Steady Stage Research Articles

Role of dislocation behavior during aging in high-temperature microstructural evolution and creep property of single crystal superalloys

Single-crystal superalloys of turbine blades suffer unexpected performance deterioration, even when manufactured with optimal γ/γ′ phase morphology. This study successfully reproduced this abnormal decrease in high-temperature creep properties by applying optimal aging treatments to a skillfully designed model single-crystal superalloy. Microstructural evidence indicates that interfacial dislocations deposited during aging processes weaken dislocation distribution anisotropy (DDA) in the steady creep stage and place γ′-topological inversion ahead of the competition between γ′-rafting and it, leading to an increase in the minimum creep rate. Through constitutive equations and inductive research, a linear negative correlation between the minimum creep rate and DDA was established. A new concept of “phase-interface freshness” is proposed as a quantitative characterization of interfacial dislocation deposition after preparation to reflect the ability to stimulate the beneficial DDA. These results help us further understand thermal processes such as aging, coating, and welding, providing theoretical support for the design and optimization of thermal processes.

Experimental study of type-I crack propagation in rock monitored by fiber Bragg grating

The occurrence of rock mass engineering disasters can be reduced significantly by obtaining the key information in the process of rock internal fracture accumulation and evolution through advanced monitoring means and taking certain preventive measures. Through fiber Bragg grating monitoring tests of the type-I crack propagation in rock, the spectral characteristics of the fiber Bragg grating in the process of rock failure were analyzed, the bandwidth expansion was extracted to characterize the local tensile strain during the crack propagation process, and the damage variable based on the bandwidth expansion was calculated to describe the type-I crack propagation process. The research results showed the following: (1) The fiber Bragg grating generated a non-uniform local tensile strain during type-I crack propagation. The bandwidth expansion of the wave spectrum was positively correlated with the local tensile strain. The change in the characteristics of the wave spectrum could provide the local real strain in the process of crack propagation. (2) During the steady propagation of the type-I crack, the bandwidth increased obviously, while the number of acoustic emission events was relatively small, and most of them were in the process zone. The gentle increase in the bandwidth corresponded to the unstable growth stage of the type-I crack, which could be used as a precursor of rock sample instability. During loading, the maximum tensile strain of the type-I crack was 6 %, while the maximum shear strain reached 1.8 %, primarily attributed to tensile failure. The average value of fracture toughness KIC, based on the equivalent linear elastic fracture mechanics model, was determined to be 1.21 MPa·m1/2, and the average value of fracture energy Gf was calculated as 57.7 N/m. The variation of peak reflectivity in fiber Bragg grating was associated with the closure of pre-existing defects and the propagation of microcracks in rocks, resulting in unstable shear strain at crack extension sites. (3) The damage variable D defined by the bandwidth broadening began to become concentrated and accumulated in the crack steady growth stage, and it increased slowly in the crack intensification and evolution stage. The grating was sensitive to changes when it was pasted to the surface at 90°, but it could easily fracture or become unable to capture spectral signals in time. Based on a comprehensive comparison, the monitoring effect was the best when the grating was pasted at 60° relative to the crack.

Identifying the bottleneck and its shifts for the nexus across water supply, power generation and environment systems: Hehuang, China

Identifying the bottleneck is the key to alerting and preventing unexpected failures of the nexus across water supply, power generation, and environment (WPE) systems. However, the bottleneck identification is challenged by the unclear concept of bottleneck as well as the difficulty of simulating complex emergent behaviors. Here, we develop a generic framework for identifying the bottleneck for the WPE nexus, which is defined as the subsystem that has the highest risk of leading to the failure of WPE nexus. First, the evolution of uncertainties of the state variables of WPE nexus is simulated by a generic stochastic dynamical system. Next, the propagation matrix, accumulation ratio (AR), and risk contribution ratio are defined as effective metrics and tools to identify the system bottleneck. Finally, the effects of human decisions and input stochasticity on the shifts of bottleneck are analyzed using sensitivity and scenario analysis. The WPE system in Hehuang Region, China, is selected as a case study. Results indicate that: (a) The effects of human decisions on ARs can be superimposed, suggesting a “superimposition method” for policy-making of Hehuang Region; (b) The subsystems can be classified as “endogenous” or “exogenous”, depending on the sources of accumulated uncertainties that are from local inputs, or inputs from the other subsystems; (c) There exist multiple bottlenecks at the same time that could shift from one subsystem to another, which complicates the prevention of the failures of WPE nexus. For the Hehuang Region, water and energy subsystems are more likely to be bottlenecks at the beginning stage, while society and environment subsystems are more likely to be bottlenecks at the steady stage. This study provides the first attempt to identify the bottleneck within the WPE nexus, which helps to provide realistic insights for preventing unexpected failures.

