The paper is focused on the examination of the internal quality of joints created in a multi-material additive manufacturing process. The main part of the work focuses on experimental production and non-destructive testing of restrained joints of modified PLA (polylactic acid) and ABS (Acrylonitrile butadiene styrene) three-dimensional (3D)-printed on RepRap 3D device that works on the “open source” principle. The article presents the outcomes of a non-destructive materials test in the form of the data from the Laser Amplified Ultrasonography, microscopic observations of the joints area and tensile tests of the specially designed samples. The samples with designed joints were additively manufactured of two materials: Specially blended PLA (Market name—PLA Tough) and conventionally made ABS. The tests are mainly focused on the determination of the quality of material connection in the joints area. Based on the results obtained, the samples made of two materials were compared in the end to establish which produced material joint is stronger and have a lower amount of defects.

This paper discusses the possibility of studying composite materials by non-destructive laser-ultrasonic testing technique. Concrete samples and carbon-epoxy composites were examined, defects located and elastic wave velocities measured. The internal structure of the samples was visualized in 2D images.

In relation to extraction of coal seams at significant depths, the issue of protection of safety equipment against pressure exerted by rock becomes very important. In many surveys of the effects of pressure exerted by rock it was demonstrated that the intensity of stress around the mine works increases the greater the depth of the mine works. However, surveys of technological mine works have shown that the level of deformation of the mine bracing varies in various types of rock at identical depths and no precise rule was established between the increase in pressure exerted by rock and the increasing depth of the mine works.

The explosive properties and stability of benzimidazole compounds are studied to determine the influence of substituents and their position. The results obtained reveal the conjugation of substituents as one of the crucial factors for the thermal stability of these compounds. We also found that two -CH₃ substituents increase the thermal stability of the parent compound, while nitro groups decrease it. Moreover, the study clearly exhibits that the combination of an -NO₂ substituent with -CH₃ does not change the stability of the benzimidazole. On the other hand, nitro groups increase the chemical stability and explosive properties of the compounds under investigation, but their sensitivity could not fully satisfy the requirements of their safety and increase their toxicity. The main results of the study indicate that high thermal and chemical stability, low toxicity and sensitivity, and good explosive properties could be achieved by the precise combination of nitro, -CH₃, and triazole ring substituents. These findings are very important for the design of new, effective, and non-sensitive explosives.

During the operation of engineering structures made of natural stone, for industrial and civil purposes, an important parameter in monitoring their technical condition is the assessment of their reliability and safety under the influence of various external influences. In this case, high-quality monitoring of the stress–strain state of natural stone structures, its physical, mechanical and filtration properties, as well as internal structural features is necessary to study the possibility of replacing individual elements of objects that have lost their original characteristics. To assess the state of geomaterials, this article proposes using a complex of introscopic methods, including infrared radiometry and laser-ultrasound structuroscopy. An important aspect is the calculation based on the Green–Christoffel equation of the velocity of a quasi-longitudinal wave in limestone consisting of densely packed, chaotically oriented calcite grains with a small quartz content. For the first time, using laser-ultrasonic structuroscopy and standard methods for determining open porosity, both total and closed porosity were determined. This allowed us to find the values of specific heat capacities of dry and water-saturated samples. The obtained values are used to find the ratio of changes in the temperature of dry and water-saturated samples at the same stress values. The results obtained demonstrate the need to take into account changes in the intensity of thermal radiation of limestone with different moisture content under conditions of uniaxial compression, when identifying changes in the stress state of elements of stone structures in real conditions.

The paper presents the results of measurements of compressional and shear wave velocities in the near-surface zone in the Zhelezny open pit mine, the Kovdor GOK (Kovdor Mineral Producing and Processing Company). Data on the seismic wave velocities are used to estimate Young's modulus and Poisson's ratio. Poisson's ratios derived from the compressional-to-shear velocity ratios are used to locate fractures that are due to stress redistribution and weathering processes in the stepped walls of the open pit mine.