A method for compiling an upper platform test load spectrum

Abstract

The present application belongs to the field of helicopter fatigue test design, and relates to a method for preparing an upper platform test load spectrum. The method comprises: completing task section division according to task requirements and flight states in a helicopter mission profile; sorting non-deterministic states in each task section according to randomness principles; listing corresponding calculated loads for the sorted states, and performing rainflow to obtain a preliminary test low-cycle load spectrum; preparing a low-cycle load spectrum based on the task profile according to measured load data of key parts on the upper platform, and preparing a high-cycle load spectrum based on state rainflow to obtain measured high-cycle and low-cycle load spectra; comparing high-cycle and low-cycle damage ratios under the life requirement of the upper platform based on the measured high-cycle and low-cycle load spectra to obtain high-cycle and low-cycle load ratios; and amplifying the loads in the preliminary low-cycle load spectrum according to the ratios to obtain a test load spectrum considering high-cycle damage.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of helicopter fatigue test design, and relates to a method for preparing an upper platform test load spectrum. BACKGROUND

[0002] The helicopter mission profile is various, and the use is flexible. Most of the machine parts bear low cycle loads caused by take-off and landing and state conversion, and also bear high cycle loads caused by rotating parts such as rotors and tail rotors. Especially in the rotor installation area (such as the upper platform and the tail reduction installation platform), the above load characteristics are more obvious. Therefore, the traditional load spectrum preparation method mainly considering low cycle load cycles needs to be appropriately modified.

[0003] On the other hand, although the helicopter has been load tested, the test data is difficult to cover all the loads required by the upper platform test, which requires that the load spectrum preparation process of the upper platform test needs to modify the calculated load with the measured load data to obtain a test load spectrum that meets the actual use.

[0004] At present, there is no corresponding method to modify the test load spectrum. SUMMARY

[0005] The application provides a fatigue test load spectrum preparation method for the upper platform, which combines the use characteristics and load characteristics of the helicopter, and solves the problem of load spectrum preparation of the upper platform components of the helicopter.

[0006] TECHNICAL SCHEME

[0007] The application provides an upper platform test load spectrum preparation method, which comprises the following steps:

[0008] According to the task requirements and flight states in the helicopter mission profile, the task section division is completed;

[0009] For each non-deterministic state in the task section, the states are sorted according to the randomness principle; the corresponding calculated load is listed for the above sorted states, and the rain flow is performed to obtain a preliminary test low cycle load spectrum;

[0010] According to the measured load data of the key parts of the upper platform, the low cycle load spectrum is prepared based on the mission profile, the high cycle load spectrum is prepared based on the state rain flow, and the measured high and low cycle load spectrums are obtained;

[0011] Based on the measured high and low cycle load spectrums, the high and low cycle damage ratios under the upper platform life requirement are compared to obtain the high and low cycle load ratios; the loads in the preliminary low cycle load spectrum are amplified according to the ratio to obtain a test load spectrum considering the high cycle damage.

[0012] Further, for each non-deterministic state in the task section, the states are sorted according to the randomness principle, which comprises the following steps:

[0013] For any task segment, the deterministic states in the task segment are sorted according to the occurrence sequence;

[0014] For the non-deterministic states in the task segment, the states are first refined according to the flight profile to obtain n non-deterministic refined states, and for a non-deterministic state, one parameter in the non-deterministic refined state changes linearly and other parameters remain unchanged;

[0015] According to the load, the n non-deterministic refined states are sorted according to the low-high-low principle to obtain the non-deterministic state sequence.

[0016] Further, the rain flow is performed to obtain the preliminary test low-cycle load spectrum, including:

[0017] First, the loads of the deterministic states are put into the load sequence according to the sorting order of the deterministic states of each task segment, and the loads of the non-deterministic states are also put into the load sequence according to the sorting order of the non-deterministic states of each task segment;

[0018] The above load sequence is rain flow counted; if the i-th dynamic load is 1 / 10 of the maximum dynamic load, it is discarded and not counted in the load cycle, thereby obtaining the preliminary test low-cycle load spectrum.

[0019] Further, based on the task profile, a low-cycle load spectrum is compiled, and a high-cycle load spectrum is compiled based on the rain flow within the state, including:

[0020] Select the load measured data of the key points on the platform, after data conversion, deburring and other cleaning procedures, take the mean value of each state and the dynamic load to perform rain flow, and obtain the rain flow counting result under each state;

[0021] According to the time proportion of each state formed by the task profile, the frequency in the rain flow counting result under each state is converted into the frequency under the flight profile.

