Crack Position Research Articles

Influence of tension cracks on moisture infiltration in loess slopes under high-intensity rainfall conditions

Loess slopes with steep gradients are particularly prone to vertical tension cracks at the crest, resulting from unloading and other factors. These cracks significantly affect the spatiotemporal distribution of moisture infiltration during rainfall, potentially leading to slope instability. This study investigates the impact of crest-tension cracks on moisture infiltration in loess slopes under extreme rainfall conditions, focusing on crack position, depth, and width. Soil moisture content and the dynamics of wetting fronts were monitored to assess how these tension cracks influence infiltration patterns. The results indicate that tension cracks at the slope crest act as preferential infiltration pathways, causing water retention within the cracks and forming a “U-shaped” preferential infiltration zone. The extent of this “U-shaped” wetting front is influenced by the crack’s width, depth, and proximity to the slope shoulder; wider, deeper cracks closer to the shoulder result in a more pronounced wetting front. Over time, as rainfall persists, the influence of preferential infiltration decreases, and the infiltration patterns of slopes with crest cracks begin to resemble those of homogeneous slopes. In both cases, wetting fronts exhibit intersecting patterns: one parallel to the slope crest and the other parallel to the slope surface. During the initial stages of rainfall, the migration speed of wetting fronts in slopes with crest-tension cracks was significantly higher than in homogeneous slopes. However, after prolonged rainfall, the migration speeds of wetting fronts in both scenarios converged. A strong linear correlation was observed between the average migration depth of the horizontal wetting front at the slope crest and the parallel wetting front on the slope surface, for both slope types. These findings deepen our understanding of moisture migration dynamics in loess slopes with crest-tension cracks, providing insights for developing effective slope hazard mitigation strategies.

Effect of Initial Crack Position on Low‐intensity Impact Ignition Performance of Solid Propellant

ABSTRACTThe micro‐crack defects produced in the process of storage and use of solid propellants have an important influence on the safety of solid propellants. In this study, the low‐intensity impact ignition performance of crack‐containing hydroxyl‐terminated polybutadiene (HTPB) propellant was studied. According to the typical HTPB solid propellant formula, the mesoscopic models of defect‐free HTPB propellant and HTPB propellant with different crack positions were established. The Cohesive element was inserted globally. The friction heat generation inside the material and microcracks, the deformation heat generation of ammonium perchlorate (AP) particles and the exothermic reaction of AP particles were considered. The drop hammer impact process of HTPB propellant with crack defects was simulated, and the influence of initial crack position on the low‐intensity impact ignition response time of solid propellant was studied. The results show that the ignition response time of the defect‐free HTPB propellant is 0.38 ms, and the ignition temperature is 621 K; the ignition time of HTPB propellant with crack defects in AP particles, interface, and matrix is 0.33, 0.34, and 0.36 ms, respectively. The ignition temperature is 578, 584, and 597 K.

Numerical Study on the Static Bending Response of Cracked Wind Turbine Blades Reinforced with Graphene Platelets.

With the growing demand for wind energy, the development of advanced materials for wind turbine support structures and blades has garnered significant attention in both industry and academia. In previous research, the authors investigated the incorporation of graphene platelets (GPLs) into wind turbine blades, focusing on the structural performance and cost-effectiveness relative to conventional fiberglass composites. These studies successfully demonstrated the potential advantages of GPL reinforcement in improving blade performance and reducing the blade's weight and costs. Building upon prior work, the present study conducts a detailed investigation into the static bending behavior of GPL-reinforced wind turbine blades, specifically examining the impact of crack location and length. A finite element model of the SNL 61.5 m wind turbine blade was rigorously developed and validated through comparison with the existing literature to ensure its accuracy. Comprehensive parametric analyses were performed to assess deflection under various crack lengths and positions, considering both flapwise and edgewise bending deformations. The findings indicate that GPL-reinforced blades exhibit reduced sensitivity to crack propagation compared to traditional fiberglass blades. Furthermore, the paper presents a thorough parametric analysis of the effects of crack location and length on blade performance.

Simulation of cohesive fracture method in concrete structures

The objective of fracture mechanics is to analyze the materials behavior and its failure modes applied to structures. Thereby, it is possible to identify the parameters that impact directly on crack evolution. Geometry, loading, and material properties are examples of crucial failure factors. There are some existing methods to analyze structural collapses, but the cohesive fracture is well known because of its efficiency, being used to calculate many different engineering materials. This paper uses the fundamental concepts of cohesive fracture to link experimental and numerical data. In other words, this paper aims to study two different concrete structures in which were applied cohesive fracture method and then compare the theoretical results with experimental ones. Moreover, some parameters such as crack position, width, thickness, and fracture energy, were defined by finite element analyses. In general, the obtained results show conformity between both simulations.

