Upper platform test load spectrum compilation method

Abstract

The invention belongs to the field of helicopter fatigue test design, and relates to an upper platform test load spectrum compilation method. The method comprises the following steps: completing task segment division according to task requirements and flight states in a helicopter task profile; ranking the non-deterministic states in each task segment according to a randomness principle; the sorted states are listed into corresponding calculation loads, rain flow is carried out, and a preliminary test low-cycle load spectrum is obtained; according to actually measured load data of key parts of the upper platform, a low-cycle load spectrum is compiled based on a mission profile, a high-cycle load spectrum is compiled by rain flow in a state, and actually measured high and low-cycle load spectrums are obtained; based on the actually-measured high-cycle load spectrum and the actually-measured low-cycle load spectrum, the high-cycle damage ratio and the low-cycle damage ratio under the upper platform service life requirement are compared, and the high-cycle load ratio and the low-cycle load ratio And amplifying the load in the initial low-cycle load spectrum according to the ratio to obtain a test load spectrum considering high-cycle damage.

Description

Technical Field

[0001] The invention belongs to the field of helicopter fatigue test design and relates to a method for compiling an upper platform test load spectrum. Background Art

[0002] Helicopters have diverse mission profiles and are flexible to use. Most of the body parts are subject to both low-cycle loads caused by take-off and landing and state conversion, and high-cycle loads caused by rotating parts such as rotors and tail rotors. Especially in areas close to the rotor installation area (such as the upper platform, tail reduction installation platform, etc.), the above load characteristics are more obvious. This requires appropriate corrections to the traditional load spectrum compilation method that mainly considers low-cycle load cycles.

[0003] On the other hand, although the helicopter has undergone actual load measurements, the test data is difficult to cover all the loads required by the platform test. This requires that the measured load data be used to correct the calculated loads during the preparation of the platform test load spectrum in order to obtain a test load spectrum that meets actual use.

[0004] At present, no corresponding method has been proposed to correct the test load spectrum. Summary of the invention

[0005] Purpose of the invention: The present invention provides a method for compiling fatigue test load spectra for upper platforms that combines the use characteristics and load characteristics of helicopters, thereby solving the problem of compiling load spectra for upper platform components of helicopters.

[0006] Technical solution:

[0007] A method for compiling a load spectrum for an upper platform test is provided, comprising:

[0008] Complete the mission segment division according to the mission requirements and flight status in the helicopter mission profile;

[0009] The non-deterministic states in each mission segment are sorted according to the principle of randomness; the sorted states are included in the corresponding calculation loads, and rain flow is performed to obtain the preliminary test low-cycle load spectrum;

[0010] According to the measured load data of key parts of the upper platform, the low-cycle load spectrum is compiled based on the mission profile, and the high-cycle load spectrum is compiled based on the state internal rain flow to obtain the measured high and low-cycle load spectra;

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

[0012] Furthermore, the non-deterministic states in each task segment are sorted according to the randomness principle, including:

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

[0014] For the non-deterministic state in the mission segment, the state is first refined according to the flight spectrum to obtain n non-deterministic refined states. 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 refinement states are sorted according to the load low-high-low principle to obtain the non-deterministic state order.

[0016] Furthermore, rain flow was conducted to obtain the preliminary test low cycle load spectrum, including:

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

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

[0019] Furthermore, a low-cycle load spectrum is compiled based on the mission profile, and a high-cycle load spectrum is compiled based on the state internal rain flow, including:

[0020] The measured load data of the key points of the upper platform are selected. After data conversion, deburring and other cleaning procedures, the mean value of each state is removed and the dynamic load is carried out to obtain the rain flow counting results in each state;

[0021] According to the time proportion of each state formed by the mission profile, the frequency of the rainflow counting results in each state is converted into the frequency under the flight spectrum.

[0022] Furthermore, for the i-th state, the frequency n_s under the flight spectrum i,j The calculation formula is:

[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 measured flight under the i-th state, and j is the order.