Evolution of Lubrication Characteristics of Double-Nut Ball Screws Based on an Efficient Surface Roughness Modeling Method

Abstract Accurate prediction of lubrication characteristics, specifically film thickness and pressure distribution, is pivotal for ensuring optimal performance in ball screws. Despite its significance, there is a notable dearth of studies investigating the evolution of lubrication characteristics resulting from the changing surface roughness over prolonged operation of ball screws. Furthermore, obtaining the surface roughness of ball screws poses a challenge due to the limited loading capacity of measurement instruments. Traditional methods involving cutting the screw for surface roughness measurement are impractical for continuous monitoring during extended operation. To address this issue, the present study introduces an efficient approach to model the surface roughness of the raceway in double-nut ball screws. A profilometer is employed to measure profile roughness along two directions (parallel and perpendicular to the rolling direction) without the need to cut the screw raceway. The 2D power spectral densities and height probability densities of profile roughness are calculated to model the surface roughness, and the synthesized data are utilized to solve the Reynolds equation. The simulation method is validated through friction torque tests, demonstrating a calculation accuracy exceeding 92%. The study further explores the evolution of film thickness and pressure distribution in double-nut ball screws during running-in and steady wear stages, revealing severe asperity contact in the two nuts. Additionally, variations in load ratio, friction coefficient, and film thickness ratio (λ) are investigated. Considering the load ratio and λ of the slave nut, it can be inferred that boundary lubrication persists in the two nuts throughout the operation.

Magma fizz: Tremor during the Kīlauea summit reservoir decompression

Typical eruptions at Kīlauea volcano involve the evacuation of magma from the summit and/or south caldera reservoirs towards the East or Southwest rift zones. The reservoir drainage provokes the summit deflation, and on extreme occasions, such as in 2018, the summit caldera collapse. Systematically, seismic tremor, often with a particular multichromatic spectral signature characterized by frequency gliding, accompanies summit deflation episodes. In 2018, this type of continuous tremor accompanied the steady subsidence stage, whereas discrete earthquakes dominated the collapse stage. In this work, we aim to understand the source mechanism of the syn-deflation tremor of 2018. To locate the seismic source, we develop a novel machine-learning-based algorithm as an alternative to the amplitude source location technique. We use a large high-resolution catalog to resolve a composite amplitude decay function. Under these conditions, our method outperforms the traditional technique. We locate the tremor source 1 km below the eastern perimeter of the Halema‘uma‘u crater, which coincides with the position of the summit magma reservoir, as determined in many other studies. Furthermore, we model the seismic source as pressure oscillations driven by gas porous flow at the roof of the reservoir. In this model, gas accumulates temporarily in many gas pockets between the magma and the roof. Our modeling shows that the gas flux is responsible for the tremor amplitude modulations, whereas the gas pocket thickness controls the frequency variations. Beyond a critical point of depressurization, the magma cannot contribute further to the tremor oscillations via decompression-driven degassing, nor support the roof above it, resulting in rock failure. This work advances our understanding of magma-degassing dynamics and tremor generation at Kilauea volcano, and provides novel seismological techniques for volcano seismology monitoring and research.