[0022] Further, for the i-th state, the frequency n_s i,j under the flight profile is calculated according to the following formula:

[0023]

[0024] n_f i,j is the load frequency in the rain flow counting result; p i is the time proportion of the i-th state; t i is the completion time of the i-th state under the measured flight, and j is the order.

[0025] Further, based on the measured high and low cycle load spectrum, the high and low cycle damage ratio under the platform life requirement is compared to obtain the high and low cycle load ratio; the load in the preliminary low cycle load spectrum is enlarged according to the ratio to obtain the test load spectrum considering high cycle damage, including:

[0026] Calculating the load cycle in the load spectrum to the allowable number of times N i , calculating the high and low cycle life L under the fatigue property h And L l , so as to calculate the high and low cycle damage ratio k;

[0027] According to the high and low cycle damage ratio k, the high cycle load spectrum is equivalent to the low cycle load spectrum, so as to obtain the test load spectrum considering the high cycle damage.

[0028] Further, according to the high and low cycle damage ratio k, the high cycle load spectrum is equivalent to the low cycle load spectrum, so as to obtain the test load spectrum considering the high cycle damage, comprising:

[0029] When k is less than the preset threshold, the load frequency in the test low cycle spectrum is kept unchanged, the low cycle load is amplified by 1+k times, so as to obtain the test load spectrum considering the high cycle damage.

[0030] Further, according to the high and low cycle damage ratio k, the high cycle load spectrum is equivalent to the low cycle load spectrum, so as to obtain the test load spectrum considering the high cycle damage, comprising:

[0031] When k is greater than or equal to the preset threshold, the fatigue limit is amplified by 1+k times, and the corresponding life is searched and taken;

[0032] According to the amplification formula, the load frequency amplification coefficient k" is calculated, and the amplification formula is:

[0033]

[0034] Wherein, L' is the life corresponding to the amplified fatigue limit, and L is the life corresponding to the fatigue limit before amplification;

[0035] The low cycle load is kept unchanged, and the low cycle load frequency is amplified by k" times, so as to obtain the test load spectrum considering the high cycle damage.

[0036] Beneficial effects:

[0037] The helicopter platform load spectrum compilation method is designed, the problem of verifying the life of the component bearing high and low cycle load by low cycle test method is solved, and a solution is provided for subsequent similar structure test load spectrum compilation. BRIEF DESCRIPTION OF DRAWINGS

[0038] Figure 1 It is a test load spectrum compilation process schematic diagram.

[0039] Figure 2 It is a task segment division schematic diagram.

[0040] Figure 3 It is a schematic diagram of the task profile low cycle spectrum.

[0041] Figure 4 is the schematic diagram of maximum and minimum values of the flat flight (H = 900 m, V = 150 km / h, side slip 0°) state.

[0042] Figure 5 is the fatigue limit-life relationship diagram under the high and low cycle load spectrum of the upper platform M1.

[0043] Figure 6 is the schematic diagram of the test spectrum. DETAILED DESCRIPTION

[0044] A method for preparing an upper platform test load spectrum, characterized in that, according to a helicopter mission profile, mission segments are divided and deterministic states are sorted; for each non-deterministic state in the mission segment, the states are sorted according to the randomness principle; the states in the above sorting are listed corresponding to the calculated load, and rainflow is performed to obtain a preliminary test low cycle load spectrum; according to the measured load data of the key parts of the upper platform, a low cycle load spectrum is prepared based on the mission profile, a high cycle load spectrum is prepared by rainflow within the state, and the measured high and low cycle load spectrum is obtained; based on the measured high and low cycle load spectrum, the high and low cycle damage ratio under the life requirement of the upper platform is compared to obtain the high and low cycle load ratio; the load in the preliminary low cycle load spectrum of the upper platform is amplified according to the ratio to obtain a test load spectrum considering high cycle damage. The specific steps are shown in the attached Figure 1 , and briefly described as follows:

[0045] [1] According to the mission profile, the mission segments are divided

[0046] According to the mission requirements and flight states in the mission profile, states with obvious distinction are merged and aggregated to form mission segments.

[0047] [2] Sort the states in the mission segment by category

[0048] For each deterministic state in the mission segment, the states are sorted according to the occurrence; for each non-deterministic state in the mission segment, the states are sorted according to the randomness principle.

