of finger-jointed bamboo scrimber. However, the MOR of the finger-jointed bamboo scrimber specimens decreased significantly, by more than 50% compared to the control, while the MOE increased. The ultimate load capacity and displacement of the V-type beams were higher. Under bending, the V-type beams demonstrated elastic deformation, whereas the H-type beams exhibited initial elastic deformation followed by elasto-plastic deformation. Strain distribution along the height of both beam types remained linear, consistent with the plane-section assumption.

Merging behaviour and fatigue life evaluation of multi-cracks in welds of OSDs

Experimental studies were conducted to investigate the merging behaviour of multiple fatigue cracks (MFCs) in rib-to-deck welds of orthotropic steel decks (OSDs). Numerical simulations were conducted to investigate the mechanism of the merging behaviour of MFCs on fatigue life. In addition, the sensitive parameter in the MFCs affecting the fatigue life were revealed. Finally, a comprehensively failure criterion for MFCs was proposed. Results show that the merging behaviour of MFCs can be effectively observed by the beach marks on the fracture surface of the rib-to-deck weld. The merging behaviour is a key factor driving cracks penetrating through the deck, which significantly increases the crack length and decreases the crack shape ratio. The fatigue life of MFCs with different crack sizes is mostly determined by the larger crack, while the shape ratio effect can be ignored. The crack number has the most significant effect on fatigue life, where the five-cracks case reducing the fatigue life by up to 39 % compared to a single crack. Due to the nonlinear effect of crack spacing on fatigue life, MFCs with the same fatigue life may have significantly different final crack length. Therefore, the proposed failure criterion for MFCs considers the effects of both crack depth and length.

Damage modes and mechanisms for fine woven pierce SiO2f/SiO2 composite under quasi‐static compression

AbstractFinite element analysis (FEA) for fine woven pierce SiO2f/SiO2 composites quasi‐static compression is conducted in weft and Z yarn directions, strain–stress curves with experiments and FEA are compared, and finite element model proves to be valid. During quasi‐static compression, the strain difference between matrix and fiber rise. As for compression in the weft direction, matrix micro‐cracks increased into large cracks and mainly distribute around warp fibers. The interfacial stress increases and results in interface damage around the warp fiber. The stress fields are superimposed and rise in warp and weft yarns overlapping regions, in which damage modes include matrix cracks, fiber debonding, and breakage. Obvious V‐shaped shear bands are formed on YZ surface. As for compression in the Z‐direction, interfacial stresses around the warp and weft fibers are superposited and strengthened, fibers debonding occurs continuously with increasing interfacial stress; stress field inside composites in the Z yarn gets great, SiO2f/SiO2 composites have greater compression strength in the Z‐yarn direction than that in the weft direction.

Diffusive-length-scale adjustable phase field fracture model for large/small structures

In phase field fracture (PFF) method, the sharp crack is approximated by a phase field crack zone whose size is characterized by a diffusive length scale. Recently, the diffusive length scale is usually regarded as a constant material parameter determined by the fracture toughness, material strength, and young's modulus. As a result, the application of the PFF method poses challenges when dealing with structures whose sizes are much too large or small compared to the constant diffusive length scale. In details, for a large-scale structure, a significant computational burden is inevitable due to the limitation imposed by the constant diffusive crack length scale on the element size (i.e. the element size is generally at least smaller than half of the diffusive crack length scale to achieve the sufficient precision for the phase field process zone). For a small-scale structure, the crack patterns tend to be unclear and unrealistic due to the excessively large diffusive crack zone. To address these limitations, we propose a novel PFF method to make the relation between the diffusive length scale and the material parameters adjustable via modifying the energetic degradation functions. It is found that with the increase of the diffusive crack length scale, a transition from quasi-brittleness to brittleness is observed in the constitutive relationship curves, which coincides with the classical size effect on structural strength. Further, the Bažant's size effect in classical fracture mechanics can be reproduced by the present PFF method through scaling the size of a geometrically similar structure, i.e. a large-scale structure exhibits toughness-dominated fracture while a small-scale structure behavior strength-dominated fracture. The present PFF method efficiently addresses the mismatch of diffusive length scales for various material constituents by examining phase field crack growth in particle-reinforced composite plates. By adjusting the diffusive crack length scale based on structure size, it avoids high computational costs from large structures and unrealistic crack patterns from small ones. Moreover, it outperforms traditional PFF methods using a constant diffusive length scale in handling composite materials.

