Internal Stress Research Articles

Safety Control Technology and Monitoring Analysis for Shield-Tunnel-Stacked Underpass High-Speed Rail Bridge Excavation

In order to ensure the safety of the Beijing–Shanghai high-speed railway during the construction and operation of the shield tunnel on Line R1 of the Jinan Metro, a numerical simulation of geological disturbance during the underpass of the small-radius stacked tunnel was carried out. We analyzed the mechanism of geological deformation and the construction factors affecting settlement and found that bridge settlement far exceeded safety standards without taking safety control measures. In this regard, safety control technologies such as setting isolation pile sleeve valve pipes, controlling shield tunneling parameters, grouting control technology, and trolley support technology have been proposed. Monitoring was conducted on the uneven settlement of the bridge surface, the internal and external stresses of the pipe segments, and the soil pressure they were subjected to. The results showed that the surface settlement of the bridge after safety control measures was controlled within the safety standard range, and the stress and soil pressure changes of the pipe reinforcement were within the allowable range, further verifying the effectiveness of the safety control measures.

Maternal nitric oxide homeostasis impacts female gametophyte development under optimal and stress conditions.

In adverse environments, the number of fertilizable female gametophytes (FGs) in plants is reduced, leading to increased survival of remaining offspring. How the maternal plant perceives internal growth cues and external stress conditions to alter FG development remains largely unknown. We report that homeostasis of the stress signaling molecule nitric oxide (NO) plays a key role in controlling FG development under both optimal and stress conditions. NO homeostasis is precisely regulated by S-nitrosoglutathione reductase (GSNOR). Prior to fertilization, GSNOR protein is exclusively accumulated in sporophytic tissues and indirectly controls FG development in Arabidopsis (Arabidopsis thaliana). In GSNOR null mutants, NO species accumulated in the degenerating sporophytic nucellus and auxin efflux into the developing FG was restricted, which inhibited FG development, resulting in reduced fertility. Importantly, restoring GSNOR expression in maternal, but not gametophytic tissues, or increasing auxin efflux substrate significantly increased the proportion of normal FGs and fertility. Furthermore, GSNOR overexpression or added auxin efflux substrate increased fertility under drought and salt stress. These data indicate that NO homeostasis is critical to normal auxin transport and maternal control of FG development, which in turn determine seed yield. Understanding this aspect of fertility control could contribute to mediating yield loss under adverse conditions.

Prediction of shape distortions in thermosetting composite parts using neural network interfaced visco-elastic constitutive model

The work aims to enhance the capabilities of a Finite Element tool, specifically related to a rheological thermo-chemo-viscoelastic constitutive model. This enhancement is intended to improve the tool’s ability to predict the distortions in composite parts caused by the polymerization of the thermoset composite matrix. These distortions occur due to internal residual stress generated by the inherent anisotropic properties of the thermoset composite material, including coefficients of thermal expansion and chemical shrinkage. The research work’s improvement is tied to the precise modelling of curing behaviour, which literature acknowledges as having a significant impact on manufacturing defects. In order to accommodate the influence of curing behaviour on various process variables—specifically, different thermal loading rates—a neural network model is implemented as an alternative to a standard diffusion cure-kinetics model. The neural network model is trained using Differential Scanning Calorimetry data and is integrated with the classical visco-elastic constitutive model to more accurately predict the progression of distinct thermoset resin states. This transition between cure states is assessed using two cure state variables: the degree of cure and the glass transition temperature. The enhanced predictions of state transitions lead to accurate assessments of internal residual stresses, especially when dealing with thick components subjected to thermal fluctuations. The anisotropic properties of thermoset composites, crucial for numerical analysis, are captured at various stages of cure. Ultimately, this methodology is employed to compare process-induced defects in the case study of the Z-shaped carbon/epoxy woven part, and the defects closely align with experimental measurements.

