Crack Monitoring Research Articles

Monitoring of steel corrosion and cracking in cement paste exposed to combined sulfate–chloride attack with X-ray microtomography

The degradation process of reinforced cement paste exposed to cyclic wetting and drying with a designated salt solution was monitored through X-ray microtomography (μCT). Three exposure conditions (a 3 wt% NaCl solution, a 5 wt% Na2SO4 solution, or a mixed solution of 3 wt% NaCl and 5 wt% Na2SO4) were studied to investigate the potential synergistic effects between chloride and sulfate ions on the deterioration of reinforced cement-based materials. The time-dependent evolution of steel corrosion and cracking of cement paste cover were tracked and visualized, while the volumes of steel loss, corrosion products and cracks were quantified by image analysis. The results indicated that the presence of sulfate ions significantly delayed the initiation of chloride-induced corrosion, but did not seem to greatly affect the corrosion rate once the corrosion occurred. The existence of chloride ions, in turn, also mitigated the damage of cement paste cause by sulfate attack as evidenced by the reduced volumes of cracks. The conventional volume expansion coefficient of corrosion products can be measured by μCT, but this coefficient may not be applicable for modelling the corrosion-induced cracking process when sulfate ions were present. The use of μCT provides a new angle to directly measure the interfacial displacement in reinforced cement paste, which can be used as a valuable input for modelling non-uniform chloride-induced corrosion in the presence of sulfate ions.

Research on crack monitoring technology of multilayer structure based on TMR-eddy current sensor

The flexible eddy current array sensor has the characteristics of flexibility, bendability and light weight, which has a great application prospect in the field of structural health monitoring. The traditional flexible eddy current array sensor is affected by the skin effect and the crack monitoring depth is relatively low. This paper proposes an eddy current array sensor which uses TMR (tunnel magneto-resistance) sensor as sensing channels. It reduces the excitation frequency and increases the eddy current skin depth. The TMR sensor realizes the quantitative monitoring of cracks by the array arrangement. First, the finite element model of the sensor is established, and the influence of the cracks on the different layers of the multilayer structure on the magnetic induction intensity at the test point is analyzed. The simulation and results show that when the crack passes through the sensor, the magnetic induction intensity at the three test points changes in sequence and gradually increases to the maximum value. The direct relative position of the maximum value of the three test points is approximately the same as the distance among the test points. Then, the simulated crack growth experiment of the corresponding sensor is carried out. The experimental results show that as the crack grows, the signals of the three TMR sensors on the eddy current sensor change in sequence, and the distance between the characteristic points is consistent with the distance between the TMR sensors. The output voltage of the sensor decrease with the crack depth increases. The experimental results are consistent with the simulation results, which further verifies the correctness of the simulation model.

Cracks Monitoring and Resistivity Test for a Double-Storey House due to Cavity in the Soil

This paper presents the feasibility study of structural assessment and monitoring of two-story house due to soil settlement which was not well-compact before construction commenced. Two stages assessments were conducted to monitor and evaluate the structural integrity of existing double-story house which involves preliminary investigation and detailed assessment. Preliminary investigation includes visual inspection of cracks, soil settlement and structural damages. Meanwhile, detailed assessment comprises of crack width measurement, Non-Destructive Test (NDT) and resistivity test. The first detail assessment was carried out on 18th July 2019 which involved crack width measurement, Ultrasonic Pulse Velocity (UPV) test and rebound hammer test. The second inspection was conducted on 19th October 2019 to monitor and identify the integrity of the structure and the main causes of the problem. Visual inspection and non-destructive test indicate that the defects found in the house can be categorized as partial damage due to soil settlement. Resistivity test showed that there were cavities and void areas underneath the house and during raining season these void areas were filled with water. The soil underneath the house consists of clay, sand, alluvium and limestone. Results from rebound hammer and Ultrasonic Pulse Velocity (UPV) during the monitoring works showed that low compressive strength and poor quality of concrete were developed, respectively. Besides that, monitoring crack width using veneer caliper showed that the crack was active and extended in a short period of time. Therefore, it is recommended to fill up the void area underneath the house with self-compacting concrete in order to control the cracks and structural damages of double-story house.

