Maximum Crack Depth Research Articles

Improvement of Fatigue Characteristics of Friction Stir Welded A6061-T6 Applying Shot Peening

Recently, researchers have developed the method as a harmless the crack by the surface modification. For the purpose of contributing to reliability improvement of the A6061-T6 structure by harmless method, the following research was carried out: The tensile residual stress of friction stir welding was added by shot peening, resulting in a more significant compressive residual stress than that of the base metal. The effect of the surface crack aspect ratio on the maximum harmless crack depth (ahml) of A6061-T6 was evaluated for residual stress distribution. The detectable depth was evaluated in the relationship between ahml and the maximum detectable crack depth (aNDI) by non-destructive inspection (NDI).

Prognosis of reflective pavement cracking development with Bayesian updating and surrogate models

ABSTRACT The main objective of this study is to establish an integrated prognostic method for predicting the development of thermal-induced reflective cracking in asphalt overlay on concrete pavement. The integrated prognosis process for crack growth is developed on the modified Paris’ law and includes three steps: (1) calculation of J-integral; (2) Bayesian updating of crack growth parameters and (3) prediction of remaining life. Finite element modelling (FEM) was conducted to calculate J-integrals at different crack depths and cold weather conditions. A surrogate model was built based on the original Kriging method and it shows high accuracy in predicting J-integrals from maximum air temperature, temperature drop and crack depth. The Bayesian updating process starts from the laboratory-measured distribution of fracture model parameters (A and n) in Paris’ Law and converges to the true values to match the measured crack depths at different loading cycles from field inspection. On the other hand, the consideration of material damage in asphalt overlay avoids over-estimation of remaining loading cycles for reflective cracking to reach the pavement surface. Further study is recommended to accurately assess in-situ pavement modulus and detect crack depth over concrete joints for implementation of the proposed prognostics method.

Failure of the SRC under freeze- thaw cycles by the push-out tests

This paper explores the impact of freeze-thaw cycles, the thickness of the protective layer, embedment length, and volumetric hoop ratio on the bond performance at the SRC interface, assessed through freeze-thaw and push-out tests. Results from SEM indicated significant cracking in concrete exposed to freeze-thaw cycles, with an increase in both the number and diameter of pores. Despite significant damage to the concrete exterior, the interface exhibited considerably less deterioration. Following 200 freeze-thaw cycles, the specimens displayed a maximum crack depth of 2.3 mm and a porosity rate of 35.1 %. As the cycles progressed, the failure mode of specimens under push-out loading transitioned from splitting to interfacial shear failure. Notably, the length of cracks on the end surfaces was markedly reduced, and the majority of specimens exhibited minimal cracking on the side surfaces. Additionally, interfacial bond stress decreased progressively with the increasing number of cycles. The ultimate bond stress declined more rapidly than residual bond stress, with the rate of decrease stabilizing after surpassing 100 cycles. Enhancements in protective layer thickness, embedment length, and volumetric hoop ratio effectively mitigated the reductions in bond stress. Among these, the protective layer had the most significant impact, followed by the volumetric hoop ratio, while embedment length had the least influence. The study concludes with proposed formulas for calculating bond stress and slip eigenvalues after freeze-thaw cycles, integrating experimental results and theoretical analysis.

Study of Prefabricated Crack Propagation on Monocrystalline Silicon Surfaces for Grinding Damage Analysis.

Crack generation and propagation are critical aspects of grinding processes for hard and brittle materials. Despite extensive research, the impact of residual cracks from coarse grinding on the cracks generated during fine grinding remains unexplored. This study aims to bridge this gap by examining the propagation law of existing cracks under indentation using the extended finite element method. The results reveal that prefabricated cracks with depths less than the crack depth produced on an undamaged surface tend to extend further without surpassing the latter. Conversely, deeper prefabricated cracks do not exhibit significant expansion. A novel method combining indentation and prefabricated cracks with fracture strength tests is proposed to determine crack propagation. Silicon wafers with varying damaged surfaces are analyzed, and changes in fracture strength, measured by the ball-on-ring method, are utilized to determine crack propagation. The experimental results confirm the proposed crack evolution law, validated by damage assessments across different grinding processes, which is suitable for crack damage. The findings demonstrate that residual cracks from coarse grinding are negligible in predicting the maximum crack depth during fine grinding. This research provides a crucial foundation for optimizing the wafer thinning process in 3D stacked chip manufacturing, establishing that changes in fracture strength are a reliable indicator of crack propagation feasibility.

