CN115307855B - Rotor blade high-cycle fatigue test method and device considering centrifugal force effect - Google Patents
Rotor blade high-cycle fatigue test method and device considering centrifugal force effect Download PDFInfo
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- CN115307855B CN115307855B CN202210860106.3A CN202210860106A CN115307855B CN 115307855 B CN115307855 B CN 115307855B CN 202210860106 A CN202210860106 A CN 202210860106A CN 115307855 B CN115307855 B CN 115307855B
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- G01M7/00—Vibration-testing of structures; Shock-testing of structures
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Abstract
The invention discloses a rotor blade high-cycle fatigue test method and a test device considering centrifugal force effect, wherein the device comprises a classical vibration module, a blade clamping module and an electromagnet control module. The test device has the advantages of optimized structure, low test cost, easy control of the process and consideration of the centrifugal force effect, so that the stress state of the rotor blade in the high-cycle vibration fatigue test is closer to the actual service environment, and compared with the test result obtained by the conventional test means, the test result is more accurate.
Description
Technical Field
The invention relates to the technical field of aero-engine rotor blades, in particular to a rotor blade high-cycle fatigue test method and device considering centrifugal force effect.
Background
In addition to being subjected to centrifugal forces during service, engine rotor blades may vibrate due to some uncertainty factors (e.g., flow field non-uniformity). When the rotating speed is constant, the stress value generated by the centrifugal force at each point in the blade is basically unchanged with time, and can be simplified into constant stress; the stress generated by vibration at each point of the blade changes periodically along with time, so that the symmetrical cyclic stress (namely the stress ratio is-1) can be simplified. The two forms of stress are combined at the same point of the blade, and the resulting combined stress can be regarded as an asymmetric cyclic stress (i.e. a stress ratio greater than 1). Such composite stresses are more prone to fatigue cracking within the blade, which in turn can lead to a serious series of consequences such as blade breakage. Therefore, rotor blades are one of the most critical components in engine construction, and their reliability directly constrains the engine's requirements for high thrust to weight ratio and high applicability.
Journal article of air force engineering university Tang Ling et al, "analysis and test of a type of engine fan blade composite fatigue test loading system" (Tang Ling, shang Bailin, gao Xingwei, chen Pengfei, yin Zhipeng. Analysis and test of a type of engine fan blade composite fatigue test loading system [ J ]. Mechanical strength, 2018,40 (01): 61-67) discloses an engine fan blade composite fatigue test loading system. The method comprises the steps of fixing a blade on an excitation table, and simulating high-cycle fatigue stress by using vibration of the excitation table; and the root of the blade is connected by a steel cable, and the low cycle fatigue stress caused by centrifugal load is simulated by the tensile force of the steel cable. The scheme has the following defects: the tension of the wire rope acts only on the root of the blade, i.e.: the low cycle fatigue stress is applied only to the root of the blade, and the vibrating body, the blade body, is also only subjected to high cycle fatigue stress. The invention patent application of Beijing strength environment institute Chen Liwei et al, namely an aero-engine blade vibration fatigue test method based on an electric vibration table (China, publication No. CN104748928A, publication date 2015.07.01) discloses an aero-engine blade vibration fatigue test method based on an electric vibration table. The vibration stress level at the maximum stress point of the blade is monitored by calibrating the maximum vibration stress response point and selecting an auxiliary monitoring point. The defects are that: centrifugal loads to which the rotor blades are subjected are not considered.
In order to improve the reliability of the rotor blade of the engine in actual working, a high-cycle fatigue test needs to be carried out before the blade is in service, the fatigue limit of the rotor blade is measured, and the bearing capacity of the rotor blade in actual working is predicted. However, in the high-cycle fatigue test, other types of loads are difficult to equivalently replace centrifugal force, and the most direct and effective scheme is to enable the blades to rotate on the vibration table at a high speed so as to realize the coupling of the vibration of the blades and the centrifugal force. However, the scheme is different from the actual test run, the test cost is high, and the real-time monitoring of the centrifugal force in the test process is a great difficulty.
Accordingly, there is a need in the art for a rotor blade high cycle fatigue test method and apparatus that addresses the above issues, taking into account the effects of centrifugal forces. Therefore, a rotor blade high-cycle fatigue test device and a test method considering the centrifugal force effect are designed to solve the problems.
Disclosure of Invention
The invention aims to solve the defects that in the prior art, stress consideration is incomplete, centrifugal load borne by a rotor blade is not considered, and the result of the vibration fatigue test of the rotor blade is not accurate enough, and provides a rotor blade high-cycle fatigue test device and a test method considering the centrifugal force effect.
