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In this work, we demonstrate the feasibility of applying electric pulses to heal surface cracks on nickel-based alloy GH4169 under compressive load. There exists an incubation time for the onset of the healing of a crack, which is associated with local temperature at the crack tip. The crack size decreases with increasing the pulsing time at a constant healing rate prior to complete healing of the crack. Increasing compressive load accelerates the healing process. The electric pulsing leads to the formation of an influential zone surrounding the crack with the finest grain sizes in the healed crack and the coarsest grain sizes away from the influential zone. The indentation hardness increases with the increase the distance to the crack tip of the healed crack. A model of viscous flow in the crack channel is proposed for the crack healing. The resultant force on the crack faces due to the crack healing increases with the increase of the healing time and the decrease of the crack width.

Stratified rock masses comprise various rocks with different thicknesses, lithologies, and compositions. They exhibit unique cracking morphology and failure modes when subjected to external loads. Understanding and mastering the fracture morphology and failure laws of stratified rock masses under three-dimensional mechanical conditions is crucial for researching disasters in underground engineering geology. This paper presents a three-dimensional double-layer rock mass model established using the numerical calculation method based on mesoscopic statistical damage mechanics. The model simulates the cracking mode of the rock surface under biaxial tensile conditions. The simulation results are quantified using PCAS software. Crack indexes, such as the number of cracked blocks, average cracked block area, and surface crack rate, are used to evaluate the degree of influence of different factors on the cracking of the rock surface layer. The results indicate that the degree of surface crack development varies linearly with the degree of homogeneity (m). Additionally, the layer thickness ratio (η) is positively correlated with the average fragmentation area, and the two are logarithmic. Regardless of the model scale, the average circumference of each block is approximately equal to the model side length. The model exhibits the highest degree of crack development when the loads in the x and y directions are equal. Moreover, the degree of crack development in the model is also influenced by the loading per step, and the two are proportional. [ABSTRACT FROM AUTHOR]

In this work, a two-parameter inversion problem is analyzed, related to surface crack widths for measuring depths of normal surface notches, based on a laser-based ultrasonic measurement method in the time domain. In determining the depth measurement formulas, the main technique is the time delay between reflected and scattered waves. Scattered waves are generated by two reflections along the bottom and three mode transformations at the surface of the crack tips. Moreover, the scattering angle of the mode-conversion waves is 30°. These two key factors lead to corrected item "2wβ" in the depth measurement formula. A laser-based ultrasonic experimental platform is built to generate and receive surface waves in a non-contact manner on aluminum and steel specimens with surface cracks. The depth measurement method proposed in this paper has been validated through theoretical, simulation, and experimental methods. Finally, in this paper, an effective approach for quantitatively measuring crack depths, based on laser ultrasound, using the time-domain properties of surface wave propagation is provided. [ABSTRACT FROM AUTHOR]

Scanning electromagnetic induction thermography (SEIT) has great potential for industrial applications, such as rapid visualising of surface cracks. This dynamic non-destructive testing method has improved detection efficiency but has led to blurred or discontinuous defect boundaries at varying scanning speeds. To alleviate this problem, we explore the use of the patch-based sparse decomposition (PSD) technique. This technique improves dynamic imaging by retaining only the information associated with sparse regression and introducing a locally adaptive threshold. Besides, this method offers a potential thermal image preconditioned scheme for follow-up artificial intelligence detection. Experimental results show that PSD can correct blurred images caused by relative motion, thus improving defect detection accuracy. Moreover, it is suitable for both translational and rotational detection systems. Images reconstructed through the deblurring process demonstrate the ability to visualise holes with a radius of 0.5 mm at velocities up to 150 mm/s, while cracks with a defect width of 0.2 mm on a railroad wheel can be detected at speeds ranging from 25 mm/s to 75 mm/s. [ABSTRACT FROM AUTHOR]

One advantage of twin-roll casting for aluminum alloys is that hot rolling can be omitted, thus shortening the process. The effect of inline hot rolling on the anisotropy of the mechanical properties, especially the elongation, of the roll-cast strip has not been investigated. In a high-speed twin-roll caster, inline hot rolling forms the metal shape before the temperature of the cast strip decreases below the temperature needed for hot rolling. In this study, inline hot rolling of Al-5%Mg strips cast using an unequal diameter twin-roll caster was performed to validate the technique and evaluate its ability to reduce surface cracking and improve the elongation anisotropy. A rolling speed of 30 m/min was used, and the effects of temperature and thickness reduction during inline hot rolling on the surface and mechanical properties were investigated. Inline hot rolling was found to effectively reduce the formation of surface cracks and the anisotropy of the mechanical properties. [ABSTRACT FROM AUTHOR]

