Cabin door corner fatigue rated value test method based on dog bone test piece

Abstract

The invention discloses a cabin door corner fatigue rated value test method based on a dog bone test piece. S1, a cabin door part is selected, and cabin door corner detail features are determined; s2, designing a dog bone test piece and a test piece matrix according to cabin door corner detail features; s3, carrying out a fatigue test by adopting a fatigue rated value test method; and S4, calculating a cabin door corner detail feature fatigue rated value based on fatigue test data. The fatigue characteristic of the cabin door corner or porthole corner area can be accurately represented, the fatigue weak part is exposed, the universality and timeliness are achieved, and the application range is wide.

Description

Technical Field

[0001] This invention belongs to the field of aircraft structural fatigue strength testing technology, and particularly relates to a method for testing the fatigue rating of cabin door corners based on canine bone test specimens. Background Technology

[0002] The pressurized compartments of transport aircraft often require large openings, especially the door openings. Extensive data from in-service aircraft inspections indicate that door corner areas are prone to cracking under combined pressurization and flight loads. Therefore, fatigue issues in these door corner areas must be a primary focus during the initial design phase. Fatigue life calculations for these door corner areas typically employ the DFR method, requiring experimental determination of the fatigue rating. However, the currently used DFR method does not consider the detailed characteristics of door corners, such as the corner radius, fastener diameter, and the distance of fasteners from the edge, leading to inaccurate calculation results. Summary of the Invention

[0003] The purpose of this invention is to provide a method for testing the fatigue rating of hatch corners based on canine bone test specimens. This invention can accurately characterize the fatigue characteristics of hatch corners or porthole corners, expose fatigue-weak areas, and has versatility, timeliness, and wide applicability.

[0004] To achieve the above objectives, the present invention employs the following technical solution: A method for testing the fatigue rating of a hatch corner based on a canine bone test specimen, comprising: S1. Select the hatch area and clarify the detailed features of the hatch corner; S2. Design the canine bone test piece and test piece matrix based on the detailed features of the hatch corner; S3. Conduct fatigue tests using the fatigue rating test method; S4. Calculate the fatigue rating of the detailed features of the door corner based on fatigue test data.

[0005] In the aforementioned test method for fatigue rating of hatch corner based on canine bone test specimens, in S1, the detailed features of the hatch corner include the hatch corner radius R, the fastener diameter D, and the distance S from the center of the fastener to the edge of the hatch corner.

[0006] In the aforementioned test method for fatigue rating of hatch corner based on canine bone test specimen, in S2, the thickness of the test specimen is taken as the corresponding hatch corner skin thickness t, the radius of the arc of the canine bone test area is taken as R, the diameter of the circular hole in the canine bone test area is taken as D, and the distance from the circular hole in the canine bone test area to the edge of the arc is taken as S.

[0007] In the aforementioned test method for fatigue rating of hatch corner based on canine bone test specimens, in S2, the length of the transition end of the test specimen is 150mm and the width of the test specimen is 120mm.

[0008] In the aforementioned test method for fatigue rating of hatch corner based on canine bone test specimens, in S2, the test specimen matrix is ​​designed as follows: the test data is processed according to the two-point method of data dispersion, and the number of valid data in each test group is not less than 5+5.

[0009] In the aforementioned test method for fatigue rating of hatch corners based on canine bone test specimens, in S3, the fatigue test method is as follows: the maximum stress level of the test specimen is determined according to the material and the form of the test specimen; the stress ratio of all test items is 0.06; the test load is determined based on the gross cross-sectional area of ​​the test section of the test specimen; a two-point method is adopted, and each type of test specimen is tested in two groups; by adjusting the stress level, the life at which the test specimen fails is controlled at 10. 4 ~10 5 Between and 10 5 ~10 6 between.

