Method and device for determining damage safety high-cycle fatigue life of laminated metal tension-torsion strip

Abstract

The invention provides a method and a device for determining the damage safety high-cycle fatigue life of a laminated metal tension-torsion strip. The method comprises the following steps: step 1, acquiring the initial torsional rigidity E of the tension-torsion strip to be tested; step 2, initialization is carried out; step 3, carrying out N times of load circulation, obtaining new torsional rigidity E'of the to-be-tested tension and torsion bar when the to-be-tested tension and torsion bar is not broken, and judging whether (E-E ') / E is greater than 10%; if so, entering step 4; if not, entering the step 5; step 4, obtaining fatigue performance S infinity according to the number m of tests and the alternating torsional angle; according to the fatigue performance S infinity, the tension-torsion strip breakage safety high-cycle fatigue life is obtained; and 5, adding 1 to the number m of tests, increasing the alternating torsional angle by a preset angle, and entering the step 3. And a basis can be provided for calculating the high-cycle fatigue life of the stacked tension-torsion strip of the helicopter after partial failure of the tension-torsion sheet of the stacked tension-torsion strip.

Description

Technical Field

[0001] The invention belongs to the field of fatigue calculation of helicopter rotor torsion strips, and in particular relates to a method and a device for determining the damage safety high-cycle fatigue life of a stacked metal torsion strip. Background Art

[0002] The laminated metal torsion strip is a load-bearing structure commonly used in helicopter hub structures. The structure is composed of several laminated metal torsion strips. Its main function is to withstand the centrifugal force generated by the rotation of the blades and produce torsional deformation to achieve the pitch change movement of the blades. It has the characteristics of simple and compact structure, light weight, safe use and easy maintenance.

[0003] In addition, the laminated metal tension-twist strip structure also has certain damage safety characteristics. When some tension-twist strips fail, the structure can still withstand certain high-cycle fatigue loads. There is currently no analysis method for damage safety high-cycle fatigue life in China. Summary of the invention

[0004] The present invention provides a method and device for determining the damage safe high cycle fatigue life of a laminated metal torsion strip, which can determine the damage safe high cycle fatigue life of the laminated metal torsion strip.

[0005] The first aspect of the present invention provides a method for determining the damage safety high cycle fatigue life of a laminated metal tension and torsion strip, comprising the following steps:

[0006] Step 1, obtaining the initial torsional stiffness E of the tension-twist strip to be tested; the tension-twist strip to be tested is a partially failed laminated metal tension-twist strip;

[0007] Step 2: Set the test number m to 1, and apply a centrifugal static load Fc and an initial alternating torsion angle θ to the tension-torsion strip to be tested;

[0008] Step 3, perform N load cycles, and when the torsion bar to be tested is not disconnected, obtain the new torsional stiffness E' of the torsion bar to be tested, and determine whether (EE') / E is greater than 10%; if so, proceed to step 4; if not, proceed to step 5; the value of N is a positive integer;

[0009] Step 4: Obtain fatigue performance S based on the number of tests m and alternating torsion angle ∞ ; According to fatigue performance S ∞ , obtain the safe high cycle fatigue life of the tension and torsion strip damage;

[0010] Step 5: Increase the number of tests m by 1, increase the alternating torsion angle by a preset angle, and proceed to step 3.

[0011] Optionally, fatigue performance S can be obtained based on the number of tests and alternating torsion angle ∞ ,include:

[0012] According to the number of tests and the alternating torsion angle, the fatigue performance S is obtained using the following formula ∞ ;

[0013]

[0014] Among them, A and α are the shape parameters of the SN curve of the tension-twist strip material, S aj is the alternating torsion angle in the jth test; j is a positive integer from 1 to m, S ∞ For fatigue performance.

[0015] Optional, according to fatigue performance S ∞ , obtain the safe high cycle fatigue life of the tension and torsion strip, including:

[0016] According to fatigue performance S ∞ and fatigue strength reduction factor Jp to obtain the safety fatigue limit S of the tension-torsion bar to be tested ∞ ';

[0017] According to the calculated load spectrum or measured load spectrum of the tension-torsion bar to be tested, and the safety fatigue limit S ∞ ', obtain the damage safe high cycle fatigue life of the tension-torsion strip to be tested.

[0018] Optional, safety fatigue limit S ∞ ' = S ∞ / Jp.

[0019] Optionally, the preset angle is 3°.

[0020] Optionally, obtaining the torsional stiffness E of the tension-torsion strip to be tested includes:

[0021] Apply a centrifugal static load Fc to the tension-torsion strip to be tested;

[0022] Apply M alternating torsion angles of gradually increasing preset angles to the tension-torsion bar to be tested, and measure the torque at each alternating torsion angle; the value of M is a positive integer;

[0023] The torsional stiffness E is obtained according to each alternating torsion angle and the corresponding torque.

