Crack Location Research Articles

Characterization and Fault Diagnosis of Vibration Characteristics of Tenon Disks with Cracks Based on Blade Tip Timing

Abstract The tenon-structured disk is a critical component of the rotor system in aeroengines. Under the repeated cyclic loads and inherent material defects, the disk is susceptible to the initiation of fatigue cracks. The impact of disk cracks on the shaft vibration response is subtle and challenging to monitor, however, it can induce periodic vibrations in the blades near the crack location. Therefore, this paper proposes a method for crack identification in rotor disks based on Blade Tip Timing (BTT) technology, which allows for the reflection of rotor disk crack parameters (type, location) through the blade tip vibration parameters, enabling online monitoring and fault diagnosis of rotor disk cracks. To guide the implantation of cracks, this study analyzes the weak points of the disk and conducts a comparative analysis of the effects of cracks of different depths on the blade tip vibration characteristics. Experimental validation confirms the accuracy of the proposed method, providing theoretical support for the onboard online identification of cracks in aeroengine disks.

Feasibility study of FFPP thermoplastic lining for concrete pipeline rehabilitation: a case study

This study investigates the feasibility and efficacy of Flexible Fiber-reinforced Polypropylene (FFPP) thermoplastic lining technology for the rehabilitation of concrete pipelines, specifically focusing on BONNA pipes. A custom-built test bench, featuring a 2-m high platform and multiple 90° bends, was designed to simulate the impact of pipe gallery space, adaptability and material accessibility of bent pipes, and cooling issues of long-distance dragging of materials. The simulation process utilizes a modified polyvinyl chloride (PVC) liner with unique thermomechanical properties. The liner, folded into an "H" shape, is mechanically inserted into the host pipe using a 2-ton winch and pulley system. During insertion, continuous high-temperature steam injection softens the material, facilitating expansion and conformity to the pipe's internal surface. Subsequently, cold air application rigidifies the liner below 60 °C while maintaining pressure, ensuring structural integrity and adherence to the pipe wall. Results revealed that while the FFPP liner successfully navigated through confined spaces, including a 300 mm expansion joint, spatial constraints led to localized cracking defects during inflation. Traction feasibility tests using a 2-ton winch demonstrated high pulling resistance in sections with multiple bends. The liner exhibited excellent adhesion in straight pipe sections but showed significant wrinkling and poor adhesion in 90° bends. Notably, the liner demonstrated remarkable strength, withstanding internal pressures exceeding 3.3 MPa in a DN300 pipe with a 10 cm diameter intentional defect, far surpassing the on-site hydrostatic test pressure of 9 bar. This study addresses a significant gap in trenchless rehabilitation research by evaluating the FFPP thermoplastic lining technique in complex pipeline geometries, an area previously understudied. While the technique shows promise for structural reinforcement in straight pipe sections, our findings reveal that its application in complex pipeline geometries requires further refinement. The study contributes to the field of trenchless pipeline rehabilitation in several ways: (1) it provides empirical data on FFPP liner performance in multi-bend configurations and confined spaces, (2) it identifies specific challenges such as localized cracking and poor adhesion in bends, and (3) it demonstrates the liner's exceptional strength under high pressure conditions. These insights advance our understanding of FFPP technology's potential and limitations in concrete pipe repair, paving the way for future research and development in optimizing trenchless rehabilitation techniques for complex pipeline systems.

Detection of matrix cracks in composite laminates using embedded fiber-optic distributed strain sensing

We used an optical frequency-domain reflectometry fiber Bragg grating (FBG) distributed strain measurement system to detect matrix cracks in carbon fiber-reinforced plastics. Load/unload tests were performed on cross-ply laminates under ambient-, high-, and low-temperature conditions using embedded 100mm gauge FBG sensors. We measured the strain distributed along the gauge and examined the crack initiation using optical microscopy and soft X-ray inspection. A peak appeared in the distributed strain corresponding to the occurrence of cracks. The strain distribution during crack initiation was calculated in each temperature range via finite element analysis and compared with the measurement results. We determined that the number and location of cracks can be determined by extracting the peaks from the distributed strain. However, the peaks in the distributed strain do not correspond to the occurrence of cracks that are close to each other, warranting a measurement method with a higher strain resolution.

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.

