Method for compiling helicopter composite hub damage safety test spectrum

Abstract

The present application belongs to the field of helicopter structure fatigue design, and relates to a kind of helicopter composite material hub damage safety test spectrum compilation method.The method comprises: selecting square hole and flexible arm as fatigue dangerous position of helicopter composite material hub;Square hole is located at the position of flexible arm close to rotor shaft;Determine the characteristic load as the flap bending moment load of square hole and the flap oscillation bending moment load of flexible arm;For monitoring the characteristic load of composite material hub, strain gauges should be attached at the corresponding cross section, and calibration should be carried out;During damage safety test, load is applied to all flexible arms of helicopter composite material hub simultaneously;According to the damage test results, the helicopter composite material hub actual load spectrum is compiled.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of helicopter structure fatigue design, and relates to a helicopter composite hub damage safety test spectrum compilation method. BACKGROUND

[0002] As shown in the figure, the composite hub is the core element of the helicopter rotor system, and mainly functions to transfer and balance the centrifugal force load from the blades, transfer the lift and control moment, and form the horizontal hinge and vertical hinge. The compilation of the composite hub damage safety test load spectrum is a key technology for helicopter fatigue life evaluation. Figure 1

[0003] The main damage tolerance test spectrum is compiled for the airframe structure at home and abroad, and the damage tolerance test spectrum is mainly subjected to "ground-air-ground" low cycle load. The composite hub is mainly subjected to "high frequency + ground-air-ground" fatigue load, and the fatigue damage mode is mainly characterized by debonding and delamination. The damage tolerance test spectrum of the airframe structure mainly subjected to low cycle load cannot truly evaluate the fatigue damage of the composite hub in flight. Therefore, no one has proposed a method for compiling the damage tolerance test spectrum for the fatigue load of the composite hub. SUMMARY

[0004] The application aims to provide a helicopter composite hub damage safety test spectrum compilation method, which is convenient for engineering application and meets the needs of composite hub test verification.

[0005] TECHNICAL SCHEME

[0006] The application provides a helicopter composite hub damage safety test spectrum compilation method, which comprises the following steps:

[0007] Selecting a square hole and a flexible arm as the fatigue dangerous position of the helicopter composite hub; the square hole is located at the position of the flexible arm close to the rotor shaft;

[0008] Determining the characteristic load as the flap bending moment load of the square hole and the flap oscillation bending moment load of the flexible arm;

[0009] For monitoring the characteristic load of the composite hub, strain patches are attached to the corresponding cross sections and are calibrated;

[0010] During the damage safety test, loads are simultaneously applied to all the flexible arms of the helicopter composite hub;

[0011] According to the damage test results, a helicopter composite hub actual measured load spectrum is compiled.

[0012] Further, the cross section comprises:

[0013] The cross section where one end of the square hole rotor shaft is located, and the cross section is close to the root of the flexible arm;​

[0014] The cross section is selected between the first step and the second step of the flexible arm, and the selected cross section is close to the top end of the flexible arm.

[0015] Further, during the damage safety test, loads are simultaneously applied to all the flexible arms of the helicopter composite hub, including:

[0016] The flap excitation is applied at the spherical elastic bearing close to the side of the square hole near the top end of the flexible arm, and the pitch excitation and the roll excitation are applied at the top end of the flexible arm to realize simultaneous load application.

[0017] Further, the applied load includes:

[0018] 1) Load F acting on the top end of the flexible arm in the flap direction b1 , to determine the flap bending moment of the B-B cross section of the flexible arm of the composite hub, with the direction being that the upper surface is compressed to be positive;

[0019] 2) Load F acting on the end of the flexible arm in the pitch direction T1 , to determine the pitch bending moment of the B-B cross section of the flexible arm of the composite hub, with the direction being that the leading edge is compressed to be positive;

[0020] 3) Centrifugal force F, with the direction being positive to the end of the flexible arm;

[0021] 4) Load F acting on the spherical elastic bearing in the flap direction b2 , to determine the flap bending moment of the A-A cross section of the square hole of the composite hub, with the direction being that the upper surface is compressed to be positive;

[0022] 5) Load F acting on the spherical elastic bearing in the pitch direction T2 , to offset F T1 ;

[0023] Among them, the pitch excitation and the roll excitation applied at the top end of the arm are realized by 1) and 2); the flap excitation applied at the spherical elastic bearing is realized by 3)-5).

