Method for calculating fatigue limit of aluminum alloy by utilizing defects and yield strength

Abstract

The invention provides a method for calculating the fatigue limit of an aluminum alloy by utilizing defects and yield strength, which comprises the following steps: S1, obtaining the yield strength of the aluminum alloy by utilizing a tensile test; s2, a fatigue test is utilized, a large load is loaded, the sample is broken within 2 hours, and a fatigue fracture is obtained; s3, observing a fatigue crack source, and measuring the defect area and the like of the crack source; s4, according to the results of the steps S1 and S3, calculating the fatigue limit by using a mathematical relationship between the yield strength, the defect area and the like and the fatigue limit to obtain a first fatigue strength value; s5, repeating the steps S2, S3 and S4 to obtain a second fatigue strength value; repeating the steps S2, S3 and S4 again to obtain a third fatigue strength value; and by parity of reasoning, after three or more fatigue strength values are obtained, an average value, namely the fatigue limit, is obtained. The method has the beneficial effects that the defect and the yield strength are comprehensively considered, the accuracy of the calculated fatigue limit is higher, and time, manpower and material resources are saved.

Description

Technical Field

[0001] The invention belongs to the field of aluminum alloy fatigue limit calculation, and in particular relates to a method for calculating the aluminum alloy fatigue limit by utilizing defects and yield strength. Background Art

[0002] Fatigue limit refers to the ability of a material to resist microstructural damage under alternating stress, which is usually manifested as the ability of a material's microscopic cracks to expand into macroscopic visible cracks. When a material is repeatedly subjected to alternating stress, fatigue fracture occurs. From a microscopic scale, when the material is subjected to stress, dislocation slip occurs, i.e., microscopic plastic deformation occurs. From a macroscopic scale, fatigue fracture specimens often do not undergo obvious plastic deformation, especially high-cycle fatigue fracture.

[0003] In the prior art, for aluminum alloy materials with a yield strength less than 1400MPa, it is believed that the fatigue limit and the yield strength are approximately in a certain proportional relationship, so the fatigue limit is roughly calculated using the yield strength. However, the yield strength refers to the yield limit of the metal material when the yield phenomenon occurs, that is, the stress to resist a small amount of plastic deformation. From a microscopic scale, when the material is subjected to stress, dislocation slip occurs, that is, microscopic plastic deformation occurs. From a macroscopic scale, the yielded specimen often undergoes obvious plastic deformation. Therefore, although the yield strength and the fatigue limit have a certain degree of relationship, the fatigue limit is calculated only by using the proportional relationship, and the error is large.

[0004] In the prior art, the fatigue limit of aluminum alloy is obtained in the following way: for a specific aluminum alloy material, its fatigue limit is usually obtained through fatigue testing, and periodic stress is applied to the material to simulate its stress conditions in actual use. The lifting method is currently the most widely used test method for testing fatigue limit. It starts from a stress level higher than the fatigue limit of the measured material and gradually reduces the stress until the material is damaged or reaches a predetermined number of cycles. If the first specimen fails before reaching the fatigue life, the second specimen is tested at a reduced stress level. Otherwise, the second specimen is tested at an increased stress level, and so on. A failed specimen and a non-failed specimen are grouped together, and the average value is calculated as the fatigue limit of the material. For aluminum alloys, a complete lifting method test requires at least 5 groups of specimens, that is, 10 specimens (there is a high probability that several specimens pass or fail, and cannot be paired and grouped, so at least 10 specimens are required); an aluminum alloy specimen is considered to have passed if the number of cycles exceeds 25 million. If the fatigue test is carried out at a test frequency of 125Hz, that is, 125 times per second, an aluminum alloy specimen that passes the fatigue test takes about 56 hours of testing time, so a complete aluminum alloy lifting method test takes at least 560 hours. Therefore, determining the fatigue limit of aluminum alloys requires a lot of manpower, material resources and financial resources.

[0005] In the prior art, it is believed that the fatigue limit is closely related to the defects of the test sample, especially the defect area, because most fatigue cracks are located at the defects. For aluminum alloy materials, it is believed that the fatigue limit and the defect area have a certain mathematical relationship, and the fatigue limit is calculated using the defect area. However, even for the same alloy with the same defect area, if their structures or states are different, such as different grain sizes, the fatigue limits of cast samples and heat-treated samples will be different. Therefore, the error in calculating the fatigue limit using the defect area is large.

