Invisible Cracks Research Articles

Cracking characteristics evaluation for reinforcement basalt fiber reactive powder concrete beam using acoustic emission

New types of fibers such as basalt fibers are gradually being used to reinforce cement-based concrete materials. To provide a basis for the further popularization of basalt fibers and basalt fiber reinforced reactive powder concrete (BFRPC) materials, the bending mechanical properties and fracture properties of BFRPC beams were investigated by innovatively applying four-point bending test and multiple acoustic parameter analysis methods. On the one hand, the load vs. displacement curve and crack pattern of reinforcement BFRPC beam were obtained from the four-point bending test. On the other hand, Acoustic emission (AE) technology was used to monitor the cracking process of reinforcement BFRPC beam under four-point bending load, and the AE signal was analyzed to illustrate the cracking characteristics of reinforcement BFRPC beam. The results revealed that AE hits, amplitude, counts, duration, and energy have a similar changing trend with bending load. Cumulative hits and cumulative energy are positively linearly related to the displacement and quadratically related to the sum of crack widths, and the correlation coefficients are all above 0.95. Besides, the cracking process of reinforcement BFRPC beam can be divided into four stages by the variation of AE basic parameters with bending load. The main rebars yielding is an important turning point of the crack characteristic of reinforcement BFRPC beam. AE signal data varies greatly in different locations, and it has an obvious advantage to detect the formation of invisible cracks. The results of predicting concrete damage and cracking by AE signal data are consistent with the experimental phenomenon. The low-stress brittle fracture caused by tensile fracture was reduced, and the tensile resistance and flexural bearing capacity of the reinforcement BFRPC beam were increased. The results obtained in this paper support the damage assessment and structural health monitoring for cement base concrete materials under bending load.

Crack Identification by Digital Image Correlation Method Using Crack Shape as Prior Information

Abstract A new crack identification method that estimates the cracks in invisible locations based on the surface deformation measured by digital image correlation (DIC) is developed. An inverse problem is setup to estimate such invisible cracks from surface deformations. The inverse problem has an ill-condition because of noise contained in surface deformations. Our proposed regularization method uses prior information and Expectation a Posteriori (EAP) estimation. Prior information includes candidate crack shapes and surface deformations due to cracks. The candidate crack shapes are created by determining a crack's starting point and propagating it based on the force at its perimeter (ligament). A prior distribution is the surface deformations due to the candidate crack shapes. The likelihood distribution is a surface deformation measured by the DIC method. A posterior distribution is defined from the prior and likelihood distributions. In this study, the estimated result is the expected value of the posterior distribution. The validation test was performed, and the result shows that the proposed method superior to the conventional L1-norm regularization method.

Impact localization and force reconstruction for composite plates based on virtual time reversal processing with time-domain spectral finite element method

Composite structures are widely used in different industries as important load-carrying components due to their excellent performance. These structures are prone to be damaged under low-velocity impacts with invisible cracks. Hence, impact identification is a critical part of composite structural health monitoring. In this paper, an approach is developed, which is based on time-reversal (T-R) processing and time-domain spectral finite element method. The spatial and temporal focusing properties of T-R are utilized to locate the impact source and restore the impact force, respectively. Moreover, the impact energy is evaluated by establishing the function of impact force and kinetic energy at the impact moment. The proposed method is validated experimentally for different scenarios. The influences of the signal length and accuracy of the numerical model on the proposed method are discussed in detail. The results demonstrate that the proposed method can correctly locate the impact source in composite structures, and the identified impact force can reproduce the impact event efficiently. The impact localization is essentially independent of the effect of signal length while it is vulnerable to the mesh grid. Besides, the developed method has consistent results in the case of data perturbation of material properties in the numerical model, which shows its good robustness.

Effect of partitioning YBaCuO bulk on the levitation force in Halbach external field

When a YBaCuO bulk superconductor (SC) is subdivided, its levitation force may not be significantly reduced after this partitioning process. The force will decrease even less if the sectional surface introduced by partitioning is parallel to the induced current loop. Moreover, the levitation force can be maintained because the partitioning makes the SC more magnetizable. These findings have implications for longitudinal maglev technology. A method for calculating levitation forces in nonuniform fields based on critical-state theory is proposed. In this method, an SC is divided into several regions where the external field is approximately uniform within each subvolume. To minimize the force degradation introduced by partitioning, the cutting surfaces should be parallel to the induced current. This approximate approach can effectively reproduce the experiment and improve the calculation accuracy. Another application of combining and recovering discrete SCs is demonstrated, and it is shown that a recombined SC according to the small-loss partitioning condition can achieve 68% of the levitation capacity of an intact sample. In addition, the invisible cracks inside the bulk sample can be predicted by comparing its levitation force with that of the intact sample.