Influence of dysprosium addition on corrosion behavior of NdFeB magnets

PurposeThis paper aims to investigate the corrosion kinetics and corrosion behavior of NdFeB magnets with the addition of heavy rare earth dysprosium (Dy) for its inhibitory activity on poor corrosion resistance of NdFeB magnets.Design/methodology/approachTo study the effect of dysprosium addition on corrosion behavior of NdFeB magnets and investigate its mechanism, potentiodynamic polarization, scanning electron microscopy (SEM), electrochemical impedance, energy dispersion spectrum (EDS) and scanning Kelvin probe force microscopy (SKPFM) were applied in the research. Besides, microstructures were observed by SEM equipped with EDS. Atomic force microscopy was introduced to analyze the morphology, potential image as well as the contact potential difference. The SKPFM mapping scan was applied to obtain the contact potential around Nd-rich phase at 0.1 Hz. The magnets were detected via X-ray diffraction.FindingsSubstitution of Nd with Dy led to improvement of corrosion resistance and reduced the potential difference between matrix and Nd-rich phase. Corrosion resistance is Nd-rich phase < the void < metal matrix; maximum potential difference between matrix and Nd-rich phase of Dy = 0, Dy = 3 and Dy = 6 Wt.% is 411.3, 279.4 and 255.8 mV, respectively. The corrosion rate of NdFeB magnet with 6 Wt.% Dy is about 67% of that without Dy at steady corrosion stage. The addition of Dy markedly enhanced the corrosion resistance of NdFeB magnets.Originality/valueThis research innovatively investigates the effect of adding heavy rare earth Dy to NdFeB permanent magnets on magnetic properties, as well as their effects on microstructure, phase structure and most importantly on corrosion resistance. Most scholars are studying the effect of element addition on magnetic properties but not on corrosion resistance. This paper creatively fills this research gap. NdFeB magnets are applied in smart cars, robotics, AI intelligence, etc. The in-depth research on corrosion resistance by adding heavy rare earths has made significant and outstanding contributions to promoting the rapid development of the rare earth industry.

A dual-stage wear rate model based on wear mechanisms analysis during cutting Inconel 718 with TiAlN coated tools

Inconel 718 is recognized as the difficult-to-cut material. TiAlN coated tool is frequently applied in machining of such material, due to its excellent hot hardness and oxidation resistance. However, research on the wear rate model during the cutting of Inconel 718 with TiAlN coated tools is limited. Therefore, this paper proposes a novel dual-stage wear rate model to predict wear of TiAlN coated tools when cutting Inconel 718 using finite element (FE) simulation. The dual-stage model integrates impacts from adhesive wear, diffusion wear and abrasive wear, and includes two wear rate models for the initial wear stage and steady wear stage, respectively. Subsequently, an in-depth analysis of tool wear mechanisms is conducted through Energy Dispersive Spectrometer (EDS) and Scanning Electron Microscope (SEM) techniques. The analysis results reveal that the adhesive wear dominates in the initial wear stage, while the steady wear stage witnesses the concurrent involvement of abrasive wear, diffusion wear and adhesive wear. Moreover, extensive cutting experiments validate that the model can predict wear of the TiAlN coated tools with an error margin of less than 8.5 %.

Development and manufacturing of beryllium-armoring ITER enhanced heat flux FW toward series production in China

ITER’s enhanced heat flux (EHF) first wall (FW) provides thermal shielding to the other components behind it and limits its plasma boundary, consequently bearing high surface heat loads up to 4.7 MW m−2. China developed the EHF FW technologies in steady stages by making small mock-ups, semi-prototypes and a full-scale prototype (FSP), working toward series production at the Southwestern Institute of Physics. All the key technologies for bimetallic diffusion bonding, welding and assembly have been fully qualified. The Be armor tile size effects on thermal-fatigue performance have been evaluated using a pulsed high heat flux test with an EMS-400 electron beam facility. It was found that both the Be/CuCrZr bonding and its thermal-fatigue life are highly dependent on the tile size, and 12 × 12 mm2 Be tiles are acceptable for the required performance, either as individual tiles or in castellation by cutting larger ones. Small-scale mock-ups with such Be tiles survived 16 000 thermal cycles at 4.7 MW m−2, while EHF FW fingers with 16 × 16 mm2 Be tiles demonstrated unstable performance. In contrast, only BE tiles larger than 24 × 12 mm2 showed reliable diffusion bonding with the CuCrZr heat sink by hot isostatic pressing and consequently should be castellated into smaller ones. The manufacturing of the FSP finger goes through complex thermal cycles, using CuCrZr alloys in age-strengthening plus cold-rolling states, enabling it to maintain its tensile strength to the level of 285 MPa and its mean grain size less than 100 µm. The pipe welding for finger pairing and its assembly with the central beam are demonstrated, including enabling welding to be carried out twice for repair in a narrow space. The FSP showed good finger alignment, dimensional control and reliable vacuum tightness without any blockage of cooling channels.

