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The effects of the dip angles of the echelon notches on the acoustic emission (AE) are studied under uniaxial compression. For this comprehensive analysis, discrete-element simulations are used. Therefore, model dimensions of 150×150 mm were specially prepared. These models contained three echelon cracks with different lengths of 4.5, 3, and 1.5 cm, and a 2 mm vertical distance between the cracks. The inclination angles of the middle crack varied as 0°, 15°, 30°, 60°, 75°, and 90° in the specimens containing echelon cracks with different configurations. Two neighboring cracks were perpendicular to the middle cracks. Twelve different models were designed and tested under uniaxial compression. It was observed that the failure process and crack propagation patterns in the rock-like material specimens were affected by changes in cracks' angles and their configurations. The AE events in the loaded specimens grew rapidly during the initial loading phase. Numerous AE events showed a decline in the induced stresses at the peak load states. [ABSTRACT FROM AUTHOR]

To provide the functional adequacy, aesthetic qualities, and durability of the process of restoration of the elements of the dentofacial system, it is required to have the information on the properties of dental materials (physical, chemical, mechanical, technical, biological, etc). The method of acoustic emission is successfully used in the investigations of the materials' properties providing live information on the development of damage or fracture. The dental polymers of the provisional prosthetic solution have been tested to determine their strength, plasticity, fracture toughness, water absorption, shrinkage, and microhardness. The authors have made a comprehensive ranking of polymers based on the experimental results. Using the energy identification criterion of fracture modes the percentage of brittle fracture for each material has been evaluated during tensile loading. The paper proposes a new express-method of the ranking of polymer materials, which allows one to significantly reduce material costs and time for experimental investigations. [ABSTRACT FROM AUTHOR]

The results of studies of the effect of acoustic interaction in flat systems of cylindrical piezoceramic radiators with a liquid filling, due to the multiple exchange of radiated and reflected sound waves between the elements of the systems during the formation of their acoustic fields in the surrounding space to the resonance state of these systems are presented. In the computational model of the planar system the relations between the electric, mechanical and acoustic fields of the piezoceramic radiators in the process of energy transformation and their acoustic interaction during the formation of the acoustic field of the system are taken into account. The result of such interaction of the cylindrical piezoceramic radiators with their radial-symmetric electric excitation in the system is the breaking of radial symmetry of acoustic load that depends on many characteristics of the system. It is found that due to the breaking of this symmetry in mechanical fields of radiators of the system new forms of oscillations following the main one are generated, and there is an effective redistribution of energy between them which is "pumped" into radiator at the used variant of their electrical excitation only by the main form of oscillations. It is shown that this phenomenon causes appearance of number of new resonances in the oscillation spectrum of the planar system and essential changes of amplitudes and phases of full oscillation velocities of their radiators which depend on location of radiators in the planar system, wave sizes of radiators and system, physical characteristics of fluids filling the radiators, and frequency range. [ABSTRACT FROM AUTHOR]

This paper presents the results of investigations on the microcracking of composite ceramic materials, such as electrical engineering porcelain and silicon nitride ceramics, using the acoustic emission technique. The analytical expression describing the kinetics of microcrack accumulation is refined. The influence of the loading rate on the strength characteristics of ceramics and the special features of acoustic emission during their cracking are studied. The dependence of the total acoustic emission count on the stressed surface area of specimens is found. The notion of the microcracking modulus of ceramic composite materials is introduced and its mismatching with the Weibull modulus in strength tests of ceramics is shown. [ABSTRACT FROM AUTHOR]

The paper addresses the dependence of acoustic emission produced in rolled hafnium GFÉ-1 under tensile deformation on the material's structural state. A correlation has been established between the material structure, the level of mechanical properties and the values of acoustic parameters. Acoustic emission in non-recrystallized hafnium under tensile deformation is recorded only at the stages that precede fracture. Upon recrystallization annealing at temperatures of 1123 and 1373 K acoustic emission occurs at all the stages of tensile deformation. The highest level of acoustic emission activity in hafnium is observed during the transition from elastic to elastic-plastic strain. [ABSTRACT FROM AUTHOR]

The optical systems operating under great ambient temperature drops use materials with special properties, e.g., with invariable geometric characteristics, such as Zerodur glass ceramic with zero coefficient of thermal expansion. Strong precision joints of parts are necessary elements of systems. Fracture processes in loaded materials are studied by the method of acoustic emission, which allows one to record the instant of crack initiation and to study crack development in a brittle material during loading. The evaluation of the strength of brittle optical materials and their nanojoints by the method of acoustic emission has been shown to have good prospects. It has been found that the number of acoustic emission pulses depends on specimen strength. In tests of nanojoints of pyroceramics, two characteristic fracture modes are possible: with crack propagation into the specimen material and without crack propagation beyond the seam limits. The method of acoustic emission assures reliable recording of these fracture modes. [ABSTRACT FROM AUTHOR]