In order to achieve the above purpose, the present invention adopts the following technical scheme:
a rotor blade high-cycle fatigue test method considering centrifugal force effect comprises the following steps:
the first step: determining the position of a rotor blade dangerous point, establishing a rotor blade three-dimensional model by using three-dimensional software, carrying out modal analysis on the rotor blade model by using finite element software, and taking the centrifugal load effect of the rotor blade into consideration to obtain the vibration mode of the rotor blade and the position of the rotor blade dangerous point, and marking the vibration mode and the position as a point P;
and a second step of: according to the geometric shape of the rotor blade, a centrifugal force calculation formula is adopted to calculate the centrifugal force of the point P at the rotating speed, wherein the centrifugal force calculation formula is as follows:
wherein ρ is the density of the blade material, ω is the rotational angular velocity of the rotor, zk represents the distance from the tip to the rotation axis, zi represents the distance from the point P to the rotation axis, Z represents the projection of the distance from the point P to the rotation axis in the direction of the blade height, and a (Z) represents the sectional area of the blade where the point P is located;
and a third step of: establishing a three-dimensional assembly model of a rotor blade, a blade tip resin chuck and a spherical armature, carrying out modal analysis on the three-dimensional assembly model by finite element analysis software, giving an initial value of blade tip cutting length L, taking centrifugal load action (rotating speed is n) of the rotor blade into consideration, obtaining a vibration mode of the three-dimensional assembly model and a maximum alternating stress position under first-order resonance, marking as a point P ', taking the blade tip cutting length L as a design variable, taking the position of the point P and the vibration mode as targets, establishing a multi-target optimization program, giving the initial value of the blade tip cutting length L again when the position of the point P' is not similar to that of the point P and the vibration modes corresponding to the two points are not equal, calculating to obtain the vibration mode of the three-dimensional assembly model and the position P 'of the maximum alternating stress point under first-order resonance, and obtaining the output blade tip cutting length L as the blade tip cutting length when the position of the point P' is similar to that of the point P and the vibration mode corresponding to the two points is equal;
fourth step: manufacturing a test piece, namely cutting off a material with the length L at the tip of a rotor blade according to the tip cutting length L, forming a tip resin chuck through a casting process, immersing the tip of the rotor blade into molten epoxy resin in the casting process, cooling, fixing and forming, and bonding one side of the tip resin chuck with the rotor blade to obtain the test piece;
fifth step: the method comprises the steps of clamping a test piece, setting a magnetic field, fixing the test piece on a classical vibration module by using a blade clamping module, and setting the magnetic field of the test piece by using an electromagnet control module;
sixth step: and (3) current calibration and vibration setting, switching on a power supply, generating a magnetic field through an electromagnet control module, wherein the attractive force generated by the magnetic field is equal to the value of the centrifugal force obtained in the second step, calibrating the current value at the moment, starting a classical vibration module to perform vibration setting, testing a test piece, and measuring the high-cycle fatigue limit of the rotor blade.
Further, the formula integration (1) is solved by adopting a numerical integration method, the blade is divided into n sections, the sections from the blade tip to the blade root are respectively provided with 0,1,2, … … and n, the total number of sections is n+1, the first section, namely the blade section between the 0 th section and the 1 st section, and the centrifugal force of the blade mass of the section along the blade height direction is as follows:
ΔF 1 ＝ρω 2 A m1 Z m1 Δz 1 (2)
wherein A is m1 Represents the average cross-sectional area of the first segment of blade, Z m1 Representing the average coordinates in the direction of the leaf height, ΔZ 1 Representing the absolute height of the first segment of blades;
ΔZ 1 ＝Z 0 -Z 1 (5)
in the above, Z 0 ，Z 1 The coordinates of the 0 th section and the 1 st section along the height direction of the leaf are respectively A 0 ，A 1 Cross-sectional areas of section 0 and section 1, respectively;
similarly, ΔF is obtained 2 ，ΔF 3 ，……，ΔF n The section where the set point P is located is the i-th section, the centrifugal force to which the point P is subjected is:
F i separation ＝ΔF 1 +ΔF 2 +…+ΔF i (6)。
Further, in the fifth step, the test piece clamping is to fix the tenon of the rotor blade of the test piece in the blade clamp of the blade clamping module by using a screw, and the method for setting the magnetic field of the test piece comprises the following steps:
step 1, pushing a spherical armature of an electromagnet control module into a groove of a blade tip resin chuck, and fixing the spherical armature by using a first positioning screw;
step 2, winding a coil on an annular iron core of the electromagnet control module, aligning a groove of the annular iron core with a boss of an iron core clamp of the electromagnet control module, pushing in the groove, and fixing the annular iron core on the iron core clamp by using a second positioning screw;
and 3, adjusting the position of the iron core clamp to enable the annular iron core to face the spherical armature, and fixing the iron core clamp base on an electric vibration table of the classical vibration module by using a screw.
