Transverse Cracks Research Articles

Road damage detection using UAV images based on multi-level attention mechanism

Pavement damage detection is essential for subsequent road maintenance decisions. However, recent detection networks have low accuracy and fail to detect most diseases on the road, which means that testing is very inefficient. Therefore, this study uses the unmanned aerial vehicle (UAV) road damage database and describes a multi-level attention mechanism called Multi-level Attention Block (MLAB) to strengthen the utilization of essential features by the You Only Look Once version 3 (YOLO v3). Adding MLAB between the backbone and feature fusion parts effectively increases the mAP value of the proposed network to 68.75%, while the accuracy of the original network is only 61.09%. The network is able to detect longitudinal cracks, transverse cracks, repairs, and potholes with high accuracy, and significantly improves the accuracy of alligator cracks and oblique cracks. The findings of this study will accelerate the application of non-destructive automatic road damage detection.

Transverse Crack Patterns of Long-Term Field Asphalt Pavement Constructed with Semi-rigid Base

Transverse Crack Patterns of Long-Term Field Asphalt Pavement Constructed with Semi-rigid Base

Novel energy identification method for shallow cracked rotor system

Many factors like period stress or fatigue may lead to cracks in the rotating shaft which can cause economic losses and accidental risk. Early crack faults will introduce very slight local changes in the whole rotor system. And the monitoring data on rotor systems are disturbed by multiple factors. These problems may make subtle fault information be ignored, resulting in the collection of a possible rotor fault becoming tougher. To overcome such issues, novel energy methods including the vibration energy analysis and the 3D energy model representation are presented to investigate the rotor system with transverse crack. For the rotor system with a shallow crack, the energy response analysis shows the existence of shallow cracks mainly affects the peak response values. Meanwhile, the 3D energy model is used to visualize the fault characteristics. The results show that even shallow cracks can cause special phenomena in the 3D energy model, which can promote the identification of crack faults more accurately. The influence of parameters on rotor vibration energy is studied and the corresponding results are obtained. To validate the theoretical analysis results, relevant experiments are applied. The results show that the experimental results agree with the theoretical analysis. The conclusions achieved in this paper can provide a reference for fault diagnosis of rotor systems in engineering practice.

Ultimate strength analysis of pitted plates with transverse cracks

Numerical analysis using computer code ANSYS was employed to analyze the ultimate strength of pitted plates with transverse cracks under uniaxial compression. It was found that pitting was more critical in the thick plate and cracking in the thin plate, and the plate with a center crack had the lowest effect on the reduction of the ultimate strength, regardless of the crack length and thickness of the plate. For small cracks, plates with two edge cracks had a lower reduction factor than plates with a single edge crack, while for long cracks it was vice versa. The maximum reduction factor of the ultimate strength of the cracked plate occurred in thin plates with two edge cracks. The results showed that the combined effect of cracking and pitting reduced the ultimate strength of the plate by up to 400% and 50% with respect to cracking and pitting alone, respectively. Thus, it can be concluded that cracking of plates prior to pitting is more detrimental, since sharp decreases of the ultimate strength.

Oxidation of typical Zr-1 Nb alloy in high-temperature air under 700–900 °C

In order to promote the understanding of Zirconium alloy cladding failure under loss of coolant accidents (LOCA), air oxidation behavior of Zr-1 Nb-0.12 O (M5) alloy at 700–900 °C for 1–2 h was investigated. At different temperatures and times, m-ZrO2 was always the dominant phase of surface oxides, whereas oxide shapes, the integrity and roughness of oxide films differed noticeably. At 900 °C, M5 alloy exhibited accelerated kinetics and breakaway oxidation after approximately 80 min air exposure. The presence of ZrO and ZrO0.35 sub-oxides accounts for the high reaction activation energy (149.6 kJ/mol). During the kinetics acceleration, some intergranular cracks turned transgranular. The oxide/metal (O/M) interface became wavy, massive long transverse cracks and small radial cracks appeared in the oxide film, and pores distributed on the oxide layer and O/M interface. Air ingress through the oxide layer to initiate the matrix oxidation is jointly affected by air transport and ion diffusion.