[0049] [3] List the loads and perform rainflow to obtain a test low cycle spectrum

[0050] List the corresponding loads of all sorted states and process them according to the rainflow calculation method, eliminate the load cycles that do not constitute damage, and obtain a test low cycle spectrum.

[0051] [4] Obtain a low cycle load spectrum according to the measured load of the key parts

[0052] Using the measured load data of the key components, after data cleaning, taking the maximum and minimum values of each state, according to the low cycle state sequence formed in step 2, a low cycle measured load spectrum is obtained.

[0053] [5] Obtain high cycle load spectrum according to key position measured load

[0054] After data cleaning, take the mean of each state and then rain flow the dynamic load, obtain the high cycle measured load spectrum according to the state time proportion formed by the mission profile.

[0055] [6] Obtain high and low cycle damage ratio according to the upper platform life requirement

[0056] Using the full range S-N curve, calculate the fatigue limit-life relationship under the high and low cycle measured load spectrum of the key position, respectively, calculate the life under the high and low cycle measured load spectrum with the same fatigue limit, until the total life meets the upper platform life requirement, at this time, obtain the high and low cycle damage ratio.

[0057] [7] Correct the test low cycle spectrum and obtain the upper platform test spectrum

[0058] The damage ratio obtained in the previous step is the contribution of the high cycle load to the total damage, consider the damage ratio in the low cycle spectrum fatigue limit-life relationship diagram, obtain the low cycle load amplification coefficient, and finally obtain the upper platform test spectrum.

[0059] Example 1

[0060] The following embodiment of the preparation of the upper platform test load spectrum of a certain type of aircraft will be further described in detail. The test steps are as follows:

[0061] [1] Divide the mission section according to the mission profile

[0062] According to the mission profile of this type, the following principles are used to divide the continuous states with obvious differences into mission sections:

[0063] 1) The states such as altitude and speed have obvious differences; the difference in altitude is less than the preset altitude difference, and the difference in speed is less than the preset speed difference;

[0064] 2) The purpose is obviously different;

[0065] Figure 2 This flight profile is divided into hovering, climbing, cruising, maneuvering and descending, a total of 5 mission sections.

[0066] [2] Sort the states in the mission section by category

[0067] First, sort the deterministic states in each mission section according to their occurrence;

[0068] Take the Appendix Figure 2Taking the cruise mission segment as an example, it is required to experience the process of flying-straightening-flying, and the deterministic state and sequence are: flying (H=900 m, V=150 km / h)-straightening (H=900 m, V=150 km / h, straightening slope angle 20°)-flying (H=900 m, V=150 km / h)

[0069] Secondly, for each non-deterministic state S i in each mission segment, the state is refined into S ji according to the flight profile;

[0070] In the above step, the S1 flying (H=900 m, V=150 km / h) state is refined in the flight profile according to the sideslip angle as:

[0071] S 11 flying (H=900 m, V=150 km / h, sideslip 0°)

[0072] S 21 flying (H=900 m, V=150 km / h, sideslip 5°)

[0073] S 31 flying (H=900 m, V=150 km / h, sideslip -5°)

[0074] …

[0075] S 91 flying (H=900 m, V=150 km / h, sideslip -35°)

[0076] Thirdly, for the non-deterministic refined state S ji , the non-deterministic state sequence is obtained according to the load low-high-low principle;

[0077] In the above step, the S1 flying sequence is:

[0078] S 11 flying (sideslip 0°)-S 21 flying (sideslip 5°)-S 11 flying (sideslip 0°)-S 31 flying (sideslip -5°)-…-S 91 flying (sideslip 35°)-…-S 31 flying (sideslip -5°)-S 11 flying (sideslip 0°)-S 21 flying (sideslip 5°)-S 11 flying (sideslip 0°)

[0079] [3] Rainflow is added to the load to obtain the test low-cycle spectrum

[0080] First, the upper platform load is listed according to the order of the previous step state to obtain the load sequence;

[0081] Secondly, the above load sequence is counted by rain flow, and the dynamic load is counted from large to small (F ai ,F si ,n i ), where F ai is the i-th order dynamic load, F si is the i-th order static load, n i is the i-th order frequency. If the i-th order dynamic load F ai If it is 1 / 10 of the first-order dynamic load (i.e., the maximum dynamic load), it will be discarded and not included in the load cycle;

[0082] right Figure 2 Typical mission profiles for rain flow post-load and sequence are shown in the attached Figure 3 shown.

