Crack Shape Research Articles

Crack characterisation in a thin plate with unknown acoustic properties based on phase difference of Lamb wave propagation

ABSTRACT A method is presented to characterise a crack in a thin plate with unknown acoustic properties when the position of the acoustic source is approximately known. Due to the unknown source generation waveform, a method based on the phase difference of Lamb wave propagation is proposed to determine the propagation distance difference between two different direct Lamb waves and extract the propagation distances of crack-scattered Lamb waves. The acoustic properties are inverted by establishing their relationship with the dispersion degree of intersections between any two hyperbolas formed by direct Lamb waves, and these intersections determine the source position. The difference in amplitude of crack-scattered Lamb waves is used to distinguish reflections from diffractions, and both edge points and endpoints of the crack are identified using the ellipse method to estimate the crack location, size, and shape. Linear, arc-shaped, and kinked cracks in aluminium plates are experimentally verified using a line-scanning laser vibrometer to collect Lamb wave signals from an acoustic source that is generated by a PZT transducer installed on the plate. The results show that the obtained cracks agree well with the actual cracks in terms of location, size, and shape, with mean relative errors of less than 1.59%.

압력 조건 변화에 따른 수소 압력 용기의 균열 거동 및 안전성에 대한 연구

In this study, the fatigue lives of a 300-L high-pressure vessel and 1000-L medium-pressure vessel were determined using ANSYS. The maximum operating pressures were set at 83 and 50 MPa using SA-372 Grade J/Class 70 material. Considering the axisymmetric shape of the pressure vessels, crack shapes were established according to ASME Band PV code standards to evaluate the impact of internal cracks. The analysis results showed that the fatigue life of cracks oriented along the length was significantly shorter than that of circumferential cracks. A trend was observed in which the fatigue life increased as the crack depth decreased, and the fatigue life increased proportionally with the pressure differential. These findings provide crucial information for assessing the safety of pressure vessels and clearly demonstrate the effects of the crack size and operating pressure range on the fatigue life. The results of this study can serve as a foundationfor enhancing the safety of pressure vessels.

Crack shape evolution of single edge through cracked specimens under mode-I loading

Crack shape evolution of single edge through cracked specimens under mode-I loading

Merging behaviour and fatigue life evaluation of multi-cracks in welds of OSDs

Experimental studies were conducted to investigate the merging behaviour of multiple fatigue cracks (MFCs) in rib-to-deck welds of orthotropic steel decks (OSDs). Numerical simulations were conducted to investigate the mechanism of the merging behaviour of MFCs on fatigue life. In addition, the sensitive parameter in the MFCs affecting the fatigue life were revealed. Finally, a comprehensively failure criterion for MFCs was proposed. Results show that the merging behaviour of MFCs can be effectively observed by the beach marks on the fracture surface of the rib-to-deck weld. The merging behaviour is a key factor driving cracks penetrating through the deck, which significantly increases the crack length and decreases the crack shape ratio. The fatigue life of MFCs with different crack sizes is mostly determined by the larger crack, while the shape ratio effect can be ignored. The crack number has the most significant effect on fatigue life, where the five-cracks case reducing the fatigue life by up to 39 % compared to a single crack. Due to the nonlinear effect of crack spacing on fatigue life, MFCs with the same fatigue life may have significantly different final crack length. Therefore, the proposed failure criterion for MFCs considers the effects of both crack depth and length.

High-Cycle Fatigue Fracture Behavior and Stress Prediction of Ni-Based Single-Crystal Superalloy with Film Cooling Hole Drilled Using Femtosecond Laser

