Method for analyzing validity of fatigue crack detection data

Abstract

The invention relates to the technical field of material performance detection, and provides a fatigue crack detection data validity analysis method, which comprises: preparing a detection sample; establishing a coordinate system; performing a fatigue test; a data detection point is selected on the fatigue crack along the X axis at a preset interval; selecting a detection point which obviously starts to deviate from the X axis; taking the detection point as an initial point, and continuously selecting m detection points along the X-axis direction; fitting into a straight line, and calculating an L value and a deflection angle theta value; and judging data validity: when L is greater than or equal to 0.1 W and theta is less than or equal to 20 degrees, judging the data to be valid. Therefore, a coordinate system is established according to the structure of the detection sample, and reference point selection and deflection angle measurement in American standard are converted into coordinate detection and data calculation. The operation is simplified, the measurement difficulty is reduced, and the detection accuracy and the detection efficiency are improved at the same time. Quick and accurate analysis and judgment of validity of fatigue crack detection data meeting American standard requirements are realized.

Description

Technical Field

[0001] The present invention belongs to the technical field of material property detection, and particularly relates to an analysis method for the validity of fatigue crack detection data. Background Art

[0002] Fatigue failure is the main way of failure of engineering structural components. Therefore, fatigue performance is an important index of the performance of metal materials. Judging whether the fatigue test data is valid is a prerequisite for evaluating the fatigue performance of materials. Combining Figure 1 , in the national standard GB / T6398 for the test results of fatigue crack propagation, three criteria for invalid data are specified:

[0003] 1. If the difference in crack sizes on the front and back surfaces of the test specimen exceeds 0.25B before and after detection, the data is judged to be invalid;

[0004] 2. For M(T) specimens, if the difference in the lengths of two cracks on the same side surface exceeds 0.025W, the data is judged to be invalid;

[0005] 3. Draw a horizontal line through the tip of the prefabricated notch 1 as the reference line 12; select a measurement point on the fatigue crack 11 and measure the distance h from it to the reference line 12; when h≥0.05W, the data is judged to be invalid.

[0006] The American standard ASTM E647 also specifies three criteria for invalid data. The first two are the same as those in the national standard, and the third is different. The specific requirements are as follows:

[0007] Determine the reference point (the starting point where the fatigue crack shows a significant deviation) of the fatigue crack 11 from the reference line 12; starting from this reference point, translate along the reference line 12 by L (L≥0.1W), and take a detection point on the fatigue crack 11; connect this detection point with the reference point and measure the angle θ between this line segment and the reference line 12; when θ≥20°, the data is judged to be invalid; then select a new detection point and repeat the above operation.

[0008] Note: B is the thickness value of the specimen; W is the width value from the starting point of the prefabricated notch 1 to the side of the specimen; those skilled in the art can obtain the detailed regulations of B and W from relevant standard documents.

[0009] Comparing the two regulations, it can be seen that the national standard only needs to measure the deviation amount h, with less measurement data, high measurement accuracy, and is relatively easy to implement. The American standard requires accurate determination of the reference point. Deviation of the reference point will lead to incorrect judgment of invalid data points or missed measurements; and the operation is complex, the measurement difficulty is large, and the accuracy is low. With the increase in the export volume of aluminum alloys, the demand for implementing the American standard detection is large, and currently there is a lack of an effective method for implementing the American standard detection.

[0010] In summary, it is obvious that the existing technology has inconveniences and defects in actual use, so it is necessary to improve it. Summary of the Invention

[0011] In view of the above defects, the present invention mainly provides an analysis method for the validity of fatigue crack detection data, which solves the technical problems of low measurement accuracy and easy omission in the measurement of the validity of fatigue crack data in the American standard.

[0012] To solve the above problems, the present invention provides an analysis method for the validity of fatigue crack detection data, including the following steps:

[0013] S1. Prepare a test specimen for fatigue test, and make a prefabricated notch on the test specimen; a pre-crack with a predetermined length is provided at the end of the prefabricated notch.

[0014] S2. Establish a coordinate system.

[0015] Set the straight line segment where the pre-crack is located as the X-axis; draw a straight line segment perpendicular to the X-axis, denoted as the Y-axis; the intersection point of the X-axis and the Y-axis is denoted as point 0.

[0016] S3. Clamp the test specimen onto a fatigue testing machine to conduct a fatigue test, and form a fatigue crack on the test specimen.

[0017] S4. Select a data detection point on the fatigue crack at every predetermined length along the X-axis, and record the coordinate values (x n , y n ) of the detection point.

[0018] S5. Display each detection point in the coordinate system.