[0083] [4] Obtain low-cycle load spectrum based on measured loads at key locations

[0084] First, the measured load data of the key point M1 on the upper platform is selected. After data conversion, deburring and other cleaning procedures, the maximum and minimum values ​​of each state are taken to obtain the measured quasi-static load of each state. 11 Take level flight (H=900m, V=150km / h, sideslip 0°) as an example. The measured load in this state is shown in the attached figure. Figure 4 As shown, the state low cycle load is:

[0085] F max,11 =552,F min,11 =403

[0086] Secondly, according to the low-frequency state sequence formed in step 2, the low-frequency measured load spectrum is obtained.

[0087] [5] Obtain high cycle load spectrum based on measured loads at key locations

[0088] First, the measured load data of the key point M1 on the upper platform is selected. After data conversion, deburring and other cleaning procedures, the mean value of each state is taken to perform dynamic load rain flow, and the rain flow counting result (F) under each state (i) is obtained. ai,j ,F si,j ,n_f i,j ). 11 Taking level flight (H = 900m, V = 150km / h, sideslip 0°) as an example, the results of high-frequency dynamic load rain flow in this state are shown in Table 1:

[0089] Table 1

[0090] Serial number Dynamic load F ai,j ]] Static load F si,j ]] Frequency n_f i,j ]] 1 0.506001 476.1672 23 2 14.3875 465.2665 1 3 26.9977 485.6625 10 4 34.39417 489.6718 43 5 43.4163 483.9276 10

[0091] Secondly,

[0092]

[0093] where t i is the measured flight time for the state, and p Figure 4 is the proportion of the flight profile for the state S 11 . For the example of steady flight (H = 900 m, V = 150 km / h, sideslip 0°), t i = 1.56 s, and p i = 2.58%. Table 2 is the conversion of Table 1 to the flight profile:

[0094] Table 2

[0095] Serial number Dynamic load F ai,j ]]> Static load F si,j ]]> Frequency n_s i,j ]] 1 0.506001 476.1672 1369 2 14.3875 465.2665 60 3 26.9977 485.6625 595 4 34.39417 489.6718 2560 5 43.4163 483.9276 595

[0096] Finally, the repeated flight states are split, and if a state is repeated m times, then the proportion of the flight profile for each state is p i / m. According to the first two methods, the high-cycle load spectrum of the flight profile is obtained.

[0097] [6] Obtain the high-low cycle damage ratio according to the platform life requirement

[0098] First, assuming the fatigue limit F -1 , the allowable number of cycles N i is calculated for the load cycle (F ai , F si , n i ) in the load spectrum using the following formula.

[0099]

[0100] where A and a are material parameters determined according to the material grade and failure mode.

[0101] Second, the component life L is calculated for the fatigue characteristic using the following formula.

[0102]

[0103] Third, for the measured high and low cycle load spectrum, the corresponding life L is calculated according to different fatigue limits F -1 , and the fatigue limit F -1 -life L relationship under the high and low cycle load spectrum is obtained. The fatigue limit F -1 -life L relationship under the high and low cycle load spectrum at the key point M1 of the platform is shown in FIG. 4. Figure 5

[0104] Fourth, based on the fatigue limit F -1 -life L relationship under the high and low cycle load spectrum, the high and low cycle life L is calculated when the fatigue limit is F -1,i .h,i L l,i Total life is calculated as follows:

[0105]

[0106] Fifth step, iteratively calculate until life requirement is met, obtain fatigue limit F -1 high cycle life L h low cycle life L l High and low cycle damage ratio k is calculated as follows:

[0107]

[0108] The results of the key points M1 on the platform are shown in the attached Figure 5 When the life index is met, the fatigue limit F -1 = 200 με, the high cycle life L h = 1.2 x 10 5 h, the low cycle life L l = 1.6 x 10 4 h, and k = 0.13

[0109] [7] Modify the low cycle spectrum to obtain the test spectrum on the plateau

[0110] If k < 0.2, the load frequency in the test low cycle spectrum in step 3 is unchanged, and the load size is enlarged according to the following coefficient:

[0111] k' = 1 + k

[0112] The test load spectrum considering the influence of high cycle load is obtained.

[0113] If k ≥ 0.2, the fatigue limit F -1 that meets the life requirement obtained in step 6 is enlarged according to the following coefficient:

[0114] k' = 1 + k

[0115] According to the enlarged fatigue limit F - '1 = (1 + k) F -1 , the corresponding life L' is obtained from the relationship between the fatigue limit F -1 and life L in step 6. All load frequencies in the original load spectrum are enlarged according to the following coefficient:

[0116]

[0117] For this example, k = 0.13 < 0.2, so the load is enlarged, and the final test spectrum is shown in the attached Figure 6 .