Reducing the Energy Consumption during Microwave Drying of Coal Slime Dough by Optimizing Parameters: Experiment and Modeling.

Reducing the energy consumption in microwave drying processes is essential for the sustainable management of coal slime. Utilizing a self-constructed microwave thermogravimetric apparatus, the research investigates critical parameters, including microwave power, spherical diameter, and granule size, affecting drying kinetics and energy efficiency. The results show that it was observed that the drying process progresses through three distinct stages, marked by variations in temperature and moisture content: the initial warming phase, a steady drying stage, and a final phase where the drying rate decreases; optimal pellet sizes for efficient moisture evaporation and diffusion were identified, with smaller particles enhancing heat transfer and drying efficiency; and the Nadhari model was determined to best represent the drying kinetics of coal slime under microwave radiation. The findings indicate a positive correlation between drying efficiency and particle size while being inversely related to increased microwave power for smaller granules. A direct positive relationship between moisture migration and increased power levels was established, while an inverse relationship with the enlargement of particle sizes was observed, negatively affecting the efficiency. For granule sizes of 30, 40, and 50 mm, a decrease in activation power was recorded, with values of 8.215 ± 2.301, 7.936 ± 1.547, and 3.393 ± 0.248 W·g-1, respectively; and through the comparative analysis of energy consumption, it was demonstrated that for coal slurry particles sized 0.15-0.18 mm subjected to a drying duration of 600 s, an increase in power leads to a reduction in drying efficiency, whereas larger diameter contributes to improved efficiency.

Fault Characterization for AC/DC Distribution Networks Considering the Control Strategy of Photovoltaic and Energy Storage Battery

In order to cope with the failure of existing fault analysis schemes for AC/DC distribution networks with a high proportion of distributed generations, this paper proposes a fault characteristic analysis method for AC/DC distribution networks that considers the influence of distributed generation control strategies. Firstly, a transient model for the AC/DC distribution network connected to distributed generations is built. Then, the fault characteristics of the AC/DC distribution network in different stages, such as the capacitor discharge stage, inductive renewal stage, and steady state stage, is analyzed. Finally, detailed simulation analysis is conducted using PSCAD/EMTDC to validate the effectiveness of the developed scheme by the superior approximation performance between simulated curves and calculated curves.

Fatigue crack propagation life analysis of propeller

Fatigue crack fracture is a common failure mode in structures. For the propeller with initial crack, the hydrodynamic effect cannot be ignored when studying the fatigue crack propagation behavior. Taking the full-size KP505 propeller as the research object, its hydrodynamic performance is simulated and verified. By using the fluid-structure interaction (FSI), the pressure distribution and stress distribution of propeller under different working conditions are analyzed comprehensively, and the position of propeller hot spot stress is obtained. According to the principal stress and its direction of the hot spot stress, the location and orientation of possible macroscopic crack initiation are determined. By using the linear elastic fracture mechanics and finite element method (FEM), the propeller fatigue crack propagation law and life are calculated. The analysis results show that the Forman-Newman-de Koning (FNK) model predicts more complete fatigue crack propagation life than Paris model. The fatigue crack propagation of propeller has two stages, steady propagation stage, and accelerated propagation stage. The crack breaking blade thickness is the dividing point between the two stages. In addition, the effects of the advance coefficient, stress ratio, and initial crack size on the computed results are also analyzed, which provide reference for ship driving and propeller maintenance.

