CN108763839B - A design method for the simulation part of centrifugal impeller boss crack propagation characteristics - Google Patents

Abstract

The invention relates to a design method for a simulated part of a centrifugal impeller boss crack propagation feature. The geometric model of the centrifugal impeller is obtained, the transition fillet radius of the boss structure and the radial length of the boss are measured, and the working conditions and working conditions of the centrifugal impeller are obtained. The material performance parameters under the conditions; the finite element analysis model of the centrifugal impeller is established, and the maximum stress point at the boss of the centrifugal impeller is calculated and obtained; the rectangular plate specimen is used as the basic shape, and the symmetrical positions on both sides of the plate have a boss structure, and the boss and rectangular The transition radius of the plate and the radial length of the boss are consistent with the actual structure. By adjusting the length of the test piece, the maximum stress in the tensile direction of the simulated part near the boss is consistent with the actual structure, and the stress gradient is the same; check The relationship between the stress intensity factor of the simulated piece and the thickness of the test piece is used to determine the thickness of the test piece. The obtained simulated piece can simulate the stress-strain field of the centrifugal impeller boss structure and can be used for crack propagation tests.

Description

A design method for the simulation part of centrifugal impeller boss crack propagation characteristics

technical field

The invention relates to a design method for an aeroengine centrifugal impeller boss crack propagation feature simulating part, which is a crack propagation feature simulating part design method which can consider the centrifugal impeller structure stress concentration and stress gradient, and belongs to the technical field of aerospace engines.

Background technique

The complex structural features of centrifugal impellers in aero-engines often cause stress concentration in local areas, resulting in non-uniform distribution of loads at the far end of the crack along the crack propagation path. Because the crack growth test based on standard parts cannot reflect the stress concentration in the local area, the discrete crack growth step is generally used, and the load is approximated as a uniform load on each crack growth increment. When the crack growth increment decreases To a certain extent, a relatively close crack propagation law can be obtained. However, since the local stress concentration is more obvious (the local stress gradient is larger), the deviation of this approximation method is larger. Therefore, it is necessary to design a characteristic structural simulation part and carry out a crack propagation test to simulate the local stress concentration in a laboratory environment, and obtain Corresponding crack propagation law.

The existing patent CN201710255317.3 "Test method for a blade structure simulation part" designed a fatigue life simulation part for the blade structure. The design principle of the simulation part is mainly that the equivalent stress of multiple dangerous points is similar to the actual structure, and the simulation part is not designed. The stress distribution in the adjacent area of the hazardous point is considered to be equivalent.

Existing literature "Yang Xingyu, Dong Liwei, Geng Zhongxing, et al. Design and test of a low-cycle fatigue simulation part of a compressor disc tongue and groove [J]. Aerodynamics Journal, 2008, 23(10): 1829-1834" according to the compressor The low-cycle fatigue life test of the tongue-and-groove structure design ensures that the maximum tensile force, stress gradient, and strain gradient of the simulated part are relatively consistent with the actual structure, but the design and evaluation of crack propagation-related characteristics have not been carried out, and the test piece can be applied to low-cycle Fatigue life test, but not fatigue crack growth test.

SUMMARY OF THE INVENTION

The technical solution of the present invention is to overcome the deficiencies of the prior art, and to provide a design method for the simulation of the crack propagation characteristics of the centrifugal impeller boss, which can fully reflect the stress concentration and stress gradient of the centrifugal impeller boss.

The technical solution of the present invention is: a design method for a simulated part of the crack propagation characteristic of a boss of a centrifugal impeller. Combined with the static analysis results of the centrifugal impeller, a simulation part of the crack propagation that can reflect the characteristic structure is designed, and the simulation of the real structure under laboratory conditions is realized. Crack growth behavior. The implementation steps are as follows:

The first step is to obtain the geometric model of the centrifugal impeller, and measure the transition fillet radius of the centrifugal impeller boss and the radial length of the centrifugal impeller boss. The geometric model refers to the three-dimensional geometric model of the centrifugal impeller designed and completed according to the actual engineering requirements with the aid of computer-aided design software; the transition fillet radius refers to the radius of the transition fillet between the centrifugal impeller boss and the impeller; the boss The radial length refers to the radial length of the centrifugal impeller boss.