Formation Mechanism and Control Strategy of Transverse Corner Cracks in Continuous Casting of 55SiCr Spring Steel

An experimental study is conducted to reveal the formation mechanism of transverse corner cracks by analyzing the metallurgical structure, crack morphology, and hot ductility. The results reveal that the corner temperature of the billet tends to be lower during mold solidification, leading to the formation of grain boundary low‐plasticity ferrite. Additionally, during the straightening process, the corner temperature of the billet falls into the serious low‐temperature brittle zone with temperature lower than 850 °C. These two factors contribute to the formation and propagation of cracks along the grain boundary ferrite under straightening forces. Therefore, after the verification of mold simulation test and industrial trial, the temperature at billet (section size 150 × 150 mm2) corner is improved by increasing the mold chamfer radius from 6 to 12 mm. This adjustment ensures that the straightening temperature at billet corner elevated from 830 to 880 °C, remaining outside the serious low‐temperature brittle zone, and the maximum depth of corner cracks decreases from 741.49 to 344.89 μm.

Differential roof cutting for roadway support in dual gob-side entry retention on a single working face − Multilevel continuous anchor-grouting control technology: A case study

The coal pillar-free gob-side entry retention technology (GER), which enhances resource recovery rates and reduces the amount of tunnel excavation, has been applied in multiple mining areas in China. However, cases of implementing gob-side entry retention on both sides of a single working face are rare. The asynchronous extraction of long-distance working faces leads to significant differences in the stress environment of roadways on both sides, and uniform technical means are poorly adapted to the control of surrounding rock on both sides, affecting the safe and efficient production. This paper, taking the dual gob-side entry retention on both sides of the 61001 W working face with thick mudstone roofs in Zhao Guan Coal Mine, Shandong Province, as the engineering background, utilizes a combination of theoretical calculations, numerical simulations, and on-site detailed monitoring to analyze the uncoordinated deformation characteristics of the upper part bulging and the lower part concaving of the two roadways. It clarifies the differentiated spatiotemporal evolution law of the number of fractures and the development turning points at different depths of the surrounding rock of the two entries, revealing the differential deformation mechanism of the surrounding rock of the two entries caused by stress state and fracture development differences. A “cutting roof to relieve pressure-multilevel continuous anchor-grouting” combined control technology system is proposed. By cutting off the stress transmission of the roof through drilling and blasting, and then reconstructing the integrity of the surrounding rock and improving the rock strength with the help of anchor-grouting. With the application of this new technology, the deformation of the surrounding rocks of the two entries was reduced by more than 60 % and 29 %, respectively, and the maximum crack depth of the roof was controlled within 3 m, significantly enhancing the stability of the roadways. The research results of this paper provide a reference for the control of surrounding rock in gob-side entry retention under similar conditions.

Investigation into the Failure Characteristics and Mechanism of Rock with Single Elliptical Defects under Ultrasonic Vibrations

In order to investigate the effects of elliptical defects on rock failure under ultrasonic vibrations, ultrasonic vibration tests and PFC2D numerical simulations were conducted on rocks with single elliptical defects. The research results indicated that the fracture fractal dimension, axial strain, and crack depth of specimens with elliptical defects at 45° and 90° were the smallest and largest, respectively. The corresponding strain and fractal dimension showed a positive linear and logarithmic function relationship with time. The maximum crack depth of 46.50 mm was observed on the specimens with an elliptical defect angle of 90°. Specimens with elliptical defects at 0°, 30°, 75°, and 90° exhibited more dense and frequent acoustic emission events than those with elliptical defects at 15°, 45°, and 60°. During the ultrasonic vibration process, the maximum total energy (87.86 kJ) and energy consumption coefficient (0.963) were observed on specimens with elliptical defect angles of 30° and 45°, respectively. The difference in the stress field led to varying degrees of plastic strain energy in the specimens, resulting in different forms of crack propagation and triggering differential acoustic emission events, ultimately leading to specimen failure with different crack shapes and depths. The fractal dimensions of elliptical defect specimens under ultrasonic vibration have a high degree of consistency with the changes in axial strain and failure depth, and the fractal dimension of defect specimens is positively correlated with the degree of failure of defect specimens.

