Method for rapidly evaluating fatigue performance of plate forming part

Abstract

The invention discloses a method for rapidly evaluating the fatigue performance of a plate forming part. The method comprises the following steps: acquiring the deformation of a key position of the part by virtue of a grid strain analysis system, performing bulging simulation on a deformation mode and the deformation of the key position of the part, processing a fatigue sample on a simulated bulging test piece, and performing fatigue performance test on the fatigue sample. According to the method, additional tools and clamps are not needed, the fatigue performance of parts which are machined in different modes such as stamping and rolling and are made of different materials and in different shapes can be simply and rapidly evaluated, and the method can be adopted for evaluating the parts obtained after plate deformation, the parts obtained through stamping deformation or rolling deformation and the complexity of the characteristics of the parts; the device is wide in application range, is suitable for testing the fatigue performance of the part after machining deformation in various modes such as stamping and rolling, is short in test period, and is not restricted by the material, surface quality, shape and size of the part; the method has the characteristics of simplicity, convenience, low cost, high precision and simplicity and convenience in operation.

Description

Technical Field

[0001] This invention relates to the field of sheet metal forming performance evaluation technology, and in particular to a method for rapidly evaluating the fatigue performance of sheet metal formed parts. Background Technology

[0002] Fatigue failure is a major cause of mechanical component damage. Statistics show that 70% of automotive component failures are caused by fatigue. Fatigue cracks typically occur at stress concentration points, and if not assessed in advance, they can lead to sudden fracture, causing equipment failure or even catastrophic accidents. Fatigue performance assessment can quantify the durability limit of components under cyclic loading, thereby mitigating risks in the design process.

[0003] However, current fatigue performance assessments are mostly limited to the sheet metal level. In actual production, sheet metal undergoes a series of deformations to become parts before bearing loads and serving in service. Work hardening or void defects generated during deformation can alter material properties, including fatigue performance. Therefore, sheet metal fatigue performance cannot effectively characterize the fatigue properties of parts. Accurately obtaining part fatigue performance requires applying working loads, which is impossible without specific fixtures. However, parts vary in size and characteristics, making it impossible to share fixtures. Furthermore, fabricating fixtures for each test part in the laboratory is too costly and impractical. Therefore, there is an urgent need to develop a simple, convenient, and rapid laboratory method for evaluating part fatigue performance. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a simple, convenient and rapid method for evaluating the fatigue performance of sheet metal molded parts.

[0005] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows: the deformation amount at key locations of the part is obtained by means of a grid strain analysis system, the deformation mode and deformation amount at key locations of the part are simulated by bulging, fatigue specimens are processed on the simulated bulging test piece, and fatigue performance tests are performed on the fatigue specimens.

[0006] Further, the following steps are included: (1) Select the part to be evaluated, print a grid on the original sheet metal before deformation, and put the original sheet metal into the mold to deform it into the target part. (2) Use a grid strain analysis system to analyze and test the target part and obtain the strain mode and primary and secondary strain values ​​of the key location area of ​​the target part; (3) Take the bulging material sheet and use a flat-head punch die to conduct bulging tests and analyze the strain in the deformation plane area of ​​the test piece; (4) Adjust the strain mode and strain of the test piece by adjusting the width and bulging height of the bulging sheet until they are consistent with the deformation mode of the key position of the target part, and record the width w and bulging height h of the test piece; (5) A flat-head bulging test with a width of w was conducted to obtain a bulging test piece; a fatigue test piece was machined in the middle of the bulging test piece by wire cutting. (6) Perform high-cycle fatigue or low-cycle fatigue tests on fatigue specimens according to the service conditions of the parts to obtain fatigue performance, which is the predicted fatigue property of the parts.

[0007] Furthermore, in step (1), an electrochemical etching method is used to print a grid on the sheet metal before deformation.