Analysis and Research on the crack of a type of pressed PBX column

Abstract In this paper, aiming at the crack found in a type of press loaded PBX column during ammunition charging, in order to reveal the cause of the crack, the industrial CT nondestructive testing technology was used to scan and analyze the column. The results shown that there was a bulge on the column surface in the crack area, and the internal structure of the bulge was a clearance surface parallel to the outer surface of the column; The finite element method was used to simulate the stress distribution in the pressing process of explosives and the stress after the column collides with the rigid plane. The simulation results of the pressing process shown that the stress concentration area and the area with the first plastic deformation were not at the crack position, but at the corner of the central hole; The rigid plane simulation results of column collision shown that the stress wave propagates in the axial and radial direction, which was consistent with the crack morphology and crack propagation direction on the surface of explosive column, and also matches the internal morphology of column crack. Through comprehensive analysis and judgment, the crack of the pressed PBX column was more likely to be caused by external force collision, and the probability of being caused by internal stress was very small.

Effects of Beads and Shot Peening Intensity on the Surface Integrity and Fatigue Performance of a Stainless Gear Steel

Shot peening was performed on stainless gear steel using multiple kinds of beads at multiple intensities. The effects of shot peening on surface integrity and the rotational bending fatigue performance were tested with the crack origin location observed. The results showed that the average surface roughness increases from Sa0.408 μm to Sa1.165 μm as the shot peening intensity increases, which does not necessarily lead to an increase in surface stress concentration coefficient. The compressive residual stress profile and the depth of the hardened layer increase with the increase of shot peening intensity. During ceramic bead peening, the fatigue improvement, with a maximum of 25 times, increases with the raise of intensity (0.06–0.20 mmA), while the fatigue improvement decreases when intensity (0.2–0.30 mmA) increases using cast steel shot. Based on ceramic shot peening, a method was proposed to predict the origin location of rotational bending fatigue cracks of gear stainless steel, in which the effects of surface stress concentration, compressive residual stress, and external load introduced were all considered. By using the superposition method of external load and residual stress, the maximum actual stress corresponding depth is obtained, which is the origin position of the rotational bending fatigue crack.

Calculation method for brittle fracture of functional gradient materials

Combined the phase field model with the wavelet dummy node-virtual crack closure technique (WDN-VCCT) used for stress intensity factors (SIFs) calculation. Calculated the node displacement using an improved brittle fracture phase field method, established the relationship between node displacement and node force using WDN-VCCT, and calculated the SIFs at the crack tip. The correctness and accuracy of the proposed method were verified through functional gradient material (FGM) tensile experiment. The influence of crack inclination angle, crack position and gradient index on mechanical response, and SIFs values at the crack tip was discussed. This study provides important computational tools for estimating the service life of FGMs and important references for structural optimization design methods.

Use of deep learning and data augmentation by physics-based modelling for crack characterisation from multimodal ultrasonic TFM images

ABSTRACT In this article, we study a machine learning-based approach for characterising crack-like defects in specimens with complex geometries using the multi-modal total focusing method (M-TFM) applied to ultrasonic full matrix capture (FMC) data. In particular, this work frames into a scientific machine learning perspective leveraging the use of physics-based numerical solvers as an efficient yet accurate data augmentation strategy. Toward this end, the numerical simulations have been tailored to built a suitable data set aiming at gathering the uncertainties in M-TFM images encountered when the reconstruction parameters are barely known. That is, the use of such a physical knowledge has been exploited to train a deep convolutional neural network designed for retrieving crack size and position based on multi-modal TFM images. Furthermore, for validating the learning proposed scheme, an experimental campaign has been also carried out accordingly to the most relevant factors that typically impact the quality of reconstructed M-TFM images. The developed approach has been tested on both synthetic and experimental data sets never shared in the training phase.