[0010] In the aforementioned test method for fatigue rating of hatch corners based on canine bone specimens, the calculation method for S4 is as follows: S41. Eliminate items with a lifespan of 10 years or more. 6 Data points that exceed twice the average lifespan are then removed. S42. Determine the characteristic life of each group of test specimens. The estimated value ; When all n test specimens in a set of test specimens fail:

[0011] When m out of a set of n test specimens fail:

[0012] When none of the n test specimens fail:

[0013] Let i be the number of fracture cycles for the i-th test specimen in each group of test specimens; The shape parameter of the two-parameter Weibull distribution for fatigue life; The number of test pieces per group; S43. Determine N for each test piece group. 95 / 95 :

[0014] The sample coefficient; Reliability coefficient; Confidence coefficient; S44. Solve for the DFR value of each test piece using the multi-point method: If there are n sets of test data, and the maximum stress level of each set is S... maxi First, calculate N for each group. 95 / 95 The data points of each group of experiments [S] maxi (N95 / 95) i The equation of the line is obtained by fitting the line using the least squares method. Fitting coefficients A and B:

[0015]

[0016] The corresponding N on the linear equation 95 / 95 equals 10 5 The points satisfy:

[0017] but: .

[0018] In the aforementioned test method for fatigue rating of hatch corners based on canine bone test specimens, in S44, when N 95 / 95 Located at 10 5 When looping one side, select N. 95 / 95 Approximately 10 5 The DFR value of each test specimen was calculated using the cyclic test data and the standard SN curve equation.

[0019] These are material characteristic parameters; X represents the maximum stress; X is the calculation parameter. S is the slope parameter of the SN curve.

[0020] In the aforementioned test method for fatigue rating of hatch corners based on canine bone test specimens, S41 is as follows: S411. Sort each set of data from smallest to largest; S412. Remove test data containing values ​​greater than or equal to 10. 6 Data from the next loop; S413. Calculate the mean of the remaining data after removing the largest data; S414. If the largest data point in the remaining data is greater than or equal to twice the mean, then discard that largest data point; S415. Repeat S413 and S414 until the largest data point in the remaining data is less than twice the mean; S416. Based on the results of S415, calculate the DFR values ​​of the remaining data that include and do not include the maximum data. If the relative difference between the two DFR values ​​is greater than or equal to 5%, discard the maximum data. S417. Repeat S416 until the relative difference between the two DFR values ​​is less than 5%. This DFR value is the final DFR value for this group of test specimens.

[0021] Beneficial effects: This invention takes into account the detailed features of the hatch structure corner radius, fastener diameter, and the distance between the hatch structure fastener and the edge, and considers the stress characteristics of the hatch corner area. It has versatility and a wide range of applications.

[0022] Specifically, cracks are prone to occur in the corners of pressurized cabin doors or windows. This invention uses the canine bone test method to determine the fatigue rating of conventional aircraft structural door corners. During the aircraft development concept and design stages, the fatigue rating of typical door corner areas can be demonstrated based on this invention. This invention considers detailed characteristics such as the corner radius of the door structure, the diameter of the fasteners, and the distance of the fasteners from the edge of the door structure. It also considers the stress characteristics of the structural door corner area, which can well characterize the fatigue characteristics of the door corner or window corner area, expose fatigue weak points, and has versatility and timeliness, with a wide range of applications. Attached Figure Description

[0023] Figure 1 This is a flowchart illustrating the experimental method. Figure 2 This is a schematic diagram of the canine bone test specimen. Figure 3 This is a schematic diagram of the corner of the hatch structure. Detailed Implementation

[0024] The features and illustrative embodiments of various aspects of the present invention will now be described in detail. Numerous specific design details are set forth in the following detailed description to provide a more complete understanding of the invention. However, it will be apparent to those skilled in the art that the invention can be practiced without some of these specific details. The following description of embodiments is merely intended to provide a better understanding of the invention by illustrating examples of the invention. The invention is by no means limited to any specific setup and method set forth below, but covers any improvements, substitutions, and modifications to the structures, methods, and devices without departing from the spirit of the invention. In the drawings and the following description, any parts not exhaustively described are considered to be common knowledge or conventional practices in the art.

[0025] It should be noted that, unless otherwise specified, the embodiments of the present invention and the features thereof can be combined with each other, and the various embodiments can be referenced and cited in each other. The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0026] Example 1. A method for testing the fatigue rating of a hatch corner based on a canine bone test specimen, such as... Figures 1-3 As shown, it includes: Step 1: Select the hatch area and identify its detailed features; Step 2: Design the canine bone test piece and test piece matrix based on the detailed features of the hatch corner; Step 3: Conduct fatigue tests using the fatigue rating test method; Step 4: Calculate the fatigue rating of the detailed features of the door corner based on fatigue test data.

[0027] In step 1, the fatigue rating of the hatch corner is mainly related to the hatch corner radius R, the fastener diameter D, and the distance S from the center of the fastener to the edge of the hatch corner. The detailed characteristic parameters R, D and S are determined.