A high-temperature, high-cycle fatigue test was conducted on a nickel-based single-crystal superalloy with a pore structure. Optical and scanning electron microscopy were utilized to examine the crack propagation paths and fatigue fracture surfaces at the macro and micro scales. The analysis of crack initiation and propagation related to the pore structure facilitated the development of a crack shape factor reflecting these distinct fracture behaviors. Predictions about the high-cycle fatigue stress experienced by the specimen were made, accompanied by an error analysis, providing critical insights for precise stress calculations and structural optimization in engine blade design. The results reveal that high-cycle fatigue cracks originate from corner cracks at pore edges, with the initial propagation displaying smooth crystallographic plane features. Subsequent stages show clear fatigue arc patterns in the propagation zones. The fracture surface exhibits the significant layering of oxide layers, primarily composed of NiO, with traces of CoO displaying columnar growth. AL2O3 is predominantly found at the interfaces between the matrix and oxide layers. Short and straight dislocations near the oxide layers and within the matrix suggest that dislocation multiplication and planar slip dominate the slip mechanisms in this alloy. The orientation of the fracture surface is mainly perpendicular to the load direction, with minor inclined facets in localized areas. Correlations were established between the plastic zone dimensions at the crack tips and the corresponding fatigue stresses. Without grain boundaries in single-crystal alloys, these dimensions are easily derived as parameters for fatigue stress analysis. The selected crack shape factor, “elliptical corner crack at pore edges”, captures the initiation and propagation traits relevant to porous structures. Subsequent calculations, accounting for the impact of oxide layers on stress assessments, indicated an error ratio ranging from 1.00 to 1.21 compared to nominal stress values.

Numerical simulation of fracture patterns in roof strata with different thicknesses

Roof breaking is the root cause of rock burst and mine earthquake. However, the classical “thin plate theory” and “thick plate theory” cannot fully reveal the mechanical mechanism of the influence of roof thickness-span ratio on the fracture mode. In this paper, based on the cohesive element technology, the mechanical behavior of cohesive element failure was studied according to the maximum nominal stress criterion and BK fracture criterion, and the fracture mechanical behavior of roofs with different thicknesses fixed on four sides under uniform load was numerically simulated. The fracture pattern and the maximum principal stress evolution laws of roofs with different thicknesses were obtained. The results show that there are three fracture modes of the plates with different thickness: pure tensile fracture mode at the bottom surface, mixed fracture mode around the “X” shape crack, and pure shear fracture mode along the long edge boundary. The crack morphology of thin plate is the transverse “O−X” type, and the crack morphology of thick plate is the “O−❋” type. With the increase of thickness, the tensile-shear mixed failure mode gradually changes from the tensile dominant to the shear dominant.

Study on the surface state induced by ultrasonic impact treatment and its influence on high-temperature tension-tension fatigue behavior

To reveal the influence of ultrasonic impact treatment (UIT) parameters on surface state and the influence of surface state on high-temperature tension-tension fatigue behavior, UIT tests were conducted and 400 ℃ high-temperature fatigue tests were performed on UIT specimens with different surface states. The relationship between surface state and process parameters was analyzed, and the fatigue failure mechanism of UIT specimens was revealed. The finite element method was used to explore the influence of different residual stress distributions on the distribution of stress intensity factors at the crack front and the evolution of crack shape. The results show that the surface roughness changes between 0.43 μm and 0.72 μm with the variation of UIT intensity. As the increase of UIT intensity, the maximum residual stress can reach −1085 MPa, located approximately 30 μm below the surface. And the corresponding maximum surface hardness can reach 561 HV0.025. Microstructure elongation and extrusion intensification results in a maximum deformation layer depth of 9 μm, with a nanocrystalline layer on the outermost surface. The maximum average fatigue life is 6.431×106 cycles and the cracks initiate under the surface with quasi-cleavage as the initiation mode. As the cracks deepen, the stress intensity factor increases, and the crack shape eventually tends to be circular. Alterations in residual stress amplitude and depth do not influence the final crack shape. However, increased amplitude and depth can accelerate the consistency of the stress intensity factor outside the compressive stress region.

Investigations on the fracture mechanisms of Z-shaped fissured rock-like specimens

Complex shapes of cracks exist in natural rock masses, however, present research has simplified it into straight line-shaped fissures. In view of this, three-dimensional (3D) printing is employed to make Z-shaped fissured specimens with different main fissure angle α and secondary fissure angle β. The compress fracture experiments are conducted, and full-field strain distributions during crack propagations are obtained using Digital Image Correlation (DIC) technology. Traditional Smoothed Particle Hydrodynamics (SPH) method is improved to examine damage process as well as fracture mechanisms in Z-shaped fissured specimens. It can be concluded that: Wing Crack (WC), Main Crack (MC), Outer Crack (OC) and Inner Crack (IC) are observed in the experiment. The secondary fissure angle β guides the initiation of MC, while the main fissure angle α guides the initiation of WC. Stress–strain curve of 3D printing samples with Z-shaped fissures shows similar trends to that of real rock, experiencing four typical parts. Numerical results show high similarities with experimental results. We have also discussed the crack initiation mechanisms in various main fissure angle α and secondary fissure angle β in the end, and concluded the stress distribution characters. The findings of this research will offer some references for correct understanding of the crack evolution processes and fracture mechanics of Z-shaped fissured rock masses.