Effect of colloidal nano silica on the freeze-thaw resistance and air void system of portland cement concrete

The present study investigates the impact of colloidal nano silica (CNS) on the freeze-thaw durability of concrete, with a particular focus on understanding the fundamental mechanism via a systematic analysis of the air void system. Experimental results suggest that the incorporation of CNS increases the total air content of the sample while reducing the average void size. This phenomenon can be attributed to the remarkable capacity of CNS to stabilize air bubbles within the concrete matrix, by a heightened viscosity and lower surface tension of the fresh concrete mixture. The increase in air void chambers facilitates the release of internal stress during freezing expansion, thereby enhancing the freeze-thaw resistance of the concrete. Additionally, the inclusion of CNS results in the formation of a denser cement matrix that improves the water impermeability of the concrete and prevents the ingress of water and other potentially corrosive substances.

Improved the mechanical properties of SiCf/SiC-GH536 joints by in-situ introducing better toughness MoNiSi phase to the brazing seam

Brazing, a crucial technology for connecting composites with metals, emerges as an effective solution to the intricate challenges posed by alternative joining methods. This investigation employs foam Ni and MoNi as intermediary layers to establish connections between silicon carbide reinforced silicon carbide composites (SiCf/SiC) and GH536 superalloy. The diverse joint structures, scrutinizing their intricate impact on the mechanical properties of the brazed joints are systematically explored in this study. Findings reveal distinctive characteristics depending on the intermediary layer: Ni foam widens the brazing seam, with a significant portion of Ni elements in the nickel foam adopting the Ni(s, s) form within the brazing seam. Meanwhile, MoNi foam as the intermediary layer prompts the in-situ formation of a substantial MoNiSi phase within the brazing seam. The alternation between the MoNiSi and FCC phases contributes to a harmonized internal stress state within the joint, resulting in an impressive strength of 106.7 MPa. This study delineates a novel technical trajectory for the practical engineering application of SiCf/SiC composites.

Measuring texture-component-dependent stress of CuZn39Pb2 by neutron diffraction

Understanding the micromechanical behavior of polycrystalline material is pivotal for regulating its mechanical performance and widening its application. Taking advantage of its non-destructive nature, the neutron diffraction technique has been widely applied to investigate the micromechanical behaviors, usually at the resolution of grains sharing the same diffraction plane. This work employs a newly developed technic of the texture-component-dependent (TCD) in-situ neutron diffraction method to obtain the full strain/stress tensor of a textured CuZnPb alloy at the resolution of individual crystallographic orientation. The variation of the internal stresses and lattice strains over the grains that share the same diffraction plane has been successfully captured by the TCD method. According to the results of in situ neutron diffraction, Copper ({-1–1–2}<-1–11>) possesses the highest lattice stress while Cube ({010}<100>) and Goss ({110}<001>) bear the lowest stress of 370 MPa. In parallel, the micromechanical response of the texture components is modeled by the elastic visco-plastic self-consistent (EVPSC) model. The simulated results are in reasonable agreement with the corresponding experiments in loading direction, while the lateral stress exhibits some deviation. By crystal plasticity finite element modeling, the deviation is related to the neighbor grain which affect more significantly the lateral stress than the material parameters. The full tensor of stress within the individual crystallographic orientation measured by TCD method gives more insight into the crystal plasticity modeling.

A high-performance infrared photoacoustic sensor with improved low-frequency response microphone

Infrared photoacoustic gas sensors with the advantages of good selectivity, low interference, fast response speed, good stability, high accuracy, good explosion-proof performance, high signal-to-noise ratio, and long service life, have developed rapidly in recent years. In order to solve the problem of poor low-frequency response performance of the MEMS piezoelectric thin film microphone sensor prepared with AlN and Mo thin films in infrared photoacoustic gas sensors, this article analyzes its principle and tests an improved solution. The internal stress distribution was changed through hot tempering experiments, significantly improving its structure. The article qualitatively and quantitatively analyzes the inherent mechanism of this phenomenon. The experimental results confirm that the improved scheme improves its response performance under low-frequency signals, with good stability and repeatability.

Trace Y Doping Regulated Bulk/Interfacial Reactions of P2-Layered Oxides for Ultrahigh-Rate Sodium-Ion Batteries.

