Transverse Cracks Research Articles

Damage features and mechanism of prestressed hollow square piles subjected to non-contact underwater explosion

Critical hydraulic structures are increasingly vulnerable to underwater explosion attacks, with the supporting piles being prime targets for terrorist activities. This study investigates the damage effects and mechanisms of prestressed concrete hollow square (PCHS) piles under non-contact underwater explosions. A series of underwater explosion experiments was conducted on four PCHS piles. The dynamic response of PCHS piles throughout the underwater explosion process was simulated using a coupled fluid-solid numerical model. The mechanisms of dynamic damage to the PCHS piles were elucidated through an integrated analysis of both experimental and numerical results. The research indicates that the damage characteristics of PCHS piles include longitudinal and oblique cracks on the lateral surfaces, transverse cracks on the rear side, and localized fragmentation of concrete. Three primary damage modes have been identified: bending failure(L¯c= 0.59 m/kg1/3), combined bending-shear failure(L¯c= 0.36 m/kg1/3), and punching failure(L¯c= 0.24 m/kg1/3). The local and global responses induced by shock waves are the primary causes of structural damage. Furthermore, as the stand-off distance decreases, the impact of explosive bubbles increases the magnitude of the overall response. A comparative analysis also examined the impact of prestress and axial load on the damage behavior of hollow square piles.

Research on high-precision recognition model for multi-scene asphalt pavement distresses based on deep learning

Accurate detection of asphalt pavement distress is crucial for road maintenance and traffic safety. However, traditional convolutional neural networks usually struggle with this task due to the varied distress patterns and complex background in the images. To enhance the accuracy of asphalt pavement distress identification across various scenarios, this paper introduces an improved model named SMG-YOLOv8, based on the YOLOv8s framework. This model integrates the space-to-depth module and the multi-scale convolutional attention mechanism, while optimizing the backbone’s C2f structure with a more efficient G-GhostC2f structure. Experimental results demonstrate that SMG-YOLOv8 outperforms the YOLOv8s baseline model, achieving Pmacro and mAP50 scores of 81.1% and 79.4% respectively, marking an increase of 8.2% and 12.5% over the baseline. Furthermore, SMG-YOLOv8 exhibits clear advantages in identifying various types of pavement distresses, including longitudinal cracks, transverse cracks, mesh cracks, and potholes, when compared to YOLOv5n, YOLOv5s, YOLOv6s, YOLOv8n, and SSD models. This enhancement optimizes the network structure, reducing the number of parameters while maintaining excellent detection performance. In real-world scenarios, the SMG-YOLOv8 model, when applied to image data collected from projects, achieves a Pmacro of 80.5% and an Rmacro of 86.2%. This result demonstrates its excellent generalization capability and practicality. The model provides significant technical support for the intelligent detection of pavement distress.

Analysis of initiation and growth of new transverse cracks in high crack density regions in cross-ply laminates

In cross-ply laminates under loading, multiple intralaminar (transverse) cracking in the 90-layers causes laminate stiffness reduction which can be predicted by analytical models studying average of the stress perturbation between transverse cracks. The commonly used analytical models such as shear-lag type or variational-type models assume that stress in damaged 90-layers does not depend on the laminate thickness coordinate. But with increase in crack density, the stress perturbations created by transverse cracks start to interact, generating high stress gradients in through-the-thickness direction in the 90-layers. Location of a new crack and features of its propagation in a high stress gradient region between two cracks in a cross-ply laminate are analyzed in this paper. FEM is used to calculate stress distribution between two cracks. The location of the next crack and its initial orientation is found using principal stresses and orientation of principal axes. Most often these cracks are initiated at ply interface in the middle between already existing cracks. Their propagation across the layer thickness is analyzed using energy release rate based criterion. It is shown that at very high crack density the crack propagation across the layer thickness is unstable in the beginning, but it is stopped when approaching the middle of the layer where the crack opening becomes zero. Presence of local delaminations at the tips of existing cracks changes the energy release rate for propagation of new transverse cracks.