Effect of pavement layer temperature on fatigue performance of rib-to-deck weld details in orthotropic steel bridge decks

To investigate the effect of asphalt pavement layer temperature on the fatigue performance of welded details in orthotropic steel bridge deck (OSD), this study focuses on the critical fatigue crack regions of the rib-to-deck weld details. A systematic study was conducted based on the theory of linear elastic fracture mechanics (LEFM) and the finite element model (FEM). In this research, the elastic modulus of the pavement layer at different temperatures, and the initial crack shape, were considered as parameters. The maximum normal stress, stress intensity factor (SIF), and fatigue crack growth (FCG) shape and life of the weld details under the influence of these parameters were analyzed. The analysis results indicate that using a constant temperature of 20°C for the pavement layer will ignore the adverse effects of high summer temperatures. Under the influence of the pavement layer temperature effects, the weld toe of the top deck is the most critical welded detail. The FCG life and final crack shape at the weld toe of top deck are closely related to the effects of pavement layer temperature and the initial crack shape, higher pavement layer temperatures result in shorter fatigue life and larger final crack propagation sizes. Therefore, it is recommended that pavement layer and temperature effects be considered in the FCG analysis of welded details in OSDs.

Lifetime fatigue cracking behavior of weld defects in orthotropic steel bridge decks: Numerical and experimental study

Orthotropic steel decks (OSDs) are welded structures prone to weld defects, increasing the risk of fatigue fracture. It is crucial to clarify the fatigue evolution mechanism of weld defects throughout the entire lifecycle. In this study, the fatigue propagation behavior of weld defects is investigated from the hidden stage to final fracture. Firstly, a full-scale segmental OSD model with prefabricated defects was utilized to investigated fatigue propagation behavior of surface cracks. Secondly, stress intensity factors (SIFs) of welding defects throughout the entire process were simulated using a refined finite element model. Finally, the crack shape evolution and fatigue life were analyzed at different fatigue stages. The research identifies three stages in the fatigue evolution of hidden defects: the hidden defect stage, the initiation stage of surface crack, and the propagation stage of surface crack. Regardless of the initial aspect ratios, hidden defects evolve into a circular, while surface defects evolve into a flattened semi-ellipse. Compared to the propagation life of surface cracks, the hiding life of cracks account for a significantly larger proportion of the total life, and this proportion increases with both the initial aspect ratio and the hidden depth of the defects.

Automated repair of asphalt pavement cracks and potholes utilizing 3D printing and LiDAR scanning

This study introduces a method for automatic repair of asphalt pavement cracks and potholes using 3D printing and LiDAR scanning. A scanning method was developed to accurately detect and represent cracks and potholes in a 3D model. To address the limitations of LiDAR scanning, such as missing data points caused by the irregular shapes of cracks and potholes, the screened Poisson method was applied to reconstruct the missing data points. These models were validated through both theoretical calculations and sand test. In addition, the research focuses on optimizing key 3D printing parameters, such as printing temperature and printing speed, to enhance performance of crack repair throughout semi-circular bending test. Direct tensile strength test was employed to assess the impact of waste materials (e.g., rubber tire powder and waste glass) on the bond strength of filled sample. The results indicated a volume difference of 2–5 % between the scanning method and the sand test method, demonstrating high accuracy in detecting and reconstructing 3D cracks/potholes. Binders modified with 10 % rubber tire powder, or 20 % waste glass exhibited the highest tensile strength of 212 kPa and 207 kPa, respectively. However, using more than 30 % waste materials is not recommended due to a significant reduction in bond strength compared to conventional binders. An optimal 3D printing speed of 180 mm/min and a temperature of 117 °C are recommended for use in 3D printing in laboratory conditions. It was also noted that higher printing speeds decrease indirect tensile strength, highlighting the importance of balanced parameter settings.

