A method for fatigue safety evaluation of engineering components under alternating stress

Abstract

The application provides a fatigue safety evaluation method of engineering components under alternating stress, comprising the following steps: S1, obtaining fatigue failure cycles N and fatigue stress range Delta sigma of a failure sample; S2, obtaining a formula of the fatigue failure cycles N and the fatigue stress range Delta sigma of the sample; S3, obtaining a sample critical crack length a corresponding to the failure sample f ; S4, obtaining a formula of the fatigue stress range Delta sigma, the fatigue failure cycles N and the sample critical crack length a f ; S5, obtaining a formula of the sample critical crack length a f and the corresponding fatigue stress range Delta sigma; S6, calibrating a formula of a stress intensity factor range Delta K of a sample crack tip and a sample crack length a; S7, determining critical fracture toughness Delta K fc of the engineering component material under different stress ranges Delta sigma; the fatigue critical fracture toughness under different fatigue stress ranges obtained by the application conforms to actual fracture characteristics of the engineering component material under different fatigue working conditions, and effectively guarantees the accuracy of the fatigue safety evaluation of the engineering component.

Description

Technical Field

[0001] This invention belongs to the field of fatigue safety assessment technology, specifically relating to a method for fatigue safety assessment of engineering components under alternating stress. Background Technology

[0002] For materials with cracks, the stress intensity factor K1 is generally used to express the strength of the stress-strain field at the crack tip. Currently, the plane strain fracture toughness K is commonly used. IC As a criterion for crack instability, that is, when K1≤K IC When the component is safe, K1>K IC The component will then break and fail.

[0003] However, in practical engineering applications, it has been found that when subjected to alternating loads, the actual crack propagation length of some engineering components is less than that determined by the plane strain fracture toughness K. IC Failure or damage occurs when the calculated critical crack length is reached, i.e., when the stress intensity factor K1 is lower than the plane strain fracture toughness K. IC Fracture occurred under these conditions; that is, the plane strain fracture toughness K obtained under quasi-static uniaxial loading conditions... IC It cannot effectively assess the safety of components under alternating loads. Summary of the Invention

[0004] In view of the shortcomings of the prior art, the purpose of this invention is to provide a fatigue safety assessment method for engineering components under alternating stress, wherein the obtained fatigue critical fracture toughness is more consistent with the actual fracture characteristics of component materials under different fatigue conditions, thereby achieving the purpose of accurately assessing the fatigue safety of engineering components under alternating stress.

[0005] To achieve the above and other related objectives, the present invention provides a method for fatigue safety assessment of engineering components, the method comprising the following steps:

[0006] S1. Conduct high-cycle fatigue tests on multiple specimens made of engineering component materials under the same stress ratio but different fatigue stress ranges, and record the fatigue failure cycle N of the failed specimens. f and fatigue stress range Δσ; the failed specimen has less than 10 cycles. 7 For specimens where the crack extends to the critical length at the next fatigue failure cycle N, the fatigue failure cycle N is... f The actual number of cycles for the failed specimen; the specimen is a specimen with a circular cross-section;

[0007] S2, By analyzing the fatigue failure cycles N of each failed specimen. f The fatigue stress range Δσ is fitted with a power function to obtain the number of fatigue failure cycles N of the specimen. fThe first fitting formula with the fatigue stress range Δσ: N f =P(Δσ) q Where P is the first fitting parameter and q is the first fitting exponent;

[0008] S3. After marking the crack lead edge of each failed specimen, pull each failed specimen apart to obtain the critical crack length 'a' of the corresponding failed specimen. f ;

[0009] S4. By analyzing the fatigue stress range Δσ and fatigue failure cycles N of each failed specimen... f and the critical crack length a of the sample f By performing fitting, the fatigue stress range Δσ and the number of fatigue failure cycles N can be obtained. f and the critical crack length a of the sample f The second fitting formula: a f =N f A(Δσ) m Where A is the second fitting parameter; m is the second fitting index;

[0010] S5. Obtain the critical crack length a of the sample using the first and second fitting formulas. f The relationship between the stress range Δσ and the fatigue stress range is: a f =AP(Δσ) m+q ;

[0011] S6. Calibrate the coefficients in the relationship between the stress intensity factor range ΔK and the crack length a to determine the final relationship between the stress intensity factor range ΔK and the crack length a of the specimen:

[0012]

[0013] Where ΔF is the range of fatigue loads borne by the specimen;

[0014] D is the diameter of the cross-section at the center of the sample;

