Helicopter tail transmission shaft missile damage rapid assessment method

Abstract

The invention discloses a helicopter tail transmission shaft missile damage rapid assessment method. The method comprises the following steps that a missile-hit tail transmission shaft finite element simulation model is established; carrying out a striking test under a typical working condition and verifying the reliability of a striking model; establishing a simulation model of residual strength and crack propagation residual life of the damaged tail transmission shaft; carrying out a torsional buckling test and a fatigue life test, and verifying the reliability of the model; according to a simulation result of the model, establishing a mapping relationship among the bullet hole morphology of the damaged tail transmission shaft, the residual strength and the residual life under different working conditions, and constructing a failure characteristic spectrum; and comparing the bullet hole morphology of the damaged shaft with the failure characteristic spectrum, determining the bullet working condition, obtaining the residual strength and residual life of the damaged shaft, and determining whether to take further treatment measures or not according to the subsequent specific task of the helicopter. Compared with the prior art, the method solves the evaluation problem after the helicopter tail transmission shaft is subjected to elastic striking, and meets the requirement for rapidness of evaluation under the actual condition.

Description

Technical Field

[0001] The invention relates to the technical field of safety assessment of helicopter transmission systems, and in particular to a method for quickly assessing bullet damage to a helicopter tail transmission shaft. Background Art

[0002] On the modern battlefield, although the maneuverability and armed confrontation performance of helicopters are continuously improving, the inherent characteristic of weak passive protection capability has never been fundamentally solved, especially the tail beam of helicopters is mostly exposed to ground firepower and is easily damaged by bullets. After the helicopter tail drive shaft is hit by a projectile, further operation is likely to cause the tail drive shaft to break, so it needs to leave the battlefield quickly for treatment to restore its combat capability. Before the helicopter tail drive shaft is hit by a projectile and the next step of disposal is taken, it is an essential step to assess the damage of the tail drive shaft. For tail drive shafts with less damage, no repair is required, and their remaining strength and remaining life still meet the working requirements; for tail drive shafts with serious damage, further operation is likely to directly break the shaft and produce serious consequences, so it needs to be repaired or directly replaced to meet the working requirements. Therefore, the bullet damage assessment method for the tail drive shaft must have high accuracy. On the real battlefield, the damaged tail drive shaft needs to be quickly treated and returned to the battlefield immediately, and the assessment process must also meet the requirements of speed.

[0003] The existing method of using multiple sensors to judge the damage status of the damaged tail drive shaft is not intuitive and reliable enough, and cannot provide a fast and accurate damage status on the battlefield. Therefore, it is necessary to develop a new method for quickly assessing the damage of the helicopter tail drive shaft. Summary of the invention

[0004] Purpose of the invention: To solve the above-mentioned problem, the present invention provides a method for quickly evaluating bullet damage to a helicopter tail drive shaft, thereby ensuring that the damaged tail drive shaft will not be damaged during the evaluation process. At the same time, the evaluation can be performed without disassembling the tail drive shaft, thereby improving efficiency, shortening the evaluation time, solving the evaluation problem after the helicopter tail drive shaft is hit by a bullet, and meeting the requirements for rapid evaluation under actual conditions.

[0005] Technical solution: To achieve the above purpose, the method for quickly assessing bullet damage to a helicopter tail drive shaft of the present invention comprises the following steps:

[0006] S1. Establish the geometric model of the tail drive shaft and the projectile in the software, perform pre-processing settings, and then establish the impact simulation model of the tail drive shaft. Perform impact simulation analysis under different working conditions to obtain the damage morphology of the tail drive shaft after impact under different working conditions and the residual speed after the projectile penetrates;

[0007] S2. Carry out a tail drive shaft impact test under typical working conditions, compare the test results with the simulation results, and verify the reliability of the impact simulation model;

[0008] S3. The damaged tail drive shaft under different working conditions obtained by the simulation analysis of the bullet in S1 is re-imported into the simulation software, and after pre-processing settings, the residual buckling strength simulation model of the damaged tail drive shaft under different working conditions is established to obtain the critical buckling load of the damaged tail drive shaft under different working conditions;

[0009] S4. Conduct torsional buckling test on damaged tail drive shaft, compare test results with simulation results, and verify the reliability of residual buckling strength simulation model;