In order to investigate the effect of microstructure in the surface layer produced by shot peening on fatigue properties of a maraging steel, rotating bending fatigue tests were carried out using shot-peened specimens and electro-polished ones of a 350 grade 18% Ni maraging steel in the relative humidity of 25% and 85%. The shot-peened specimen tested had a fine-grained structure and a small amount of reversion austenite in the work affected layer. The shot-peened specimens showed a unique fatigue fracture surface with a ring-shaped fracture one along the surface layer in the wide range of fatigue lives. The formation mechanism of the unique fracture was explained from the coalescence of many surface cracks over the entire circumference initiated from dimples formed by shot peening at the specimen surface and the difference in the microstructure between the fine-grained surface layer and the matrix. Fatigue strength in the shot-peened specimen increased due to the grain refinement in addition to hardening and formation of compressive residual stress at the surface layer. The fish eye size, i.e., the internal crack length, increased and the depth of a surface crack inversely decreased with increasing in the fatigue life. The value of stress intensity factor obtained from the fish eye size increased with increasing in the fatigue life and approached to the one of the fatigue fracture toughness of the maraging steel in longer life beyond 107 cycles. This suggested that the fracture mode in the shot peened specimens was changed in the order of a fracture controlled by a propagation of the surface crack, a combined fracture due to propagation and coalescence of a surface crack and an internal one, and an internal fracture induced by an internal crack propagation with decreasing in the stress level.

The existing research results on mining damage identification are mainly focused on plain areas, and there is a lack of research on damage to surface buildings (structures) in mountainous areas under high-intensity mining conditions. The abnormal damage of buildings in Yetou Village, Shanxi Province was took as an example. Firstly, based on the small baselines subset interferometric synthetic aperture radar (SBAS-InSAR) technique, 20 Sentinel-1A radar images were used to invert the spatial distribution pattern and temporal evolution of surface deformation in the target area from November 14th, 2016 to July 12th, 2017. Then, combined with the house damage characteristics and surface crack data from the on-site survey, the research work on mining damage identification was carried out from the perspectives of mining subsidence theory and slope stability analysis. The research results indicate that: SBAS technology can effectively identify and extract abnormal surface deformation caused by mining, and can provide data support for the study of abnormal damage laws and the disclosure of causes. The reduction of slope stability caused by mining, leading to creep and sliding of the slope, is the cause of abnormal damage to surface buildings. The relevant conclusions have reference significance for the development and improvement of subsidence control theory and for conducting damage assessment work on houses in mountainous mining areas. [ABSTRACT FROM AUTHOR]

The stress intensity factor (SIF) distribution of a semi‐elliptical surface crack is often used for evaluating the fatigue strength of structures. Virtually exact distributions of SIFs FISE,FIISE,FIIISE can be provided along the crack front by solving the hypersingular integral equation of the body force method. In this paper, to create a very accurate SIF variation formula, the elliptical crack SIF solutions FIE, FIIE, FIIIE are used and the SIF ratios FISE/FIE, FIISE/FIIE, FIIISE/FIIIE are mainly focused. Paying attention to the corner point singularity, by applying the least squares method to the ratio FISE/FIE, FIISE/FIIE in the whole range of parametric angle β, FISE and FIISE formulas can be proposed. Instead, FIIISE formula can be proposed by applying the method of least squares to the ratio of FIIISE/FIIIE in the range β≥15° but applying directly to FIIISE in the range β≤15°. In this way, all of formulas proposed in this paper provide the SIFs with better than 1.0% accuracy. Highlights: Accurate SIF formulas for semi‐elliptical surface cracks were created within 1% error.Similar to solving the HIEM, closed form solutions of an elliptical crack were utilized.This formula assume the crack front intersects the free surface at an angle θS≅100.5°.Using singularity r‐0.5 along the crack front, the shape FISE(β)≈const. was investigated. [ABSTRACT FROM AUTHOR]

Lug is one of the most important lap joints in many engineering structures, especially airframes. Through‐thickness and part‐through cracks emanating from pin‐loaded lug hole are frequently encountered due to stress concentration. Stress intensity factors for various crack geometries are the prerequisite for damage tolerance design of attachment lug. In this paper, analytical 2D weight functions for through‐thickness crack in lug are derived considering the contact condition between the pin and lug. With the derived 2D weight function, a highly efficient 3D slice synthesis weight function method (SSWFM) is then developed to determine 3D SIFs of hole‐edge corner/surface crack in straight and tapered lugs under various pin loadings. The resulting 3D SIFs are verified by comparisons with the numerical FEM/Franc3D solutions and literature data. The SSWFM is about 1800 times faster than the numerical FEM/Franc3D and therefore will significantly enhance damage tolerance analysis capability for attachment lugs. Highlights: Accurate and wide‐range weight functions of pin‐loaded cracked lug are derived considering the contact constraint.A 3D weight function method for corner and surface cracks of lug is established.It is accurate and much faster than FEM for SIF calculation. [ABSTRACT FROM AUTHOR]