Local FRP Cracking and Global Structural Behavior of Stub Concrete-Filled FRP Tubes under Concentric and Eccentric Compression

Local FRP Cracking and Global Structural Behavior of Stub Concrete-Filled FRP Tubes under Concentric and Eccentric Compression

The Effect of σ Phase Content on the Hot Working Properties of Super Austenitic Stainless Steel Containing 7Mo-0.42N

In the present study, super austenitic stainless steel containing 7Mo-0.42N was isothermally treated at 1100 °C, 1200 °C, and 1250 °C for different times, in order to obtain the samples with different σ precipitate content of 7%, 1.4%, and 0.7%. The effect of σ phase content on the hot working properties of the specimens was investigated under hot compression conditions at 900~1200 °C and strain rates of 0.01~5 s−1. Results show that, with the increase in σ content, the recrystallized grains increase gradually, and the internal stress decreases firstly and then increases. Therefore, the σ phase has two roles in the thermal deformation process. One is that the σ phase promotes recrystallization and the other is that the σ phase hinders dislocation motion. In the hot working diagram of super austenitic stainless steel with different σ phase contents, the distribution of high power consumption and instability regions is significantly different. The sample containing 1.4% σ phase does not show the region where the power dissipation coefficient η is negative, and there is a large number of dynamic recrystallized grains in the high power region, showing good hot working performance. However, the local rheology and cracking in samples containing 0.7% and 7% σ phase after deformation are more serious. Combined with the constitutive equation, hot working diagram, and microstructure, it is found that the optimum hot working property of the super austenitic stainless steel containing 7Mo-0.42N could be obtained when it is deformed at a temperature of 1200 °C with a strain rate of 5 s−1 when the content of σ phase is 1.4%.

Coupled lattice discrete particle model for the simulation of water and chloride transport in cracked concrete members

AbstractA novel coupled mechanical and mass transport lattice discrete particle model is developed to quantitatively assess the impact of cracks on the mass transport properties in concrete members subjected to short‐ and long‐term loading conditions. In the developed approach, two sets of dual lattice networks are generated: one to resolve the mechanical response and another for mass transport analysis. The cracks simulated by the mechanical lattice are mapped onto the transport elements to investigate the effect of cracks on the global transport properties in concrete members. A new quantitative relationship is proposed for the estimation of the diffusion coefficient based on local crack information, and the developed model is capable of describing both convection and diffusion mechanisms. Moreover, creep behavior is incorporated to account for the influence of cracks induced by long‐term loading conditions. Numerical results, in the form of dynamic changes in cumulative water and chloride contents in concrete members under tension, compression, and bending with various stress levels show remarkable accuracy when compared to available experimental observations. The developed model provides an effective means for incorporating mesoscale information in simulations of water and chloride transport in concrete members under varying short‐ and long‐term loading conditions.

Effect of a variable electrode force on the LME crack formation during resistance spot welding of 3G AHSS

AbstractIn the pursuit of lightweight vehicles, third-generation advanced high-strength steels (3G AHSS) with increased mechanical properties are desired to be used for critical components. However, the exposure of these zinc-coated AHSS to the manufacturing conditions during resistance spot welding can trigger liquid metal embrittlement (LME), possibly compromising the mechanical properties. As the reproducibility of LME cracks in resistance spot welding is a challenge, the effect on the static and dynamic mechanical properties of the welds is not yet fully clarified and therefore a distinction between critical and non-critical cracks is not implemented in current standards. To achieve this, it is necessary to provoke LME cracks of a given size, for example by increasing the welding current, reducing the electrode force and hold time, or using manufacturing discontinuities. Due to its significant effect on the heat input and the tensile stresses during the resistance spot welding process, which impacts the LME crack propagation, the focus of this paper is on the electrode force. An expulsion-free decreasing force profile, which consists of a force run-in, force decrease, and force run-out time, has been derived in a two-stage Face-Centered-Central-Composite design of experiment for an electrogalvanized third-generation advanced high-strength steel (3G AHSS) DP1200 HD. The crack location, length, depth, and nugget geometries were investigated for each weld. With the decreasing force profile, it was possible to generate type A, B, and C cracks by parameter adaption, with type B and C cracks being the most dominant. The type C crack formation was investigated by aborting the welding process in defined time steps and the LME cracking mechanism was confirmed by welding dezincified samples. Based on the investigations carried out, the force profile was found suitable for generating different LME crack sizes to further investigate the mechanical joint properties as it was able to reproducibly generate defined cracks without expulsion and excessive electrode indentation while maintaining a minimum nugget diameter.