Further, in the sixth step, the current calibration method includes:
step 1, firstly, mounting a pressure sensor of an electromagnet control module on a contact surface of a groove of an annular iron core and a boss of an iron core clamp;
step 2, switching on coil current to generate a magnetic field so as to generate attractive force between the spherical armature and the annular iron core, and changing the numerical value of the pressure sensor;
and 3, adjusting the current of the coil through a current controller to ensure that the value of the pressure sensor is equal to the centrifugal force calculated in the second step, calibrating the current at the moment, recording the current as a current calibration value I, closing a power supply, and taking out the pressure sensor.
Further, in the sixth step, the vibration is set to: and (3) switching on a power supply, adjusting the value of the coil current, enabling the reading value of the coil current to be equal to the current calibration value I, setting the amplitude and frequency parameters of the classical vibration module, starting an electric vibration table and a power amplifier of the classical vibration module, and measuring the high cycle fatigue limit value of the test piece.
Further, the three-dimensional software comprises any one or two of CAE software and UG software, and the finite element software comprises any one or more of ABAQUS software, ANSYS software or MSC software.
An experimental device applied to the rotor blade high-cycle fatigue test method considering centrifugal force effect, the experimental device comprises:
a classical vibration module, the classical vibration module comprising: the system comprises an electric vibration table, a power amplifier, a computer and a laser displacement sensor, wherein the computer is connected with the electric vibration table, the power amplifier and the laser displacement sensor through signal wires, and the power amplifier is connected with the electric vibration table through the signal wires;
blade clamping module, blade clamping module includes: the blade clamp and the blade tip resin chuck are fixedly arranged on one side of the electric vibration table, and the blade clamp clamps tenons for fastening the rotor blades;
the electro-magnet control module, electro-magnet control module includes: the device comprises an iron core clamp, an annular iron core, a coil, a spherical armature, a pressure sensor and a current controller, wherein the spherical armature is installed and fixed on a blade tip resin clamp, the iron core clamp is fixed on one side of an electric vibration table, one end of the annular iron core is clamped and fixed on the iron core clamp, the coil is wound on the outer peripheral surface in order, the pressure sensor is arranged on the contact surface of the annular iron core and the iron core clamp, and the current controller is connected with the coil.
Further, the blade tip resin chuck is formed through a casting process, the blade tip of the rotor blade is immersed into molten epoxy resin in the casting process, cooling, fixing and forming are carried out, one side of the blade tip resin chuck is bonded with the rotor blade, and a stepped first boss is arranged on the other side of the blade tip resin chuck.
Further, one end of the spherical armature is in a spherical curved surface structure, a first groove is formed in the middle of the spherical armature, and the first boss is inserted into the first groove and fastened by a first positioning screw.
Further, the iron core clamp is formed by casting an epoxy resin material, one end of the iron core clamp is provided with a stepped second boss, one side of the annular iron core is of a concave curved surface structure, the annular iron core corresponds to the spherical curved surface of the spherical armature, the other side of the annular iron core is provided with a second groove, and the second boss is clamped in the second groove and fastened by a second positioning screw.
Compared with the prior art, the invention has the beneficial effects that: the invention constructs an electromagnetic field on the basis of a classical fatigue testing machine, uses the magnetic attraction force generated by the magnetic field to equivalent the centrifugal force of a first-order resonance point, controls the magnitude of the magnetic force through current, optimizes the equipment structure, is easy to control, can monitor the testing process in real time in the testing process, and provides effective support for test demonstration; the method provided by the invention can simulate the stress state of the rotor blade when the rotor blade vibrates under the actual service condition, the test device provided by the invention is used for carrying out high-cycle fatigue test measurement on the rotor blade, the stress analysis is comprehensive, the centrifugal force and the vibration are simultaneously applied to the rotor blade, the defect of influence of mutual interference is avoided, and the obtained high-cycle fatigue test result of the rotor blade is more similar to the actual service condition, so that the accuracy of the high-cycle fatigue test result of the rotor blade of the engine is improved.
Drawings
FIG. 1 is a front view of the overall structure of a test device according to the present invention;
FIG. 2 is an enlarged view of a portion of a test device blade clamping module and an electromagnet control module of the present invention;
FIG. 3 is a top view of a test device blade clamping module and an electromagnet control module of the present invention;
FIG. 4 is an assembly view of a toroidal core and coil of the test device of the present invention;
FIG. 5 is a front three-axis view of an iron core clamp of the test apparatus of the present invention;
FIG. 6 is a schematic view of a tip resin cartridge of the test apparatus of the present invention;
FIG. 7 is a schematic view of a ball armature of the test device of the present invention;
FIG. 8 is a flow chart of a test method of the present invention for determining the tip cut length.