Deep Insight into Reactivity of Li3PS4 Electrolyte for Solid Li-Ion Batteries Towards Humidity Using Large Instruments

Wide commercialization of Li-ion batteries (LIBs) for electric transport stimulates a demand for safer batteries with higher energy density. Thiophosphate solid electrolytes (TSEs) for LIBs are one of the most promising candidates to replace a classical liquid electrolyte with volatile components owing to their high ionic conductivity values and appropriate mechanical properties for processing [1]. However, one of the main drawbacks of TSEs is their high sensitivity towards humidity even in trace amounts. The reactivity with water and moisture impacts the electrochemical properties of the electrolytes and leads to toxic H2S emissions. This aspect plays a crucial role for the choice of LIB manufacturing environment (dry room characteristics) and requires fine understanding of underlying mechanisms to optimize a performance / cost ratio for solid-state batteries (SSBs).In the present study, a unique combination of characterisation methods was applied to investigate the reaction between densified Li3PS4 pellet and different levels of humidity (dew point (DP) -40 °C and DP=12 °C for 15 min and 2 h) from chemical and morphological/microstructural points of view. H2S gas evolution was accurately quantified upon a TSE exposure to humid atmosphere using a home-made flow-through setup with differentiation between surface and bulk pellet reactivity [2]. Further, top-view propagation of Li3PS4 pellet degradation was investigated using SEM and EDX techniques showing fractures generated through gas released leading to some increase in the pellet porosity at DP= -40 °C; apparition of cracks and oxygen content raise in case of DP = 12 °C exposure. The bulk of the exposed pellets was probed using non-destructive X-ray nanotomography (ESRF, ID16b). Different scenarios were observed at low and high levels of humidity during 15 min and 2 h of the pellet exposure (see Fig.). Degradation front containing large pores and cracks propagated up to 50 µm to the depth of the pellet (~400 µm total thickness) after 2 h of exposure to DP= 12 °C. X-ray diffraction-computed tomography (XRD-CT, ESRF, ID15a) was employed to observe structural changes in 3D for Li3PS4 SE upon its reaction with humidity at different depths. Minor changes were find in crystalline structure of Li3PS4 after DP= -40 °C exposure while a reaction at DP=12 °C provoked formation of new phases propagating up to 90 µm depth of the pellet. Some of newly formed compounds were identified, i.e. P2S2O3, Li2HPO3, P2O5 and Li2S2O6.2H2O. Structural strains for Li3PS4 crystalline phase after its exposure to DP=12 °C were revealed thanks to advanced XRD-CT analysis. Finally, the impact of the pellet exposure to humidity at different conditions on its ionic conductivity was investigated.As a result of this study, a solid link was found between the morphological, microstructural, chemical degradation of the TSE and its ionic conductivity upon reaction with water. It was evidenced that the crack formation and propagation to the bulk of TSE pellet is a result of a complex cyclic mechanism, which includes chemical attack of H2O molecules on Li3PS4 pellet surface, creation of mechanical strain for the TSE lattice, formation of solid degradation products and gaseous H2S, crack propagation due to the strain release and the gas evolution, further penetration of water to the bulk of the pellet, etc. To the best of our knowledge, this is a first comprehensive study of reaction between SSE and humidity taking into account all the aspects above. This work contributes to understanding of key triggers for TSE deterioration in contact with different concentrations of water and to definition of proper environment for solid-state batteries production and handling.Beamtime at the ESRF was granted within the Battery Pilot Hub MA4929 “Multi-scale Multi-techniques investigations of Li-ion batteries: towards a European Battery Hub.