Ultrasonic monitoring of stress and cracks of the 1/3 scale mock-up of nuclear reactor concrete containment structure

To evaluate the stress level and damage of a reinforced concrete containment wall (similar to those used in nuclear power plants) and its reaction to pressure variations, we conducted successive ultrasonic experiments on the exterior surface of the containment wall in the gusset area for three consecutive years (2017, 2018 and 2019). During each experiment, the pressure inside the containment wall increased gradually from 0 MPa to 0.43 MPa and then decreased back to 0 MPa. From the analysis of the ultrasonic coda waves obtained in the multiple scattering regime (80–220 kHz), we performed Coda Wave Interferometry to calculate the apparent velocity changes in the structure (denoted by dV/V a ) and Coda Wave Decorrelation (DC) measurements to produce 3D cartographies of stress and crack distribution. From three source–receiver pairs, located at the top, middle and bottom of the experimental region, we observe that coda waves dilate, shrink and remain almost unchanged, respectively. This corresponds to the decreasing, increasing and invariant pressure inside the concrete. The comparison of 3 years’ results demonstrates that the variation of dV/V a and DC under the same pressure test increases through the years, which indicates the progressive deterioration and ageing of the concrete. From a large collection of source–receiver pairs at different times, the spatial–temporal variations of dV/V a and DC are then used to produce a map of the structural velocity and scattering changes, respectively. We observe a decreasing velocity on the top part and an increasing in the middle one, which is in line with the dV/V a analysis. The reconstructed scattering changes (or structural changes) highlight the active region during the inflation–deflation procedure, corresponding to the opening and closing (and sometimes the development) of cracks. The larger magnitude in 2019 than in 2017 indicates the increasing damage in the concrete.

Concrete Cracks Detection and Monitoring Using Deep Learning-Based Multiresolution Analysis

In this paper, we propose a new methodology for crack detection and monitoring in concrete structures. This approach is based on a multiresolution analysis of a sample or a specimen of concrete material subjected to several types of solicitation. The image obtained by ultrasonic investigation and processed by a customized wavelet is analyzed at various scales in order to detect internal cracks and crack initiation. The ultimate objective of this work is to propose an automatic crack type identification scheme based on convolutional neural networks (CNN). In this context, crack propagation can be monitored without access to the concrete surface and the goal is to detect cracks before they are visible. This is achieved through the combination of two major data analysis tools which are wavelets and deep learning. This original procedure is shown to yield a high accuracy close to 90%. In order to evaluate the performance of the proposed CNN architectures, we also used an open access database, SDNET2018, for the automatic detection of external cracks.

Longitudinal Crack Detection Approach Based on Principal Component Analysis and Support Vector Machine for Slab Continuous Casting

Longitudinal cracks are the typical surface defects of continuous casting slabs, resulting in additional processing or even casting interruption. Monitoring longitudinal crack defects is of great significance in stabilizing and improving the slab quality. Herein, a monitoring model is developed to recognize the longitudinal crack defect of continuous casting slabs using principal component analysis (PCA) and support vector machine (SVM). First, the typical characteristics of the temperature patterns corresponding to the longitudinal crack defect are extracted, including the normal casting temperature with small and large fluctuations, as well as the longitudinal crack temperature. Then, PCA is used to reduce the dimension of these characteristics for removing the redundancy and reducing the computational burden. Subsequently, an SVM is applied to identify normal and longitudinal crack temperature patterns for training the monitoring model PCA–SVM. The monitoring performance is verified by the test data, in which the training accuracy and test accuracy are 100% and 96%, respectively. It is worth mentioning that the model can successfully predict all the real longitudinal crack defects, showing excellent detection performance. The established model is expected to provide a theoretical basis and a reliable way for online monitoring of slab surface cracks.