[0019] S6. According to the trend of the fatigue crack, select the detection point that obviously starts to deviate from the X-axis; and take this detection point as the starting point, and continuously select m detection points along the X-axis direction.

[0020] S7. Fit the m detection points into a straight line, and denote the equation of the straight line as y = a * x + b; the intersection point of this straight line and the X-axis is the reference point (x0, y0), and calculate the coordinate values of the reference point.

[0021] S8. Calculate the L value and the deflection angle θ value.

[0022] Denote the coordinates of any one of the m detection points as (x j , y j ); calculate L = x j - x0; and calculate the angle value of the angle between the connection line of this point and the reference point and the X-axis, which is the deflection angle θ value.

[0023] S9. Repeat step S8 to complete the calculation of the L value and the θ value for all points, and record the calculation results.

[0024] S10, Data validity judgment: When L≥0.1W and θ≤20°, the data is determined to be valid; W is the distance value between the origin of the coordinate system and the side of the specimen.

[0025] S11, Continue to take multiple groups of detection points along the X-axis direction, and the number of detection points in each group is m; repeat steps S7 - S10.

[0026] According to the analysis method for the validity of fatigue crack detection data of the present invention, the length of the pre-crack is 2 mm.

[0027] According to the analysis method for the validity of fatigue crack detection data of the present invention, the interval distance along the X-axis of the data detection points on the fatigue crack is 0.5 mm.

[0028] According to the analysis method for the validity of fatigue crack detection data of the present invention, in step S6, the point where the deviation amount reaches or exceeds 0.2 mm is used as the initial deviation point.

[0029] According to the analysis method for the validity of fatigue crack detection data of the present invention, in step S7, the method of fitting m detection points into a straight line equation is the least squares method.

[0030] According to the analysis method for the validity of fatigue crack detection data of the present invention, in step S7, the number of m detection points is not less than 5.

[0031] According to the analysis method for the validity of fatigue crack detection data of the present invention, in step S4, an image measuring instrument or a fatigue testing machine is used to collect and record the coordinate values of each detection point.

[0032] According to the analysis method for the validity of fatigue crack detection data of the present invention, in step S10, when L<0.1W and θ≤20°, the data is determined to be valid.

[0033] According to the analysis method for the validity of fatigue crack detection data of the present invention, the test specimen is an M(T) specimen, and a prefabricated notch is provided at the center of the M(T) specimen 2; the origin of the coordinate system is set at the center of the prefabricated notch;

[0034] The M(T) specimen includes a left front edge crack, a left rear edge crack, a right front edge crack, and a right rear edge crack; for each edge, the analysis method for the validity of fatigue crack detection data is used to judge the validity of the data of each detection point;

[0035] If the data of the detection points of the four edge cracks with the same X-axis coordinate are all valid, the data is determined to be valid.

[0036] According to the analysis method for the validity of fatigue crack detection data of the present invention, the test specimen is a C(T) specimen, and the prefabricated notch 1 is opened on one side of the C(T) specimen; the 0 point of the coordinate system is set at the starting position of the prefabricated notch;

[0037] The C(T) specimen includes a front edge crack and a rear edge crack; for each edge, the analysis method for the validity of fatigue crack detection data is respectively used to judge the validity of the data at each detection point;

[0038] If the data of the detection points of the two edge cracks with the same X-axis coordinate are all valid, the data is determined to be valid.

[0039] In summary, the present invention establishes a coordinate system according to the structure of the test specimen, and converts the selection of the reference point and the measurement of the deflection angle in the American standard into coordinate detection and data calculation. It simplifies the operation, reduces the measurement difficulty, and improves the detection accuracy and detection efficiency at the same time. It realizes the rapid and accurate analysis and judgment of the validity of fatigue crack detection data meeting the requirements of the American standard. Description of the Drawings

[0040] Figure 1 is a schematic diagram of the principle for determining invalid fatigue crack data;

[0041] Figure 2 is a schematic diagram of the principle for analyzing the validity of fatigue crack data of the present invention;

[0042] Figure 3 is a schematic diagram of the structure of the M(T) specimen of the present invention;

[0043] Figure 4 is Figure 3 the schematic diagram of the A-A cross-section in ;

[0044] Figure 5 is a schematic diagram for analyzing the validity of the left front edge crack data of the M(T) specimen of the present invention;

[0045] Figure 6 is a schematic diagram for analyzing the validity of the left rear edge crack data of the M(T) specimen of the present invention;

[0046] Figure 7 is a schematic diagram for analyzing the validity of the right front edge crack data of the M(T) specimen of the present invention;