Enhanced Mass Transportation for the Oxygen Evolution Reaction in Flexible Mesoporous Hydrogel Electrodes

Water electrolysis is of great importance for the hydrogen production from renewable energy. The efficiency of water electrolysis depends highly on the performance of anodes because of the high overpotential of the oxygen evolution reaction (OER). Mesoporous electrodes with high surface area and relatively small pore size (2-50 nm) have attracted much attention as highly active OER electrodes; however, the mass transportation of generated oxygen molecules and hydroxide ions in mesopores often limit the OER current density.In this study, we propose a novel class of materials, namely flexible mesoporous hydrogel electrodes which consist of assemblies of CoOOH nanosheets. Flexible mesoporous hydrogel electrodes were prepared by electrochemical deposition of cobalt hydroxide nanosheets modified with tris(hydroxymethyl)aminomethane (depicted as Co-ns [1]) on nickel substrates. Co-ns formed a house-of-cards assembly, having characteristics of hydrogels, during the deposition process. The surface modifying group of Co-ns was anodically decomposed and Co-ns was transformed into CoOOH nanosheets. Because of the weak connections among CoOOH nanosheets the resultant assemblies provided flexible mesoporous frameworks.The flexible mesoporous electrodes with different thicknesses (4-37 μm) were prepared, changing the deposition time. The porosity of the flexible mesoporous electrodes were estimated to be approximately 97% because of the very thin thickness of the CoOOH nanosheets. Rigid mesoporous electrodes with Co3O4 frameworks with different thicknesses (11-60 μm) were also prepared by dip-coating method, using Pluronic F127 as a template. The porosity of the rigid mesoporous electrodes was approximately 78%. The electrochemical tests were performed in a three electrode cell at 30 ºC.The OER polarization curves of the flexible mesoporous electrodes and the rigid mesoporous electrodes in 1.0 M KOH electrolyte are shown in the Figure 1. The OER current densities of the rigid mesoporous electrodes depend quantitatively on the thickness of the films at 1.50 V vs. RHE, though the current densities became independent of the thickness of the films at 1.60 V vs. RHE. On the other hand, the OER current densities of the flexible mesoporous electrodes depend quantitatively on the thickness of the films at wide potential region, even at 1.60 V vs. RHE, indicating that the high mass transport ability of generated oxygen molecules and hydroxide ions in the mesopores.In conventional rigid mesoporous electrodes, oxygen bubbles should form within mesopores with defects, i.e. large nanospace and cracks, and the generated bubbles plug the mass transport paths. The flexible mesoporous hydrogel electrodes are expected to have defect-less mesoporous structures because they can change the mesoporous structures flexibly to reduce defects, and defects can be self-healed once they are formed. It is also expected that the flexible frameworks change their mesoporous structure to optimize the mass transportation path during OER.In conclusion, novel mesoporous hydrogel electrodes were prepared for the first time by the electrochemical deposition of Co-ns. The flexible mesoporous hydrogel electrodes exhibited high OER performance, depending on the thickness of the films quantitatively at high current density region. Flexible mesoporous hydrogel electrodes are promising as novel types of electrodes to improve the efficiency of water electrolysis. This work was supported by the JSPS KAKENHI (grant number 24K01580).

Quantifying Aging-Induced Irreversible Volume Change of Porous Electrodes

Automotive manufacturers are working to improve cell and pack design by increasing their performance, durability, and range. One of the critical factors to consider as the industry moves towards materials with higher energy density is the ability to consider the irreversible volume change characteristic of the accelerated SEI layer growth tied to the large volume change and particle cracking typically associated with active material strain. Here, we add to a previously developed mechano-electrochemical model[1-8] to more practically understand the impact of irreversible volume change, primarily assigned to SEI layer growth. As the time from initial design to manufacture of electric vehicle is decreased in order to rapidly respond to consumer demands and widespread adoption of electric vehicles, the ability to link aging and volume change to end of life vehicle requirements using virtual tools is critical.[9] In this study[10], we apply a model to determine the irreversible volume change at the electrode and cell level, allowing for virtual design iterations to predict the volume change at battery cell aged states, and probe possible changes in the SEI layer over life.

