Helicopter propeller hub support arm fatigue damage assessment method

Abstract

The invention belongs to the technical field of structural fatigue, and discloses a helicopter propeller hub support arm fatigue damage evaluation method, which comprises the following steps of: 1, acquiring a time history data curve of a propeller hub support arm flapping bending moment Mb and a shimmy bending moment Mt of an evaluation sortie; 2, determining geometric parameters of a propeller hub support arm lug force conversion structure; 3, calculating a time history curve of the upper lug force F1 and the lower lug force F2 of the propeller hub support arm; fourthly, rain flow counting is conducted on the time history curves of the upper lug force F1 and the lower lug force F2, and the alternating loads S1j and the load frequency n1j of all levels of the upper lug force of the propeller hub supporting arm and the alternating loads S2j and the load frequency n2j of all levels of the lower lug force of the propeller hub supporting arm are obtained; 5, determining a propeller hub support arm waving bending moment fatigue limit Mb infinity and a corresponding shimmy bending moment fatigue limit Mt infinity; 6, calculating the fatigue life cycle index N of each stage of fatigue alternating load S; and 7, calculating the damage D1j of the upper lug, calculating the damage D2j of the lower lug, and calculating the total damage of the upper lug and the lower lug of the propeller hub support arm.

Description

Technical Field

[0001] The invention belongs to the technical field of structural fatigue, and in particular relates to a method for evaluating fatigue damage of a helicopter hub arm. Background Art

[0002] Among the main components of a helicopter, the hub arm is extremely important. The hub arm has a complex structure, with one end connected to the blades and the other end connected to other components such as the hub centerpiece. During flight, the helicopter rotor is simultaneously subjected to centrifugal force, flapping shear force, shimming shear force, flapping bending moment, shimming bending moment, and hinge moment. All these loads need to be transmitted through the hub arm, and the fatigue damage assessment of the hub arm is extremely complex. Since the fatigue loads that cause fatigue damage to the hub arm are mainly flapping bending moment and shimming bending moment, the fatigue damage assessment of the hub arm of a helicopter was previously based on the ratio of flapping bending moment / shimming bending moment under typical flight conditions. The fatigue limit of the hub arm with flapping bending moment as the characteristic load was obtained, and then the fatigue damage assessment calculation was performed based on the measured flapping bending moment. This method requires that the flapping load and shimming load frequencies of the actual flight fatigue damage condition of the helicopter hub arm are equivalent, and the actual flight flapping bending moment / shimming bending moment ratio is not much different from the pre-set typical flight condition flapping bending moment / shimming bending moment ratio. The loads of non-rigid rotor hub arms such as articulated and star-shaped flexible ones basically meet this characteristic.

[0003] With the application of rigid rotors in modern helicopters, the ratio of rotor flapping moment to swing bending moment varies greatly under different flight conditions. The error of fatigue damage assessment of hub support arms using only a single typical flapping ratio and flapping bending moment as the characteristic load is large, which is difficult to meet the needs of fatigue damage assessment of rigid rotor hub support arms. Summary of the invention

[0004] Purpose of the invention: The present invention uses the hub arm / blade connection ear force synthesized in time by the flapping bending moment and the swing bending moment as the characteristic load for fatigue damage assessment, which overcomes the deviation caused by the inaccurate corresponding swing bending moment when only the flapping bending moment is used as the fatigue damage characteristic load for fatigue damage assessment, and realizes more accurate fatigue damage assessment of the helicopter hub arm.

[0005] Technical Solution

[0006] A method for assessing fatigue damage of a helicopter hub arm comprises the following steps:

[0007] Step 1: Collect the time domain data of the flapping bending moment and the shimmying bending moment of the hub support arm / blade interface, and obtain the time history data curve of the hub support arm flapping bending moment Mb and the time history data curve of the shimmying bending moment Mt of the evaluated sorties;

[0008] Step 2: Determine the geometric parameters of the hub arm ear force conversion structure, the horizontal spacing d between the arm / blade connection ear hole centers and the vertical spacing h between the arm / blade connection ear hole centers;