[0010] S5. The damaged tail drive shaft under different working conditions obtained by the simulation analysis of the bullet in S1 is re-imported into the simulation software, and after pre-processing settings, a fatigue crack propagation simulation model of the damaged tail drive shaft under different working conditions is established to obtain the fatigue life of the damaged tail drive shaft under different working conditions;

[0011] S6. Conduct fatigue life test on damaged tail drive shaft, compare test results with simulation results, and verify the reliability of fatigue crack growth simulation model;

[0012] S7. According to the mapping relationship between the bullet hole morphology of the damaged tail drive shaft and the critical buckling load and the remaining fatigue life under different working conditions, a damage failure characteristic map is constructed;

[0013] S8. Perform visual inspection on the actual damaged tail drive shaft, compare the detected bullet hole morphology with the damage failure characteristic map, quickly evaluate the remaining buckling strength and remaining fatigue life of the damaged tail drive shaft, and decide whether emergency repair measures are needed based on the subsequent specific mission of the helicopter.

[0014] Furthermore, in S1, the specific operations are as follows:

[0015] 1.1 Establish the geometric model of the tail drive shaft and the projectile body in the simulation software, use the Johnson-Cook constitutive model and failure criterion to set the material parameters, and assemble the projectile body and the tail drive shaft according to the projectile body offset and incident angle corresponding to different working conditions;

[0016] 1.2 Divide the models of the missile body and the tail transmission shaft. The mesh density of the missile body is set through the global seed to perform mesh division. The middle impact area of ​​the tail transmission shaft uses an encrypted mesh, and the non-impact area uses a transitional mesh. The unit type of the missile body and the tail transmission shaft is selected as C3D8R unit;

[0017] 1.3 Select the dynamic explicit analysis step, set the field output and history output;

[0018] 1.4 Set a reference point at the center of mass of the missile body, apply rigid body constraints to the missile body, set the initial velocity of the missile body through the predefined field, set both ends of the tail drive shaft to be completely fixed, and define the contact between the missile body and the tail drive shaft and between the tail drive shaft and itself;

[0019] 1.5 Create a job to simulate and solve the impact process under different working conditions, obtain the bullet hole morphology of the damaged tail drive shaft under different working conditions, and extract the residual velocity of the projectile after the impact through post-processing.

[0020] Furthermore, in S2, the typical working conditions include the projectile impacting the center, middle and edge of the tail transmission shaft in the vertical direction, and the projectile impacting the center, middle and edge of the tail transmission shaft in the oblique 45° direction.

[0021] Furthermore, in S2, the reliability of the projectile impact simulation model is verified by conducting a projectile impact simulation test under typical working conditions, and using a high-speed camera to shoot the process of the projectile penetrating the tail drive shaft, and then calculating the residual speed of the projectile after penetration, and finally comparing the residual speed of the projectile under typical working conditions and the damage morphology of the tail drive shaft obtained from the test with the results obtained from the simulation calculation.

[0022] Furthermore, in S3, the specific operations are as follows:

[0023] 3.1 Post-process the damaged tail drive shaft under different working conditions obtained from the simulation analysis of S1 being hit, delete the hidden failure units, and then import the post-processed model into the simulation software;

[0024] 3.2 Define density, Poisson's ratio and elastic modulus, set the unit type to C3D8I unit, use the buckling analysis step in linear perturbation to perform linear buckling analysis, set displacement boundary conditions and load boundary conditions for the damaged tail drive shaft, edit keywords, output the first-order buckling mode displacement obtained by linear buckling analysis, create a job, and solve;

[0025] 3.3 Import the tail drive shaft model post-processed in 3.1 into the simulation software, define density, elasticity and plasticity, set the unit type to C3D8I unit, set the static riks analysis step, field output and history output;

[0026] 3.4 Turn on geometric nonlinearity, set displacement boundary conditions and load boundary conditions, and edit keywords to introduce the first-order buckling mode displacement obtained from the linear buckling analysis into the nonlinear buckling analysis as the initial defect in a certain proportion;

[0027] 3.5 Create a job and perform nonlinear buckling simulation analysis to obtain the critical buckling load of the damaged tail drive shaft under different working conditions.