Effect of temperature variation on bonding properties of magnesium potassium phosphate cement: A multiscale analysis

In magnesium potassium phosphate cement (MKPC) repair work, varying ambient temperatures significantly affect the repair outcomes. To quantitatively characterize the effect of temperature variation on the bonding properties of MKPC, this paper comprehensively explores the issue at multiple levels, evaluating the bonding properties of the combined specimens using double-shear tests, scanning electron microscope tests, and nuclear magnetic resonance tests, followed by quantitatively characterizing the form of interfacial damage using digital image processing of interfaces. Finally, the Pearson correlation coefficient method was employed to analyze the correlation between different scales. The results indicate that, for the MKPC combined specimens, the interface shear bearing capacity slightly decreased at low temperatures and improved back to normal temperature, with a retention coefficient (K) of 0.977. The internal structure was dominated by small holes, whereas at high temperatures, the capacity severely decreased, with K only 0.4, and a large number of large holes and cracks were present internally. The DIP results reveal that the interface damage forms of the combined specimens at low temperatures were dominated by the MKPC-NC interface, which accounted for 76.38 %. At high temperatures, the damage was mostly within the MKPC, with the MKPC interface accounting for 52.06 % of the fracture interface of the specimen. Pearson correlation analysis demonstrates that temperature has a strong relationship with the scale indicators, with an |R| value greater than 0.7. The |R| value between macroscopic performance and microstructure is 0.95, providing strong evidence that macroscopic performance can be characterized by the microstructure.

Limiting possibilities of detecting cracks in ferromagnetic structures through an anti-corrosion coating using a smartphone based eddy current flaw detector

Detection of cracks in ferromagnetic steel structures by the eddy current method is often limited by additional noise associated with magnetic and structural heterogeneity, especially when it is necessary to detect structural cracks through a layer of dielectric anti-corrosion coating. A promissing approach to problem solution is based on the use of selective eddy current probes, which include the eddy current probes of double differential type. One of the features of such eddy current is the possibility of detecting hidden defects even through a layer of dielectric anti-corrosion coating. In this paper, the limiting possibilities of crack detection using an improved low-frequency eddy current probe of double-differential type with a diameter of 15 mm and a smartphone based eddy current flaw detector were investigated. This probe provides a high depth of penetration necessary to detect defects under the dielectric coating. The greater depth of penetration of this probe is achieved by increasing the diameter of the windings, the distance between them and the number of turns. The research was carried out using a rectangular specimen, in which a large crack (or through wall structure fracture) was simulated by a joint of two identical polished rectangular parts. The assembled specimen was covered with dielectric plates of different thicknesses up to 25 mm thick to simulate anti-corrosion coating of different thicknesses. It is shown, in particular, the possibility of detecting large cracks or structural fractures through an anti-corrosion dielectric coating up to 25 mm thick. The principle of design of an eddy current flaw detector based on a smartphone using the EddySmart application, which can provide remote control of ferromagnetic steel structures with wireless transmission of inspection results via mobile communication channels and the use of autonomous automated scanners, is considered.

Visualization and Simulation of Foam-Assisted Gas Drive Mechanism in Surface Karst Slit-Hole Type Reservoirs

Nitrogen injection technology has become an important production technology after water injection development in the karst fracture-vuggy reservoir in Tahe Oilfield. However, due to the influence of reservoir heterogeneity and the high mobility of gas fluid, nitrogen easily forms a dominant channel and gas channeling occurs, and the recovery effect time is short. Based on this, a visual surface karst model is designed and created to study nitrogen foam-assisted gas drive. The results show that after gas channeling occurs in the dominant channel of nitrogen flooding, foam injection-assisted gas flooding can improve oil recovery. In the longitudinal direction, foam-assisted gas drive mainly displaces the remaining oil because of gravity differentiation and the reduction of oil–water interfacial tension. In the horizontal direction, foam-assisted gas drive is mainly used to block the large pore cracks and dominant channels, promote the gas to turn into large tortuous and small cracks, and expand the swept efficiency of the gas. After forming the dominant channel, injecting 0.3 pv salt-sensitive foam with a gas–liquid ratio of 2:1 in the middle of the gas channel can improve the recovery rate of the model from 4% to about 25%, and the recovery rate can be increased by about 20%, which improves the effect of gas flushing and improves the development efficiency of the oil field at the same time.