Monitoring soil cracking using OFDR-based distributed temperature sensing framework

Soil cracking induced by extreme drought represents a widespread natural phenomenon occurring across the earth surface, capable of triggering multiple weakening mechanisms within surface soils, potentially leading to the instability and failure of slopes and agricultural infrastructures. This study proposes an innovative geophysical monitoring framework for detecting field soil cracking by combining the actively heated fiber-optic (AHFO) method and distributed fibre optical sensing (DFOS) based on optical frequency domain reflectometry (OFDR) technique, referred to as AH-OFDR framework. Laboratory calibration tests, field monitoring tests, numerical simulations, and sensitivity analyses were employed to comprehensively evaluate the feasibility, effectiveness, and limitations of the AH-OFDR framework for soil crack monitoring. Laboratory calibration confirmed that the DFOS-OFDR technique achieves a minimum spatial resolution and readout accuracy of 1 mm, along with a temperature measurement accuracy of ±0.1 °C. Field monitoring verified that the AH-OFDR framework can accurately detect soil cracks ranging in width from 0.01 m to 0.12 m. Additionally, numerical simulations not only validated the effectiveness of the AH-OFDR framework across a broader range of crack widths, from 0.01 m to 0.50 m, but also established a quantitative relationship between temperature changes and the spatial distribution of crack positions and widths. Notably, a critical crack width threshold of 0.30 m was identified within the AH-OFDR framework, significantly impacting the prediction of soil crack widths. Sensitivity analysis demonstrated the remarkable crack detection capabilities of the AH-OFDR framework, irrespective of the soil crack width and spacing. The AH-OFDR framework holds substantial potential as an innovative and high-resolution observational method for advancing our understanding of diverse geological and hydrogeological processes.

A novel damage index for crack identification of a drilling riser during deployment based on the modal vibration energy flow

Early detection of structural damage especially small cracks in marine deepwater drilling risers is of paramount importance. Small cracks are always hard to detect because of weak vibration signals if using traditional damage indices, such as natural frequencies and mode shapes including modal displacements, cross-section slopes, and curvatures. Especially when the deepwater riser is during deployment, the variable suspension riser length and strong sea environment noise make the small crack identification more difficult. To address this problem, this study formulates a new concept of damage detection by integrating the vibration energy flow theory into the vibration-based damage detection (VDD) technique. A novel damage-sensitive feature (DSF) named modal vibration energy flow (MVEF) is established for detecting and locating the small cracks in deepwater drilling risers. The capability of the approach is verified by using the same riser model and the numerical results in the literature. The sensitivities versus crack positions and depths, variable suspension riser length, and sea noise are studied in detail. Results show that the proposed index MVEF is more sensitive than the classic traditional DSFs, i.e., modal slope, modal strain (or curvature), and modal strain energy. In total, the MVEF approach can accurately identify the small cracks and is robust against noise interference, suitable for detecting and locating small cracks in the deepwater drilling riser during deployment.

Analysis of tooth root three-dimensional fatigue crack initiation, propagation, and fatigue life for spur gear transmission

The gears in aviation gear systems are susceptible to fatigue fracture due to high-speed, heavy-load, and load alternation operating conditions. Therefore, a numerical calculation model with multiple mesh positions loading form has been proposed in this paper to analyze the fatigue crack initiation and propagation behavior, and to estimate the fatigue life of these gears. The fatigue life of the gear is determined by separately calculating the fatigue crack initiation life and the fatigue crack propagation life. The tooth root fatigue stress and the fatigue initiation life are calculated by the multi-axial fatigue life prediction method with the Smith-Watson-Topper criterion and the critical plane method. Afterwards, the tooth root stress–strain field is calculated in Finite element (FE) software and the stress intensity factors of the crack tip are calculated in three-dimensional (3D) crack analysis software. Then, the tooth root fatigue crack propagation trajectory and the fatigue crack propagation life are obtained separately. Finally, the influence mechanism of the loading conditions, the geometry parameters of gears, and the initial crack positions on the tooth root fatigue crack initiation life, propagation life, and fatigue crack propagation trajectory are analyzed, and a tooth fatigue test bench is built for verifying the crack propagation trajectory.

Failure characteristics and pressure relief effectiveness of non-persistent jointed rock mass with holes

In tunnel engineering, the rock mass contains a significant number of irregularly distributed joints, and typically exhibits high energy accumulation, thereby posing a risk of rockburst occurrence. Therefore, it is of paramount importance to investigate the fracture propagation behavior in jointed rock masses and assess the impact of borehole pressure relief on mitigating rockburst occurrences for effective prevention and control measures. This paper focuses on failure characteristics and pressure relief effectiveness of non-persistent jointed rock mass with holes through laboratory testing and numerical simulation. In laboratory experiments, rock samples are prepared to include a range of crack dip angles and circular holes. Then, the crack propagation law of crack inclination and circular hole is studied by AE and DIC technology. The experimental results show that with the increase of fracture dip angle, the peak strength and energy change of the sample decrease first and then increase. Due to the existence of holes, the crack propagation direction of the original crack is changed. After drilling, the strain energy of the sample is obviously reduced, which shows that the drilling pressure relief effect is obvious, which can effectively reduce the energy accumulated inside the rock mass and reduce the risk of rockburst. Finally, the PFC numerical simulation software is used to analyze the micro-failure process and energy change law of the sample from three aspects: the relative position of cracks and holes, the diameter of boreholes and the spacing of boreholes. Further understanding of the energy dissipation law and mechanical behavior characteristics of jointed rock mass provides a reference for exploring the pressure relief effect of rock mass and preventing rockburst.