Study on non-destructive visualization identification of concrete internal cracks based on SH array ultrasound

Ultrasonic nondestructive testing (NDT) technology was one of the most frequently used and fastest-developing NDT techniques in detection field. This method had high detection sensitivity, more accurate defect localization, and was harmless to the human body. With the development of ultrasonic testing technology, modern ultrasonic imaging technology generally had automatic data acquisition and processing functions, which allowed for intuitive and clear recognition of internal defects by the human eyes. The overall purpose of this study was to visualize the cracks in concrete by synthetic aperture focusing technique (SAFT) and full-waveform inversion (FWI) algorithms on the basis of ultrasonic nondestructive testing technology. At present, there have been studies on the use of ultrasonic instruments to detect the internal defects of concrete. However, the accuracy and authenticity of this method have not been compared in previous studies. Therefore, in this experiment, four concrete specimens with different buried depths, angles, shapes, and thicknesses of cracks were designed. Based on SH ultrasonic wave NDT technology, two types of operations were performed on the collected ultrasonic wave data: one was the application of SAFT method, and the other was the first application of FWI method for detecting internal cracks in concrete. The study found that both algorithms were most accurate in determining the burial depth of cracks, with error results not exceeding 10 %. They also showed good recognition effects for the angle, shape, and thickness of the buried cracks. This proved that both identification methods had the capability to recognize internal cracks. The Introview software bundled with the ultrasonic instrument could identify cracks using SAFT directly and quickly. When FWI was used with MATLAB computation, the results were more precise and intuitive. The overall purpose of this study was to detect cracks in concrete by SAFT and FWI algorithms on the basis of ultrasonic nondestructive testing technology. Combining the two crack identification techniques could be of great significance for ensuring the long-term safety and stability of concrete structures, providing strong support for structural maintenance and reinforcement.

Crack Detection, Classification, and Segmentation on Road Pavement Material Using Multi-Scale Feature Aggregation and Transformer-Based Attention Mechanisms

This paper introduces a novel approach to pavement material crack detection, classification, and segmentation using advanced deep learning techniques, including multi-scale feature aggregation and transformer-based attention mechanisms. The proposed methodology significantly enhances the model’s ability to handle varying crack sizes, shapes, and complex pavement textures. Trained on a dataset of 10,000 images, the model achieved substantial performance improvements across all tasks after integrating transformer-based attention. Detection precision increased from 88.7% to 94.3%, and IoU improved from 78.8% to 93.2%. In classification, precision rose from 88.3% to 94.8%, and recall improved from 86.8% to 94.2%. For segmentation, the Dice Coefficient increased from 80.3% to 94.7%, and IoU for segmentation advanced from 74.2% to 92.3%. These results underscore the model’s robustness and accuracy in identifying pavement cracks in challenging real-world scenarios. This framework not only advances automated pavement maintenance but also provides a foundation for future research focused on optimizing real-time processing and extending the model’s applicability to more diverse pavement conditions.

Thermal shock behavior of andalusite‐based refractories: Microstructural investigation of crack bridging and grain‐matrix interactions

AbstractAndalusite‐based refractories are characterized by superior thermal shock resistance. Although the demand for alternative raw materials is increasing, it is proving difficult to replicate the thermal shock behavior of andalusite with alternative materials. The physico‐mechanical properties of andalusite refractories are well‐studied. However, comprehensive chemical and microstructural analysis is still needed to fully understand factors influencing the thermal shock resistance. This investigation highlights the use of complementary microstructural techniques (3D digital microscopy, scanning electron microscopy–energy‐dispersive X‐ray spectroscopy, and micro‐X‐ray fluorescence) to analyze crack propagation as well as glass bridge formation and composition in aluminosilicate‐based refractory castables. Andalusite‐based refractories are compared with chamotte 45 and chamotte 60, before and after a thermal shock, as well as after an additional firing. Factors influencing the thermal shock resistance of aluminosilicate refractory castables include (1) crack shape, size, occurrence, and propagation (2) glass bridge formation, size, occurrence, and composition, and (3) aggregate‐matrix interactions.

