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In response to the frequent occurrence of coal face spalling affecting the working face production during the mining of extra-thick hard coal seams, this study investigates the characteristics of typical hard coal face damage. Coal face spalling is categorized into three stages: dynamic load influence, crack propagation, and bending instability phase. Employing the Rayleigh-Ritz method and the principle of stationary potential energy in conjunction with beam plate strength theory and maximum tensile stress strength theory, a displacement formula for coal face spalling has been developed. The formula has been validated using numerical simulation software. Additionally, a three-dimensional similitude modeling experimental platform was utilized to explore the development and failure patterns of spalling. Experimental results confirm the consistency between the theoretical derivation and the observed trajectories and locations of coal face spalling movement. The findings provide a theoretical foundation and technical reference for the management and prevention of spalling in extra-thick hard coal seam faces.

This study aims to simulate the process of rockburst and spalling failure of roadway surrounding rock under three-dimensional stress in deep rock engineering. Utilizing an independently developed true triaxial rockburst experimental setup, the failure process of a circular tunnel under initial in-situ stress at a depth of 500 m was investigated using red sandstone with prefabricated holes. A miniature camera device and acoustic emission (AE) monitoring system were used to monitor and record the experimental process in real time. Using the collected data, the process of rockburst and spalling failure of the circular tunnel was reproduced. Finally, the difference between rockburst and spalling failure was analyzed and compared based on four aspects of stress characteristics, acoustic emission characteristics, fragment characteristics, and V-shaped notch morphology characteristics. The experimental results show that the failure of surrounding rock was more likely to occur under dynamic disturbance load, resulting in particle ejection. The spalling failure was found to be a slow and gradual static failure process. The mechanism of rockburst was more complex involving tension-shear coupling failure, whereas, the mechanism of spalling failure was simple involving a tensile failure. Compared with spalling failure, rockburst was more intense, producing more debris, and the V-shaped notch was narrow and deep.HighlightsFailure process of rockburst and spalling is reproduced in a laboratory.The stress characteristics of rockburst and spalling failure are calculated based on elastic theory.Frequency-amplitude characteristics and crack types based on acoustic emission are analyzed.The failure intensity of rockburst and spalling is investigated based on the rock fragments and morphology of V-shaped notch.The failure process of rockburst and spalling is discussed along with strain energy.

In response to the issue of linear cutting of PMMA materials, this study conducted finite element simulations to model and calculate the linear cutting of PMMA targets using shaped charge liners made of copper and lead. Corresponding linear cutting experiments on PMMA targets were also carried out to investigate the influence of shaped charge liner materials on the linear cutting of PMMA. The research results indicate that the fracture of PMMA targets under the action of linear cutting with the cutting cord is mainly caused by jet penetration and spalling. The copper liner cutting cord exhibits superior jet penetration capability, approximately 28% higher than that of the lead liner under 0 mm standoff conditions. Additionally, after the action of the copper liner cutting cord, copper wire residues are produced, whereas no residue issue is observed with the lead liner cutting cord.

Viscoelastic elements of Kelvin-Feugt type are supposed to be used for modelling dynamic influences from the transport side and dynamic behaviour of separate elements and the whole structure as a whole. Periodic monitoring of bridge crossings using the considered approaches will make it possible to detect the presence of defects in the span itself, associated with the formation of cracks, spalling, because in the presence of such defects the estimated frequencies change.

The D-shaped cross section is a commonly used tunnel cross section in underground engineering. To simulate the failure process of a D-shaped hole under deep three-dimensional (3D) high-stress conditions, true-triaxial tests were conducted on cubic granite specimens with a through D-shaped hole, and the failure process of the hole sidewall was recorded in real time. Results show that the spalling failure process of the D-shaped hole sidewall can be divided into four periods: calm, fine particle ejection, crack generation and propagation, and rock slab gradually buckling and spalling. Afterwards, symmetrical V-shaped notches were formed on both sidewalls between the corner and arch springing. The spalling failure shows tensile failure characteristics. Under high vertical stress and constant horizontal axial stress, increasing the lateral stress reduces the severity of the spalling failure and the depth of the V-shaped notch. The initial failure vertical stress of the D-shaped hole sidewall is higher than that of circular hole sidewall, and the failure of D-shaped hole sidewall is mainly characterized by static failure. The failure of the circular hole sidewall is a more severe dynamic failure. When the vertical applied stress is the maximum principal stress, the position of the V-shaped notch tip is 0.20–0.25 h (h is the height of the D-shaped tunnel) from the tunnel floor, whereas that in the circular tunnel is 0.5 d (d is the diameter of the circular tunnel) from the tunnel floor. Specific support schemes should therefore be designed for tunnels with different cross sections according to the damage location, depth of failure zone, and severity of failure.

