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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]

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]

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]

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]

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]

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]

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]

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]

The present work investigates a surface crack found in an input shaft of e-motor used for no-road applications such as electrical lawn mower and scissor lift applications. Detailed failure analysis was carried out involving visual inspection, chemical analysis, microstructural analysis, fractography, SEM and EDS analysis. The analysis concluded that the surface crack observed is due to the delay in tempering process. Experimental simulation was conducted to validate, and it revealed that the crack got developed in the as-quenched specimens when they were not immediately subjected to tempering process. It is recommended to carry out the tempering process right after quenching to avoid such kind of failures. [ABSTRACT FROM AUTHOR]

The laser ultrasonic method using the characteristics of transmitted Rayleigh waves in the frequency domain to determine micro-crack depth is proposed. A low-pass filter model based on the interaction between Rayleigh waves and surface cracks is built and shows that the stop band, called the sensitive frequency range, is sensitive to the depth of surface cracks. The sum of transmission coefficients in the sensitive frequency range is defined as an evaluated parameter to determine crack depth. Moreover, the effects of the sensitive frequency range and measured distance on the evaluated results are analyzed by the finite-element method to validate the robustness of this depth-evaluating method. The estimated results of surface cracks with depths ranging from 0.08 mm to ~0.5 mm on the FEM models and aluminum-alloy samples demonstrate that the laser ultrasounds using the characteristics of Rayleigh waves in the frequency domain do work for quantitative crack depth. [ABSTRACT FROM AUTHOR]

Fatigue crack growth in Al 2024 and Al 7050 specimens was assessed experimentally and numerically. In the experimental investigation, various specimen configurations and loading conditions were used to achieve pure mode I, pure mode II, and mixed mode I/II, I/III, and I/II/III. Sample configurations were as follows: first, compact tension shear (CTS) specimen to reproduce pure mode‐I and pure initial mode‐II loading conditions; second, surface crack tension (SCT) specimen to analyze the behavior of semielliptical surface cracks in mode‐I and mixed‐mode conditions; and third, hollow cylindrical (HC) specimen with initial semielliptical surface crack to analyze fatigue crack growth under complex stress state. In the numerical study, finite element method (FEM) simulations were performed by means of FRANC3D and ABAQUS solver. The numerical predictions were validated with the experimental results. These predictions resulted to be accurate estimation of the crack growth across the broad range of the investigated loading conditions. [ABSTRACT FROM AUTHOR]

This paper introduces a machine vision-based system promising low-cost solution for detecting a fatigue crack propagation caused by alternating mechanical stresses. The fatigue crack in technical components usually starts on surfaces at stress concentration points. The presented system was designed to substitute a strain gauge sensor-based measurement using an industrial camera in cooperation with branding software. This paper presents implementation of a machine vision system and algorithm outputs taking on fatigue crack propagation samples. [ABSTRACT FROM AUTHOR]

In order to accurately assess creep crack initiation (CCI) and growth (CCG) life for elevated temperature cracked structures, both out‐of‐plane and in‐plane constraints need to be considered, and the unified creep constraint parameter solutions should be investigated. In this work, the new unified creep constraint parameter Ac values for plate structures with various surface crack sizes subjected to tensile and bending loads have been investigated and obtained using three‐dimensional (3D) finite element (FE) analysis. The effects of material creep properties, crack sizes, loading modes, and plate thickness on the parameter Ac have also been analyzed. The estimation equation of Ac for materials with different creep exponent n has been fitted. The parameter Ac solutions can be used in CCI and CCG life evaluation of the C*‐Ac two‐parameter approach for cracked plates subjected to tensile and bending loads. Highlights: The Ac solutions for cracked plates under tensile and bending loads are investigated.The equations for estimating Ac for materials with different creep exponent n are given.The effects of the crack size, loading mode and plate geometry on Ac are analyzed.The constraint‐dependent CCG rate and CCI time of cracked plates are investigated. [ABSTRACT FROM AUTHOR]

