Damaged Elements Research Articles

Visual investigation of simultaneous clay swelling and migration mechanisms and formation damage consequences using micromodels

One of the most important constituents of oil and gas reservoirs is clay minerals; they may cause formation damage by swelling and migration. When water with lower salinity than formation water invades clay-rich porous media, the clays absorb the water, which results in swelling and, therefore, limit the available space for fluids to flow. Clays may also detach from rock surfaces and start to migrate and block pore throats. Both mechanisms lead to permeability impairment as a critical formation damage element. A better understanding of damage due to clays helps us to control and overcome the problem, which affects oil recovery. In this work, the swelling and migration of clays are studied at the pore scale using clay coated micromodels. The effect of the composition and salinity of injected brines on sodium bentonite swelling and migration were visualized, investigated, and analyzed by a novel approach based on an image processing technique. The effect of simultaneous clay swelling and migration on porosity alteration at different sections of the micromodel was studied to estimate damage, qualitatively and quantitatively. Our experiments showed that the presence of KCl salt in the brine used in drilling, completion, and development operations is vital to control formation damage. The best damage remedy performance was reached when a salt with small hydrated radius cations, such as KCl is combined with a salt with divalent and small hydrated radius cations, such as CaCl2. The combination of KCl and CaCl2 showed only 2.8% reduction of porosity, while KCl showed around 7% reduction of porosity. In migration control, KCl showed the best ability to control migration and most of the migrated clays were re-adsorbed in the porous media.

A method for quantitative damage identification in a high-piled wharf based on modal strain energy residual variability

Damage may occur in the pile foundations of high-pile wharfs due to the complex and diverse working conditions. To identify the damage in pile foundations in early stage is very important for the operation and maintenance on wharfs. Research on pile damage identification based on modal strain energy is one of the hot research topics. This study presents the concept of the modal strain energy residual variability using the characteristics of sensor placement and pile mode shapes of high-pile wharfs, which provide a simple, accurate and practical method to identify the damage in pile foundations of high-pile wharfs in early stage. The qualitative and quantitative relationships between the modal strain energy residual variability and element damage extent are deduced. This concept not only enhances the sensitivity of the modal strain energy to damage but also realizes the decoupling of damage element identification, which is easy to calculate in practical engineering. A damage identification method is constructed base on the concept, and the accuracy of the method is verified by a finite element numerical simulation and model test. A sensor placement method for engineering detection is studied by comparing the damage identification effect in different sampling intervals. The results show that this method can accurately locate a damage area and accurately identify the damage extent in numerical simulation and model test, which provides a new method for the practice of pile foundation damage identification of high-pile wharfs.

Strengthening and restoration of damaged reinforced concrete structures with composite plastics

This paper considers directions to devise methods for restoring the operational suitability of reinforced concrete structures. Mistakes of designers and non-compliance with the concreting technology of monolithic reinforced concrete structures lead to the formation of cracks and deflections of unacceptable size in reinforced concrete beams and floor slabs, as well as to insufficient strength of the elements. Such structures require not only an increase in bearing capacity but also the restoration of the operational suitability of damaged structures. A technique for restoring the serviceability of bendable reinforced concrete structures with increased deflections and excessive crack opening is proposed. To restore bendable reinforced concrete structures, surface reinforcement with pre-stressed fiber-reinforced plastics is suggested, which is ensured by the creation of a building lift in the damaged elements. Fiber-reinforced plastics have a high strain modulus, elastic nature of the diagram, and increased frost resistance; they tolerate fatigue effects well and are resistant to the effects of chemically active substances. Unlike conventional reinforcement methods, surface reinforcement techniques are characterized by high gain efficiency, corrosion resistance, low labor intensity, and short terms of work; they ensure strength increase and provide for economic feasibility. This study's results established that the use of fiber-reinforced plastics not only increases the bearing capacity of reinforced concrete structures but also helps reduce the width of the cracks formed. Thus, it is possible to avoid an increase in the cross-section of structures and reduce the time of operations, which could lead to additional costs

Experimental study on seismic performance of novel fabricated T-joint with replaceable steel hinges

