Yulia Petronyuk

Methods of pulsed acoustic microscopy in industrial diagnostics

A brief review of the methods of pulsed acoustic microscopy is presented. The problems and possibilities of nondestructive ultrasonic high-resolution monitoring are discussed. It is shown that methods of pulsed acoustic microscopy can be used to control the integrity of multilayer constructions and associated mechanical units. Micron resolution of acoustic images is attained by focusing the probing ultrasonic beam (50–100 MHz). Original results obtained in joint efforts with developers of 3D miroelectronics and the technology for producing turbine blades are presented.

Edge Diffraction Phenomena in High-Resolution Acoustical Imaging

In flat and homogeneous areas reflected radiation is the sole reason of output signal formation. Distinctions in reflectivity, interference of directly reflected radiation and leaky surface waves cause variations of the output signal values and, finally, contrast in acoustic images. But quality of images is determined also by definition (sharpness) of linear and point elements– phase boundaries, object contour and inclusion borders, edges and so on. At all these positions the secondary radiation includes, besides the reflected part, the diffracted waves also. The work is aimed at analysis and experimental investigation of imaging features caused by contribution of diffracted waves. It has been shown that, while defocusing the signals are separated in time. The diffracted wave is received within a rather wide range of lens positions; its arrival time varies when shifting the probe beam axis about the edge position. Elements originating from edge diffracted waves are indispensable details of all acoustic images – echo patterns, B- and C-scans. It has been shown edge diffracted waves are the main cause of line blurring in C-scans under defocusing.

Studying the dynamics of microdefect growth in carbon fiber reinforced plastics under mechanical loading by means of ultrasonic microscopy

Strength characteristics of carbon fiber reinforced plastics (CFRPs) are investigated by nondestructive means as microstructural changes in a material’s bulk under external mechanical loads. CFRP microstructure is studied experimentally via pulsed ultrasonic microscopy at the level of mechanical deformation resulting in degradation of a material’s properties. The process of composite deformation is studied by means of stepped stretching. Acoustic emissions are used to identify the stage preceding final destruction (the accumulation of microcracks, fibers breaking, and delamination) as an indicator of a material’s degradation. Pulse acoustic microscopy is used to observe the accumulation of microcracks in individual layers of a material. To study the behavior of a CFRP microstructure upon mechanical loading, tensile stress was applied to samples with cross-ply packing of fibers (0°, 90°) and (45°, −45°). It is shown that the brittle fracturing of reinforcing fibers is typical of CFRPs with fiber orientation (0°, 90°), and is accompanied by growing areas of stress concentration and a rise in of acoustic emission activity, with a subsequent increase in the signal energy and the formation of extensive interlaminar delamination. Acoustic emission shows a low level of activity for CFRP samples with fiber orientation (45°, −45°), which is accompanied by the formation of structural microdefects that are clearly visible in acoustic images.

Ultrasonic microscopy of contact joints

Ultrasonic techniques allow examination of internal structure and the detection of discontinuities at the interface of various joints. Contact joints obtained via diffusion welding, sintering, and other adhesive methods are investigated using impulse acoustic microscopy. It is shown that short probing pulses of focused ultrasound with frequencies of 50–100 MHz reveal areas with different adhesion strengths, areas of partial contact, peeling or air bubbles, and buffer layer thicknesses. Mechanisms of acoustic contrast at such interfaces are discussed. The results are of interest to specialists in the field of high-resolution ultrasonic nondestructive testing. They are needed to predict the failure mechanisms of composite products, from carbon fiber–reinforced plastics for the aviation industry to high-density ceramics used in medical prosthetics.

Local Elastic Measurements with Focused Impulse Ultrasound

The paper is devoted to experimental grounds for using short pulses of focused ultrasound for measuring local elastic properties (microacoustical technique).