PSI - Issue 30

L.A. Prokopyev et al. / Procedia Structural Integrity 30 (2020) 120–127

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Prokopyev L.A. et al. / Structural Integrity Procedia 00 (2020) 000–000

1. Introduction Instrumental methods of non-destructive testing are aimed, as a rule, at finding defects, and any inconsistencies with the normative documentation of the object of control. There are many types of non-destructive testing: ultrasound testing, radiography, magnetic particles, liquid penetrant, eddy current testing, etc. For each type of control, according to Jolly (2015) normative standards have been developed that allow the safe operating of the constructions. The main parameters for assessing defects, as a rule, are the level of various signals recorded by specialized devices that reflect the size and shape of the found defect. One of the most proceeding instrumental methods for estimate the stress-strain state of constructions with cracks is the acoustic-emission method of non-destructive testing, since there is a correlation between the parameters of fracture mechanics and the characteristics of acoustic-emission signals emitted during crack development. One of the directions of development of the acoustic-emission method, according to Andreev (2017) is the local low temperature thermal loading of the local part of construction. A significant advantage of this method relative to traditional loading methods is a low level of noise and ease of control. There are standard procedures for calculating the risk of structural failure based on fracture mechanics, for example, GOST 55724-2013. For each case of the considered crack, fracture mechanics parameters, such as stress intensity factor, J-integral, are calculated and compared with the limiting values for the given material. Analytical and numerical methods for calculating Kc are used for various loading conditions. In the presence of various factors, such as biaxial loading, plastic deformations, correction factors are introduced, for example, the concept of effective stress intensity factors, a master curve. The development of diagnostic methods for materials and structures requires the determination of more and more specialized parameters of fracture mechanics and non-destructive testing methods. To estimate the risk of failure of cracked constructions, according to Matvienko (2011) and Bol'shakov (2016) it is required to determine the specialized parameters of fracture mechanics, such as T-stresses. A common problem with computational techniques is the selection of the most suitable computational models for operating constructions. There are many factors, such as deviations from the shape of structures, various forms of cracks, which make it difficult to select adequate theoretical schemes. Nomenclature � � specific volume of the plastic zone � linear size of the plastic zone along the crack extension line � � stress intensity factor (SIF) � � T-stress � � material yield point � Poisson ratio �� � polar coordinate axis � Т tensor of angular functions of fracture mechanics equations � Т tensor of stresses around a crack tip It can be noted that, in the field of fracture mechanics, to assess and predict crack growth, new approaches are required that combine computational and instrumental techniques. The most suitable instrumental method for controlling cracks is acoustic emission control, since the relationship between acoustic characteristics and recovery factor has been experimentally shown. If there is a correlation between the fracture mechanics parameters and the acoustic control signals, it is possible to develop new techniques based on thermal loading and registration of acoustic signals, which derive important fracture mechanics parameters, for example, the stress intensity factor. A theoretically substantiated scientific base is required to develop new methods for assessing and predicting crack growth based on acoustic emission control. To combine the advantages of instrumental and computational assessment methods for predicting crack growth, it is necessary to develop a new technique based on recording acoustic signals that can reasonably derive the most important parameters of fracture mechanics. This requires a theoretical substantiation of the relationship between the characteristics of acoustic signals and parameters of fracture mechanics.