The reference numerals in the drawings: 11. an electric vibration table; 12. a power amplifier; 13. a computer; 21. a rotor blade; 22. a blade clamp; 23. a blade tip resin chuck; 31. an iron core clamp; 32. an annular iron core; 33. a coil; 34. a spherical armature; 41. a first positioning screw; 42. a second set screw; 51. a second groove; 52. a second boss; 53. a first boss; 54. a first groove; 61. a contact surface.
Detailed Description
The following description of the embodiments of the present invention will be made clearly and completely with reference to the accompanying drawings, in which it is apparent that the embodiments described are only some embodiments of the present invention, but not all embodiments.
Embodiment one:
the invention provides a rotor blade high-cycle fatigue test method considering centrifugal force effect based on the defects existing in the prior art, which comprises the following steps:
performing modal analysis on the three-dimensional model of the rotor blade by utilizing finite element analysis software, and taking the centrifugal load effect (the rotating speed is n) into consideration to obtain the vibration mode of the rotor blade and the maximum alternating stress position under first-order resonance, and marking the vibration mode and the maximum alternating stress position as a point P; the position of the point P can be regarded as the crack initiation position of the actual blade at the rotating speed, and the danger coefficient is the highest, so that the rotor high-cycle fatigue limit considering the centrifugal force effect can be measured only by ensuring that the centrifugal force and the vibration mode of the point P are equivalent to the actual situation in the test process.
According to the geometric shape of the rotor blade, a centrifugal force calculation formula is adopted to calculate the centrifugal force of the P point at the rotating speed, a micro-element section with the height dZ is taken on the rotor blade, a micro-element body dXdYdZ is taken on the micro-element section, the area dXdY=dA of the micro-element body is made, and the centrifugal force dF of the micro-element body is:
dF＝ρω 2 Z′dAdZ
wherein ρ is the density of the blade material, ω is the rotational angular velocity of the rotor, Z ' is the distance from the center of gravity of the hogels to the rotational axis, and Z ' is the projection of Z ' in the direction of the blade height
In the method, in the process of the invention,
indicating the angle formed by the Z' direction and the leaf height direction.
The component of the microcell body centrifugal force dF in the leaf height direction is:
therefore, the centrifugal force along the Z direction generated by the blade micro-segment mass with the sectional area of A (Z) is as follows:
∫ A(Z) dFz＝ρω 2 ZdZ∫ A(Z) dA＝ρω 2 A(Z)ZdZ
in this way, the component of the centrifugal force of the blade mass above a certain section of the rotor blade (z=zi) in the direction of the blade height can be determined as:
where Zk denotes the distance from the tip to the rotation axis, zi denotes the distance from the point P to the rotation axis, Z denotes the projection of the distance from the point P to the rotation axis in the blade height direction, and a (Z) denotes the sectional area of the blade where the point P is located.
Considering that magnetic force and centrifugal force have certain similarity, the magnetic force belongs to field force, and the principle of magnetic force generation is simple, so that the attractive force generated by an electromagnetic field is used for equivalent centrifugal force; the electromagnet is mainly composed of a coil, an iron core and an armature, wherein the iron core and the armature are made of soft iron or silicon steel, so that the electromagnet can be demagnetized immediately at the moment of power failure, the armature is fixed at the blade tip, the iron core and the coil are fixed at the opposite side of the armature, the intensity of a magnetic field is controlled by adjusting the magnitude of current, and the magnitude of magnetic force can be controlled.
The armature is fixed on the blade tip to increase the weight of the blade tip, so that the vibration mode of the blade is increased, the material of a part of the blade tip can be cut in advance to adjust the vibration frequency and the vibration mode after the armature is increased, the length of the cut material can be determined together through a finite element method and a multi-objective optimization program, a parameterized three-dimensional assembly model of the rotor blade and the armature is established, the assembly model is subjected to modal analysis by finite element analysis software, the centrifugal load effect (the rotating speed is n) is considered, and the vibration mode of the three-dimensional assembly model and the maximum alternating stress position under first-order resonance are obtained and are marked as P'. And taking the blade tip cutting length L as a design variable, taking the position and the vibration mode of the point P as targets, establishing a multi-target optimization program, and when the position and the corresponding vibration mode of P' are matched with the point P, outputting L as the blade tip cutting length.
Based on the above principle, as shown in fig. 8, the method for testing the high cycle fatigue of the rotor blade according to the present embodiment, which considers the centrifugal force effect, specifically includes the following steps:
the first step: determining the position of the rotor blade 21 hazard point; a three-dimensional model of the rotor blade 21 is built by three-dimensional modeling software (one or two combinations of UG software or CAE software), then the model of the rotor blade 21 is subjected to modal analysis by finite element software (any one or more combinations of ABAQUS software, ANSYS software or MSC software), and the centrifugal load effect (rotational speed n) is considered to obtain the vibration mode of the rotor blade 21 and the maximum alternating stress position under first-order resonance, which is denoted as point P.
