CN112485107A - Method for verifying crack propagation endurance time of girder of metal blade - Google Patents
Method for verifying crack propagation endurance time of girder of metal blade Download PDFInfo
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- G01N2203/00—Investigating strength properties of solid materials by application of mechanical stress
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Abstract
The invention belongs to the technical field of helicopter structural strength tests, and particularly relates to a method for verifying crack propagation endurance time of a metal blade girder. The method comprises the following steps: s1: obtaining an actual measurement load spectrum of the metal blade to be measured by carrying out a flight test; s2: designing and manufacturing a test piece; s3: prefabricating initial defects; s4: determining the phase relation between the test load element and the test load; s5: determining the test load for forming the through crack; s6: compiling a crack propagation endurance test load spectrum block; s7: a strain gauge is pasted on the test part (1); s8: calibrating; s9: arranging a silver paint net (7); s10: loading test and measurement; s11: and (5) verifying the endurance time. The invention verifies the running time from the occurrence of the penetrating crack of the metal blade girder to the fracture of the girder through tests, thereby estimating the allowable endurance time after the crack is generated and ensuring the flight safety of the helicopter.
Description
Technical Field
The invention belongs to the technical field of helicopter structural strength tests, and particularly relates to a method for verifying crack propagation endurance time of a metal blade girder.
Background
The metal blade of the helicopter mainly adopts a metal cementing structure with an aluminum alloy integral girder, the main bearing component of the blade is an aluminum alloy D-shaped hollow extrusion-molded girder, and the flapping, the chordwise bending moment, the torsion and the centrifugal force of the blade are all borne by the girder. Impact is considered during design of the metal paddle, and a system for detecting whether the paddle is damaged is designed. This system is called a blade integrity monitoring system and accomplishes this by monitoring the aluminum alloy extrusion (girder) of each blade. The inner cavity of the extrusion part is filled with nitrogen under the action of slight positive pressure, a pressure annunciator is arranged at the position, close to the root, of each blade, if cracks appear in part of the structure of each blade, the nitrogen can escape, and the BIM pressure annunciator displays that the girder does not contain the pressurized nitrogen any more and needs to be replaced in time.
As the blade adopts a BIM system, the fatigue test proves the running time from the nitrogen pressure loss (the penetrating crack occurs in the girder structure) to the blade failure (the girder is broken), and the estimation of the allowable endurance time after the crack is generated is necessary.
However, the existing verification technology for the crack propagation endurance time of the metal blade girder of the helicopter in China has few researches, and the verification method for the crack propagation performance of the metal blade girder of the key part of the helicopter is lacked, so that the allowable endurance time of the metal blade girder of the helicopter after the penetrating crack occurs can not be proved.
Disclosure of Invention
The purpose of the invention is: aiming at the defects in the prior art, the invention provides a verification method for crack propagation endurance time based on a metal paddle girder, and the time from the penetrating fatigue crack to the fracture of the metal paddle girder is obtained through a test, so that the endurance time allowed after the penetrating crack occurs to the metal paddle girder is accurately estimated, and the method has a good engineering application prospect.