Experimental investigation and numerical modeling of effect of specimen size on microwave-induced fracturing of diorite

The effect of specimen size on microwave-induced fracturing of rocks has not been well understood. In this study, the experimental tests using open-ended microwave and numerical simulations coupling COMSOL Multiphysics and four-dimensional lattice spring model (4D-LSM) were carried out to investigate the evolution process of microwave-induced cracks, and to elucidate the mechanisms responsible for size-dependent microwave-induced fracturing. The experiments show that with the increase of the specimen dimension, the number of microwave-induced cracks is almost constant, and the total crack length first increases and then decreases, while the maximum crack width and maximum crack depth decrease gradually. A comparison of the experimental and numerical temperature characteristics as well as cracking characteristics indicates that the models established in this study are reasonable in the simulation of the rock fracturing behaviours. The numerical results show that the crack initiation time increases logarithmically with the increase of the specimen dimension. For the small-sized specimens, the microwave-induced cracks started from the outer boundary of the specimen and propagated toward to specimen center and into the depth. For the medium-sized and large-sized specimens, the microwave-induced cracks initiated near the outer boundary of the antenna aperture, and then propagated toward to the center of the specimen and the outer boundary of the specimen. The main reason for the size-dependent of fracturing behavior is that the local fracture energy will dramatically decrease when the crack is approaching the specimen boundary.

Analytical modelling of desiccation crack depth estimation for granitic soils

Desiccation cracking has been aggravated by the frequent extreme weather events and climate change in recent years. The presence of these cracks compromises the integrity of soil structures and significantly contributes to rainfall infiltration, slope stability, as well as soil deformation. According to tensile failure theory and Hookean elastic equation, an analytical model was established to predict crack depth under continuous desiccating conditions. The essential input parameters for the modelling are the modulus ratio and tensile strength, which can be determined through uniaxial tensile and shear tests. The maximum crack depth is estimated based on the suction change profile of the soil under investigation. Herein, the suction change profiles were developed from volumetric water content monitoring at various depths and utilizing the soil water characteristic curve (SWCC) of the investigated soil. Validation of the proposed method was conducted through laboratory simulations, specifically in the context of crack formation in granitic soils under continuous drying conditions. The predicted crack depth, in a range of 0.22 ∼ 0.30 m, closely aligned with the observed values. Collectively, for a specific soil with given elastic parameters and strength, crack depth can be estimated through suction change. This approach, compared with existing crack modeling methods, offers a simple and efficient way for crack depth estimation, holding promise for practical applications.

Stability analysis of unsaturated soil slopes with cracks under rainfall infiltration conditions

Pre-existing (open) cracks at slope crests, especially tension cracks, are a significant factor in the transition from shallow to deep-seated landslides in unsaturated soil slopes induced by rainfall. This paper presents an analytical framework to assess the stability of unsaturated soil slopes for deep-seated rotational failure considering arbitrary crack depths and unsteady infiltration, and its effectiveness is verified by previous literature and finite element analysis. A closed-form formula is proposed for the maximum depth of cracks in unsaturated soils by the stability of the vertical crack boundary. A parametric study is performed to investigate the impact of some key parameters on the stability of unsaturated soil slopes with cracks. Dimensionless stability charts are developed, which can calculate the factor of safety for the slopes with cracksof any depth and can reflect that the potential slip surfaces through or without passing through the crack tip. In addition, given the existence of a critical crack depth and maximum crack depth, with a ratio ranging from 0.5 to 0.6 based on the stability charts, deep-seated rotational failure is more likely to occur than failure caused by a crack boundary.