[0047] Figure 8 is a schematic diagram for analyzing the validity of the right rear edge crack data of the M(T) specimen of the present invention;

[0048] Figure 9 is a schematic diagram of the structure of the C(T) specimen of the present invention;

[0049] Figure 10 isFigure 9 Schematic diagram of the structure in the B-B direction

[0050] Figure 11 Schematic diagram for analyzing the validity of the data of the pre-edge crack of the C(T) specimen of the present invention

[0051] Figure 12 Schematic diagram for analyzing the validity of the data of the post-edge crack of the C(T) specimen of the present invention

[0052] In the figure: 1 - prefabricated notch, 11 - fatigue crack, 12 - reference line; 2 - M(T) specimen, 21 - left pre-edge crack, 22 - left post-edge crack, 23 - right pre-edge crack, 24 - right post-edge crack; 3 - C(T) specimen, 31 - pre-edge crack, 32 - post-edge crack. Specific implementation mode

[0053] Refer to Figure 2 , the present invention provides an analysis method for the validity of fatigue crack detection data, including the following steps:

[0054] S1, Prepare a detection specimen for the fatigue test, and open a prefabricated notch 1 on the detection specimen; a pre-crack with a predetermined length is provided at the end of the prefabricated notch 1;

[0055] During the fatigue test, stress concentration occurs at the pre-crack, and the fatigue crack forms along the pre-crack, facilitating data collection.

[0056] Preferably, the length of the pre-crack of the present invention is 2 mm.

[0057] S2, Establish a coordinate system;

[0058] Set the straight line segment where the pre-crack is located as the X-axis; draw a straight line segment perpendicular to the X-axis and denote it as the Y-axis; denote the intersection point of the X-axis and the Y-axis as point 0;

[0059] Refer to Figure 3 , optionally, the detection specimen is an M(T) specimen 2, and a prefabricated notch 1 is opened at the center position of the M(T) specimen 2; point 0 of the coordinate system is set at the center position of the prefabricated notch 1;

[0060] Refer to Figure 9 , optionally, the detection specimen is a C(T) specimen 3, and the prefabricated notch 1 is opened on one side of the C(T) specimen 3; point 0 of the coordinate system is set at the starting position of the prefabricated notch 1;

[0061] S3, Clamp the detection specimen onto a fatigue testing machine to conduct a fatigue test, and form a fatigue crack on the detection specimen;

[0062] S4. At every predetermined length along the X-axis, select a data detection point on the fatigue crack and record the coordinate values (x n , y n ) of the detection point;

[0063] Preferably, in step S4, the interval distance of the data detection points on the fatigue crack along the X-axis is 0.5 mm;

[0064] As an implementation manner, in step S4 of the present invention, an image measuring instrument is used to collect and record the coordinate values of each detection point.

[0065] Optionally, the present invention can also use a fatigue testing machine to collect and record the coordinate values of each detection point.

[0066] See Figure 2 , S5. Display each detection point in the coordinate system;

[0067] S6. According to the trend of the fatigue crack, select the detection point that obviously starts to deviate from the X-axis; and take this detection point as the initial point, and continuously select m detection points along the X-axis direction;

[0068] As an example, the point with a deviation amount reaching or exceeding 0.2 mm is used as the initial point of deviation.

[0069] S7. Fit the m detection points into a straight line, and the equation of the straight line is denoted as y = a*x + b; the intersection point of this straight line and the X-axis is the reference point (x0, y0), and calculate the coordinate values of the reference point;

[0070] Optionally, substitute y0 = 0 into the straight line equation to obtain the value of x0.

[0071] Optionally, in step S7, the method of fitting the m detection points into a straight line equation is the least squares method;

[0072] As an example, in step S7 of the present invention, the number of m detection points is not less than 5; preferably 8 - 12. Using more detection points to fit the straight line equation makes the equation have a certain representativeness and small calculation result error.

[0073] S8. Calculate the L value and the deflection angle θ value;

[0074] The coordinates of any one of the m detection points are denoted as (x j , y j ); Calculate L = x j - x0; and calculate the angle value of the angle between the connection line of this point and the reference point and the X-axis, which is the deflection angle θ value;

[0075] Optionally, the θ value can be calculated by the following formula:

[0076]

[0077] S9. Repeat step S8 to complete the calculation of the L values and θ values for all points, and record the calculation results.

[0078] S10. Data validity judgment: When L ≥ 0.1W and θ ≤ 20°, the data is determined to be valid; W is the distance value between the origin of the coordinate system and the side of the specimen.