• Fatigue crack growth rates in base metal and heat-affected zone of butt-welded high-strength steels Q960, Q890, and HG785 were obtained. • Fatigue behavior of butt-welded high-strength steel connections with semielliptical surface cracks was studied experimentally. • An accurate theoretical method is proposed to predict the fatigue life and crack propagation trajectories of surface crack specimens. This paper presents a study on the fatigue behavior of butt-welded high-strength steels (HSSs) Q960, Q890, and HG785. Fatigue crack growth rate (FCGR) experiments in the base metal (BM) and heat-affected zone (HAZ) are conducted, and the fatigue parameters are fitted using the Paris Law. Scanning electron microscopy (SEM) is also performed. The results reveal that the FCGR in the HAZ is slower than that in the BM for HSS; Q960 exhibits the highest fatigue crack growth (FCG) resistance, followed by Q890 and HG785. Surface crack propagation experiments are conducted at a maximum stress of half yield strength and 200 MPa. At half yield strength, the fatigue life decreases as the stress range increases, while at 200 MPa, the fatigue life decreases as the steel yield strength decreases. Furthermore, it is found that the surface cracks initially grow faster in the depth direction and then shift to the through thickness crack along the width direction. Finally, a theoretical method for predicting the fatigue life and crack propagation trajectories of surface crack specimens is proposed based on the Paris Law to consider multidimensional crack propagation behavior. [ABSTRACT FROM AUTHOR]

[Display omitted] • The new dynamic models of BEC and BSC are built based on the 3-dimensional solid element. • A comparative analysis of vibration characteristics between BEC and BSC is conducted. • Edge crack has a more obvious effect on the vibration responses of blades than surface cracks. The edge crack and surface crack are two typical cracks of blades. To accurately compare and analyze nonlinear dynamic responses induced by edge cracks and surface cracks of the rotating blade with varying sections and twisted shapes, a modeling method based on solid elements is proposed and validated by measured natural frequencies of an intact blade. The dynamic models of both the blade with edge cracks (BEC) and the blade with surface cracks (BSC) are established considering breathing effects and the proposed dynamic model is also validated by ANSYS software in three aspects, including natural frequencies, vibration characteristics, and contact characteristics between crack surfaces. Finally, the effects of crack depths, crack positions, aerodynamic amplitudes, and rotating speeds on the nonlinear vibration responses of cracked blades are investigated, and the vibration characteristics between BEC and BSC are compared and analyzed. The results show that with the increase of crack depth ratio and the decrease of crack position ratio, the first resonance frequency of the BEC significantly decreases, but that of BSC only fluctuates within a narrow range. In addition, the response amplitude of BEC consistently surpasses that of BSC under the same excitation conditions, which indicates that BEC is more dangerous than BSC. [ABSTRACT FROM AUTHOR]

When various alloying elements are added or the cooling rate is increased, steel grades with U- or V-typed ductility behavior show N-shaped ductility behavior in which the ductility decreases in the low-temperature region. This study proposes a method that uses N-shaped data fitting and random forest to predict ductility behavior of steel grades that have bainite microstructure. To include the phenomenon in which that ductility decreases below the intermediate temperature, the data range was extended to temperature T < 700 °C. To identify the T range in which the ductility decreases at T < 700 °C, an N-shaped data fitting method using six parameters was proposed. Comparison with the experimental values confirmed the effectiveness of the proposed model. Also, the model has better ability than models to predict bainite start temperature TBS. In a case study, the change of ductility behavior according to the cooling rate was observed for Nb-added steel. As the cooling rate increased from 1 °C/s to 10 °C/s, the formation of hard phase was relatively promoted, and different transformation behaviors appeared. This ability to predict the ductility behavior of alloy steels with a bainite microstructure, and to predict TBS below the intermediate temperature enables effective control of the secondary cooling conditions during continuous casting process, minimizing the formation of cracks on the slab surface. [ABSTRACT FROM AUTHOR]