The stress intensity factor (SIF) is the foundation of fracture mechanics analysis. Accurate determination of SIFs is at the very heart of damage tolerance design and fatigue crack growth life prediction. The weight function method (WFM) is a powerful method for SIF‐determination involving complex load conditions. This article presents a review of the historical development over the past five decades and the current state‐of‐the‐art in three‐dimensional (3D) WFMs. The discussions are focused on the slice synthesis weight function method (SSWFM) and the point weight function method (PWFM). The powerfulness of the 3D WFMs is shown by a variety of examples with complex part‐through crack configurations under uni‐ and bi‐variant loadings. Solution accuracy is verified by comparisons of SIFs with various numerical methods. Use of the substitute geometry concept to expand the capability of 3D WFMs for solving real‐world engineering 3D crack problems is demonstrated. Some remaining challenges are briefly discussed. Highlights: This article presents a review of the historical development and the current state‐of‐the‐art in 3D WFMs.The 3D WFMs is powerful for complex part‐through crack configurations.The WFMs can solve real‐world 3D crack problems with substitute geometry concept.Some remaining challenges are briefly discussed. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Geodesy & Geodynamics (1671-5942) is the property of Editorial Board Journal of Geodesy & Geodynamics and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Pressure vessels are susceptible to flaws which may be introduced during fabrication. Hence, existing approach based on plasticity is insufficient for failure prediction for all the materials. Methodology based on fracture mechanics is required for the design. Fracture analysis of a pressure vessel structure made up of AA2219-T87 Al alloy material was carried out using R6 procedure. R6 procedure is being widely used because of its applicability in elasto-plastic regime and accuracy of Failure Assessment Diagram (FAD). Service surface cracks were chosen; for each crack size and specimen/pressure vessel thickness, FAD was obtained. A typical pressure vessel having the configuration of cylindrical shell capped with tori-spherical end domes was considered for the study. Burst pressure was found based on plasticity approach as well as fracture methodology (R6 method). Stresses at critical locations were used for estimation of assessment points. Fracture based burst pressure was found which, as expected, proved to be less than that found by plasticity approach. The result insists the additional requirement of fracture mechanics design principles for analyzing critical structures. The difference between the two approaches in the analysis carried out was quantified. [ABSTRACT FROM AUTHOR]

Surface cracks are commonly observed in coatings and films. When structures with coatings are subject to stretching, opening mode cracks are likely to form on the surface, which may further lead to other forms of damage, such as interfacial delamination and substrate damage. Possible crack forms include cracks extending towards the interface and channeling across the film. In this paper, a two-dimensional numerical model is proposed to obtain the structural strain energy at arbitrary crack lengths for bilayer structures under uniaxial tension. The energy release rate and structural stress intensity factors can be obtained accordingly, and the effects of geometry and material features on fracture characteristics are investigated, with most crack patterns being confirmed as unstable. The proposed model can also facilitate the analysis of the stress distribution in periodic crack patterns of films. The results from the numerical model are compared with those obtained by the finite element method (FEM), and the accuracy of the theoretical results is demonstrated. [ABSTRACT FROM AUTHOR]

In this work, the thermal contact problem of a rigid flat punch sliding over functionally graded material (FGM) coating with a surface crack is investigated. The surface of a homogeneous isotropic substrate is ideally coated by FGM. The coefficient of friction on the contact surface is assumed to be constant, and dry Coulomb friction law is applied. The major purpose of this study is to compute the stress intensity factors at the tip of a surface crack under thermomechanical loading. In this perspective, the thermoelastic contact and the surface crack problems are modeled using finite element method. An iterative solution procedure based on finite elements is developed to solve the contact/crack problem until generated frictional heat reach the steady‐state condition. Obtained results are compared to those available in the open literature, and a good agreement is observed. Presented results involve stress intensity factors computed under various thermoelastic sliding conditions. Highlights: A surface crack problem in an FGM coating subjected to sliding contact is examined.Frictional heat due to punch has a remarkable influence on stress intensity factors.The iterative computational method is developed to determine stress intensity factors.Frictional heat and material properties significantly affect stress intensity factors. [ABSTRACT FROM AUTHOR]

Nitinol 60 (NiTi60) is a shape memory alloy (SMA) where the atomic percentage of nickel is slightly higher than titanium. It advantages the material to have higher hardness and better sensitivity to phase transformation. One of the machining techniques that is preferred to cut hard material is electrical discharge machining (EDM). This study aims to examine the fatigue characteristics of a NiTi60 alloy that has undergone electro-discharge machining and examine the impact of machining parameters on microstructural changes. In this investigation first, the influence of EDM process parameters such as pulse current, voltage, pulse on time, and pulse off time on surface integrity aspects was investigated. Second, the impact of these process variables on fatigue strength was examined. The surface integrity parameters of EDM-machined specimens, such as microcracks, surface crack density (SCD), white layer thickness (WLT), and residual stress formation have been examined by various characterization techniques. The obtained results show that pulse current and voltage are dominating factors affecting SCD. The thickness of the white layer seems to be increased with the rise in the pulse current and pulse on time, and tensile kinds of residual stresses are present in the WLT region, whose magnitude is dependent on process parameters. The fatigue tests were performed using a servo hydraulic testing machine at a frequency of 20 Hz for 106 number of cycles. The fatigue crack initiation, propagation, and effects of process parameters have been examined. It has been found that an increase in pulse current and voltage leads to the generation of microvoids in the WLT region and thereby causes fatigue cracks to take birth. Later on, a correlation between WLT and SCD was observed by implementing an artificial neural network (ANN) model. The accuracy of ANN model prediction is reported to be high, where WLT and SCD have a 0.98 observed correlation coefficient. [ABSTRACT FROM AUTHOR]

