An efficient approach to approximation and practical application of DGS diagrams

Abstract

A nonstandard experimental and mathematical approach to the development of analytical and numerical multidimensional approximations for DGS diagrams is proposed. This method features sufficiently high accuracy, versatility, and reliability for different types of piezoelectric probes (PPs) and test objects (TOs). The efficiency of the approach is demonstrated by a test example and is also checked in its implementation in software for the UD4-S device based on standard specimens simulating flaws. Issues related to the solution of the direct and inverse problems of ultrasonic nondestructive testing are discussed.This paper is a logical continuation of the analysis and results presented in report [1] regarding methods for ultrasonic nondestructive testing (NDT) of objects based on the use of DGS (distance-gain-size) diagrams. For the sake of the reader's convenience, we briefly describe the main assumptions of the method.During the last 10-20 years, ultrasonic testing is known [2] to have significantly expanded and renewed the scope of its methods and means for testing flaws, visualizing them, assessing their parameters, etc. Apart form the rapid development of information and computer technologies, this progress has obviously been facilitated by the application of such powerful physical methods as holography and tomography to acoustical diagnostics [2]. However, in spite of a number of separate spectacular results in flaw detection in some critical test objects (TOs) by these methods, their application to practical nondestructive testing (NDT) is developing rather slowly. This is due to the more sophisticated nature of the equipment needed and its correspondingly high cost.At the same time, classical, more accessible, simpler, and less expensive methods continue to play an important role in ultrasonic NDT. These methods are based on measuring amplitude, energy, and time parameters of the signals reflected by flaws. They are known [3-11] to include a method based on using DGS diagrams; this method is closely related to the NDT instruments' electroacoustic channel (EAC). The popularity and "longevity" of this category of methods is also explained by the fact that a solid framework of regulations and technical norms has been created for them. The number of studies related in one way or another to DGS diagrams that have been published over the last 30-40 years is now counted in the hundreds. Moreover, this information flow is not weakening, thus attesting that it is a profound and substantial method.The modern level in the development of NDT instrumentation increased the requirements for mathematical simulation of processes that occur in an ultrasonic nondestructive-testing instrument's EAC. Because of the trend toward a growth in the accuracy, sensitivity, informativity, and reliability of instruments and for an improvement in NDT confidence, electroacoustic problems need increasingly more detailed and realistic formulation and, as a result, increasingly sophisticated analytical and numerical algorithms for their solut...