Beam-column joint plays an important role in structural integrity as well as the mechanical behaviour of precast concrete structure, which has been widely applied in civil infrastructures. To improve the seismic performance and the earthquake resilience of precast concrete structure, a novel replaceable steel hinges was applied in the fabricated T-joint in this paper. The T-joint is composed of prefabricated column, prefabricated beam, a replaceable steel hinge with a steel damper, and the core area of the steel damper is constrained by steel sleeves. Pseudo-static tests on the seismic performance of the fabricated T-joint with replaceable steel hinges and the monolithic reinforced concrete joint were first carried out, and then the repaired fabricated T-joint after replacing the damaged steel damper in steel hinge was tested again under cyclic loading. The failure mode, hysteretic behaviour, degradation in strength and stiffness were discussed, and earthquake resilience of the proposed joint was evaluated. The results demonstrated that the bearing capacity, energy dissipation capacity, and ductility of the novel fabricated T-joint with replaceable steel hinges were better than that of the monolithic reinforced concrete joint. It was observed that the damage region of the novel fabricated T-joint was concentrated in the steel dampers of the replaceable steel hinge, while the prefabricated column remained in elastic state without visible cracks. Moreover, the repaired fabricated T-joint could develop desired bearing capacity, ductility, energy dissipation compared with the original specimen, though the stiffness of the repaired fabricated T-joint decreased a bit in the early stage. It was validated that the function of the damaged fabricated joint could be well restored after replacing the damage elements, therefore, the novel fabricated T-joint with replaceable steel hinges could develop favourable earthquake resilience.

Dynamic Behavior of Kinetic Projectile Impact on Honeycomb Sandwich Panels and Multi-Layer Plates

In order to study the dynamic response associated with the impact of a kinetic projectile on the internal structure of an artificial satellite, we propose a kinetic projectile configuration with non-metallic material wrapping and multiple damage elements. The artificial satellite is simplified as a honeycomb sandwich panel and multi-layer plates. We carried out a ground damage test and finite element dynamic simulation, and we determined the lateral effect and penetration performance of the projectile. Then, we studied the dynamic behavior of the projectile penetrating the honeycomb sandwich panel using a theoretical model. We found that its ballistic limit velocity was 150 m/s, and the deformation of the opening had little relationship with the projectile velocity. Finally, we studied the dynamic response of the kinetic projectile impacting the multi-layer plates under various launch parameters. We found that the launch velocity required to meet the damage requirements was within 325 ± 25 m/s. Projectiles with a higher initial velocity had a stronger ability to penetrate the plates, but initial velocities higher than 325 m/s led to a reduced damage area. The kinetic projectile could adapt to incident angles less than 5° when damaging the plates. With the increasing incident angle, the penetration ability was reduced, and the damage area increased.

Mixed-mode fracture behaviour of refractories with asymmetric wedge splitting test. Part I: Numerical implementation and validation

The suitability of asymmetric wedge splitting test (WST) for mode I/II mixed-loading was validated by FE simulation with a three-dimensional heterogeneous continuum FE model. The unsymmetrical strain and stress patterns were observed for mixed-mode loading. Compared with mode I loading of symmetric WST, the introduction of in-plane shear accelerates the crack extension and deviation from symmetry plane with a smaller fracture process zone. Additionally, the asymmetric WST with small, medium and large wedge angles were simulated for sensitivity analysis. With the increasing of asymmetric wedge angle, the recorded vertical load-displacement curves turn from “mild” to “steep”, and the ratio of mode I to mode II fracture energy GI/GII decreases accordingly while the symmetric one has the highest GI proportion. The asymmetric WST with large wedge angle deforms the most at same applied vertical loading displacement, while all WSTs show similar damaged elements amount at the same crack mouth opening displacement.

Parameter optimization of L-joint of composite sandwich structure based on BP-GA algorithm

Composite superstructure could provide excellent performances during surface combat. L-joint in the superstructure plays a significant role in the long-term service and would bear a complicated external load. In this paper, an all-composite L-joint was proposed and subjected to a bending test. A progressive damaged finite element analysis was performed to reveal its failure mode. An optimization based on the BP-GA algorithm was conducted to obtain the optimal geometries. The results showed that the primary failure mode of the L-joint was the crack of the stiffener outer skin. It was dominated by the fiber compressive failure. The average ultimate loadbearing capacity of the L-joint was 2.321 kN. And the simulated result was 10.09% lower than the experiment. The maximum relative error between the BP-GA prediction and actual values was less than 8%. The optimal structure obtained showed an enhancement of the load-bearing capacity about 1.41 times and stiffness about 1.65 times.