Buildings and infrastructure in congested metropolitan areas are continuously deteriorating. Various structural flaws such as surface cracks, spalling, delamination, and other defects are found, and keep on progressing. Traditionally, the assessment and inspection is conducted by humans; however, due to human physiology, the assessment limits the accuracy of image evaluation, making it more subjective rather than objective. Thus, in this study, a multivariant defect recognition technique was developed to efficiently assess the various structural health issues of concrete. The image dataset used was comprised of 3650 different types of concrete defects, including surface cracks, delamination, spalling, and non-crack concretes. The proposed scheme of this paper is the development of an automated image-based concrete condition recognition technique to categorize, not only non-defective concrete into defective concrete, but also multivariant defects such as surface cracks, delamination, and spalling. The developed convolution-based model multivariant defect recognition neural network can recognize different types of defects on concretes. The trained model observed a 98.8% defect detection accuracy. In addition, the proposed system can promote the development of various defect detection and recognition methods, which can accelerate the evaluation of the conditions of existing structures. [ABSTRACT FROM AUTHOR]

An impact analysis model is built to describe the effect of nanoscale amorphization on dislocation emission from a surface semi-elliptical crack tip in nanocrystalline materials. The nanoscale amorphization is formed by the splitting transformation of grain boundary(GB)disclinations caused by the motion of GBs. The analytical solution of the model is obtained by using the complex method, and the influence of nanoscale amorphization, dislocation emission angle, crack length, and curvature radius of surface crack tip on the critical stress intensity factor (SIF) of the first dislocation emission is investigated through numerical analysis. The numerical analysis shows that the impact of nanoscale amorphization on the critical SIF corresponding to dislocation emission depends on the dislocation emission angle, the position and the size of the nanoscale amorphous, the curvature radius, and the length of surface crack. As the curvature radius of surface crack tip and the crack length increase, the normalized critical SIF increases. When the nanoscale amorphization size is small, it has a great impact on the critical SIF for dislocation, but when the size is relatively large, the effect becomes small. The effect of the increasing strength of the nanoscale amorphization on dislocation emission from the surface crack tip is related to the distance between the nanoscale amorphization and the crack tip, and there is a critical crack-junction for which the increase of dislocation strength has little effect on dislocation emission. [ABSTRACT FROM AUTHOR]

The propagation of vertical cracks on the surface of thermal barrier coating (TBC) may be affected by the surrounding cracks. In this study, a TBC model with multiple cracks is developed to study the effects of surrounding cracks on surface vertical crack evolution and coating spalling. Dynamic TGO growth, continuous ceramic sintering, and dynamic crack propagation are considered in the model. The general characteristics of stress state and crack evolution in the coating are first examined. Then, the effects of the surrounding horizontal and vertical cracks on the overall crack growth are investigated. The results show that the vertical crack expands to the interface and merges with the horizontal crack rapidly. The crack length variation by simulation is consistent with the reported results by experiment. The surrounding horizontal crack close to the coating surface can prevent the surface vertical crack from propagating to the interface, which is independent of the surrounding crack length. A certain density of vertical cracks with equal spacing and initial length is conducive to delaying the horizontal crack propagation near the interface. Some optimized design methods proposed in this work provide another option for developing TBC with high durability. [ABSTRACT FROM AUTHOR]

The effect of specimen thickness on the rupture properties of cast Ni-based polycrystal superalloy M951 was investigated in this paper. The results of the rupture tests in air under 980 ​°C/90 ​MPa revealed that the rupture life and elongation obviously decreased with decreasing specimen thickness. The thin-wall effect for polycrystal superalloy M951 is associated with several factors. First, the surface oxidation and internal nitridation induce the reduction in the load-bearing section, which accelerates the rupture fracture of thin specimens. Second, the combined effect of oxidation and stress at the surface grain boundary facilitates the premature initiation and propagation of the surface cracks in thin specimen. Third, the through-grain boundaries introduce by specimens machining are detrimental for rupture property. A direct comparison of rupture properties of thin-wall samples with different grain morphologies indicate that thin-wall effect can be diminished by avoiding through-grain boundary introduction. [Display omitted] • Thin-wall debit of M951 alloy under 980 ​°C/90 ​MPa rupture test was systematically studied. • Surface intergranular cracks were the main cracks for thin specimen during rupture deformation. • Through-grain boundaries introduce by machining in thin specimens are detrimental for rupture property. [ABSTRACT FROM AUTHOR]