Segregation flow behavior of polydisperse particle mixture with skewed distribution in a rotating drum

Industrial particle mixtures are naturally polydisperse due to the variations in size distribution during mineral processing, which makes it necessary to investigate segregation behaviors of polydisperse particle mixtures. In this work, five groups of polydisperse particle mixtures were defined separately by different skewed distributions. Based on discrete element method, the polydisperse particle segregation behaviors of in rotary drums were simulated. The results indicate that in the polydisperse particle system with normal distribution, larger particles tend to accumulate towards the both sides, while smaller particles tend to be in the middle of the drum. In this case, the medium-sized particles are uniformly distributed throughout the system. However, once the polydisperse particle mixture transitions from the coarse particle to the fine particle system, the size of medium particles exhibiting uniform distribution characteristics decreases with an increase in the skewness coefficient. Moreover, the smaller the skewness coefficient of the polydisperse particles, the slower the initial particle segregation rate, and the lower the steady particle segregation degree. Furthermore, whether the drum length to diameter (L / D) ratio or drum filling rate increases, the particle segregation rate in initial stage and the particle segregation degree in steady stage are subsequently significantly reduced, while the size of medium particles with uniform distribution characteristics remains essentially constant.

Construction of meta-dynamic recrystallization dynamic model of 316L stainless steel based on grain orientation spread during continuous variable rate thermal deformation

Because the deformation parameters (temperature, strain rate) in the actual manufacturing process are non-constant. We investigate meta-dynamic recrystallization behavior under the transient mutation state. First, based on a single-pass thermal deformation experiment and electron backscatter diffraction (EBSD) technique, this study establishes a quantitative calculation method for the volume fraction of meta-dynamic recrystallization under different deformation conditions, and find the GOS threshold basis for judging the occurrence of meta-dynamic recrystallization. Comparing the experimental results with the numerical simulation results, it is found that the MDRX behavior of the material could be accurately described. The meta-dynamic recrystallization evolution law of the material in the thermal deformation insulation stage under the variable strain rate state is investigated by continuous variable rate thermal deformation experiment and numerical simulation. It is observed that an increase of the average strain rate in the continuous variable strain rate state would promote the meta-dynamic recrystallization softening behavior of the material in comparison with the steady state deformation stage, and vice versa.

Bibliometric and visual analyses of advancements in chronic kidney disease management.

Chronic kidney disease (CKD) is characterized by high incidence, prolonged course, significant health damage, and a heavy societal burden. Understanding the history and content of CKD research is crucial to further its recognition and management, in addition to reducing its individual and societal burdens. This study aimed to assess the management history of CKD to provide a foundation for clinical medical staff to systematically understand its evolution. The Web of Science Core Collection database was screened for CKD management studies published between January 1, 1948, and December 31, 2021. From the search results, we performed statistical descriptions of the publication date, volume, and type. Using VOS-viewer 1.6.19, variables from the included articles were obtained for keyword co-occurrence clustering and sequence analyses to determine research themes, segment phases based on publication volumes over varied timeframes, assess the dynamic progression of CKD management, and anticipate future research trends. In total, 26,133 articles met the inclusion criteria. The analysis revealed 3 stages of CKD management research: the slow development stage (1948-1998), which was initiated by epidemiological studies without ideal clustering; the steady growth stage (1999-2010), which was focused on CKD complication management and quality-of-life research; and the rapid development stage (2011-2022), which was dominated by 7 major clusters, mainly regarding the treatment and management of severe conditions and management patterns. The CKD research journey is comprised of 3 stages, the contents of which form an interconnected research model. Future research should focus on the establishment of management models and the application of intelligent management tools. Furthermore, this work can serve as a reference for the further expansion of research in this field and in improving its management.