And a second step of: the centrifugal force at the rotational speed at the point P is calculated from the geometry of the rotor blade 21 using a centrifugal force calculation formula:
wherein ρ is the density of the blade material, ω is the rotational angular velocity of the rotor, zk is the distance from the blade tip to the rotational axis, zi is the distance from the blade root to the rotational axis, Z is the projection of the distance from the point P to the rotational axis in the direction of the blade height, and A (Z) is the cross-sectional area of the blade where the point P is located;
solving the formula (1) integral by adopting a numerical integration method, dividing the rotor blade 21 into n sections, wherein the sections from the blade tip to the blade root are 0,1,2, … … and n, and the total number of sections is n+1, and the first section, namely the blade section between the 0 th section and the 1 st section, has the following centrifugal force of the blade mass along the blade height direction:
ΔF 1 ＝ρω 2 A m1 Z m1 ΔZ 1 (2)
wherein A is m1 Represents the average cross-sectional area of the first segment of blade, Z m1 Representing the average coordinates in the direction of the leaf height, ΔZ 1 Representing the absolute height of the first segment of blades;
ΔZ 1 ＝Z 0 -Z 1 (5)
in the above, Z 0 ，Z 1 The coordinates of the 0 th section and the 1 st section along the height direction of the leaf are respectively A 0 ，A 1 Cross-sectional areas of section 0 and section 1, respectively;
similarly, ΔF is obtained 2 ，ΔF 3 ，……，ΔF n The section where the set point P is located is the i-th section, the centrifugal force to which the point P is subjected is:
F i separation ＝ΔF 1 +ΔF 2 +…+ΔF i (6)。
And a third step of: establishing a three-dimensional assembly model of the rotor blade 21, the blade tip resin chuck 23 and the spherical armature 34, carrying out modal analysis on the three-dimensional assembly model by using finite element analysis software (any one or more of ABAQUS software, ANSYS software and MSC software), giving an initial value of blade tip cutting length L, taking the centrifugal load action (rotating speed is n) of the rotor blade 21 into consideration, obtaining a vibration mode of the three-dimensional assembly model and a maximum alternating stress position under first-order resonance, marking as a point P ', taking the blade tip cutting length L as a design variable, taking the position and the vibration mode of the point P as targets, establishing a multi-objective optimization program, re-giving an initial value of the blade tip cutting length L when the position of the point P' is not similar to the position of the point P and the vibration modes corresponding to the two points are not equal, and calculating to obtain the vibration mode of the three-dimensional assembly model and the position P 'of the maximum alternating stress point under first-order resonance, wherein the output blade tip cutting length L is the blade tip cutting length when the position of the point P' is similar to the position of the point P and the vibration modes corresponding to the two points are equal;
fourth step: manufacturing a test piece, cutting a material with the length L from the tip of the rotor blade 21 according to the tip cutting length L, forming a tip resin chuck 23 through a casting process, immersing the tip of the rotor blade 21 into molten epoxy resin in the casting process, cooling, fixing and forming, and bonding one side of the tip resin chuck 23 with the rotor blade 21 to obtain the test piece;
fifth step: the method comprises the steps of clamping a test piece, setting a magnetic field, fixing the test piece on a classical vibration module by using a blade clamping module, fixing a blade clamp 22 on one side of an electric vibration table 11 of the classical vibration module by using a screw, and fixing tenons of rotor blades 21 of the test piece in the blade clamp 22 of the blade clamping module by using the screw; the electromagnet control module is utilized to set a magnetic field of the test piece by adopting the following steps:
step 1, pushing a spherical armature 34 of an electromagnet control module into a first boss 53 of a blade tip resin chuck 23, and fixing the first boss 51 by using a first positioning screw 41;
step 2, winding the coil 33 on the annular iron core 32 of the electromagnet control module, wherein a second groove 51 of the annular iron core 32 is aligned with a second boss 52 of the iron core clamp 31 of the electromagnet control module and pushed in, and the annular iron core 32 is fixed on the iron core clamp 31 by using a second positioning screw 42;
and 3, adjusting the position of the iron core clamp 31 to enable the annular iron core 32 to face the spherical armature 34, and fixing the base of the iron core clamp 31 on the other side of the electric vibration table 11 of the classical vibration module by using screws.