Effect of geometric parameters on dynamic fracture toughness of compact tensile specimens

In this paper, the dynamic fracture toughness test and numerical simulation of CT specimens of 2A12-T4 aluminum alloy were carried out by using strain gauge method and finite element method based on Hopkinson tensile bar experiment device. The influence of crack transverse shape, loading hole size and dimension on the dynamic fracture performance of CT specimens was explained. The experimental and simulation results show that for CT specimens with different internal cracks, the time to reach stress equilibrium at the same tensile stress wave loading is roughly the same, while the time of initial cracking varies slightly. The dynamic fracture toughness obtained by concave arc-shaped internal crack and straight line-shaped internal crack is basically the same, while other changes in crack shape have a large impact. For CT specimens with straight line-shaped cracks, the position of the loading hole has a small effect on the dynamic fracture of the CT specimen under the same tensile stress wave. However, when the position of the loading hole is fixed, changing the diameter of the loading hole has a significant effect on the dynamic fracture toughness of the CT specimen.

Effects of Surface Crack Shape on Fracture Behavior of Oil Pipelines Based on the MMC Criterion.

This study employs a hybrid numerical-experimental calibration method based on phenomena to determine the fracture parameters of the Modified Mohr-Coulomb (MMC) model. Using a self-developed VUMAT subroutine and the element deletion technique, the fracture process of a wide plate pipeline is thoroughly analyzed. This study investigates the impact of various crack shapes on the fracture response under tensile loading and the influence of surface crack size on the initiation location of a wide plate. These results demonstrate the calibrated MMC fracture model's accurate prediction of the toughness fracture behavior of X80 pipeline steel. Under equal area conditions of the dangerous section, circular cracks exhibit lower bearing capacity compared to elliptical cracks. Elliptical cracks predominantly propagate in the thickness direction, whereas circular cracks show nearly uniform growth in all directions. Furthermore, when the crack depth is less than half of the wall thickness, the damage accumulation value at the midpoint of the crack front is maximized; conversely, when the crack front is closer to the internal measurement point of the wide plate, the damage accumulation value is maximized.

Evaluation of hair surface structure and morphology of patients with lichen planopilaris (LPP) by atomic force microscopy (AFM).

Lichen planopilaris (LPP) is a chronic lymphocytic skin disease manifested by progressive scarring alopecia. The diagnosis of LPP is made based on histopathological examination, although it is not always definite. The current study evaluates the effectiveness of non-invasive atomic force microscopy (AFM) hair examination in detecting morphological differences between healthy and diseased hair. Here, three to five hairs from lesional skin of 10 LPP patients were collected and examined at nine locations using AFM. At least four images were taken at each of the nine sites. Metric measurements were taken and metric (length, width, and scale step height) and morphological features (striated and smooth surface of scales, the presence of endocuticle and cortex, shape of scales edges, scratches, pitting, cracks, globules, and wavy edge) were compared with hair from healthy controls. In addition, areas on diseased hair where the process of pathological, unnatural delamination of the hair fiber occurs are described. There was a statistically significant difference in the number of scratches in the initial sections of the LPP hair, in the intensity of wavy edges along the entire length of the tested hair, and in the number of scales with pitting in the middle section of the hair. In addition, a statistically significant higher number of scales with striated surface was found in LPP group starting at 3.5cm from the root continuing towards the free end of the hair. Other morphological changes such as presence of cortex, globules, oval indentations, and rod-like macrofibrillar elements were also assessed, however, detailed results are not presented, as the differences shown in the number of these morphological changes were not significantly different. This publication outlines the differences between virgin, healthy Caucasian hair, and the hair of LPP patients. The results of this study can be used for further research and work related to LPP. This is the first attempt to characterize the hair of LPP patients using AFM.

Experimental and analytical study on non-tip initiation behavior of three-dimensional non-planar cracks in rock-like materials