Towards antifragility of cloud systems: An adaptive chaos driven framework

ContextUnlike resilience, antifragility describes systems that get stronger rather than weaker under stress and chaos. Antifragile systems have the capacity to overcome stressors and come out stronger, whereas resilient systems are focused on their capacity to return to their previous state following a failure. As technology environments become increasingly complex, there is a great need for developing software systems that can benefit from failures while continuously improving. Most applications nowadays operate in cloud environments. Thus, with this increasing adoption of Cloud-Native Systems they require antifragility due to their distributed nature. ObjectiveThe paper proposes UNFRAGILE framework, which facilitates the transformation of existing systems into antifragile systems. The framework employs chaos engineering to introduce failures incrementally and assess the system's response under such perturbation and improves the quality of system response by removing fragilities and introducing adaptive fault tolerance strategies. MethodThe UNFRAGILE framework's feasibility has been validated by applying it to a cloud-native using a real-world architecture to enhance its antifragility towards long outbound service latencies. The empirical investigation of fragility is undertaken, and the results show how chaos affects application performance metrics and causes disturbances in them. To deal with chaotic network latency, an adaptation phase is put into effect. ResultsThe findings indicate that the steady stage's behaviour is like the antifragile stage's behaviour. This suggests that the system could self-stabilise during the chaos without the need to define a static configuration after determining from the context of the environment that the dependent system was experiencing difficulties. ConclusionOverall, this paper contributes to ongoing efforts to develop antifragile software capable of adapting to the rapidly changing complex environment. Overall, the research provides an operational framework for engineering software systems that learn and improve through exposure to failures rather than just surviving them.

A faulty feeder selection method for SLG faults based on active injection approach in non-effectively grounded DC distribution networks

Identifying single-line-to-ground faults in non-effectively grounded DC distribution networks is challenging because the fault current is fleeting in the transient stage and negligible in the fault steady stage. First, an active signal injection method is proposed to inject signals into the DC network after the fault occurs. And the fault characteristics of the zero-mode fault circuit including the injected signal are analyzed. Second, a zero-mode parameter identification algorithm is proposed to calculate the length of each feeder based on the injected signal in the fault steady stage. It is found that the calculated length of the healthy feeder corresponds to its actual length, but the calculated result of the faulty feeder is the opposite of the total length of all healthy feeders. Finally, a faulty feeder selection method based on the polarity of the calculated length is proposed. The simulation results shown that the method can select faulty feeders under conditions of up to 5000 Ω transient resistance and 20 dB noise.

Liquid plug characteristics and heat transfer performance of a silicon-based ultra-thin flat heat pipe at different incline angles

Silicon-based ultra-thin flat heat pipes (UFHPs) that can be integrated with semiconductor devices provide an opportunity for electronic thermal management. To meet the requirements of various operation states, the impacts of gravity on the liquid plug characteristics and heat transfer performance of an UFHP are investigated by a visualization experiment conducted at different incline angles. Condensate flows back through microgrooves under the capillary pressure and gravity under a low heating power (capillary flow stage), and then excess condensate flows back along the edges of the UFHP under a higher heating power (gravitational flow stage). Over a certain heating power (Q ≥ 14 W), liquid plug fluctuations caused by vapor entrainment are observed with periodic dry-out at the evaporator under large incline angles (α ≥ 60°), corresponding to temperature fluctuations. Intense fluctuations of the liquid plug enhance sensible heat transfer, although the liquid plug occupies the condenser area and impedes the vapor flow. Meanwhile, evaporation at the evaporator benefits from corner-film evaporation until a large area of dry-out occurs. Due to the increased gravity and buoyancy, a larger incline angle is conducive to thermal performance enhancement, but this effect becomes restricted as the heating power rises. At a cooling-water temperature of 20 ℃ and an incline angle of 90°, the lowest thermal resistances of the UFHP yield a value of 1.14 ℃/W at 4 W in the steady stage and a value of 1.22 ℃/W at 18 W in the fluctuation stage, respectively. The heat transfer limit of UFHP with overfilling reaches 24 W, compared with the theoretical heat transfer capacity of 8.9 W at an incline angle of 90°. Additionally, a higher cooling-water temperature is beneficial for the thermal performance in the capillary flow stage, but not in the gravitational flow stage and fluctuation stage. This study provides guidance for the operational design of silicon-based UFHP for electronic thermal management.