The second step is to obtain the working conditions of the centrifugal impeller and the material performance parameters under the working conditions. The working conditions include the working temperature field of the centrifugal impeller and the working speed of the centrifugal impeller; the material performance parameters include the density of the centrifugal impeller material; the elastic modulus, Poisson's ratio, plastic constitutive parameters and expansion at the working temperature Coefficient, fracture toughness value. The working temperature field of the centrifugal impeller is obtained through heat transfer analysis or actual measurement; the working speed of the centrifugal impeller is obtained through the statistics of the external engine operating data; the material performance parameters are obtained through material performance tests or material data manuals. For the material performance parameters that change with temperature, obtain the corresponding parameter values at 100°C, such as the corresponding parameter values at 100°C, 200°C, and 300°C, the temperature range to be taken needs to be the maximum value in the working temperature field of the centrifugal impeller and The minimum value is included.

In the third step, according to the geometric model of the first step, the working conditions of the second step and the material performance parameters under the working conditions, a finite element analysis model of the centrifugal impeller is established, and the stress of the centrifugal impeller boss under the working conditions is calculated and obtained. strain data; the

The stress data includes the radial stress value and radial stress gradient at the point of maximum stress in the tensile direction of the centrifugal impeller boss.

In the fourth step, based on the stress-strain data of the centrifugal impeller boss under the working conditions obtained from the static analysis in the third step, the rectangular plate specimen is used as the basic shape, and the uniaxial tensile loading along the length of the simulated part is Load form, design a simulation of the crack propagation feature of the centrifugal impeller boss, define the stretched direction of the simulation as the length direction, and the radial direction of the boss as the width direction. First, three times the distance of the circumferential stress distribution obtained in the third step is used as the initial width of the simulated part, and half of the width is used as the initial thickness. The length of the simulated part can be freely given according to the working stroke of the testing machine and the design of the clamping end , to establish the finite element analysis model of the centrifugal impeller boss simulation. By adjusting the radius and width of the transition fillet of the simulated part, the radial length of the boss, and the method of changing the magnitude of the tensile load, the finite element static analysis model of the simulated part is repeatedly subjected to finite element static analysis, so that the simulation The maximum stress value of the piece boss along the tensile loading direction is equal to the maximum radial stress value obtained in the third step; at the same time, the relative error between the maximum stress value in the tensile loading direction on the simulated piece and the obtained third step is within Within ±5%; further, further, make the stress distribution along the width of the simulated piece consistent with the radial stress distribution obtained in the third step. After meeting the above requirements, the size parameters of the center hole simulation part and the load size of the uniaxial tension can be preliminarily determined.

The fifth step is to determine the thickness of the simulated piece by calculating the stress intensity factor of the simulated piece. The stress intensity factor is a parameter describing the strength of the stress field at the crack tip of the cracked structure, and its numerical value is a function of the applied load, the crack length and the structure geometry. The value of stress intensity factor can be obtained by finite element numerical calculation or empirical formula of stress intensity factor. When the stress intensity factor value is greater than or equal to the fracture toughness value of the material, it is considered that the cracked structure will be unstable and fracture. Based on the size of the simulated part of the centrifugal impeller boss determined in the fourth step and the size of the uniaxial tensile load, the critical crack length corresponding to the stress intensity factor reaching the fracture toughness value is obtained; the principle of determining the thickness is that the thickness of the simulated part should be within More than half of the critical crack length to fully cover the stable propagation process of the crack in the thickness direction; at the same time, after the thickness is determined, the external load required for the simulated part should be within the loading capacity of the testing machine used. So far, the design work of the simulation of the crack propagation characteristic of the central hole of the centrifugal impeller is completed. Place

The design simulator can simulate the stress field of the centrifugal impeller center hole structure and can be used to carry out crack propagation tests.

In the fourth step, since the size of the simulated part is not finalized and the cross-sectional area changes with the design process, it is recommended to set the load boundary condition in the form of stress when performing finite element analysis. When the size of the simulated part is completely determined, the load force required for the test is converted according to the cross-sectional area of the test. For example, the uniaxial tensile external load stress determined in the fourth step is σ, the unit is MPa; the final section area of the examination section is A, the unit is mm ² , then the load force F applied by the testing machine on the simulated part can be The calculation is as follows:

F=σA

The unit of F is N.