Machine learning-based models for thermal cracking prediction of flexible pavements

Prediction of transverse cracking is crucial for pavement practitioners and decision-makers to prognosticate the cracking development and allocate maintenance budgets. This research investigates thermal crack predictions, using four various machine learning techniques: the support vector regression (SVR), the regression artificial neural network (RNN), the Gaussian process regression (GPR) and the least-square boost ensemble method (LSBoost). Predictions were based on 214 pavement sections with 1262 data points from the Long-Term Pavement Performance (LTPP) database. The models are developed using 20 variables representing age, binder, mix, aggregate and climate properties. The LSBoost ML algorithm exhibited the best performance, with a coefficient of determination (R2) of 0.926 for training and 0.727 for testing. Sensitivity analysis revealed that pavement age is the predominant factor in transverse crack prediction followed by the freezing index (FI). Overall, climatic parameters played an important role in transverse crack predictions compared to the mix and binder properties.

Estimation of the Service Life of Approach Slabs of Road Bridges Based on the Statistical Modeling Method

The article discusses the durability and reliability of a separate element – bridge approach slab, which is justified by the need to maintain a satisfactory technical condition of Ukrainian bridges in general and traffic safety on public roads with limited funding during martial law. The scope of the research is forecasting the residual service life of bridge elements (on the example of approach slabs) using probabilistic methods. Approach slabs are designed to smoothly and safely connect the road approach embankment with the bridge to gradually equalize the elastic modulus of the carriageway from a less rigid asphalt pavement on an elastic base to a more rigid one on a reinforced concrete slab. The main defects in the destruction of approach slabs are: changes in the longitudinal profile of the road due to the collapse and subsidence of the soil under the approach slabs; longitudinal and transverse cracks in the asphalt concrete pavement on the bridge approaches; and potholes that lead to an increase in the additional dynamic load on the bridge deck.

Development of an intelligent geographic information system for mountain roads monitoring: Ground data collection and analysis

This study examines the development of an intelligent geographic information system for mountain road monitoring. To make well-informed and timely management decisions in the planning, construction, and maintenance of mountain roads, and to anticipate potential critical situations and their effects on road conditions, it is imperative to employ modern methodologies. This study involves data collection from a specific section of a mountain road situated near Almaty, Kazakhstan. We gathered data on the road section through visual assessment, measurements of the coefficient of adhesion, and the acquisition of material samples from the structural layers of the roadbed. Based on the visual assessment and surface adhesion measurements, it became evident that the deformation of the studied road section, which includes a network of cracks and "non-standard" transverse cracks, is attributed to mountain mass shifts and water flows from slopes. Laboratory analysis of the collected samples revealed that excessive water saturation could result in cracks during freeze-thaw cycles, while a low resistance coefficient would lead to softening during humid conditions. An Intelligent Geographic Information System (IGIS) will incorporate the collected data alongside open remote sensing and weather data. The objective is to utilize this integrated system in the future for forecasting road conditions and maintenance requirements for similar roads in mountainous regions of the area. The measurements are carried out according to the state standards. That makes the system useful for government management purposes.

Natural frequencies of a Timoshenko beam with cracks

A problem of calculating of natural frequencies of a Timoshenko beam weakened by a finite number of transverse open cracks is considered. The problem is solved for both known crack models. In one model every crack is simulated by a single, massless rotational spring. In the other model every crack is simulated by two massless springs (one extensional and another one rotational). An effective method for calculation of the natural frequencies of a vibrating beam with cracks, which was previously successfully applied to Euler-Bernoulli beams, is extended to the case of Timoshenko beam. The developed method makes it possible to significantly reduce the order of the determinant, the zeros of which are natural frequencies. Numerical examples are considered. The results are compared with the known where it is possible.