The technical scheme of the invention is as follows: in order to achieve the purpose, the method for verifying the crack propagation endurance time of the girder of the metal blade is characterized by comprising the following steps of:
s1: obtaining an actual measurement load spectrum of the metal blade to be measured by carrying out a flight test;
s2: designing and manufacturing a test piece; the test piece comprises a test part 1, a plugging cover 2, a fixed clamping plate 3, a loading clamping plate 4, a fixed joint 5 and a loading joint 6, wherein the test part 1 is of a wing-shaped structure with openings at two ends, the plugging cover 2 is respectively connected with the openings at two ends of the test part 1 in a sealing fit manner, one end of the test part 1 is sequentially connected with the fixed clamping plate 3 and the fixed joint 5, and the other end of the test part 1 is sequentially connected with the loading clamping plate 4 and the loading joint 6;
s3: prefabricating initial defects;
determining an initial defect position and a defect size through finite element simulation, and prefabricating and forming an initial defect on the test part 1 by utilizing laser cutting processing according to the initial defect position and the defect size determined through the finite element simulation;
s4: determining the phase relation between the test load element and the test load;
determining a load element of a crack propagation test according to the measured load spectrum in the step 1, wherein the load element comprises a centrifugal force FcWaving bending moment MbAnd shimmy bending moment Mt；
Based on the determined load elements, enabling the load directions corresponding to synchronous opening and closing of cracks generated by flap bending and shimmy bending to be phase relations of the test load;
s5: determining the test load for forming the through crack;
performing a through crack formation test by using an accelerated test method, wherein the formed through crack test load is the maximum load appearing in the actually measured load spectrum in the step S1;
s6: compiling a crack propagation endurance test load spectrum block;
compiling to obtain crack propagation duration test load spectrum blocks according to the actual measurement load spectrum, wherein each 1 crack propagation duration test load spectrum block represents the crack propagation duration of 1 flight hour;
s7: a strain gauge is attached to the test portion 1;
pasting a strain gauge for measuring waving bending moment and shimmy bending moment to the test part 1;
s8: calibrating;
carrying out ground load calibration on the test part 1 by adopting a direct calibration method;
s9: arranging a silver paint net 7;
in order to determine that the test part 1 has through cracks, arranging silver paint nets at the position of an initial defect on the surface of the test part 1 in a prefabrication mode, wherein the silver paint nets are symmetrically arranged on the upper portion and the lower portion of the prefabricated defect along the spanwise direction of blades, and the effective working length of the silver paint nets along the spanwise direction of the blades is not less than 40 mm;
s10: loading test and measurement;
the test piece is subjected to a loading test on a fatigue test bed, the fatigue test bed comprises a fixed end 8, a steel cable 9, a horizontal actuator 10 and a vertical actuator 11, a fixed joint 5 on the test piece is connected with the fixed end of the fatigue test bed, a loading joint 6 is connected with the vertical actuator and is respectively connected with the horizontal actuator through the steel cable, and the horizontal actuator is used for applying a centrifugal force in the horizontal direction on the test piece; the vertical actuator is used for applying waving bending moment and shimmy bending moment on the test piece;
loading by controlling a centrifugal force applied to the horizontal direction by a horizontal actuator and a waving bending moment and a shimmy bending moment applied by a vertical actuator through a controller according to the crack propagation endurance test load spectrum block compiled in the step S6, repeatedly performing the step 6 until the test part 1 is damaged, performing measurement data acquisition and processing and test load monitoring by using a dynamic signal test analysis system, and recording the number of accumulated effective crack propagation endurance test load spectrum blocks;
s11: verifying the endurance time;
testing the number n of load spectrum blocks according to the accumulated effective crack propagation endurance time0Calculating the endurance time L of the metal blade girder after the through crack occurs by the following formula:
number n of load spectrum blocks of the effective crack propagation endurance test completed with endurance time L ═0Fatigue life dispersion coefficient f;
the fatigue life dispersion coefficient f is the dispersion of the fatigue life, can well obey the log-normal distribution, and can be used for controlling the fatigue failure probability of the flight structure.
In a possible embodiment, in step S1, the flight test further includes the following steps,
firstly, carrying out surface mounting at a measuring point position of the metal paddle to be measured;
carrying out ground load calibration on the metal blade to be measured by adopting a direct calibration method;
and according to the flight use state spectrum of the helicopter, measuring the flight load of the metal blade to be measured in each flight state to obtain an actual measurement load spectrum.
Preferably, according to the flight use state spectrum of the helicopter, the flight load of the metal blade to be measured in each flight state is measured, the state measurement point in the maneuvering state at least completes 2-3 times of load measurement, and the load measurement error is not more than 5%.
In a possible embodiment, in step S2, the manufacturing process of the test piece specifically includes:
firstly, cutting a main blade girder with a certain length as a test part 1;
then, the two ends of the test part 1 are sealed by adopting the plugging covers 2;
clamping the two ends of the test part 1 by adopting clamping plates, wherein one end of the clamping plate 3 is fixed with the fixed joint 5 and is connected with the other end of the clamping plate 4 through a fastening device, and the other end of the clamping plate is loaded with the loading joint 6 and is connected with the fastening device.
In one possible embodiment, in step S7, the flap bending moment measuring strain gauge is attached to a chord line 25% of the distance between the upper and lower surfaces of the blade of the test part 1 and the leading edge of the blade, and a shimmy bending moment measuring strain gauge is attached to a position where the coupling effect of the flap bending moment on the shimmy bending moment is eliminated.
In a possible embodiment, the location for eliminating the coupling influence of the flap bending moment on the shimmy bending moment refers to a location where the coupling influence of the flap bending moment on the shimmy bending moment is less than 5% through decoupling.