Investigation of Utilizing Bacteria to obtain Self-Healing of Invisible Cracks in Mortar

Investigation of Utilizing Bacteria to obtain Self-Healing of Invisible Cracks in Mortar

Early detection and assessment of invisible cracks in compressed oral solid dosage forms

In the pharmaceutical manufacturing industry, real-time in situ quality monitoring for detecting defects at an early stage is a desirable ability, especially in high-rate production, to minimize downstream quality-related issues, financial losses, and timeline risks. In this study, we focus on the early detection of crack formation in compressed oral solid dosage (OSD) forms at its onset before complete delamination and/or capping in downstream processing. The detection of internal tablet cracks related to local micro-stress/strain states, internal granularity (texture), and micro-structure failures is rather unlikely by traditional testing methods, such as the USP reference standards for friability, fracturing, or hardness testing. In addition, these tests do not permit the objective and quantitative evaluation of the influence of formulation and process parameters, which are critical for the development of high-quality drug products manufactured at high rates on a large scale. Internal cracks (potentially resulting in ‘capping’ and/or ‘lamination’) under high-strain compaction of highly visco-elastic powder materials are a common failure mode. In the current study, two approaches are introduced and utilized for non-destructively detecting and evaluating hidden cracks in pharmaceutical compacts based on (i) varying axial load–displacement measurements and (ii) ultrasonic reflection ray tracing. The reflection ray tracing technique is a non-destructive, inexpensive, rapid, and material-sparing approach, which makes it advantageous for real-time quality monitoring and defect characterization applications. The varying axial load–displacement technique is more suitable for analytical studies, especially in the design and development phases of compressed OSD products. In this study, as a model application, utilizing these two approaches, it is demonstrated how internal and external cracks can be detected, localized, characterized, and analyzed as a function of disintegrant ratio and main compression force. Various uses of these two techniques in practice, such as in Continuous Manufacturing (CM) and Real-Time Release Testing (RTRT), are also discussed.

Identification of Crack Shapes by Digital Image Correlation Using Joint Estimation Maximum a Posteriori Method

AbstractA method that estimates invisible cracks from the surface based on the surface deformation measured by digital image correlation (DIC) is being developed. An inverse problem is setup to estimate such invisible cracks from the surface deformation. Surface deformation, measured by the DIC method, contains noise. Inverse problems have ill-conditions. The regularization method applied in this study is an extension of the joint estimation maximum a posteriori (JE-MAP) method. The JE-MAP algorithm alternates between MAP method estimation and the grab-cut (GC) method to avoid ill-conditions. The physical constraints on displacement and the forces at the cracks and the crack perimeters (ligaments) are added to the MAP method. The displacement and load at the cracks and the ligaments have a cross-sparse relationship. The MAP method estimates the displacement or the load at the cracks and the ligaments. The estimated result varies greatly at the boundary between the cracks and the ligaments. This boundary is determined by the GC method based on the estimated result. This study amplified the changes at the boundary between the cracks and the ligaments in the estimated results. The amplified results were input into the GC method to improve the boundary-determination accuracy. The regularization method developed from the JE-MAP method was combined with DIC method to estimate the cracks in invisible locations. The method proposed in this study estimated cracks more accurately than L1-norm regularization in inverse problems where the observed data were strain distributions measured by the DIC method.

Remaining useful life prediction framework for crack propagation with a case study of railway heavy duty coupler condition monitoring

A general Remaining useful life (RUL) framework for predicting crack propagation of mechanical system structures based on limited condition monitoring data was proposed. For states of invisible cracks, a method that considers the common characteristics of the object was proposed by using the crack propagation stage as the delay time, combining statistical distribution and hypothesis testing. Then, for the states of visible cracks, methods based on a hypothetical distribution and support vector regression with the Kalman filter considering the current state and individual degradation characteristics were proposed. Finally, taking the condition monitoring data of the coupler body crack state as a case, the RUL prediction from the whole to the individual differences is achieved. The research results indicate that the framework achieves a competitive effect in RUL of internal crack propagation structures of railway wagons, which have important theoretical and practical value for integrity assessment and reliability life prediction.