Gas permeability mitigation of cryogenically cycled stitched composites using thin plies

3D through-thickness stitched composites can be used to produce lightweight, unitized structures for cryogenic applications. However, to fully utilize stitched composites for these applications, cryogenic fuel leakage through transverse cracks in these structures must be prevented. In this study, thin plies (cured thickness ≈ 0.032 mm) are incorporated directly into three-dimensional stitched polymer matrix composites (PMCs) to reduce gas permeability and prevent through-thickness cracking. Stitched carbon/epoxy composites ([+45/−45]4s) with standard thickness plies were used as baseline laminates. Thin plies were added to the baseline design to fabricate three different laminates with one thin ply placed on (a) both laminate surfaces, (b) two plies from each laminate surface, and (c) at the laminate midplane. Test coupons were thermally cycled from ambient (23 °C) to cryogenic (−196 °C) temperatures. Gas permeability and ply-level microcrack densities were measured as a function of cryogenic cycles. Results show that both the presence and location of the thin plies impact the gas permeation characteristics of stitched composites. Thin plies were effective in resisting microcrack growth and acted as integral liners to prevent excessive gas flow through the stitched specimens.

Modeling, Nonlinear Dynamics, and Bifurcation Analysis of the Rotor–Seal System Using a Subharmonic Sampling Strategy

Abstract Rotors are used to transfer power from one component to the other component in various rotor dynamics applications like steam turbines, aerospace systems, and power generators. In certain applications, the seal is an important and inevitable component of the rotor dynamic system. The linear dynamics of the rotor is converted into nonlinear in the presence of a seal. The presence of a seal, can sometimes, trigger self-excited vibrations in rotor/seal systems. Generally, the amplitude of vibration during such vibrations is several times higher than normal steady-state vibrations. Due to this, other faults like transverse crack initialization and rotor/stator rub get accelerated. The rotating machinery working at high spinning speeds is more prone to this type of instability. Hence, the stability limits of the rotor/seal system must be known in advance for the safe operation of the rotating machinery. The dynamic behavior of such a system qualitatively varies corresponding to different system parameters of the rotating machinery. Cumbersome analytical methods have been used in the past for bifurcation analysis of rotor/seal systems. In the present work, system bifurcations have been investigated using a subharmonic sampling rate strategy. The proposed method is easy to implement and numerically efficient. The effect of various parameters like the spinning speed of the rotor, unstable mass, and seal clearance is investigated for the stability of the rotor/seal system. Experimental testing is done to verify the simulation results.

Automatic Pavement Crack Identification Based on an Improved C-Mask Region-Based Convolutional Neural Network Model

A pavement crack identification method based on an improved C-mask region-based convolutional neural network (R-CNN) model is proposed to solve problems whereby existing crack recognition algorithms exhibit low accuracy and cannot perform detection and segmentation tasks simultaneously. The crack dataset that was collected in this study included three categories: transverse cracks, longitudinal cracks, and alligator cracks. The model integrates the detection task and the segmentation task into one model, and segments the crack pixels in the generated detection box while achieving target positioning. Firstly, based on the mask R-CNN model, the improved C-mask R-CNN method is designed, which improves the quality of the region proposal box by combining the detectors that are cascaded with different intersections over union thresholds, and achieves accurate crack location under high-threshold detection. Secondly, the ratio of the anchor in the model is adjusted, and a series of optimization parameters and experimental comparisons are carried out for the improved model to realize the segmentation of the crack pixels in the generated detection box during the crack location. The effectiveness of the proposed model is verified, and finally, an evaluation method for cracks is proposed. Furthermore, the calculation of the crack geometric parameters is completed. The experimental results demonstrate that the mean average precision (mAP) of the C-mask R-CNN model detection part reached 95.4%, and the mAP of the segmentation part reached 93.5%. Moreover, the proposed model is convenient for researchers to deploy and implement.

Nonlinear dynamic analysis of two-disk rotor system containing an unbalance influenced transverse crack

Nonlinear dynamic analysis of two-disk rotor system containing an unbalance influenced transverse crack