[0028] Furthermore, in S4, the reliability of the residual buckling strength simulation model is verified by performing a torsional buckling test on the damaged tail drive shaft after a bullet impact under typical working conditions, and comparing the critical buckling load obtained from the test with the critical buckling load obtained from the bullet impact simulation analysis to verify the reliability of the residual buckling strength simulation model.

[0029] Furthermore, in S5, the specific operations are as follows:

[0030] 5.1 Carry out material-level non-standard fracture toughness test to obtain the fracture toughness of the material, and carry out material-level non-standard fatigue crack growth test to fit the test data to obtain the relevant parameters of the Paris criterion expression;

[0031] 5.2 Import the tail drive shaft model post-processed in 3.1 into the simulation software, create a shell solid model as a crack, define the density, Poisson's ratio and elastic modulus, and set the unit type of the tail drive shaft to C3D8R unit;

[0032] 5.3 Create a direct loop analysis step, set the field output and history output, determine the location of the prefabricated crack on the tail drive shaft, set the relevant contact properties, and set the load boundary conditions and displacement boundary conditions according to the actual load spectrum of the helicopter tail drive shaft;

[0033] 5.4 Edit keywords, input relevant material parameters, and simulate low-cycle fatigue crack growth;

[0034] 5.5 Create a job to perform fatigue crack propagation simulation analysis. After post-processing, obtain the crack length-cycle load number curve and obtain the remaining life of the damaged tail drive shaft under different working conditions.

[0035] Furthermore, in S6, the reliability of the fatigue crack propagation simulation model is verified by performing a fatigue test on the damaged tail drive shaft after a bullet impact under typical working conditions to obtain a crack length-cycle load number curve, and comparing the crack length-cycle load number curve obtained by the bullet impact simulation analysis to verify the reliability of the fatigue crack propagation simulation model.

[0036] Furthermore, in S7, the establishment of the damage failure characteristic map includes: subdividing and arranging and combining the incident angle and offset range of the projectile to form a rich set of working conditions, and performing impact simulation on these working conditions by using a verified impact simulation model, a residual buckling strength simulation model and a crack extension simulation model, and obtaining the residual strength and remaining life of the corresponding damaged tail drive shaft, mapping the bullet hole morphology, residual strength and remaining life of the damaged tail drive shaft with the corresponding impact working conditions to form a damage failure characteristic map.

[0037] Furthermore, in S8, the damage condition of the tail drive shaft is determined by comparing the size, number, morphology and distribution position of the bullet holes in the damaged tail drive shaft to determine the impact condition. If the damage failure characteristic map contains data corresponding to the impact condition, the remaining strength and remaining life of the damaged tail drive shaft can be directly obtained; if the damage failure characteristic map only contains data corresponding to impact conditions similar to the damaged tail drive shaft, the remaining strength and remaining life of the damaged tail drive shaft are obtained by interpolating the remaining strength and remaining life under the similar impact conditions in the map.

[0038] Beneficial effects: Compared with the prior art, the present invention has the following significant effects: by establishing a bullet impact simulation model, a residual buckling strength simulation model and a residual fatigue life simulation model through experiments, the reliability of the evaluation result is guaranteed; the simulation model is used to simulate and analyze the bullet impact process under different working conditions and the corresponding residual strength and remaining life of the damaged tail drive shaft, thereby improving the research and development efficiency; the evaluation result can be obtained by visually comparing the damage failure characteristic map, thereby shortening the evaluation time; and it is ensured that the damaged tail drive shaft will not be damaged during the evaluation process, and at the same time, the evaluation can be performed without disassembling the tail drive shaft, thereby improving work efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 It is a schematic diagram of the process of the present invention.

[0040] Figure 2 It is a schematic diagram of the simulation model of the tail drive shaft of the present invention.

[0041] Figure 3 The figure is a schematic diagram of the morphology of the bullet hole produced when the projectile of the present invention impacts the middle part of the tail transmission shaft in the vertical direction.

[0042] Figure 4 The figure is a schematic diagram of the morphology of bullet holes produced when the projectile of the present invention impacts the middle of the tail transmission shaft in the vertical direction.

[0043] Figure 5 The figure is a schematic diagram of the morphology of bullet holes produced when the projectile of the present invention impacts the edge of the tail transmission shaft in the vertical direction.