A multi-physics dual-phase field model for chloride-induced localized corrosion process and cracking in reinforced concrete

Corrosion-induced deterioration poses a significant threat to the serviceability of reinforced concrete (RC) structures. This study develops a comprehensive mesoscale model utilizing dual-phase field methods to capture the entire time-dependent chloride-induced corrosion and cracking mechanisms, incorporating interactive multi-physics. The model accurately delineates the evolution of corrosion morphology and cracking patterns, focusing on their interdependent interactions within localized areas through detailed electro-chemo-mechanical processes, from steel dissolution to precipitation. The robustness of the proposed numerical method is confirmed through alignment with previously reported experimental results. Extensive parametric studies investigate the impacts of various geometric and material characteristics on corrosion processes. Furthermore, the model’s applicability to RC configurations with multiple reinforcements is also demonstrated. These findings offer pivotal insights into the substantial correlations between rebar corrosion and concrete cracking across multi-physics fields, with their coupling driven by the variable corrosion current density.

A novel guided wave testing method for identifying rail web cracks using optical fiber Bragg grating sensing and orthogonal matching pursuit

Ensuring safe operation of railway systems is essential. Detecting early-stage rail defects is crucial to prevent catastrophic incidents, such as derailments. Traditional manual inspection routines are often inefficient and lack robustness. This paper proposes a novel guided wave testing (GWT) method using optical fiber sensing combined with an orthogonal matching pursuit (OMP)-based data processing technique to detect rail damage by reconstructing defect-related reflective wave from complex raw signals. First, a finite element model (FEM) is constructed to simulate ultrasonic guided wave (UGW) signals and subsequent signal reconstruction using OMP demonstrates capabilities. In the experimental part, a rail segment with a vertical crack is installed with a fiber Bragg grating (FBG) sensor to receive UGW. The reconstructed signals confirm the effectiveness of our method in identifying the rail web crack location. This method offers a novel approach for rail crack identification, promoting more efficient inspection methods for extensive rail transportation networks.

Ultrasensitive and Breathable Hydrogel Fiber‐Based Strain Sensors Enabled by Customized Crack Design for Wireless Sign Language Recognition

AbstractWearable strain sensors, capable of continuously detecting human movements, hold great application prospects in sign language gesture recognition to alleviate the daily communication barriers of the deaf and mute community. However, the unsatisfactory strain sensing performance (such as low sensitivity, narrow detection range, etc.) and wearing discomfort severely hinder their practical application. Here, high‐performance breathable hydrogel strain sensors are proposed by introducing an adjustable localized crack in a closed‐loop connected hydrogel fiber encapsulated by porous elastomer films. Upon loading/unloading of external strain, the dynamic opening/closing of the pre‐cut crack causes a rapid switching in the hydrogel conductive path, resulting in sharp changes in resistance and a high sensitivity. Consequently, the hydrogel‐based crack‐effect strain sensor exhibits a superb sensitivity (GF up to 3930), a broad detection range (from 0.02% to 80%), fast response/recovery time (78/52 ms), repeatability, and structural stability. Based on the capability to accurately detect various strains across the full range of human movements, a wireless sign language recognition system is developed to achieve a high recognition accuracy of 98.1% by encoding and decoding various sign language gestures with the assistance of machine learning, providing a robust platform for efficient sign language intelligibility and barrier‐free communication.

Strain distribution prediction in UHPC beams using deep learning model

AbstractOver the last three decades, ultra‐high‐performance concrete (UHPC) has emerged as a highly innovative cementitious engineering material. This paper utilizes a distributed fiber optic sensor based on optical frequency domain reflectometry (OFDR) combined with the deep learning model to monitor and predict the strain distribution in UHPC T‐beams subjected to two point bending experiment. These sensors are deployed on the side surfaces of the UHPC T‐beams to capture the strain distribution when subjected to vertical loads, facilitating the determination of crack locations based on strain distribution peaks. While time series modeling is widely used in civil engineering to monitor potential damage using sensor data, its application in tracking and predicting known cracks is less explored. To address this gap, a Long Short‐Term Memory (LSTM) neural network model is developed to forecast the increase in the peak value of the strain distribution prior to structural damage, thus predicting crack initiation. The accuracy of the proposed LSTM model in predicting the UHPC strain distribution was thoroughly investigated. The results demonstrate excellent agreement between the predicted strain distributions and those detected by the ODISI 6000 monitoring system. The root‐mean‐square errors of the model‐predicted strains are generally below 10 με, with an average coefficient of determination (R2) reaching up to 98%, indicating a high degree of accuracy.