The failure process was characterized by complex diffusion of elements in the bonding layer, TGO growth and growth stress inside the coating. We studied the aluminum migration phenomenon of NiCoCrAlY and NiCoCrAlYHf coatings under high temperature oxidation, TGO growth characteristics, the microstructure and composition of the bonding layer, and integrates them into the description of the surface strain under coating tension. The experimental results show that the TGO growth rate of NiCoCrAIYHf coating is lower than that of NiCoCrAIY coating, and the formed TGO is thinner. After high temperature oxidation, the cracking time of NiCoCrAIY coating is advanced, while the cracking time of rare earth doped coating is delayed. The addition of rare earth elements can effectively inhibit the generation of spinel phase, improve the fracture toughness of TGO, refine the grains in the bonding layer, and increase the grain boundary strengthening by 29.1 MPa which is consistent with the experimental value. Therefore, the yield strength of the doped coating is improved and the crack time of the coating is delayed. [ABSTRACT FROM AUTHOR]

In this work, a two-parameter inversion problem is analyzed, related to surface crack widths for measuring depths of normal surface notches, based on a laser-based ultrasonic measurement method in the time domain. In determining the depth measurement formulas, the main technique is the time delay between reflected and scattered waves. Scattered waves are generated by two reflections along the bottom and three mode transformations at the surface of the crack tips. Moreover, the scattering angle of the mode-conversion waves is 30°. These two key factors lead to corrected item “2wβ” in the depth measurement formula. A laser-based ultrasonic experimental platform is built to generate and receive surface waves in a non-contact manner on aluminum and steel specimens with surface cracks. The depth measurement method proposed in this paper has been validated through theoretical, simulation, and experimental methods. Finally, in this paper, an effective approach for quantitatively measuring crack depths, based on laser ultrasound, using the time-domain properties of surface wave propagation is provided.

One advantage of twin-roll casting for aluminum alloys is that hot rolling can be omitted, thus shortening the process. The effect of inline hot rolling on the anisotropy of the mechanical properties, especially the elongation, of the roll-cast strip has not been investigated. In a high-speed twin-roll caster, inline hot rolling forms the metal shape before the temperature of the cast strip decreases below the temperature needed for hot rolling. In this study, inline hot rolling of Al-5%Mg strips cast using an unequal diameter twin-roll caster was performed to validate the technique and evaluate its ability to reduce surface cracking and improve the elongation anisotropy. A rolling speed of 30 m/min was used, and the effects of temperature and thickness reduction during inline hot rolling on the surface and mechanical properties were investigated. Inline hot rolling was found to effectively reduce the formation of surface cracks and the anisotropy of the mechanical properties.

Abstract The experimental study on the variation law of coal fracture and stress was carried out in the laboratory and engineering fields, respectively. A multiparameter monitoring system including electromagnetic radiation and a high‐speed camera was built, and three stress paths, uniaxial compression, cyclic loading, and graded loading, were used to monitor the dynamic expansion process of surface cracks during uniaxial compression failure of coal specimens. Through the quantitative analysis of the electromagnetic radiation signal in the crack propagation process, it is found that the electromagnetic radiation and the stress change trend are consistent, and the electromagnetic radiation signal is ahead of the failure of coal‐generating rock mass 1–2 s. The surface crack changes after the peak value of electromagnetic radiation and presents a stepwise growth trend, crack length changes on the millisecond time scale, and the crack propagation speed is about 2000 mm/s. The surface cracks appear when the stress reaches a certain degree, and the propagation of the principal cracks is consistent with the failure of the specimen. The electromagnetic radiation value of the coal mass from static period to dynamic is analyzed by using electromagnetic radiation at the engineering site, and it was found that the electromagnetic radiation is consistent with the stress distribution of the mining face. Through normalization, the variation rule of electromagnetic radiation in laboratory and engineering sites is similar, but the peak value of electromagnetic radiation in engineering sites is more significant. Therefore, electromagnetic radiation has a good monitoring effect on the stress distribution and cracks propagation of underground coal mining working faces, which could guide the layout of underground drilling.