[0044] Figure 6 The figure is a schematic diagram of the morphology of the bullet hole produced when the projectile of the present invention impacts the middle part of the tail transmission shaft along an oblique 45° direction.

[0045] Figure 7 The figure is a schematic diagram of the morphology of the bullet hole produced when the projectile of the present invention impacts the middle part of the tail transmission shaft along an oblique 45° direction.

[0046] Figure 8 This is a schematic diagram of the morphology of bullet holes produced when the projectile of the present invention impacts the edge of the tail transmission shaft along a 45° direction.

[0047] Fig. 9 It is a schematic diagram of the nonlinear buckling shape of the damaged tail drive shaft according to the present invention.

[0048] Fig.10 It is a relationship curve between the loading torque of the damaged tail transmission shaft and the support reaction torque borne by the non-loaded end according to the present invention.

[0049] Fig.11 Schematic diagram of the crack propagation path of the damaged tail drive shaft according to the present invention. DETAILED DESCRIPTION

[0050] The present invention discloses a method for quickly assessing bullet damage to a helicopter tail drive shaft. Figures 1 to 11 As shown, the helicopter tail drive shaft bullet damage rapid assessment method provided by the present invention is further described in detail below: The helicopter tail drive shaft bullet damage rapid assessment method comprises the following steps:

[0051] Step 1: First, Figure 2 As shown in the figure, the geometric model of the tail drive shaft and the projectile is established in ABAQUS, the Johnson-Cook constitutive model and failure criterion are used to set the material parameters, and the projectile target parameters under different working conditions, namely the projectile offset and the incident angle, are defined. Then, different projectile offsets and incident angles are selected according to different working conditions, and the assembly of the projectile and the tail drive shaft is completed according to the projectile offset and the incident angle. In the actual process of the projectile penetrating the tail drive shaft, the core of the projectile plays a role. Therefore, the core is selected as the model of the projectile in the simulation process. In the process of pre-processing the assembly of the projectile and the tail drive shaft, the projectile is kept as close to the tail drive shaft as possible when the offset and the incident angle of the projectile are determined, which can effectively reduce unnecessary calculation costs.

[0052] Then, the models of the missile body and the tail transmission shaft are segmented, and the mesh can be better divided after segmentation; the mesh density of the missile body is set through the global seed to perform mesh division, the middle impact area of ​​the tail transmission shaft uses an encrypted mesh, and the non-impact area uses a transition mesh, which greatly reduces the number of units and improves the calculation efficiency without affecting the calculation accuracy. The unit type of the missile body and the tail transmission shaft is selected as C3D8R unit;

[0053] Secondly, select the dynamic explicit analysis step and set the field output and history output;

[0054] Next, a reference point is set at the center of mass of the projectile, a rigid body constraint is applied to the projectile, the initial velocity of the projectile is set through a predefined field, both ends of the tail drive shaft are set to be completely fixed, and the contact between the projectile and the tail drive shaft and between the tail drive shaft and itself is defined;

[0055] Finally, if Figures 3 to 8As shown, a job is created to simulate and solve the impact process under different working conditions, obtain the bullet hole morphology of the damaged tail drive shaft under different working conditions, and extract the residual velocity of the projectile after the impact through post-processing.

[0056] Step 2: Carry out a projectile impact test on the tail drive shaft under typical working conditions, compare the test results with the simulation results, and verify the reliability of the projectile impact simulation model. Among them, six working conditions are selected as typical working conditions, namely, the projectile impacts the center, middle, and edge of the tail drive shaft in the vertical and 45° directions; a projectile impact simulation test under typical working conditions is carried out, and a high-speed camera is used to shoot the process of the projectile penetrating the tail drive shaft, and the residual speed after the projectile penetrates is calculated. The residual speed of the projectile under typical working conditions obtained in the test and the damage morphology of the tail drive shaft are compared with the results obtained by simulation calculation to verify the reliability of the simulation model.

[0057] Step 3: First, post-process the damaged tail drive shaft under different working conditions obtained by the impact simulation in the first step, delete the hidden failure units, and then re-import the post-processed model into ABAQUS. The failure units in the impact simulation process are hidden in the visual interface instead of deleted. If they are directly imported into the pre-processing module of the software, the over-distorted units will reappear, and subsequent analysis cannot be performed without deletion.