Experimental and numerical investigations on hydraulic fracture growth using rock-like resin material containing an injecting inner pre-crack

A new transparent resin material with a compression-tension strength ratio of up to 6.6 at −15∼-10 °C has been developed. It possesses more brittle fracture properties than before and can competently simulate many kinds of engineering rocks. The fabrication demands strict temperature control and treatments. Specimens are inventively made with a hollow injecting inner pre-crack. Based on self-designed water injection devices and low-temperature loading equipment, uniaxial and biaxial hydraulic fracturing experiments are carried out under fixed water pressures. The specimens' uniaxial hydraulic failure process can be separated into four stages. At each stage, the variation of water injection is analysed. For all experiments, both crack initiation stress and peak strength have declined significantly, by more than 80% and 70% compared with dry specimens. The evolution of wrapping wing cracks and fin-like cracks in biaxial experiments has rarely been reported before. Moreover, numerical verification is conducted by FLAC3D. A novel fluid-solid coupled model has been developed that takes into account both the pre-peak damage and post-peak sharp degeneration. The principles are dependent on the element's failure type, i.e., tensile failure, shear failure, or a combination of the two. The mechanical parameters and permeability coefficient of damaged elements are redefined. The simulation results match well with experiments, demonstrating the feasibility of this method. Finally, the proposed model is applied to explore the hydraulic failure of the specimen under triaxial compression with fixed stress. The impact of injecting pre-crack on hydraulic fracture growth is illustrated.

Fatigue Crack Propagation Estimation Based on Direct Strain Measurement during a Full-Scale Fatigue Test.

Military aircraft are subjected to variable loads, which are the main cause of initiation and propagation of cracks in the most stressed locations of the airframe. The aim of a Full-Scale Fatigue Test (FSFT) is to represent actual load conditions in such a way that the results obtained are a good representation of the actual loads and may be used as data that give insight into the development of real fatigue damage in critical locations. The FSFT load spectrum is a generalized depiction of the expected service loads and is designed to give an overall good representation of loads exerted on the airframe’s structural elements during operation. Moreover, the discrete method of load application on the structure (exerting loads with hydraulic actuators rather than pressure fields or inertia loads expected in actual operation) may cause some local effects, which may not be present in operation. The proposed usage of direct strain data from the test include such local effects. Moreover, operational loads may vary between individual aircraft, therefore it is crucial to understand the whole process of fatigue crack onset and development in order to determine safe inspection intervals and thereby mitigate risk. This paper presents crack propagation calculations regarding the development of a crack in a critical location of the PZL-130 “Orlik” TC-II aircraft, discovered during FSFT. The discussed crack was found already developed, hence the information about nucleation and initial propagation of the crack was not available. Therefore, there was a need to recreate the whole propagation process by means of numerical estimations using the FSFT results like location of the crack and total life for model validation. Moreover, in order to gather real load data for calculations a dedicated stain gage was installed on the damaged load path to monitor the actual remote strain in the element during the FSFT. This allowed for the definition of load sequence exerted on the damaged element directly during the test rather than estimating it from the general load conditions of the wing. The calculations allowed for the estimation of crack propagation curves from initiation to critical crack length causing fatal damage. The obtained curves allowed to visualize the crack behavior due to applied load and furthermore define initial and recurring inspection intervals for the entire fleet during operation, which allowed to define which cracks could be found before they reach critical size in order to carry out mitigation actions like repair or replacement of the damaged part. The authors present the methodology for load spectrum development based on direct strain measurements and furthermore crack propagation curves estimation, validated with the actual FSFT results, which allowed to propose nondestructive inspection intervals for future operation.

Experimental and numerical investigations of beam-to-column joints with a double-core buckling-restrained connector

Based on the ideas of damage control and element replaceability, this paper proposes an earthquake-resilient, beam-to-column joint with a double-core buckling-restrained connector (DBRC). First, the composition and function of the joint are introduced, and the bearing capacities corresponding to four failure modes are theoretically calculated. Then, quasistatic tests were carried out on three specimens to investigate the influence of the stiffeners on the end plate and the ear plate connection on the hysteretic responses of the joints. The test results showed that the use of a DBRC can change the failure mode of the joint, in which the plastic deformation was concentrated in the DBRC, which dissipated most of the energy. The ear plate connection affects the bearing capacity of the joint, while the stiffeners have little effect on the hysteretic response of the joint. The finite element models for the joints were built using ABAQUS and validated by test results. Finally, parametric analyses were performed to determine the influences of the friction force of the core plate, the existence of a buckling restraining system, the thickness of the end plate and the cross-sectional area of the core plate. The results showed that these parameters mainly affect the in-plane and out-of-plane deformation of the core plate, end plate damage and joint damage distribution.