Machine Learning-Based Structural Health Monitoring Technique for Crack Detection and Localisation Using Bluetooth Strain Gauge Sensor Network

Within the domain of Structural Health Monitoring (SHM), conventional approaches generally are complicated, destructive, and time-consuming. It also necessitates an extensive array of sensors to effectively evaluate and monitor the structural integrity. In this research work, we present a novel, non-destructive SHM framework based on machine learning (ML) for the accurate detection and localisation of structural cracks. This approach leverages a minimal number of strain gauge sensors linked via Bluetooth Low Energy (BLE) communication. The framework is validated through empirical data collected from 3D carbon fibre-reinforced composites, including three distinct specimens, ranging from crack-free samples to specimens with up to ten cracks of varying lengths and depths. The methodology integrates an analytical examination of the Shewhart chart, Grubbs’ test (GT), and hierarchical clustering (HC) algorithm, tailored towards the metrics of fracture measurement and classification. Our novel ML framework allows one to replace exhausting laboratory procedures with a modern and quick mechanism for the material, with unprecedented properties that could provide potential applications in the composites industry.

Deliquescence of damaged rock salt under high humidity and its effect on inter-seasonal salt cavern gas storage

Salt cavern underground gas storages (UGSs) are ideal for mitigating demand fluctuations in gas resources such as hydrogen, helium, and natural gas. Rock salts surrounding the cavern are chronically exposed to high humidity during the inter-seasonal operation, and the effect of its deliquescence is worth investigating. In this study, deliquescence rates of damaged rock salt at the humidity of UGSs was measured. Undamaged rock salts deliquesce slowest. The rate increases by 532 % as the strain reaches 2.40 %. This ratio decreases to 372 % when rocks enter plastic deformation stages. Cracks and crystal defects in damaged rocks are inferred to accelerate deliquescence by increasing the local relative humidity through the Kelvin effect and lowering reaction energy barriers, respectively. As the crack widens with deformation, imbibed brine inhibits the deliquescence by healing defects and reducing water-salt contact. A subroutine coupling deformation and deliquescence of rock surrounding the cavern was developed. Its application in Jintan, China shows that deliquescence increases the cavern span, intensifying local creep and crack evolution. The volume shrinkage of the cavern increased by 2.80 %, and the safety factor was reduced, but empirical safety criteria were still satisfied. This study helps to assess UGS salt caverns' storage performance more accurately.

Water Leakage Detection and Management System

In this era of globalization, water leakage significantly contributes to water waste and can adversely affect the environment if left unchecked. Much water is wasted due to unsupervised and poorly managed actions. The primary objective of leak detection is to locate leaks and measure their dimensions in secured products and systems. The process begins with hardware development, which is crucial for obtaining raw data by measuring water flow velocity at specific crack locations. Software-based methods use computer systems to monitor pressure and flow rate data to detect leaks continuously. This involves converting the velocity data into audio frequency signals. The gathered signals are then processed in MATLAB, a high-performance technical computing software, through four phases: segmentation, pre-processing, feature extraction, and classification, with Internet of Things (IoT) features integrated. Finally, the data is analyzed using the k Nearest Neighbour (kNN) classifier for classification.

Evaluation of the characteristics of ferrite garnet films for magneto-optical control of materials

A setup based on a polarization microscope was developed to study the characteristics of two types of ferrite-garnet films with the chemical composition Lu1.51Ho0.56Bi0.93Fe4.1Al0.9O12. The parameters of the hysteresis loop, values of residual magnetization, and the saturation field of the studied films were determined experimentally. The domain structure period was estab-lished, and a compact device for visualizing defects in steel samples was created. Using this device, a series of experiments were conducted on test samples with cracks of various sizes, and magneto-optical images of the cracks were obtained. The hysteresis loop of the two types of ferrite-garnet films was constructed in the “magnetiza-tion coefficient-magnetic field induction” coordinates. The magnetization coefficient was cal-culated based on the relative change in the area of bright and dark domains when the external magnetic field, directed perpendicular to the film plane, was varied. The efficiency of using two types of films, grown under different technological conditions but having the same chemical composition, in non-destructive testing methods was analyzed. It was found that the investigated films had the same domain period, but their residual magnetization and saturation field values varied significantly. Diagrams of the experimental setup and the developed device, as well as the characteristics of some of their components, are presented. To generate the magnetic field in the test samples, a coil wound on a U-shaped ferrite core was used, pressed against the sample surface on the opposite side relative to the crack location. The experiments were conducted under constant magnetic fields of varying intensity. The device was tested on specially prepared test samples with pre-grown cracks of known sizes. The tests demonstrated that films with higher residual magnetization and saturation field values were more sensitive to detecting defects such as enclosed cracks.