In one possible embodiment, the silver paint net is drawn as a network by silver paint, and forms a loop with the electrified equipment, and the equipment gives an early warning after the silver paint net is broken due to crack propagation of the metal parts.
In one possible embodiment, in the step S9, the silver paint mesh has a width of 3mm in the chord direction.
The invention has the beneficial effects that: the method for verifying the crack propagation endurance time of the metal blade girder of the helicopter can verify the running time from the occurrence of the penetrating crack of the metal blade girder to the fracture of the girder through a test, thereby estimating the allowable endurance time after the crack is generated and ensuring the flight safety of the helicopter.
Drawings
FIG. 1 is a flow chart of the method of the present invention
FIG. 2 is a schematic view of the structure of the test piece of the present invention
FIG. 3 is a schematic view of an arrangement of silver paint mesh in an embodiment of the present invention
FIG. 4 is a schematic view of a loading test in an embodiment of the present invention
Wherein:
1. the device comprises a test part, 2, a plug cover, 3, a fixed clamping plate, 4, a loading clamping plate, 5, a fixed joint, 6, a loading joint, 7, a silver paint net, 8, a fixed end, 9, a steel cable, 10, a horizontal actuator, 11 and a vertical actuator.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.
As shown in fig. 1, a method for verifying crack propagation endurance of a metal blade girder includes the following steps:
s1: obtaining an actual measurement load spectrum of the metal blade to be measured by carrying out a flight test; said flight test in turn comprises in particular the following steps,
firstly, carrying out surface mounting at a measuring point position of the metal paddle to be measured;
carrying out ground load calibration on the metal blade to be measured by adopting a direct calibration method;
measuring the flight load of the metal blade to be measured in each flight state according to the flight use state spectrum of the helicopter;
preferably, the state measuring point in the maneuvering state at least completes 2-3 times of load measurement, and the load measurement error is not more than 5%. When the actual measurement load of the metal blade is measured, at least 2-3 times of load measurement is completed on each test point, and the error of the 2-3 times of load measurement is not more than 5%;
s2: designing and manufacturing a test piece; as shown in fig. 2, the test piece comprises a test part 1, a plug cover 2, a clamping plate 3, a fixed joint 4 and a loading joint 5; firstly, cutting a main blade girder with a certain length as a test part 1; then, the two ends of the test part 1 are sealed by adopting the plugging covers 2; clamping two ends of the test part 1 by using clamping plates 3; one end of the clamping plate 3 is connected with the fixed joint 4 through a fastening device, and the other end of the clamping plate 3 is connected with the loading joint 5 through a fastening device;
s3: prefabricating initial defects; determining an initial defect position and a defect size through finite element simulation, and prefabricating and forming an initial defect on the test part 1 by utilizing laser cutting processing according to the initial defect position and the defect size determined through the finite element simulation;
s4: determining the test load for forming the through crack; carrying out a through crack formation test by adopting an accelerated test method, wherein the test load takes the maximum load appearing in the actually measured load spectrum in the S1 as the test load;
s4: determining the phase relation between the test load element and the test load; determining a load element of a crack propagation test according to the actually measured load spectrum; the load elements comprise a centrifugal force Fc, a flapping bending moment Mb and a shimmy bending moment Mt; determining the phase relation of the test load: based on the determined load elements, enabling the swinging bending and the shimmy bending to enable the direction corresponding to the synchronous opening and closing of the crack to be the phase relation of the test load;
s5: determining the test load for forming the through crack; carrying out a through crack formation test by adopting an accelerated test method, wherein the test load takes the maximum load appearing in the actually measured load spectrum in the S1 as the test load;
s6: compiling a crack propagation test load spectrum block; and compiling 1 crack propagation duration test load spectrum block according to the actually measured load spectrum, wherein each 1 crack propagation duration test spectrum block represents the crack propagation duration of 1 flight hour.