P2-phase layered cathodes play a pivotal role in sodium-ion batteries due to their efficient Na+ intercalation chemistry. However, limited by crystal disintegration and interfacial instability, bulk and interfacial failure plague their electrochemical performance. To address these challenges, a structural enhancement combined with surface modification is achieved through trace Y doping. Based on a synergistic combination of experimental results and density functional theory (DFT) calculations, the introduction of partial Y ions at the Na site (2d) acts as a stabilizing pillar, mitigating the electrostatic repulsions between adjacent TMO2 slabs and thereby relieving internal structural stress. Furthermore, the presence of Y effectively optimizes the Ni 3d-O 2p hybridization, resulting in enhanced electronic conductivity and a notable rapid charging ability, with a capacity of 77.3mA h g-1 at 40C. Concurrently, the introduction of Y also induces the formation of perovskite nano-islands, which serve to minimize side reactions and modulate interfacial diffusion. As a result, the refined P2-Na0.65 Y0.025 [Ni0.33 Mn0.67 ]O2 cathode material exhibits an exceptionally low volume variation (≈1.99%), an impressive capacity retention of 83.3% even at -40°C after1500 cycles at 1C.

Friction and wear behavior of molybdenum-disulfide doped hydrogen-free diamond-like carbon films sliding against Al2O3 balls at elevated temperature

Diamond-like carbon (DLC) films quickly experience lubrication failure due to oxidation and mechanical degradation when used above 300 °C, which limits their application. Molybdenum disulfide (MoS2) doping is considered as a feasible method to improve high-temperature properties of DLC films. However, the effect of MoS2 doping on the high-temperature friction behavior of MoS2-DLC composite films and its mechanism remain unclear. Here, MoS2-DLC composite films with different contents of MoS2 were synthesized by a superimposed deposition system consisting of high-power impulse magnetron sputtering (HiPIMS) and direct current magnetron sputtering (DCMS). The MoS2 content in the films was controlled by varying the number of MoS2 pellets in the graphite-MoS2 (C–MoS2) mosaic target. The effect of MoS2 doping content on the structure and mechanical properties of MoS2-DLC films was analyzed. In addition, the friction and wear behavior and mechanism of MoS2-DLC composite films sliding against Al2O3 balls at 25–450 °C were studied. The results indicated that MoS2 was successfully incorporated into DLC matrix, and the content of Mo in the films ranged from 0 to 6.15 at. %. The as-deposited MoS2-DLC composite films exhibited a dense and featureless structure. The doping of MoS2 improved the adhesion strength and released the internal stress of MoS2-DLC composite films, but reduced the hardness and elastic modulus of the films. In particular, MoS2-DLC composite films with 3.78–6.15 at. % Mo maintained excellent anti-friction and anti-wear performances in the temperature range of 25–450 °C. Abrasive wear and fatigue wear occurred in the friction test of the films at different temperatures. However, the friction mechanism of the films varied with the temperature of friction test. At 25 °C, MoS2-DLC composite films showed excellent lubrication and anti-wear abilities due to the carbon suspension bond was passivated by H2O molecules. At 250 °C, MoS2 phase precipitated on the surface of the films, resulting in low friction. At 350 °C, MoS2-xOx solid solution was generated on the surface of the wear track to maintain lower friction and wear. Interestingly, MoS2-DLC composite films with high Mo content still achieved relatively low coefficient of friction and wear rate up to 450 °C due to the continuous availability of MoS2-xOx generated on the surface of wear track.

Mechano-responsive chameleon-gel integrated with dumbbell-shaped spiropyran cross-linker

Stimuli-responsive hydrogels are being extensively studied altering their structures and physiochemical properties in response to external changes. However, technologies to visualize the internal stress of a gel generated by swelling and deswelling are still lacking. Here, we present a dumbbell-shaped spiropyran cross-linker synthesized by top-down grafting with poly(ethylene glycol) (PEG) acrylates. The cross-linker consists of spiropyran core that exhibits optical changes in response to mechanical stress, hydrophilic 2-arm PEGs that allow the cross-linker soluble in an aqueous solution, and acrylate units at each end of PEGs that cross-links the gel. As a result, the chameleon-gels integrated with the dumbbell-shaped spiropyrans were proved to visualize the internal stress generated by swelling and deswelling in a controlled manner. Overall, this new strategy to prepare the mechano-responsive hydrogel would be actively used in sensing, imaging, and display for drug delivery, tissue engineering, and environmental engineering, etc.