THz-TDS characterization of stress evolution of EB-PVD TBCs under thermal cycling

The failure of thermal barrier coatings (TBCs) during service is a critical issue affecting aeroengine efficiency. In this study, electron beam physical vapor deposition (EB-PVD) TBCs were subjected to thermal cycling at 1100 °C. Terahertz time-domain spectroscopy (THz-TDS) was employed to characterize the relationship between the evolution of characteristic frequency and the number of thermal cycles, along with the development of stress in the ceramic layer. In situ tensile test revealed a linear correlation between the characteristic frequency and micro strain derived from THz-TDS data, with a proportional coefficient of −9.94 between the characteristic frequency and the slope of the refractive index curve. The results show that the stress evolution can be effectively monitored by recording the trend of characteristic frequency. During the non-failure stage, the characteristic frequency followed a parabolic trend as thermal cycles increased, influenced by the growth of thermally grown oxide (TGO), ceramic layer sintering, and thermal mismatch. Approaching the failure stage, stress evolution was dominated by the expansion of vertical cracks in the ceramic layer and the widening of transverse cracks at the interface, which corresponded to a sudden change in the characteristic frequency.

Crack behaviour and failure mechanisms of air plasma sprayed (Gd, Yb) doped YSZ thermal barrier coatings under oxy-acetylene flame thermal shock

This paper examines the performance and failure mechanisms of atmospheric plasma sprayed (Gd, Yb)-doped YSZ (RYSZ) thermal barrier coatings (TBCs) under oxy-acetylene flame thermal shock conditions. The study involved cyclic thermal shock testing at temperatures of 1400 °C, 1500 °C, and 1600 °C for 10-min intervals until failure occurred, with failure counts recorded as 6, 2, and 2, respectively. During the thermal shock tests, tensile stress in the top coat (TC) caused vertical cracks. The growth of the thermally grown oxide (TGO) layer concentrated stress at the top coat/bond coat interface, leading to transverse interfacial cracks. As the shock temperature increased, the density of vertical cracks and the length of transverse interfacial cracks also increased. Additionally, transverse cracks developed in the TC due to sintering of the surface region at higher shock temperatures. The interaction between vertical and transverse cracks was critical to the spalling of the TC. Variations in crack densities and lengths resulted in different failure modes of the TBCs, depending on the thermal shock temperatures (1400 °C, 1500 °C, and 1600 °C).

Acoustic Emission Measurements During a Four-Point Bending Test on a Reinforced Concrete Specimen

Acoustic emission (AE) measurements were carried out during a four-point bending test to in-vestigate the influence of the shear load-bearing capacity of reinforced concrete beams (so-called Leonhardt beam) with shear reinforcement. The results of AE measurements show that the AE activity begins immediately after starting loading. During the test approximately 3.500 AE events could be automatically located using longitudinal and transverse wave arrival times. Most AE events are in the central region of the specimen within the sensor network. Therefore, only the flexural tensile cracks are represented through AE locations. The transverse shear crack that occurred during the ultimate failure of the specimen is outside the sensor arrangement and has not been detected. Due to the localization error, the AE events are distributed in a cloud-like manner, and as a result, they do not sharply depict the macroscopic flexural tensile cracks. Ra-ther, acoustic emission indicates that a crack network of many small microscopic cracks formed in the tensile area, resulting in a very rough and fragmented crack morphology. Additional to the conventional source location, we applied the so-called collapsing method to highlight structures already inherent within the unfocused AE events clouds.

CURRENT LITERATURE REVIEW ON IMAGE PROCESSING ANALYSIS FOR CONCRETE DAMAGE ASSESMENT

Numerous studies have employed computer vision algorithms to analyze images of concrete damage. Therefore, conducting an image processing survey to detect concrete damage is very crucial. Thus, an image processing algorithm analysis survey to detect concrete damage was conducted using various algorithms and types of data from the last decade. The data observed were the first is damage to concrete, which included surface cracks, hairlines, crack width, patterns, holes, diagonal cracks, longitudinal cracks, and transverse cracks. The second part is figuring out where roads, bridges, and buildings are. The third is data sources like digital cameras, cameras built into phones, camera sensor systems, and unmanned aerial vehicles (UAVs). The study's findings indicate that image processing algorithms will play an essential role in future assessment research on the automation of concrete damage detection. This is particularly the case in high-risk regions for security reasons, and UAV technology is required to reach these locations.