[0028] In step 2, a canine bone specimen was used as the test piece, with a thickness corresponding to the skin thickness t at the corner of the hatch. The radius of the arc in the canine bone test area, the circular hole, and the distance from the circular hole to the edge of the arc were taken as R, D, and S, respectively. The length of the transition end was 150 mm, and the width of the test piece was 120 mm. The test data were processed using the two-point dispersion method, and the number of valid data points for each test group was no less than 5+5.

[0029] In step 3, the maximum stress level of the test specimen is determined based on the material and specimen type. The stress ratio for all test items is R=0.06, and the test load is determined using the gross cross-sectional area of ​​the test specimen's assessment section as the benchmark. A two-point method is used, with each type of test specimen tested in two groups. By adjusting the stress level, the lifespan at failure of the test specimen is controlled to be within 10... 4 -10 5 Between and 10 5 ~10 6 between.

[0030] Step 4 is as follows: a) Data selection: Fatigue life exhibits some dispersion, and data points with excessively high or low lifespans should be appropriately discarded. The discarding method used is as follows: firstly, data points with lifespans reaching or exceeding 10 years are excluded. 6 Data points with a lifespan of more than twice the average lifespan are then removed, while data points with a short lifespan are retained.

[0031] The specific steps are as follows: 1) Sort each set of data from smallest to largest; 2) Remove test data with a value greater than or equal to 10. 6 Data from the next loop; 3) Calculate the mean of the remaining data (excluding the largest data); 4) If the largest data point in the remaining data is greater than or equal to twice the mean, then discard that largest data point; 5) Repeat steps 3) and 4) until the largest data point in the remaining data is less than twice the mean; 6) Based on the results of 5), calculate the DFR values ​​of the remaining data that include and do not include the largest data. If the relative difference between the two DFR values ​​is greater than 5%, discard the largest data. 7) Repeat step 6) until the relative difference between the two DFR values ​​is less than 5%. This DFR value is the final DFR value of the test specimens.

[0032] b) Determine the characteristic life of each group of test specimens. The estimated value

[0033] When all n test specimens in a set of test specimens fail:

[0034] When m out of a set of n test specimens fail:

[0035] When none of the n test specimens fail:

[0036] in: — This represents the number of fracture cycles for the i-th test specimen in each group of test specimens; —The shape parameter of the two-parameter Weibull distribution of fatigue life is taken in this experiment as... ; —Number of test specimens per group; —Characteristic life of the test specimen.

[0037] c) Determine the N95 / 95 (reliability and confidence level are both 95%) for each test piece group. N test pieces per group 95 / 95 Calculate using the following formula:

[0038] In the formula: —Sample coefficient, taken as ; —Reliability coefficient, aluminum alloy ; — Confidence coefficient, values ​​are shown in Table 1.

[0039] Table 1 Confidence Coefficients for Aluminum Alloy Materials

[0040] d) Solve for the DFR value of each test specimen using the standard SN curve equation:

[0041] In the formula: —Material characteristic parameters, for aluminum alloy test pieces, take

[0042] —Maximum stress.

[0043] X is the calculation parameter, which is obtained by the following formula:

[0044] In the formula: S——the slope parameter of the SN curve. For aluminum alloy test pieces, S=2.0.

[0045] e) Solve for the DFR value of each test specimen using the multi-point method: If there are n sets of experimental data, the maximum stress level of each set is S maxi (i=1, 2, ..., n) (R=0.06), first calculate the double 95% lifetime (N) for each group. 95 / 95 ), and the data points of each group of experiments [S maxi (N95 / 95) i The equation of the line is obtained by fitting the line using the least squares method. Fitting coefficients A and B:

[0046]

[0047] The corresponding N on the linear equation 95 / 95 equals 10 5 The points satisfy:

[0048] but:

[0049] When both are 95% lifespan (N) 95 / 95 ) located at 10 5 This method is no longer applicable when cycling on one side. In this case, a double 95% lifetime (N) should be selected. 95 / 95 (Approximately 10) 5 The DFR value is calculated from the cyclic test data using the standard SN curve equation.

