RU2685438C1 - Method for determining cyclic durability of rotating part - Google Patents

Abstract

The invention relates to engine, in particular to methods for determining the resource of rotating parts. Essence: carry out calculations of the stress-strain state and cyclic durability in a typical cycle of operation of a rotating part, taking into account its design features, creating zones of stress concentration. Determine the location of the zone of stress concentration and the minimum cyclic durability in this area. Make a model sample in compliance with the geometric similarity with respect to the rotating parts and a certain diameter. The approximate value of the frequency of rotation of the model sample is determined in accordance with the parameters of the test setup. The thickness of the model sample is chosen identical to the thickness of the rotating part, while the model sample is performed taking into account the design features of the rotating part. Then the model sample is installed in the test installation and its maximum speed is specified according to a certain ratio. Using the obtained calculation results, the maximum rotational speed of the model sample is set, the model sample is tested, creating conditions like during a typical cycle of the rotating part, and the number of test cycles is recorded until the crack appears in the model sample. Technical result: the ability to determine the cyclic durability of rotating parts with regard to their various design features, creating zones of stress concentration. 7 il.

Description

The invention relates to engine, in particular to methods for determining the resource of rotating parts.

There is a class of parts, for example, disks of turbomachines, the destruction of which in the course of work can lead to dangerous consequences associated with damage to the product, such as an engine, and creating a threat to people's lives. The main damaging factor for these parts is low-cycle fatigue under the influence of re-static load, which manifests itself in areas of high stress concentration (holes, fillets, grooves, etc.) in the form of cracks. In order to prevent dangerous consequences, prior to putting the product into operation, cyclic tests of full-scale parts are carried out as part of a turbomachine or at boosters, the results of which determine their cyclic durability. The main problems in conducting cyclic tests are their long duration and complexity, as well as providing the necessary equipment that requires high energy costs. Therefore, an urgent task is to simplify the object of testing, reduce the time of testing while maintaining the necessary parameters and resources.

A known method of cyclic testing of castle joints of the rotor element of a turbomachine (US 7204153, 2007), where for the tests use cut out protrusions of the protrusion of the disk and field working blades. Tests carried out on a testing machine, thereby achieving a reduction in test time. The disadvantage of this method is the lack of cyclic testing in other areas of stress concentration of the disk.

A technical solution is known (RU 155239, 2015), which describes a method for studying contact stresses in locking joints, in which they reproduce the stress-strain state of locking joints of ceramic blades in accordance with the actual operating conditions of the engine on a model sample. The technical solution allows to reduce the consumption of materials and the time of testing through the use of small parts in the form of a model sample. The disadvantage is the ability to study only the contact areas of the interlocking connection of ceramic blades.

A known method of experimental research of biaxial stress-strain state (US 8601881, 2013), where they form a model rotating disk with an outer diameter of from 50 to 100 mm and a thickness of from 6 to 10 mm. The test of a model rotating disk is performed on the acceleration stand using its mounting through the adapter to the drive spindle. Due to the use of a high-speed drive with a maximum speed in a model rotating disk, it is possible to reproduce the stress level realized in full-size disks. However, when implementing this technical solution, it is impossible to reliably determine the cyclic durability of the disk due to the absence of stress concentration zones in the model disk.

The closest to the proposed technical solution is the method of determining the durability of the disks of turbomachines (RU 2511214, 2014). In this method, contact stresses are created in the mounting hole of the disk rim element, the disk rim element is loaded with repetitive cyclic tensile forces, reproduces the origin and trajectory of crack growth in the critical areas of the turbomachine disks, fixes the number of loading cycles before the disk rim breaks. This solution allows to reduce the time of the test cycle. The disadvantage of this method is the lack of testing critical areas located in the elements of the hub and blade disc.

The technical problem solved by the claimed invention is to eliminate the above disadvantage and to expand the arsenal of technical means, namely to create a method for determining the cyclic durability of a rotating part.

The technical result provided by the invention is the realization of its purpose, i.e. in creating a method for determining the cyclic durability of a rotating part, taking into account its design features, creating zones of stress concentration.

