Vol 53, No 6 (2017)

Results of the analysis of acoustic-emission signals generated due to ultrasonic waves propagating in a polymer composite material and registered with piezoelectric and fiber-optic sensors are presented. The fiber-optic sensors were arranged into an adaptive interferometer based on using a dynamic hologram formed in a photorefractive crystal. Reducing the setpoint fading has made it possible to improve the noise immunity and sensitivity of the measurement system when using an adaptive interferometer on a photorefractive crystal. Optical fibers in the interferometer’s measurement system served as sensors of ultrasonic waves and were built into a polymer composite material when the sample was manufactured. The sample was a rectangular plate made of a multilayer fiberglass material. It has been discovered that the sensitivity of the adaptive interferometer makes it possible to detect acoustic- emission signals generated by a Hsu–Nielsen source. When determining the speed of sound in the polymer composite material, peculiarities of registering a group wave by fiber-optic sensors have been established that are due to the anisotropy of the medium the wave propagates in and the distributed character of sensor placement in the studied composite material. The wavelet transform has been used to separate the informative component of the wanted signal.

The acoustic-emission method for inspecting flaws that form during laser bonding with the use of a CO₂ continuous-wave laser with a power of up to 8 kW and characteristics that can be preadjusted prior to welding is considered. The structure of acoustic-emission signals registered in a specimen’s flawed domain has been analyzed using the wavelet transform. It has been shown that the structural coefficients of the acoustic-emission signals localized in specimen’s flawed sections become identical over time.

The problem of determining the stray field of an OZ-axis–infinite wedge with a constant magnetic permeability μ placed in a constant inhomogeneous magnetic field is considered. The problem statement is given, the properties of the solution are examined, and some examples are provided.

Moulded foam (MF) is proliferating on the market of porous materials. It consists of separate factions (of different shapes and sizes) of the previously produced and often used polyurethane foam that has been crushed into crumbs and bound together by fresh polyurethane foam. In terms of rigidity, such structure forms an inhomogeneous porous material (IPM). The technology of manufacturing such materials a priori implies the inhomogeneity of rigidity both in the sheet plane and between different sheets that are cut to a prescribed thickness from a pre-formed rectangular parallelepiped of the porous material. Being able to control the rigidity of inhomogeneous porous sheet materials is an important requirement for the future high-quality produce. The testing technique used for these purposes needs to be accurate enough, nondestructive, practically feasible, and not time-consuming. In this paper, moulded foam is used as an example to consider theoretical aspects of modeling the process of IPM formation as well as practical issues related to developing and researching a nondestructive technique and a tool for measuring the rigidity of porous sheet materials, to monitoring the measurement accuracy, and to testing the created prototype of such a device.