[0006] A large number of studies have shown that, for aluminum alloys, the structure and state of the alloy are closely related to the yield strength, while defects have little effect on the yield strength. If defects and yield strength are considered comprehensively, the error in calculating the fatigue limit will be reduced.

[0007] In the prior art, the yield strength of aluminum alloy is obtained in the following way: for a specific aluminum alloy material, its yield strength is usually obtained through a room temperature tensile test. At room temperature, a tensile force is applied to a metal sample to cause it to undergo tensile deformation until it breaks, and the yield strength is obtained. Generally, it takes less than 20 minutes for a sample to break, and the time required is very short. The yield strength of the material can be obtained by measuring three to five samples and taking the average value, and very few samples are required.

[0008] In the prior art, the defect area is obtained by placing the fatigue fracture surface of a specific aluminum alloy material under a scanning electron microscope, finding the defects at the crack source, and measuring the defect area. The time and cost required are very low. Therefore, if the fatigue limit of the alloy can be accurately calculated using defects and yield strength, a lot of time, manpower, material and financial resources will be saved.

[0009] Based on this, the present invention comprehensively considers defects and yield strength that are closely related to the fatigue limit of aluminum alloys, and provides a method for calculating the fatigue limit of aluminum alloys using defects and yield strength. Summary of the invention

[0010] In view of this, the present invention aims to propose a method for calculating the fatigue limit of aluminum alloy using defects and yield strength, so as to solve at least one problem existing in the above-mentioned prior art.

[0011] To achieve the above object, the technical solution of the present invention is achieved as follows: A method for calculating the fatigue limit of aluminum alloy using defects and yield strength comprises the following steps: S1. Obtaining yield strength: For the aluminum alloy for which fatigue limit needs to be calculated, the yield strength of the aluminum alloy is obtained by using a room temperature tensile test method; S2. Obtaining fatigue fracture: For the aluminum alloy for which fatigue limit calculation is required, a fatigue test method is used to load a large load, so that the aluminum alloy sample is fatigue fractured within a time not exceeding 2 hours, and the fatigue fracture of the aluminum alloy is obtained; S3. Obtaining the defect area of ​​the fatigue crack source: observing the fatigue crack source, measuring the defect area of ​​the crack source, etc.; S4, calculating the first fatigue strength value: according to the results of steps S1 and S3, the fatigue limit is calculated using the mathematical relationship between the yield strength, the defect area, etc. and the fatigue limit to obtain the first fatigue strength value of the alloy; S5. Calculate the fatigue limit: repeat steps S2, S3, and S4 to obtain the second fatigue strength value of the alloy; repeat steps S2, S3, and S4 again to obtain the third fatigue strength value of the alloy; and so on, and then calculate the average value of all fatigue strength values, which is the fatigue limit of the alloy.

[0012] Furthermore, in step S4, the mathematical relationship between the yield strength, defect area, etc. and the fatigue limit is as follows: When the ratio of the defect diameter to the distance from the defect center to the fracture edge is ≥1.6: When the ratio of the defect diameter to the distance from the defect center to the fracture edge is less than 1.6: In the formula, It is a constant related to the material composition and is the essential property of the material, such as M=10.5 for Al-7Si alloy and M=3.5 for Al-5Cu alloy; is the yield strength; is the area of ​​the defect.

[0013] Furthermore, in step S5, the number of fatigue strength values ​​must be ≥3.

[0014] An electronic device comprises a processor and a memory which is in communication with the processor and is used to store instructions executable by the processor. The processor is used to execute a method for calculating the fatigue limit of an aluminum alloy by using defects and yield strength.

[0015] A server includes at least one processor and a memory connected to the processor in communication, wherein the memory stores instructions executable by the at least one processor, and the instructions are executed by the processor to enable the at least one processor to execute the method for calculating the fatigue limit of an aluminum alloy using defects and yield strength.

[0016] A computer-readable storage medium stores a computer program, and when the computer program is executed by a processor, the method for calculating the fatigue limit of an aluminum alloy by using defects and yield strength is implemented.