[0058] Secondly, define the density, Poisson's ratio and elastic modulus, set the unit type to C3D8I unit, use the buckling analysis step in linear perturbation to perform linear buckling analysis, set displacement boundary conditions and load boundary conditions for the damaged tail drive shaft, edit keywords, output the first-order buckling mode displacement obtained by linear buckling analysis, create a job, and solve;

[0059] Edit the keywords as follows:

[0060] *node file

[0061] U,

[0062] Among them, in the linear buckling simulation model, reference points are created at both ends of the damaged tail drive shaft, and the two end faces are coupled to the reference points, and the boundary conditions are applied through the reference points; an axial torque of 1 is applied to a section as a load boundary condition, so that the eigenvalue obtained by simulation is the linear buckling critical load, and the displacement boundary conditions of the damaged tail drive shaft include the axial degrees of freedom constrained by the load loading end and all degrees of freedom constrained by the non-loaded section;

[0063] Then, copy the tail drive shaft model post-processed in the third step into ABAQUS, define density, elasticity and plasticity, set the unit type to C3D8I unit, set the static riks analysis step, field output and history output;

[0064] Next, turn on geometric nonlinearity, set displacement boundary conditions and load boundary conditions, edit keywords, and introduce the first-order buckling mode displacement obtained from the linear buckling analysis into the nonlinear buckling analysis as the initial defect according to a certain ratio;

[0065] Edit the keywords as follows:

[0066] *imperfection,file=name,step=a

[0067] 1,b

[0068] The name is the name of the job created for the linear buckling analysis, step=a indicates the selected analysis step, the 1 in the second row indicates the first-order modal buckling displacement, and b indicates the ratio of the introduced first-order modal buckling displacement;

[0069] Among them, in the nonlinear buckling simulation model, the displacement boundary condition adopts the same setting as the linear buckling simulation model, and an axial torque is applied at one end of the tail drive shaft as the load boundary condition, and the magnitude is the linear buckling critical load obtained by simulation. The critical load obtained by linear buckling is generally too large, so nonlinear buckling analysis is performed. Buckling will occur when the load has not yet been loaded to the maximum, resulting in plastic deformation;

[0070] Finally, if Figures 9 and 10 As shown, a job is created to perform nonlinear buckling simulation analysis, and the simulation results are post-processed to extract the support reaction moment at the non-loaded end and the turning point data to obtain the critical buckling load of the damaged tail drive shaft.

[0071] Step 4: Conduct a torsional buckling test on the damaged tail drive shaft, compare the test results with the simulation results, and verify the reliability of the residual buckling strength simulation model. In particular, a torsional buckling test is conducted on the damaged tail drive shaft after a bullet strike under typical working conditions, and the critical buckling load obtained is compared with the critical buckling load obtained by simulation to verify the reliability of the residual buckling strength simulation model.

[0072] Step 5: First, carry out material-level non-standard fracture toughness test to obtain the fracture toughness of the material; carry out material-level non-standard fatigue crack growth test, fit the test data to obtain the relevant parameters of the Paris criterion expression;

[0073] Then, copy the tail drive shaft model post-processed in the third step into ABAQUS, create a shell solid model as a crack, define the density, Poisson's ratio and elastic modulus, and set the element type of the tail drive shaft to C3D8R element;

[0074] Secondly, create a direct cycle analysis step, set the field output and history output, determine the location of the prefabricated crack on the tail drive shaft, set the relevant contact properties, and set the load boundary conditions and displacement boundary conditions according to the actual load spectrum of the helicopter tail drive shaft; among them, after the bullet impact test is completed, the cracks around the bullet holes on the damaged tail drive shaft are detected, and the stress concentration around the bullet holes is analyzed based on the results of the buckling strength simulation. After comprehensive consideration, the area where the crack is most likely to expand is determined, and the prefabricated crack is assembled here; torque is applied to one end of the damaged tail drive shaft. The torque is a periodic load. The axial degrees of freedom are constrained at the loading end of the damaged tail drive shaft, and all degrees of freedom are constrained at the non-loading end. After the crack assembly is completed, it is necessary to pick up the crack to determine the location of the crack and allow the crack to grow, so that the crack tip will expand forward when the growth conditions are met;

