Modeling the Radiation of Ultrasonic Waves by a Unit Source of Acoustic Emission Noise

Abstract

The generation of radial Lamb waves by a system of volume and surface loads acting within a finite region of an isotropic elastic plate is studied. General solutions are used to model the emission of ultrasonic waves in an isotropic plate by a unit source of acoustic emission noise of two model configurations: linear and point. It is established that the results for a pulsating linear source are in qualitative agreement with Torwick's solution to the physically equivalent problem of the emission of Lamb waves by a longitudinal harmonic force acting at the end of a half-strip. The generation of Lamb waves in a plate by a point source is modeled to asses how effectively the energy of elastic vibrations is extracted from the source and is transferred through the plate by different modes and at different frequencies Keywords: acoustic emission, Lamb waves, nondestructive testing Introduction. Of many nondestructive testing methods, the acoustic-emission method has recently become more and more popular. This method has the following considerable advantages. First, the method is applied not to detect current damage, but to predict, by analyzing test data, the development of damage depending on the operating conditions. Such a prediction does not assume conducting external calculations or invoking the structure design and operation history [11]. Second, unlike the active methods in which the parameters of radiation are a factor that affects, to some extent, the test data, the "primary source" in this method is a defect [9]. Third, the diagnostic process does not require constant active participation of the personnel after installation and setting of the diagnostic system. Moreover, during diagnostics, the personnel and the analytical data processing units of the system can be far from the object, which is important in case of risk of an emergency [1,11]. The method is most frequently used for continuous monitoring usually for a rather long time, sometimes for the entire service life.Experimental research has reliably established a relationship between the spectral and energy characteristics of acoustic emission noise and the scales of the deformation processes in materials [2,3,9,11,14,16,19,20,25,27]. Moreover, the current understanding of fracture mechanics [10,17,[21][22][23] allows us to provide a well-founded (to some extent) physical interpretation for this relationship.An experimentally proved fact is that the acoustic-emission method can be used to measure stresses (strains) in a material, detect various defects, determine their coordinates, assess the danger of defects, and solve other problems of structural assessment. These methods have not, however, been applied in practice at a level appropriate to their real capabilities. This is due to their relative novelty and some unclear aspects of the acoustic-emission theory such as the mechanism of delivery of energy from a source of acoustic emission noise along structural elements as waveguides to an electroacoustic transducer detecting ultrasonic waves. A featur...