Digital Image Correlation for Evaluation of Cracks in Reinforced Concrete Bridge Slabs

In proof-loading of concrete slab bridges, advanced monitoring methods are required for identification of stop criteria. In this study, Two-Dimensional Digital Image Correlation (2D DIC) is investigated as one of the governing measurement methods for crack detection and evaluation. The investigations are deemed to provide valuable information about DIC capabilities under different environmental conditions and to evaluate the capabilities in relation to stop criterion verifications. Three Overturned T-beam (OT) Reinforced Concrete (RC) slabs are used for the assessment. Of these, two are in situ strips (0.55 × 3.6 × 9.0 m) cut from a full-scale OT-slab bridge with a span of 9 m and one is a downscaled slab tested under laboratory conditions (0.37 × 1.7 × 8.4 m). The 2D DIC results includes full-field plots, investigation of the time of crack detection and monitoring of crack widths. Grey-level transformation was used for the in situ tests to ensure sufficient readability and results comparable to the laboratory test. Crack initiation for the laboratory test (with speckle pattern) and in situ tests (plain concrete surface) were detected at intervals of approximately 0.1 mm to 0.3 mm and 0.2 mm to 0.3 mm, respectively. Consequently, the paper evaluates a more qualitative approach to DIC test results, where crack indications and crack detection can be used as a stop criterion. It was furthermore identified that crack initiation was reached at high load levels, implying the importance of a target load.

Detection of Faults and Vibration Analysis in Beam Structures - A Review

This review focuses on vibrating beam structures with different constraints. The review is also aimed to analyse the different fault detection approaches for condition monitoring of cracks in vibrating structures. The advancement in this field with significant and diversified techniques namely analytical, numerical and experimental approaches are elaborated and presented here. The significance of crack location and the severe effects on the responses of the vibrating structure are discussed. The application of piezoelectric material on structures, as well as different fault detection and soft computing techniques are summarized to monitor the conditions of a structure. A concise review study has also been conducted for better improvement in the service period. The integrity of the structure can be improved with the aid of vibration control and Structural Health Monitoring (SHM) approaches.

Chipless RFID Multisensor for Temperature Sensing and Crack Monitoring in an IoT Environment

Nowadays, structural health monitoring and thermal contemplation of remote places are of serious significance. In this scenario, chipless radio frequency identification (RFID) sensors are the vital enablers to monitor remote circumstances in the low-cost pervasive network. This letter presents a compact 7-bit chipless RFID multiparameter sensor designed on smart Rogers RT/Duroid <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">®</sup> 6010.2LM material. The material alters its dielectric properties concerning temperature fluctuations. Six inverted “U” and “L” shaped resonators are designed with specific length and width to resonate within the desired frequency band of 2-8 GHz. A circular microstrip patch antenna is used for the characterization of the crack. The measurements are performed outside the anechoic chamber in an electromagnetically quiet environment. The realized novel smart sensor can be attached to monitor any crack in the metal surface, where temperature monitoring is also crucial. The proposed state-of-the-art robust multisensor is suitable for long-term applications.

Application of Optical Fiber Sensors for Crack Monitoring in a Masonry Structure during Geotechnical Foundation Remediation

Application of Optical Fiber Sensors for Crack Monitoring in a Masonry Structure during Geotechnical Foundation Remediation

Dual crack growth prognosis by using a mixture proposal particle filter and on-line crack monitoring

On-line prognosis of fatigue cracks in the structure is challenging due to various uncertainties affecting fatigue crack initiation and growth. This paper proposes an on-line prognosis strategy for fatigue cracks by incorporating the mixture proposal particle filter (MPPF) and structural health monitoring (SHM) results. In this method, a dynamic crack evolution model is proposed to deal with the situation that more than one crack occurs and grows in the structure. Meanwhile, crack sizes monitored by the SHM technique are incorporated to construct an effective mixture proposal of the importance probability density, which is the key for sampling new particles. Further, posterior estimations of the fatigue crack sizes and the crack evolution model parameters are evaluated with these particles, based on which the prognosis of fatigue crack growth is carried out. A leave-one-out validation is performed on the dual crack growth problem of the hole-edge-cracked structure, demonstrating the effectiveness of the proposed method.