The presence of fractures, joints, bedding planes, and faults within rock masses results in their inherent heterogeneity and discontinuity. These structural defects alter the mechanical properties of rock masses, reducing their structural strength and stiffness, and contributing to anisotropy. In addition to planar cracks, non-planar cracks are frequently found within rock masses due to geological evolution and local stress variations. While the mechanisms of planar crack propagation and fracture in both two-dimensional and three-dimensional spaces have been extensively studied and understood, research on non-planar cracks has largely been confined to two-dimensional aspects. This study addresses the limitations by successfully creating brittle solid specimens with three-dimensional non-planar internal cracks. Uniaxial compression tests and numerical simulations were conducted to investigate the propagations and fracture behaviors of various shapes of three-dimensional non-planar internal cracks. The experiments identified two primary macroscopic failure modes: symmetric non-planar internal cracks exhibiting non-tip initiation failure, and asymmetric non-planar internal cracks displaying tip initiation on the upper side and non-tip initiation on the lower side. The failure strengths of non-planar internal cracks were significantly higher than those of planar cracks, and the size of the cracks had minimal effect on their failure strengths. Notably, from initiation to failure, symmetric non-planar internal cracks did not generate any wing cracks, whereas asymmetric non-planar internal cracks were accompanied by petal-shaped cracks, wing cracks, and lance-shaped cracks. Under uniaxial compression, non-planar internal cracks propagated at extremely high speeds, resulting in rough and uneven fracture surfaces. In addition to Type III lance-shaped cracks, dynamic fracture characteristic areas and Wallner lines were also observed on the fracture surfaces. This study provides valuable insights into the fracture behavior of three-dimensional non-planar cracks and a reference basis for understanding their propagation and failure mechanisms.

Concrete Surface Crack Detection Algorithm Based on Improved YOLOv8.

Concrete surface crack detection is a critical research area for ensuring the safety of infrastructure, such as bridges, tunnels and nuclear power plants, and facilitating timely structural damage repair. Addressing issues in existing methods, such as high cost, lengthy processing times, low efficiency, poor effectiveness and difficulty in application on mobile terminals, this paper proposes an improved lightweight concrete surface crack detection algorithm, YOLOv8-Crack Detection (YOLOv8-CD), based on an improved YOLOv8. The algorithm integrates the strengths of visual attention networks (VANs) and Large Convolutional Attention (LCA) modules, introducing a Large Separable Kernel Attention (LSKA) module for extracting concrete surface crack and local feature information, adapted for features such as fracture susceptibility, large spans and slender shapes, thereby effectively emphasizing crack shapes. The Ghost module in the YOLOv8 backbone efficiently extracts essential information from original features at a minimal cost, enhancing feature extraction capability. Moreover, replacing the original convolution structure with GSConv in the neck network and employing the VoV-GSCSP module adapted for the YOLOv8 framework reduces floating-point operations during feature channel fusion, thereby lowering computational complexity whilst maintaining model accuracy. Experimental results on the RDD2022 and Wall Crack datasets demonstrate the improved algorithm increases in mAP50 by 15.2% and 12.3%, respectively, and in mAP50-95 by 22.7% and 17.2%, respectively, whilst achieving a reduced model computational load of only 7.9 × 109, a decrease of 3.6%. The algorithm achieves a detection speed of 88 FPS, enabling real-time and accurate detection of concrete surface crack targets. Comparison with other mainstream object detection algorithms validates the effectiveness and superiority of the proposed approach.

Influence of crack configurations of asphalt mortar on the loading response characteristics of cracks under low-temperature conditions

Asphalt mortar is the base material used in asphalt concrete, and its mechanical properties directly affect those of the prepared asphalt concrete. An analysis of the loading response characteristics of cracks in asphalt mortar under low-temperature conditions can help reveal the interaction effect of multiple cracks in asphalt concrete and the influence mechanism of aggregates on the crack propagation and evolution behaviors. In this study, various forms of pre-cracks were generated in asphalt mortar specimens using the water jet cutting technology. Combined with the discrete element method (DEM), an indirect tensile (IDT) test and a virtual IDT test were conducted to analyze the effects of the crack deflection angle (β) and crack length (r) on the crack propagation behavior from macro- and meso-perspectives. The main results showed that: (1) Changes in the crack shape parameters (β and r) not only induced multiple branch cracks in the asphalt mortar but also led to the development of II Mode fractures; (2) With the increase in the crack shape parameters, the low-temperature crack resistance of the asphalt mortar decreased, with β having a greater effect on the crack propagation behavior than r; (3) At the mesoscale, with the increase in the crack shape parameters, there was a gradual transformation of the fracture mode from I Mode to II Mode, and the crack propagation process accelerated, resulting in a significant decrease in the low-temperature crack resistance at the macroscale. The research results establish a theoretical foundation for revealing the characteristics of multi-crack propagation in asphalt concrete under environmental influences, and offer technical support for pavement crack repair and maintenance.