• Deal with the nonlinear term using product to sum formula for the first time. • Simulate the variation of elastic layer depth by sine wave. • Discretize the stresses in the J-integral loop to compute SIF. • Study the effect of vehicle-road coupled vibration on crack propagation. To reflect the characteristics of soil more accurately, an improved two-parameter foundation-plate model is built. A vehicle-road coupled model is modeled as a 2-DOF vehicle moving along a plate with finite length and width on a cubic nonlinear foundation. The variation of depth of elastic layer is modeled using sine wave. The Galerkin truncation method is used to discretize the partial differential equations into ordinary differential control equations. Using product to sum formula and introducing the Dirac delta function, the double integral term resulted from nonlinearity is removed. The effects of parameters from vehicle and foundation-plate on vehicle-road coupled model responses are studied. In addition, in order to analyze the influence of vehicle-road coupled vibration on crack propagation, initial cracks with certain length and width are set on the pavement. Using the J-integral Criterion of crack propagation, the stress intensity factors (SIF) of mode I and mode II cracks for mixed cracks are obtained through the stress on the discrete integral loop, and then the propagation path of surface crack of road is obtained. The propagation of the vehicle-road coupled model considering pavement crack, the vehicle-road coupled model without considering pavement crack and the traditional foundation-plate model are computed and compared. It can be found that the influence of vehicle-road coupled vibration for pavement crack can not be ignored. In short, the results presented in this paper realize the fast and accurate calculation of foundation-plate model described by ultra-high dimensional nonlinear ordinary differential equations, and then can realistically simulate the crack propagation path, which is helpful to better understand the cracking behavior of asphalt pavement. [ABSTRACT FROM AUTHOR]

In order to predict and assess creep life for plate structures with semi‐elliptic surface cracks under high temperature condition, the accurate calculation of the creep fracture mechanics parameter C* is a critical step. In this paper, the effects of crack sizes, plate geometries, and material creep properties on the parameter C* have been investigated under tensile and bending loads by extensive finite element analyses. Based on the results, the creep influence functions Hc for calculating C* values were obtained and fitted into equations for surface cracks in plates under both loads. The equations have been verified by finite element calculations. The C* solutions were obtained through these equations which are suitable for wide ranges of crack sizes, plate geometries, and materials. [ABSTRACT FROM AUTHOR]

Surface cracked steel plates reinforced with single-side Fiber-Reinforced Polymer (FRP) subjected to cyclic tension are experimental studied. The main purpose is to analyze the effect of FRP reinforcement on the crack growth. The failure modes and their effects are analyzed as well. Given the single-side reinforcement, reinforcing the cracked surface significantly prolonged the fatigue life, while reinforcing the reversed side resulted in the opposite consequence. Most specimens did not encounter debonding failures, indicating such failures are avoidable by improving the reinforcement quality. The results also indicate the bond layer number is an insensitive factor – an optimum number is existed. [ABSTRACT FROM AUTHOR]

Surface cracks are one of common forms of flaws in thin‐walled structures such as pressure vessels, oil, and gas pipelines. Accurate evaluation of the growth driving force of such surface cracks is important for integrity analyses of these structures. In this study, the combined effect of the depth and the length of a given surface crack under tension was analyzed using combined elastoplastic finite element analysis (EPFEA) and crack propagation experiments with selected crack shapes. Based on the consideration of the distribution profile of the J integral as the crack growth driving force along crack front, the crack growth stability with different crack shapes was analyzed. Finite element analysis (FEA) results showed that the growth from partial to through‐wall penetration is affected by the shape of the initial crack. As shown by the distribution profile of the J integral along the crack front, the location(s) of the maximum J, that is, the highest crack driving force, is (are) found to vary with the crack shape and development. [ABSTRACT FROM AUTHOR]

A finite element simulation analysis of micromagnetic signals of surface crack defects on a titanium (Ti) alloy plate was performed, and a verification experiment was designed. Simulation results showed that micromagnetic detection exhibited strong detection capability when used for crack defects with 0.15–0.6 mm widths. Good detection capability could be ensured if the detection lift-off height was controlled within 1 mm. The best detection effect was achieved when the angle of crack inclination was 90°. Micromagnetic detection was highly sensitive when the crack space between two adjacent independent crack defects was larger than 0.4 mm. Experimental results showed that the critical defect width of surface cracks in the Ti alloy was 0.6 mm. When the defect width was less than the critical value, the magnitude of magnetic anomaly increased with the increase in crack width, and the sensitivity of micromagnetic detection was enhanced. The experimental results were consistent with the simulation ones. Moreover, micromagnetic detection could accurately locate the surface crack defects of Ti alloy. The defect morphology could be visually displayed using 2D imaging on the basis of the magnetic gradient characteristics, but sufficiently accurate quantification of defect size remained a challenge. [ABSTRACT FROM AUTHOR]