In seed processing for commercial production, the collision or friction between mechanical parts and seed is inevitable. These collisions or friction can cause cracks on the surface of the seed, which can affect germination rates and ultimately reduce crop yields. Using the difference of the seed motion trajectories with different crack degrees in the magnetic field, the grading of the surface crack seed can be realized. In this study, the motion law of seed in a non-uniform magnetic field was analyzed by taking the delinted cottonseed as an object. A magnetic separation device for crop seeds was developed. This device was essentially composed of the feed throat, magnetic roller, conveyor belt, and variable-frequency adjustablespeed motor. The magnetic powder adhering seeds enter the magnetic separation device through the feed throat and are conveyed to the magnetic roller through the conveyor belt. The magnetic roller has different adsorption forces on seeds with different degrees of cracking, and seeds fall into different outlets, thus completing the grading of the seeds. By adjusting working parameters such as the magnetic field strength and the speed of the conveyor belt, magnetic separation could be made. In order to verify the grading effect, the magnetic separation accuracy was taken as the inspection index, the magnetic powder's mesh number, the mass mixing ratio between magnetic powder and delinted cottonseed, and the rotation speed of the magnetic roller were taken as the inspection factors. The response surface methodology was used to optimize the working parameters of the experimental device. The results showed that the optimal process parameters of the magnetic separation device were as follows: the number of magnetic powder meshes was 250, the mass mixing ratio between magnetic powder and delinted cottonseed was 1:20, and when the rotational speed of the magnetic separation roller was 20 r/min, the detection rate reached 92.5%. The designed magnetic separation device can realize the non-destructive batch detection of seed surface cracks with high work efficiency and has guiding significance for the high-precision and low-damage classification detection and classification of commercial seed. [ABSTRACT FROM AUTHOR]

Coal seams were buried extremely shallowly in the trench slope area, which is prone to inducing surface cracks, seriously threatening the surface environment and mine safety production. The development of surface mining cracks varies at different locations in the trench slope area. In this research, we aimed to study the dynamic characteristics and laws of surface crack widths at different mining locations in the trench slope area and reveal the evolution mechanism of surface crack widths. Taking the 125,203 working face in Anshan Coal Mine in Shaanxi Province, China, as the geological prototype, we analyzed the full-cycle dynamic change law and planar distribution law of the surface crack widths in the trench slope area by combining the unmanned aerial vehicle remote sensing technology and field actual measurements and revealed the dynamic evolution mechanism of surface mining cracks in the trench area. The research results showed that the dynamic changes of surface crack widths varied at different locations of the slope. The surface crack width in the downslope area increased first and then stabilized with the advance of the working surface; the crack width at the bottom of the trench shows the dynamic change characteristic of increasing–decreasing–slightly increasing–stabilizing with the continuous advance of the working surface. The surface crack width in the upslope area showed the dynamic change of increasing–decreasing–stabilizing with the continuous advance of the working surface. Influenced by the surface morphology, the development mechanisms of surface mining cracks were different. The research results can provide practical guidance for selecting the best treatment time for surface cracks in different areas. [ABSTRACT FROM AUTHOR]

Copyright of Geology & Exploration is the property of Geology & Exploration Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

In this study, the concrete cone capacity, concrete cone angle, and load–displacement response of cast-in headed anchors in geopolymer concrete are explored using numerical analyses. The concrete damaged plasticity (CDP) model in ABAQUS is used to simulate the behavior of concrete substrates. The tensile behavior of anchors in geopolymer concrete is compared with that in normal concrete as well as that predicted by the linear fracture mechanics (LFM) and concrete capacity design (CCD) models. The results show that the capacity of the anchors in geopolymer concrete is 30%–40% lower than that in normal concrete. The results also indicate that the CCD model overestimates the capacity of the anchors in geopolymer concrete, whereas the LFM model provides a much more conservative prediction. The extent of the difference between the predictions by the numerical analysis and those of the above prediction models depends on the effective embedment depth of the anchor and the anchor head size. The influence of concrete surface cracking on the capacity of the anchor is shown to depend on the location of the crack and the effective embedment depth. The influence of the anchor head profile on the tensile capacity of the anchors is found to be insignificant. [ABSTRACT FROM AUTHOR]

Copyright of Railway Construction Technology is the property of Railway Construction Technology Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The experimental study on the variation law of coal fracture and stress was carried out in the laboratory and engineering fields, respectively. A multiparameter monitoring system including electromagnetic radiation and a high‐speed camera was built, and three stress paths, uniaxial compression, cyclic loading, and graded loading, were used to monitor the dynamic expansion process of surface cracks during uniaxial compression failure of coal specimens. Through the quantitative analysis of the electromagnetic radiation signal in the crack propagation process, it is found that the electromagnetic radiation and the stress change trend are consistent, and the electromagnetic radiation signal is ahead of the failure of coal‐generating rock mass 1–2 s. The surface crack changes after the peak value of electromagnetic radiation and presents a stepwise growth trend, crack length changes on the millisecond time scale, and the crack propagation speed is about 2000 mm/s. The surface cracks appear when the stress reaches a certain degree, and the propagation of the principal cracks is consistent with the failure of the specimen. The electromagnetic radiation value of the coal mass from static period to dynamic is analyzed by using electromagnetic radiation at the engineering site, and it was found that the electromagnetic radiation is consistent with the stress distribution of the mining face. Through normalization, the variation rule of electromagnetic radiation in laboratory and engineering sites is similar, but the peak value of electromagnetic radiation in engineering sites is more significant. Therefore, electromagnetic radiation has a good monitoring effect on the stress distribution and cracks propagation of underground coal mining working faces, which could guide the layout of underground drilling. [ABSTRACT FROM AUTHOR]

