Diagnostics of aircraft
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Diagnostics of aircraft

Diagnostics of aircraft

 

Determination of the volume and frequency of diagnosis

Volume and control technology are largely dependent on the methods of operation of the AT - on resource, and as a combination.

If the operation is carried out by the state, the planned periodic control and verification work, which resulted in the decision to further exploitation. When combined method of operation of the elements of the object operated on a technical condition, the other - on the resource. Just off to the 60 75% of units and systems of modern aircraft fails to translate into operation as of (the experience of airlines, "Pan American", "Air Canada" and so forth.). Therefore, the combined method of operation is currently the principal.

Daylight-condition maintenance and operation of the combined method improves the reliability of the Armed Forces through the introduction of the most careful control a much larger number of parts OK in terms of operation and maintenance. This significantly increases the proportion of parts, the state of the material is determined by the methods of inspection.

The order of maintenance and control is determined by the type of the sun and may be different. However, facilities maintenance programs carried out some general principles for the use of funds flaw. Consider the major ones. Frequent testing is supposed to carry out visually. For inspections with a large mezhkontrolnym period used tools.

As an example, the organization of the Tax Code of the aircraft type In-707. At the initial stage of operation, a part of the loaded glider elements was checked by flaw detection methods in 3000 h. Through 12 500 h (5 years of operation), all heavily loaded elements were evaluated with an assessment of the state of the material properties. The next such control was carried out already in 6500 h (in 3 years after the first careful monitoring with a total running time of 19000 h). After using the 25000 airplane for an hour (through 10 years of operation), a complete control of the materials of all the critical elements was carried out with control by the methods of flaw detection. With increasing operating time and the occurrence of fatigue cracks and corrosion, intercontrol intervals are reduced. Details and units of structures with the same control schedules are conditionally combined into groups.

To implement these principles for determining the frequency of monitoring is necessary to know the probability of occurrence of defects in the critical parts in different time intervals aircraft operation and speed of development defects. For example, if a defect is detected in a large number of copies at a considerable operating time, it is necessary to significantly change the timing and frequency control.

Work on monitoring and diagnosis of the main function laboratories NC companies. The information collected by the laboratory used to generate proposals for the further operation. Such information is also required to adjust the systems of maintenance and repair. The most objective correction system is provided by a detailed analysis of statistical information.

 

Expertise and technology diagnostic systems

Technical diagnostics, based on the methods of inspection - a reliable indicator of safety. Retrieving the Quality Score, the properties and characteristics of the material OK due to the large volume of information. In world practice, distinguished expert system for maintenance which amounts of information are minimized, and the probability of correct decisions increases.

Consider the trends and prospects of assessing the technical condition of aircraft structures in the process of maintenance, repair and operation. The development of such systems are divided into five major areas.

  • The first - the use of non-destructive testing components, parts, components, aircraft systems.

  • The second - the development of methodology for determining the physical methods of nondestructive testing of stress-strain state of the diagnosis objects.

  • The third - the creation of methods of diagnosing test design aircraft based on the methods of NDT.

  • Fourth - the construction of monitoring systems based on the development of methods and control of specific products.

  • Fifth - substantiation of principles of evaluation of non-destructive testing for the certification of the AT.

Let us consider each of these areas.

  • 1. The method of selection of NDT methods of aircraft parts and assemblies is substantiated. The technique is based on the identification of cracks of critical dimensions and the determination of the defect shape parameter, which are placed in the control samples, and on the processing of signals from the sensors of the primary information of the NDT tools.

Given that under the control of aeronautical engineering parts are commonly used manual control, use documentation of the origin and the size of the identified defects and computer processing of the results.

  • 2. Factors influencing the stress-strain state and fatigue strength are taken into account and studied, and effective methods and means of their determination are developed. Structural heterogeneity affects the stress concentration, strength, corrosion resistance, plasticity, tightness, wear resistance, etc. Defects in welded joints play the role of notches, weaken the section, create stress concentration and volumetric stress state. It was found that under vibration loads, even small defects noticeably affect the fatigue strength of the material. The defect is the more dangerous, the smaller the radius of curvature of its top and the larger its size. The plasticity of the material turns out to be sufficient to stop the growth of stresses in

field concentration as long as the average voltage in the weakened section does not reach the yield point.