The formation causes and oxidation behaviour of two types of small-sized and irregular morphological surface cracks on S355 hot-rolled thick plate were investigated. The study employed surface pickling, microstructure analysis and inclusion observation to characterise the cracks. It was observed that the surface morphology of two types of cracks exhibited similarities, while their subsurface morphology differed. The Type-A cracks displayed a bulge shape with a rounded tail, while the Type-B cracks had a V-shaped morphology with a slender tail. The Type-A cracks predominantly consisted of FeO. The surface part of the Type-B cracks contained unusual large-sized carbon particles and Al2O3 inclusions, and the iron oxides within the subsurface part followed the sequence of FeO–Fe2O3–Fe from the centre of the cracks to the steel matrix. It was observed that the Type-A cracks originated from subsurface bubbles in the continuous casting slab, which deformed and developed into surface cracks during the rolling process. The iron oxide inside these cracks was formed through a single oxidation process, and the bulge shape in the subsurface part was a distinguishing characteristic. The Type-B cracks were attributed to surface microcracks on the continuous casting slab, which were linked to the presence of unusual large-sized inclusions. The iron oxides within these cracks underwent two oxidation processes. The subsurface morphology and oxide characteristics are the significant features to identify these small-sized and irregular morphological cracks. [ABSTRACT FROM AUTHOR]

The free vibration of cracked functionally graded material (FGM) plate in fluid is investigated in this paper. The material components are supposed following the power law and formulated by the Voigt model. The Mindlin plate theory (MPT) including the shear deformation effect is established and the physical neutral plane is adopted to simplify the derivation due to the in-plane displacements of this plane assumed as zero. A massless linear rotational spring model (LRSM) is established to simulate the through-width surface crack. The hydrodynamic pressure at the fluid-plate interface is derived by the potential flow theory, and is regarded as the added mass of cracked FGM plate during the analyses of fluid-plate coupled vibration. The derivation and discretization of vibrational equations for cracked FGM plates in fluid are respectively achieved though the Hamilton's principle and differential quadrature (DQ) method. The frequencies and mode shapes are iteratively calculated with these values of the vacuum case. The influences of immersed depth, fluid density, gradient index, crack depth, crack location, length-to-width ratio, length-to-thickness ratio, and boundaries on vibration characteristics are conducted in the section of numerical results. The present vibration analyses of cracked structures can be applicable to avoid structural resonance and failure. [ABSTRACT FROM AUTHOR]

• Influence law of different electroshock treatment modes on crack healing was studied. • Energization time, current density, and crack angle affect the crack repair ability. • The mechanism of the microstructure regulation of the healing area was explored. • Tensile strength and fracture strain increased by 20.1% and 40.3%, respectively. • The healing mechanism of two-stage progressive atomic diffusion was revealed. The Ti-43.5Al-4Nb-1Mo-0.1B (TNM) alloy is prone to emerge surface cracks and other defects during processing and service, which will deteriorate the mechanical properties and fatigue life of the materials. In this work, a novel electroshock treatment (EST) for the surface crack repair and strengthening process has been proposed. Combined with near-in-situ experiments and theoretical analysis, the influence law and healing mechanism of different current densities and EST modes on the healing of surface cracks in the alloy were investigated. The scanning electron microscopy (SEM) near-in-situ observation reveals that the main factors influencing the healing of surface cracks relate to the time of energization, the current density, and the cracking angle. Meanwhile, the crack tip and locally bulging deflected positions are more likely to be healed in a short time under continuous EST mode and medium current density (75 A/mm2). The surface crack width at the calibration position decreases from 0.47 μm and 2.23 μm to 0 μm and 0.03 μm, respectively. The electron back scattered diffraction (EBSD) results show that the dislocation density increases around the surface crack healing area, and the dislocation density at the crack tip and away from the healing region is decreased and uniformly distributed after EST, which can further suppress the generation and propagation of the crack, resulting in a 20.1 % increase in tensile strength and a 40.3 % increase in fracture strain. Considering the coupling influence of the thermal and non-thermal effects of EST, a two-stage progressive atomic diffusion of thermal compressive stresses and crack bonding interfaces has been proposed to describe the evolution process of surface crack healing during EST. [ABSTRACT FROM AUTHOR]