[0025] Furthermore, based on the measured high- and low-cycle load spectra, the high- and low-cycle damage ratios under the upper platform life requirements are compared to obtain the high- and low-cycle load ratios; the loads in the preliminary low-cycle load spectrum are amplified according to this ratio to obtain the test load spectrum considering high-cycle damage, including:

[0026] Calculate the allowable number N of load cycles in the load spectrum i , calculate the high and low cycle life L under this fatigue characteristic h and L l , thus calculating the high-low cycle damage ratio k;

[0027] According to the high-cycle to 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] Furthermore, according to the high-to-low-cycle damage ratio k, the high-cycle load spectrum is equivalent to the low-cycle load spectrum, thereby obtaining the test load spectrum considering high-cycle damage, including:

[0029] When k is less than the preset threshold, the load frequency in the test low-cycle spectrum is kept unchanged, and the low-cycle load is amplified by 1+k times to obtain the test load spectrum that takes high-cycle damage into account.

[0030] Furthermore, according to the high-to-low-cycle damage ratio k, the high-cycle load spectrum is equivalent to the low-cycle load spectrum, thereby obtaining the test load spectrum considering high-cycle damage, including:

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

[0032] According to the amplification formula, calculate the load frequency amplification factor k″, the amplification formula is:

[0033]

[0034] Among them, L′ is the life corresponding to the fatigue limit after amplification, and L is the life corresponding to the fatigue limit before amplification;

[0035] Keeping the low-cycle load unchanged, the frequency of the low-cycle load is magnified by k″ times to obtain the test load spectrum considering high-cycle damage.

[0036] Beneficial effects:

[0037] The present invention designs a method for compiling a load spectrum for a helicopter platform, solves the problem of verifying the life of components subjected to high and low cycle loads by a low cycle test method, and provides a solution for compiling subsequent load spectra for similar structural tests. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 It is a schematic diagram of the test load spectrum preparation process.

[0039] Figure 2 This is a diagram of task segment division.

[0040] Figure 3 It is a schematic diagram of the low-frequency spectrum of the mission profile.

[0041] Figure 4 It is a schematic diagram of the maximum and minimum values ​​in level flight (H=900m, V=150km / h, sideslip 0°).

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

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

[0044] A method for compiling a test load spectrum for an upper platform, characterized in that, according to a helicopter mission profile, the mission segments are divided and the deterministic states are sorted; the non-deterministic states in each mission segment are sorted according to the principle of randomness; the sorted states are included in the corresponding calculated loads, and rain flow is performed to obtain a preliminary test low-cycle load spectrum; based on the measured load data of key parts of the upper platform, a low-cycle load spectrum is compiled based on the mission profile, and a high-cycle load spectrum is compiled with rain flow within the state to obtain the measured high- and low-cycle load spectra; based on the measured high- and low-cycle load spectra, the high- and low-cycle damage ratios under the upper platform life requirements are compared to obtain the high- and low-cycle load ratio; the loads in the preliminary low-cycle load spectrum are amplified according to this ratio to obtain a test load spectrum that takes high-cycle damage into account. The specific steps are shown in the attached. Figure 1 , briefly described as follows:

[0045] [1] Divide the mission into segments according to the mission profile

[0046] According to the mission requirements and flight status in the mission profile, the states with obvious distinctions are merged and clustered to form a mission segment.

[0047] [2] Sort the status in the task segment by category

[0048] The deterministic states in each task segment are sorted according to the order of occurrence; the non-deterministic states in each task segment are sorted according to the principle of randomness.

[0049] [3] Load rain flow is included to obtain the test low frequency spectrum

[0050] All the loads corresponding to the sorted states are included and processed according to the rain flow calculation method, and the load cycles that do not cause damage are eliminated to obtain the test low-frequency spectrum.

[0051] [4] Obtain low-cycle load spectrum based on measured loads at key locations

[0052] The measured load data of key components are used. After data cleaning, the maximum and minimum values ​​of each state are taken, and the low-frequency measured load spectrum is obtained according to the low-frequency state sequence formed in step 2.

[0053] [5] Obtain high cycle load spectrum based on measured loads at key locations

[0054] The measured load data of key components are used. After data cleaning, the dynamic load is removed from the mean value of each state and rain flow is performed. According to the state-time ratio formed by the mission profile, the high-cycle measured load spectrum is obtained.

[0055] [6] Obtain high and low cycle damage ratios based on upper platform life requirements

[0056] The full-range SN curve is used to calculate the fatigue limit-life relationship under the high- and low-cycle measured load spectra of key parts respectively. The life under the high- and low-cycle measured load spectra is calculated respectively with the same fatigue limit until the total life meets the upper platform life requirement. At this time, the high- and low-cycle damage ratio is obtained.

