A rapid assessment method for helicopter tail drive shaft bullet damage

Abstract

The present invention discloses a method for rapidly assessing bullet damage to a helicopter tail drive shaft. The method comprises the following steps: establishing a finite element simulation model of a bullet-impacted tail drive shaft; conducting bullet impact tests under typical operating conditions and verifying the reliability of the bullet impact model; establishing a simulation model of the residual strength and crack propagation residual life of the damaged tail drive shaft; conducting torsional buckling tests and fatigue life tests and verifying the reliability of the model; establishing a mapping relationship between the bullet hole morphology of the damaged tail drive shaft under different operating conditions and the residual strength and residual life based on the simulation results of the model, and constructing a failure characteristic map; comparing the bullet hole morphology of the damaged shaft with the failure characteristic map to determine the bullet impact operating condition and obtain the residual strength and remaining life of the damaged shaft, and then determining whether further treatment measures are needed based on the specific subsequent mission of the helicopter. Compared with the existing technology, the present invention solves the problem of assessing a helicopter tail drive shaft after being struck by a bullet, and meets the requirement for rapid assessment in practical situations.

Description

Technical Field

[0001] The present 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, despite the continuous improvement of helicopter maneuverability and armed confrontation performance, their inherent weakness in passive protection remains largely unaddressed. In particular, the tail boom of a helicopter is largely exposed to ground fire and is susceptible to projectile damage. After a projectile impact, further operation of a helicopter's tail drive shaft is likely to result in fracture, necessitating prompt removal from the battlefield for repair and restoration of operational capability. Before further action can be taken after a helicopter's tail drive shaft has suffered projectile damage, a damage assessment is essential. Minor damage does not require repair, and its remaining strength and lifespan still meet operational requirements. However, severe damage can lead to shaft fracture and severe consequences from further operation, necessitating repair or replacement to meet operational requirements. Therefore, a highly accurate damage assessment method for the tail drive shaft is crucial. In a real-world battlefield, damaged tail drive shafts require rapid repair and immediate return to the battlefield, and the assessment process must also be rapid.

[0003] The existing method of using multiple sensors to determine the damage status of a damaged tail drive shaft is neither intuitive nor reliable enough, and cannot provide a quick and accurate damage report on the battlefield. Therefore, a new method for quickly assessing bullet damage to a helicopter tail drive shaft is needed. Summary of the Invention

[0004] Purpose of the invention: In order to solve the above problems, the present invention provides a method for quickly assessing bullet damage to a helicopter tail drive shaft, which ensures that the damaged tail drive shaft will not be damaged during the assessment process. At the same time, the assessment can be performed without disassembling the tail drive shaft, thereby improving efficiency, shortening the assessment time, solving the assessment problem after the helicopter tail drive shaft is hit by a bullet, and meeting the requirements for rapid assessment in actual situations.

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

[0006] S1. Build a geometric model of the tail drive shaft and projectile in the software, perform pre-processing, and then establish a tail drive shaft impact simulation model. Perform impact simulation analysis under different operating conditions to determine the damage morphology of the tail drive shaft after impact and the residual velocity of the projectile after penetration.

[0007] S2. Conduct tail drive shaft impact tests under typical operating conditions and compare the test results with simulation results to verify the reliability of the impact simulation model.

[0008] S3. Import the damaged tail drive shaft under different working conditions obtained from the impact simulation analysis in S1 back into the simulation software. After pre-processing settings, establish the residual buckling strength simulation model of the damaged tail drive shaft under different working conditions and obtain the critical buckling load of the damaged tail drive shaft under different working conditions.

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

[0010] S5. Import the damaged tail drive shaft under different operating conditions obtained from the impact simulation analysis in S1 back into the simulation software. After pre-processing settings, establish a fatigue crack growth simulation model for the damaged tail drive shaft under different operating conditions to obtain the fatigue life of the damaged tail drive shaft under different operating conditions.

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

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

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

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

[0015] 1.1 Establish the geometric model of the tail drive shaft and 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 tail drive shaft according to the projectile body offset and incident angle corresponding to different working conditions;

[0016] 1.2 Segment the models of the missile body and tail drive shaft. Set the mesh density of the missile body using the global seed and perform mesh division. Use a refined mesh in the middle impact area of ​​the tail drive shaft, and a transitional mesh in the non-impact area. Select C3D8R elements for the missile body and tail drive shaft.