[0079] S11. Continue to take multiple groups of detection points along the X-axis direction, and the number of detection points in each group is m (such as Figure 2 the green points in

[0080] As an embodiment, to avoid the exclusion of valid data, in step S10, when L < 0.1W, the data is determined to be valid when θ ≤ 20°.

[0081] The present invention establishes a coordinate system according to the structure of the test specimen, and converts the selection of reference points and the measurement of deflection angles in the American standard into coordinate detection and data calculation. It simplifies the operation, reduces the measurement difficulty, and improves the detection accuracy and efficiency at the same time. It realizes the rapid and accurate analysis and judgment of the data validity of fatigue crack detection meeting the requirements of the American standard.

[0082] Embodiment 1:

[0083] Refer to Figure 3 and Figure 4 , the present invention provides a data validity analysis of an M(T) specimen 2, with the material being: 7050-T7451 aluminum alloy; the plate thickness B = 6.5 mm. The width is 2W = 135 mm; the fatigue test is carried out in accordance with the requirements of ASTM E647-24.

[0084] Using the operation steps of the above-mentioned analysis method for the data validity of fatigue crack detection, analyze and judge the left front edge crack 21, left rear edge crack 22, right front edge crack 23, and right rear edge crack 24 respectively, and the results are shown in Table 1.

[0085] Note: 1. Select a detection point every 0.5 mm on the X-axis for all edges; 2. The initial recording point of the X-axis coordinate is selected after excluding the lengths of the prefabricated notch 1 and fatigue crack 11 in Table 1; 3. At the end of the test, the crack extends rapidly and turns into tensile tearing, and this part of the crack no longer belongs to the fatigue crack, so its coordinate value is no longer measured.

[0086] Refer to Figures 5 - 8 , according to the fatigue crack trend of each edge, select the detection points that obviously start to deviate from the X-axis; calculate the L values respectively and record them in Table 2; in this embodiment, the point with a deviation amount reaching or exceeding 0.2 mm is used as the initial point of deviation.

[0087] Calculate the θ values of the deflection angles at each point in Table 2 and record them in Table 3.

[0088] Judge the valid data. If the data of the four edge cracks with the same X-axis coordinate are all valid, it is determined to be valid.

[0089] Table 1: Coordinate values of each edge crack of the M(T) specimen

[0090]

[0091]

[0092] Table 2: L values of each edge crack of the M(T) specimen

[0093]

[0094]

[0095] Table 3: Deflection angle θ values of each edge crack of the M(T) specimen

[0096]

[0097]

[0098] Example 2:

[0099] Refer to Figure 9 and Figure 10 , the present invention provides a data validity analysis of the C(T) specimen 3, the material is: 7050-T7451 aluminum alloy; the plate thickness B = 4.5 mm, the width is W = 50 mm; the fatigue test is carried out according to the requirements of ASTM E647-24.

[0100] Using the operation steps of the foregoing analysis method for the data validity of fatigue crack detection, analyze and judge the front edge crack 31 and the rear edge crack 32 respectively, and the results are shown in Table 4.

[0101] Note: 1. Select a detection point every 0.5 mm on the X-axis for all edges; 2. The initial recording point of the X-axis coordinate is selected after removing the length of the prefabricated notch 1 and the fatigue crack 11 in Table 4; 3. At the end of the test, the crack extends rapidly and turns into tensile tearing, and this part of the crack no longer belongs to the fatigue crack, so its coordinate value is no longer measured.

[0102] Refer to Figure 11 and Figure 12 , according to the fatigue crack trend of each edge, select the detection points that obviously start to deviate from the X-axis; calculate the L values respectively and record them in Table 5; in this example, the point with a deviation amount reaching or exceeding 0.2 mm is used as the initial point of deviation.

[0103] Calculate the θ values of the deflection angles at each point in Table 5 and record them in Table 6.

[0104] Judge the valid data. If the data of the front and rear edge cracks with the same X-axis coordinate are both valid, it is determined to be valid.

[0105] Table 4: Coordinate values of each edge crack of the C(T) specimen

[0106]

[0107]

[0108] Table 5: L values of each edge crack of the C(T) specimen

[0109]

[0110] Table 6: Deflection angle θ values of each edge crack of the C(T) specimen

[0111]

[0112]

[0113] In summary, the present invention provides an analysis method for the validity of fatigue crack detection data. By establishing a coordinate system according to the structure of the test specimen, the selection of reference points and the measurement of deflection angles in the American standard are transformed into coordinate detection and data calculation. This simplifies the operation, reduces the measurement difficulty, and at the same time improves the detection accuracy and detection efficiency. It realizes the rapid and accurate analysis and judgment of the validity of fatigue crack detection data that meets the requirements of the American standard.

