Том 54, № 6 (2018)

Based on the analysis of literature data, it has been shown that a system of microcracks rapidly nucleates and develops in a surface layer of several grain sizes under fatigue loading. This brings about changes in the elastic modulus and density of the material. These can be described in the form of material’s effective characteristics.

The problem of the propagation of a surface wave has been solved for a microscopically inhomogeneous medium with dispersion and insignificant surface-layer variations. Using the example of testing 08Kh18N10T steel samples for low-cycle fatigue, it has been shown that the propagation speed of surface waves changes at a higher rate than that of bulk (longitudinal and shear) waves; this can be used in the tasks of testing materials at early stages of fatigue failure.

The paper investigates a disk-shaped piezoelectric transducer with plano-concave surface. Special form of the construction enhances the flexibility of the transducer and improves its effectiveness similar to the known transducers of Cymbal and Moonie types. The analysis of the transducer was performed using the finite element technologies and ANSYS finite element software. The influence of the porosity of the piezoceramic material of the transducer on its performance was studied both in static analysis and steady-state oscillations mode. The porosity of the piezoceramic material was taken into account by the effective properties of porous piezoceramic as a composite structure, which were calculated in numerical experiments on solving the homogenization problems by the effective moduli method and the finite element method.

In order to study acoustic emission (AE) characteristics of damage process of mortar in different aggregate size, mortar specimens were tested under axial compression in the experiment, the whole damage evolution processes were monitored by full-digital AE acquisition system. The effects of mortar in different aggregate size on damage processes and failure mode were conducted by cumulative AE energy, amplitude, peak frequency and the ratio N/E (hits/energy) respectively. The ratio of cumulative AE hits of each frequency band and amplitude band to the whole cumulative AE hits in different stress level were counted, and the difference and evolution process of microcracks of mortar in different aggregate size in the failure process were revealed. The results show that cumulative AE energy increase with the increase of aggregate size in mortar. Distribution of cumulative AE hits of each amplitude band versus the stress in different aggregate size are the same, and AE hits of each amplitude band increase sharply suggests that the specimen will be destroyed. Besides, AE hits focus on low-frequency band at low stress level, while all peak frequency bands are active at high stress level, and the aggregate size of mortar have significant influence on cumulative hits of each peak frequency band. The ratio N/E decreased with the increase of aggregate size, and which increased linearly with the increase of the stress.

It is proposed to use the tomographic approach to the problem of detecting and imaging concealed utility networks. This approach is based on generating the three-dimensional radio images of the space being explored from the results of measuring its location wave projections in a dual-polarization measurement mode. The problem is solved by focusing radiation first on the “air–dielectric” interface and then inside the dielectric. Experimental data processing results and reconstructed threedimensional radio tomograms are provided for a “twisted pair” cable and a fiber-optic cable with no metallic inclusions. The results confirm the operability of the approach.

Five methods that have been developed by the authors since 2006 for benchmarking the reliability of semiconductor articles using electrostatic discharges are described.