[0009] Step 3: Take the flapping bending moment Mb i and the shimmying bending moment Mt i at time point i, calculate the upper ear force and the lower ear force of the hub support arm, traverse the time history data curve of the flapping bending moment Mb and the shimmying bending moment Mt of the hub support arm, and obtain the time history curves of the upper ear force F1 and the lower ear force F2;

[0010] Step 4: Count the rain flow of the time history curves of the upper ear force F1 and the lower ear force F2 respectively, set the counting threshold with reference to the fatigue limit of the arm, and obtain the alternating loads S1j and load frequencies n1j of the upper ear force of the hub arm, and the alternating loads S2j and load frequencies n2j of the lower ear force at all levels;

[0011] Step 5: Full-size hub support arm ground bench fatigue test to determine the hub support arm flapping moment fatigue limit Mb - and the corresponding shimmy bending moment fatigue limit Nt ∞ , calculated and converted into the fatigue limit S of the hub arm represented by the lug force ∞ ;

[0012] Step 6: Calculate the fatigue life cycle number N of each level of fatigue alternating load S according to the SN curve formula;

[0013] Step 7: According to the linear cumulative damage theory, calculate the damage D1j of the upper ear, calculate the damage D2j of the lower ear, calculate the total damage of the upper and lower ears of the hub support arm, and determine the total damage of the hub support arm.

[0014] Furthermore, in step one, the data collection starts when the helicopter is powered on on the ground and ends when the power is turned off after landing. The start time of the data collection of the flapping bending moment and the swing bending moment time domain data is the same, and the sampling rate is the same.

[0015] Furthermore, in step 2, the geometric parameters of the ear piece force calculation conversion structure are the horizontal spacing between the centers of the arm / blade connecting ear holes and the vertical spacing between the centers of the arm / blade connecting ear holes.

[0016] Further, in step 3, the calculation process of the upper ear piece force F1 i is as follows:

[0017]

[0018] The calculation process of the lower ear force F2 i is as follows:

[0019]

[0020] Furthermore, in step 4, the rain flow counting method is used to process the time history curves of the upper ear force F1 and the lower ear force F2, and the counting threshold is set with reference to the fatigue limit of the arm to obtain the fatigue alternating loads S1j and load frequencies n1j of the upper ear force of the hub arm, and the fatigue alternating loads S2j and load frequencies n2j of the lower ear force of the hub arm.

[0021] Furthermore, in step 5, the fatigue limit of the hub arm represented by the ear force is S The calculation process of ∞ is as follows:

[0022]

[0023] Further, in step 6, the calculation formula of the fatigue life cycle number N1j of the upper ear piece and the fatigue life cycle number N2j of the lower ear piece are the same, which is as follows:

[0024]

[0025] Furthermore, in step 7, the calculation process of the upper ear damage and the lower ear damage is the same, and the formula is as follows:

[0026]

[0027] The total damage of the upper ear piece is equal to the sum of all D1j; the total damage of the lower ear piece is equal to the sum of all D2j.

[0028] In summary, the beneficial effects of the present invention are as follows:

[0029] The use of the present invention to evaluate the fatigue damage of a helicopter hub arm can overcome the deviation caused by the inconsistency between the corresponding moment and the flapping moment / swing moment ratio of a typical flight state selected by a ground fatigue test, which exists in the previous fatigue damage evaluation method of the hub arm using only the flapping moment as the characteristic load, thereby improving the accuracy of the fatigue durability design and evaluation of the helicopter hub arm. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 It is the typical time history data curve of swinging bending moment Mb.

[0031] Figure 2 It is the typical time history data curve of the shimmy bending moment Mt.

[0032] Figure 3 This is a schematic diagram of the typical structure of the hub support arm.

[0033] Figure 4 This is a typical time history data curve of the ear force F1 on the hub support arm.