Analysis of the mechanical behavior of asphalt pavement under multiple coupling effects

To reveal the damage mechanism of asphalt pavement caused by the spatial rotation of the stress principal axis, and the influence range of excess pore water pressure on the pavement under the coupling action of multiple fields, the finite element software was used to build the three-dimensional highway asphalt pavement models. Under the consideration of gravity's impact on dynamic computation results, the study investigated the variation patterns of the direction cosines of the principal stress axes of asphalt structural pavement elements under the action of moving loads, as well as the distribution laws of excess pore water pressure. The results indicate that the influence of gravity on dynamic computation results increases gradually with the depth of the pavement, reaching an error of first principal stress of 40.1 % at the bottom of the lower layer. During the movement of loads, the pavement elements directly under the load undergo rotation of the principal stress axes in the xy, xz, and yz planes under different physical fields. With increasing pavement depth, the angle between the first principal stress and the z-axis primarily fluctuates between −90° to 0° and 90° to 180°. The cosine of the angle between the first principal stress and the x-axis and z-axis undergoes instantaneous positive and negative conversion, which can easily lead to transverse and longitudinal cracks on the road surface. The influence widths of excess pore water pressure along the longitudinal and transverse directions of the pavement increase with the pavement depth, with maximum widths of 5.426 m and 2.075 m, respectively. These findings offer new insights into the mechanisms behind the formation of transverse and longitudinal cracks on asphalt pavement and hold significant implications for the improvement of asphalt design methods.

A deep learning framework for predicting slab transverse crack using multivariate LSTM-FCN in continuous casting

Accurate and timely predictions of transverse cracks in slabs are crucial for ensuring efficient and high-quality production in continuous casting. However, the accumulation of substantial amounts of complex, multi-dimensional time series data during the casting process considerably affects the modeling performance. In order to increase the prediction accuracy, this paper introduces a novel prediction framework for slab transverse cracks (PF-STC), which comprises three stages: data preparation, data processing, and model training. First, a synchronized scheme is developed for real-time data tracking to achieve one-to-one matching between the process data in the data preparation phase. Second, the data preprocessing stage tackles the multidimensionality of time series data through normalization and mean aggregation downsampling. Finally, in the model training phase, a multivariate long short-term memory-fully convolutional network (MLSTM-FCN) algorithm is utilized to improve the predictive performance. Experimental results on a real dataset from a steel manufacturing company demonstrate that the PF-STC framework outperforms recent state-of-the-art methods, reducing the number of parameters by 49.97% and training time by 33.83%. The PF-STC achieves an AUC score of 0.9435, with accuracy, precision, recall, and F1 scores of 0.9163, 0.8657, 0.8286, and 0.8467, respectively. The proposed PF-STC is poised to provide support for online transverse crack monitoring, with the application demands of monitoring production processes for the steel industry.

Damage and fracture studies of continuous flax fiber-reinforced composites 3D printed by in-nozzle impregnation additive manufacturing

Additive manufacturing (AM) of continuous yarn-reinforced biobased composites presents multi-functional properties and low environmental impact of this technology. Few studies focused on the mechanical damage mechanisms of continuous biobased composites obtained by AM processes, while it is a topic of high interest for the mastery of mechanical behaviors and optimization of the materials for high requirement applications. This study aims to assess the damage and fracture modes of continuous flax yarn-reinforced PLA manufactured by AM, with different yarn orientations. The additively manufactured biobased composites were characterized by tensile test, 3D microscopy and micro-tomography to link the process-structure-properties relationships regarding the damage and fracture modes. The results showed that the 0° manufactured composite had a significant enhancement of tensile properties compared to other configurations. The damage mechanism presented fiber rupture with polymer transverse cracks at 0°, while the 45° and 90°-oriented composites showed premature fiber/matrix interface debonding. This study aims to find the relationship between damage mechanisms, deposition strategy, and anisotropy of the additively manufactured long vegetal fibers-reinforced biobased composite materials. The results bring a new understanding of the anisotropy and defects in printed composite materials regarding their mechanical behaviors during damage.