S7: a strain gauge is attached to the test portion 1; the pasting of the fatigue test piece comprises the following steps: pasting a strain gauge for measuring waving bending moment and shimmy bending moment to the test part 1; the flapping bending moment measuring strain gauge is adhered to a chord line which is 25% of the distance between the upper surface and the lower surface of the blade of the test part 1 and the front edge of the blade, and a shimmy bending moment measuring strain gauge is adhered to a position where the coupling influence of the flapping bending moment on the shimmy bending moment is eliminated;
s8: calibrating; carrying out ground load calibration on the test part 1 by adopting a direct calibration method;
s9: arranging a silver paint net 7; as shown in fig. 3, in order to determine that the test part 1 has a through crack, a silver paint net 7 is arranged at a position of an initial defect prefabricated on the surface of the test part 1, the silver paint net 7 is arranged along the spanwise direction of the blade, the typical width of the silver paint net along the chord direction is 3mm, and the effective working length of the silver paint net 7 along the spanwise direction of the blade is 100 mm;
s10: loading test and measurement; as shown in fig. 4, the test is carried out on a fatigue test bed, the fatigue test bed comprises a fixed end, a horizontal actuator and a vertical actuator, the fixed joint 4 is connected with the fixed end of the fatigue test bed, the loading joint 5 is connected with the vertical actuator and is connected with the horizontal actuator through the steel cable, and the horizontal actuator is used for applying a centrifugal force in the horizontal direction on a test piece; the vertical actuator is used for applying waving bending moment and shimmy bending moment on a test piece, controlling the horizontal actuator to apply centrifugal force in the horizontal direction according to a crack propagation test load spectrum block compiled by S6, controlling the vertical actuator to apply waving bending moment and shimmy bending moment to carry out loading to damage, and carrying out data acquisition processing and test load monitoring by using a dynamic signal test analysis system;
s11: evaluating test results; and selecting a crack propagation endurance test load spectrum block finished by the metal paddle girder, and giving endurance capacity of the metal paddle girder after the crack is penetrated by the metal paddle girder by considering the fatigue life dispersion coefficient.
While the preferred embodiments of the present invention have been described in detail, the present invention is not limited to the above embodiments, and various changes can be made without departing from the spirit of the present invention within the knowledge of those skilled in the art.
Claims (8)
1. A method for verifying crack propagation endurance time of a girder of a metal blade is characterized by comprising the following steps:
s1: obtaining an actual measurement load spectrum of the metal blade to be measured by carrying out a flight test;
s2: designing and manufacturing a test piece; the test piece comprises a test part (1), a plugging cover (2), a fixed clamping plate (3), a loading clamping plate (4), a fixed joint (5) and a loading joint (6), wherein the test part (1) is of a wing-shaped structure with openings at two ends, the plugging cover (2) is respectively in sealing fit connection with the openings at two ends of the test part (1), one end of the test part (1) is sequentially connected with the fixed clamping plate (3) and the fixed joint (5), and the other end of the test part is sequentially connected with the loading clamping plate (4) and the loading joint (6);
s3: prefabricating initial defects;
determining an initial defect position and a defect size through finite element simulation, and prefabricating and forming an initial defect on the test part (1) by utilizing laser cutting processing according to the initial defect position and the defect size determined through the finite element simulation;
s4: determining the phase relation between the test load element and the test load;
determining a load element of the crack propagation test according to the measured load spectrum in the step S1, wherein the load element comprises a centrifugal force FcWaving bending moment MbAnd shimmy bending moment Mt；
Based on the determined load elements, enabling the load directions corresponding to synchronous opening and closing of cracks generated by flap bending and shimmy bending to be phase relations of the test load;
s5: determining the test load for forming the through crack;
performing a through crack formation test by using an accelerated test method, wherein the formed through crack test load is the maximum load appearing in the actually measured load spectrum in the step S1;
s6: compiling a crack propagation endurance test load spectrum block;
compiling to obtain crack propagation duration test load spectrum blocks according to the actual measurement load spectrum, wherein each 1 crack propagation duration test load spectrum block represents the crack propagation duration of 1 flight hour;
s7: a strain gauge is pasted on the test part (1);
pasting a strain gauge for measuring waving bending moment and shimmy bending moment to the test part (1);
s8: calibrating;
carrying out ground load calibration on the test part (1) by adopting a direct calibration method;
s9: arranging a silver paint net (7);
in order to determine that the test part (1) has a through crack, arranging silver paint nets at the position of an initial defect on the surface of the test part (1), wherein the silver paint nets are symmetrically arranged at the upper part and the lower part of the prefabricated defect along the spanwise direction of blades, and the effective working length of the silver paint nets along the spanwise direction of the blades is not less than 40 mm;