[0034] Figure 5 This is the typical time history data curve of the lug force F2 under the hub support arm. DETAILED DESCRIPTION

[0035] A fatigue damage assessment method for helicopter hub arms that combines the combined effects of flapping moment and swing moment is different from the previous hub arm fatigue damage assessment method that uses flapping moment as the characteristic load. It uses the hub arm / blade connection ear force synthesized from the time domain data of flapping moment and swing moment as the characteristic load for fatigue damage assessment. It has important application value for the fatigue durability design of rigid rotors with extremely large swing ratio changes, and can also more accurately assess the fatigue damage of non-rigid rotor hub arms with little difference in swing ratio under typical working conditions. The specific steps are as follows:

[0036] Step 1: By calibrating the measured flight load on the hub arm patch of the target helicopter, the flapping moment and the swing bending moment time domain data of the hub arm / blade interface are obtained.

[0037] It is determined that the flapping bending moment and the shimmying bending moment have the same starting time and the same sampling rate. The data are collected from the time the helicopter is powered on and the time the power is turned off after landing. The time history curves of the hub arm flapping bending moment Mb (unit Nm) and the shimmying bending moment Mt (unit Nm) are obtained, as shown in Figure 2. Figure 1 and Figure 2 As shown, it is used for hub arm fatigue damage assessment.

[0038] Step 2: Refer to the hub arm design drawings and measure the actual structure to obtain the structural geometric parameters used to convert the flapping bending moment Mb and the swing bending moment Mt of the hub arm / blade interface into the hub arm upper ear force F1 and the lower ear force F2.

[0039] The connection between the hub arm and the blade of a typical helicopter generally adopts a double-pin structure. The flapping bending moment and the swing bending moment of the hub arm / blade interface are transmitted to the hub arm through the arm ear hole by double-pin shear. Figure 3 As shown, d is the horizontal distance between the centers of the arm / blade connection ear holes (unit: m), and h is the vertical distance between the centers of the arm / blade connection ear holes (unit: m).

[0040] Step 3: The flapping bending moment Mb and the swing bending moment Mt of the hub support arm are calculated and converted into the upper ear force F1 and the lower ear force F2 of the hub support arm.

[0041] Take the flapping bending moment Mbi and the shimmying bending moment Mti at time point i, calculate the upper ear force F1i and the lower ear force F2i of the hub support arm according to formula (1) and formula (2) respectively, traverse the time history curve of the flapping bending moment Mb and the shimmying bending moment Mt of the hub support arm, and obtain the time history curves of the upper ear force F1 and the lower ear force F2 respectively, as shown in Figure 4 and Figure 5 shown.

[0042]

[0043]

[0044] Step 4: Use the rain flow counting method to process the load time history curve into a series of fatigue alternating loads S and their corresponding frequency n load spectra for fatigue damage accumulation calculation according to the linear damage theory.

[0045] The time history curves of the upper ear force F1 and the lower ear force F2 of the hub arm are processed by rain flow counting respectively, and the counting threshold is set according to the fatigue limit of the arm to obtain the fatigue alternating loads S1j and load frequencies n1j of the upper ear force of the hub arm, and the fatigue alternating loads S2j and load frequencies n2j of the lower ear force of the hub arm.

[0046] Step 5. Obtain the flapping bending moment fatigue limit and swing bending moment fatigue limit of the hub support arm through a full-size hub support arm ground bench fatigue test, determine the fatigue performance of the hub support arm, and calculate and convert it into the corresponding arm ear force, so as to calculate the fatigue damage accumulation of the hub support arm according to the linear damage theory.

[0047] With reference to the load spectrum calculated for the target helicopter rotor, based on the ratio of flapping moment to shimmy moment under typical flight conditions, fatigue test loads such as centrifugal force, flapping shear force, shimmy shear force, flapping moment, shimmy moment, and torque were applied in the hub support arm ground bench fatigue test to obtain the hub support arm flapping moment fatigue limit Mb verified by the fatigue test. ∞ (Unit: Nm) and the corresponding shimmy bending moment fatigue limit Mt ∞ (Unit: Nm), and the hub arm fatigue limit s represented by the arm ear force is calculated according to formula (3): ∞ (Unit N).

[0048]

[0049] Step 6: According to the SN curve formula, calculate the fatigue life cycle number N corresponding to each level of fatigue alternating load S, so as to be used for the subsequent calculation of the fatigue damage of each level of alternating load of the measured load.