ДЕФЕКТИ МОНОЛІТНИХ ТРАНСПОРТНИХ СПОРУД І МОЖЛИВІ ШЛЯХИ ЇХ УСУНЕННЯ

Introduction. Defects that occur during the operation of monolithic transport structures, in particular overpasses, rectangular pipes and cattle drives, are considered. A comprehensive approach to the selection of constructive solutions, materials and technologies is proposed for their prevention and improvement of some provisions of the current norms for the design of such structures. Problem Statement. In the constructions of span structures of monolithic rectangular pipes, overpasses and cattle runs, during their operation under load, transverse cracks of the span structure appear, as well as shrinkage cracks, which can harm their normal operation. Purpose. The purpose of the work is the need to draw the attention of balance-keepers of structures, work customers and project organizations to the importance of ensuring proper indicators of the operational condition of transport structures at all stages of the life cycle, from project development and construction to the performance of regular work on their operational maintenance. Materials and methods. Research methods consist in identifying the influence of structural defects of monolithic transport structures on durability and safe operation. Analytical materials were used, in particular, based on the results of supervision of monolithic transport structures during the implementation of scientific support for their construction or reconstruction, as well as based on the results of survey and diagnostic work during the updating and filling of the analytical expert bridge management system (AESUM) at the facilities Poltava region. Results. The paper analyzes and provides recommendations for preventing cracking and eliminating defects in the constructions of monolithic transport structures. Conclusions. Monolithic transport facilities require complex solutions for the design of span structures and coverings, ensuring the proper organization of water drainage and compliance with the requirements of current regulatory documents and technological regulations during construction and operational works. When performing calculations of monolithic span structures of transport facilities, stricter requirements should be put forward regarding crack resistance indicators when calculating the formation and opening of cracks. It is also necessary to pay more attention to the technology of installing a cement-concrete coating. In order to reliably establish the bearing capacity of monolithic span structures, it is proposed to investigate dynamic effects during the inspection of structures and take into account the actual forces from moving loads in the presence of irregularities formed on the carriageway.

Macro-cell corrosion between crossed steel bars in cracked concrete

• Macro-cell corrosion current I g included crack-induced macro-cell current I g s and current between two crossed steels I g d . • Both I g s and I g d increased in varying degrees with wider crack and the I g s / I g d ratio was always around 2. • Crack location was proved to influence the value and the direction of I g s and. I g d . To investigate the corrosion behavior of coupled crossed steel bars in cracked concrete, a study on the influence of crack width W and crack location L on the microcell and macro-cell corrosion of coupled crossed steels in cracked concrete is presented. The corrosion process of crossed steel bars in concrete specimens with crack widths of 0, 0.1, 0.2, 0.5 and 1.0 mm, respectively, were continuously monitored in an artificially created chloride environment for 26 weeks. The results showed that the corrosion of steel bars in cracked areas was much severer than that of steel bars in uncracked areas. Both microcell corrosion current ( I c o r r ) and macro-cell corrosion current ( I g ) of coupled active steel bars in a cracked area increased with the increase of the transverse crack width, and I c o r r was found to be more sensitive to the change of crack width. The I g / I c o r r ratio decreased with time, which meant that while macro-cell corrosion made a fair contribution, microcell corrosion played a dominant role in the whole corrosion period. In addition, the distance between the concrete crack and the intersection of the crossed steel bars, defined as the crack location L in the study, was proved to have a significant impact on the value and the direction of total macro-cell corrosion current I g .

Fractographic analysis of fracture features of a slugger punch and profile bending roll made of Kh12MF steel

A slugger punch and a roll forming roller made of C1.5Cr12MoV steel destroyed during operation are studied. It was established by spark spectrometry that the steel was up to the requirements for the chemical composition. Metallographic studies have shown that the steel structure represents martensite with carbides precipitates along the grain boundaries. Typical of this steel grade sulfides were found in the structure by the method of energy-dispersive X-ray spectral microanalysis. Fractographic analysis of fractures made it possible to determine the location of the initial crack and the subsequent fracture nature of the tool. The punch geometry discrepancy to the drawing is established. Its working surface has a one-sided slope. This fact led to unequal lateral stresses and brittle fracture of the punch support surface. Wear marks and transverse cracks were found on the roller working surface. They are caused by high contact stresses in conjunction with the difference in relative speeds of the roller surface and the workpiece. The propagation of main cracks in the radial direction of the roller led to its fatigue failure. Measurements of the punch and roller hardness by the Rockwell method revealed a deviation of the values from the normative documentation. It is found that the punch has extra hardness, which increases the fragility of the tool and reduces its resistance to impact loads. The working surface hardness of the roller is lowered, which leads to a decrease in the strength characteristics of the tool. Thus, the destruction of the tool was caused by the uneven action of operating stresses in combination with a violation of the recommendations on the tool hardness.

