Defects In Structural Elements Research Articles

Diagnosis of fatigue cracks in structural elements manufactured by additive manufacturing

Recently, the production of metal structural elements using additive processes is gaining popularity. They allow the production of an element of any geometry and structure, while reducing the mass of the produced part. Unfortunately, the AM technology causes structural elements to be burdened with numerous defects in the form of porosity, unmelted powder, weak interlayer bonds or residual stresses, etc. These defects translate into the possibility of an early, uncontrolled fatigue crack. For this reason, it is important to find ways to quickly detect damage caused by random variable loads. The work presents methods of diagnosing cracks and fatigue damage in structural elements produced using 3D printing. The division of research methods allowing for the detection of defects in structural elements and the characteristics of the most popular methods, taking into account their advantages and limitations, were presented. Methods appropriate for a given type of material, test conditions and damages are indicated. The most important methods of diagnosing defects in printed elements include: penetrating, ultrasonic, radiographic, eddy current and thermal imaging methods.

A reliability indicator based on assessment entropy of mining building and structure elements

The quality reconstruction of the mine industrial facilities is the maximum possible elimination of the identified defects. Assess the suitability of the object for further operation or reconstruction based on the inspection results of a building or structure as actual values of the controlled parameters. Provide the science-based methodology for diagnosing the technical state, assessing the reliability and physical wear for mining buildings and structures by using the probabilistic and statistical methods. A retrospective analysis of the results of surveys, collection, processing and generalization of information on states (diagnoses) and characteristic defects (diagnostic features), based on the probabilistic-statistical apparatus of technical diagnostics and elements of information theory. An assessment of state and reliability, physical wear of structures of all levels. The Kulbak-Leibler distance as a key indicator in the method of estimating the ”survivability of the element” provides for the probability distribution of the tensile strength. Developed methods of using technical diagnostics based on probabilistic statistical methods – the Bayes method, statistical solutions - including the concepts of theory information. When performing a probabilistic analysis of the technical condition of all elements, the numerical solution showed the effectiveness of the proposed diagnostic methodology. The innovative method is to analyze and assess the reliability of mine facilities using a mathematical modeling to determine the probabilistic characteristics of defects in structural elements. The analysis method in the survey allows for determining the technical state of the object, the set of further measures, effective planning the operating and restoring costs.

Assessment of failure probabilities and the allowable size of defects in structural elements using the criteria of fracture mechanics

The possibility of assessing the safe size of the defects of metal continuity using risk criteria are considered. Such defects occur at all stages of the life cycle of structures. Assessment of their hazard and determination of their allowable size becomes important when the defects can lead to brittle or quasi-brittle fracture. In this case, models of linear and nonlinear fracture mechanics are used. In these models, defects are considered as internal elliptical or surface semi-elliptical cracks. The stochastic variety of shapes, sizes, locations, and orientations of defects has a significant effect on the destruction mechanisms. In this regard, the relevant probabilistic problem of assessing the permissible size of defects according to the criteria of the risk of destruction comes to the fore. We consider a general approach to assessing hazard of defects by risk criteria. Two settings of the probabilistic problem of risk assessment based on of one- and two-parameter fracture criteria are presented. The risk function in the form of the probability of fracture according to a given criterion is used as the main calculated characteristic. The expression of the risk function based on one-parameter criteria of fracture mechanics is presented. The main attention is paid to the probabilistic model based on the two-parameter fracture criterion by E. M. Morozov. This criterion provides ample opportunities for analyzing fracture mechanisms with a change in the size of defects. An expression for the risk function based on the family of two-dimensional probability distributions of Lu – Bhattacharya of the Weibull type is obtained. It is shown that the correlations of the fracture mechanisms can significantly affect the values of the fracture probabilities, and, consequently, the allowable size of defects.

Совершенствование методов визуального осмотра зданий и инженерных сооружений путем внедрения технологий компьютерного зрения и интеллектуальной обработки данных

For the safe operation of engineering facilities, periodic surveys are carried out to assess their technical condition. To form an expert opinion and establish cause-and-effect relationships of changes in the state of an object from the influence of external factors, the first in the sequence of work, according to the terms of reference, is a visual inspection of the object or a visual inspection. As a result of visual inspection, it is possible to fix the occurrence of cracks in structures, the formation of a corrosion layer that damages structures, violations of the protective layer of the surfaces under study, violations of the paintwork of elements and parts of the structure of the object, etc. In order to improve the visual inspection technique, a hardware-software complex has been developed that makes it possible to apply computer vision technologies to provide automated visual monitoring of an object and analyze the obtained images by using intelligent algorithms for their processing. The use of a hardware-software complex for automated visual monitoring of an object in real time will allow performing: automated visual monitoring of a plurality of structural elements of an object at the same time due to a stationary installation of a network of video cameras at the object; intelligent analysis of the stream of video im-ages in real time, as a result of which information is given not only on the defects present, found on the object, but on the dynamics of their changes; identify defects in structural elements in hard-to-reach places where they cannot be visually determined, but it is possible to install a video camera; minimize the human factor.