[0024] Optionally, the method further includes:

[0025] Apply centrifugal static load Fc and initial alternating torsion angle θ to the tension-twist strip with complete structure, and perform N load cycles to determine whether the tension-twist strip is damaged. If no damage occurs, increase the alternating torsion angle by a preset angle, and perform N load cycles again until the tension-twist strip is damaged, thereby obtaining the tension-twist strip to be tested.

[0026] A second aspect of the present invention provides a device for determining the breakage safety high-cycle fatigue life of a stacked metal torsion strip, which is used to execute a method as described in any one of the first aspects.

[0027] The present invention proposes a method and device for determining the safe high-cycle fatigue life of a stacked metal torsion strip, which can be used to calculate the high-cycle fatigue life of the metal stacked torsion strip after partial failure of the torsion sheet, and can provide a basis for calculating the high-cycle fatigue life of the stacked torsion strip of a helicopter after partial failure of the torsion sheet. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 The structure of the tension and twist strip to be tested is shown in Fig. Figure 1 ;

[0029] Figure 2 The structure of the tension and twist strip to be tested is shown in Fig. Figure 2 ;

[0030] Figure 3 Schematic diagram of the loading of the tension-torsion strip to be tested. DETAILED DESCRIPTION

[0031] The technical solution of the method for determining the breakage safety high-cycle fatigue life of the stacked metal torsion strip provided by the present invention is explained below in conjunction with the accompanying drawings.

[0032] like Figure 1-3 The present invention proposes a method for determining the damage safety high cycle fatigue life of a laminated metal torsion strip, comprising the following steps:

[0033] Step 1, obtaining the initial torsional stiffness E of the tension-twist strip to be tested; the tension-twist strip to be tested is a partially failed laminated metal tension-twist strip;

[0034] Step 2: Set the test number m to 1, and apply a centrifugal static load Fc and an initial alternating torsion angle θ to the tension-torsion strip to be tested;

[0035] Step 3, perform N load cycles, and when the torsion bar to be tested is not disconnected, obtain the new torsional stiffness E' of the torsion bar to be tested, and determine whether (EE') / E is greater than 10%; if so, proceed to step 4; if not, proceed to step 5; the value of N is a positive integer;

[0036] Step 4: Obtain fatigue performance S based on the number of tests m and alternating torsion angle ∞ ; According to fatigue performance S ∞ , obtain the safe high cycle fatigue life of the tension and torsion strip damage;

[0037] Step 5: Increase the number of tests m by 1, increase the alternating torsion angle by a preset angle, and proceed to step 3.

[0038] In a specific embodiment, the present invention provides a method for determining the damage safety high cycle fatigue life of a laminated metal torsion strip, comprising:

[0039] S1. Determination of torsional stiffness of the tension and torsion strip before the test. Before the fatigue test, the torsional stiffness of the tension and torsion strip with a complete structure is first measured. The measurement method is: apply the centrifugal static load required by the test to the fatigue test piece, and then calibrate the torsion angle step by step according to 0, 3, 6, 9, 12 degrees (and so on), determine the relationship between torque and torsion angle, and thus obtain the torsional stiffness E1 of the tension and torsion strip.

[0040] S2. Fatigue test of the tension-torsion strip with complete structure. The tension-torsion strip test piece with complete structure is installed on the test bench to simulate the actual installation state, and the centrifugal static load Fc and the first initial alternating torsion angle θ are applied to the tension-torsion strip. If the tension-torsion strip is not damaged after every 500,000 load cycles, the alternating torsion angle is increased by 3° and the test is continued until the tension-torsion strip breaks, and the test is stopped.

[0041] S3. Determination of torsional stiffness after failure of some of the torsion strips. Determination of torsional stiffness of the torsion strips after the torsion strips are broken is performed according to the method in step S1, and the torsional stiffness E at this time is recorded.

[0042] S4, fatigue test of the torsion bar after some torsion plates fail. The torsion bar test piece after some torsion plates fail is installed on the test bench to simulate the actual installation state, and the centrifugal static load Fc and the second initial alternating torsion angle θ are applied to the torsion bar according to the method in step S2.

[0043] S5. Torsional stiffness measurement during the test. After every 500,000 load cycles, the torsional stiffness of the tension and torsion strip test piece is measured, and the torsional stiffness value E' is recorded each time. When (EE') / E>10%, the test is stopped and the number of tests is recorded. Otherwise, the alternating torsion angle is increased by 3° and the test is continued until the test stop condition is met.

[0044] S6. Calculation of fatigue performance of torsion strips. According to the fatigue test of torsion strips after some torsion strips fail, the alternating torsion angles θ at different levels are calculated. i (i=1,2,3……) and the number of load cycles n experienced by the corresponding torsion angle i (i=1,2,3……) Calculate fatigue performance S ∞ .