Study on deformation and instability characteristics and control technology of deep soft rock roadway with strong mining

With the development of deep mining of coal resources, the problem of deep roadway management is becoming increasingly prominent. This study aims to analyze the deformation and failure mechanism of deep-buried soft rock roadway under the influence of mining. Taking the material roadway of 3205 working face in Xin’an Coal Mine as the engineering background, this study analyzed the characteristics of roadway deformation and failure and its influencing factors through field investigation. This study firstly expounded the principles of graded continuous anchorage for roadway roof and then proposed a new support scheme whose feasibility was verified by numerical simulation. Field verification shows that the optimized support scheme can effectively control the deformation of roadway surrounding rock. Specifically, the deformation of roof and two sides is reduced by 91% and 50% respectively; the maximum crack depth decreases from 9.56 to 3.26 m, indicating that the roof crack development has been significantly inhibited. The new support scheme builds a solid anchored rock beam structure with thick roof layer, which can maintain the long-term stable bearing capacity of deep-buried composite roof roadway. This study provides a solution for the surrounding rock control of deep soft rock roadway.

Pipeline reliability assessment and predictive maintenance considering multi-crack dependent degradation

Cracks due to corrosion are one of the main reasons for natural-gas pipeline leaks. Making the reliability assessment, prediction, and maintenance decision of pipelines based on measurable crack data is a central issue at present. The failure of pipelines is usually a result of the cumulative impact of multiple cracks. The interaction between adjacent cracks accelerates crack propagation, and greatly affects the degradation mechanism of pipelines. In this study, the reliability prediction and maintenance decisions were studied by considering the dependent degradation between multiple cracks in pipelines. Firstly, the initiation and propagation of pipeline cracks were modeled using a non-homogeneous Poisson process and a Gamma process, respectively. The interaction between cracks was defined to be a function of the random crack distance, which could be reflected by the change of shape parameters in the Gamma process. Secondly, the pipeline’s failure was defined as the competitive failure of the number of cracks, the maximum crack depth, and the total crack depth. The reliability prediction model of a pipeline under this failure mode was determined. A non-periodic combined maintenance policy considering both the pipeline condition and its predictive reliability was then proposed, and an optimal predictive maintenance decision model was constructed to minimize the long-term average cost rate. Finally, the effectiveness of the proposed model and policy was verified by a numerical experiment and a crack dataset of a transnational pipeline.

Research on spatiotemporal evolution law of surrounding rock fractures and hierarchical collaborative control technology in high-stress soft rock roadway: A case study

Safe and efficient coal mining has always been restrained in high-stress roadways due to their highly rheological property and large-scale deformation, which are key technical problems to be solved in this industry. In this work, the high-stress roadway of Wuju Coal Mine in Gansu, China is taken as the engineering background. First, long-term field tracking survey was conducted on the cracks of the surrounding rock during excavation to quantitatively analyze the spatial-temporal evolution law. Meanwhile, using the principle of simplicity, the variation trends of radial and axial permeability were revealed and the optimal grouting time in this roadway was determined. We proposed the theory of anchor grouting support with fixed anchor length, as well as hierarchical collaborative control technology (HCCT). The high-strength hollow grouting cables and corresponding anchor-grouting methods were also investigated and identified, which addresses the long-standing technical contradiction between grouting support and pressure deformation. Engineering test proves that this new technology can realize the safe and efficient control of high-stress rock roadway, with the maximum crack depth on the roof reduced from 7.65 m to 3.10 m and the surrounding rock deformation decreased by more than 56%. This paper provides new ideas for the maintenance and control of rock roadways or tunneling projects in similar conditions.