The global objective of this study was to investigate the best features of the surface topography for fatigue‐damage detection and classification. The presence of the stress concentration in valleys of the surface topography causes a grain slip and a crack initiation at the surface of the machined structure and finally leads to fatigue failures. Therefore, the surface topography has a major influence on the fatigue strength of the machined structure. An optical confocal measurement system (Alicona) was applied to measure six surface topography parameters. In this paper, feature selection using the Pearson correlation method was adopted to select the best surface textures that provide best the neural network (NN) model performance. The NN model is capable of detecting and classifying the damage with an accuracy of up to ∼ 94.4%. [ABSTRACT FROM AUTHOR]

Copyright of Engineering Mechanics / Gongcheng Lixue is the property of Engineering Mechanics Editorial Department and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

When the thin slab caster produces low-carbon steel, the uneven cooling alarm can easily occur at both sides of the nozzle in the thermal image, and there are cracks at the corresponding positions where the uneven cooling occurs. The causes of uneven cooling are studied, and the mechanism of uneven cooling causing surface cracks is proposed. The results show that the generation of uneven cooling is greatly related to the carbon content of molten steel, the thickness of the copper plate, and the hydrogen content. The surface roughness method shows that the uneven cooling index increases with the increase of carbon content. The uneven cooling index gradually increases with the decrease of the copper plate thickness. When the copper plate thickness is less than 41 mm, the uneven cooling index of the mold increases from the 1.1 to about 14.7. With the increase of H content, the uneven cooling index increases. When H exceeds 7 ppm, the uneven cooling index can reach 14.5. By adopting reasonable and effective control measures, the uneven cooling index of the mold is significantly reduced from 3.85 to 0.73, and the surface crack defects in multi-mode continuous casting-rolling line are effectively alleviated. [ABSTRACT FROM AUTHOR]

This study describes a semi-analytical method for determining the J-R curves of round bars with elliptical cracks. This method develops the semi-analytical equations for load, displacement, and J-integral for surface-cracked round bars considering different materials and crack sizes. The validation of the semi-analytical expressions evaluated by three-dimensional finite element analysis reveals that the load–displacement curves and J-integral-load curves anticipated by the equations match the simulation results well. The average J-R curves of the surface-cracked round bars are obtained from fracture toughness tests on carbon steel 45 and the semi-analytical equations. In addition, this study also measured the J-R curves at different positions on the crack-front using the distributions of the J-integral along the fracture front obtained from three-dimensional finite element analyses. [ABSTRACT FROM AUTHOR]

It's challenging to use the machine vision to inspect the hot-rolled steel pipes with complex surface texture, uneven colour greyscale, and micro-cracks. On the basis of the principle of magnetic particle detection, a visual inspection method of steel pipe surface cracks based on the dry magnetic particle feature enhancement is proposed, in which the dry red magnetic particles are applied to the steel pipe's surface to form magnetic particle indication, and complementary colour images are captured in red and green light sources, and image difference is used to eliminate background noise and enhance magnetic particle indication features in view of the fact that the red light source improves and the green light source reduces the magnetic particle indication greyscale. Afterwards, the principle of selection of complementary colours and the detection principle are presented and analysed. Then, the magnetic particle images acquisition and the processing operations of the magnetic particle indication feature enhancement and crack segmentation are presented in detail. Finally, the feasibility of the method proposed in this paper is verified by experiments, and image segmentation metrics demonstrate that it has a good detection effect on the hot-rolled steel pipes with complex surface texture, uneven colour greyscale, and fuzzy cracks. [ABSTRACT FROM AUTHOR]

In order to study the effect of different surface crack parameters on the fracture failure of steel plate, the model was established by FEM. The results showed that the edge surface crack has the greatest influence on the fracture failure of the steel plate, and for non-edge surface cracks, the central surface crack has the greatest influence on the fracture failure of the steel plate. The larger the a/t and the smaller the a/c, the easier the steel plate fracture failure occurs. The a/c has a certain influence on the variation law of K and the position where Kmax appears. [ABSTRACT FROM AUTHOR]