[0075] Next, edit the keywords and input the relevant parameters of the material to simulate the low-cycle fatigue crack growth;

[0076] Edit the keywords as follows:

[0077] *Fracture Criterion,type=FATIGUE,mixed mode behavior=POWER

[0078] c1,c2,c3,c4,Gthresh / G c ,Gpl / G c ,G Ic ,G IIc , G IIIc ,a m ,a n ,a0

[0079] Where c1 and c2 are material constants that characterize the initiation of fatigue cracks; c3 and c4 are material constants that characterize the growth of fatigue cracks; G thresh / G c is the ratio of the energy release rate threshold based on the Paris law to the critical energy release rate; G pl / G c is the ratio of the upper limit of energy release rate to the critical energy release rate; G Ic is the critical energy release rate of type I; G IIc is the critical energy release rate of type II; G IIIc is the critical energy release rate of Class III; a m , a n and a0 is the calculation of G based on the Power law equivC Constants needed when

[0080] Finally, if Fig.11As shown, a job is created to perform fatigue crack propagation simulation analysis. After post-processing, the crack length-cycle load number curve is obtained, and the remaining life of the damaged tail drive shaft under different working conditions is obtained.

[0081] Step 6: Conduct fatigue life test on damaged tail drive shaft, compare test results with simulation results, and verify the reliability of fatigue crack growth simulation model. In particular, fatigue test is conducted on damaged tail drive shaft after bullet impact under typical working conditions, and crack length-cycle load number curve is obtained, which is compared with the crack length-cycle load number curve obtained by simulation to verify the reliability of fatigue crack growth simulation model;

[0082] Step 7: Based on the mapping relationship between the bullet hole morphology of the damaged tail drive shaft and the critical buckling load and the remaining fatigue life under different working conditions, a damage failure characteristic map is constructed. Among them, the incident angle and offset range of the projectile are subdivided and arranged and combined to form a rich set of working conditions. By using the verified bullet impact simulation model, the residual buckling strength simulation model and the crack extension simulation model, these working conditions are simulated by bullet impact, and the residual strength and remaining life of the corresponding damaged tail drive shaft are obtained. The bullet hole morphology, residual strength and remaining life of the damaged tail drive shaft are mapped with the corresponding bullet impact working conditions to form a damage failure characteristic map;

[0083] Step 8: Visually inspect the actual damaged tail drive shaft, then compare the morphology of the bullet holes detected with the damage failure characteristic map, quickly evaluate the residual buckling strength and residual fatigue life of the damaged tail drive shaft, and decide whether to take emergency repair measures based on the subsequent specific mission of the helicopter. The evaluation results can be obtained by visually comparing the damage failure characteristic map, which shortens the evaluation time. Among them, according to the size, number, morphology and distribution position of the bullet holes in the damaged tail drive shaft, the damage failure characteristic map is compared to determine the impact condition. If the damage failure characteristic map contains data corresponding to the impact condition, the residual strength and remaining life of the damaged tail drive shaft can be directly obtained; if the damage failure characteristic map only contains data corresponding to the impact condition similar to the damaged tail drive shaft, the residual strength and remaining life of the damaged tail drive shaft under the similar impact condition in the interpolation map are obtained. In the process of constructing the damage failure characteristic map, the established projectile impact simulation model, residual buckling strength simulation model and residual fatigue life simulation model were all verified for reliability through corresponding tests, thus ensuring the reliability of the evaluation results; after verifying the reliability of the simulation model, the simulation model was fully utilized to simulate and analyze the projectile impact process under different working conditions and the corresponding residual strength and remaining life of the damaged tail drive shaft, thereby improving R&D efficiency and saving time and costs; during the evaluation process, the damaged tail drive shaft will not be damaged and the evaluation can be carried out without disassembling the tail drive shaft, thereby improving work efficiency, solving the evaluation problem of the helicopter tail drive shaft after being hit by a projectile, and meeting the requirements for rapid evaluation under actual conditions.

