The paper deals with the impact deformation and fracture behaviour of commercial plain carbon pipe steel 17Mn1Si. The explicit account of the internal grain structure, temperature and geometry of the notch have been made in theoretical physical mesomechanics formulation aiming at in depth understanding of the role of strain energy factors in dynamic fracture. Theoretical method of excitable cellular automata and laboratory impact bending tests followed by fractographic analysis were paired with time-frequency analysis of acoustic emission accompanying local deformation and fracture processes. It was shown that formulation of the crack opening criterion under dynamic loading conditions should explicitly account for rotation energy accumulation and incorporate the microscopic temporal and spatial details of defect generation from internal (grain) boundaries. A fairly good agreement has been found between the strain energy characteristics obtained from mechanical loading data and independently measured acoustic emission signal being distinguished in terms of consumed and released energy. The impact toughness almost linearly decreased with temperature, which was consistent with fractographic observations. At the stage of crack initiation, when the energy dissipation processes at the internal structure elements significantly affect the initiation of dynamic fracture, the acoustic emission energy reduced in proportion to the expended mechanical energy, which considerably decreased with temperature. The vital role of the energy release at interface/grain boundaries and its decreased significance with decreasing temperature was demonstrated both in numeric simulations and in dynamic experiments.

The optimal mode for ultrasonic welding (USW) of the “PEEK–ED (PEEK)–prepreg (PEI impregnated CF fabric)–ED (PEEK)–PEEK” lap joint was determined by artificial neural network (ANN) simulation, based on the sample of the experimental data expanded with the expert data set. The experimental verification of the simulation results showed that mode 10 (t = 900 ms, P = 1.7 atm, τ = 2000 ms) ensured the high strength properties and preservation of the structural integrity of the carbon fiber fabric (CFF). Additionally, it showed that the “PEEK–CFF prepreg–PEEK” USW lap joint could be fabricated by the “multi-spot” USW method with the optimal mode 10, which can resist the load per cycle of 50 MPa (the bottom HCF level). The USW mode, determined by ANN simulation for the neat PEEK adherends, did not provide joining both particulate and laminated composite adherends with the CFF prepreg reinforcement. The USW lap joints could be formed when the USW durations (t) were significantly increased up to 1200 and 1600 ms, respectively. In this case, the elastic energy is transferred more efficiently to the welding zone through the upper adherend.

Regularities and procedure of suppression of oil flame through a gas-salt layer of water are determined as a result of laboratory experiments. Conclusion about defining role of surface activity of foam concentrates in guaranteeing of reliable flame suppression by foam in process of its supplying into the bottom of tank through a gas-salt layer of water is drawn. Time of oil product suppression, which includes the time of saturation of a gas-salt layer of water by surface-active substances and the time of burning elimination, is defined. It is revealed that foam rising through a gas-salt layer of water in an initial time point loses the part of active substances (mainly hydrocarbon component) and partially destructs. Influence of hardness salts on a superficial tension of foam concentrates solutions is shown.

The structure, mechanical and tribological properties of the polyimide-based composites reinforced with chopped carbon fibers (CCF) and loaded with solid-lubricant commercially available fillers of various natures were investigated. The metal- and ceramic counterparts were employed for tribological testing. Micron sized powders of PTFE, colloidal graphite and molybdenum disulfide were used for solid lubrication. It was shown that elastic modulus was enhanced by up to 2.5 times, while ultimate tensile strength was increased by up 1.5 times. The scheme and tribological loading conditions exerted the great effect on wear resistance of the composites. In the tribological tests by the ‘pin-on-disk’ scheme, wear rate decreased down to ~290 times for the metal-polymer tribological contact and to ~285 times for the ceramic-polymer one (compared to those for neat PI). In the tribological tests against the rougher counterpart (Ra~0.2 μm, the ‘block-on-ring’ scheme) three-component composites with both graphite and MoS2 exhibited high wear resistance. Under the “block-on-ring” scheme, the possibility of the transfer film formation was minimized, since the large-area counterpart slid against the ‘non-renewable’ surface of the polymer composite (at a ‘shortage’ of solid lubricant particles). On the other hand, graphite and MoS2 particles served as reinforcing inclusions. Finally, numerical simulation of the tribological test according to the ‘block-on-ring’ scheme was carried out. Within the framework of the implemented model, the counterpart roughness level exerted the significantly greater effect on wear rate in contrast to the porosity.