[0024] Further, according to the damage test results, a measured load spectrum of the helicopter composite hub is compiled, including:

[0025] The measured load spectrum of the composite hub is compiled: according to the measured load data of the characteristic loads of the square hole and the flexible arm of the composite hub, through state division, peak detection, false peak elimination, filtering, and “rainflow” counting, the flight measured load amplitude and frequency of the characteristic loads of the square hole and the flexible arm of the helicopter composite hub are obtained.

[0026] Further, the method further includes:

[0027] The corresponding states less than a predetermined proportion of the maximum dynamic load in the measured load spectrum of the composite hub are removed to form a final composite hub damage tolerance test state spectrum.

[0028] During the damage safety test of the composite hub, the static load is superimposed on each dynamic load spectrum block, and a damage safety fatigue test load spectrum is compiled.

[0029] Further, the predetermined proportion is 10% to 15%.

[0030] Further, the damage safety fatigue test load spectrum comprises an A spectrum block and a B spectrum block, the A spectrum block is a 1-hour spectrum block, and the B spectrum block is a 5-hour spectrum block.

[0031] Further, the following is applied during the test loading process of one load spectrum block:

[0032] a) the static load is applied;

[0033] b) the damage safety fatigue test load spectrum block is applied to the flap bending moment and the edgewise bending moment;

[0034] c) the flap bending moment and the edgewise bending moment are returned to zero, and then the centrifugal force is returned to zero.

[0035] Further, the load spectrum block of the composite hub damage safety test is arranged in the order of A-A-B-A-A-A, that is, a 5-hour corresponding test dynamic load spectrum is formed.

[0036] Beneficial effects:

[0037] The present application proposes a helicopter composite hub damage safety test spectrum compilation method according to the loading characteristics of the helicopter composite hub, which can truly reflect the fatigue damage of the composite hub in actual flight and can maximize the load simplification, so as to save the test period and economic cost. BRIEF DESCRIPTION OF DRAWINGS

[0038] Figure 1 is a schematic view of a composite hub structure;

[0039] Figure 2 is a schematic view of a damage test patch.

[0040] Figure 3 is a schematic view of a dynamic load test loading.

[0041] Figure 4 is a schematic view of a damage test loading. DETAILED DESCRIPTION

[0042] In order to make the purpose, technical scheme and advantages of the present application clearer, the technical scheme in the embodiments of the present application will be described in more detail below with reference to the drawings in the embodiments of the present application. In the drawings, the same or similar notations represent the same or similar elements or elements having the same or similar functions throughout. The described embodiments are part of the embodiments of the present application, rather than all the embodiments. The embodiments described below with reference to the drawings are exemplary and are intended to explain the present application, and cannot be understood as a limitation of the present application. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative labor fall within the scope of protection of the present application. The embodiments of the present application will be described in detail below with reference to the drawings.

[0043] In the description of the present application, it should be understood that the terms "center", "axial", "vertical", "upper", "lower", "upper end", "bottom end", "inner", "outer" and the like indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the devices or elements referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as a limitation on the scope of protection of the present application.

[0044] The present application provides a helicopter composite hub damage safety test spectrum compilation method, the steps are as follows:

[0045] [1] The helicopter composite hub damage safety test load spectrum compilation method of the present application selects square holes and flexible arms as the fatigue dangerous parts of the helicopter composite hub, as shown in Figure 1 , the composite hub includes three flexible arms and three square holes. The characteristic load is the flap bending moment load of the square hole and the flap and pitch bending moment load of the flexible arm.