Simulated Lamb wave propagation method for nondestructive monitoring of matrix cracking in laminated composites

The estimation of the damping coefficient may help to improve the damage detection in composite materials. The purpose of this study was to develop the simulated Lamb wave propagation method for nondestructive monitoring of matrix cracking in laminated composites via the accurate estimation of their damping coefficient. Cross-ply composite specimens with different crack densities were fabricated and tested by the Lamb wave propagation technique. The phase velocity of the Lamb wave and the damping coefficient of the specimens were measured. The finite element models were developed at micro-scale (representative volume elements) and macro-scale (laminated specimens) levels to simulate the Lamb wave propagation in composite specimens. An optimization process was performed through the model updating procedure to achieve finite element models that were in good agreement with experiments. The phase velocity and damping coefficient, obtained from the updated FE models for two crack densities other than those used in the model updating procedure, were successfully examined by experimental results. It was also revealed that the damping coefficient and the rate of increase in the damping coefficient in terms of the crack density were higher for the composite laminates with a higher number of 90° layers. The damping of the fiber–matrix interphase and crack regions were considered in the model and shown as a significant contribution to the overall damping of the composite specimens. The proposed simulated Lamb wave propagation method can be used as a virtual lab for in-situ monitoring of laminated composites with different material properties, stacking sequences, and crack densities.

Fatigue Crack Monitoring of T-Type Joints in Steel Offshore Oil and Gas Jacket Platform.

Several approaches have been used in the past to predict fatigue crack growth rates in T-joints of the offshore structures, but there are relatively few cases of applying structural health monitoring during the non-destructive testing of jacket platforms. This paper presents an experimental method based on the sensing of the piezoelectric sensors and finite element analysis method for studying the fatigue cracks in the offshore steel jacket structure. Three types of joints are selected in the current research work: T-type plate, T-type tube-plate, and T-type tube joints. The finite element analysis model established in the current study computes and analyzes the high stress and high strain regions in the T-type joints. The fatigue damage in the T-type joints was successfully detected by utilizing both the finite element analysis and experimental methods. The results showed that fatigue cracks of the three types of joints are prone to appear at the weld toe and spread in the welding direction. The fatigue damage location of T-type plate and T-type tube-plate joints is more concentrated in the upper weld toe area, and the fatigue damage location of the T-type tube joint is closer to the lower weld toe area.

Integration of eddy current sensors into repair patches for fatigue reinforcement at rivet holes

AbstractFatigue cracks at rivet holes occur at advanced service life of aircrafts due to cyclic loading. As a repair method, adhesively bonded stiffener patches enhance the fatigue life of the structure by delaying crack initiation and reducing crack growth. Combining a crack sensor with a repair patch to a sensor‐based stiffener patch allows crack growth reduction and monitoring at the same time. This paper presents a feasibility study on the integration of eddy current sensors into carbon fibre reinforced plastic (CFRP) repair patches. To this end, a specific patch design is developed, and samples are manufactured by ultrasonic fabrication. The performance of the patches is investigated in fatigue tests in terms of ‘crack reinforcement’ and ‘crack detection.’ Both requirements are met. The undertaking of future efforts to tailor the sensor‐based repair patch concept to an individual application in aircraft maintenance seems reasonable.

Crack Monitoring in the Welding Parts of Different Alloys of Aluminium using Digital Image Correlation

Crack Monitoring in the Welding Parts of Different Alloys of Aluminium using Digital Image Correlation

Decoupled Monitoring Method for Strain and Cracks Based on Multilayer Patch Antenna Sensor.

As the rapid development of high-end intelligent equipment continues, the design requirements for crack and strain monitoring equipment are increasing daily. In this paper, a decoupled monitoring method for strain and cracks based on a multilayer patch antenna sensor is studied. First, the monitoring principle for strain and crack decoupling is analyzed. Second, the design method for the multilayer patch antenna sensor is studied, and the hierarchical arrangement, patch size, substrate layer thickness, and feeding line structure are designed on the basis of this method. A quarter-wavelength impedance converter is designed to perform impedance matching and optimize the resonant frequency information. The effects of strain and crack propagation on the resonant frequency of the patch antenna are analyzed through simulations, and the decoupled monitoring method for the structural stress state and crack propagation is discussed. Lastly, the feasibility of decoupled monitoring of strain and cracks is verified experimentally. The results of the theoretical analysis, simulations, and experiments show that the proposed patch antenna sensor based on the multilayer structure can realize decoupled monitoring of strain and cracks in the structure, and the sensor has broad application prospects.