[0057] [7] Correct the low frequency spectrum of the test to obtain the upper platform test spectrum

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

[0059] Example 1

[0060] The present invention is further described in detail below in conjunction with an example of a load spectrum compilation for a certain type of aircraft platform test. The test steps are as follows:

[0061] [1] Divide the mission into segments according to the mission profile

[0062] According to the mission profile of this model, the mission segments are divided into distinct continuous states according to the following principles:

[0063] 1) The height, speed and other status are obviously different; the height difference is less than the preset height difference, and the speed difference is less than the preset speed difference;

[0064] 2) The purpose is obviously different;

[0065] Figure 2 This is a typical mission profile and mission segment. This flight profile is divided into five mission segments: hovering, climbing, cruising, maneuvering and descending.

[0066] [2] Sort the status in the task segment by category

[0067] First, the deterministic states in each task segment are sorted according to the order of occurrence;

[0068] Attach Figure 2Taking the cruise mission as an example, it is clearly required to go through the process of level flight-turn-level flight, so the deterministic state and sequence are: level flight (H = 900m, V = 150km / h)-turn (H = 900m, V = 150km / h, turning slope angle 20°)-level flight (H = 900m, V = 150km / h)

[0069] Secondly, for each non-deterministic state S in the task segment i According to the flight spectrum, the state is refined into S ji ;

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

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

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

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

[0074] …

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

[0076] Again, for the non-deterministic refinement state S ji , sorted according to the load low-high-low principle to obtain the non-deterministic state order;

[0077] In the previous step, the S1 level flight sorting results are:

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

[0079] [3] Load rain flow is included to obtain the test low frequency spectrum

[0080] First, according to the sequence of the upper step states, the upper platform load is listed 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 ith 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 as 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 are selected. After data conversion, deburring and other cleaning procedures, the mean value of each state is removed and the dynamic load is used for rain flow. 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 rain flow in this state are shown in Table 1:

[0089] Table 1

[0090] Serial number <![CDATA[Dynamic load F ai,j > <![CDATA[Static load F si,j > <![CDATA[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 The actual flight completion time for this state is shown in the attached figure. Figure 4 State S shown 11 Take level flight (H = 900m, V = 150km / h, sideslip 0°) as an example, t i =1.56s, p i =2.58%. Table 1 is converted to Table 2 under the flight spectrum:

[0094] Table 2

[0095] Serial number <![CDATA[Dynamic load F ai,j > <![CDATA[Static load F si,j > <![CDATA[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 state is split. If it is repeated m times, the proportion of each state in the flight spectrum is p i / m. According to the first two methods, the high-frequency load spectra of all flight spectrum states are obtained.

[0097] [6] Obtain high and low cycle damage ratios based on upper platform life requirements

[0098] The first step is to assume that the fatigue limit F -1 , for the load cycle pair (F ai ,F si ,n i ), use the following formula to calculate the allowed number of times N i .

[0099]

[0100] Among them, A and α are material parameters, which are determined according to material grade and failure mode.

[0101] The second step is to calculate the component life L under the fatigue characteristics according to the following formula

[0102]

[0103] The third step is to measure the high and low cycle load spectra according to different fatigue limits F -1 , calculate the corresponding life L, and obtain the fatigue limit F under high and low cycle load spectra -1 -Life L relationship. Fatigue limit F under high and low cycle load spectrum of key point M1 on upper platform -1 - Lifespan L as attached Figure 5 shown.

[0104] The fourth step is to determine the fatigue limit F based on the high and low cycle load spectra. -1 -Life L relationship, calculated fatigue limit is F -1,i High and low cycle life Lh,i ,L l,i . Calculate the total lifespan as follows:

[0105]

[0106] The fifth step is to iterate the calculation until the life requirement is met and obtain the fatigue limit F at this time. -1 , high cycle life L h , low cycle life L l , calculate the high- and low-frequency damage ratio k according to the following formula

[0107]

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

[0109] [7] Correct the low frequency spectrum of the test to obtain the upper platform test spectrum

[0110] If k<0.2, the load frequency in the low-frequency spectrum of the third step test remains unchanged, and the load magnitude is amplified according to the following coefficient:

[0111] k′=1+k

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

[0113] If k ≥ 0.2, the fatigue limit obtained in step 6 that meets the life requirements is magnified by the following factor:

[0114] k′=1+k

[0115] According to the enlarged fatigue limit F - ′1=(1+k)F -1 , from step 6 the fatigue limit F -1 -Life L relationship to obtain the corresponding life L'. Amplify all load frequencies in the original load spectrum according to the following coefficients:

[0116]

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

Claims

1. A method for compiling a load spectrum for an upper platform test, characterized in that: include: Complete the mission segment division according to the mission requirements and flight status in the helicopter mission profile; The non-deterministic states in each task segment are sorted according to the principle of randomness; the sorted working conditions are included in the corresponding calculation loads, and rain flow is carried out to obtain the preliminary test low-cycle load spectrum; According to the measured load data of key parts of the upper platform, the low-cycle load spectrum is compiled based on the mission profile, and the high-cycle load spectrum is compiled based on the state internal rain flow to obtain the measured high and low-cycle load spectra; Based on the measured high- and low-cycle load spectra, the high- and low-cycle damage ratios under the upper platform life requirements are compared to obtain the high- and low-cycle load ratios; the loads in the preliminary low-cycle load spectrum are amplified according to this ratio to obtain the test load spectrum considering high-cycle damage.

2. The method according to claim 1, characterized in that The non-deterministic states in each task segment are sorted according to the principle of randomness, including: For any task segment, the deterministic states in the task segment are sorted according to the order of occurrence; For the non-deterministic state in the mission segment, the state is first refined according to the flight spectrum to obtain n non-deterministic refined states. For a non-deterministic state, one parameter in the non-deterministic refined state changes linearly, and other parameters remain unchanged. According to the load, the n non-deterministic refinement states are sorted according to the load low-high-low principle to obtain the non-deterministic state order.

3. The method according to claim 2, characterized in that Conduct rain flow to obtain preliminary test low cycle load spectrum, including: First, the loads in the deterministic state are placed in the load sequence according to the sorting order of the deterministic state of each task segment, and the loads in the non-deterministic state are also placed in the load sequence according to the sorting order of the non-deterministic state of each task segment; The above load sequence is subjected to rain flow counting; if the i-th order dynamic load is 1 / 10 of the maximum dynamic load, it is discarded and not counted in the load cycle, thus obtaining a preliminary test low-cycle load spectrum.

4. The method according to claim 3, characterized in that The low-cycle load spectrum is compiled based on the mission profile, and the high-cycle load spectrum is compiled based on the state internal rain flow, including: The measured load data of the key points of the upper platform are selected. After data conversion, deburring and other cleaning procedures, the mean value of each state is removed and the dynamic load is carried out to obtain the rain flow counting results in each state; According to the time proportion of each state formed by the mission profile, the frequency of the rainflow counting results in each state is converted into the frequency under the flight spectrum.

5. The method according to claim 4, characterized in that For the i-th state, the frequency n_s under the flight spectrum i,j The calculation formula is: n_f i,j is the load frequency in the rainflow counting result; p i is the time proportion of the i-th state; t i is the completion time of the measured flight under the i-th state, and j is the order.

6. The method according to claim 5, characterized in that Based on the measured high- and low-cycle load spectra, the high- and low-cycle damage ratios under the upper platform life requirements are compared to obtain the high- and low-cycle load ratios; The load in the preliminary low-cycle load spectrum is amplified according to this ratio to obtain the test load spectrum considering high-cycle damage, including: Calculate the allowable number N of load cycles in the load spectrum i , calculate the high and low cycle life L under this fatigue characteristic h and L l , thus calculating the high-low cycle damage ratio k; According to the high-cycle to 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.

7. The method according to claim 6, characterized in that According to the high-to-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 high-cycle damage, including: When k is less than the preset threshold, the load frequency in the test low-cycle spectrum is kept unchanged, and the low-cycle load is amplified by 1+k times to obtain the test load spectrum that takes high-cycle damage into account.

8. The method according to claim 6, characterized in that According to the high-to-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 high-cycle damage, including: When k is greater than or equal to the preset threshold, the fatigue limit is magnified by 1+k times, and the corresponding life is found; According to the amplification formula, calculate the load frequency amplification factor k″, the amplification formula is: Among them, L′ is the life corresponding to the fatigue limit after amplification, and L is the life corresponding to the fatigue limit before amplification; Keeping the low-cycle load unchanged, the frequency of the low-cycle load is magnified by k″ times to obtain the test load spectrum considering high-cycle damage.

Images