s10: loading test and measurement;
the test piece is subjected to a loading test on a fatigue test bed, the fatigue test bed comprises a fixed end (8), a steel cable (9), a horizontal actuator (10) and a vertical actuator (11), a fixed joint (5) on the test piece is connected with the fixed end of the fatigue test bed, a loading joint (6) is connected with the vertical actuator and is respectively connected with the horizontal actuator through the steel cable, and the horizontal actuator is used for applying centrifugal force in the horizontal direction on the test piece; the vertical actuator is used for applying waving bending moment and shimmy bending moment on the test piece;
loading by controlling a centrifugal force applied to the horizontal direction by a horizontal actuator and a waving bending moment and a shimmy bending moment applied by a vertical actuator through a controller according to the crack propagation endurance test load spectrum block compiled in the step S6 until the test part (1) is damaged, performing measurement data acquisition processing and test load monitoring by using a dynamic signal test analysis system, and recording the number of the accumulated effective crack propagation endurance test load spectrum blocks;
s11: verifying the endurance time;
testing the number n of load spectrum blocks according to the accumulated effective crack propagation endurance time0Calculating the endurance time L of the metal blade girder after the through crack occurs by the following formula:
number n of load spectrum blocks of the effective crack propagation endurance test completed with endurance time L ═0Fatigue life dispersion coefficient f;
the fatigue life dispersion coefficient f is the dispersion of the fatigue life, can well obey the log-normal distribution, and can be used for controlling the fatigue failure probability of the flight structure.
2. The method for verifying crack propagation endurance time of a metal blade girder according to claim 1, wherein in step S1, the flight test further comprises the following steps,
firstly, carrying out surface mounting at a measuring point position of the metal paddle to be measured;
carrying out ground load calibration on the metal blade to be measured by adopting a direct calibration method;
and according to the flight use state spectrum of the helicopter, measuring the flight load of the metal blade to be measured in each flight state to obtain an actual measurement load spectrum.
3. The method for verifying the crack propagation endurance time of the girder of the metal blade as claimed in claim 2, wherein the flight load of the metal blade to be tested in each flight state is measured according to the flight use state spectrum of the helicopter, the load measurement is performed at least 2-3 times at the state measurement point in the maneuvering state, and the load measurement error is not more than 5%.
4. The method for verifying crack propagation endurance time of a metal blade girder according to claim 1, wherein in the step S2, the manufacturing process of the test piece specifically includes:
firstly, cutting a main blade girder with a certain length as a test part (1);
then, two ends of the test part (1) are sealed by adopting plugging covers (2);
clamping plates are adopted to clamp two ends of the test part (1), wherein one end of the clamping plate is fixed with the fixed joint (5) and is connected with the fixed joint through a fastening device, and the other end of the clamping plate is loaded with the loading joint (4) and is connected with the loading joint (6) through the fastening device.
5. The method for verifying the crack propagation endurance time of the girder of the metal blade as claimed in claim 1, wherein in the step S7, the flap bending moment measuring strain gauge is attached to a chord line of 25% of a distance between the upper and lower surfaces of the blade of the test part (1) and a lead edge of the blade, and a lead-lag bending moment measuring strain gauge is attached to a position where the coupling influence of the flap bending moment on the lead-lag bending moment is eliminated.
6. The method for verifying the crack propagation endurance time of the metal blade girder according to claim 5, wherein the point where the coupling influence of the flapping bending moment on the shimmy bending moment is eliminated refers to a position where the coupling influence of the flapping bending moment on the shimmy bending moment is less than 5% through decoupling.
7. The method for verifying the crack propagation endurance time of the metal blade girder according to claim 1, wherein the silver paint mesh is drawn as a network by silver paint and forms a loop with a power-on device, and the device gives an early warning when the crack propagation of the metal part causes the crack propagation of the silver paint mesh.
8. The method for verifying crack propagation endurance of a metal blade girder according to claim 1, wherein in step S9, the silver paint mesh has a chord-wise width of 3 mm.
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| CN202011192574.5A CN112485107B (en) | 2020-10-30 | 2020-10-30 | Method for verifying crack propagation endurance time of girder of metal blade |
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| CN202011192574.5A CN112485107B (en) | 2020-10-30 | 2020-10-30 | Method for verifying crack propagation endurance time of girder of metal blade |
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Cited By (2)
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| CN113443169A (en) * | 2021-06-11 | 2021-09-28 | 航空工业第一飞机设计研究院 | A test method for active control of damage and fracture of integral panel structures |
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