Reasons for formation of transverse cracks in longitudinal weld of a pipe of the main gas pipeline

Investigations of transverse cracks in a longitudinal weld of a main gas pipeline pipe are presented, and the reasons for the formation of defects are analyzed. A comparative analysis of the results of in-line diagnostics and additional non-destructive testing with the actual parameters of cracks in microsections was carried out. The microhardness of the weld metal was measured in the crack zone and at a distance of up to 20 mm from it in both directions, which showed the presence of residual stresses in the region of the crack tip. The methods of optical and electron scanning microscopy were used to study the crack zone with the determination of the chemical composition of the weld base metal and inclusions in the crack zone. The results obtained made it possible to classify defects as “cold cracks” that formed in the weld metal after a long period of operation and developed further according to the stress corrosion cracking mechanism.

Damage evolution characterization of glass fabric composites at cryogenic temperatures via in-situ tensile X-ray computed tomography tests

The woven fabric composites (WFCs) are promising materials for cryogenic applications. The internal microstructure of composites influences the cryogenic mechanical properties obviously. However, few works focused on the microstructure and damage evolution process of WFCs at cryogenic temperature. The mechanism of cryogenic effect on WFCs is still unclear due to the lack of in-situ characterization of damage evolution at different cryogenic temperatures. Herein, novel cryogenic in-situ tensile tests with micro X-ray-computed tomography (μCT) were designed to study the microstructure and morphology evolution of glass/epoxy WFCs. The damage evolution processes of glass/epoxy WFCs under tension at 293 K, 173 K, and 93 K were elucidated via in-situ CT scanning and 3D reconstruction. The results indicate that the initiation of multiple transverse cracks within the weft yarns and delamination damage are the primary microscale characteristics of glass/epoxy WFCs at low temperatures. The initiation of cracks and delamination damage promote the release of mechanical energy and decrease the effect of initial manufacturing defects, which are the main strengthening mechanisms of the glass/epoxy WFCs under tension at cryogenic temperature.

Asphalt pavement fatigue crack severity classification by infrared thermography and deep learning

Fatigue cracking is usually associated with the structural failure of asphalt pavement. This work aims to apply infrared thermography and deep learning, especially convolutional neural network (CNN), for asphalt pavement fatigue crack severity classification. A dataset of asphalt pavement fatigue cracking was built with four severity levels (no, low-severity, medium-severity, and high-severity) and three image types (visible, infrared, and fusion; fusion is the fusion of visible and infrared images). Thirteen CNN models were trained and evaluated based on accuracy, complexity (computational and model), and memory usage. This work applied Grad-CAM and Guided Grad-CAM to interpret the CNN model for classifying the different severity levels of different crack types (fatigue and longitudinal or transverse cracks) for the three image types. This work investigated the effect of image types on classifying different severity levels of fatigue crack and discussed the applicability of infrared thermography on crack detection (crack severity classification and crack segmentation). The results show that the CNN model had the highest accuracy on the infrared image, followed by the fusion image, and the lowest on the visible image. EfficientNet-B4 achieved the highest accuracy on all three image types, while the accuracy of CNN exceeded 0.95 on all three image types. Different image types made the CNN model have different accuracy in classifying the different severity levels of different crack types, which was interpreted by Grad-CAM and Guided Grad-CAM. Based on the high accuracy and reliability, the fusion image could be an accurate, efficient, and reliable method for crack detection.

Nb–Ti composite precipitation behaviour and its effect on the growth of austenite grains in peritectic steel

ABSTRACT Refinement of solidification austenite grains is an important way to control the transverse corner cracks. In the present work, the effect of Ti–Nb carbonitride on the refinement of solidification austenite grains is studied by laboratory experiments. Then, the precipitation temperature of Nb–Ti carbonitride is analysed by establishing a thermodynamic model. The results show that the austenite diameter decreases slowly from 1.45 to 1.16 mm (without Ti addition) and significantly decreases from 0.84 to 0.21 mm (with 0.02 wt-% Ti addition) with the Nb content varying from 0.03 to 0.09 wt-%. The pinning pressure provided by composite precipitation greatly increases with 0.02 wt-% Ti addition. The thermodynamic model of Nb–Ti carbonitride shows that the precipitation temperature of (Nb, Ti)(C, N) increases by approximately 20°C compared to Nb(C, N), which is the main reason for the increase in the pinning pressure.

Evaluation of the Transverse Crack Depth of Rail Bottoms Based on the Ultrasonic Guided Waves of Piezoelectric Sensor Arrays.