Native Crystal Growth Revealed by a Joint Microscopy–Calorimetry Technique in (GeS2)0.1(Sb2S3)0.9 Thin Amorphous Films: A Critical Role of Internal Stress and Mechanical Defects

Native Crystal Growth Revealed by a Joint Microscopy–Calorimetry Technique in (GeS₂)_0.1(Sb₂S₃)_0.9 Thin Amorphous Films: A Critical Role of Internal Stress and Mechanical Defects

Topology optimization of wheel spoke under fatigue tests considering the rotation characteristics of automobile wheels

The topology structure of wheel spoke has a great impact on the safety and lightweight of automobile wheels. However, the rotation process of the wheels is difficult to be reflected in the design and optimization. In this paper, the topology optimization of wheel spoke under fatigue tests considering the rotation characteristics is studied. The bending fatigue test and radial fatigue test are first introduced and the corresponding computation models are presented to calculate the mechanical performances of the wheel hub. The relationship between the internal stress and the number of the wheel spokes is established, and the mechanical performances with different number of wheel spokes are analyzed to guide the selection to the number. Then, the rotation characteristics of the wheel hub are simplified as static loads at different directions or positions according to the configuration of the wheel spokes. A comprehensive evaluation function which includes the test and load levels is defined by the compromise programming method to simulate the stress during the rotation process. Two levels of topology optimization methods are determined. Next, a mathematical model of multi-objective topology optimization for the wheel spoke is established based on the Solid Isotropic Material with Penalization, and a new wheel hub is obtained. Finally, the mechanical performances are compared with the original wheel hub. The obtained results show that the stiffness and strength of the wheel hub are improved under two test conditions, while the weight is reduced by 2.75%.

Peculiarities Formation of Welded Joints under the External Electromagnetic Influence

Controlling the movement of liquid metal by selecting the parameters of an external electromagnetic effect makes it possible to change the conditions of dynamic equilibrium of the weld pool and, as a result, the formation of a weld. Magnetic process control has advantages over mechanical control methods, since it is carried out without contact with the welding zone. The study of processes leading to a decrease in the concentration of defects in metals, recombination of dislocations, polygonization, recrystallization, defect healing, etc., is an urgent task for technologists. The purpose of the work is to study the laws of formation of phase composition, microhardness, grain, lath, subgrain, dislocation structures of low-alloy steel welds in underwater welding and the relationship of structural parameters with the properties of strength and crack resistance of these joints. Microstructure studies were carried out by light, scanning, and transmission electron microscopy. Mathematical modelling was carried out to optimize the research efficiency. The developed computer application implements the idea of sequential calculation of quantities, where the value of the welding current and the current in the inductor is selected by the researcher. The influence of structural factors at the dislocation level on local internal stresses, which determine the deformation localization zones in the structures of the upper and lower bainites in the deposited metal, is analyzed. The conditions for obtaining high-quality welded joints in the welding of low-alloy steels, which ensure their strength and crack resistance, are established.

Effect of Additive and Current Density on Microstructures and Corrosion Behavior of a Multi-Component NiFeCoCu Alloy Prepared by Electrodeposition

High-entropy alloys (HEAs) have been attracting growing interest for decades due to their unique properties. Electrodeposition provides a low-cost and convenient route for producing classified types of HEAs, compared to other synthesis techniques, making it an attention-grabbing method. However, fabricating high-quality HEAs through electrodeposition in aqueous electrolytes remains a great challenge. In this study, the effects of additives and current densities on the compositions, surface morphologies, microstructures, and corrosion behavior of the electrodeposited NiFeCoCu alloy are studied. The results indicate that saccharin plays a key role in achieving a flat and bright surface for NiFeCoCu coatings, while also relieving the internal stress and improving anti-corrosion properties. Electrodeposition under a current density of 20–40 mA/cm2 results in a uniform and dense deposit with favorable properties. The present work provides a low-cost and feasible industrial solution for the preparation of HEA coatings, which holds great potential for innovation in the field of HEA coatings through electrodeposition.