[0017] Compared with the prior art, the method for calculating the fatigue limit of aluminum alloy using defects and yield strength described in the present invention has the following advantages: (1) The method for calculating the fatigue limit of aluminum alloy using defects and yield strength described in the present invention comprehensively considers defects and yield strength, two factors that are closely related to the fatigue limit, and the calculated fatigue limit is more accurate and has more reference significance. In the prior art, only defects or only yield strength are considered.

[0018] (2) The method for calculating the fatigue limit of aluminum alloy by using defects and yield strength described in the present invention takes a short time to obtain fatigue fracture specimens, and only requires at least 3 fatigue specimens, thus saving a lot of time, manpower, material and financial resources.

[0019] (3) The method for calculating the fatigue limit of aluminum alloy using defects and yield strength described in the present invention has simple test and calculation methods and strong operability. In the prior art, the lifting method for measuring fatigue limit is complicated and requires rich experience and accumulation of original data to reasonably set the stress size, and it is necessary to constantly try to change the stress size. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] The accompanying drawings constituting a part of the present invention are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the accompanying drawings:

[0021] Figure 1 This is a schematic diagram of a fatigue crack source according to Embodiment 1 of the present invention; Figure 2 This is a schematic diagram of the test results of the lifting method according to the first embodiment of the present invention; Figure 3 This is a schematic diagram of a fatigue crack source according to the second embodiment of the present invention; Figure 4 This is a schematic diagram of a fatigue crack source according to Embodiment 3 of the present invention; Figure 5 It is a schematic diagram of the process of the present invention. DETAILED DESCRIPTION

[0022] It should be noted that, in the absence of conflict, the embodiments of the present invention and the features in the embodiments may be combined with each other.

[0023] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside" and the like indicate positions or positional relationships based on the positions or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as limiting the present invention. In addition, the terms "first", "second", and the like are only used for descriptive purposes, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, features defined as "first", "second", and the like may explicitly or implicitly include one or more of the features. In the description of the present invention, unless otherwise specified, "multiple" means two or more.

[0024] In the description of the present invention, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood by specific circumstances.

[0025] The present invention will be described in detail below with reference to the accompanying drawings and in conjunction with embodiments.

[0026] like Figure 5 As shown, a method for calculating the fatigue limit of aluminum alloy using defects and yield strength comprises the following steps: S1. Obtaining yield strength: For the aluminum alloy for which fatigue limit needs to be calculated, the yield strength of the aluminum alloy is obtained by using a room temperature tensile test method; S2. Obtaining fatigue fracture: For the aluminum alloy for which fatigue limit calculation is required, a fatigue test method is used to load a large load, so that the aluminum alloy sample is fatigue fractured within a time not exceeding 2 hours, and the fatigue fracture of the aluminum alloy is obtained; S3. Obtaining the defect area of ​​the fatigue crack source: observing the fatigue crack source, measuring the defect area of ​​the crack source, etc.; S4, calculating the first fatigue strength value: according to the results of steps S1 and S3, the fatigue limit is calculated using the mathematical relationship between the yield strength, the defect area, etc. and the fatigue limit to obtain the first fatigue strength value of the alloy; S5. Calculate the fatigue limit: repeat steps S2, S3, and S4 to obtain the second fatigue strength value of the alloy; repeat steps S2, S3, and S4 again to obtain the third fatigue strength value of the alloy; and so on, and then calculate the average value of all fatigue strength values, which is the fatigue limit of the alloy.

[0027] The present invention also proposes an electronic device, comprising a processor and a memory connected to the processor for storing executable instructions for the processor, wherein the processor is used to execute the method for calculating the fatigue limit of aluminum alloy using defects and yield strength.

[0028] The present invention also proposes a server, comprising at least one processor and a memory communicatively connected to the processor, wherein the memory stores instructions executable by the at least one processor, and the instructions are executed by the processor so that the at least one processor executes the method for calculating the fatigue limit of an aluminum alloy using defects and yield strength.

[0029] The present invention also provides a computer-readable storage medium storing a computer program, wherein when the computer program is executed by a processor, the method for calculating the fatigue limit of an aluminum alloy using defects and yield strength is implemented.

[0030] Advantages of the present invention: The present invention comprehensively considers two factors closely related to fatigue limit, namely, defect and yield strength, and the calculated fatigue limit is more accurate and has more reference significance. In the prior art, only defect or yield strength is considered.

[0031] The time required for obtaining the fatigue fracture specimens in the present invention is short, and at least only three fatigue specimens are required, thus saving a great deal of time, manpower, material resources and financial resources.