[0008] The beneficial effects of adopting the above technical solution are as follows: This invention requires no additional tooling or fixtures, and can simply and quickly evaluate the fatigue performance of parts processed by different methods such as stamping and rolling, as well as parts of different materials and shapes. Any part that has been deformed from sheet metal, whether it is obtained by stamping or rolling, and no matter how complex the characteristics of the part, can be evaluated using this method. It has a wide range of applications and is suitable for fatigue performance testing of parts deformed by various methods such as stamping and rolling. The test cycle is short and is not limited by the material, surface quality, shape, or size of the part. It is simple, convenient, low-cost, high-precision, and easy to operate. Attached Figure Description

[0009] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0010] Figure 1 This is a schematic diagram of the method flow of the present invention; Figure 2 This is the original sheet metal drawing of the target part for the printed mesh described in Embodiment 1 of the present invention; Figure 3 This is a drawing of the target part to be stamped after printing the grid, as described in Embodiment 1 of the present invention. Figure 4 This is a diagram showing the strain analysis results of the key location area of ​​the part described in Embodiment 1 of the present invention; Figure 5 This is a drawing of the bulging part obtained by stamping the printed grid as described in Embodiment 1 of the present invention; Figure 6 This is a diagram showing the distribution of fatigue test specimens taken from the stamped and bulging part according to Embodiment 1 of the present invention. Figure 7 This is a fatigue curve diagram of the part described in Embodiment 1 of the present invention; Figure 8 This is the original sheet metal drawing of the target part for the printed mesh described in Embodiment 2 of the present invention; Figure 9 This is a drawing of the target part to be stamped after printing the grid, as described in Embodiment 2 of the present invention. Figure 10This is a diagram showing the strain analysis results of the key location area of ​​the part described in Embodiment 2 of the present invention; Figure 11 This is a drawing of the bulging part obtained by stamping the printed grid as described in Embodiment 2 of the present invention; Figure 12 This is a diagram showing the distribution of fatigue test specimens taken from the stamped and bulging part according to Embodiment 2 of the present invention. Figure 13 This is a fatigue curve diagram of the part described in Embodiment 2 of the present invention; Figure 14 This is the original sheet metal drawing of the target part for the printed mesh described in Embodiment 3 of the present invention; Figure 15 This is a drawing of the target part to be stamped after the printed grid is described in Embodiment 3 of the present invention; Figure 16 This is a diagram showing the strain analysis results of the key location area of ​​the part described in Embodiment 3 of the present invention; Figure 17 This is a drawing of the bulging part obtained by stamping the printed grid as described in Embodiment 3 of the present invention; Figure 18 This is a diagram showing the distribution of fatigue test specimens taken from the stamped and bulging part according to Embodiment 3 of the present invention. Figure 19 This is a fatigue curve diagram of the part described in Embodiment 3 of the present invention. Detailed Implementation

[0011] Figure 1 As shown, this method for rapidly evaluating the fatigue performance of sheet metal parts includes the following steps: (1) Select the part to be evaluated and print a grid on its original sheet metal before deformation, preferably using an electrochemical etching method, such as... Figure 2 As shown, the original sheet metal is placed in a mold and deformed under stress to form the target part. The shape and size of the grid are adjusted according to the size of the part to facilitate the analysis of strain mode and primary and secondary strain values; the grid shape can be square, hollow circle or solid circle, and the grid size can be adjusted according to the size of the part, using 5×5mm to 1×1mm.

[0012] (2) The target part is analyzed and tested using the printed grid strain analysis system to obtain the strain mode and primary and secondary strain values ​​of the key location area of ​​the target part; the key location area refers to the location with the greatest deformation, the most severe thinning, and the greatest risk of failure; the strain mode includes three types: tensile and compressive strain, plane strain, and bitensile strain; the primary strain value refers to the maximum strain value when the part is plastically deformed, and the secondary strain refers to the strain value under the primary strain.