In the fifth step, the form of cracks on the simulated part of the center hole needs to refer to the form of cracks actually appearing at the center hole on the centrifugal impeller. Usually the crack form of the pore structure is the crack at the corner of the hole. Referring to the situation of arc angle cracks in infinite section in the manual of stress intensity factor, the calculation formula of stress intensity factor is as follows:

M={1.13-0.09(a/c)}

+{-0.54+0.89·[0.2+(a/c)] ^-1 }(a/B) ²

+{0.5-[0.65+(a/c)] ^-1

+14(1-a/c) ²⁴ }(a/B) ⁴

Φ ² =1+1.464(a/c) ^1.65

where a is the crack depth, c is the crack length, B is the thickness of the specimen, σt is the tensile load, π is the pi, K is the stress intensity factor, the value of the dimensionless coefficient M and the position of the calculation point on the crack front Relevant, determined by querying the chart of the Stress Intensity Factor Manual;

The beneficial effects of the present invention and the prior art are as follows: the existing patent CN201710255317.3 "Test method for a blade structure simulating part" designs a fatigue life simulating part for the blade structure, and the design principle of the simulating part is mainly based on multiple dangerous points. The equivalent stress is close to the actual structure without considering the equivalent stress distribution in the adjacent area of the dangerous point. Existing literature "Yang Xingyu, Dong Liwei, Geng Zhongxing, et al. Design and test of a low-cycle fatigue simulation part of a compressor wheel disc tongue and groove [J]. Aerodynamics Journal, 2008, 23(10): 1829-1834" According to the compressor The low-cycle fatigue life test of the tongue-and-groove structure design ensures that the maximum tensile force and stress gradient of the simulated part are relatively consistent with the actual structure, but the design and evaluation of the crack propagation-related characteristics have not been carried out, and the test piece can be applied to the low-cycle fatigue life test. , and the fatigue crack growth test cannot be carried out.

According to the stress distribution state of the centrifugal impeller boss, the present invention designs a crack propagation characteristic simulation piece with a rectangular flat plate simulation piece as the basic shape, and simulates the maximum stress and stress distribution state of the actual boss structure. The determination of the geometric size of the simulated part is completed by adjusting the geometric size and the external load of the simulated part. By calculating the stress intensity factor of the simulated part, the critical crack length is determined, so that the simulated part can be used for low-cycle fatigue crack growth experiments.

Description of drawings

Fig. 1 is the flow chart of the design method of centrifugal impeller boss crack propagation characteristic simulation part of the present invention;

Figure 2 is the geometry drawing of the simulated part, (a) top view; (b) front view; (c) left side view; L is the length of the simulated part; W is the width of the simulated part; B is the thickness of the simulated part; B1 is the diameter of the boss direction length; R is the transition fillet radius; W1 is the boss width;

Figure 3 is a finite element stress cloud diagram of an example of a simulated part;

Figure 4 is a comparison diagram of the stress distribution of an example of the simulated part and the structural stress distribution.

Detailed ways

The technical scheme of a method for designing a simulation part of a centrifugal impeller boss crack propagation feature of the present invention will be further described below with reference to the accompanying drawings.

As shown in FIG. 1 , the present invention relates to a design method for a simulation part of a centrifugal impeller boss crack propagation feature. The implementation steps are as follows: (1) Obtain the geometric model of the centrifugal impeller, measure the transition radius of the boss, the radial radius of the boss (2) Obtain the working conditions of the centrifugal impeller and the material performance parameters under the working conditions, including load, temperature, elastic modulus, yield strength, etc.; (3) Establish a finite element analysis model of the centrifugal impeller, and calculate the centrifugal impeller The maximum stress point of the boss is obtained, and the radial stress value and radial stress gradient of this point are obtained; (4) The rectangular plate specimen is used as the basic shape, and the boss simulation part is designed, so that the simulation part has a stretching direction near the boss. The maximum stress is consistent with the actual structure, and the stress gradient and equivalent strain are guaranteed to be the same; (5) Check the relationship between the stress intensity factor of the simulated piece and the thickness of the specimen, and determine the thickness of the specimen. The obtained simulated piece can simulate the center hole of the centrifugal impeller. structural stress and can be used to carry out crack propagation tests.