Compression-induced failure characteristics of brittle flawed rocks: Mechanical confinement-dependency

The flaw tips in brittle rocks are often the sources of crack initiation and growth due to the stress concentration, which commonly governs the rock strength. However, a unified framework identifying the compression-induced crack types, ultimate failure patterns and the cracking levels of brittle flawed rocks under different mechanical confinements is not yet available. This study conducts the laboratory compression experiments with the AE monitoring to explore the failure characteristics of flawed limestone and its confinement-dependency. Four new crack types including loop crack, secondary transverse crack, near-field transverse crack and far-field transverse crack are found experimentally, and then a modified crack type classification strategy is proposed. Four failure patterns including the σ1-axisymmetric flaw-disturbed spalling for uniaxial compression, the σ3-transverse-symmetric flaw-disturbed spalling for biaxial compression, the σ1 −axisymmetric flaw-disturbed shearing for conventional triaxial compression, and the mixed σ3-transverse-symmetric flaw-disturbed shearing and σ2-transverse-symmetric flaw-disturbed spalling for true triaxial compression, are documented for the first time. Moreover, an acousto-mechanics-based classification methodology of rock cracking levels is established, as well as an AF (average frequency)-RA (rising angle)-based Kernel density estimation method for interpreting the rock cracking nature and the strength mechanism. This paper gets insights into the mechanical confinement-dependency of the rock failure characteristics incorporating the pre-existing flaws and help interpret the field observations.

Process parameters selection for multi-layer friction surfacing of 7075 aluminium alloy

The effect of deposition parameters on the microstructure and mechanical properties are studied in multi-layer friction surfacing of 7075 aluminium alloy. These multi-layer structures were successfully manufactured after a parametric study which allows the generation of a deposition window, including an interface quality comparison. A higher rotational speed leads to a larger grain sizes. The coarse precipitates size and volume fraction decrease along the build direction in correlation with the thermal cycles’ profile. The top layer has a higher hardness after deposition, while bottom layers are in annealed state due to the growth of the strengthening phases. Fracture surface analysis revealed that transversal cracks are due to interlayer decohesion and that voids nucleated on the coarse precipitates.

Simultaneous Measurement of Fiber-Matrix Interface Debonding and Tunneling Using a Dual-Vision Experimental Setup

BackgroundFiber-matrix debonding is a precursor for transverse cracking and several other types of damage in fiber composites. However, to date, there are limited experiment-based reports that study the fundamental mechanisms of fiber-matrix debonding.ObjectiveThis work aims to uncover the governing mechanisms of fiber-matrix interface debonding by full-field measurements supplemented by numerical simulations. In particular, the application of a dual-vision image-based characterization approach on single glass macro fiber samples is discussed and proven useful in understanding the in-plane and out-of-plane debonding characteristics at the fiber-matrix interface.MethodsFull-field strain and displacement measurements based on digital image correlation are performed on model single-fiber composites. The use of a dual-vision system allows strain measurements in the vicinity of the fiber-matrix interface, also allowing for the identification of critical strain and stress values corresponding to the initiation and propagation of debonding damage. The experimental data are used to calibrate an inverse identification approach that outputs the shape of the debonded interface along the fiber length.ResultsFull-field measurements allow for establishing correlations between local and global strain fields. Observation of debonding propagation along the fiber axis seems to be representative of the crack tunneling during the early stages of the failure process, i.e., when the crack tip is subjected to opening mode only.ConclusionsSide view measurements are useful as a first-order approximation of the debonding propagation velocity along the fiber axis but fail to provide accurate measurements for the debonding shape, esp. in areas where the crack is under a dominantly shear stress state. This issue can be resolved by full-field measurements coupled with computational simulations.