JE-MAP法を用いたデジタル画像相関法によるき裂形状の同定

We are developing a method that estimates cracks that are invisible from the surface based on the surface deformation measured by digital image correlation (DIC). An inverse problem is set up to estimate such invisible cracks from the surface deformation. Surface deformation, measured by the DIC method, contains noise. Inverse problems have an ill condition. The regularization method applied in this study is an extension of the JE-MAP method. The JE-MAP algorithm alternates between Maximum a Posteriori (MAP) estimation and the Grab-cut (GC) method to avoid ill-conditions. The physical constraints on displacement and the forces at the cracks and the crack perimeters (ligaments) are added to the MAP method. The displacement and load at the cracks and the ligaments have a cross-sparse relationship. The MAP method estimates the displacement or the load at the cracks and the ligaments. The estimated result varies greatly at the boundary between the cracks and the ligaments. This boundary is determined by the GC method based on the estimated result. In this study, we further amplified the changes in our estimates at the boundary between the cracks and the ligaments. The amplified results were input into the GC method to improve the boundary-determination accuracy. Our extension of the JE-MAP method was combined with DIC to estimate the cracks in invisible locations.

Detection of invisible cracks in ceramic materials using by pre-trained deep convolutional neural network

Ceramic materials are an indispensable part of our lives. Today, ceramic materials are mainly used in construction and kitchenware production. The fact that some deformations cannot be seen with the naked eye in the ceramic industry leads to a loss of time in the detection of deformations in the products. Delays that may occur in the elimination of deformations and in the planning of the production process cause the products with deformation to be excessive, which adversely affects the quality. In this study, a deep learning model based on acoustic noise data and transfer learning techniques was designed to detect cracks in ceramic plates. In order to create a data set, noise curves were obtained by applying the same magnitude impact to the ceramic experiment plates by impact pendulum. For experimental application, ceramic plates with three invisible cracks and one undamaged ceramic plate were used. The deep learning model was trained and tested for crack detection in ceramic plates by the data set obtained from the noise graphs. As a result, 99.50% accuracy was achieved with the deep learning model based on acoustic noise.

Using plants distribution pattern to determine potentially unstable zone on the top of sea cliffs in Gurdim (Gulf of Oman, Iran)

Determination of hazard zones or potentially unstable zones on the top of sea cliffs to prevent construction in coastal areas is an important issue of coastal management. On the top of the high elevated cliffs in Gurdim, in the Iranian coastline of Gulf of Oman, plants have grown and distributed along the lines parallel to cliff top line likely relating to covered and invisible cracks. In the present study, first, the probable relation between the special distribution pattern of plants and mass movements was assessed according to field observations as well as the correlation between different geometric factors of cliffs and landslides. Then, the potentially unstable zones on top of the cliffs were estimated according to the distribution pattern of plants. Also, the hazard zones were estimated and drawn on top of these cliffs using previous criteria and methods in order to be compared with the unstable zones determined by plants distribution pattern. Finally, some criteria were proposed to estimate the potentially unstable zones for the purpose of coastal management in the northern rocky coastlines of the Gulf of Oman.

Technological Sensor on Coupled Radial Spirals

We present the sensor with a sensitive element (SE) based on coupled radial spirals, which can be used for monitoring technological processes in the Electronic Industry, as well as for detecting damages on the pipelines under protective coatings. The main properties and characteristics of such SE are analyzed and measured. It is shown that the concentration of the electromagnetic field in a measuring space, caused by slowing down of the the wave, and splitting of the electric and magnetic fields leads to a significant increase in sensitivity, whereas the multiple increases in the slowdown makes it possible to use the advantages of SE with distributed parameters at relatively low operating frequencies. The practical realization of the described sensor is demonstrated in measuring the ion implantation processes and the thickness of the metallization, as well as in monitoring the invisible cracks and damages through the protective coats on the metal surfaces.