Considering the stress concentration and stress gradient of the centrifugal impeller structure, the design method for the simulation part of the crack propagation characteristics of the centrifugal impeller boss proposed by the present invention is shown in Figure 1.

The technical solution of the present invention is: a design method for a characteristic simulation part of crack propagation in a central hole of a centrifugal impeller, and combined with the static analysis results of the centrifugal impeller, a characteristic simulation part of crack propagation that can reflect the characteristic structure is designed.

Embodiment 1, the implementation steps of the present invention are as follows:

The first step is to obtain the geometric model of the centrifugal impeller, and measure the transition radius of the centrifugal impeller boss and the radial length of the boss. The geometric model refers to the three-dimensional geometric model of the centrifugal impeller designed and completed according to the actual engineering requirements by means of computer-aided design software; the transition fillet radius refers to the radius of the transition fillet between the boss and the impeller; the boss radial Length refers to the radial length of the centrifugal impeller boss. For example, the transition fillet radius of a centrifugal impeller boss is 20mm, and the radial length is 4mm.

The second step is to obtain the working conditions of the centrifugal impeller and the material performance parameters under the working conditions. The working conditions include the working temperature field of the centrifugal impeller and the working speed of the centrifugal impeller; the material performance parameters include the density of the centrifugal impeller material; the elastic modulus, Poisson's ratio, plastic constitutive parameters and expansion at the working temperature Coefficient, fracture toughness value. The working temperature field of the centrifugal impeller is obtained through heat transfer analysis or actual measurement; the working speed of the centrifugal impeller is obtained through the statistics of the external engine operating data; the material performance parameters are obtained through material performance tests or material data manuals. For the material performance parameters that change with temperature, obtain the corresponding parameter values at 100°C, such as the corresponding parameter values at 100°C, 200°C, and 300°C, the temperature range to be taken needs to be the maximum value in the working temperature field of the centrifugal impeller and The minimum value is included.

In the third step, according to the geometric model of the first step, the working conditions of the second step and the material performance parameters under the working conditions, a finite element analysis model of the centrifugal impeller is established, and the stress of the centrifugal impeller boss under the working conditions is calculated and obtained. Strain data; the stress data includes the radial stress value and radial stress gradient of the maximum stress point in the tensile direction of the centrifugal impeller boss. In this example, the radial stress value at the maximum point of radial stress of the boss structure calculated by static analysis is 459MPa, and the radial stress distribution along the radial direction is as follows: at 0.8mm, the stress value is 409MPa; at 1.8mm , the stress value is 359MPa, and at 4mm, the stress value is 334MPa.

In the fourth step, based on the stress data of the centrifugal impeller boss under the working conditions obtained by the static analysis in the third step, the rectangular plate specimen is used as the basic shape, and the uniaxial tensile loading along the length direction of the simulated part is used as the load. Form, the simulation of the crack propagation characteristics of the centrifugal impeller boss is designed, as shown in Figure 2. Define the stretched direction of the simulated part as the length direction, L is the length of the simulated part; the radial direction of the boss is the width direction, W is the width of the simulated part; B is the thickness of the simulated part; B1 is the radial length of the boss; R is the transition Corner radius; W1 is the boss width. First, three times the distance of the circumferential stress distribution obtained in the third step is used as the initial width of the simulated part, and half of the width is used as the initial thickness. The length of the simulated part can be freely given according to the working stroke of the testing machine and the design of the clamping end , to establish the finite element analysis model of the centrifugal impeller boss simulation. By adjusting the radius and width of the transition fillet of the simulated part, the radial length of the boss, and the method of changing the magnitude of the tensile load, the finite element static analysis model of the simulated part is repeatedly subjected to finite element static analysis, so that the simulation The maximum stress value of the piece boss along the tensile loading direction is equal to the maximum radial stress value obtained in the third step; at the same time, the relative error between the maximum stress value in the tensile loading direction on the simulated piece and the obtained third step is within Within ±5%; further, further, make the stress distribution along the width of the simulated piece consistent with the radial stress distribution obtained in the third step. After meeting the above requirements, the size parameters of the center hole simulation part and the load size of the uniaxial tension can be preliminarily determined. The size parameters of the simulation piece determined in the embodiment of the present invention are: L=100mm, W=20mm, B=8mm, B1=7.3mm, R=4mm, W1=6mm. The finite element stress cloud diagram of the simulated part is shown in Figure 3. The cloud map indicates the stress value in the x-direction of the simulated part. The stress unit on the figure is Pa. The maximum stress value appears at the assessment section of the simulated part. The maximum stress value of the structure calculated by the force analysis is consistent; the comparison chart between the stress distribution of the simulated part and the structural stress distribution is shown in Figure 4. In the chart, the abscissa represents the distance from the maximum stress point, in mm, and the ordinate represents the stress value, The unit is MPa, the hollow dot data is the actual stress value of the roulette boss structure, and the cross data is the stress value on the simulated part. It can be seen that the stress distribution of the designed simulated part is more consistent with the stress distribution of the central hole structure. The external tensile stress of the simulated part required to generate the stress and stress distribution is 346.8MPa.