Claims

1. A method of generating an on-platform test load spectrum, characterized by, Comprise: According to the helicopter task profile in the task requirements and flight state, complete the task segment division; For each task segment in the non-deterministic state, sort according to the randomness principle; For the above sorted working condition, list the corresponding calculation load and carry out the rain flow to obtain the preliminary test low cycle load spectrum; According to the measured load data of the key parts of the platform, based on the task profile, compile the low cycle load spectrum, and compile the high cycle load spectrum according to the state rain flow to obtain the measured high and low cycle load spectrum; Based on the measured high and low cycle load spectrum, compare the high and low cycle damage ratio under the platform life requirement to obtain the high and low cycle load ratio; The load in the preliminary test low cycle load spectrum is amplified according to the ratio to obtain the test load spectrum considering high cycle damage; For each task segment in the non-deterministic state, sort according to the randomness principle, including: For any task segment, sort the deterministic states in the task segment according to the occurrence; For the non-deterministic state in the task segment, first refine the state to obtain n non-deterministic refined states according to the flight spectrum, for a non-deterministic state, one parameter in the non-deterministic refined state changes linearly, and other parameters remain unchanged; Sort n non-deterministic refined states according to the load low-high-low principle to obtain the non-deterministic state sequence; Obtain the preliminary test low cycle load spectrum, including: First, according to the sorting order of the deterministic state of each task segment, the load of the deterministic state is put into the load sequence, and the load of the non-deterministic state is also put into the load sequence according to the sorting order of the non-deterministic state of each task segment; The load sequence is rain-flow counted; if the 1st l If the step dynamic load is 1 / 10 of the maximum dynamic load, the load cycle is discarded and not counted, thereby obtaining a preliminary test low-cycle load spectrum.

2. The method of claim 1, wherein, Based on the task profile, compile the low cycle load spectrum, and compile the high cycle load spectrum according to the state rain flow, including: Select the measured load data of the key points of the platform, after data conversion, deburring and cleaning program, take the mean value of each state to carry out rain flow, and obtain the rain flow counting result under each state; According to the time proportion of each state formed by the task profile, convert the frequency in the rain flow counting result of each state to the frequency under the flight spectrum.

3. The method of claim 2, wherein, For the i-th state, the frequency of flight profile is calculated as: ； Load frequency in rainflow counting results; p i is the time proportion for the i-th state; is the measured flight down completion time for the i-th state, j is the order.

4. The method of claim 3, wherein, Based on the measured high and low cycle load spectrum, compare the high and low cycle damage ratio under the platform life requirement to obtain the high and low cycle load ratio; The load in the preliminary test low cycle load spectrum is amplified according to the ratio to obtain the test load spectrum considering high cycle damage, including: Calculating the allowable number of cycles corresponding to the load cycles in the load spectrum , calculating high and low cycle life and , thereby calculating the high and low cycle damage ratio k ; According to the high-low cycle damage ratio k The high cycle load spectrum is equivalent to the low cycle load spectrum, so as to obtain a test load spectrum considering high cycle damage.

5. The method of claim 4, wherein, According to the high-low cycle damage ratio k equivalent the high cycle load spectrum to the low cycle load spectrum to obtain a test load spectrum considering high cycle damage, comprising: When k If the value is less than the preset threshold, the load frequency in the preliminary test low-cycle load spectrum is kept unchanged, and the low-cycle load is amplified by 1 k times, thereby obtaining a test load spectrum considering high-cycle damage.

6. The method of claim 5, wherein, According to the high-low cycle damage ratio k equivalent the high cycle load spectrum to the low cycle load spectrum to obtain a test load spectrum considering high cycle damage, comprising: When k greater than or equal to a preset threshold, the fatigue limit is amplified by 1 k times, and the corresponding life is searched for. According to the amplification formula, the load frequency amplification coefficient is calculated The amplification formula is: ； wherein, is the life corresponding to the fatigue limit after amplification, is the life corresponding to the fatigue limit before amplification; The low cycle load was kept constant, and the high cycle load frequency was multiplied by 2, thus obtaining the test load spectrum considering high cycle damage. The low cycle load was kept constant, and the high cycle load frequency was multiplied by 2, thus obtaining the test load spectrum considering high cycle damage.

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