[0013] (3) Select a bulging sheet with the same material as the original sheet, print a grid on the bulging sheet, preferably using an electrochemical etching method; use a flat-head punch mold to perform a bulging test to obtain a test piece, and use the printed grid strain analysis system to analyze the strain in the deformation plane area of ​​the test piece.

[0014] (4) If the strain mode and strain of the test piece are consistent with the strain mode and primary and secondary strain values ​​obtained in step (2), record the width w and bulging height h of the test piece; if the strain mode and strain of the test piece are inconsistent with the strain mode and primary and secondary strain values ​​obtained in step (2), adjust the width and bulging height of the expansion sheet to adjust the strain mode and strain of the test piece, conduct a bulging test and analyze the strain until the strain mode and strain of the obtained test piece are consistent with the strain mode and primary and secondary strain values ​​obtained in step (2), and record the width w and bulging height h of the test piece. During the adjustment process, different strain paths are obtained by changing the width of the test piece, and the deformation amount of the test piece is adjusted by adjusting the deformation height, so as to obtain a test piece with the same deformation mode as the target part.

[0015] (5) A flat-head bulging test with a height of h is performed using a sample with a width of w. The sample material is the same as that of the original sheet material to obtain the bulging test piece. A fatigue test piece is machined in the middle of the bulging test piece using wire cutting. Multiple copies of the test piece can be made as needed. The sample is rectangular or dog-bone shaped. To ensure the pass rate of bulging sample preparation, it is best to use a dog-bone shaped sample. w represents the width of the parallel section in the middle of the dog-bone shaped sample. The sample length only needs to ensure that the bulging test machine can press it down completely. It can be adjusted according to the specific situation of the test machine.

[0016] (6) Perform high-cycle fatigue or low-cycle fatigue tests on fatigue specimens according to the service conditions of the parts to obtain fatigue performance, which is the predicted fatigue property of the parts.

[0017] (7) Based on the obtained predicted fatigue properties, the stress transmission or fatigue failure simulation prediction analysis of the part structure formed by the original sheet material can guide the application of stress loading on the part or predict the fatigue failure of the part.

[0018] Example 1: Figure 1 As shown, the method for rapidly evaluating the fatigue performance of sheet metal formed parts is described in detail below.

[0019] (1) Figure 2 As shown, an electrochemical etching method is used to print a grid on a sheet of material to be made of QP980 base plate with a thickness of 1.0 mm. Then, the sheet is placed in a mold, and the sheet is deformed under force to become the target part - the base plate part.

[0020] (2) Figure 3 , Figure 4As shown, the key locations of part deformation were determined, and analysis and testing were carried out using a mesh strain analysis system to obtain the strain mode and primary and secondary strain values ​​of the key location area. The analysis revealed that the strain at the location of the maximum deformation of the part under stress was plane strain, the secondary strain was 0, and the primary strain was 0.25.

[0021] (3) Use a flat-head punch mold to conduct a bulging test and analyze the strain in the deformation plane area of ​​the test piece. The strain analysis method is consistent with the strain analysis method of the part in steps (1) and (2).

[0022] (4) Adjust the strain mode and strain of the test piece by adjusting the width and bulging height of the material sheet until they are consistent with the deformation mode of the key position of the target part. At this time, the width w of the bulging sample is 130 mm and the bulging height h is 22 mm. At this time, the secondary strain and principal strain of the planar area of ​​the bulging part are 0 and 0.25, respectively.

[0023] (5) Figure 5 As shown, a flat-head bulging test was conducted using a specimen with a width w of 130 mm and a height h of 22 mm to obtain a bulging test piece. A fatigue specimen was then machined from the middle of the test piece using wire cutting. Figure 6 As shown.

[0024] (6) Based on the service conditions of the base plate parts subjected to tensile stress during operation, fatigue performance tests under tensile stress are performed on the deformed specimens to obtain the fatigue life, fatigue strength, etc. of the parts. Figure 7 As shown, the fatigue relationship in the finite life period is: S a =9129*(2N f ) -0.19821 The fatigue limit is 955 MPa.