Strain concentration applied on crack inspection based on marker-based and homography matrix algorithm

ABSTRACT The detection and identification of ship damages have become a significant area of research. This study proposes an image-based structural crack monitoring method that marks the crack locations in the form of strain concentrations by analyzing the overall strain of the structure. Most existing studies focus on using fixed cameras for structural crack monitoring. However, during the actual operation of structures, continuous monitoring around these structures is challenging. To overcome this limitation, this paper implements the transformation from non-fixed camera images to fixed images using a marker-based approach and homography matrix algorithm. In laboratory-scale structural experiments, the algorithm is capable of locating structural crack positions by observing the behavior of strain concentration. Additionally, this study explores the application of markers in structures and verifies the capability of marker attachment methods in crack inspection.

Finite element analysis of macro-crack behavior in the cortical bone of a human tibia

The bone is a biological tissue that possesses a highly complicated hierarchical structure; hence, the tissue components of the bone exhibit variable mechanical proper-ties and a complex bone geometry. This is why the creation of a three-dimensional mod-el through CAD software facilitates the study of the mechanical behavior of bones. Com-bining the concepts of linear elastic fracture mechanics and finite element analysis pro-vides a practical solution to study the fracture behavior of the tibial bone. The objective of this study is to analyze the behavior of cracks in the cortical bone of the human tibia us-ing stress intensity factors in mode I, II, and III as rupture criteria to assess the bone damage response. The tibial bone is one of the most common sites for lower limb stress fractures, which pose problematic injuries. The results investigating the effect of the crack position in the bone demonstrate that the risk of crack propagation is mainly due to mode I opening and is highly favored in the distal zone compared to the middle and proximal regions, regardless of bone density. For the second case study, it is observed that regardless of the crack size, the maximum values of stress intensity factors KI are obtained in the distal zone. Regarding the effect of crack orientation, the results indicate the dominance of mode II for angles α = – 45°, 30°, 45°, leading to high values of stress intensity factors KII.

Research on the propagation characteristics of multiple cracks in steel bridge joints

This study explores the morphological changes and interaction mechanisms of multiple crack propagations in steel bridge joints. Fatigue testing was conducted to determine the locations at which multiple cracks initiated and to obtain fatigue fracture surfaces with easily discernible crack propagation traces. Based on the theory of fracture mechanics, the propagation behavior of coplanar and out-of-plane cracks in joints was simulated using ABAQUS and FRANC3D joint simulation technology. The characteristics of the morphological changes were analyzed, and the interaction mechanism between different crack spacings was investigated to quantitatively characterize the relative positions at which cracks were enhanced or suppressed. The results showed that coplanar cracks exhibited different morphological trends and propagation rates in different stages of propagation. The shape of the crack front continuously changed, and the merging point that appeared during fusion rapidly expanded and evolved into a semi-elliptical crack. The fatigue life was more sensitive to the relative position of multiple cracks. In particular, the fusion of coplanar cracks significantly reduced the fatigue life, and the mutual suppression effect between heterogeneous cracks increased the fatigue life. When the ratio of coplanar crack spacing to crack length (s/2c) was less than 0.2, the crack fusion process significantly accelerated. In addition, when the a2/a1 ratio of the crack propagation depth dropped below 0.5, the suppression effect was significant. Finally, by determining the spacing between multiple cracks, the method established this study can provide a reference for the design of fatigue resistance and joint optimization.

A Crack Detection Method for an Insulator Based on the Optical Frequency Domain Reflectometry Fiber Sensing System

In this paper, a method for detection of crack locations and the width of basin insulators is proposed. Based on the optical frequency domain reflectometry (OFDR) system, the system utilizes an FBG with high feedback for strain as well as temperature, which is affixed to the surface of the tub insulator, and a common single-mode optical fiber, which is used for transmitting data and connected to the optical backscattering reflectometry interrogator. The interrogator measures the backscattered light from the FBG, which varies with temperature or strain. The method has been used to measure the location and width of several different cracks and can locate the crack position with a spatial resolution of 1 mm and measure the crack width with a resolution of 0.77 mm. The method has been used to measure the position and width of insulators. This method provides a simple and fast approach to crack detection in insulators.