[0046] [2] As shown in Figure 2 , to monitor the characteristic load of the composite hub, strain gauges should be attached to the corresponding cross sections, and calibration should be performed: a) strain gauges are attached to the A-A cross section to measure the flap bending moment of the square hole; b) strain gauges are attached to the B-B cross section to measure the flap and pitch bending moment of the flexible beam arm.

[0047] [3] As shown in Figure 3 , the composite hub damage safety test load, during the damage safety test, loads should be applied to the three flexible arms of the composite hub. In order to facilitate test loading, the flap bending moment borne by the square hole of the composite hub and the flap and pitch bending moment borne by the flexible arm can be obtained by applying 5 test loads to each flexible arm:

[0048] 1) Centrifugal force F, the direction points to the end of the flexible arm as positive;

[0049] 2) Static load F acting on the elastic bearing in the direction of the pendulum T2 ;

[0050] 3) Load F acting on the elastic bearing in the direction of the flap b2 , determine the flap bending moment of the composite propeller hub square hole A-A section, the direction is the upper surface under compression is positive;

[0051] 4) Load F acting on the flexible arm end in the direction of the flap b1 , determine the flap bending moment of the composite propeller hub flexible arm B-B section, the direction is the upper surface under compression is positive;

[0052] 5) Load F acting on the flexible arm end in the direction of the pendulum T1 , determine the pendulum bending moment of the composite propeller hub flexible arm B-B section, the direction is the leading edge under compression is positive.

[0053] [4] Compile the measured load spectrum of the composite propeller hub, according to the measured load data of the characteristic load of the composite propeller hub square hole and flexible arm, through state division, peak detection, false elimination, filtering, "rainflow" counting, obtain the flight measured load amplitude and frequency of the characteristic load of the composite propeller hub square hole and flexible arm.

[0054] [5] Remove the corresponding states in the composite propeller hub measured load spectrum which are smaller than the maximum dynamic load by a predetermined proportion, form the final composite propeller hub damage tolerance test state spectrum. The predetermined proportion is generally valued at 10%~15%, if the predetermined proportion is too large, it will affect the effectiveness of the damage safety test result, and if the predetermined proportion is too small, it will not achieve the effect of simplifying the state, preferably 10%.

[0055] [6] When the composite propeller hub damage safety test, the dynamic load of each dynamic load spectrum block is superimposed on the static load, starting from 0, and finally returning to 0, the dynamic load spectrum is controlled by 5 takeoffs and landings per hour, and the damage safety fatigue test load spectrum A spectrum block (1 hour spectrum block), B spectrum block (5 hour spectrum block) two test load spectrum blocks are compiled.

[0056] 1 load spectrum block test loading process is as follows:

[0057] A) the action of centrifugal force static load;

[0058] B) action damage safety fatigue test load spectrum block flap bending moment, pendulum bending moment;

[0059] C) flap bending moment, pendulum bending moment load back to zero, and then the centrifugal force back to zero.

[0060] [7] If Figure 4The composite hub damage safety test load spectrum block application sequence is shown as follows: A-A-B-A-A-A arrangement, that is, 5 hours of test dynamic load spectrum is constituted.

[0061] [8] Composite hub damage safety fatigue test loading sequence:

[0062] 1) 30 hours of the spectrum block;

[0063] 2) 100% ultimate load test, at least 30 seconds under this load.

[0064] 3) 60 hours of the spectrum block;

[0065] 4) 100% ultimate load test, at least 3 seconds under this load.

[0066] Other embodiments of the disclosure will be apparent to those skilled in the art from consideration of the specification and practice of the disclosure disclosed herein. It is intended that the specification and examples be considered as exemplary only, with the true scope and spirit of the disclosure being indicated by the following claims.