The fifth step is to determine the thickness of the simulated piece by calculating the stress intensity factor of the simulated piece. The stress intensity factor is a parameter describing the strength of the stress field at the crack tip of the cracked structure, and its numerical value is a function of the applied load, the crack length and the structure geometry. The value of stress intensity factor can be obtained by finite element numerical calculation or empirical formula of stress intensity factor. When the stress intensity factor value is greater than or equal to the fracture toughness value of the material, it is considered that the cracked structure will be unstable and fracture. Based on the size of the simulated part of the centrifugal impeller boss determined in the fourth step and the size of the uniaxial tensile load, the critical crack length corresponding to the stress intensity factor reaching the fracture toughness value is obtained; the principle of determining the thickness is that the thickness of the simulated part should be within More than half of the critical crack length to fully cover the stable propagation process of the crack in the thickness direction; at the same time, after the thickness is determined, the external load required for the simulated part should be within the loading capacity of the testing machine used. So far, the design work of the simulation of the crack propagation characteristic of the central hole of the centrifugal impeller is completed. The designed simulator can simulate the stress field of the central hole structure of the centrifugal impeller, and can be used to carry out the crack propagation test.

In the fourth step, since the size of the simulated part is not finalized and the cross-sectional area changes with the design process, it is recommended to set the load boundary condition in the form of stress when performing finite element analysis. When the size of the simulated part is completely determined, the load force required for the test is converted according to the cross-sectional area of the test. For example, the uniaxial tensile external load stress determined in the fourth step is σ, the unit is MPa; the final section area of the examination section is A, the unit is mm ² , then the load force F applied by the testing machine on the simulated part can be The calculation is as follows:

F=σA

The unit of F is N.

In the fifth step, the form of cracks on the simulated part of the center hole needs to refer to the form of cracks actually appearing at the center hole on the centrifugal impeller. Usually the crack form of the pore structure is the crack at the corner of the hole. Referring to the situation of arc angle cracks in infinite section in the manual of stress intensity factor, the calculation formula of stress intensity factor is as follows:

M={1.13-0.09(a/c)}

+{-0.54+0.89·[0.2+(a/c)] ^-1 }(a/B) ²

+{0.5-[0.65+(a/c)] ^-1

+14(1-a/c) ²⁴ }(a/B) ⁴

Φ ² =1+1.464(a/c) ^1.65

where a is the crack depth, c is the crack length, B is the thickness of the specimen, σt is the tensile load, π is the pi, K is the stress intensity factor, the value of the dimensionless coefficient M and the position of the calculation point on the crack front Relevant, determined by consulting the Stress Intensity Factors Handbook chart.

The critical crack length of the example simulated part is obtained as 3mm. The principle of determining the thickness is that the thickness of the simulated part should be more than half of the critical crack length to fully cover the stable propagation process of the crack in the thickness direction; at the same time, after the thickness is determined, the external load required by the simulated part should be within the loading capacity of the testing machine used. , determine the thickness of the simulated piece B=6mm; the required external load is 54.4kN.

The above embodiments are provided for the purpose of describing the present invention only, and are not intended to limit the scope of the present invention. The scope of the invention is defined by the appended claims. Various equivalent replacements and modifications made without departing from the spirit and principle of the present invention should be included within the scope of the present invention.