Image-driven prediction of fatigue crack growth in metal materials via spatiotemporal neural network

This study proposes an image-driven model based on the SimVP spatiotemporal neural network (STNN) to predict the fatigue crack growth (FCG) in aluminum alloys. This methodology represents a novel usage of STNNs for FCG analysis. It does not require repetitive modeling, extensive computations, or conventional mechanical assumptions. The datasets used during this study were gathered from fatigue experiments with a variety of crack positions, angles, and load levels; they contained a total of 17,925 image frames obtained from DIC measurements. Subsequently, the displacement fields were interpolated onto uniform grids and then augmented, so they could be fitted into an STNN. The proposed method was validated using specimens with edge and central cracks subjected to loads equal to 15.0 % and 20.0 % of the ultimate load. The generalization capability of the proposed method was studied by predicting the FCG under load levels and crack angles outside the training set. In addition, its predictive capability was investigated for both short and long step sizes by employing datasets in which the image data were collected at varying intervals. The overall structural similarity index measurement values were greater than 0.968, and the root mean square errors were held within 0.025 mm. The predicted displacement fields, crack lengths, and crack growth rates agreed well with experimental measurements.

Machine learning supported ultrasonic testing for characterization of cracks in polyethylene pipes

This study aims to develop a machine learning supported ultrasonic guided wave testing (UGWT) for detection and characterization of cracks in polyethylene (PE) pipes used for natural gas distribution. Ultrasonic testing is conducted to investigate the wave-crack interaction and determine damping properties of PE pipes. Finite element models are further built with material properties fine-tuned by wave attenuation experiments combined with cross-correlation analysis between the simulated and experimental signals. A synthetic database is populated using sensed signals over a wide range of crack geometries from numerical simulations. Finally, support vector machine (SVM) models are developed with different feature selections for classification of crack geometry and the accuracy is evaluated using both simulated and experimental cases. The findings demonstrate the potential of locating the circumferential position of crack with the ring-focusing method and classifying crack geometry in PE pipes using SVM model with central frequency features.

Transient thermal fracture analysis of a honeycomb layer with a central crack

Auxetic honeycomb materials with negative Poisson’s ratio received rapidly growing attention in recent years owing to their exceptional thermomechanical properties in constructing sandwich composites. The objective of this article is to investigate the transient thermal behavior and fracture risk of a honeycomb layer with a central crack subject to a sudden thermal shock by theoretical modeling. Two different material configurations along both orthogonal directions, as well as the conventional and auxetic hexagonal alumina honeycomb cells, are examined to illustrate their effects on the thermal stress intensity factors. To solve the thermoelastic governing equations subject to complex boundary conditions, the methodology of integral transform with singular integral equation is employed. The numerical results demonstrate that the auxetic honeycombs can reduce the thermal stress intensity factors significantly compared to their conventional counterparts. The ratio of stress intensity factors in auxetic to non-auxetic honeycombs under the same absolute value of the internal cell angle θ decreases monotonically with increasing |θ|. In addition, the effects of the relative density, crack length, and crack position are investigated. Our findings would provide a more comprehensive understanding of the honeycomb’s fracture behaviors and contribute to the material design of the sandwich composites with honeycomb cores.

Fatigue life prediction of cracked cross beam of mining linear vibrating screen under cyclic load

The cross beam of a mining linear vibrating screen is prone to cracking under long-term cyclic load. In order to accurately predict the fatigue life of the cracked cross beam, a coupled analysis method of vibration and crack propagation is proposed. A 2D dynamic model of the vibrating screen is established based on the finite element method, which is verified by the vibration test platform. The cracked Euler beam element is used to model the cracked cross beam. The effects of crack depth, amplitude of excitation force, frequency of excitation force, and crack location on the crack-tip stress intensity factor of the cracked cross beam are investigated in detail. In addition, an iterative method is proposed on the basis of the Paris model. The residual service life of the beam under different frequencies of excitation force, amplitudes of excitation force, spring stiffness, crack positions, and degrees of stiffness imbalance are discussed. The results demonstrate that the fatigue life of the beam increases as the frequency of excitation force and spring stiffness increase. The increase of the amplitude of excitation force and spring permanent deformation reduces the fatigue life. The conclusion obtained provide some theoretical guidance for the design and routine maintenance of mining linear vibrating screens.