Dynamic Response of a Hypersonic Rocket Sled Considering Friction and Wear

The dynamic response of a hypersonic rocket sled was studied by considering the time-varying friction coefficient and the gap caused by wear between the slipper and track. A multibody dynamic model for a hypersonic rocket sled system was established by considering the time-varying mass and moment of inertia, nonlinear aerodynamic loads, engine thrust, track irregularity, and nonlinear contact force. As for the wear calculation, the ductile and shear criteria were used as the material damage criteria, and slipper wear was determined by the number of damaged elements. A rocket sled test was also carried out, and the dynamic response of the sled was measured. The results showed that the computational sliding displacement and velocity of the third-stage sled matched well with the test values. The computational root mean square (RMS) values of the vertical acceleration of the third-stage sled front slipper considering friction and wear matched better with the test values than with the case without considering friction and wear, which underestimated the RMS value by approximately 20.1% at Mach 5. The importance of considering friction and wear and the correctness of the computational method were validated. It is also found that the kinetic friction coefficient decreased with an increase in the product of the pressure and velocity. The wear height of the slipper increased almost linearly with the sliding displacement. The test results showed that the vertical acceleration power spectral density of the third-stage sled front slipper increased with time in the full frequency band below 2000 Hz. This study will guide the design and optimization of hypersonic rocket sleds.

Structural Assessment under Uncertain Parameters via the Interval Optimization Method Using the Slime Mold Algorithm

Damage detection of civil and mechanical structures based on measured modal parameters using model updating schemes has received increasing attention in recent years. In this study, for uncertainty-oriented damage identification, a non-probabilistic structural damage identification (NSDI) technique based on an optimization algorithm and interval mathematics is proposed. In order to take into account the uncertainty quantification, the elastic modulus is described as unknown-but-bounded interval values and the proposed new scheme determines the upper and lower bounds of the damage index. In this method, the interval bounds can provide supports for structural health diagnosis under uncertain conditions by considering the uncertainties in the variables of optimization algorithm. The model updating scheme is subsequently used to predict the interval-bound of the Elemental Stiffness Parameter (ESP). The slime mold algorithm (SMA) is used as the main algorithm for model updating. In addition, in this study, an enhanced variant of SMA (ESMA) is developed, which removes unchanged variables after a defined number of iterations. The method is implemented on three well-known numerical examples in the domain of structural health monitoring under single damage and multi-damage scenarios with different degrees of uncertainty. The results show that the proposed NSDI methodology has reduced computation time, by at least 30%, in comparison with the probabilistic methods. Furthermore, ESMA has the capability to detect damaged elements with higher certainty and lower computation cost in comparison with the original SMA.

Structure health monitoring of a composite wing based on flight load and strain data using deep learning method

An investigation was made into a method for Structural Health Monitoring (SHM) of a composite wing using Convolutional Neural Network (CNN) model. In this method, various aerodynamic loads of an aircraft during flight and corresponding strain data were used for CNN model training. The proposed method was demonstrated by numerical simulation using vortex lattice method for aerodynamic loads of an A350-type aircraft in over a thousand flight conditions and a Finite Element (FE) model as a digital twin of the full-scale composite wing. To represent the measurement of 324 sensors mounted in the 18 skin-rib joints of the inboard wing, strain data from the 18 × 18 elements of the FE model in the sensor locations were calculated corresponding to the flight loadings. The strain data from the original structure FE model were employed to train a CNN model that was classified as healthy samples. Damaged elements were then introduced in random locations to produce data samples corresponding to the same set of flight loads for the CNN model training. In the subsequent damage detection process using the trained CNN model, confusion matrix, uncertainty and sensitivity analysis were evaluated. The study results show that robust damage detection results can be obtained with 99% accuracy without noise and 97% accuracy with 2% Gaussian noise. In the damage localization process, threshold value was set at 1.5, 2 or 2.5, and 83% overall accuracy was achieved using the CNN model when the threshold value was 1.5. The study demonstrated that the proposed method is efficient, accurate and robust.