The corrosive anions (e.g., Cl − ) have been recognized as the origins to cause severe corrosion of anode during seawater electrolysis, while in experiments it is found that natural seawater (~0.41 M Cl − ) is usually more corrosive than simulated seawater (~0.5 M Cl − ). Here we elucidate that besides Cl − , Br − in seawater is even more harmful to Ni-based anodes because of the inferior corrosion resistance and faster corrosion kinetics in bromide than in chloride. Experimental and simulated results reveal that Cl − corrodes locally to form narrow-deep pits while Br − etches extensively to generate shallow-wide pits, which can be attributed to the fast diffusion kinetics of Cl − and the lower reaction energy of Br − in the passivation layer. Additionally, for the Ni-based electrodes with catalysts (e.g., NiFe-LDH) loading on the surface, Br − causes extensive spalling of the catalyst layer, resulting in rapid performance degradation. This work clearly points out that, in addition to anti-Cl − corrosion, designing anti-Br − corrosion anodes is even more crucial for future application of seawater electrolysis. It is known that chloride anions cause severe anode corrosion during seawater electrolysis. Here we found that bromide in seawater is even more harmful to Ni-based anodes, causing the spalling of the catalyst layer and the formation of shallow-wide pits on the substrate, leading to performance degradation.

Traditional heat transfer analysis has been adopted to predict the damage in a tunnel under fire without considering the effect of concrete spalling, which leads to underestimation of the fire damage of concrete. However, accounting for the spalling effect of concrete under high temperature in an analytical heat transfer model is difficult because of the complexity of the spalling mechanism. This study aims to establish an analytical model to estimate the influence of concrete spalling on the fire-damage depth prediction. To overcome this challenge, first, a series of fire tests were conducted in a unidirectional heating system. The spalling phenomenon and spalling characteristics were observed. Based on the experimental test results, the moisture content of concrete is one of the key factors of spalling. Obvious layered spalling characteristics of concrete samples without drying could be observed under the unidirectional heat conduction system. The critical temperature of spalling is 600 °C, and the thickness of the spalling layer is 2 cm~2.5 cm. These two parameters are critical spalling conditions. Second, a multilayer model for the heat transfer analysis considering the spalling effect of tunnel lining under fire was proposed. By using Laplace transform and the series solving method for ordinary differential equations, the time-dependent temperature and stress fields of concrete lining during tunnel fire could be obtained, which are the basis of damage evolution. The analytical results agreed with the experimental data. The spalling depth of tunnel lining related to the temperature rise of tunnel fire could be predicted by using the proposed analytical model. The results of this research can be used to provide a better damage evaluation of tunnel lining under fire.

Spalling alters a gear’s time-varying meshing stiffness (TVMS), thereby affecting its vibration characteristics. However, most studies focus on single-spalling gears and overlook the possibility of multi-spalling gears. Additionally, because most spalls are irregular, traditional analytical models neglect the torsional effects that are caused by asymmetric spalling. In this study, a shape-independent model for calculating the TVMS of multi-spalling gears, which considers torsional stiffness, was developed. A 16-degree-of-freedom dynamic model was established to analyze the dynamic response, incorporating the multi-spalling TVMS. The model was then validated through experiments. The results show that the proposed method accurately calculates the TVMS of a multi-spalling spur-gear system. Changes in the relative position of the spalling can significantly affect the TVMS. Multiple-tooth spalling influences the TVMS over several meshing cycles, while single-tooth multiple spalling affects the TVMS based on the specific spalling parameters. Different spalling patterns lead to substantial differences in the system’s dynamic behavior. Multiple spalling teeth generate several pulses, whereas a single tooth with multiple spalls only generates one significant pulse. This study provides a solid foundation for understanding the dynamic behavior of spalled gear systems, revealing their dynamic characteristics and failure mechanisms.

The thermal erosion behavior of two-kind Cr coating on PCrNi3MoVA steel under 350 MPa erosive pressure is compared. Microscopic observations and elemental analyses of the two-kind Cr coatings are carried out by scanning electron microscopy (SEM) and energy dispersion spectrometer (EDS), which led to their exfoliation mechanism. It is found the spalling mechanism of the two-kind Cr coatings after thermal erosion is different: the spalling of the electroplating Cr coating is in the form of localized delamination to overall spalling over a large area, and the spalling of the multi-arc ion plating Cr coating is in the form of horizontal and vertical extended spalling. The results show that the electroplated Cr coating has weaker erosion resistance than the multi-arc ion plating Cr coating and the Cr coating by multi-arc ion plating is more suitable as a protective layer to extend the life of the gun barrel.

Spalling has been recognized as a stress-induced brittle fracture adjacent to the underground openings when tunneling or mining deeply in a hard massive rock mass. Using a database consisting of 29 spalling cases of gneissic granite during the excavation of Qirehataer tunnels, a comprehensive evaluation of rock mass spalling strength, spalling failure depth and the influence of excavation damaged zone (EDZ) and the cross-section shapes is performed and presented. Relationships between the spalling failure depth and the rock mass damage index for D-shape and Horse-shoe shape cross-sections of non-circular tunnels with and without consideration of EDZ are analyzed and discussed. The study found that EDZ has a significant influence on the maximum tangential stress adjacent to the boundary of tunnels that the EDZ has a trend to result in a deeper failure depth than not taking the EDZ into account. The influence degree of EDZ on spalling failure depth could be 1.85 and 2.18 times higher than that without considering EDZ, for the D-shape and Horse-shoe shape tunnels, respectively. Through comparisons with the analysis based on in-situ geophysical testing data, it is found Martin and Christiansson’s method may have a trend to overestimate the spalling failure depth, the overestimation ratio of influence degree may be up to 1.35, and the overestimation becomes more significant with the increase of the rock mass damage index. Based on the analysis and comparisons with different shapes of tunnel cross-sections, it is also found that the D-shape geometry of tunnels has the advantage of avoiding spalling failure over than Horseshoe-shape in the hard and brittle rock mass.