Studies have shown that the increased fragility of the steel may be a consequence of aging during deformation by stretching at 100-500 ° C. Work hardening and the resulting aging significantly increases the fragility of steel and nominal strength threshold shift towards positive temperatures.

Additional causes of failure at operating stresses are residual stresses arising during welding and assembly due to uneven temperature distribution and the occurrence of a force effect on the metal that expands when heated from the side of the colder metal surrounding it. With a certain combination of uneven temperature distribution and rigidity of the object, the developing mechanical stresses reach the yield point of the material, which is accompanied by its plastic deformation. Residual stresses also affect the propensity of the material and welded joints to brittle fracture. However, the compressive stress is a barrier in the path of the moving crack.

The nature of the stress distribution can be set using the following methods: polarization-optical, fragile surfaces, magneto-elastic, vortex-current. For this purpose, a range of indicators and instruments to determine the stress-strain state. Physical and mechanical properties of the surface of products made from steel austenitic and austenitic-ferritic grades are determined by the vortex-current devices operating at high frequencies (100 400 MHz).

Based on the long experience of flaw detection of welded joints and the determination of the stress-strain state of welded structures, as well as theoretical generalization of the stresses around the defects of butt welded joints depending on their location in the seam and the elastic characteristics of the seam and the base metal under different types of loading, a methodology for determining the coefficients Concentration of stresses in the tops of defects according to the results of nondestructive testing of tubular structures, vessels And apparatus. The principle of determining the stress concentration coefficients is based on the application of quantitative criteria for the evaluation of defects-the size of the critical crack and the shape of the defect-as well as the correlation dependencies between the stress concentration coefficient and parameters (amplitude, phase, etc.) of the signals emitted by non-destructive testing equipment.

The implementation of analytical methods for predicting the durability of objects can diagnose the presence of the experimental data on the actual state of the object of control.

  • 3. The purpose of the third direction is to develop a methodology for test diagnostics of products during their operation. The methodology is based on the requirements of regulatory and technical documentation, correlations between the stress state, size and type of defects. The developed system of test diagnostics includes the following blocks: characteristics of the diagnosed object; formalized object model; formalized defect models; mathematical model of the system and diagnostic algorithm; system hardware. Determination of the quantitative values ​​of the indicators used in assessing the technical condition is carried out using an integrated monitoring system created for a specific diagnostic object. For example, for a vessel - the state of the base metal and metal of the welded joint, corrosion and corrosion-erosion damage, the size of the body and wall thickness, the presence of leaks, their location, the magnitude and nature of the distribution of the stress-strain state; the presence of cracks within the sensitivity of the controls. The mathematical model for processing diagnostic data is based on a basic matrix. Its elements are signs and identifiers of a number of stresses and defects, ordered according to the hierarchical structure of the vessel by the code designations of the elements.

When constructing an algorithm for the operation of a technical diagnosis system for a particular task, in general, deterministic and logical diagnostic features are used. Methodological principles of the diagnostic system are to collect data on failures in the process of operation, registration in the technological maps of the diagnosed parameters during the operation of the diagnostic object with a given loading regime. These data are obtained by means of built-in control or during periodic flaw detection, visual-optical control and measurements. Indicators of the technical state of the structural elements are determined after it is removed from the technological cycle. Further processing of the received information, analysis and decision-making is carried out. Identification of defects and damages is based on the requirements of regulatory documentation.