Study on Failure Mechanism of Roadway Surrounding Rock and Hierarchical Continuous Support Technology in Unidirectional Fault Area

A fault is a common geological structure in coal mining. Large deformation or even instability and collapse often occur in roadways in fault areas, which restricts the safe and efficient production of mines. With the track roadway of the 5206 working face of Xin’an Coal Mine as the engineering background, this study aims to explore the failure mechanism of surrounding rock under the influence of fault structures. Field investigation and numerical simulation were used comprehensively to analyze the failure characteristics of the surrounding rock under the influence of a unidirectional fault structure. Based on the principle of thick-layer transboundary anchorage, the hierarchical continuous support technology of transboundary anchoring in the fault structure area was proposed. The results show that the stress near the fault area is relatively concentrated, and the rock mass strength is low, which may easily cause the deformation and failure of the surrounding rock under the dynamic stress response. Using the new technology to reconstruct the bearing structure of the broken surrounding rock mass, the deformation of the surrounding rock can be effectively restrained. According to the monitoring feedback, the roadway deformation in the roof and two sides is reduced by 68.5% and 35.4%, respectively; and the maximum evolutionary depth of the roof crack is reduced to 3.5 m from 7.5 m in the original support scheme. Moreover, this study also explored the necessity of wedge anchorage for corner anchor cables and the deformation characteristics of surrounding rock at different fault dip angles. These results provide an important reference for the maintenance and control of coal roadways under the influence of unidirectional fault structures.

Prediction of moisture-induced cracks in wooden cross sections using finite element simulations

Wood absorbs and desorbs moisture due to its hygroscopic behavior, leading to moisture gradients in timber elements as well as swelling and shrinkage. These processes are constrained due to the orthotropic material properties of wood, leading to moisture-induced stresses, which can cause crack initiation and propagation. A significant amount of the damage in timber constructions indoors can be related to changes of the moisture content (MC). However, more information is needed about the correlation between moisture changes or gradients and specific damage characteristics, like crack depths. Thus, based on numerical simulations, the crack depth development within two solid timber and one glued laminated timber (GLT) cross section over time for different relative humidity (RH) reductions and initial MCs is analyzed. For this purpose, a multi-Fickian transport model is used to determine moisture fields, which are then used as loads in a subsequent stress simulation, where linear elastic material behavior is considered. An extended finite element approach, supported by a multisurface failure criterion defining the failure behavior, allows for the simulation of moisture-induced discrete cracking. Based on simulation results, correlations between potential maximum crack depths and moisture gradients in indoor climate conditions are derived, which enables the prediction of crack depths in wood. Finally, it is shown that the initial MC level significantly influences the maximum crack depth that can be expected.

Three Visual-Diagnostic Methods for the Detection of Enamel Cracks: An In Vitro Study.

Tooth fractures are a common cause of tooth loss, frequently starting as enamel cracks. However, methods for the detection of enamel cracks are poorly investigated. The aim of the study was the validation of three clinical methods for the detection of enamel cracks: dental operating microscope (DOM), near-infrared transillumination (NIR), and fiber-optic transillumination (FOTI), with hard-tissue slices serving as controls. A total of 89 extracted teeth, set up as diagnostic models, were investigated, and the maximum crack depth was scored by two examiners. The actual crack depth was determined microscopically (25×) using horizontal sections. The accuracy of each method was analyzed using receiver operating characteristic (ROC) curves. Across all tooth surfaces, the area under the curve (AUC) amounted to 0.57 (DOM), 0.70 (FOTI), and 0.67 (NIR). For crack detection on vestibular/oral surfaces, the AUC was 0.61 (DOM), 0.78 (FOTI), and 0.74 (NIR); for proximal surfaces, it was 0.59 (DOM), 0.65 (FOTI), and 0.67 (NIR). However, the actual crack depth was underestimated with each method (p < 0.001). Under in vitro conditions, FOTI and NIR are suitable for detection of enamel cracks, especially on vestibular and oral tooth surfaces. However, an exact estimation of crack depth is not possible. Therefore, FOTI and NIR seem to be helpful for the clinical detection of enamel cracks.