Particle flow numerical simulation model for coal and gas outburst and its microscopic outburst mechanism description

The finite difference model and particle flow model were constructed to reproduce the process of coal and gas outburst in front of the tunnel. The reliability of the particle flow model was verified by studying the internal stress, gas pressure, and related parameters of gas and coal two-phase flow. Then the process of coal and gas outburst is described from a microscopic perspective. The results show that the particle flow numerical model of coal and gas outburst is in line with reality and can intuitively and conveniently monitor relevant parameters; The concentrated stress caused by excavation of tunnels can reach 1.2 times the in-situ stress; High stress causes the adhesion between coal particles to break down, which is the main reason for the initiation of coal and gas outbursts; The intermittent breakthrough of gas on the coal particle collection that blocks the release channel has caused pulsating characteristics of coal and gas outbursts.

Anticorrosive barrier coatings modified by core-shell rubber particles: effects on the property transients and premature crack initiation susceptibility of particle type and concentration

AbstractProtective epoxy coatings, as a result of their inherent brittleness, show insufficient resistance towards initiation and propagation of cracks, which can occur as early as during the curing process. To improve premature crack initiation resistance, it is essential to understand the underlying mechanisms. In this work, a solvent-based novolac epoxy, cured with a cycloaliphatic amine, was reinforced with either an epoxypropoxypropyl-terminated polydimethylsiloxane (PDMS), nanoparticles of strontium titanate (SrTiO3), or core-shell rubber (CSR) nanoparticles. The effects on coating property transients, curing-induced internal stress, and premature crack initiation susceptibility of the modifier types and CSR (MX 217 and MX 267) concentrations were investigated. In addition, using a digital microscope, the defect and crack morphology in coatings applied to rigid, flat substrates and inner 90-degree angles were characterized. Finally, to evaluate the anticorrosive barrier performance of the reinforced coatings, an electrochemical impedance spectroscopy analysis was employed. Despite a slightly reduced crack initiation susceptibility, the flexible PDMS chains, due to phase separation, resulted in a deteriorated barrier performance. The inclusion of SrTiO3 nanoparticles also led to a reduced anticorrosion performance, relative to a neat epoxy coating, with a slightly lower crack initiation susceptibility and a minor increase (around 0.2 MPa) in the average internal stress. For 5 wt% MX 217 and MX 267 CSR toughened coatings, the maximum internal stress and crack initiation susceptibility in the series, as well as an associated reduced corrosion resistance, were seen. In spite of a reduction in the elastic modulus, an improved barrier performance and a reduced internal stress and crack initiation susceptibility were observed for 25 wt% MX 217 and 37 wt% MX 267 CSR toughened coatings. To improve barrier properties and avoid premature crack initiation of epoxy coatings, guidelines on modifier selection are provided.

Electrodeposition of Nickel-Tungsten Alloy with Functional Concentration Periodically Graded Material Structure for Low Stress and High Hardness

A nickel-tungsten alloy film was deposited using an electrodeposition process. The tungsten concentration in the nickel-tungsten alloy was controlled by the applied current density. The surface morphology, micro-structure, internal stress, and hardness were characterized as a single-layer structure. Hardness increased as the tungsten content increased, but micro-cracks occurred on the surface. A multi-layered structure was selected to increase the hardness without micro-cracks. The multi-layered nickel-tungsten alloy film was deposited to form two types: functional periodic materials and functional graded materials. These multi-layered structures were deposited by changing the applied current density periodically and gradually, respectively, during the deposition process. The mechanical properties, such as internal stress and hardness of the nickel-tungsten alloy, were characterized as a function of the tungsten concentration of the nickel-tungsten alloy film. As the number of periods increased, the internal stress decreased, and micro-cracks were removed from the surface. However, the gradually varied nickel-tungsten alloy had higher internal stress than the periodically varied alloy. Similar hardness was observed because the concentration of nickel-tungsten film at the top of the multi-layered structure was the same. Overall, we demonstrated enhanced mechanical properties, including low internal stress and high hardness, of concentration periodically graded nickel-tungsten alloy.