• A method is developed for rapid detection and automatic identification of surface cracks. • A new approach for feature extraction is purposed to enhance the surface crack pattern and eliminate the interference of array spots. • The proposed method enables the accurate recognition of complex surface crack, further enhancing the performance of the crack detection of LAST. In this paper, a method for rapid detection and automatic identification of complex surface cracks based on laser array spots thermography with PCA-Frangi processing is developed. With the Laser Array Spots Thermography (LAST), a complex surface crack in a relatively large surface area can be detected rapidly. In addition, a novel approach utilizing the PCA-Frangi algorithm for feature extraction is proposed to enhance the imaging performance of surface cracks with complex morphology. The results show that the proposed method can extract the cracks and eliminate the interference of array spots to crack identification. Furthermore, this method effectively mitigates the impact of thermal inhomogeneity and thermal noise during the heating process. Finally, the crack features are automatically identified. The simulation and experimental results illustrated that the method enables the accurate recognition of complex surface crack characteristics, further enhancing the overall performance of the crack detection with LAST. [ABSTRACT FROM AUTHOR]

A series of fracture toughness and fatigue crack growth rate tests were performed on the X70 pipeline steel base and weld metals under 10 MPa of a natural/hydrogen gas mixture with 1% H2 blends. It is observed that the 10 MPa gas mixture with 1% H2 causes a significant reduction in the fracture toughness in both metals. The fatigue crack growth rates are markedly accelerated under the gas mixtures with 1 % hydrogen blend compared with the tests performed in ambient air. The obtained fracture parameters serve as inputs for fatigue life assessment analyses under the effect of a hydrogen-containing environment. The observed design fatigue life depends strongly only on the environmental conditions. The design fatigue strength of the structural pipeline exposed to hydrogen is much shorter than that under ambient air owing to the decrease in fracture toughness properties and acceleration of the fatigue crack growth rate. [ABSTRACT FROM AUTHOR]

Paris' law is a commonly used formula in the assessment of fatigue life of structures. In the present study, we sought to improve the accuracy of this law in marine engineering using a probability model to experimentally assess fatigue life. First, a fatigue crack growth test was performed using compact tension specimens made of marine high-strength steel to obtain a reasonable range of material coefficients C and m in Paris' law. The material coefficient m was then determined as a constant, C followed a log-normal distribution, and Paris' law with different probabilities dependent on C was established. Finally, the probability model based on Paris' law was used to calculate fatigue life of a welded component with a surface crack caused by combined compressive and bending stresses. The results were then compared with the data from a fatigue test that used a crack front marking technique to depict the fractography. The findings of this study show a linear relationship between log C and m that caused a mutual constraint of the material coefficients. In summary, the structure fatigue life calculated by the probability mode based on Paris' law is reliable, thus it can greatly improve safety and accuracy of fatigue life assessment in marine engineering. [ABSTRACT FROM AUTHOR]

This paper is focused on the interaction of surface cracks of an egg-shaped pressure shell of manned deep-sea submersibles. The surface cracks of the egg-shaped shell were subjected to the combined action of uniform external pressure and welding residual stress. The stress intensity factors were calculated using the M-integral method as an important parameter to characterize the stress and displacement fields in the vicinity of crack tips. The study is to evaluate the influence degree of the disturbing crack on the main crack and investigate the interaction between multiple cracks. The results provide references for optimizing the design and manufacture of egg-shaped pressure shells. [ABSTRACT FROM AUTHOR]