  • 4. Monitoring of the technical condition of mechanical systems operating in aggressive environments is provided by a two-level monitoring system. As a basis for monitoring, test diagnostics are used at the stage of manufacturing and operating the system. If functional relationships between the structural parts of the system are taken into account, the formalized model is the "mechanical system module - node - element". Such a four-level model allows monitoring quite fully in accordance with the structural-hierarchical scheme. All composite vectors of the technical state of the system are grouped into 4 parameters and 18 subparameters. They are determined by means of NDT during flaw detection, converted using formulas into features and entered into a computer for processing in accordance with the developed algorithm. Using statistical values, the indicators of the state of the constituent units of the system are calculated separately and compared with the preliminary normative permissible (nominal) or maximum values. The magnitude of the deviations is necessary to predict the residual life based on the criteria of crack resistance, strength, corrosion resistance, changes in geometry, etc. After calculating and comparing the indicators of signs, a decision is made to eliminate negative changes in the elements, the volume of repair and restoration work of the mechanical system. To automate the operations of observation and operational management to eliminate the consequences, the following construction sequence is followed: development of a formalized and mathematical model of the system; development of a diagnostic algorithm; control system hardware. Its implementation in production is an automated workstation for a mechanic (operator) of a section.

  • 5. With the transition to a market economy, the need arose for certification of products and quality systems. One of the functions of the quality system at the enterprise is technical diagnostics. To carry out work on certification of quality systems and certification of personnel for technical diagnostics, independent bodies are created - certification and expert centers. The certification of specialists is carried out in accordance with the requirements of European standards.

The centers define the principles for assessing the quality level, develop rules for certification of methodologies and regulatory documents, accreditation of NDT units and technical diagnostics. The principles of assessment of NDT and technical diagnostics consist in verifying: the normative and technical documentation for all types (methods) of control that are applied in the enterprise; Organizational structure of control services; Degree of participation of designers and technologists in the selection and designation of methods for monitoring and diagnosis; Applied technologies and means of their changes; Qualifications and powers of NDT specialists and flaw detection; Metrological support of control; Availability of documentation at the workplace; Acceptance criteria (rejection); Registration of control results; Condition of workplaces and control areas.

The above approach is implemented in the aviation rules and successfully used during the certification work in enterprises producing, operating, servicing and repair of aircraft.

Practice shows that exploitation, much of the failure of aircraft structural elements due to a crack-like lesions - nicks, fatigue cracks, corrosion cracking, erosion and so on. N. In the case of aircraft engines, the responsible elements of the rotor part design - compressor and turbine working blades - are subject to such damages. Therefore, one of the important problems of complex diagnostics of gas turbine engines is the determination of the TC of the blades during the engine operation and the identification of crack-like lesions at an early stage of their development. This will significantly reduce the likelihood of blade failure during the operation of the gas turbine engine. One of the most effective and promising methods for solving the problem of detecting crack-like damages of gas turbine blades on stationary and non-stationary operating conditions are methods of vibration and vibro-acoustic diagnostics.

Vibration and vibro-acoustic diagnostics - is the direction of technical diagnostics as diagnostic information using different oscillatory processes: mechanical vibrations, variable (dynamic) deformation, acoustic vibrations in solid, liquid and gaseous media.

Vibrational and vibro-acoustic control of the engine's TC is one of the most important directions in the general system of technical diagnosis of GTE and has a number of advantages in comparison with other methods. Methods of vibration and vibro-acoustic diagnostics provide an estimate of the TS of the rotating elements of the engine due to the processing of information on the vibrational processes occurring during the operation of the gas turbine engine. The appearance and propagation of acoustic and mechanical vibrations is due to operational dynamic loads. The parameters of such oscillations depend both on the characteristics of the vibrational disturbances and on the characteristics of the vibro-acoustic channel located between the excitation source and the information receiving point, i.e., on the state of the diagnostic object.

The use of vibroacoustic diagnostic techniques opens the possibility of early detection and prevention of defects in comparison with other methods, as well as the exclusion of cases of unreasonable removal of the engine from service. The use of methods and means of vibro-acoustic diagnostics of GTE is facilitated by high information content of vibrational and acoustic signals, their simplicity into electrical signals, the possibility of using these methods without dismantling the engine under operating conditions, as well as the wide automation capabilities of the entire diagnostic process.