Evaluating the power generation capability of devices utilizing piezoelectric materials and the resonance problem

This paper presents a sophisticated device leveraging piezoelectric materials to seamlessly convert mechanical energy into electricity. This innovation is especially pertinent in meeting the escalating power requirements of smart devices in the dynamic of Industry 4.0. Piezoelectric materials capitalize on the piezoelectric effect, manifesting electricity generation as an external force that induces polarization within the crystal lattice, leading to the accumulation of oppositely charged elements. These specialized materials are affixed to a cantilever beam, fostering consistent oscillations that facilitate a continuous charge flow and, consequently, the generation of a reliable electric current. The oscillations of the cantilever beam embody a fusion of diverse mode shapes, each characterized by distinctive natural frequencies. The resonance phenomenon comes into play when external forces synchronize with these frequencies, thereby inducing maximum stress on the material block. Simultaneously, the voltage produced in the piezoelectric material aligns proportionally with the internal stress, resulting in an augmented power output as the amplitude of external forces increases. The efficacy of the device in power generation is contingent upon two pivotal factors: the resonance frequency of external forces, determined by resonance conditions, and the maximum amplitude, regulated by durability considerations. Although the electrical output may not be voluminous, the device’s unique advantages arising from the inherent properties of the materials and the piezoelectric effect underscore its substantial potential in addressing the intricacies of practical energy challenges.

Mechanisms of Offshore Solid and Liquid Freshwater Flux from the East Greenland Current

Abstract The mechanisms that control the export of freshwater from the East Greenland Current, in both liquid and solid form, are explored using an idealized numerical model and scaling theory. A regional, coupled ocean–sea ice model is applied to a series of calculations in which key parameters are varied and the scaling theory is used to interpret the model results. The offshore ice flux, occurring in late winter, is driven primarily by internal stresses and is most sensitive to the thickness of sea ice on the shelf coming out of Fram Strait and the strength of alongshore winds over the shelf. The offshore liquid freshwater flux is achieved by eddy fluxes in late summer while there is an onshore liquid freshwater flux in winter due to the ice–ocean stress, resulting in only weak annual mean flux. The scaling theory identifies the key nondimensional parameters that control the behavior and reproduces the general parameter dependence found in the numerical model. Climate models predict that winds will increase and ice export from the Arctic will decrease in the future, both of which will lead to a decrease in the offshore flux of sea ice, while the influence on liquid freshwater may increase or decrease, depending on the relative changes in the onshore Ekman transport and offshore eddy fluxes. Additional processes that have not been considered here, such as more complex topography and synoptic wind events, may also contribute to cross-shelf exchange. Significance Statement The purpose of this study is to provide a basic understanding of what controls the flux of sea ice and low-salinity water from the East Greenland shelf into the interior of the Greenland and Iceland Seas. This is a potentially important process since it has been shown that sufficient freshening of the surface waters in the interior of the Nordic seas can inhibit deep convection and the associated air–sea heat flux and water mass transformation. A combination of idealized computer models and basic theory indicates that the fluxes of liquid and solid freshwater are controlled by different mechanisms and occur at different times of the year. Accurate representation in climate models will require representation of small-scale processes such as mesoscale eddies and gradients of ice thickness across the shelf.

Development of a dual-mode energy-resolved neutron imaging detector: High spatial resolution and large field of view

Energy-resolved neutron imaging is an effective way to investigate the internal structure and residual stress of materials. Different sample sizes have varying requirements for the detector's imaging field of view (FOV) and spatial resolution. Therefore, a dual-mode energy-resolved neutron imaging detector was developed, which mainly consisted of a neutron scintillator screen, a mirror, imaging lenses, and a time-stamping optical fast camera. This detector could operate in a large FOV mode or a high spatial resolution mode. To evaluate the performance of the detector, the neutron wavelength spectra and the multiple spatial resolution tests were conducted at CSNS. The results demonstrated that the detector accurately measured the neutron wavelength spectra selected by a bandwidth chopper. The best spatial resolution was about 20 μm in high spatial resolution mode after event reconstruction, and a FOV of 45.0 mm × 45.0 mm was obtained in large FOV mode. The feasibility was validated to change the spatial resolution and FOV by replacing the scintillator screen and adjusting the lens magnification.