In the present paper, we develope a 3-D M srf -integral to evaluate the surface energy that is corresponding to formation of multiple surface cracks. The M srf -integral is formulated by modifying the conventional 3-D M-integral with deliberate origination of the coordinate system and proper delimitation of the integral surface. The integral is demonstrated to be surface-independent in a modified manner and so can be accurately evaluated provided an integration surface remote from the crack fronts is selected. With this feature, the theory of integration can be straightforwardly incorporated into the finite element method. In fact, it is not necessary to simulate the near-front regions with very fine FE simulations to obtain accurate solutions of M srf. [ABSTRACT FROM AUTHOR]

The effect of precooling on hot ductility of a low‐carbon steel is investigated. It shows a wide reduction of ductility in the temperature range of 700–900 °C with a general hot tensile test. The hot ductility is increased by applying precooling before the hot‐tensile test. The increase in the reduction of area (RA) reaches 40–50% when the steel is precooled to 500 °C. Active precipitation of (Mn, Cu)‐sulfide is observed during the precooling. The increased RA is attributed to the active sulfide formation, which decreases sulfur segregation at grain boundaries. [ABSTRACT FROM AUTHOR]

Quantitative evaluation of surface cracks using detection signal is of great significance for accurate prediction of cracks in eddy current testing. It is very difficult to evaluate both the width and depth of small cracks. A quantitative evaluation method based on Bayesian network is proposed for estimating the width and depth of surface cracks in the ferromagnetic materials. First, the simulation model of eddy current testing (ECT) is established and verified by the experimental results. Then, the variation of induced voltage with crack size is studied. Four feature points of real and imaginary part of induced voltage of the receiver coil are selected to characterize the crack size. Finally, a Bayesian network is applied to evaluate the crack size based on numerical simulation results. The evaluation results show that Bayesian network can accurately estimate the width and depth of small cracks. [ABSTRACT FROM AUTHOR]

In this study, a TE01 mode converter was developed to locate an axial crack on the inner surface of a metal pipe. Three-dimensional finite element simulation was conducted to evaluate the effect of inserted coaxial cables on the transmission characteristic of the mode converter. The result showed that the energy of TE mode microwaves leaned to transmit to one side when the cables penetrated with inclination. To demonstrate the effectiveness of the mode converter, experimental verification was conducted. The mode converter was fabricated based on the simulation result. Microwaves were emitted through the pipe wall of the converter to propagate on both sides ('right side' and 'left side') of a pipe with an artificial slit. Compared with the signals from each side, the reflection from the slit on the right side was more significant than that on the left side. This result is consistent with the numerical simulation result. [ABSTRACT FROM AUTHOR]

The laser array spot thermography (LAST) is a fully non-contact and non-destructive method for the inspection of surface cracks with high efficiency. In this study, the detection capability of this method for the inspection of surface cracks in structures with curved surfaces is experimentally studied. The influence of the inspection angle on the crack imaging results is also investigated. The experiment results show that cracks in surface of the pipes with different dimeters can be detected and imaged by LAST. [ABSTRACT FROM AUTHOR]

For a positive displacement motor (PDM), the threaded joint connecting drive shaft shell (DSS) and universal shaft shell that is close to the bit is inclined to fracture. In this paper, elastic-plastic fracture performance of the threaded connection is simulated under both make-up torque and bending moment. Firstly, an FE model, which includes a cracked external thread of the DSS and an engaging internal thread of the universal shaft shell, is established and validated. Secondly, influences of both plastic deformation and the helix angle on fracture properties of the cracked thread are evaluated quantitatively. Meanwhile interactions between two cracks are also discussed. Finally, under the two kinds of loading conditions, i.e. loaded by pre-load only and loaded by both pre-load and bending moment, explicit relationships between characteristic J-integrals and the crack depth are obtained for the DSS. [ABSTRACT FROM AUTHOR]

• A new method for obtaining ultrasonic inspection data of axle cracks is proposed. • The detection ability of UT equipment for axle crack is quantified for the first time. • Equivalent crack parameter is proposed to describe the location, area and direction. • The POD range of cracks with different depths was obtained. Obtaining the ultrasonic probability of the detection (POD) curve of railway hollow axle cracks through experiments in an effective way has always been a pending issue. A new method of obtaining ultrasonic testing data for railway hollow axles crack is proposed, which can obtain a large amount of detection data from a small number of specimens. A new equivalent crack parameter which can characterize the location, area and direction of cracks is proposed, and the POD curve is analyzed by using this parameter, quantifying the crack detection capability of ultrasonic detection equipment for the first time. The range of POD for different crack depths under in-service detection methods was calculated using semi-circular crack and chordal crack as the critical state of semi-elliptical crack, respectively. When the crack depth reaches 10 mm, the POD can reach more than 80% regardless of the shape of the crack. [ABSTRACT FROM AUTHOR]