[0045] S7, fatigue performance reduction of the torsion bar. According to the number of test pieces, a certain confidence level γ and survival rate p are used to take the fatigue strength reduction factor Jp, and the calculated fatigue performance in S6 is reduced to obtain the safety fatigue limit S of the torsion bar. ∞ ', the formula is as follows:

[0046] S ∞ ' = S ∞ / Jp

[0047] S8, damage safety high cycle fatigue life calculation. According to the load spectrum calculated by the tension and torsion bar or the measured load spectrum, combined with the safety fatigue limit S obtained in S7 ∞ ', the safe high-cycle fatigue life of the tension-torsion strip can be obtained.

[0048] For example, a plurality of torsion strips are usually provided on the same helicopter. For a damaged torsion strip, only one of them needs to be selected and the method provided by the present invention is adopted to obtain the damage safe high-cycle fatigue life, which can be used as the damage safe high-cycle fatigue life of the torsion strip of the same helicopter / helicopter of the same model / with the same service time / and the same degree of damage.

Claims

1. A method for determining the damage safety high cycle fatigue life of a laminated metal tension and torsion strip, characterized in that: The following steps are involved: Step 1: Obtain the initial torsional stiffness E of the tension-torsion strip to be tested; The tension-twist strip to be tested is a partially failed laminated metal tension-twist strip; Step 2: Set the test number m to 1, and apply a centrifugal static load Fc and an initial alternating torsion angle θ to the tension-torsion strip to be tested; Step 3: Perform N load cycles, and when the tension-twist strip to be tested is not disconnected, obtain a new torsional stiffness E' of the tension-twist strip to be tested, and determine whether (EE') / E is greater than 10%; If yes, go to step 4; if no, go to step 5; the value of N is a positive integer; Step 4: Obtain fatigue performance S based on the number of tests m and alternating torsion angle ∞ ; According to fatigue performance S ∞ , obtain the safe high cycle fatigue life of the tension and torsion strip damage; Step 5: Increase the number of tests m by 1, increase the alternating torsion angle by a preset angle, and proceed to step 3.

2. The method for determining the damage safety high cycle fatigue life of laminated metal tension and torsion strips according to claim 1 is characterized in that: Obtain fatigue performance S based on the number of tests and alternating torsion angle ∞ ,include: According to the number of tests and the alternating torsion angle, the fatigue performance S is obtained using the following formula ∞ ; Among them, A and α are the shape parameters of the SN curve of the tension-twist strip material, S aj is the alternating torsion angle in the jth test; j is a positive integer from 1 to m, S ∞ For fatigue performance.

3. The method for determining the damage safety high cycle fatigue life of laminated metal tension and torsion strips according to claim 1 is characterized in that: According to fatigue performance S ∞ , obtain the safe high cycle fatigue life of the tension and torsion strip, including: According to fatigue performance S ∞ and fatigue strength reduction factor Jp to obtain the safety fatigue limit S of the tension-torsion bar to be tested ∞ '; According to the calculated load spectrum or measured load spectrum of the tension-torsion bar to be tested, and the safety fatigue limit S ∞ ', obtain the damage safe high cycle fatigue life of the tension-torsion strip to be tested.

4. The method for determining the damage safety high cycle fatigue life of a laminated metal tension and torsion strip according to claim 3 is characterized in that: Safety fatigue limit S ∞ ' = S ∞ / Jp.

5. The method for determining the damage safety high cycle fatigue life of laminated metal tension and torsion strips according to claim 1, characterized in that: The torsional stiffness E of the tension-torsion strip to be tested is obtained by: Apply a centrifugal static load Fc to the tension-torsion strip to be tested; Apply M alternating torsion angles of gradually increasing preset angles to the tension-torsion bar to be tested, and measure the torque at each alternating torsion angle; the value of M is a positive integer; The torsional stiffness E is obtained according to each alternating torsion angle and the corresponding torque.

6. The method for determining the damage safety high cycle fatigue life of laminated metal tension and torsion strips according to claim 1, characterized in that: The method further comprises: Apply centrifugal static load Fc and initial alternating torsion angle θ to the tension-twist strip with complete structure, and perform N load cycles to determine whether the tension-twist strip is damaged. If no damage occurs, increase the alternating torsion angle by a preset angle, and perform N load cycles again until the tension-twist strip is damaged, thereby obtaining the tension-twist strip to be tested.

7. The method for determining the damage safety high cycle fatigue life of a laminated metal tension and torsion strip according to claim 1 is characterized in that: The default angle is 3°.

8. A device for determining the damage safety high cycle fatigue life of a laminated metal torsion strip, characterized in that: Used to perform the method according to any one of claims 1 to 7.

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