Sixth step: the method comprises the steps of current calibration and vibration setting, installing a pressure sensor on a contact surface 61 of a second groove 51 of an annular iron core 32 and a second boss 52 of an iron core clamp 31, switching on a power supply, enabling a coil 33 to pass through current to generate a magnetic field, enabling a spherical armature 34 and the annular iron core 32 to generate attractive force, enabling the readings of the pressure sensor to change along with the changes, adjusting the magnitude of the current passing through the coil 33 through a current controller, enabling the readings of the pressure sensor to be equal to the centrifugal force value of a point P calculated in the second step, recording the current magnitude as a current calibration value I, switching off the power supply and taking out the pressure sensor, switching on the power supply again, adjusting the magnitude of the current of the coil 33 through the current controller, enabling the readings of the current of the coil 33 to be equal to the current calibration value I, setting amplitude and frequency parameters of a classical vibration module through a software system in a computer 13, starting an electric vibration table 11 and a power amplifier 12 of the classical vibration module, and measuring the high-cycle fatigue limit value of a test piece.
Embodiment two:
the experimental device of the embodiment provides equipment support for the smooth implementation of the rotor blade high-cycle fatigue test method taking the centrifugal force effect into consideration in the first embodiment, and comprises a classical vibration module, a blade clamping module and an electromagnet control module;
as shown in fig. 1, the classical vibration module comprises: the electric vibration table 11, the power amplifier 12, the computer 13 and the laser displacement sensor, wherein the computer 13 is connected with the electric vibration table 11, the power amplifier 12 and the laser displacement sensor through signal wires, the power amplifier 12 is connected with the electric vibration table 11 through signal wires, vibration control software of a classical vibration module is installed in the computer 13, and the laser displacement sensor is installed on the classical vibration module and used for collecting and transmitting vibration signals to the computer 13.
As shown in fig. 2 and 6, the blade clamping module includes: the blade clamp 22 and the blade tip resin clamp 23, the blade clamp 22 is fixedly arranged on one side of the electric vibration table 11, the blade clamp 22 clamps and fastens the tenon of the rotor blade 21, the base of the blade clamp 22 is connected with the electric vibration table 11 through bolts, and the number of the bolts is 6; the tip resin chuck 23 is formed by a casting process, in which the tip of the rotor blade 21 is immersed in molten epoxy resin, and is cooled and fixed to be formed, one side of the tip resin chuck 23 is bonded to the rotor blade 21, and the other side is provided with a stepped first boss 53.
As shown in fig. 2 to 5 and 7, the electromagnet control module includes: iron core fixture 31, toroidal iron core 32, coil 33, spherical armature 34, pressure sensor and current controller; the spherical armature 34 is installed and fixed on the blade tip resin chuck 23, the iron core clamp 31 is fixed on one side of the electric vibration table 11, one end of the annular iron core 32 is clamped and fixed on the iron core clamp 31, the outer peripheral surface is orderly wound with the coil 33, the annular iron core 32 and the spherical armature 34 form an electromagnet together, the pressure sensor is arranged on the contact surface 61 of the annular iron core 32 and the iron core clamp 31, the current controller is connected with the coil 33 and used for controlling the current of the coil 33 and indirectly controlling the generated magnetic attraction force.
One end of the spherical armature 34 is in a spherical curved surface structure, a first groove 54 is formed in the middle of the spherical armature, and a first boss 53 is inserted into the first groove 54 and fastened by a first positioning screw 41.
The first groove 54 in the middle of the spherical armature 34 is matched with the stepped first boss 53 of the blade tip resin chuck 23, the first boss 53 is inserted into the first groove 54 and fastened by the first positioning screw 41, and the annular iron core 32 is prevented from bouncing in the vertical direction in the vibration process.
The iron core clamp 31 is formed by casting an epoxy resin material, the base of the iron core clamp is provided with 5 bolt holes, the iron core clamp is connected with the electric vibration table 11 through screws, one end (clamping end) of the iron core clamp 31 is provided with a stepped second boss 52, one side of the annular iron core 32 is of an inwards concave curved surface structure and corresponds to the spherical curved surface of the spherical armature 34, the distance between the two parts in the vibration process is kept unchanged all the time, the other side of the annular iron core 32 is provided with a second groove 51, the second groove is matched with the stepped second boss 52 on the iron core clamp 31 for use, and the second boss 52 is clamped in the second groove 51 and fastened by a second positioning screw 42.