[0025] (7) Material selection recommendation evaluation or finite element simulation analysis as needed: The obtained part fatigue curve is used to predict that the part will fail after about 70,378 cycles under 1000MPa / 100MPa cyclic loading (obtained from the finite life fatigue curve). The actual part failed after 70,000 cycles under the same cyclic stress loading. Therefore, the predicted fatigue life is very accurate and can effectively guide the application of the part. Replacement can be carried out before failure to avoid hidden dangers. The stress conditions of the part can also be optimized according to the fatigue limit of 955MPa to ensure that the long-term continuous cyclic loading stress at the maximum deformation position does not exceed 955MPa, and the part will not fail due to fatigue.

[0026] Example 2: Figure 1 As shown, the method for rapidly evaluating the fatigue performance of sheet metal formed parts is described in detail below.

[0027] (1) Figure 8As shown, an electrochemical etching method is used to print a grid on the sheet material of the DP980 longitudinal beam connecting plate part with a thickness of 1.2 mm. Then, the sheet material is placed in a mold, and the sheet material is deformed under force to become the target part - the longitudinal beam connecting plate.

[0028] (2) Figure 9 , Figure 10 As shown, the key locations of part deformation were determined, and analysis and testing were carried out using a mesh strain analysis system to obtain the strain mode and primary and secondary strain values ​​of the key location area. The analysis revealed that the strain at the location of the maximum deformation of the part under stress was bitensile strain, with a secondary strain of 0.12 and a primary strain of 0.20.

[0029] (3) Use a flat-head punch mold to conduct a bulging test and analyze the strain in the deformation plane area of ​​the test piece. The strain analysis method is consistent with the strain analysis method of the part in steps (1) and (2).

[0030] (4) Adjust the strain mode and strain of the test piece by adjusting the width and bulging height of the material sheet until they are consistent with the deformation mode of the key position of the target part. At this time, the width w of the bulging sample is 160 mm and the bulging height h is 18 mm. At this time, the secondary strain and principal strain of the planar area of ​​the bulging part are 0.12 and 0.20, respectively.

[0031] (5) Figure 11 As shown, a flat-head bulging test was conducted using a specimen with a width w of 160 mm and a height h of 18 mm to obtain a bulging test piece. A fatigue specimen was then machined from the middle of the test piece using wire cutting. Figure 12 As shown.

[0032] (6) Based on the service conditions of the base plate parts subjected to tensile stress during operation, fatigue performance tests under tensile stress are performed on the deformed specimens to obtain the fatigue life, fatigue strength, etc. of the parts. Figure 13 As shown, the fatigue relationship in the finite life period is: S a =20902*(2N f ) -0.2665 The fatigue limit is 890 MPa.

[0033] (7) Material selection recommendation evaluation or finite element simulation analysis as needed: The obtained part fatigue curve is used to predict that the part will fail after about 94,857 cycles under 1000MPa / 100MPa cyclic loading (obtained from the finite life fatigue curve). The actual part failed after 93,200 cycles under the same cyclic stress loading. Therefore, the predicted fatigue life is very accurate and can effectively guide the application of the part. Replace it before failure to avoid hidden dangers. The stress conditions of the part can also be optimized according to the fatigue limit of 890MPa to ensure that the long-term continuous cyclic loading stress at the maximum deformation position does not exceed 890MPa, and the part will not fail due to fatigue.

[0034] Example 3: Figure 1 As shown, the method for rapidly evaluating the fatigue performance of sheet metal formed parts is described in detail below.

[0035] (1) Figure 14 As shown, an electrochemical etching method is used to print a grid on the sheet material of DP780 reinforcing plate with a thickness of 1.4 mm to be prepared. Then, it is placed in a mold, and the sheet material is deformed under force to become the target part - the reinforcing plate.

