Materials

When carrying out acoustic-emission (AE) testing, the degree of danger of the identified defects is assessed. In total, there are 4 hazard classes: passive, active, critically active and catastrophically active. The definition of the hazard class is carried out according to the standard criteria.

In industrial NDT, the classification of AE sources is mainly carried out using two criterion parameters - the amplitude criterion and the local-dynamic index. To apply the amplitude criterion, calculate the limiting value of the allowable amplitude. The classification is carried out by comparing the average amplitude of the source AE and the magnitude of the allowable amplitude. In this case, the threshold value depends on the material of the tested object and is determined in preliminary experiments.

The local dynamic indicator is also often used in industrial AE testing. It is based on the power-law relationship between the total AE (N_∑) parameter and the object loading level (P):

N_∑=aP^m,

where a – constant of material and expirement conditions, m – parameter characterizing the degree of danger of a defect.

The classification of AE sources is based on the value of the parameter m. The higher the value of the exponent, the higher the hazard class of the source of acoustic signals. It should be noted that the emergence of an active noise source can complicate the procedure for applying a locally dynamic criterion.

Due to the issues of standard methods, INTERUNIS-IT pays much attention to the development of specialized criterial parameters, on the basis of which it is possible to reliably determine the state of technical facilities. In the framework of laboratory experiments, the company's employees analyze the process of accumulation of damages and create new criteria applicable to both standard AE monitoring and industrial equipment monitoring systems.

Also, INTERUNIS-IT is adapting existing methods for conducting AE testing of unique objects. Such techniques take into account not only the parameters of operation and material properties, but also the intensity of the noise flow. Employees of the company conducted additional studies on the effect of the microstructure of the material on the parameters of the flow of impulses of AE.

Using many years of experience in the field of AE testing, INTERUNIS-IT offers its services for a wide range of tasks, such as:

• assessment of the applicability of standard criteria in the operating conditions of technical devices;
• carrying out laboratory and field tests to adapt the standard criteria estimates;
• development of new criterial parameters taking into account noise activity, properties of the material of the facility and the conditions of its operation.

At present, composite materials are used in many fields of industry. Because of their wide distribution, the urgency of the task of diagnosing industrial objects made of composite materials is increasing. Solve this problem with the help of physical methods of nondestructive testing (NDT), one of which is the method of acoustic emission (AE).

Composite materials are inhomogeneous anisotropic materials, consisting mainly of reinforcing filler and binder. When carrying out AE diagnostics of such materials, there are a number of features. The main features of testing include the complexity of the organization of testing and interpretation of data AE, caused by anisotropy of both mechanical and acoustic properties.

INTERUNIS-IT together with the Mechanical Engineering Research Institute of the Russian Academy of Sciences ("IMASh RAN") conducted a large number of laboratory tests for the destruction of samples of composite materials. As part of the research, new approaches have been developed for the processing and filtration of acoustic signals, methods for assessing the level of damage and predicting the residual resource. Also, new approaches are being developed to determine the location of AE sources, taking into account the influence of the complex structure of composites.

Testing of a three-stringer compression panel

Using experience in testing composite products, INTERUNIS-IT together with the Federal Research Center "Krasnoyarsk Scientific Center of the Siberian Branch of the Russian Academy of Sciences" developed a "Method for the Qualification of Metal Composite High Pressure Tanks" using statistical and frequency parameters of the AE data stream .

Metal-composite vessel for pneumatic tests

With the help of this technique, the actual task of ranking vessels from composite materials according to the level of accumulated damage was solved.

Taking into account the great practical experience and theoretical developments in the field of AE testing of composite materials, INTERUNIS-IT can provide support in solving the following scientific and technical problems:

• improvement of standard location algorithms taking into account the anisotropy of the acoustic properties of composite materials;
• development of criterial parameters for assessing the stages of destruction of composites in the framework of full-scale and laboratory tests;
• the development of new technologies for the testing of industrial objects, made of composite materials, taking into account operating conditions and acoustic properties.

INTERUNIS-IT together with Research, Design and Technological Institute for Concrete and Reinforced Concrete is actively working on the development of techniques aimed at monitoring, as well as predicting the strength characteristics of concrete at the initial stages of its hardening using the AE method.

Among the main areas of work can be identified:

• Monitoring of hardening of concrete and concrete structures;
• Investigation of the processes of structure formation of concretes;
• Forecasting the strength of concrete for a regulatory period at the initial stages of its hardening.

The urgency of this kind of work is reinforced by the fact that often the concreting of building structures is carried out with violation of the requirements and rules regulated by normative and technical documents, non-observance of which leads to a decrease in strength characteristics of the structure. For example, unsatisfactory strength values ​​of concrete at the project age entail significant costs for rehabilitation works that could be avoided if timely measures are taken at the initial stages of hardening, when concrete has not yet gained significant strength. In this regard, particular interest for the reliability and durability of building structures is testing, as well as predicting the strength characteristics of concrete even at the initial stages of its hardening.

Despite the cheapness and simplicity of manufacturing, concrete has a very complex structure. When it is hardened, many processes take place at the micro, meso, and macro levels.

Concrete structure under the microscope

When hardening concrete, three main stages are identified: dissolution, colloidation and crystallization of the concrete composition. Each stage is characterized by a certain activity and certain parameters of the AE. According to the data of the AE, it is possible to distinguish different stages of hardening of concrete, as well as carry out an assessment of the current and prediction of the normative strength of concrete.

AE for the structural formation of concrete

The testing scheme for concrete at the initial stages of its hardening, using the AE method, is realized as follows: in a freshly poured concrete, the waveguide is immersed onto which the AE sensor is mounted to record the acoustic signals that arise during the hardening of concrete. On the basis of the data obtained, an analysis is made of the structural changes in the composition, which in turn are related to the processes of typing strength and the formation of the structure of concrete, and therefore can be used to evaluate and predict its mechanical properties

Current results:

• The process of structure formation of concrete using the AE method was studied;
• Informative parameters of acoustic emission data obtained for the first day of hardening of concrete composition correlating with the strength of concrete at the age of 28 days are singled out;
• An empirical model is constructed that allows one to predict the strength of concrete for a regulatory period;
• Patent application: "Acoustic method for predicting the strength of cement materials" was filed.

The project is at the testing stage.