Experimental Study on Flexural Bearing Characteristics of Ceramsite Concrete Beams after Creep at Different Curing Ages

Ceramsite concrete is increasingly used for structural applications due to its lightweight, high-strength, and high-temperature resistance advantages. However, research into the postcreep properties of ceramsite concrete has yet to keep pace with other areas. Therefore, this paper aims to investigate the flexural bearing properties of ceramsite concrete beams after creep and make recommendations for future research. To study the flexural load-bearing performance of ceramsite concrete beams after creep, a comparison test was carried out on four ceramsite concrete beams subjected to 200 d creep loading and four beams subjected to static load without creep loading for four curing ages. The results showed that, at first, the deformation capacity of the ceramsite concrete beams would increase after creep and the toughness and energy absorption capacity would also strengthen. Secondly, the creep could improve the ultimate bearing capacity of the ceramsite concrete beams. It was an approximate 10% increase after 200 d creep. Then, the stiffness, toughness, and ultimate bearing capacity of the ceramsite concrete beams would increase gradually with the increase of the curing age after the creep. In addition, the ultimate bearing capacity of the ceramsite concrete beams increased gradually with the increase of the curing age. The growth rate was faster in the early stage, slower after 120 d, and slower and more stable after 228 d. Finally, creep could cause the maximum crack width and depth of the ceramsite concrete beams decreased and the number of cracks would grow with the curing age. The conclusions obtained in the study provide a theoretical basis for the design of light aggregate structures for creep.

Distribution Characteristics of Sub-Surface Cracks in Fused Quartz Ground with Different Worn Wheels.

The crack distribution characteristics in grinding damage have a significant impact on subsequent polishing efficiency and part strength. Grinding tests were carried out on fused quartz using grinding wheels with different wear states. The results showed that the cracks produced by sharp abrasive grits were mainly near chevron cracks and had no preferred direction. However, the blunt abrasive grits produced near partial cone cracks had a preferred direction. At a depth of 96.7 μm from the surface, the amount of cracks in the range of 50°~90° with an inclination angle between the crack and the cutting direction could reach 88.9%. The statistical results showed that the depth and total length of cracks produced by sharp grits were larger than those produced by blunt grits (the maximum crack depth difference was about 40 μm). Therefore, it was concluded that sharp abrasive grits were not conducive to damage control. The findings of this research enhance our understanding of the formation mechanism of grinding damage.

Multilayer perceptron neural network and eddy current technique for estimation of the crack depth on massive metal structures

This paper introduces a method for estimating the maximum depth (sub-millimeter) of minor cracks on the surface of aluminum plates used in the aeronautical industry. A set of C-scan eddy current (EC) images, including real and imaginary parts of the impedance, is analyzed to extract suitable features after reducing noise effects, such as background noises and edge noises. Based on the obtained features, e.g. maximum impedance, the background feature, background noises, type of sensors, a Multilayer Perceptron (MLP) Neural Network is built to estimate the maximum depth of the cracks. The network is optimized based on loss functions, such as mean absolute error and mean squared error. An optimal network structure with five neurons in the first hidden layer and eight neurons in the second hidden layer is chosen. The obtained result indicated that the relative error of estimations is lower than 10% for almost all experimental tested samples.

Performance of composite and tubular columns under close-in blast loading: A comparative numerical study

In the present scenario, rapid industrialization and political conflicts across the globe result rise in malicious terrorist activities in the form of blasts and explosions targeting specific civil engineering structures. Damage caused by such blast loading may be of serious consequences in terms of huge material loss and fatalities. Therefore, investigations on construction and strengthening technique to improve the blast resistance of the critical components of the structure are of considerable interest. In the present study, an experimentally tested square RC column with seismic lateral reinforcement carrying axial load subjected to an explosive charge of 100 kg ANFO (82 kg-TNT equivalent) at a scaled distance of 1.00 m/kg1/3 with 10 mm mesh size using ABAQUS/CAE software equipped with concrete damage plasticity model is considered for validation. To have the superior performance of the RC column, efforts have been made by considering eight equivalent RC columns including composite, CFST, CFST with in-plane cross reinforcement, and CFDST to the experimentally tested one under close-in blast are analyzed. The numerical models have been developed by considering equivalent peak pressure of 8.71 MPa under the close-in blast. Parameters such as maximum transverse displacement, stresses, crack depth, and damage to the columns are studied and compared. It has been found that the CFST column with in-plane cross reinforcement and the composite column with seismic reinforcement give superior blast performance under the close-in blast loading. The two superior columns are strengthened with C-FRP wrapping over the mid-height region and analyzed under the same loading. Improved performance of the columns is discussed and compared and the column giving the best performance is identified.