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

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

[0019] 1.5 Create a job to simulate and solve the bullet 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 bullet 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 S1 bullet impact simulation analysis, delete the hidden failure units, and then import the post-processed model into the simulation software;

[0024] 3.2 Define the density, Poisson's ratio, and elastic modulus, set the element type to C3D8I, and perform a linear buckling analysis using the buckling analysis step in the linear perturbation. Set displacement and load boundary conditions for the damaged tail drive shaft, edit keywords, output the first-order buckling mode displacement obtained from the 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 element type to C3D8I element, set the static RICS 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 according to a certain ratio;

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

[0031] 5.2 Import the post-processed tail drive shaft model 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 element type of the tail drive shaft to C3D8R element;

[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 based on 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 growth simulation analysis. After post-processing, obtain the crack length-cycle load number curve and determine 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 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 propagation 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 to 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 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 impact conditions similar to those of 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 results 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 results can be obtained by visually comparing the damage failure characteristic maps, 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 carried out 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 This is a schematic diagram of the tail drive shaft simulation model of the present invention.

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

[0042] Figure 4 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.

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

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

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

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

[0047] Figure 9 Schematic diagram of the nonlinear buckling shape of the damaged tail drive shaft according to the present invention.

[0048] Figure 10 This is a curve showing the relationship 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] Figure 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 method for quickly assessing bullet damage to a helicopter tail drive shaft provided by the present invention is further described in detail below: The method for quickly assessing bullet damage to a helicopter tail drive shaft 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 target parameters under different working conditions - 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 offsets and incident angles. In the actual process of the projectile penetrating the tail drive shaft, the core of the projectile plays a major role. Therefore, the core is selected as the model of the projectile in the simulation process. In the pre-processing process of assembling the projectile and the tail drive shaft, the projectile is kept as close to the tail drive shaft as possible when the offset and incident angle of the projectile are determined, which can effectively reduce unnecessary calculation costs.

[0052] Then, the projectile body and tail drive shaft models are segmented to better facilitate meshing. The projectile body is meshed by setting the mesh density using a global seed. The central impact area of ​​the tail drive shaft uses an encrypted mesh, while the non-impact area uses a transitional mesh. This significantly reduces the number of elements and improves calculation efficiency without compromising accuracy. The element type for the projectile body and tail drive shaft is C3D8R.

[0053] Next, 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 using 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 in the figure, 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] The second step was to conduct projectile impact tests on the tail drive shaft under typical operating conditions and compare the test results with the simulation results to verify the reliability of the projectile impact simulation model. Six typical operating conditions were selected: projectile impacting the center, middle, and edge of the tail drive shaft vertically and at a 45-degree angle. Projectile impact simulation tests under these typical operating conditions were conducted, using a high-speed camera to film the projectile penetrating the tail drive shaft and calculate the residual velocity after penetration. The residual velocity and tail drive shaft damage morphology obtained under these typical operating conditions were compared with the simulation results to verify the reliability of the simulation model.

[0057] Step 3: First, post-process the damaged tail drive shaft under different working conditions obtained from 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 visualization interface rather than deleted. If they are directly imported into the pre-processing module of the software, the excessively distorted units will reappear. Subsequent analysis cannot be performed without deleting them.

[0058] Next, define the density, Poisson's ratio, and elastic modulus, set the element type to C3D8I, and perform a linear buckling analysis using the buckling analysis step in the linear perturbation. Set displacement and load boundary conditions for the damaged tail drive shaft, edit keywords, output the first-order buckling mode displacements obtained from the linear buckling analysis, create a job, and solve.

[0059] Edit the keywords as follows:

[0060] *node file

[0061] U,

[0062] 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. Boundary conditions are applied through the reference points. An axial torque of 1 is applied to one section as a load boundary condition. The characteristic value obtained by the simulation is the linear buckling critical load. The displacement boundary conditions of the damaged tail drive shaft include constraining the axial degrees of freedom at the loaded end and constraining all degrees of freedom at the unloaded section.