[0114] Of course, the present invention can also have many other embodiments. Without departing from the spirit and essence of the present invention, those skilled in the art can make various corresponding changes and deformations according to the present invention, but these corresponding changes and deformations should all fall within the protection scope of the appended claims of the present invention.

Claims

1. A method for analyzing the validity of fatigue crack detection data, characterized in that, The steps are as follows: S1. Prepare a test specimen for fatigue test and make a prefabricated notch on the test specimen; a pre-crack with a predetermined length is provided at the end of the prefabricated notch; S2. Establish a coordinate system; Set the straight line segment where the pre-crack is located as the X-axis; draw a straight line segment perpendicular to the X-axis and denote it as the Y-axis; denote the intersection point of the X-axis and the Y-axis as point 0; S3. Clamp the test specimen onto a fatigue testing machine to conduct a fatigue test and form a fatigue crack on the test specimen; S4. At every predetermined length along the X-axis, select a data detection point on the fatigue crack and record the coordinate values (x n , y n ) of the detection point; S5. Display each detection point in the coordinate system; S6. According to the trend of the fatigue crack, select the detection points that obviously start to deviate from the X-axis; and take m consecutive detection points along the X-axis direction with this detection point as the starting point; S7. Fit the m detection points into a straight line, and denote the equation of the straight line as y = a * x + b; the intersection point of this straight line and the X-axis is the reference point (x0, y0), and calculate the coordinate values of the reference point; S8. Calculate the value of L and the value of the deflection angle θ; The coordinates of any one of the m detection points are denoted as (x j , y j ); calculate L = x j - x0; and calculate the angular value of the angle between the line connecting this point and the reference point and the X-axis, which is the deflection angle θ value; S9. Repeat step S8 to complete the calculation of the L values and θ values of all points and record the calculation results; S10. Data validity judgment: When L ≥ 0.1W and θ ≤ 20°, the data is determined to be valid; W is the distance value between point 0 in the coordinate system and the side of the specimen; S11. Continue to take multiple groups of detection points along the X-axis direction, with the number of detection points in each group being m; repeat steps S7 - S10.

2. The analysis method for the validity of fatigue crack detection data according to claim 1, characterized in that The length of the pre-crack is 2 mm.

3. The analysis method for the validity of fatigue crack detection data according to claim 1, wherein The interval distance of the data detection points on the fatigue crack along the X-axis is 0.5 mm.

4. The analysis method for the validity of fatigue crack detection data according to claim 1, wherein In step S6, the point with a deviation amount reaching or exceeding 0.2 mm is used as the initial point of deviation.

5. The analysis method for the validity of fatigue crack detection data according to claim 1, characterized in that, In step S7, the method of fitting the m detection points into a straight line equation is the least squares method.

6. The analysis method for the validity of fatigue crack detection data according to claim 1, characterized in that In step S7, the number of m detection points is not less than 5.

7. The analysis method for the validity of fatigue crack detection data according to claim 1, characterized in that In step S4, an image measuring instrument or a fatigue testing machine is used to collect and record the coordinate values of each detection point.

8. The analysis method for the validity of fatigue crack detection data according to any one of claims 1 to 7, characterized in that, In step S10, when L < 0.1W and θ ≤ 20°, the data is determined to be valid.

9. The analysis method for the validity of fatigue crack detection data according to claim 8, characterized in that The test specimen is an M(T) specimen, and a prefabricated notch is made at the center position of the M(T) specimen 2; point 0 of the coordinate system is set at the center position of the prefabricated notch; The M(T) specimen includes a left front edge crack, a left rear edge crack, a right front edge crack, and a right rear edge crack; each edge respectively adopts the analysis method for the validity of the fatigue crack detection data to judge the validity of the data of each detection point; If the data of the detection points of the four edge cracks with the same X-axis coordinate are all valid, the data is determined to be valid.

10. The analysis method for the validity of fatigue crack detection data according to claim 8, characterized in that, The test specimen is a C(T) specimen, and the prefabricated notch 1 is made on one side of the C(T) specimen; point 0 of the coordinate system is set at the starting position of the prefabricated notch; The C(T) specimen includes a front edge crack and a rear edge crack; each edge respectively adopts the analysis method for the validity of the fatigue crack detection data to judge the validity of the data of each detection point; If the data of the detection points of the two edge cracks with the same X-axis coordinate are all valid, the data is determined to be valid.

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