[0050] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A method for testing the fatigue rating of a hatch corner based on a canine bone specimen, characterized in that, include: S1. Select the hatch area and clarify the detailed features of the hatch corner; S2. Design the canine bone test piece and test piece matrix based on the detailed features of the hatch corner; S3. Conduct fatigue tests using the fatigue rating test method; S4. Calculate the fatigue rating of the detailed features of the door corner based on fatigue test data.

2. The method for testing the fatigue rating of a hatch corner based on a canine bone test specimen according to claim 1, characterized in that, In S1, the detailed features of the hatch corner include the hatch corner radius R, the fastener diameter D, and the distance S from the center of the fastener to the edge of the hatch corner.

3. The method for testing the fatigue rating of a hatch corner based on a canine bone specimen according to claim 2, characterized in that, In S2, the thickness of the test piece is taken as the thickness t of the skin at the corner of the hatch, the radius of the arc of the canine bone test area is taken as R, the diameter of the circular hole in the canine bone test area is taken as D, and the distance from the circular hole to the edge of the arc in the canine bone test area is taken as S.

4. The method for testing the fatigue rating of a hatch corner based on a canine bone specimen according to claim 3, characterized in that, In S2, the length of the transition end of the test piece is 150mm, and the width of the test piece is 120mm.

5. The method for testing the fatigue rating of a hatch corner based on a canine bone specimen according to claim 1, characterized in that, In S2, the test specimen matrix is ​​designed as follows: the test data dispersion is processed using the two-point method, and the number of valid data in each test group is no less than 5+5.

6. The method for testing the fatigue rating of a hatch corner based on a canine bone specimen according to claim 1, characterized in that, In S3, the fatigue test method is as follows: the maximum stress level of the test specimen is determined based on the material and specimen form; the stress ratio for all test items is 0.06; the test load is determined based on the gross cross-sectional area of ​​the test specimen's assessment section; a two-point method is used, with each type of test specimen tested in two groups; by adjusting the stress level, the lifespan at failure of the test specimen is controlled to be within 10... 4 ~10 5 Between and 10 5 ~10 6 between.

7. The method for testing the fatigue rating of a hatch corner based on a canine bone specimen according to claim 1, characterized in that, The calculation method for S4 is as follows: S41. Eliminate items with a lifespan of 10 years or more. 6 Data points that exceed twice the average lifespan are then removed. S42. Determine the characteristic life of each group of test specimens. The estimated value ; When all n test specimens in a set of test specimens fail: When m out of a set of n test specimens fail: When none of the n test specimens fail: Let i be the number of fracture cycles for the i-th test specimen in each group of test specimens; The shape parameter of the two-parameter Weibull distribution for fatigue life; The number of test pieces per group; S43. Determine N for each test piece group. 95 / 95 : The sample coefficient; Reliability coefficient; Confidence coefficient; S44. Solve for the DFR value of each test piece using the multi-point method: If there are n sets of test data, and the maximum stress level of each set is S... maxi First, calculate N for each group. 95 / 95 The data points of each group of experiments [S] maxi (N95 / 95) i The equation of the line is obtained by fitting the line using the least squares method. Fitting coefficients A and B: The corresponding N on the linear equation 95 / 95 equals 10 5 The points satisfy: but: 。 8. The method for testing the fatigue rating of a hatch corner based on a canine bone specimen according to claim 7, characterized in that, In S44, when N 95 / 95 Located at 10 5 When looping one side, select N. 95 / 95 Approximately 10 5 The DFR value of each test specimen was calculated using the cyclic test data and the standard SN curve equation. These are material characteristic parameters; X represents the maximum stress; X is the calculation parameter. S is the slope parameter of the SN curve.

9. The method for testing the fatigue rating of a hatch corner based on a canine bone specimen according to claim 7, characterized in that, S41 is as follows: S411. Sort each set of data from smallest to largest; S412. Remove test data containing values ​​greater than or equal to 10. 6 Data from the next loop; S413. Calculate the mean of the remaining data after removing the largest data; S414. If the largest data point in the remaining data is greater than or equal to twice the mean, then discard that largest data point; S415. Repeat S413 and S414 until the largest data point in the remaining data is less than twice the mean; S416. Based on the results of S415, calculate the DFR values ​​of the remaining data that include and do not include the maximum data. If the relative difference between the two DFR values ​​is greater than or equal to 5%, discard the maximum data. S417. Repeat S416 until the relative difference between the two DFR values ​​is less than 5%. This DFR value is the final DFR value for this group of test specimens.

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