[0015] S0 is the original cross-sectional area at the center of the sample, derived from the formula... Sure;

[0016] The geometric factor coefficient of the sample;

[0017] k0~k n The coefficients obtained from calibration;

[0018] n+1 is the number of different cycles in the calibration test, and n is usually 4;

[0019] S7. The critical crack length a of the specimen under different fatigue stress ranges Δσ. fThe corresponding stress intensity factor range ΔK of the specimen is calculated, and then the critical fracture toughness ΔK of the engineering component material under different stress ranges Δσ is determined. fc ; through the critical fracture toughness ΔK of the engineering component material fc The fatigue safety of engineering components under different stress ranges Δσ is evaluated;

[0020] The critical fracture toughness ΔK of the engineering component material fc The stress range Δσ satisfies the following formula:

[0021]

[0022] Preferably, the critical fracture toughness ΔK of the engineering component material is obtained. fc The ratio of the stress range Δσ to the fatigue critical crack length a of the engineering component is then obtained. fc ; through the fatigue critical crack length a of the engineering component fc The fatigue safety of engineering components under different stress ranges Δσ is evaluated; the critical fatigue crack length a of the engineering components is determined. fc The calculation formula is:

[0023]

[0024] Where α is the geometric shape factor of the engineering component, which can be obtained by looking up a table.

[0025] Preferably, the calibration process in step S6 includes the following steps:

[0026] S61. Conduct fatigue tests on n+1 specimens made of engineering component materials under different cycles, the same stress ratio, and the same fatigue load range, and record the number of specimens n+1, the fatigue load range ΔF, and the crack length a of the specimen corresponding to the number of cycles.

[0027] S62. Obtain the stress intensity factor range ΔK for the corresponding number of cycles;

[0028] S63. Using the obtained fatigue load range ΔF, the crack length a of the specimen under different cycles, and the corresponding stress intensity factor range ΔK, calculate the coefficients k0~k in the relationship between the stress intensity factor range ΔK and the crack length a of the specimen. n .

[0029] Preferably, step S61 is replaced by: performing a calibration fatigue test on a specimen made of engineering component material under the same stress ratio and the same fatigue load range, with the number of cycles increasing sequentially, to obtain the number of different cycle numbers n+1, the fatigue load range ΔF, and the specimen crack length a corresponding to the number of cycles.

[0030] Preferably, the stress intensity factor range ΔK corresponding to the number of cycles is obtained by mathematical analysis, boundary configuration, or finite element method.

[0031] Preferably, the crack leading edge of the failed specimen in step S3 is marked using a heat-coloring method or a secondary fatigue method.

[0032] As described above, the fatigue safety assessment method for engineering components under alternating stress according to the present invention has the following beneficial effects:

[0033] The fatigue safety assessment method for engineering components under alternating stress of the present invention fully considers the influence of alternating stress on the fatigue critical fracture toughness of the engineering component material. By conducting high-cycle fatigue tests on the specimens made of the engineering component material, the critical crack length of the specimens under different stress ranges is obtained, and then the stress intensity factor range of the corresponding crack tip of the specimen is obtained, thereby obtaining the fatigue critical fracture toughness of the engineering component material under the corresponding stress range, that is, obtaining the actual fracture characteristics of the engineering component material under different fatigue conditions, thereby achieving an accurate assessment of the fatigue safety of the engineering component.

[0034] Compared to traditional fatigue safety assessments, which require calculating the stress intensity range at the crack tip of an engineering component, resulting in high computational complexity and long calculation time, this invention first uses the slope of the curve relating fatigue critical fracture toughness to stress range to quickly determine the fatigue critical crack length of the corresponding engineering component, and then measures the actual crack length of the engineering component to conduct fatigue safety assessment, effectively improving assessment efficiency. Attached Figure Description

[0035] Figure 1 This is a flowchart of the fatigue safety assessment method for engineering components under alternating stress according to the present invention.

[0036] Figure 2 The fitting curve of the failure cycle and stress range of the failed specimen in the embodiments of the present invention.

[0037] Figure 3 This is a curve showing the relationship between the fatigue critical crack length, fatigue critical fracture toughness, and stress range of the engineering component in an embodiment of the present invention. Detailed Implementation

[0038] The following specific embodiments illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification.