High-temperature oxidation behavior and mechanical properties of PS-PVD sprayed Yb2Si2O7 environmental barrier coatings

The high-temperature oxidation behavior and mechanical properties of the Yb2Si2O7/Si environmental barrier coatings (EBCs) prepared by plasma spray-physical vapor deposition at 1250 °C and 1350 °C were investigated, and obvious delamination was observed after oxidation for 4000 h. The results showed that element diffusion occurred during oxidation, and the diffusion of oxygen led to the formation of thermal growth oxides (TGO), which induced pores and microcracks. The TGO played a role in hindering element diffusion, but the mismatching coefficients of thermal expansion and phase transition caused vertical and transverse cracks in the TGO layer. These cracks became channels for oxygen diffusion and ultimately resulted in delamination between TGO and the bonding coating (BC) layer. Furthermore, temperature significantly affects the oxidation kinetics of EBCs, and the oxidation within the BC layer alters its elastic modulus. The elastic modulus of the BC layer first increased and then decreased. The oxidation damage was more pronounced at 1350 °C.

Crack fault diagnosis in rotor bearing system by transient and study state time domain analysis

Online condition monitoring methodologies for rotor dynamic systems are an emerging trend and an essential for safe system operation. During operation fatigue cracks in rotor shaft can lead to catastrophic failures if not identified at early stage. Therefore, these systems require a reliable crack fault detection methodology. The vibrations may induce in the system due to different type of faults, like shaft transverse cracks, oil whirl and whip. To make the detection methodologies robust and reliable, redundancy in crack detection methodologies is vital. The present research is a foolproof procedure to detect the travers fatigue crack in the rotor shaft. Rotor response, orbital pattern, and response FFT during transient (runup/cost down) and study state operations at 2X & 3X sub critical speeds are analyzed to identify the presence of crack in rotor bearing system. The rotor system is analyzed by numerical Finite Element Modeling (FEM) simulations and experimental means. Open Wedge Crack (OWC) and Breathing Wedge Crack (BWC) are modeled and their behavior is studied. The effectiveness of Newton Rapson method, Houbolt numerical method, and Harmonic Balance Method (HBM) in crack diagnosis are studied. Numerical FEM results are validated with experimental and published literature results. FEM simulated and experimental response FFT shows similar response behavior with presence of crack with 98 % correlation and less than 2 % error. FEM simulated and literature response orbital pattern at 2X sub critical backward speed are similar with less than 3 % error (97.76 % close) and at 2X sub critical forward speed are similar with less than 1 % error (99.33 %).

Oxidation behavior and structural damage mechanism of LaMgAl11O19 dual-ceramic thermal barrier coating with varying thickness of Al plating layer

Previous results clearly confirmed that the presence of an Al plating layer promotes the development of a dense Al2O3 barrier layer when exposed to high temperatures. This enhances the structural stability and improves the oxidation resistance of the dual ceramic coating. In the work, a continuous study was conducted to investigate the effect of varying Al plating layer thickness on the high-temperature oxidation characteristics of a CoCrNiAlY–YSZ–LMA dual ceramic coating. The results indicate that, compared to samples lacking Al layers, all Al-coated samples exhibit dense surface morphology, effectively inhibiting the permeation of O2. This results in slower growth of the TGO and minimal elemental diffusion. However, significant differences are observed in structural damage. Al layers of 5 μm and 10 μm thickness show slight local fracture damage and good structural stability. In contrast, the 15 μm Al-coated samples experience more severe structural fracture damage within the YSZ layer, including transverse cracking. These potential oxidation and structural damage mechanisms of the coatings with varying Al plating layer thickness were systematically discussed.