[0036] (2) Figure 15 , Figure 16 As shown, the key locations of part deformation were determined, and analysis and testing were carried out using a mesh strain analysis system to obtain the strain mode and primary and secondary strain values ​​of the key location area. The analysis showed that the strain at the location of the maximum stress deformation of the part was tensile and compressive strain, the secondary strain was -0.18, and the primary strain was 0.30.

[0037] (3) Use a flat-head punch mold to conduct a bulging test and analyze the strain in the deformation plane area of ​​the test piece. The strain analysis method is consistent with the strain analysis method of the part in steps (1) and (2).

[0038] (4) Adjust the strain mode and strain of the test piece by adjusting the width and bulging height of the material sheet until they are consistent with the deformation mode of the key position of the target part. At this time, the width w of the bulging specimen is 80 mm and the bulging height h is 28 mm. At this time, the secondary strain and principal strain of the planar area of ​​the bulging part are -0.18 and 0.30, respectively.

[0039] (5) Figure 17 As shown, a flat-head bulging test was conducted using a specimen with a width w of 80 mm and a height h of 28 mm to obtain a bulging test piece. A fatigue specimen was then machined from the middle of the test piece using wire cutting. Figure 18 As shown.

[0040] (6) Based on the service conditions of the base plate parts subjected to tensile stress during operation, fatigue performance tests under tensile stress are performed on the deformed specimens to obtain the fatigue life, fatigue strength, etc. of the parts. Figure 19 As shown, the fatigue relationship in the finite life segment is: Sa = 4308 * (2Nf) -0.14284 The fatigue limit is 750 MPa.

[0041] (7) Material selection recommendation evaluation or finite element simulation analysis as needed: The obtained part fatigue curve is used to predict that the part will fail after about 126,214 cycles under 800MPa / 80MPa cyclic loading (obtained from the finite life fatigue curve). The actual part failed after 126,000 cycles under the same cyclic stress loading. Therefore, the predicted fatigue life is very accurate and can effectively guide the application of the part. Replace it before failure to avoid hidden dangers. The stress condition of the part can also be optimized according to the fatigue limit of 750MPa to ensure that the long-term continuous cyclic loading stress at the maximum deformation position does not exceed 750MPa, and the part will not fail due to fatigue.

Claims

1. A method for rapidly evaluating the fatigue performance of sheet metal formed parts, characterized in that: The deformation at key locations of a part is obtained using a mesh strain analysis system. The deformation mode and amount at key locations of the part are simulated by bulging. Fatigue specimens are then machined on the simulated bulging test piece, and fatigue performance tests are performed on the fatigue specimens.

2. The method for rapidly evaluating the fatigue performance of sheet metal formed parts according to claim 1, characterized in that, The following steps are included: (1) Select the part to be evaluated, print a grid on the original sheet material before deformation, put the original sheet material into the mold to deform it into the target part; (2) Use a grid strain analysis system to analyze and test the target part and obtain the strain mode and primary and secondary strain values ​​of the key location area of ​​the target part; (3) Take the bulging material sheet and use a flat-head punch die to conduct the bulging test, and analyze the strain in the deformation plane area of ​​the test piece; (4) Adjust the strain mode and strain of the test piece by adjusting the width and bulging height of the bulging sheet until they are consistent with the deformation mode of the key position of the target part, and record the width w and bulging height h of the test piece; (5) A flat-head bulging test with a width of w was conducted to obtain a bulging test piece; a fatigue test piece was machined in the middle of the bulging test piece by wire cutting. (6) Perform high-cycle fatigue or low-cycle fatigue tests on fatigue specimens according to the service conditions of the parts to obtain fatigue performance, which is the predicted fatigue property of the parts.

3. The method for rapidly evaluating the fatigue performance of sheet metal formed parts according to claim 2, characterized in that: In step (1), an electrochemical etching method is used to print a grid on the sheet metal before deformation.

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