Етіологія, патогенез та інтенсивна терапія метаболічного ацидозу

У статті надані дані щодо етіології, патогенезу, клінічних проявів, принципів діагностики та лікування метаболічних ацидозів: діабетичного і недіабетичного кетоацидозу, лактатацидозу в дорослих і дітей. Викладено сучасні напрямки інфузійної терапії кетоацидозу і лактатацидозу із застосуванням новітніх вітчизняних інфузійних засобів. У своїй статті автори зіставили алгоритми лікування кетоацидозу і лактатацидозу з рекомендаціями Британського товариства клінічної діабетології і Американської асоціації нефрологів, роблячи поправку на можливості вітчизняних лабораторних досліджень. Характерною особливістю деяких форм кислотно-основного дисбалансу, що часто зустрічаються, є тісне переплетення ушкоджуючих або пристосувальних елементів, чіткої межі між якими не існує. Багатофакторність і патогенетична неоднозначність порушень кислотно-основного гомео­стазу зумовлюють значні розбіжності в оцінці прогностичної значимості і стратегії лікування його складних форм. У клінічній практиці це часто призводить до невиправданої схематизації, «знеособлення» терапії, або, що ще гірше, до прагнення враховувати параметри кислотно-основного стану тільки при зміщенні рН в області загрожуючих життю значень.

A mode shape sensitivity-based method for damage detection of structures with closely-spaced eigenvalues

A new optimisation problem is proposed to facilitate a fast and reliable damage detection of structures with closely-spaced eigenvalues. The first stage of the proposed method identifies the most probable defective elements resulting in the elimination of healthy members from further investigation. This will further reduce the computational efforts of computing damage indices regarding the defective elements. The second stage of the proposed method exploits the proposed objective function to update the damage indices of the identified defective elements from the first stage. Two truss structures with multiple damaged elements in different damage scenarios are studied where measurements with different levels of noise are used as input to the proposed algorithm. Numerical results and comparison with previous studies demonstrate the superiority of the proposed method in damage detection of structures with closely-spaced eigenvalues.

Failure analysis of auxetic lattice structures under crush load

Lattice structures are promising materials in the terms of energy absorption, acoustic and vibrational damping, high strength-to-weight ratios and thermal management capabilities. In particular, auxetic lattice structures, among others, show high energy absorption performances due to their characteristic negative Poisson’s ratio. In this study, it is aimed to compare auxetic deformation mechanisms under quasi-static crush loads. Ti6Al4V tensile test specimens were produced with Electron Beam Melting (EBM) Additive Manufacturing (AM) technology. Moreover, a constitutive equation was derived and calibrated according to tensile results. The calibrated data were used to generate non-linear computational crush models including elastoplastic material data, damage initiation criterion, damage evaluation law and element deletion. The computational models are utilized for optimum topology design and mechanical performance prediction of different auxetic cells, including anti-tetrachiral, hexachiral, re-entrant and honeycomb lattice structures that are prone to prematurely fail under crush loading conditions. Consequently, it was found that the chiral auxetic deformation mechanism experienced better energy absorption ability over re-entrant deformation mechanism for metallic lattice structures.

Legal Dimension of the Protection of Critical Infrastructure – Selected Aspects

Aim: As part of this article, an attempt was made to present the legislative process in Poland regarding critical infrastructure, for which valid is the Act of 26 April 2007 on crisis management, specifying, inter alia, authorities competent in crisis management and their tasks and principles of operation in this area as well as implementing acts issued on its basis. The introduced legal regulations define both the concept of critical infrastructure, its protection and activities related to the prevention of crisis situations, reacting in the event of their occurrence and preparation to take control over them, as well as removing their effects and recreating key resources. Introduction: Regulations concerning the protection of critical infrastructure are included in legal acts covering various areas of the country’s functioning, including telecommunications activities, production and trade in fuels and electricity, performance of defence tasks by entrepreneurs, creation of strategic reserves, powers of the minister competent for the State Treasury in some companies, protection of persons and the property. The protection of critical infrastructure is related to the raison d’état, which indicates the need to make special efforts to protect the country’s key infrastructure. Therefore, it is reasonable to present selected legal elements needed to protect critical infrastructure, especially those issues that ensure the continuity of the operation of public administration bodies, which are to ensure the safety of the citizens. Methodology: The article was prepared based on the analysis of the literature on the subject and the analysis of legal acts in the area of strengthening the concept of critical infrastructure, taking into account the current situation related to the pandemic and, consequently, the loss of some officers and employees. During the analysis of the conducted research, compact publications, acts of Polish law as well as guidelines and recommendations published on the websites of governmental institutions were used. Conclusions: In the protection of critical infrastructure, there is a need to introduce legal regulations within the framework of cooperation between institutions. The preparation of effective activities in the area of critical infrastructure requires a comprehensive approach, including: physical, technical, personal, ICT, legal protection, as well as assistance from the government in the reconstruction of the damaged element. Each of the areas mentioned above is a complex set of activities requiring general and specialist knowledge, sometimes expert knowledge, extensive practical experience (using the so-called good practices), risk analysis skills, and risk prediction (profiling). Keywords: act on crisis management, legal acts, crisis management, protection of critical infrastructure, identification Type of article: review article