The claimed technical result is achieved due to the fact that the method of determining the cyclic durability of a rotating part carries out calculations of the stress-strain state and cyclic durability during a typical working cycle of a rotating part, taking into account its design features that create stress concentration zones, determine the location of the stress concentration zone and the minimum cyclic durability in this area, make a model sample in compliance with the geometric similarity with respect to the rotary part, the model sample diameter is determined from the relationship:

Where

D _Yes - diameter of the model sample, mm;

D _Д1 - diameter of the rotating part, mm;

ω _D1 - the maximum rotational speed of the rotating part, rpm;

ω _D2 - the estimated value of the rotational speed of the model sample, rpm,

moreover, ω _{Da is} determined in accordance with the parameters of the test facility, and the thickness of the model sample is chosen identical to the thickness of the rotating part, the model sample is performed taking into account the design features of the rotating part, then the model sample is installed in the test installation, the maximum rotation frequency ω _{D2_MAX} model sample is _determined from the relationship:

Where

N _{D2_MIN} - the minimum calculated cyclic durability of a model sample during a test work cycle, cycle;

N _{D1_MIN} - the minimum calculated cyclic durability of a rotating part with a typical work cycle, cycle,

using the obtained calculation results, set the maximum rotational speed of the model sample, test the model sample, creating conditions as in the typical cycle of the rotating part, and record the number of test cycles until the crack appears in the model sample.

These essential features provide a solution to the technical problem with the achievement of the stated technical result, since only the set of essential features that characterize the invention, allows you to create a method for determining the cyclic durability of the rotating part, taking into account its design features that create stress concentration zones.

The present invention is explained in detail describing a method for determining the cyclic durability of a rotating part with reference to the illustrations shown in FIG. 1-7, where

in fig. 1 shows a rotating part with design features in the form of holes;

in fig. 2 - a rotating part with a structural feature in the form of fillets;

in fig. 3 - rotating part with design features in the form of grooves;

in fig. 4 - model sample with design features in the form of holes;

in fig. 5 - model sample with a construction feature in the form of fillets;

in fig. 6 - model sample with design features in the form of grooves;

in fig. 7 is a graph for determining the maximum frequency of rotation of a model sample with a structural feature in the form of a fillet.

FIG. 1-6, the following notation is used:

1 - hole in the rotating part;

2 - fillet in a rotating part;

3 - groove in the rotating part;

4 - hole in the model sample;

5 - a fillet in a model sample;

6 - groove in the model sample;

7 - jumper between the slots 3 in the rotating part;

8 - jumper between the grooves 6 in the model sample;

9 - mounting area in the test setup;

10 - model wall;

11 - model flange.

The method for determining the cyclic durability of a rotating part is implemented as follows. Calculate the stress-strain state (VAT) and cyclic durability in a typical cycle of the rotating parts, taking into account its design features, creating zones of stress concentration. The design features of the rotating part can be made in the form of holes 1, fillets 2 and grooves 3 (see Fig. 1-3). Calculations of VAT and cyclic durability are carried out according to the method known from the prior art (Gas turbine engines, A. A. Inozemtsev, V. L. Sandratsky. Aviadvigatel OJSC, Perm, 2006, pp. 1013-1014). Moreover, the cyclic durability before the appearance of cracks is determined by empirical dependence:

Where

f - empirical dependence;

N _Д1 - the calculated cyclic durability of the rotating part, the cycle;

T- part temperature, ° С;

Δε is the range of deformations in the part,%;

σ _m - the average stress of the part, MPa.

Next, determine the location of the zone of stress concentration and the minimum cyclic durability N _{D1_MIN} in this area. As a rule, zones with a minimum cyclic durability are located in the holes 1, the slots 2 and the fillets 3 of the rotating part, creating a stress concentration. After that, a model sample of a rotating part is made with respect to its geometric similarity. The model sample is made from the same material as the rotating part. The diameter of the model sample is determined from the relationship:

Where

D _D2 - diameter of the model sample, mm;

D _Д1 - diameter of the rotating part, mm;

ω _D1 - the maximum rotational speed of the rotating part, rpm;

ω _D2 - approximate value of the frequency of rotation of the model sample, rpm.

The approximate value of the rotation frequency ω _{D2 of the} model sample is determined in accordance with the parameters of the test setup, and the thickness s of the model sample is chosen identical to the thickness of the rotating part. Moreover, the model sample is performed taking into account the design features (holes, fillets, grooves) of the rotating part, creating zones of stress concentration.

The model sample, made with consideration of the design features of the rotating part, is installed in the test installation. The model sample has a mounting zone 9 in the test facility. To secure the sample can be applied landing with a tightness, a threaded connection or another method of fastening. Typical model samples are shown in FIG. 4-6.

Conduct a series of calculations of the minimum cyclic durability N _{D2_MIN} in the critical zone of the model sample at different values of rotation frequency in the test loading cycle.

Next, specify the maximum frequency of rotation ω _{D2_MAX} model sample from the relationship:

Using the obtained calculation results, the maximum rotational speed for the model sample is set on the test set. During the test, create the conditions of rotation of the model sample are the same as in the typical cycle of the rotating parts. Then fix the number of test cycles until the appearance of cracks in the model sample.