Analysis of crack propagation in longitudinal beam of high- pile wharf during winter temperature decrease period

Ports play an increasingly important role in economic development and are the core strategic advantages that drive regional economic development. As hydraulic structure, the working environment of the wharf is relatively complicated. There are many factors affecting its normal use. Visible or invisible cracks are common in wharf components. Temperature stress change is the main factor for the formation of cracks on the surface of concrete beams. When affected by temperature changes, existing fine cracks will connect, expand, and even penetrate the entire component. It will not only affect the aesthetics of the wharf, but also affect its service life, and bring considerable economic losses to later maintenance. Therefore, it has certain reference value and significance to study on crack propagation for assessment of safety, reliability and durability of engineering structures. In view of this, this paper carries out numerical analysis on crack propagation of reinforced concrete longitudinal beams of a high-piled wharf in China with ABAQUS software and extended finite element method (XFEM). In the simulation process, only temperature drop factor is considered. At the same time, this paper introduces the research progress and some basic theories of XFEM at home and abroad. The results show that the numerical simulation results are similar to the crack opening degree measured by the seam gauge. XFEM can effectively describe the crack propagation in concrete, which is more accurate and feasible than the conventional finite element method (CFEM).

HYDRO ISOLATION MATERIALS, LUMINOPHORE AND OTHER DEFICIENT PRODUCTS, INNOVATIVE TECHNOLOGY


 
 
 
 One of the main objectives of the project is to develop a methodology for obtaining high quality water-proofing materials. The above- mentioned high-melting tar mass will be used as the main raw material. Especial treatment and further homogenization of the mass – mixture of high-dispersive quartz sand, silicates and other wastes – gives possibility to make various universal and inexpensive compositions. With the aim to improve hydro-insulating and other specific characteristics of the compositions they will be varied by changing the ratio of ingredients. The elasticity of these compositions is conditioned by macromolecular paraffin-ceresin and the polymeric (rubber) components; varying the strength and adhesion is possible by soluble and insoluble silicate-quartz components. The mentioned components can be got in a large amount in region. Therefore, products obtained from cheap raw materials will be inexpensive. The use of the mentioned waste is also important to avoid the pollution of nature. Operating characteristics of the proposed luminophore satisfy requirements of international standarts. In particular, the solutions made from it have an ability to detect invisible cracks of the thick < 1 mm. The light intensity in its greenish-yellow area is 4,5-5 times more than that of standard - uranyl nitrate. It is stable with high quantum efficiency (40-45%).
 
 
 

Non-Destructive Testing for Building Diagnostics and Monitoring: Experience Achieved with Case Studies

Building inspection on site, in other words in-situ examinations of buildings is a troublesome work that necessitates the use of non-destructive investigation (NDT) techniques. One of the main concerns of non-destructive testing studies is to improve in-situ use of NDT techniques for diagnostic and monitoring studies. The quantitative infrared thermography (QIRT) and ultrasonic pulse velocity (UPV) measurements have distinct importance in that regard. The joint use of QIRT and ultrasonic testing allows in-situ evaluation and monitoring of historical structures and contemporary ones in relation to moisture, thermal, materials and structural failures while the buildings themselves remain intact. For instances, those methods are useful for detection of visible and invisible cracks, thermal bridges and damp zones in building materials, components and functional systems as well as for soundness assessment of materials and thermal performance assessment of building components. In addition, those methods are promising for moisture content analyses in materials and monitoring the success of conservation treatments or interventions in structures. The in-situ NDT studies for diagnostic purposes should start with the mapping of decay forms and scanning of building surfaces with infrared images. Quantitative analyses are shaped for data acquisition on site and at laboratory from representative sound and problem areas in structures or laboratory samples. Laboratory analyses are needed to support in-situ examinations and to establish the reference data for better interpretation of in situ data. Advances in laboratory tests using IRT and ultrasonic testing are guiding for in-situ materials investigations based on measurable parameters. The knowledge and experience on QIRT and ultrasonic testing are promising for the innovative studies on today’s materials technologies, building science and conservation/maintenance practices. Such studies demand a multi-disciplinary approach that leads to bring together knowledge on materials science and building science.