ОБҐРУНТУВАННЯ НЕОБХІДНОСТІ ВДОСКОНАЛЕННЯ НАУКОВО-МЕТОДИЧНОГО АПАРАТУ ФОРМУВАННЯ ВИМОГ ДО ЕНЕРГЕТИЧНИХ ХАРАКТЕРИСТИК ПОРАЖАЮЧОГО ЕЛЕМЕНТА КІНЕТИЧНОЇ ЗБРОЇ НЕСМЕРТЕЛЬНОЇ ДІЇ

The scientific-methodical apparatus for predicting damage to biological objects of non-lethal kinetic weapons is considered, which mainly takes into account only the energy characteristics of the damaging elements, namely, kinetic and specific energy. An analysis of the nominal ballistic characteristics of samples of non-lethal kinetic weapons, which are in service with law enforcement agencies and military formations of Ukraine, was carried out, based on the determination of only the specific energy of the striking elements. The energy characteristics of bullets or striking elements for various samples of non-lethal kinetic weapons vary within fairly wide limits. In particular, such an important indicator as the specific energy varies from 0.34 to 1.33 J/mm2, that is, even the same type of weapon, intended for use at certain distances to the target, in the case of using different cartridges, has a significantly different specific energy (the difference reaches 30%). An analysis of known developments in the field of terminal ballistics is given, which indicates the need to take into account the speed of meeting the target under the conditions of conservation of constant kinetic energy. So, with the same mass, a bullet with a higher speed will have more energy. Such a ball has the ability to give a different part of its energy to the affected tissues. The main feature of cartridges with a traumatic effect, which distinguishes them from ordinary cartridges for firearms, is the mechanical characteristics of the striking elements. The striking elements require a high "stopping" effect, i.e. quick and complete incapacitation of the opponent when hitting any part of the body - this is a short range of "fire contact". For this, striking elements must quickly and maximally transfer their kinetic energy to the target upon hitting it. Therefore, most bullets for police and civilian weapons are blunt-end ("impact") - with a rounded or flat area on the main part. So important are the shape and strength (stiffness) of the striking elements and the shape of the main part that directly interacts with the target. The need to improve the scientific and methodological apparatus for predicting damage to biological objects when using non-lethal kinetic weapons by taking into account an expanded list of factors (speed, strength, rigidity and shape of the striking element) in order to increase the adequacy of the obtained models is substantiated.

Free vibration analysis of in-plane circular curved beams with crack damage: a semi analytical solution

In this paper, a semi-analytical method for solving circular curved beams is proposed to study the free vibration of in-plane circular curved beams in both undamaged and damaged configurations. The crack damage of the structure is represented by the cross-sectional reduction of the damaged element. Based on the discrete circular curved beam model, the coupling stiffness matrices of shear, compression and bending are derived. Combined with the lumped mass matrix and the dynamic characteristic equation of the multi-degree-of-freedom system, the frequencies and modes of the damaged and undamaged structures are calculated. The results are compared with the finite element method, and the good consistency between them is verified.

Основні вимоги до сучасних систем діагностики потужних турбогенераторів

A turbogenerators design complication and the use of new auxiliary systems for the cooling intensification with increasing power unit lead to the decrease of their reliability. Therefore, the system and methods of control and diagnostics of generators main component parts to compensate this decrease of turdogenerators reliability were developed. In the paper, a system analysis for the reliability of nuclear power stations turbogenerators was carried out, and the main damaging elements and components, that were determined. It was found that almost half of the damages are stator and rotor, a third of which — stator core and winding bars defects. Modern diagnostic methods of technical condition for stator and rotor elements of powerful generators as well as their advantages and drawback are considered. All this allowed us to formulate the basic principles of diagnostic system construction for nuclear power stations powerful turbogenerators, which are based on the continuous control of the data on their most important parameters and defects, and deviations identification occurring in the most of operation cases as well as preventing further work of equipment. The economic effect owing to the introduction of monitoring and diagnostic modern systems is ensured by increasing the reliability of electric power equipment operation, reduction downtime due to emergency shutdowns of generators, decrease unplanned electricity underproduction, reducing in time and cost of repair and restoration work, the number of consumable spare parts and materials, as well as economic losses due to unplanned downtime of nuclear power plant unit.