The tip of the rotor blade 21 with the tip cut to be L is molded with the tip resin chuck 23 through a casting process, the tip of the rotor blade 21 is immersed into molten epoxy resin in the casting process, the rotor blade is cooled and fixed for molding, and one side of the tip resin chuck 23 is bonded with the rotor blade 21, so that a test piece is obtained; with the aid of the test device, the tenon of the rotor blade 21 of the test piece is fixed on the blade clamp 22, the spherical armature 34 of the electromagnet control module is pushed into the first boss 53 of the blade tip resin chuck 23, the first boss 51 is fixed by the first positioning screw 41, then the coil 33 is wound on the annular iron core 32 of the electromagnet control module, the second groove 51 of the annular iron core 32 is aligned with the second boss 52 of the iron core clamp 31 of the electromagnet control module and pushed in, and the annular iron core 32 is fixed on the iron core clamp 31 by the second positioning screw 42, so that the test piece can be installed by the test device.
The foregoing is only a preferred embodiment of the present invention, but the scope of the present invention is not limited thereto, and any person skilled in the art, who is within the scope of the present invention, should make equivalent substitutions or modifications according to the technical scheme of the present invention and the inventive concept thereof, and should be covered by the scope of the present invention.
Claims (10)
1. The high-cycle fatigue test method for the rotor blade taking the centrifugal force effect into consideration is characterized by comprising the following steps of:
the first step: determining the position of a rotor blade dangerous point, establishing a rotor blade three-dimensional model by using three-dimensional software, carrying out modal analysis on the rotor blade model by using finite element software, and taking the centrifugal load effect of the rotor blade into consideration to obtain the vibration mode of the rotor blade and the position of the rotor blade dangerous point, and marking the vibration mode and the position as a point P;
and a second step of: according to the geometric shape of the rotor blade, a centrifugal force calculation formula is adopted to calculate the centrifugal force of the point P, wherein the centrifugal force calculation formula is as follows:
wherein ρ is the density of the blade material, ω is the rotational angular velocity of the rotor, Z k Representing tip to axis of rotation distanceZi represents the distance from the point P to the rotation axis, Z represents the projection of the distance from the point P to the rotation axis in the direction of the blade height, and A (Z) represents the sectional area of the blade where the point P is located;
and a third step of: establishing a three-dimensional assembly model of a rotor blade, a blade tip resin chuck and a spherical armature, carrying out modal analysis on the three-dimensional assembly model by finite element analysis software, giving an initial value of blade tip cutting length L, taking the centrifugal load effect of the rotor blade into consideration, obtaining a vibration mode of the three-dimensional assembly model and a maximum alternating stress position under first-order resonance, marking as a point P ', taking the blade tip cutting length L as a design variable, taking the position and the vibration mode of the point P as targets, establishing a multi-target optimization program, re-giving an initial value of the blade tip cutting length L when the position of the point P' is not similar to that of the point P and the vibration modes corresponding to the two points are not equal, and calculating to obtain the vibration mode of the three-dimensional assembly model and the position P 'of the maximum alternating stress point under first-order resonance, wherein the output blade tip cutting length L is the length of blade tip cutting when the position of the point P' is similar to that of the point P and the vibration modes corresponding to the two points are equal;
fourth step: manufacturing a test piece, namely cutting off a material with the length L at the tip of a rotor blade according to the tip cutting length L, forming a tip resin chuck through a casting process, immersing the tip of the rotor blade into molten epoxy resin in the casting process, cooling, fixing and forming, and bonding one side of the tip resin chuck with the rotor blade to obtain the test piece;
fifth step: the method comprises the steps of clamping a test piece, setting a magnetic field, fixing the test piece on a classical vibration module by using a blade clamping module, and setting the magnetic field of the test piece by using an electromagnet control module;
sixth step: and (3) current calibration and vibration setting, switching on a power supply, generating a magnetic field through an electromagnet control module, wherein the attractive force generated by the magnetic field is equal to the value of the centrifugal force obtained in the second step, calibrating the current value at the moment, starting a classical vibration module to perform vibration setting, testing a test piece, and measuring the high-cycle fatigue limit of the rotor blade.
2. The method of claim 1, wherein the (1) integral is solved by numerical integration, the blade is divided into n sections from the blade tip to the blade root, and the n sections are 0,1,2, … …, n and n+1, and the centrifugal force of the blade mass of the first section, namely the blade section between the 0 th section and the 1 st section, along the blade height direction is:
ΔF 1 ＝ρω 2 A m1 Z m1 ΔZ 1 (2)
wherein A is m1 Represents the average cross-sectional area of the first segment of blade, Z m1 Representing the average coordinates in the direction of the leaf height, ΔZ 1 Representing the absolute height of the first segment of blades;
ΔZ 1 ＝Z 0 -Z 1 (5)
in the above, Z 0 ，Z 1 The coordinates of the 0 th section and the 1 st section along the height direction of the leaf are respectively A 0 ，A 1 Cross-sectional areas of section 0 and section 1, respectively;
similarly, ΔF is obtained 2 ，ΔF 3 ，……，ΔF n The section where the set point P is located is the i-th section, the centrifugal force to which the point P is subjected is:
F i separation ＝ΔF 1 +ΔF 2 +…+ΔF i (6)。
3. The method for testing high cycle fatigue of a rotor blade considering centrifugal force effect according to claim 1, wherein in the fifth step, the test piece clamping is to fix the tenon of the rotor blade of the test piece in the blade clamp of the blade clamping module by using a screw, and the method for setting the magnetic field of the test piece comprises the following steps:
step 1, pushing a spherical armature of an electromagnet control module into a groove of a blade tip resin chuck, and fixing the spherical armature by using a first positioning screw;
step 2, winding a coil on an annular iron core of the electromagnet control module, aligning a groove of the annular iron core with a boss of an iron core clamp of the electromagnet control module, pushing in the groove, and fixing the annular iron core on the iron core clamp by using a second positioning screw;
and 3, adjusting the position of the iron core clamp to enable the annular iron core to face the spherical armature, and fixing the iron core clamp base on an electric vibration table of the classical vibration module by using a screw.