Non-Destructive Testing for Building Diagnostics and Monitoring: Experience Achieved with Case Studies

Building inspection on site, in other wordsin-situexaminations of buildings is a troublesome work that necessitates the use of non-destructive investigation (NDT) techniques. One of the main concerns of non-destructive testing studies is to improvein-situuse of NDT techniques for diagnostic and monitoring studies. The quantitative infrared thermography (QIRT) and ultrasonic pulse velocity (UPV) measurements have distinct importance in that regard. The joint use of QIRT and ultrasonic testing allowsin-situevaluation and monitoring of historical structures and contemporary ones in relation to moisture, thermal, materials and structural failures while the buildings themselves remain intact. For instances, those methods are useful for detection of visible and invisible cracks, thermal bridges and damp zones in building materials, components and functional systems as well as for soundness assessment of materials and thermal performance assessment of building components. In addition, those methods are promising for moisture content analyses in materials and monitoring the success of conservation treatments or interventions in structures. Thein-situNDT studies for diagnostic purposes should start with the mapping of decay forms and scanning of building surfaces with infrared images. Quantitative analyses are shaped for data acquisition on site and at laboratory from representative sound and problem areas in structures or laboratory samples. Laboratory analyses are needed to supportin-situexaminations and to establish the reference data for better interpretation of in situ data. Advances in laboratory tests using IRT and ultrasonic testing are guiding forin-situmaterials investigations based on measurable parameters. The knowledge and experience on QIRT and ultrasonic testing are promising for the innovative studies on today’s materials technologies, building science and conservation/maintenance practices. Such studies demand a multi-disciplinary approach that leads to bring together knowledge on materials science and building science.

A Multi-Step Source Localization Method With Narrowing Velocity Interval of Cyber-Physical Systems in Buildings

The localization for sources in the heterogeneous and complex media is of vital significance, which can be applied to monitor the invisible cracks and determine the potential damage areas of buildings with safety hazards. Based on the localization function with the model of arrival time difference (TD), a multi-step localization method (MLM) without premeasured velocity for heterogeneous and complex propagation media was proposed. The velocity interval used for localization was narrowed and optimized continuously through the multi-step localization, where the optimal velocity interval was determined when the velocity differences were less than the threshold. Then, the optimal localization results with higher accuracy corresponding to this velocity interval can be obtained with the TD algorithm. A source locating test was performed at a building of masonry structure. In addition, the locating accuracy was compared and discussed between the optimized MLM, the one-step method without premeasured velocity, and the traditional method with different premeasured velocity values. Results show that MLM is obviously superior to both the one-step method and the traditional method. The developed MLM can not only eliminate the errors caused by premeasured velocity, but also can improve the locating accuracy in the heterogeneous and complex media, which is an efficient and effective method for engineering applications.

Plastics glow to warn of invisible cracks

Plastics glow to warn of invisible cracks

Experimental study of the mechanical behaviour of pin reinforced foam core sandwich materials under shear load

Sandwich structures with a lightweight closed cell hard foam core have the potential to be used in primary structures of commercial aircrafts. Compared to honeycomb core sandwich, the closed cell foam core sandwich overcomes the issue of moisture take up and makes the manufacturing of low priced and highly integrated structures possible. However, lightweight foam core sandwich materials are prone to failure by localised external loads like low velocity impacts. Invisible cracks could grow in the foam core and threaten the integrity of the structure. In order to enhance the out-of-plane properties of foam core sandwich structures and to improve the damage tolerance (DT) dry fibre bundles are inserted in the foam core. The pins are infused with resin and co-cured with the dry fabric face sheets in an out-of-autoclave process. This study presents the results obtained from shear tests following DIN 53294-standard, on flat sandwich panels. All panels were manufactured with pin-reinforcement manufactured with the Tied Foam Core Technology (TFC) developed by Airbus. The effects of pin material (CFRP and GFRP) and pin volume fraction on the shear properties of the sandwich structure and the crack propagation were investigated and compared to a not pinned reference. It has been concluded that the pin volume fraction has a remarkable effect on the shear properties and damage tolerance of the observed structure. Increasing the pin volume fraction makes the effect of crack redirection more obvious and conserves the integrity of the structure after crack occurrence.

The Review of New NDT Methods of Metal Material Fatigue Monitoring

Non-destructive testing (NDT) techniques have been employed in all kinds of fields successfully for many years. Newly developed and applied NDT methods of detecting and monitoring fatigue crack in metal material are reviewed in this paper. Some methods based on machine vision technique and image recognition techniques are introduced for at or near surface visible crack testing. As a newborn offspring of acoustic emission technique, electromagnetically induced acoustic emission methods also introduced for both visible and invisible fatigue cracks on metal structure. Nonlinear ultrasonic method and some other NDT methods presently available are mentioned, too. The principles, applied testing fields, data processing algorithms, advantages and disadvantages of these methods are discussed.