Claims (5)

1. a kind of centrifugal impeller boss crack propagation characteristic simulation part design method, which comprises the following steps:

(1) geometrical model for obtaining centrifugal impeller measures the radius of centrifugal impeller boss structure, boss to length；

(2) working condition and the material property parameter under working condition for obtaining centrifugal impeller；The working condition include from The operating temperature field of lobus cardiacus wheel, centrifugal impeller working speed；The material property parameter includes the density of centrifugal impeller material； Elasticity modulus, Poisson's ratio, Plastic Constitutive parameter and the coefficient of expansion at the working temperature, fracture toughness value；

(3) the material property ginseng according to the geometrical model of step (1) and the working condition of step (2) and under working condition Number establishes centrifugal impeller finite element analysis model, calculates the ess-strain number for obtaining centrifugal impeller boss under working condition According to；The stress-strain data includes centrifugal impeller lug boss position draw direction maximum stress point i.e. maximum radial stress value, and Using centrifugal impeller lug boss position draw direction maximum stress point as starting point, the radial direction along centrifugal impeller boss radius augment direction is answered Power distribution；

(4) stress-strain data under the centrifugal impeller boss working condition obtained based on step (3) analysis, with rectangular plate Test specimen is that basic configuration is convenient for crackle observation, to be loaded as loading along being uniaxially stretched for simulating piece length direction, if Centrifugal impeller boss crack propagation characteristic simulation part is counted, the Finite Element Static Analysis model of the simulating piece is established, makes simulating piece Centrifugal impeller boss along tensile loads direction stress value be equal to step (3) in obtain maximum radial stress value；Further , it is consistent the stress distribution situation along the simulating piece width with the radial stress distribution obtained in step (3)；To The determination for the magnitude of load that the dimensional parameters and simulating piece for completing the simulating piece are uniaxially stretched；

(5) thickness for determining the simulating piece, size based on the simulating piece determined in step (4) and is uniaxially stretched Magnitude of load is acquired when the stress intensity factor of the simulating piece reaches fracture toughness value pair by stress intensity factor formula The critical crack length answered is that it is convex to complete the centrifugal impeller according to the thickness for determining simulating piece with the critical crack length The design work of platform crack propagation characteristic simulation part；

In the step (4), the Finite Element Static Analysis model of the simulating piece is established are as follows: be based on the simulating piece Tensile side To for length direction, the radial direction of the centrifugal impeller boss of simulating piece is width direction, with the diameter of the centrifugal impeller boss of simulating piece It is initial radial length to length, with the radius of practical structures for initial radius of corner, at least to be obtained in step (3) The three times of the distance of the radial stress distribution taken are as simulating piece original width, using the half of simulating piece original width as initially Thickness establishes the finite element analysis model of centrifugal impeller boss crack propagation characteristic simulation part, by adjusting the transition of simulating piece Radius of corner, width, the radical length of boss, the change big submethod of uniaxial tensile load, repeatedly to the limited of the simulating piece First static analysis model carries out Finite Element Static Analysis, makes the simulating piece boss along the maximum stress value etc. in tensile loads direction The maximum radial stress value obtained in step (3).

2. a kind of centrifugal impeller boss crack propagation characteristic simulation part design method according to claim 1, feature exist In: in the step (4), the error range of the radial stress distribution is within ± 5%.

3. a kind of centrifugal impeller boss crack propagation characteristic simulation part design method according to claim 1, feature exist In: in the step (3), if radial stress distribution is obtained by measuring the radial direction done in radial line to stress value.

4. a kind of centrifugal impeller boss crack propagation characteristic simulation part design method according to claim 1, feature exist In: in the step (5), stress intensity factor calculation formula is as follows:

M={ 1.13-0.09 (a/c) }+{ -0.54+0.89 [0.2+ (a/c)]^-1}(a/B)²+{0.5-[0.65+(a/c)]^-1+ 14(1-a/c)²⁴}(a/B)⁴

Φ²=1+1.464 (a/c)^1.65

Wherein a is crack depth, and c is crack length, and B is specimen thickness, and σ t is tensile load, and π is pi, and K is that stress is strong The factor is spent, the value of dimensionless factor M is related with position of the point on crack front is calculated, by inquiring stress intensity factor hand Volume chart determines.

5. a kind of centrifugal impeller boss crack propagation characteristic simulation part design method according to claim 1, feature exist In: in the step (5), determine that the thickness principle of simulating piece is: simulating piece thickness need in more than half of critical crack length, Sufficiently to cover crackle in the stabilization expansion process of simulating piece thickness direction.