[0067] It should be understood that the present disclosure is not limited to the precise structures herein described and illustrated in the drawings, and that various modifications and changes can be made without departing from its scope. The scope of the present disclosure is limited only by the claims that follow.

Claims

1. A method of compiling a spectrum of helicopter composite hub break safety tests, characterized in that, The method comprises the following steps: Selecting a square hole and a flexible arm as fatigue dangerous positions of a helicopter composite hub; The square hole is located near the flexible arm close to a rotor shaft; Determining characteristic loads as a waving bending moment load of the square hole and a waving and whirling bending moment load of the flexible arm; For monitoring the characteristic loads of the composite hub, strain patches are attached to corresponding sections and are calibrated; During a damage safety test, loads are applied to all flexible arms of the helicopter composite hub simultaneously; According to the damage test results, a measured load spectrum of the helicopter composite hub is compiled; The sections comprise: A section where one end of the square hole of the rotor shaft is located, the section being close to the root of the flexible arm; A section between the first step and the second step of the flexible arm, the selected section being close to the top end of the flexible arm; During the damage safety test, loads are applied to all flexible arms of the helicopter composite hub simultaneously, including: Waving excitation is applied to the spherical elastic bearing on one side of the square hole close to the top end of the flexible arm, and waving and whirling excitations are applied to the top end of the flexible arm to realize simultaneous load application; The applied loads comprise: 1) a load Fb1 acting on the top end of the flexible arm in the waving direction, determining a waving dynamic bending moment of the B-B section of the flexible arm of the composite hub, the direction being that the upper surface is compressed to be positive; 2) a load FT1 acting on the top end of the flexible arm in the whirling direction, determining a whirling bending moment of the B-B section of the flexible arm of the composite hub, the direction being that the leading edge is compressed to be positive; 3) a centrifugal force F, the direction being that the top end of the flexible arm is positive; 4) a load Fb2 acting on the spherical elastic bearing in the waving direction, determining a waving dynamic bending moment of the A-A section of the square hole of the composite hub, the direction being that the upper surface is compressed to be positive; 5) a load FT2 acting on the spherical elastic bearing in the whirling direction, to offset FT1; Wherein, the waving and whirling excitations applied to the top end of the flexible arm are realized by 1) and 2); the waving excitation applied to the spherical elastic bearing is realized by 3) to 5).

2. The method of claim 1, wherein, According to the damage test results, a measured load spectrum of the helicopter composite hub is compiled, comprising: The measured load spectrum of the composite hub is compiled: according to the measured load data of the characteristic loads of the square hole and the flexible arm of the composite hub, through state division, peak detection, false peak elimination, filtering, "rain flow" counting, the flight measured load amplitude and frequency of the helicopter composite hub square hole and flexible arm characteristic load are obtained.

3. The method of claim 2, wherein, The method further comprises: Eliminating corresponding states in the measured load spectrum of the composite hub which are less than a predetermined proportion of the maximum dynamic load, to form a final damage tolerance test state spectrum of the composite hub; During the damage safety test of the composite hub, the static load is superimposed on the dynamic load spectrum block, and a damage safety fatigue test load spectrum is compiled.

4. The method of claim 3, wherein, The predetermined proportion is in the range of 10% to 15%.

5. The method of claim 4, wherein, The damage safety fatigue test load spectrum comprises: A spectrum block and a B spectrum block, the A spectrum block being a 1-hour spectrum block, and the B spectrum block being a 5-hour spectrum block.

6. The method of claim 5, wherein, The following is applied during the test loading process of one load spectrum block: a) a static load is applied; b) a waving bending moment and a whirling bending moment of the damage safety fatigue test load spectrum block are applied; c) the waving bending moment and the whirling bending moment load are returned to zero, and then the centrifugal force is returned to zero.

7. The method of claim 6, wherein, The load spectrum block application sequence of the composite hub damage safety test is: A-A-B-A-A-A arrangement.

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