Using cracked pipes design standards and finite element analysis, the limit load analysis for pipes containing surface cracks was determined. The study was performed on five pipes of different diameters with a constant crack length and depth. The crack geometry is a semi-elliptical surface crack. The cracked pipes are subjected to internal pressures which are obtained from formulas of cracked pipes design standards. Due to the ductile behavior of polyethylene pipes, the failure occurs when the critical stress reaches a value equal to the ultimate tensile strength multiplied by a constraint factor. In this work, the constraint factor was calculated and its evolution with the pipe diameter was analyzed. Three different definitions of a constraint factor based on global or local approaches were also compared, so that a new failure criterion can be obtained. The new failure criterion makes the prediction of the pipe residual life possible which, in turn, facilitates a systematic approach to maintenance and replacement of pipes. • Limit load analysis for pipes containing surface cracks was determined. • constraint factor was calculated and the pipe diameter was analyzed. • The results of the standards in terms of critical failure pressures, critical stresses and constraint factors are close to each other. • The constraint factor L∗ are always smaller than the values of factor L for all diameters and for all standards. • The deduced failure criterion based upon L∗enables the prediction of the remaining life of the studied pipes so that the maintenance and replacement works of drinking water pipes can be estimated [ABSTRACT FROM AUTHOR]

Thermo-mechanically treated (TMT) bars are used conventionally in RCC constructions. Due to the heat treatment, the TMT bars, achieve their desired property, i.e. tough core and hard surface. These rebars are inspected by cold bending test. Sometimes crack appears on the rebar's surface after cold bending. These cracks reduce the load carrying capacity of rebars and may lead to failure at stress levels much below the yield strength. Cracks on rebar surface were a major problem that causes great economic losses. Hence, it becomes imperative to study the cracking of TMT bars. To find the root cause of these cracks, detailed metallurgical investigation consisting of metallographic examination, scanning electron microscope and EDAX are carried out. Initiation and propagation such rib cracks vary significantly depending on the genesis of the defects whether the defect is generated at casting stage (due to subsurface blowholes and internal cracks) or rolling stage (due to rolling abnormalities). Detailed characterization of cracks has been carried out and root cause has been identified in this paper. The sources of the cracks are numerous, ranging from steel making stage to rolling stage. • Thermo mechanical treated rebar are used in RCC construction because of its special properties i.e. tough core and hard surface. These rebars are tested by cold bending test. The cracks can be found not only on the cold bending samples, but also prior to their bending during visual inspection. • The general cracking phenomenon in rebar have been represented as different cases in the current study. The cracking originates from inherent material defect which raised from problems associated to casting or rolling process at steel maker's end. However improper conditions in the downstream process, that is use of improper tool or dies while bending can also create quality issue. • In the current study rebar failure investigation includes chemical analysis, optical micrograph, hardness measurement, SEM-EDS as and when required. from this metallographic analysis we would tried to find out the root cause of the defect. Finally, five such different cases had been presented in the current paper to highlight the common cause for rib crack in the field of rebar manufacturing. [ABSTRACT FROM AUTHOR]

Aiming to improving the manual inspection process of the elevator compensation chain, an automatic vision inspection system for detecting surface cracks of the welding joint is presented. To this end, firstly, an image acquisition system is designed to make the gray level of cracks obviously distinct from background in the captured image, which can effectively simplify the image segmentation algorithm. Then, on the basis of enhancement and de-noising of ROI image, the threshold segmentation and morphological features determination are employed to meet the demands of detection accuracy and time efficiency under the complex background and noise interference. Experimental results demonstrate that the system has good adaptability to various cracks and has achieved good performance in detection accuracy and time efficiency. [ABSTRACT FROM AUTHOR]