Influence of spatial winding distribution of flexible eddy current sensor on quantitative monitoring of subsurface cracks

This paper proposes a flexible eddy current sensor based on TMR sensor. Firstly, the influence of three kinds of sensors with different spatial winding distributions on the penetration depth of magnetic field is analyzed through theoretical derivation. Then, the finite element model is established to analyze the eddy current distribution on the cross-section of the specimen under different excitation frequency and spatial winding distribution. The distribution of eddy current can be improved by increasing the spatial winding distribution. Finally, the corresponding sensors are prepared for subsurface crack monitoring. The experimental results show that the sensor with a spatial winding distribution of 10 mm can quantitatively monitor the cracks below 3 mm of material surface, and increasing the space winding distribution of the sensor to 20 mm, it can quantitatively monitor cracks below 5 mm of material surface, and the crack monitoring accuracy is consistent with the spacing between excitation lines.

Crack Detection and Localisation in Steel-Fibre-Reinforced Self-Compacting Concrete Using Triaxial Accelerometers.

Cracking in concrete structures can significantly affect their structural integrity and eventually lead to catastrophic failure if undetected. Recent advances in sensor technology for structural health monitoring techniques have led to the development of new and improved sensors for real-time detection and monitoring of cracks in various applications, from laboratory tests to large structures. In this study, triaxial accelerometers have been employed to detect and locate micro- and macrocrack formation in plain self-compacting concrete (SCC) and steel-fibre-reinforced SCC (SFRSCC) beams under three-point bending. Experiments were carried out with triaxial accelerometers mounted on the surface of the beams. The experimental results revealed that triaxial accelerometers could be used to identify the locations of cracks and provide a greater quantity of useful data for more accurate measurement and interpretation. The study sheds light on the structural monitoring capability of triaxial acceleration measurements for SFRSCC structural elements that can act as an early warning system for structural failure.

Desiccation cracking at field scale on a vegetated infrastructure embankment

This paper presents a desiccation crack monitoring campaign conducted on a full-scale, vegetated infrastructure embankment subjected to one-year of seasonally variable weather. The field survey involved direct measurement of naturally developed, annually reoccurring cracks in a heavily instrumented, clay fill embankment (BIONICS, Newcastle University). Transient crack morphology was captured in terms of opening width, length and depth, in addition to meteorological and near-surface soil hydrological conditions. In order to assess any correlation between crack development and weather-driven changes in near surface soil conditions, the volume of cracks was estimated using an empirically derived equation. This research study identified crack behaviour in four stages: initiation, expansion, contraction and closure. These stages and the distribution of cracks on the slope are closely related to prevailing atmospheric conditions, namely wind direction, relative humidity, precipitation and potential evapotranspiration. These ultimately govern the soil hydrological conditions in the near surface, as manifested in the presented matric potential and volumetric water content data. Linearly descrete cracks are shown to form under such conditions in contrary to the polygonal patterns typically reported under laboratory conditions. Crack length growth terminates prior to full volumetric maturation with crack depth dominating the dynamic response regardless of overall crack size.

Damage detection and fatigue life estimation under random loads: A new structural health monitoring methodology in the frequency domain

AbstractThis paper presents a methodology for structural health monitoring of fatigue cracks under stationary random loads. The methodology is composed of two parts: an empirical correlation to monitor the evolution of damage indices and a numerical scheme for fatigue life estimation. The damage indices are based on the variation of the vibrational response of the structure due to crack propagation. Two damage metrics are studied, and the methodology is verified for a cantilever beam subjected to random base excitation. The case study validates the effectiveness of the methodology and shows that both metrics have the potential for damage detection. For the numerical estimation of the fatigue life, the proposed framework uses the probability density function of the stress, which is obtained from frequency‐domain methods, and an equivalent stress approach based on the Walker's equation for fatigue crack growth. Excellent agreement is found between the predicted fatigue life and the experimental values.