Using Recycled Coarse Aggregate in Reinforced Concrete Beams Strengthened for Shear by GFRP bars Using NSM Technique

The NSM technique began to apply as a modern technique to treat defects in structural elements and to increase the shear and flexural strength of structural elements. For this technique to be effective, a series of practical experiments were conducted to characterize the behavior of the element strengthened by the NSM technique for flexure and shear. Shear strengthening with GFRP rods is the focus of this paper for concrete beams that contain 30% coarse aggregate replacement ratio of thermstone (volumetric ratio) obtained from the rubble of demolished buildings. A total of 7 beams were loaded under four-point load test, the parameters examined were the angle of inclination and the distance between the GFRP bars, the presence and absence of stirrups and the thermstone aggregate replacement ratio. The characterization of the tested beams includes failure mode, load-deflection curves, load-strain curves of stirrups, rebars and GFRP rods and the surface concrete strain in the shear zone of beam. The results showed that the use of GFRP rods to strengthen concrete beams was effective, especially in the presence of stirrups, where the gain in shear strength was 29.6% and 22.2% when the distance between the GFRP bars was (200 and 300) mm, respectively with the presence of stirrups. While the gain in shear was just (3.7% and 11.1%) in the absence of stirrups, when the distance between the GFRP bars was (200 and 300) mm, respectively.

Determination of natural modes of railway overpasses

Currently, there are many software systems and environments that allow you to simulate and perform fairly complex and voluminous calculations associated with dynamic effects on structural elements of overpasses. The aim of the article is to make an analysis of a reinforced concrete railway overpass as a whole and its elements separately. The article presents the calculated and experimental data of the forms and frequencies of natural vibrations of reinforced concrete railway overpasses under constant loads and the rolling stock off the span. As a result of the analysis of the tests, it was determined that the effect of the rolling stock passing through the reinforced concrete beam spans of 16.5 m and 23.6 m appears with frequency perturbations that are in the range f = 4.41 ÷ 9.52 Hz. These studies can be further used in the design of artificial structures, as well as to identify defects in structural elements of railway bridges.

Geometrical identification of invisible defects in structural elements basing on digital image correlation data

The paper addresses an experimental-calculational technique intended to determine geometrical parameters of invisible crack-like defects in thin-wall structural elements. Object deformation response to low trial loading is used as baseline data for assessment. The response is recorded using the digital image correlation method. Further analysis consists in minimization of differences between experimental findings and serial model calculations. The description of the approach is carried out on the example of a test specimen in the form of cylindrical shell (tube section) with a non-through crack simulator on the inner surface. The expected displacement fields for different particular cases are calculated using the finite element method.

ON THE INVESTIGATION OF THE PROCESS DETECTING DEFECTS OF THE COMPRESSOR EQUIPMENT HARMONIC STRUCTURE OF THE STATOR CURRENT OF THE MOTOR

Centrifugal and axial tubing installation electric are widely used in various industries due to its high reliability, efficiency and good performance. In the operation of such facilities is a prerequisite to maintain specified by the manufacturer of process parameters in a fairly narrow range. A slight deviation from the design mode may result in the occurrence of defects in the nodes of the unit with a further loss of productivity and output of machine failure. Also, defects in structural elements of the installation can be caused by manufacturing defects. The possibility to monitor the actual state of the nodes of the centrifugal and axial compressors equipment by fixing the electrical parameters of the stator windings of the motor, such as current and voltage, with a further spectral analysis of these signals. Produced simulation character of oscillations of voltage and current of the stator of the electric motor, which appear due to the occurrence of oscillations of torque on the motor shaft due to the birth and development of mechanical defects. A simulation model of the induction motor is built in accordance with the structural and dynamic scheme based on a system of differential equations describing electromechanical energy conversion in an asynchronous machine. This simulation model is supplemented by a set of blocks defining the fluctuation of torque on the shaft. A number of experimental studies using complex laboratory equipment, consisting in simulating a heartbeat and the imbalance of the motor shaft and is detected in the spectrum of the stator current. The experiment marked informative harmonics, changing its amplitude at certain frequencies, the value of which can be seen on the availability and extent of the defect of the unit.

Evaluation of the sensitivity of polarization-current method to defects in structural elements

We demonstrate the possibility of application of the polarization-current method to the corrosion monitoring of the operating equipment and present the numerical results showing that the indicated method enables one to estimate the degree of damage to the equipment at distances from the electrochemical probe not smaller than 5 m. The sensitivity of the method depends on the resistance of the electrolyte and the sizes of the tested object.

Quantitative nondestructive evaluation of defects for failure diagnosis

Fracture mechanics requires the evaluation of defects in structural elements by nondestructive test methods. It is necessary to know the geometry of the defects, the microstructure of the material, and the stresses near the defects. Acoustic emission is used to investigate the crack growth. We also give a brief overview of recent advances in this field.

QUANTITATIVE NONDESTRUCTIVE EVALUATION USING GUIDED WAVES

Abstract This paper deals with two applications of guided waves in quantitative nondestructive evaluation (QNDE): the detection of cracks in beams and the determination of elastic material constants of filament-wound cylindrical composite shells. As an alternative to the use of bulk waves, the reflection characteristics of guided waves having a wavelength much larger than the size of a defect are used to assess defects in structural elements as beams or plates. Bending waves incident at a lateral notch in an isotropic beam of circular cross-section are considered both experimentally and theoretically. When shear effects are taken into account both in the modelling of the crack and the propagation of the elastic waves, then theory and experiment are in good agreement up to a ratio of beam radius to wavelength of 0.25. Filament-wound circular cylindrical shells were examined by measuring dispersion curves for the first two axisymmetric modes of propagation and torsional waves using a combination of resonanc...

Damage to and defects in structural elements due to design and fabrication not being adapted to the heat treatment. III: Uhlig, W. Metall. Nov.–Dec. 1990 44, (6), 175–177 (in German)

Damage to and defects in structural elements due to design and fabrication not being adapted to the heat treatment. III: Uhlig, W. Metall. Nov.–Dec. 1990 44, (6), 175–177 (in German)