Claims

1. A method for rapid assessment of bullet damage to a helicopter tail drive shaft, characterized in that: The following steps are involved: S1. Establish the geometric model of the tail drive shaft and the projectile in the simulation software, perform pre-processing settings, and then establish the impact simulation model of the tail drive shaft. Perform impact simulation analysis under different working conditions to obtain the damage morphology of the tail drive shaft after impact under different working conditions and the residual speed after the projectile penetrates; S2. Carry out a tail drive shaft impact test under typical working conditions, compare the test results with the simulation results, and verify the reliability of the impact simulation model; S3. The damaged tail drive shaft under different working conditions obtained by the simulation analysis of the bullet in S1 is re-imported into the simulation software, and after pre-processing settings, the residual buckling strength simulation model of the damaged tail drive shaft under different working conditions is established to obtain the critical buckling load of the damaged tail drive shaft under different working conditions; S4. Conduct torsional buckling test on damaged tail drive shaft, compare test results with simulation results, and verify the reliability of residual buckling strength simulation model; S5. The damaged tail drive shaft under different working conditions obtained by the simulation analysis of the bullet in S1 is re-imported into the simulation software, and after pre-processing settings, a fatigue crack propagation simulation model of the damaged tail drive shaft under different working conditions is established to obtain the fatigue life of the damaged tail drive shaft under different working conditions; S6. Conduct fatigue life test on damaged tail drive shaft, compare test results with simulation results, and verify the reliability of fatigue crack growth simulation model; S7. According to the mapping relationship between the bullet hole morphology of the damaged tail drive shaft and the critical buckling load and the remaining fatigue life under different working conditions, a damage failure characteristic map is constructed; S8. Perform visual inspection on the actual damaged tail drive shaft, compare the detected bullet hole morphology with the damage failure characteristic map, quickly evaluate the remaining buckling strength and remaining fatigue life of the damaged tail drive shaft, and decide whether emergency repair measures are needed based on the subsequent specific mission of the helicopter.

2. The helicopter tail drive shaft bullet damage rapid assessment method according to claim 1 is characterized in that: In S1, the specific operations are as follows: 1.1 Establish the geometric model of the tail drive shaft and the projectile body in the simulation software, use the Johnson-Cook constitutive model and failure criterion to set the material parameters, and assemble the projectile body and the tail drive shaft according to the projectile body offset and incident angle corresponding to different working conditions; 1.2 Divide the models of the missile body and the tail transmission shaft. The mesh density of the missile body is set through the global seed to perform mesh division. The middle impact area of ​​the tail transmission shaft uses an encrypted mesh, and the non-impact area uses a transitional mesh. The unit type of the missile body and the tail transmission shaft is selected as C3D8R unit; 1.3 Select the dynamic explicit analysis step, set the field output and history output; 1.4 Set a reference point at the center of mass of the missile body, apply rigid body constraints to the missile body, set the initial velocity of the missile body through the predefined field, set both ends of the tail drive shaft to be completely fixed, and define the contact between the missile body and the tail drive shaft and between the tail drive shaft and itself; 1.5 Create a job to simulate and solve the impact process under different working conditions, obtain the bullet hole morphology of the damaged tail drive shaft under different working conditions, and extract the residual velocity of the projectile after the impact through post-processing.

3. The helicopter tail drive shaft bullet damage rapid assessment method according to claim 1 is characterized in that: In S2, the typical working conditions include the projectile impacting the center, middle and edge of the tail transmission shaft in the vertical direction, and the projectile impacting the center, middle and edge of the tail transmission shaft in the oblique 45° direction.

4. The helicopter tail drive shaft bullet damage rapid assessment method according to claim 1 is characterized in that: In S2, the reliability of the projectile impact simulation model is verified by conducting a projectile impact simulation test under typical working conditions, and using a high-speed camera to shoot the process of the projectile penetrating the tail drive shaft, and then calculating the residual speed of the projectile after penetration, and finally comparing the residual speed of the projectile under typical working conditions and the damage morphology of the tail drive shaft obtained from the test with the results obtained from the simulation calculation.