Coal mining is necessary for the development of society but at the same time causes ecological damage that must also be repaired based on science. In the arid and semi-arid regions of northwest China, surface cracks are one of the major geo-environmental problems caused by coal mining, and studies are urgently needed to determine how to effectively repair them in a scientific manner. The rapid development of unmanned aerial vehicle (UAV) remote sensing technology in recent years has resulted in a good source of data for acquiring feature information on surface cracks. Existing studies mainly focus on high-precision crack extraction methods, and there are few studies on the methods for evaluating cracks. However, clarifying the degree of cracks requiring repair and what repair measures are required through scientific and reasonable evaluation methods is necessary to formulate effective crack repair and land reclamation plans. Given these considerations, in this study, the degree of both crack development and soil damage were evaluated based on the crack extraction results of UAV images. Based on the results of indoor experiments and field measurements, the grading criteria for the degree of crack development and soil damage were constructed. Crack density was used as the evaluation index for the degree of crack development (slight: <0.4%, moderate: 0.4–2%, severe: >2%). The distance between soil and cracks was the basis of the evaluation index for the soil damage degree (severe damage area: <0.6 m; slight damage area: 0.6–1.2 m; no obvious damage area: >1.2 m). Through the results from evaluating the degree of both crack development and soil damage in the study area, it was found that the degree of crack development was mainly moderate and located in the northern crack zone of the study area, with the cracks and damaged soil showing a striped pattern in the east-west direction. Combining the evaluation results of crack development and soil damage, the ecological restoration model of "natural restoration + crack filling + water supplementing + vegetation planting" is proposed. We conclude that crack repair should be applied in areas where moderate and severe cracks have developed, whereas soil repair should target the soil within 1.2 m of the cracks in the above area. This study is the first attempt to construct and evaluate the classification criteria of crack development degree and soil damage degree from the perspective of cracks and soil, and the results are of guiding significance for land reclamation in mining areas. [ABSTRACT FROM AUTHOR]

The stability of damaged rock mass is a critical problem in the control of surrounding rock in underground engineering. As the main macroscopic defect of rock surrounding engineering, it is of great significance to study its propagation mechanism and the experimental characteristics of rock mechanics. Surface-fractured rock mass is a typical representative of three-dimensional fracture. To reveal the failure mechanism of surface-fractured rock mass, a three-dimensional mechanical failure model of a surface-fractured rock specimen was established, including the initiation, crack propagation, and cooperative deformation of the rock micro-element. Taking the depth of the surface horizontal fissure as a variable, standard rock specimens with surface horizontal fissures of different depths were prepared, and an experimental study of surface-fractured rock specimens was carried out. The RMT rock mechanics test system was used to perform uniaxial compression tests on standard specimens containing fractured rock specimens of different depths. The complete stress–strain curves of samples with different fracture depths were obtained, and the influence of different fracture depths on rock strength and deformation characteristics was analyzed. The crack initiation, propagation, and failure modes of the specimens under uniaxial compression were analyzed based on high-speed camera technology. Through the combination of 3D image processing and acoustic emission monitoring, differences between failure before and after the peak in both asymmetrically damaged rock specimens and symmetrically damaged rock specimens were found. The mechanism of weak strength and weak stability of asymmetrically damaged rock specimens after the peak was explained theoretically. The research results showed that the existence of the horizontal joint plane directly led to a significant reduction in the strength of the jointed rock sample, and the fracture depth played an important role in controlling the failure mode of the jointed rock specimens. The uniaxial compression of rock specimens with horizontal non-penetrating surface fissures produced three-dimensional failure modes, and the depth of surface fissures changed the failure mode of the specimens under uniaxial compression. As the crack depth increased, the failure mode of the specimen changed from tensile failure to shear failure. The surface crack sample showed regional asymmetric failure and poor structural stability. [ABSTRACT FROM AUTHOR]

To quickly obtain bridge surface crack information to assist bridge condition assessment or maintenance, computer vision technology is used in this paper to quantitatively identify bridge surface cracks. The features of the bridge surface in different parts of the bridge may be quite different. To carry out crack identification research in a targeted manner, first, a classification model is trained based on deep learning to discriminate the surface pattern type of bridges. Then, for the images of bridge surfaces with different features, classification and segmentation models are used to identify the location and profile of the crack in the image; in other words, the existence of the crack is first judged by the trained classification models and pixel-level segmentation is performed by the trained segmentation models on the local region where the crack exists to determine the profile of the crack. Finally, based on the trained models of three types, crack identification is realized in combination with the improved sliding window in high-resolution bridge surface images with multiclass features. According to the identification results, the unconnected cracks are separated by the connected domain. From the results, a general algorithm for calculating the length and width of each crack is established, realizing the quantification of crack identification results regardless of the surface crack form. [ABSTRACT FROM AUTHOR]

A model experiment for in-line hot rolling was proposed, and its effectiveness in reducing surface cracking and improving the mechanical properties of cast strips of AC7A AlMg alloy was investigated. The strips were cast using an unequal-diameter twin-roll caster at 60m/min. The strips had a width of 100 mm, and were immediately cut to a length of 200mm and hot rolled at temperatures of 300, 350, 400, 450 and 500°C. The temperature of the strip surface was measured using a K-type thermocouple. The center area in the width direction of the strips was hot rolled. The thickness of the as-cast strips was 2 mm, and the width of the rolled region was 20 mm. The roll diameter was 70 mm, and the rolling speed was 15m/min. The thickness reduction caused by hot rolling ranged from 19 to 42%. Surface cracking was reduced by the in-line hot rolling process. The hot-rolled strips were cold rolled down to a thickness of 0.5mm and then annealed, and tensile tests were conducted. The in-line hot rolling process induced shear deformation of the microstructure. The most appropriate conditions for in-line hot rolling of AC7Awere a thickness reduction of 27% and a temperature of 350°C, judging from the tensile strength and elongation results. [ABSTRACT FROM AUTHOR]