4. A rotor blade high cycle fatigue test method considering centrifugal force effect according to claim 3, wherein in the sixth step, the current calibration method comprises:
step 1, firstly, mounting a pressure sensor of an electromagnet control module on a contact surface of a groove of an annular iron core and a boss of an iron core clamp;
step 2, switching on coil current to generate a magnetic field so as to generate attractive force between the spherical armature and the annular iron core, and changing the numerical value of the pressure sensor;
and 3, adjusting the current of the coil through a current controller to ensure that the value of the pressure sensor is equal to the centrifugal force calculated in the second step, calibrating the current at the moment, recording the current as a current calibration value I, closing a power supply, and taking out the pressure sensor.
5. A rotor blade high cycle fatigue test method considering centrifugal force effect according to claim 4, wherein in the sixth step, the vibration is set as: and (3) switching on a power supply, adjusting the value of the coil current, enabling the reading value of the coil current to be equal to the current calibration value I, setting the amplitude and frequency parameters of the classical vibration module, starting an electric vibration table and a power amplifier of the classical vibration module, and measuring the high cycle fatigue limit value of the test piece.
6. A method of rotor blade high cycle fatigue testing taking into account centrifugal force effects according to claim 1, wherein the three-dimensional software comprises any one or a combination of two of CAE software and UG software, and the finite element software comprises any one or a combination of more of ABAQUS software, ANSYS software or MSC software.
7. An experimental apparatus applied to the rotor blade high cycle fatigue test method considering centrifugal force effect according to any one of claims 1, 3-6, characterized in that the experimental apparatus comprises:
a classical vibration module, the classical vibration module comprising: the device comprises an electric vibration table (11), a power amplifier (12), a computer (13) and a laser displacement sensor, wherein the computer (13) is connected with the electric vibration table (11), the power amplifier (12) and the laser displacement sensor through signal wires, and the power amplifier (12) is connected with the electric vibration table (11) through the signal wires;
blade clamping module, blade clamping module includes: a blade clamp (22) and a blade tip resin chuck (23), wherein the blade clamp (22) is fixedly arranged on one side of the electric vibration table (11), and the blade clamp (22) clamps tenons for fastening rotor blades (21);
the electro-magnet control module, electro-magnet control module includes: iron core anchor clamps (31), annular iron core (32), coil (33), spherical armature (34), pressure sensor and current controller, spherical armature (34) are installed and are fixed on apex resin chuck (23), iron core anchor clamps (31) are fixed one side of electric vibration platform (11), the one end card of annular iron core (32) is established and is fixed on iron core anchor clamps (31), and the winding of periphery surface is in order coil (33), pressure sensor set up in on contact surface (61) of annular iron core (32) and iron core anchor clamps (31), current controller with coil (33) link to each other.
8. The experimental device according to claim 7, wherein the tip resin chuck (23) is formed by a casting process, the tip of the rotor blade (21) is immersed in molten epoxy resin and is cooled and fixed during the casting process, one side of the tip resin chuck (23) is bonded with the rotor blade (21), and the other side is provided with a stepped first boss (53).
9. The experimental device according to claim 8, characterized in that one end of the spherical armature (34) is in a spherical curved surface structure, a first groove (54) is formed in the middle, and the first boss (53) is inserted into the first groove (54) and fastened by a first positioning screw (41).
10. The experimental device according to claim 7, wherein the iron core clamp (31) is molded by casting an epoxy resin material, one end of the iron core clamp is provided with a stepped second boss (52), one side of the annular iron core (32) is of a concave curved surface structure and corresponds to the spherical curved surface of the spherical armature (34), the other side of the annular iron core is provided with a second groove (51), and the second boss (52) is clamped in the second groove (51) and fastened by a second positioning screw (42).
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