Vol 52, No 12 (2016)

A theoretical model is suggested that allows one to explain peculiarities of the frequency response of echo signals at the output of a receiving transducer versus geometrical parameters of reflecting surfaces. It is shown that the way the instantaneous frequency of signals at the output of the receiving transducer changes depends on the curvature radius of reflected wavefront at the receivingtransducer aperture. It has been established that the frequency modulation of the pulsed echo signal is due to nonuniformity of the distribution of the phase of acoustic signal at the receiving-transducer aperture; this can be characterized by the radii of Fresnel zones that correspond to the reflected wavefront in relationship to the aperture radius of the circular transducer. Data on the frequency modulation of pulsed echo signals expressed in terms of dimensionless parameters (normalized frequency deviations) that were obtained experimentally and calculated by the suggested theoretical model demonstrate fair qualitative and quantitative agreement.

Results of ultrasonic testing of parts that are fabricated by selective laser melting are assessed using radiography and X-ray computed tomography. Peculiarities of revealing incompletefusion flaws with the above methods are considered.

Ultrasonic testing is the primary nondestructive testing technique employed for examination of internal soundness in bulk materials. It also indicates materials condition and microstructure, and is influenced by these factors. Correlations among these shall help in establishing better understanding towards selection and application of materials for aerospace systems. This paper reviews the correlations between ultrasonic response and microstructure of different aerospace materials. It also includes the changes in ultrasonic response due to change in processing condition of material. It is noted that ultrasonic wave velocity and attenuation are modified by change in thermomechanical processing through change in microstructure.

The level of residual stresses (RS) in anisotropic electric steel (AES) is its most important functional characteristic that is responsible for losses of electric power in magnetic circuits of transformers during their service life. Reasons are given for the emergence of RS in AES and the known estimation methods are provided, the main shortcoming of the latter being the lack of quantitative estimates of RS. A simple and practically feasible method is suggested for estimating RS based on measurement of the anisotropy of magnetic properties of AES.

The problem of determining saturation magnetization in a local area of a bulky ferromagnet is considered. A mockup of the device is presented. Experimental data are provided for local measurements of the saturation magnetization of a ferromagnetic sample, based on the stray field at the boundary of the magnetized area.

A problem has been solved on determining the coordinates of the center of a circle that is a section of an infinite cylinder, its radius, and the constant permeability, based on experimental data with no contact with the cylinder.

The usage of terahertz infrared thermography for assessing the humidity of wooden samples is described. Terahertz radiation transmitted through a sample is imaged by means of a tera-thermoconverter. The temperature field of the converter is analyzed with an infrared imager. The possibility of using the technique for testing the nonuniformity of drying of timber is illustrated.