[0032] The test and calculation methods used in the present invention are simple and highly operable. In the prior art, the lifting method for measuring fatigue limit is complex to operate, requires rich experience and accumulation of original data to reasonably set the stress magnitude, and requires continuous attempts to change the stress magnitude.

[0033] Embodiment 1: The aluminum alloy selected is a cast Al-7Si alloy, hereinafter referred to as alloy A.

[0034] S1. Obtaining yield strength: For alloy A, the yield strength of the aluminum alloy is obtained by using the room temperature tensile test method. = 170 MPa; S2. Obtaining fatigue fracture: For alloy A, a large load is applied by fatigue test method, so that the aluminum alloy sample is fatigue fractured within a time not exceeding 2 hours, and the fatigue fracture of the aluminum alloy is obtained, such as Figure 1 As shown; S3. Obtain the defect area of ​​fatigue crack source: observe the fatigue crack source, measure the defect area of ​​the crack source, etc. The defect area is about =287094μm 2 .

[0035] S4, calculate the first fatigue strength value: According to the results of steps S1 and S3, the fatigue limit is calculated using the mathematical relationship between yield strength, defect area, etc. and fatigue limit, as shown below, to obtain the first fatigue strength value of the alloy. =87.04 MPa; The defect diameter is about 597 μm, the distance from the defect center to the fracture edge is about 333 μm, and the ratio of the defect diameter to the distance from the defect center to the fracture edge is 1.8. The fatigue strength value is calculated as follows: S5. Calculate fatigue limit: Repeat steps S2, S3, and S4 to obtain the second fatigue strength value of the alloy. =98.63 MPa; repeat steps S2, S3, and S4 again to obtain the third fatigue strength value of the alloy = 80.21 MPa; the average value of all fatigue strength values ​​is 88.63 MPa, that is, the fatigue limit of the alloy is 88.63 MPa.

[0036] The fatigue limit of alloy A in this state was determined to be 87 MPa by the lifting method test. It can be seen that the fatigue limit calculated by the present invention has a high accuracy. 14 specimens were used in this lifting method. It can be seen that the present invention can save a lot of time, manpower, material resources and financial resources. The test results of the lifting method are shown in Figure 2 shown.

[0037] Embodiment 2: The aluminum alloy selected is a cast Al-7Si alloy, which has a different structure compared with the embodiment 1 and is referred to as alloy B below.

[0038] The aluminum alloy selected is a cast Al-7Si alloy, hereinafter referred to as alloy B.

[0039] S1. Obtaining yield strength: For alloy B, the yield strength of the aluminum alloy is obtained by using the room temperature tensile test method. = 153 MPa; S2. Obtaining fatigue fracture: For alloy B, a large load is applied by fatigue test method, so that the aluminum alloy sample is fatigue fractured within a time not exceeding 2 hours, and the fatigue fracture of the aluminum alloy is obtained, such as Figure 3 As shown; S3. Obtain the defect area of ​​fatigue crack source: observe the fatigue crack source, measure the defect area of ​​the crack source, etc. The defect area is about =86347μm 2 .

[0040] S4, calculate the first fatigue strength value: According to the results of steps S1 and S3, the fatigue limit is calculated using the mathematical relationship between yield strength, defect area, etc. and fatigue limit, as shown below, to obtain the first fatigue strength value of the alloy. =81.34 MPa; The defect diameter is about 301 μm, the distance from the defect center to the fracture edge is about 250 μm, the ratio of the defect diameter to the distance from the defect center to the fracture edge is 1.2, and the fatigue strength value is calculated as follows: S5. Calculate fatigue limit: Repeat steps S2, S3, and S4 to obtain the second fatigue strength value of the alloy. =75.58 MPa; repeat steps S2, S3, and S4 again to obtain the third fatigue strength value of the alloy = 82.98 MPa; the average value of all fatigue strength values ​​is 88.63 MPa, which means that the fatigue limit of the alloy is 79.97 MPa.

[0041] The fatigue limit of Alloy B in this state was measured by the lift method test and was found to be 83 MPa.

[0042] Embodiment three: The aluminum alloy selected is a cast Al-5Cu alloy, hereinafter referred to as alloy C.