[0050] Calculate the fatigue life cycles corresponding to the upper ear force and the lower ear force according to formula (4), and substitute any level of upper ear force load S1j or lower ear force load S2j obtained in step 4 into the formula S, S ∞ is the fatigue limit of the hub arm ear force obtained in step 5, and A and α are the SN curve shape parameters determined by the fatigue test of a small specimen of the same material of the arm. The fatigue life cycle number N1j(10 corresponding to each level of fatigue alternating load of the upper ear force is calculated. 6 times) and the fatigue life cycles N2j (10 6 times), see Table 1 and Table 2.

[0051]

[0052] Step 7: According to the linear cumulative damage theory, the load frequency n divided by the fatigue life cycle number N is the corresponding damage D. The damage value of each level of alternating load is numerically accumulated to obtain the total damage value.

[0053] According to formula (5), the fatigue damage value D1j corresponding to each level of alternating load of the upper ear force and the fatigue damage value D2j corresponding to each level of alternating load of the lower ear force are calculated respectively. After accumulating the damage at each level, the total damage D1 of the upper ear and the total damage D2 of the lower ear are obtained respectively, as shown in Table 1 and Table 2.

[0054]

[0055] Table 1 Alternating load / frequency and damage value / total damage of the lug force on the hub support arm

[0056] Load level Alternating load S(N) Load frequency n(times) <![CDATA[Number of fatigue life cycles N (10 6 times)]]> Damage D 1 S11 N11 N11 D11 2 S12 N12 N12 D12 … … … … … j S1j N1j N1j D1j … … … … … Total damage to the upper ear D1 --- --- --- ∑

[0057] Table 2 Alternating load / frequency and damage value / total damage of the lug force under the hub support arm

[0058] Load level Alternating load S(N) Load frequency n(times) <![CDATA[Number of fatigue life cycles N (10 6 times)]]> Damage D 1 S21 n21 N21 D21 2 S22 n22 N22 D22 … … … … … j S2j n2j N2j D2j … … … … … Total damage to lower ear piece D2 --- --- --- ∑

[0059] The method of the present invention is further described in detail below in conjunction with an embodiment. A method for evaluating fatigue damage of a helicopter hub arm is characterized by the following steps:

[0060] Step 1: Calibrate the hub arm patch of the target helicopter. Measure the flapping moment and shimmy moment of the hub arm / blade interface. The sampling rate is 1024 Hz. Start collecting data when the helicopter is powered on and end when the power is turned off after landing. Get the time history curves of the hub arm flapping moment Mb (unit Nm) and shimmy moment Mt (unit Nm), see Figure 1 and Figure 2 .

[0061] Step 2: Referring to the propeller hub arm design drawings and measuring the actual structure, the propeller hub arm / blade interface flapping moment Mb and shimmy moment Mt are calculated and converted into the structural geometric parameters of the propeller hub arm upper ear force F1 and lower ear force F2, as shown in Figure 2. Figure 3 The horizontal spacing between the centers of the arm / blade connection ear holes is d = 0.150m, and the vertical spacing between the centers of the arm / blade connection ear holes is h = 0.180m.

[0062] Step 3: Press Japanese style The time history curves of the hub arm flapping bending moment Mb and the shimmying bending moment Mt are converted into the time history curves of the upper ear force F1 and the lower ear force F2, see Figure 4 and Figure 5 .

[0063] Step 4: Use the rain flow counting method to process the time history curves of the upper ear force F1 and the lower ear force F2 into a series of fatigue alternating loads S and their corresponding frequency n load spectra for fatigue damage accumulation calculation according to the linear damage theory. The counting threshold is set to 10000N, see Table 3 and Table 4.

[0064] Step 5: Obtain the hub support arm flapping moment fatigue limit Mb from the full-size hub support arm ground bench fatigue test ∞ =4635Nm and the corresponding shimmy bending moment fatigue limit Mt ∞ = 618Nm, calculate the fatigue limit of the hub arm represented by the arm ear force

[0065] Step 6: Substitute the upper ear load S1j and the lower ear load S2j at each level into the SN curve formula Calculate the corresponding fatigue life cycle numbers N1j and N2j, see Table 3 and Table 4, the hub arm ear force fatigue limit s ∞ =14935N, SN curve shape parameters A=0.01 and α=0.805.