The implementation of design features (holes, fillets, grooves) of a rotating part on a model sample is carried out, depending on their type, as follows.

The design feature of the rotating part in the form of holes 1 is performed on a model sample in the form of holes 4 with the diameter d of holes 1 being preserved (Fig. 1, 4). The location of the holes 4 is selected from the relationship:

Where

D _K - diameter of the flange 11 of the model sample, mm;

R _K - radius of transition from flange 11 to wall 10 of model sample, mm;

D _o2 - diameter of the hole 4, mm;

D _D2 - diameter of the model sample, mm.

On the model sample, the value of the radius R _{K of the} transition is chosen so that the voltages acting as a hole in the stress concentrator are higher than the voltages in the zone of this transition radius.

The number of holes 4 in the model sample is selected from the relationship:

2≤n ₂ ≤n ₁ ,

Where

n ₁ - the number of holes 1 in the rotating part;

n ₂ - the number of holes 4 in the model sample.

The design feature of the rotating part in the form of a fillet 2 is performed on a model sample in the form of a fillet 5 while maintaining the radius of the fillet 2 and is placed at the transition point from the flange 11 to the wall 10 of the model sample (Figs. 2, 5).

The design feature of the rotating part in the form of grooves 3 is performed on a model sample in the form of grooves 6 with preservation of their configuration (Fig. 3, 6).

The number of grooves 6 in the model sample, which coincides with the number of jumpers 8 between the slots, is selected from the relationship:

2≤n ₄ ≤n ₃ ,

Where

n ₃ - the number of jumpers 7 between the grooves 3 in the rotating part;

n ₄ - the number of jumpers 8 between the slots 6 in the model sample.

In this case, the following condition must be met:

s ≤s _{n3 n4}

Where

s _P3 - the thickness of the jumper 7 between the grooves of the rotating parts, mm;

s _p4 - the thickness of the jumper 8 between the grooves of the model sample, mm.

If the groove is designed for fastening blades, then the model sample is tested together with the blades or their simulators.

As an example of the implementation of the method, a model sample was made with a design feature in the form of fillets with a radius of 1 mm (Fig. 5). The diameter of the model sample in accordance with the formula was:

Where

diameter D _{Д1 of the} rotating part is 600 mm;

the maximum rotational speed ω _{D1 of the} rotating part is 15,000 rpm;

the approximate value of the rotational speed ω _{D2 of the} model sample is 90000 rpm and is determined in accordance with the existing technical capabilities of the test facility.

The maximum rotation frequency ω _{D2_MAX was} determined by the intersection of the dependence of the minimum calculated cyclic durability N _{D2 - MIN} min of a model sample with the minimum calculated cyclic durability N _{D1_MIN of the} rotating part (Fig. 7).

The proposed method provides the ability to determine the cyclic durability of rotating parts, taking into account their various design features, creating stress concentration zones, including those located in the hub and blade elements of rotating parts made in the form of discs, reduces energy consumption, the duration of the test by reducing the moment of inertia of the object tests, as well as material consumption.

Claims (13)

The method for determining the cyclic durability of a rotating part, characterized by the fact that calculations of the stress-strain state and cyclic durability are carried out with a typical cycle of operation of the rotating part, taking into account its design features that create stress concentration zones, determine the location of the stress concentration zone and the minimum cyclic durability in this zone, make a model sample in compliance with the geometric similarity with respect to the rotating part, the diameter of the model sample is determined from the ratio:

Where D _D2 - diameter of the model sample, mm; D _Д1 - diameter of the rotating part, mm; ω _D1 - the maximum rotational speed of the rotating part, rpm; ω _D2 - the estimated value of the rotational speed of the model sample, rpm, moreover, ω _{D2 is} determined in accordance with the parameters of the test facility, and the thickness of the model sample is chosen identical to the thickness of the rotating part, the model sample is performed taking into account the design features of the rotating part, then the model sample is installed in the test installation, the maximum rotation frequency ω _{D2_max} model sample is _determined from the relationship:

Where N _{D2_MIN} ^{_ the} minimum calculated cyclic durability of the model sample during a test work cycle, cycle; N _{D1_MIN} - the minimum calculated cyclic durability of a rotating part with a typical work cycle, cycle, using the obtained calculation results, set the maximum rotational speed of the model sample, test the model sample, creating conditions as in the typical cycle of the rotating part, and record the number of test cycles until the crack appears in the model sample.

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