⦁ Carbon/graphite;
⦁ SiC;
⦁ Oxide;
⦁ TRISO fuel particles/seals;
⦁ New materials for nuclear fuel cladding;
⦁ MAX phases.

Unique and advanced methods have been developed to study these materials at multiple scales. The goal is to correlate the nano/microstructure of material processing with macroscale damage and fracture under in-service conditions.

EMAM has established strong collaborative links with key national and international players in the nuclear fission, nuclear fusion and aerospace industries. The goal is to use scientific approaches to gain a mechanistic understanding of the failure modes in these materials. As a result, their industrial applications are supported.

There are active ongoing projects in the following areas with open opportunities for doctoral and postdoctoral students.

• Mechanistic understanding of damage and fracture of ceramic-matrix composites under extreme conditions: Working with many industries and processing groups, this area studies a range of aerospace and nuclear fission/synthesis CMUs in terms of their local mechanical and thermal properties, residual stresses, deformation and fracture, including crack initiation and propagation from ambient temperatures to above 1000°C by in situ imaging and diffraction techniques;
• Damage and Fracture of Nuclear-Graphite Composites at Multiple Length Scales: This topic studies a wide range of polycrystalline graphite materials, from highly oriented pyrolytic graphite to fine/medium/coarse graphite composite, unirradiated or irradiated with ions, neutrons or protons, to understand their multiple length-scale structure, physical properties before and after irradiation, at ambient temperatures and up to 1100°C;
• Thermal and Mechanical Characterization of TRISO Fuels: This program investigates a range of tristructural isotropic nuclear fuel (TRISO) particles, either free-standing or embedded in a SiC or graphite matrix, in terms of their local properties, residual stresses, and high-temperature mechanical properties that vary with processing parameters;
• Interfacial strength of heterogeneously integrated ceramic films. A number of micromechanical test methods have been developed to evaluate the interfacial toughness of thin ceramic films (e.g., GaN) integrated onto rigid substrates, including SiC, Si, and mono/polycrystalline diamond. to enable the development of new semiconductor materials for high-power radio frequency (RF) devices.

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As a rule, the program provides a stepwise application of loads for several design cases. The combination of loads, their magnitudes, the order of application by design cases, ultimate and subcritical strength conditions or the achievement of ultimate deformations (displacements) are set in a table, ribbon or three-dimensional graph.

Each design loading case is divided into two levels: operational and design. The operational level of loading is divided into 6 – 10 stages to perform preliminary measurements of displacements and VAT in the elastic region and simultaneous development and control of reproducibility of linear loading. At this level, the zones and cross-sections of possible failure or plastic hinge occurrence are determined on the basis of the VAT study.

Observation areas are marked during testing before fracture, remote instrumentation for measuring parameters at fracture is installed and graded. Depending on the task, optical, polarization-optical, moiré (raster) means of VAT registration are installed, high-speed photo and movie registration, videorecording of fracture dynamics or loss of stability by stages are used. Special safety measures are taken into account, especially when testing high-strength brittle materials and for objects accumulating significant elastic energy before fracture, for example, when testing shells of large volumes by compressible gas (air) supercharging.

Loading to design loads is carried out once, continuously increasing the load level from operational to design, and, without stopping the loading, bring the test to the maximum loads, noting a sharp (or smooth) decrease in load at failure of elements, loss of bearing capacity (stability). The rate of loading is stipulated in the program and in the specifications for the energy requirements of the stand. For static loading of metal structures, the critical speed is when the error of load reproduction due to the attached masses of the loading system becomes greater than 1% of the given current force value, and all transients from the beginning to the end of the deformation diagram depend only on the stiffness of the system, not on its mass.

In the case of carrying capacity tests with simultaneous thermal effect on the object, carried out by means of radiant heating or in chambers-thermostats, the modes of mechanical loading and heating (heating) rates are set by special schedules, taking into account the heat capacity of the specimen and the system, inertia of heat transfer regulation, dissipation and power of radiators. The program is implemented by an automatic system of output and maintenance of the temperature regime on the object in time or as a function of mechanical load. The methodology of carrying capacity testing of scale models of large-scale objects requires a rigorous theoretical justification and considerable research.

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Similar objectives are set in fatigue testing, but in this case the main parameters are the level of average stresses and the number of cycles (hours) to failure.

The development of durability and fatigue testing technology is in the direction of automation of loading, measurement of parameters, control and calibration, data processing, information generation, its accumulation and operational presentation, documentation editing and reproduction. For automation purposes, mini- and microcomputers and peripheral devices are used. Thus the replacement of long labor-intensive operations is achieved, the level of standardization of tests, metrological culture, objectivity of evaluations and increase in the number of investigated parameters are increased.

The common tool for performing all operations is CPI – measuring and computing complex, which performs direct, indirect, joint and cumulative measurements of electrical quantities, controls the process of measurement and impact on the object, presents the results of measurements to the operator in a given form. CPI provides perception, conversion and processing of electrical signals from primary converters, control of measuring instruments and generation of standardized electrical signals, which are input for analysis of measurement accuracy, controls the values of force (or other type) impact on the object, presents the results in the specified forms.

The development of automatic systems of strength (fatigue) testing has passed several stages of limited automation, before a rational combination of multi-channel and speed for IIS and UVK was developed. In some cases, it is more convenient to use only a few IIS modules, or, in case of block-modular construction of the UVK, to use separately modules (racks) ASUN (automatic load control systems) for several independent tests. Program control is performed from the processor (mini- or microcomputer) built into the CPI; as a rule, commercially available aggregate means of measurement and automation and standard interfaces are used.

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Great efforts are invested in solving advanced engineering problems, using innovative engineering knowledge and experimental methods of wide practical application. At the same time, we take into account that everything is properly prepared and organized so that experimental engineers can conduct experiments more efficiently. If we did not approach the problem in this way, the resulting know-how would be ineffective and unusable. In the various areas of research and development where practical problems are solved using experimental mechanics, development engineers work closely together and collaborate with experimental engineers so that scientific and technical knowledge and experience exchange is realized quickly and efficiently for mutual benefit. This requires that theoretical and practical knowledge, ideas and experience are systematically unified in order to enhance the practical acceptance of research effectiveness.

In addition to measuring mechanical quantities, experimental mechanics includes:

• Experimental design;
• Creation of engineering control models and preliminary analysis of the system under study, i.e., measured, to evaluate the measured values;
• Development of measurement methods and techniques;
• Design, construction and technological development of measuring systems;
• Processing of the obtained data;
• Mathematical formulation and analysis of the system under study based on measurement results.

The object of testing can be a structure or structure, mechanical system, phenomenon, problem, material sample…

Measured mechanical quantities traditionally associated with experimental mechanics are: deformations, which can function as a basis for determining stresses or loads (forces, torques); accelerations, velocities, displacements, angles, etc. In addition to the usual quantities, any appearance relevant to the object in question can be measured or recorded by means of photography or video to more effectively determine the real state by experimental methods, and knowledge of this real state can later contribute to a clearer description, i.e., a mathematical formulation of the phenomenon.

Experimental mechanics is used for:

• Solving engineering problems when numerical procedures cannot provide reliable answers;
• Validation of analytical and numerical engineering models (verification of boundary conditions and basic parameters);
• Determination of real loads / stress states of the object – forces, displacements, deformations / stresses;
• Determination of the real dynamic behavior of the system under operating conditions – vibration;
• Generation of input data for engineering models.

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