Vibration and vibro-acoustic diagnostics of GTE is quite effective. Using airborne vibration control can detect about 35% of all faults that occur during operation: wear, violations snosnosti trees, the destruction of bearing arrangements of the rotors, the destruction of compressor and turbine blades, the destruction of gears and so on.

One of the most studied theoretically and in practice common methods of vibration and vibro-acoustic diagnostics of structural elements are low-frequency methods of free and forced vibrations (0-25 kHz). These methods are available to initiate or damped resonant forced vibration diagnostics object (OD), and further analysis of their parameters and characteristics. For diagnostic use the integral and local variants of methods in which the analysis of fluctuations in money laundering as a whole and its individual parts.

It should be noted that the operation of the CCD is accompanied by forced and resonant vibrations of its individual units, components and parts. That is why most of the faults that occur in engines when they are operation, or directly caused by vibrations or influence them.

Application of vibration and vibro-acoustic diagnostics of GTE provides solutions to the following groups of tasks:

  • during the operational phase, during bench testing and fine-tuning of the engine provides an assessment of the technical condition of the engine and its components, as well as troubleshooting at the beginning of their development;

  • at all stages of production and operation are being identified vibration condition of the engine and its components (assessment of the set of parameters that characterize the vibration of the engine and its individual units, units and parts at a certain set of conditions and operating conditions) to prevent the problems that are caused by vibrations.

In the latter case provides an assessment and prediction of dynamic load design, the definition of dangerous actions in the structural elements and their dangerous vibrations, assessment of factors that affect fluctuations, determination and prediction of the stability of the structural elements of the engine to the excited oscillations, detection of vibration processes and the identification of the motor as a dynamic system .

The effectiveness of these diagnostic methods is confirmed by their wide application to determine a wide range of faults. This is the unbalance of rotating parts, the detection of defects in support of rotors, gears, pumps, damage to the blades of impellers, wear of structural elements, increased pressure pulsations in the flowing part, vibration combustion. Under operating conditions, rotor vibration monitoring provides a higher efficiency of fault detection (approximately 7 times) compared to methods that are based on monitoring parameters and physico-mechanical characteristics of the engine.

Analysis of the features of generation of vibration and acoustic noise in GTE, as well as analysis of the information properties of their spectra showed that the vibration (vibration-velocity) and noise spectra are widely used to determine the state of GTE and to diagnose many defects and damages. However, there are many factors that cause significant difficulties in the allocation and interpretation of informative diagnostic features based on the analysis of vibration and noise spectra. The main among them is the low sensitivity of the spectra, the generalized energy characteristic of the vibration of the gas turbine engine, to the initiation and development of fracture-like damages in engine components. The incipient and initial damage leads to the appearance in the measured vibrational and vibro-acoustic signals, which are composed with a small vibrational energy, which are practically not distinguished by traditional methods of spectral analysis.

To date, research into the problem of diagnosing fracture-like damage to GTE blades is mainly concentrated in the direction of determining the effect of fatigue crack type damage on free and resonant oscillations of the blade under steady-state harmonic excitation. In real conditions, aircraft engines are operated on non-stationary modes (launch, rapid climb, decrease, etc.). Non-stationary modes of engine operation are more informative from the viewpoint of the presence in them of maximum changes in the vibration and noise spectra, and the mode of changing the rotor speed during acceleration or motor coasting causes the vibrational excitation of the blades by higher harmonics of the rotor speed.

It should be noted that the use of non-stationary regimes was reflected in the development of a new method for parametric diagnostics of gas turbine engines. Such regimes should be used to diagnose blade damage. However, in order to diagnose the damage, it is necessary to have an adequate structural and functional model of the engine that must reflect its states with crack-like damage in the impeller blade and without such damage, and also ensure the formation of vibro-acoustic channels connecting the source of vibrational excitation in these modes with reaction The corresponding impeller and the engine as a whole.

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