[0063] Then, copy the tail drive shaft model post-processed in the third step into ABAQUS, define the density, elasticity, and plasticity, set the element type to C3D8I element, set the static RICS 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 field 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] In the nonlinear buckling simulation model, the displacement boundary conditions are the same as those in the linear buckling simulation model. An axial torque is applied to one end of the tail drive shaft as a load boundary condition. The magnitude is the linear buckling critical load obtained by simulation. The critical load obtained by linear buckling is generally too large, so when performing nonlinear buckling analysis, buckling will occur before the load reaches 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. 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 torsional buckling tests on the damaged tail drive shaft and compare the test results with simulation results to verify the reliability of the residual buckling strength simulation model. Specifically, a torsional buckling test was conducted on the damaged tail drive shaft after a bullet impact under typical operating conditions. The critical buckling load obtained was 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 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; among them, after the bullet impact test is completed, the cracks around the bullet hole on the damaged tail drive shaft are detected, and the stress concentration around the bullet hole 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 loaded end of the damaged tail drive shaft, and all degrees of freedom are constrained at the non-loaded end. After the crack assembly is completed, it is necessary to pick up the crack to determine the crack location 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 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 calculated based on the Power law for G equivC Constants needed when

[0080] Finally, if Figure 11As shown in the figure, a job is created to perform fatigue crack growth 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 tests on the damaged tail drive shaft and compare the test results with the simulation results to verify the reliability of the fatigue crack growth simulation model. A fatigue test was conducted on the damaged tail drive shaft after a bullet impact under typical operating conditions to obtain a crack length-load cycle curve. This was then compared with the crack length-load cycle curve obtained from the simulation to verify the reliability of the 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 residual 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 verified bullet impact simulation models, residual buckling strength simulation models, and crack propagation simulation models, bullet impact simulations are performed on these working conditions, and the residual strength and residual 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 to the corresponding bullet impact working conditions to form a damage failure characteristic map;

[0083] Step 8: Visually inspect the actual damaged tail drive shaft and compare the detected bullet hole morphology with the damage and failure characteristic map to quickly assess the remaining buckling strength and remaining fatigue life of the damaged tail drive shaft. This allows for a quick assessment of the remaining buckling strength and remaining fatigue life of the damaged shaft, and determines whether emergency repair measures are necessary based on the helicopter's subsequent mission. This assessment is achieved by visually comparing the damage and failure characteristic map, shortening the assessment time. The damage and failure characteristic map is compared to the damage and failure characteristic map based on the size, number, morphology, and distribution of the bullet holes in the damaged tail drive shaft. If the damage and failure characteristic map contains data corresponding to that impact condition, the remaining strength and remaining life of the damaged tail drive shaft can be directly determined. If the damage and 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 determined by interpolating the remaining strength and remaining life under similar impact conditions in the map. During the construction of the damage failure characteristic map, the established bullet impact simulation model, residual buckling strength simulation model and residual fatigue life simulation model were all verified for reliability through corresponding tests, 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 bullet impact process under different working conditions and the corresponding residual strength and remaining life of the damaged tail drive shaft, which improved R&D efficiency and saved time and cost; the damaged tail drive shaft will not be damaged during the evaluation process, and the evaluation can be carried out without disassembling the tail drive shaft, which improves work efficiency, solves the evaluation problem of the helicopter tail drive shaft after being hit by a bullet, and meets the requirements of rapid evaluation under actual conditions.