A method based on the high-frequency ultrasonic guided waves (UGWs) of a piezoelectric sensor array is proposed to monitor the depth of transverse cracks in rail bottoms. Selecting high-frequency UGWs with a center frequency of 350 kHz can enable the monitoring of cracks with a depth of 3.3 mm. The method of arranging piezoelectric sensor arrays on the upper surface and side of the rail bottom is simulated and analyzed, which allows the comprehensive monitoring of transverse cracks at different depths in the rail bottom. The multi-value domain features of the UGW signals are further extracted, and a back propagation neural network (BPNN) is used to establish the evaluation model of the transverse crack depth for the rail bottom. The optimal evaluation model of multi-path combination is reconstructed with the minimum value of the root mean square error (RMSE) as the evaluation standard. After testing and comparison, it was found that each metric of the reconstructed model is significantly better than each individual path; the RMSE is reduced to 0.3762; the coefficient of determination R2 reached 0.9932; the number of individual evaluation values with a relative error of less than 10% and 5% accounted for 100% and 87.50% of the total number of evaluations, respectively.

Field investigation of early-age behaviour of continuously reinforced concrete pavement with semi-rigid base

ABSTRACT This study investigates the early-age behaviour of continuously reinforced concrete pavement (CRCP) on the semi-rigid base, including structural behaviour during transverse crack propagation and curling behaviour both in the longitudinal and transverse direction. Field experiments are operated on a CRCP section in Wuhan, China. Vibrating wire strain gauges were installed at mid-slab and slab edge in the longitudinal and transverse direction for concrete strain and temperature measurement. Testing results showed the complexity of early-age behaviour of CRCP on semi-rigid base and curing with wet burlap sheets. An early-age transverse crack may originate from the bottom of the concrete slab due to the water absorption of the dry semi-rigid base. The development of a transverse crack took several cooling cycles. Curling behaviour in the longitudinal direction did not correspond to the temperature gradient after transverse crack occurrence. Typical curling motion in the transverse direction was found in the mid-slab rather than the slab edge. The findings of this study would lead to a better understanding of the early-age structure behaviour of CRCP on semi-rigid base and its impact on later road performance.

The Concrete Versus Asphalt Roadways: Case Studies

The road infrastructure is a major concern in the civilization of human being. Roads, bridges and tunnel link people together from the past to the present days. The pavement technology evolved through the centuries. The materials varied with time: from an earthy surface, to stones or cubes, from concrete slabs to hot mix polymer modified drainage asphalt. Depending upon the service condition and the atmospheric exposure, two main materials are used: concrete and asphalt. These building materials exhibited a significant mechanical property evolution in the last decades. Nonetheless, durability aspects, sustainability and maintenance costs awakened some discussions on the general performance of white (concrete) and black (bitumen) materials to be used as a pavement. The case studies focus on some main advantages and disadvantages of both cement-based and bituminous systems. They both can exhibit satisfactory general characteristics, such as surface roughness, mechanical strength, work placing velocity, recycling. Nonetheless, light reflection, surface regularity and the durability may be different. Longitudinal, transverse, net and tongue-like cracks, joints, pop-ups, wash-outs, chemical reactions and surface detachments are some of the defects that influence the functionality. These are largely related to the road layer system properties, road geometry, environment and at the end to the material choice.

Failure mechanism of ytterbium silicate/silicon bi-layer environmental barrier coatings on SiCf/SiC composites upon long-time water vapor and oxygen corrosion test

Environmental barrier coatings (EBCs) are crucial for SiCf/SiC composites to resist water vapor-oxygen corrosion and maintain the stability of their structure and properties in a complex combustion environment at high temperatures. In this work, an EBC system, composing Yb2Si2O7 topcoats and Si bond coats, has been prepared by an air plasma spraying (APS) route to completely wrap up SiCf/SiC composites. Then the corrosion and failure mechanisms of the EBC system in a water vapor-oxygen environment are systematically studied. The results indicate that the SiCf/SiC composites exhibit excellent stability under the full protection of the current EBCs. With the progression of corrosion, due to the difference of the thermal expansion coefficients (TECs) between the topcoat and bond coat materials, the vertical mud cracks generated by the thermal cycles become the intrusion passages for the corrosion species and then form transverse cracks and pores, resulting in the peeling off of the Yb2Si2O7 topcoat. Moreover, in the later stage of thermal cycles, the residue of the Si bond coat is shown to play an important protective role against the rapid corrosion of the substrates.