5. The helicopter tail drive shaft bullet damage rapid assessment method according to claim 1 is characterized in that: In S3, the specific operations are as follows: 3.1 Post-process the damaged tail drive shaft under different working conditions obtained from the simulation analysis of S1 being hit, delete the hidden failure units, and then import the post-processed model into the simulation software; 3.2 Define density, Poisson's ratio and elastic modulus, set the unit type to C3D8I unit, use the buckling analysis step in linear perturbation to perform linear buckling analysis, set displacement boundary conditions and load boundary conditions for the damaged tail drive shaft, edit keywords, output the first-order buckling mode displacement obtained by linear buckling analysis, create a job, and solve; 3.3 Import the tail drive shaft model post-processed in 3.1 into the simulation software, define density, elasticity and plasticity, set the unit type to C3D8I unit, set the static riks analysis step, field output and history output; 3.4 Turn on geometric nonlinearity, set displacement boundary conditions and load boundary conditions, and edit keywords to introduce the first-order buckling mode displacement obtained from the linear buckling analysis into the nonlinear buckling analysis as the initial defect in a certain proportion; 3.5 Create a job and perform nonlinear buckling simulation analysis to obtain the critical buckling load of the damaged tail drive shaft under different working conditions.

6. The helicopter tail drive shaft bullet damage rapid assessment method according to claim 1 is characterized in that: In S4, the reliability of the residual buckling strength simulation model is verified by performing a torsional buckling test on the damaged tail drive shaft after a bullet impact under typical working conditions, and comparing the critical buckling load obtained from the test with the critical buckling load obtained from the bullet impact simulation analysis to verify the reliability of the residual buckling strength simulation model.

7. The helicopter tail drive shaft bullet damage rapid assessment method according to claim 1 is characterized in that: In S5, the specific operations are as follows: 5.1 Carry out material-level non-standard fracture toughness test to obtain the fracture toughness of the material, and carry out material-level non-standard fatigue crack growth test to fit the test data to obtain the relevant parameters of the Paris criterion expression; 5.2 Import the tail drive shaft model post-processed in 3.1 into the simulation software, create a shell solid model as a crack, define the density, Poisson's ratio and elastic modulus, and set the unit type of the tail drive shaft to C3D8R unit; 5.3 Create a direct loop analysis step, set the field output and history output, determine the location of the prefabricated crack on the tail drive shaft, set the relevant contact properties, and set the load boundary conditions and displacement boundary conditions according to the actual load spectrum of the helicopter tail drive shaft; 5.4 Edit keywords, input relevant material parameters, and simulate low-cycle fatigue crack growth; 5.5 Create a job to perform fatigue crack propagation simulation analysis. After post-processing, obtain the crack length-cycle load number curve and obtain the remaining life of the damaged tail drive shaft under different working conditions.

8. The helicopter tail drive shaft bullet damage rapid assessment method according to claim 1 is characterized in that: In S6, the reliability of the fatigue crack propagation simulation model is verified by performing a fatigue test on the damaged tail drive shaft after a bullet impact under typical working conditions to obtain a crack length-cycle load number curve, and comparing the crack length-cycle load number curve obtained by the bullet impact simulation analysis to verify the reliability of the fatigue crack propagation simulation model.

9. The helicopter tail drive shaft bullet damage rapid assessment method according to claim 1, characterized in that: In S7, the establishment of the damage failure characteristic map includes: subdividing and arranging the incident angle and offset range of the projectile to form a rich set of working conditions, and using the verified projectile impact simulation model, the residual buckling strength simulation model and the crack extension simulation model to simulate these working conditions, and obtain the residual strength and remaining life of the corresponding damaged tail drive shaft, and form a mapping relationship between the bullet hole morphology, residual strength and remaining life of the damaged tail drive shaft and the corresponding projectile impact working condition to form a damage failure characteristic map.

10. The helicopter tail drive shaft bullet damage rapid assessment method according to claim 1, characterized in that: In S8, the damage condition of the tail drive shaft is determined by comparing the size, number, morphology and distribution position of the bullet holes in the damaged tail drive shaft to the damage failure characteristic map to determine the impact condition. If the damage failure characteristic map contains data corresponding to the impact condition, the remaining strength and remaining life of the damaged tail drive shaft can be directly obtained; if the damage failure characteristic map only contains data corresponding to the impact condition similar to the damaged tail drive shaft, the remaining strength and remaining life of the damaged tail drive shaft are obtained by interpolating the remaining strength and remaining life under the similar impact condition in the map.

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