Claims

1. A method for quickly assessing bullet damage to a helicopter tail drive shaft, characterized in that: The following steps are involved: S1. Build a geometric model of the tail drive shaft and projectile in the simulation software, perform pre-processing, and then establish a tail drive shaft impact simulation model. Perform impact simulation analysis under different operating conditions to determine the damage morphology of the tail drive shaft after impact and the residual velocity of the projectile after penetration. S2. Conduct tail drive shaft impact tests under typical operating conditions and compare the test results with simulation results to verify the reliability of the impact simulation model. S3. Import the damaged tail drive shaft under different working conditions obtained from the impact simulation analysis in S1 back into the simulation software. After pre-processing settings, establish the residual buckling strength simulation model of the damaged tail drive shaft under different working conditions and obtain the critical buckling load of the damaged tail drive shaft under different working conditions. S4. Conduct torsional buckling tests on the damaged tail drive shaft and compare the test results with simulation results to verify the reliability of the residual buckling strength simulation model. S5. Import the damaged tail drive shaft under different operating conditions obtained from the impact simulation analysis in S1 back into the simulation software. After pre-processing settings, establish a fatigue crack growth simulation model for the damaged tail drive shaft under different operating conditions to obtain the fatigue life of the damaged tail drive shaft under different operating conditions. S6. Conduct fatigue life tests on the damaged tail drive shaft and compare the test results with the simulation results to verify the reliability of the fatigue crack growth simulation model. S7. Construct a damage failure characteristic map based on the mapping relationship between bullet hole morphology, critical buckling load, and remaining fatigue life of the damaged tail drive shaft under different working conditions; S8. Perform a visual inspection of the actual damaged tail drive shaft, compare the detected bullet hole morphology with the damage failure characteristic map, quickly assess the remaining buckling strength and remaining fatigue life of the damaged tail drive shaft, and determine whether emergency repair measures are necessary based on the helicopter's subsequent specific mission.

2. The method for rapid assessment of bullet damage to a helicopter tail drive shaft according to claim 1, characterized in that: In S1, the specific operations are as follows: 1.1 Establish the geometric model of the tail drive shaft and 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 tail drive shaft according to the projectile body offset and incident angle corresponding to different working conditions; 1.2 Segment the models of the missile body and tail drive shaft. Set the mesh density of the missile body using the global seed and perform mesh division. Use a refined mesh in the middle impact area of ​​the tail drive shaft, and a transitional mesh in the non-impact area. Select C3D8R elements for the missile body and tail drive shaft. 1.3 Select the dynamic explicit analysis step and set the field output and history output; 1.4 Set a reference point at the center of mass of the projectile, apply a rigid body constraint to the projectile, set the initial velocity of the projectile through a predefined field, set both ends of the tail drive shaft to be completely fixed, and define the contact between the projectile and the tail drive shaft, and between the tail drive shaft and itself; 1.5 Create a job to simulate and solve the bullet 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 bullet impact through post-processing.

3. The method for rapid assessment of bullet damage to a helicopter tail drive shaft according to claim 1, 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 method for rapid assessment of bullet damage to a helicopter tail drive shaft according to claim 1, 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. Finally, the residual speed of the projectile under typical working conditions and the damage morphology of the tail drive shaft obtained from the test are compared with the results obtained from the simulation calculation.

5. The method for rapid assessment of bullet damage to a helicopter tail drive shaft according to claim 1, 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 S1 bullet impact simulation analysis, delete the hidden failure units, and then import the post-processed model into the simulation software; 3.2 Define the density, Poisson's ratio, and elastic modulus, set the element type to C3D8I, and perform a linear buckling analysis using the buckling analysis step in the linear perturbation. Set displacement and load boundary conditions for the damaged tail drive shaft, edit keywords, output the first-order buckling mode displacement obtained from the 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 element type to C3D8I element, set the static RICS 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 according to a certain ratio; 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 method for rapid assessment of bullet damage to a helicopter tail drive shaft according to claim 1, 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 method for rapid assessment of bullet damage to a helicopter tail drive shaft according to claim 1, characterized in that: In S5, the specific operations are as follows: 5.1 Carry out material-level non-standard fracture toughness tests to obtain the fracture toughness of the material, and carry out material-level non-standard fatigue crack growth tests to fit the test data to obtain the relevant parameters of the Paris criterion expression; 5.2 Import the post-processed tail drive shaft model 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 element type of the tail drive shaft to C3D8R element; 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 based on 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 growth simulation analysis. After post-processing, obtain the crack length-cycle load number curve and determine the remaining life of the damaged tail drive shaft under different working conditions.

8. The method for rapid assessment of bullet damage to a helicopter tail drive shaft according to claim 1, 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 method for rapid assessment of bullet damage to a helicopter tail drive shaft 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, residual buckling strength simulation model and crack propagation 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 conditions to form a damage failure characteristic map.

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

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