Fabrication of amorphous lamellar freestanding poly(N‐dodecyl acrylamide) films and their mechanical properties

AbstractAn amorphous lamellar freestanding film composed of poly(N‐dodecyl acrylamide) (pDDA) was prepared by annealing a micrometer‐thick film under humid conditions (humid‐annealing). pDDA was blade‐coated onto a glass substrate, and its lamellar formation was studied by XRD and polarized optical microscopy (POM). The XRD pattern indicates that pDDA formed a highly oriented lamellar structure by humid‐annealing at 80 °C for 6 h. Moreover, the POM image of the cross‐section of the film indicates that lamellar formation started at the polymer–substrate interface, and the amorphous lamella covered the entire film area without randomly oriented regions. In contrast, the open Nicol microscopic image exhibited large cracks in the highly oriented film owing to shrinkage of the film. A crack‐free film was prepared using water‐saturated chloroform as the solvent for blade coating. Water is thought to adsorb to an amide moiety to induce a ‘pre‐lamellar’ structure in the solution. The formation of pre‐lamellae and the decrease in the humid‐annealing temperature reduced the shrinkage of the film by lamellar formation to form a crack‐free film. The mechanical properties of the crack‐free, freestanding pDDA films were studied using a simple tensile test. The film became increasingly stronger with the formation of an amorphous lamellar structure. These results indicate that the mechanical properties of polymer films can be improved without crystallization. © 2024 The Author(s). Polymer International published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Comparison of the mechanical properties and constitutive models of carbon fiber-reinforced coral concrete cubes and prisms under uniaxial compression

Carbon fiber reinforced coral concrete (CFRCC) plays a crucial role in island construction. In engineering applications, CFRCC is often subjected to complex stress states. Multiaxial stress studies usually use cubes, and in order to maintain research consistency, uniaxial studies also often use cubes. Traditional uniaxial stress studies mainly use prisms. However, the differences in uniaxial compression mechanical properties between these two types of specimens have not been thoroughly studied. To fill this gap, this study conducted uniaxial compression tests on cubes and compared the results with previous tests on prisms.The results showed that the failure patterns of the two types of specimens were different. The main cracks of the cubes were vertically distributed, while the main cracks of the prisms mostly unfolded diagonally. The addition of carbon fibers (CFs) reduced the number of large cracks and increased the number of microcracks. The stress-strain curves, peak stress, peak strain, and initial elastic modulus of the two types of specimens show similar variations with CFs, and CFs significantly improve the mechanical properties of coral concrete. The constitutive models based on prisms cannot accurately describe the mechanical behavior of cubes, therefore, we proposed revised constitutive models. The revised constitutive models can accurately describe the mechanical behavior of cubes. This study laid the foundation for subsequent research on multiaxial stress.

Microstructure and mechanical properties of austenitic stainless steels manipulated by trace TiC–TiB2 nanoparticles

It is difficult to simultaneously increase strength and toughness of austenitic stainless steels through traditional heat treatment and alloying. However, adding nano-sized ceramic particles is a potential method to manipulate the microstructure and mechanical properties of austenitic stainless steels. In this study, TiC–TiB2 nanoparticles were introduced into austenitic stainless steel using an aluminum master alloy. Adding 0.02 wt% nanoparticles effectively refined the substrates including the dendritic ferrite and austenite and reduced the grain size from 23.7 μm to 18.4 μm. The edge-to-edge model indicated that the nanoparticles act as heterogeneous cores to facilitate the nucleation rates. For mechanical properties, the addition of nanoparticles simultaneously enhanced the hardness, yield strength, tensile strength and impact toughness of the austenitic stainless steels without sacrificing the ductility. The yield strength and tensile strength of as-cast austenitic stainless steels were enhanced by 4.8% and 2.1%, 7.2% and 3.9%, 10.0% and 5.7% at the temperatures of 20 °C, 200 °C, and 400 °C, respectively. The impact toughness was improved by 4.2%, 5.9%, and 4.3% at the temperatures of −20 °C, 0 °C, and 20 °C. Also, the presence of nanoparticles increased the yield strength and tensile strength of forged austenitic stainless steels by 16.6% and 5.9%, 17.7% and 7.7%, 18.5% and 12.2% at the temperatures of 20 °C, 200 °C, and 400 °C, respectively. The impact toughness was increased by 11.6%, 8.6% and 11.3% at the temperatures of −20 °C, 0 °C, and 20 °C. The nanoparticles refined the grains, inhibited dislocation movement, scattered large cracks and distributed the external loads more uniformly to strengthen and toughen the austenitic stainless steels. In wear tests, the nanoparticle reinforced austenitic stainless steels showed higher wear resistance against adhesive wear and abrasive wear by impeding the nucleation and growth of cracks, retarding the dislocation migration and plastic deformation and bearing the external loads. The wear volumes of as-cast and forged austenitic stainless steels were reduce by 15.7% and 21.5%. This innovative approach provided a promising strategy to produce high-performance austenitic stainless steels and serve as a reference in the development of other nanoparticle reinforced ferrous materials.

