Acoustic Emission

Structural materials of the components and structures must withstand a wide range of loads during their operation. Material ductility is an important characteristic of its reliability, i.e., the ability to absorb mechanical energy due to plastic deformation without fracture. There are many factors that affect the tendency of material to resist fracture: high or low temperature, loading rate, stress concentrators (e.g., cuts, cracks), etc. Under the influence of these factors during operation, most of the structural materials become brittle, thus reducing the time of safe operation of industrial facilities or products. Information about the ductility or brittleness of the material is crucial for the choice of a method of calculating the residual life of the relevant products and structural elements. Therefore, to increase the efficiency of technical diagnostics (TD) and nondestructive testing (NDT) of industrial facilities and products, it is important to establish the type of material fracture. The analysis of the types of fracture and their features, the state of research on the application of the method of acoustic emission (AE) and magnetoelastic AE (MAE) to detect micro- and macrofracture of structural materials, as well as the wavelet transform (WT) for the spectral analysis of AE signals are presented.

Approaches of fracture mechanics of materials are used for effective diagnostics of the technical state of the object and determination of its residual lifetime. A crack is the most dangerous defect of the material, especially in the case of brittle fracture. As a result of a jump-like propagation of cracks in the material, elastic waves are emitted, which are converted by the acoustic emission sensor into electrical signals. Analysis and processing of these signals make it possible to identify the fracture stages. The need to build physically correct calculation models of crack initiation and growth with appropriate boundary conditions and development of the methods for calculating the dynamic field of displacements that occur in this case (direct problem) is still topical. Based on the obtained solutions, analytical dependences are established between some parameters of cracks and AE signals, thus making it is possible to determine the parameters of the defect (the inverse problem) during technical diagnostics of engineering objects. This chapter of the monograph presents the constructed mathematical models of field caused by the displacement of the opposite crack surfaces of different types in the elastic half-space.

The investigation of the shape of signals and their amplitude–frequency characteristics is of great importance, first, to reveal the physical nature of radiation sources. This makes it possible to establish the kinetics of defect formation in bodies under loading. Simultaneous analysis of statistical and structural data of AE signals ensures the reliability of measurement results and facilitates their interpretation, thus increasing the efficiency of TD of engineering objects under control. This chapter describes the known methods of identification of the types of macrofracture by the energy of AE signals and presents the construction of the energy criterion by the energy parameters of AE signals and its verification. The fracture of the welded joints, the propagation of cracks of low-temperature creep, and the fracture of nonmetallic materials have been also studied.

In recent years, the use of CM as a structural component in many branches of industry, including aerospace, rocket and space, chemical, automotive, for the production of pipes for power generating industry, mechanical engineering, civil engineering and so on, is constantly increasing. The structural integrity of composites depends on a few factors, including mechanical loads, defects that arise during their manufacture and operation, environmental conditions, and so on. Any of them can cause internal damage to CM. There are several stages of macrofracture in fiber CM: matrix cracking, delamination of fiber from the matrix, fiber fracture and elongation, displacement of matrix parts, and so on. This chapter presents the results of investigation of the features of macrofracture of glass and aramid fiber reinforced composites by to the parameters of AE signals.

In modern orthopedic dentistry, three types of restorative materials are used: ceramics, metals, polymers. Metals which possess high strength and rigidity are used to ensure the ability of denture to bear significant mechanical loads. Instead, ceramics and polymers have become widespread. Combinations of different chemical materials are often practiced, as none of them alone can be considered the perfect. When choosing the appropriate material for orthopedic restorations, it is necessary to have complete information about its strength. The last one can change under the influence of various factors (defects of material in critical areas; state of the restoration surface; increased loads on the construction, etc.). For effective clinical use of certain materials, it is necessary not only to consider their mechanical properties, but also to know the dynamics of fracture processes. Such information can be obtained by using in mechanical tests the AE method with signal processing by WT. This chapter considers the mechanical characteristics and peculiarities of fracture of dental polymers, ceramics, and composites; the express technique of their ranking by the energy criterion of identification of the fracture types is constructed, and the peculiarities of fracture of the tooth-endocrown system under quasi-static compression are investigated.

To ensure the uninterrupted and safe supply of oil and gas products, it is necessary to maintain the pipeline systems in good working condition and to monitor their technical state. For this purpose, it is important to develop appropriate methods for monitoring and diagnosing the state of the pipe, separate components, and units of technological equipment. The phenomenon of generation of magnetoacoustic emission (MAE) signals under the influence of an external magnetic field, which causes the movement of the magnetic domain’s walls, is a perspective to use for local diagnostics of ferromagnetic structural elements and products. In this chapter the peculiarities of MAE signals by WT parameters during remagnetizing of structural steels with different degrees of hydrogenation are analyzed.