[0066] Step 7. Divide the load frequency n by the number of fatigue life cycles N to calculate the fatigue damage value corresponding to each level of alternating load. The total damage is obtained by accumulating the damage at each level, see Table 3 and Table 4.

[0067] Table 3 Alternating load / frequency and damage value / total damage of the ear force on the hub support arm

[0068]

[0069]

[0070] Table 4 Alternating load / frequency and damage value / total damage of the lug force under the hub support arm

[0071]

[0072]

Claims

1. A method for assessing fatigue damage of a helicopter hub arm, characterized in that: The following steps are involved: Step 1: Collect the time domain data of the flapping bending moment and the shimmying bending moment of the hub support arm / blade interface, and obtain the time history data curve of the hub support arm flapping bending moment Mb and the time history data curve of the shimmying bending moment Mt of the evaluated sorties; Step 2: Determine the geometric parameters of the hub arm ear force conversion structure, the horizontal spacing d between the arm / blade connection ear hole centers and the vertical spacing h between the arm / blade connection ear hole centers; Step 3: Take the flapping bending moment Mbi and the shimmying bending moment Mti at time point i, calculate the upper ear force and the lower ear force of the hub support arm, traverse the time history data curve of the flapping bending moment Mb and the shimmying bending moment Mt of the hub support arm, and obtain the time history curves of the upper ear force F1 and the lower ear force F2; Step 4: Count the rain flow of the upper ear force F1 and the lower ear force F2 time history curves respectively, set the counting threshold with reference to the arm fatigue limit, and obtain the alternating loads S1j and load frequencies n1j of the upper ear force of the hub arm, and the alternating loads S2j and load frequencies n2j of the lower ear force of the hub arm; Step 5: Full-size hub support arm ground bench fatigue test to determine the hub support arm flapping moment fatigue limit Mb ＝ and the corresponding shimmy bending moment fatigue limit Mt ∞ , calculated and converted into the fatigue limit S of the hub arm represented by the lug force ∞ ; Step 6: Calculate the fatigue life cycle number N of each level of fatigue alternating load S according to the SN curve formula; Step 7: According to the linear cumulative damage theory, calculate the damage D1j of the upper ear, calculate the damage D2j of the lower ear, calculate the total damage of the upper and lower ears of the hub support arm, and determine the total damage of the hub support arm.

2. The method according to claim 1, characterized in that: In step 1, the data collection starts when the helicopter is powered on on the ground and ends when the power is turned off after landing. The start time of the flapping bending moment and the shimmy bending moment time domain data collection is the same, and the sampling rate is the same.

3. The method according to claim 2, characterized in that: In step 2, the geometric parameters of the ear piece force conversion structure are the horizontal spacing between the centers of the arm / blade connecting ear holes and the vertical spacing between the centers of the arm / blade connecting ear holes.

4. The method according to claim 3, characterized in that: In step 3, the calculation process of the upper ear force F1i is as follows: The calculation process of the lower ear force F2i is as follows:

5. The method according to claim 4, characterized in that: In step 4, the rain flow counting method is used to process the time history curves of the upper ear force F1 and the lower ear force F2, and the counting threshold is set with reference to the fatigue limit of the arm to obtain the fatigue alternating loads S1j and load frequencies n1j of the upper ear force of the hub arm, and the fatigue alternating loads S2j and load frequencies n2j of the lower ear force of the hub arm.

6. The method according to claim 5, characterized in that: In step 5, the fatigue limit S of the hub arm represented by the lug force is ∞ The calculation process is as follows:

7. The method according to claim 6, characterized in that: In step 6, the calculation formula for the fatigue life cycle number N1j of the upper ear piece and the fatigue life cycle number N2j of the lower ear piece are the same, which is as follows:

8. The method according to claim 7, characterized in that: In step 7, the calculation process of upper ear damage and lower ear damage is the same, and the formula is as follows: The total damage of the upper ear piece is equal to the sum of all D1j; The total damage of the lower ear is equal to the sum of all D2j.

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