Cutting behaviors of cortical bone ultrasonic vibration-assisted cutting immersed in physiological saline

In orthopedic surgery, cortical bone cutting usually involves washing and cooling with physiological saline. However, how the saline changes the cutting behaviors of bone ultrasonic vibration cutting remains challenging. Hence, this paper simulates the clinical ultrasonic cutting condition in orthopedics to reveal the cutting behaviors of bone ultrasonic vibration orthogonal cutting immersed in physiological saline. The dynamic equation and motion process curves of ultrasonic cavitation bubbles were established. The results showed that the bone cutting immersed in physiological saline significantly improved the surface quality, reduced surface roughness and mechanical damage, and avoided large brittle cracks propagation. In saline immersed cutting, the physiological saline changes the mechanical behaviors of bone materials, resulting in plastic behaviors for the material removal and crack deflection. This study establishes the influence of physiological saline on the ultrasonic vibration cutting performance, providing guidance for orthopedic bone cutting surgery methods.

Post-irradiation examination of UN-Mo-W fuels for space nuclear propulsion

The National Aeronautics and Space Administration's return to space nuclear propulsion stems from the need for a more efficient method of space travel. Nuclear thermal propulsion systems have been shown to be two times more efficient than chemical propulsion. NASA's Sirius program was created to fabricate and test fuels for space nuclear propulsion, specifically to determine their performance under prototypical startup conditions. The Sirius project featured 4 test capsules, Sirius-1 featured uranium nitride fuel dispersed in a matrix of tungsten and rhenium, while Sirius-2A, -2B, and -3 featured uranium nitride-molybdenum-tungsten fuel (UN-Mo-W). This study discusses the Sirius-2A and -2B irradiation experiments at the Idaho National Laboratory, specifically their performance under irradiation at the Transient Reactor Test Facility. It was found that the fuel samples overall did not exhibit significant cracking, though the Sirius-2A fuel did have one large crack on the surface of the fuel. There was minimal hydrogen absorption in the samples, though it is unknown if the absorption occurred during irradiation or during fabrication. Mechanical testing indicated that the UN fuel demonstrated ceramic behavior as expected, and the Mo/W matrix demonstrated linear elastic behavior to failure.

EXPERIENCE IN THE APPLICATION OF METHODS OF RESTORATION OF DAMAGED REINFORCED CONCRETE STRUCTURES IN TRANSPORT CONSTRUCTION

Evidence suggests that concrete self-healing can be achieved by introducing bacteria into the concrete matrix. Despite the fact that a number of researchers have conducted experiments with different types of bacteria, the ideal combination of factors such as bacterial species, types of mineral substrate, types of carrier materials and the amount of each of these components has yet to be identified to make a qualitative breakthrough in solving the problem of self-healing concrete and reinforced concrete structures. The paper presents the results of a study on the development of a technology for obtaining materials with bio-additives, the study of the process of crack repair in concrete, and the establishment of physical and technical properties of concrete modified with a microbiological additive and restored materials. The article analyses the processes of structure formation, physical and mechanical properties of concrete and other cement composites, ways to improve them, degradation processes, damage and defects that reduce the durability of reinforced concrete structures, as well as methods of their repair and restoration. Based on the analysis of existing approaches to the creation of concrete using biotechnology and self-healing processes of defective reinforced concrete structures, theoretical prerequisites for the development of technology for the creation of concrete modified with microbiological additives and self-healing structures are developed. It is concluded that it is potentially possible to heal cracks in concrete under the control of bacteria as a result of mineral sludge formation. However, some areas of this concept require further development. It is necessary to clarify how effectively the deposition of minerals produced by bacteria seals large cracks, i.e. how much the permeability of cracked concrete is reduced to prevent corrosion of embedded reinforcement and thus increase the service life of the building material. In addition, it is necessary to select bacterial species that remain viable when introduced into the concrete matrix for at least the expected service life of the structure. Despite the fact that no qualitative breakthrough has yet been achieved in the field of concrete self-healing, this is a very promising area of research.