Localization of crack edge under elastic layer surface displacement

The problem of SH-wave scattering from the semi-infinite crack in the elastic waveguide is considered. The opposite waveguide surfaces are free from stresses. This structure is illumi-nated by one of the normal SH-waves that propagate along the waveguide without attenuation. The displacement of the particles in this wave is perpendicular to the direction of wave propa-gation and has the harmonic dependence on time. The problem is two-dimensional and is reduced to the mixed boundary-value problem for Helmholtz equation with the Neumann boundary conditions. The problem is formulated with respect to the unknown diffracted displacement field. Using the Fourier transform of the displacement and strength fields the problem is transformed to the functional Wiener-Hopf equation. Its exact solution was obtained using the factorization and decomposition methods. The explicit expressions for finding the displacement field were obtained and its numerical analysis was carried out on the layer surfaces for its diagnosis. The influence of the dimensionless thickness of the layer and the depth of the crack location on the distribution of the displacement field on the waveguide surfaces was investigated. Peculiarities of the behavior of the field distribution have been revealed, which allow us to estimate the location of the edge of the crack and the depth of its location.

Temperature–amplitude spectrum for early full-field vibration-fatigue-crack identification

A dynamic structure under vibration loading within its natural frequency range can experience failure due to vibration fatigue. Understanding the causes of such failure requires pinpointing the initiation time and location of fatigue cracks, tracking their propagation, and identifying the frequency range of critical stress responses. This research introduces a novel, thermoelasticity-based method – the Temperature–Amplitude Spectrum (TAS) method – for early-stage, full-field, and non-contact crack detection that operates during uninterrupted vibration testing. This method leverages high-speed infrared imaging to analyze the specimen’s temperature–amplitude spectrum, capturing comprehensive crack-related information, including initiation and propagation, in real time. Experimentally validated on both 3D-printed polymer and aluminum specimens, the TAS method accurately identified crack locations and paths without complex adjustments to the experimental setup or data processing. This new approach advances vibration-fatigue testing by enabling reliable, high-resolution crack detection and analysis while remaining computationally efficient.

Plasticity-induced crack closure identification during fatigue crack growth in AA2024-T3 by using high-resolution digital image correlation

Fatigue crack growth in ductile materials is primarily driven by the interaction between damaging and shielding mechanisms. In the Paris regime, the predominant mechanism for retardation is plasticity-induced crack closure (PICC). However, some of the mechanisms behind this phenomenon are still unclear. Identifying and separating the three-dimensional aspect from other shielding aspects during experiments is extremely complex. In this paper, we analyze the crack opening kinematics based on local crack opening displacement measurements in both 2D high-resolution digital image correlation data and 3D finite element simulations. The results confirm that the crack opening stress intensity factor Kop differs along the crack path. we present a new method to determine Kop at the crack front allowing to identify PICC as the predominant shielding mechanism in fatigue crack growth experiments. Furthermore, this work contributes to the discussion on the damage-reducing effect of PICC, since we find that the influence on fatigue damage in the plastic zone remains negligible when the crack is closed and crack surface contact is directed towards the surface.

Dynamic analysis of orthotropic bridge deck under moving vehicular loads by using Hencky bar-net model

This study extends the Hencky Bar-Net model (HBM) to dynamic analysis of vehicle-orthotropic bridge deck interaction system. The HBM was used to investigate the dynamic behaviour of an orthotropic bridge deck under moving vehicular loads and random road irregularities. The results indicate that the lower bending rigidity in width direction change the deformations of orthotropic deck from a global mode into a localized one, and dynamic magnification factors do not necessarily increase with higher vehicle speeds. However, dynamic magnification factors demonstrate an obvious increase in relation to higher vehicle speeds when the bending rigidity ratio is high. In addition, the HBM can easily handle damage of the bridge deck because of its discrete characteristic. Hence, the common longitudinal cracks that keep open are modelled by reducing the spring stiffness in the HBM. The results demonstrate longitudinal cracks show a complex influence on dynamic magnification factors of the bridge deck depending on the crack depth and location.