[0043] S1. Obtaining yield strength: For alloy C, the yield strength of the aluminum alloy is obtained by using the room temperature tensile test method. = 430 MPa; S2. Obtaining fatigue fracture: For alloy C, a large load is applied by fatigue test method, so that the aluminum alloy sample is fatigue fractured within a time not exceeding 2 hours, and the fatigue fracture of the aluminum alloy is obtained, such as Figure 4 As shown; S3. Obtain the defect area of ​​fatigue crack source: observe the fatigue crack source, measure the defect area of ​​the crack source, etc. The defect area is about =116622μm 2 .

[0044] S4, calculate the first fatigue strength value: According to the results of steps S1 and S3, the fatigue limit is calculated using the mathematical relationship between yield strength, defect area, etc. and fatigue limit, as shown below, to obtain the first fatigue strength value of the alloy. =91.90 MPa; The defect diameter is about 371 μm, the distance from the defect center to the fracture edge is about 146 μm, the ratio of the defect diameter to the distance from the defect center to the fracture edge is 2.4, and the fatigue strength value is calculated as follows: S5. Calculate fatigue limit: Repeat steps S2, S3, and S4 to obtain the second fatigue strength value of the alloy. =82.57 MPa; repeat steps S2, S3, and S4 again to obtain the third fatigue strength value of the alloy = 89.35 MPa; the average value of all fatigue strength values ​​is 87.94 MPa, that is, the fatigue limit of the alloy is 87.94 MPa.

[0045] The fatigue limit of the alloy C in this state was measured by the lifting method test and was found to be 90 MPa.

[0046] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for calculating the fatigue limit of aluminum alloy using defects and yield strength, characterized in that: The following steps are involved: S1. Obtaining yield strength: For the aluminum alloy for which fatigue limit needs to be calculated, the yield strength of the aluminum alloy is obtained by using a room temperature tensile test method; S2. Obtaining fatigue fracture: For the aluminum alloy for which fatigue limit calculation is required, a fatigue test method is used to load a large load, so that the aluminum alloy sample is fatigue fractured within a time not exceeding 2 hours, and the fatigue fracture of the aluminum alloy is obtained; S3. Obtaining the defect area of ​​the fatigue crack source: observing the fatigue crack source, measuring the defect area of ​​the crack source, etc.; S4, calculating the first fatigue strength value: according to the results of steps S1 and S3, the fatigue limit is calculated using the mathematical relationship between the yield strength, the defect area, etc. and the fatigue limit to obtain the first fatigue strength value of the alloy; S5. Calculate the fatigue limit: repeat steps S2, S3, and S4 to obtain the second fatigue strength value of the alloy; repeat steps S2, S3, and S4 again to obtain the third fatigue strength value of the alloy; and so on, and then calculate the average value of all fatigue strength values, which is the fatigue limit of the alloy.

2. The method for calculating the fatigue limit of aluminum alloy using defects and yield strength according to claim 1, characterized in that: In step S4, the mathematical relationship between the yield strength, defect area, etc. and the fatigue limit is as follows: When the ratio of the defect diameter to the distance from the defect center to the fracture edge is ≥1.6: ； When the ratio of the defect diameter to the distance from the defect center to the fracture edge is less than 1.6: ； In the formula, It is a constant related to the material composition and is the essential property of the material, such as M=10.5 for Al-7Si alloy and M=3.5 for Al-5Cu alloy; is the yield strength; is the area of ​​the defect.

3. The method for calculating the fatigue limit of aluminum alloy using defects and yield strength according to claim 1, characterized in that: In step S5, the number of fatigue strength values ​​must be ≥3.

4. An electronic device, comprising a processor and a memory connected to the processor for storing instructions executable by the processor, characterized in that: The processor is used to execute the method for calculating the fatigue limit of aluminum alloy using defects and yield strength as described in any one of claims 1 to 3 above.

5. A server, characterized in that: It includes at least one processor and a memory that is communicatively connected to the processor, wherein the memory stores instructions that can be executed by the at least one processor, and the instructions are executed by the processor so that the at least one processor executes a method for calculating the fatigue limit of an aluminum alloy using defects and yield strength as described in any one of claims 1-3.

6. A computer-readable storage medium storing a computer program, characterized in that: When the computer program is executed by a processor, the method for calculating the fatigue limit of an aluminum alloy using defects and yield strength as described in any one of claims 1 to 3 is implemented.

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