Influence of external wind on fire characteristics and smoke dynamics in a stairwell adjacent to a room

A range of fire experiments were conducted to explore fire characteristics and smoke dynamics in a 1/6-scale stairwell adjacent to a room at different external wind velocities. The results indicated that the flame volume during the initial stage and the time taken for combustion to enter the steady stage both decrease with the increasing wind velocity. There are two opposite effects of the external wind on the fire combustion in a burning room adjacent to a stairwell. The inhibition effect plays an important role at lower wind velocities, leading to a decrease in the mass loss rate (MLR) of the pool fire. Conversely, the promotion effect dominates at higher wind velocities, resulting in an increase in the MLR. Stack effect and external wind demonstrate a synergistic relationship during experiments, and a correlation of the airflow velocity, wind velocity and heat release rate (HRR) is established. There are intersections in temperature curves at different wind velocities due to the smaller temperature decay rate in the stairwell and the lower smoke temperature near the pool fire at a higher velocity. Furthermore, a prediction model is also proposed for the smoke temperature distribution inside the stairwell, taking into account the wind velocity and HRR.

Experimental study on the deformation and failure mode of surrounding rocks of a tunnel in a jointed rock mass

The existence of jointed rock masses in tunnels is a key problem that leads to the deformation and instability of the surrounding rock. Based on the engineering background of the Qingdao Metro, a physical model and a numerical model are constructed to analyze the mechanism of deformation and instability of the surrounding rock of a jointed tunnel using model blocks that conform to the characteristics of joint distribution. The results show that during the whole test process, the cracks between the blocks in the tunnel arch are in the “development − stability − closure − penetration” state. Finally, the block falls in the left area of the tunnel, and the corresponding anchor axial force transits from the linear growth stage to the steady growth stage. After the axial force of the rock bolt suddenly decreases in the loading stage, the bolt enters the stability stage, and finally, S-shaped failure occurs when the surrounding rock is unstable. Under the action of a prestressed rock bolt, the normal stress and radial stress of the rock mass increase, and the difference between the major and minor principal stresses decreases significantly. The radial stress on the surrounding rock surface of the arch is approximately 8 % greater than that in the traditional rock bolt scheme, which improves the strength reserve of the rock mass. In the field test, the prestressed rock bolt can control the deformation of the surrounding rock in the arch within 2 ∼ 5 mm, which provides a reference for the control of the surrounding rock in jointed tunnels.

Simulation of fretting wear in steel wires under variable coefficient of friction and variable wear coefficient

In this paper, the fretting wear behaviour of steel wires working in coal mining technology is studied numerically. In past studies, the fretting process of steel wires was carried out numerically considering that the coefficient of friction (COF) and wear coefficient (WC) are constant parameters. However, it has been noticed experimentally that COF increases up to a certain number of fretting cycles and then becomes constant, i.e. a steady-state stage, depending on the loading conditions. This increase in COF during the fretting process is also known as the running-up stage. The fretting wear model is modified to evaluate the influence of the varying coefficient of friction (VCOF), which is associated with the variable wear coefficient (VWC), so the influence of VWC is also considered. The subroutine UMESHMOTION used to implement the wear law is also modified to study the effect of VCOF and VWC. Therefore, in this study, the numerical results of a three-dimensional finite element (FE) model are compared, with analytical results of contact area and contact stresses, and with experimental results of peak wear depth. After validating the FE model, the wear scar, the increasing wear depth, wear volume, and the decreasing contact stress with increasing fretting cycles are determined numerically considering VCOF and VWC using cycle jump approach. The energy dissipation effect of frictional force and fretting amplitude is also studied for varying interaction properties of fretting wear models. The numerical simulations are performed by considering both elastic and plastic material properties to analyse the influence of varying interaction properties on fretting wear models at the running-up stage. The results indicate that the VWC model exhibits comparable impacts on both the elastic and plastic models. The results also show that the VWC fretting wear model leads to higher wear scar, wear volume, and wear depth values at the running-up stage as well as at the steady state stage, which are close to the experimental data.