In this study, the effects of the roll load and superheating on the appearance of surface defects in AlMg and AlSi alloy strips cast using a high-speed twin-roll caster were investigated. The band zone that existed in the center of the thickness direction was investigated. The alloy compositions were Al4.8% Mg and AlSi with Si contents of 1, 2, 3 and 11%. The diameter and width of the copper roll in the twin-roll caster were 300 and 50 mm, respectively. The superheating temperature of the molten metal was 5 and 50°C, and the roll load was varied from 2 to 88N/mm. A roll speed of 30m/min was utilized. The existence of surface cracks was investigated by penetrant inspection and bending test. The amount of surface cracking in the AlMg alloy was affected by the roll load, and the number of surface cracks decreased with decreasing roll load. Surface cracks occurred more easily in the Al4.8% Mg alloy than in the AlSi alloys. The degree of cracking could not be reduced by cold-rolling. In the AlSi alloys, the ripple marks were affected by the Si content, degree of superheating of the molten metal and the roll load. In the Al3% Si alloy, ripple marks were produced, and worsened as the roll load and the superheating of the molten metal were increased. A specimen for observation of the microstructure near the roll bite was obtained by performing a roll-stop during casting, and observed using Weck's reagent. A band zone was found to exist. The band zone in AlSi consisted of globular crystals, and that in AlMg consisted of equiaxed dendrites and Mg-rich areas. [ABSTRACT FROM AUTHOR]

A conventional twin-roll caster usually casts strips at a speed slower than 2 m/min and a roll load greater than 2 kN/mm. A vertical-type high-speed twin-roll caster can cast aluminum alloy strips at a speed higher than 10 m/min and a roll load smaller than 550 N/mm due to the effect of the large thermal conductivity of copper alloy rolls, compared with that of steel rolls. However, the properties of an aluminum alloy strip cast at a roll load smaller than 140 N/mm and at a roll speed higher than 30 m/min are not clear. In this study, Al–5%Mg strips were cast at a roll speed of 30 m/min and roll loads of 2 and 88 N/mm using a vertical-type high-speed twin-roll caster. The effects of roll load on cracking at the strip surface, the tensile mechanical properties, and the microstructure were investigated. Rotating rolls were stopped during casting, and the progression of centerline segregation and the microstructure between the rolls was investigated. Centerline segregation and surface cracking were lower at 2 N/mm than at 88 N/mm. In the strip cast at 2 N/mm, elongation in the width direction was greater than that cast at 88 N/mm, due to decreased surface cracking. The results demonstrate that a very low roll load improves the properties of the cast strip. [ABSTRACT FROM AUTHOR]

The natural frequencies and mode shapes of an Euler-Bernoulli beam with a rectangular crosssection, which has a surface crack, is investigated. The crack is modeled as a change (sudden or gradual) in the cross-section of the beam, and a modified perturbation approach is used assuming that the crack geometry is much smaller than the beam cross section. Computations of natural frequencies and mode shapes were carried out for various crack shapes and compared with a range of experiments and finite element analyses. It is concluded that the suggested modified perturbation approach gives reliable results with minimal effort for eigenfrequencies of cracked beams. Furthermore, as a new feature, the present perturbation method includes the shape of the crack in eigenfrequency computations and in principle, can work for any type of disturbance on the surface including a small bump for example. [ABSTRACT FROM AUTHOR]

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Copyright of Journal of Test & Measurement Technology is the property of Publishing Center of North University of China and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The development of UAV (unmanned aerial vehicle) technology provides an ideal data source for the information extraction of surface cracks, which can be used for efficient, fast, and easy access to surface damage in mining areas. Understanding how to effectively assess the degree of development of surface cracks is a prerequisite for the reasonable development of crack management measures. However, there are still no studies that have carried out a reasonable assessment of the damage level of cracks. Given this, this article proposes a surface crack damage evaluation method based on kernel density estimation for UAV images. Firstly, the surface crack information from the UAV images is quickly and efficiently obtained based on a machine learning method, and the kernel density estimation method is used to calculate the crack density. The crack nuclear density is then used as a grading index to classify the damage degree of the study area into three levels: light damage, moderate damage, and severe damage. It is found that the proposed method can effectively extract the surface crack information in the study area with an accuracy of 0.89. The estimated bandwidth of the crack kernel density was determined to be 3 m based on existing studies on the effects of surface cracks on soil physicochemical properties and vegetation. The maximum crack density value in the study area was 316.956. The surface damage area due to cracks was 14376.75 m2. The damage grading criteria for surface cracks in the study area (light: 0–60; moderate: 60–150; severe: >150) were determined based on the samples selected from the field survey by crack management experts. The percentages of light, moderate, and severe damage areas were 72.77%, 23.22%, and 4.01%, respectively. The method proposed in this article can effectively realize the graded damage evaluation of surface cracks and provide effective data support for the management of surface cracks in mining areas. [ABSTRACT FROM AUTHOR]