[0039] Please see Figures 1 to 3It should be understood that the structures, proportions, sizes, etc., illustrated in the accompanying drawings are merely for illustrative purposes to aid those skilled in the art and to facilitate understanding and reading. They are not intended to limit the scope of the invention and therefore have no substantial technical significance. Any modifications to the structure, changes in proportions, or adjustments to size, without affecting the effectiveness and purpose of the invention, should still fall within the scope of the technical content disclosed in this invention. Furthermore, the terms such as "upper," "lower," "left," "right," "middle," and "one" used in this specification are merely for clarity and not intended to limit the scope of the invention. Changes or adjustments to their relative relationships, without substantially altering the technical content, should also be considered within the scope of the invention's implementation.

[0040] like Figure 1 As shown, this invention provides a method for fatigue safety assessment of engineering components under alternating stress, the method comprising the following steps:

[0041] S1. Conduct high-cycle fatigue tests on multiple specimens made of engineering component materials under the same stress ratio but different fatigue stress ranges, and record the fatigue failure cycle N of the failed specimens. f and fatigue stress range Δσ; the failed specimen has less than 10 cycles. 7 For specimens where the crack extends to the critical length at the next fatigue failure cycle N, the fatigue failure cycle N is... f The actual number of cycles for the failed specimen; the specimen is a specimen with a circular cross-section;

[0042] It is understood that the specimen with a circular cross-section can be a cylindrical specimen or an hourglass-shaped specimen, and there is no limitation on this. The present invention preferably uses an hourglass-shaped specimen.

[0043] It is understood that the hourglass-shaped specimen in this invention includes two heads and a connecting shaft for connecting the two heads, and the hourglass-shaped specimen has a centrally symmetrical structure, and its cross-section at any position is circular; wherein, the cross-section at the center of the specimen refers to the cross-section of the connecting shaft.

[0044] It is understood that the high-cycle fatigue test in this invention is controlled by the standard GB / T 3075-2008 Axial Force Control Method for Fatigue Testing of Metallic Materials. The test equipment is the GPS2000 high-frequency vibration fatigue testing machine from Changchun Testing Machine Factory. When the crack in the specimen extends to the critical crack length, the resonant frequency deviates from the set value, causing the fatigue testing machine to automatically stop. At this time, the specimen is considered a failed specimen.

[0045] S2, By analyzing the fatigue failure cycles N of each failed specimen. f The fatigue stress range Δσ is fitted with a power function to obtain the number of fatigue failure cycles N of the specimen. fThe first fitting formula with the fatigue stress range Δσ: N f =P(Δσ) q (1); where P is the first fitting parameter; q is the first fitting index;

[0046] S3. After marking the crack leading edge of each failed specimen using the heat-dyeing method or the secondary fatigue method, each failed specimen is broken to obtain the critical crack length 'a' of the corresponding failed specimen. f ;

[0047] S4. By analyzing the fatigue stress range Δσ and fatigue failure cycles N of each failed specimen... f and the critical crack length a of the sample f By performing fitting, the fatigue stress range Δσ and the number of fatigue failure cycles N can be obtained. f and the critical crack length a of the sample f The second fitting formula: a f =N f A(Δσ) m (2); where A is the second fitting parameter; m is the second fitting index;

[0048] S5. Obtain the critical crack length a of the sample using the first and second fitting formulas. f The relationship between the stress range Δσ and the fatigue stress range is: a f =AP(Δσ) m+q (3);

[0049] S6. Calibrate the coefficients in the relationship between the stress intensity factor range ΔK and the crack length a to determine the final relationship between the stress intensity factor range ΔK and the crack length a of the specimen:

[0050]

[0051] Where ΔF is the range of fatigue loads borne by the specimen;

[0052] D is the diameter of the cross-section at the center of the sample;

[0053] S0 is the original cross-sectional area at the center of the sample, derived from the formula... Sure;

[0054] The geometric factor coefficient of the sample;

[0055] k0~k n The coefficients obtained from calibration; the value of n can be determined according to the actual situation, and is generally not less than 4.

[0056] It is understandable that the coefficients k0~k in formula (4) nThere are two specific calibration methods, the only difference being the number of test specimens in the fatigue test during calibration.

[0057] First calibration method:

[0058] Fatigue tests were conducted on n+1 specimens made of engineering component materials under different cycles, the same stress ratio, and the same fatigue load range. The number of specimens n+1 (i.e. the number of different cycles n+1), the fatigue load range ΔF, and the crack length a of the specimen for the corresponding cycle number were recorded.

[0059] The stress intensity factor range ΔK for the corresponding number of cycles can be obtained by mathematical analysis, boundary configuration, or finite element method.

[0060] Substituting the obtained n value, fatigue load range ΔF, crack length a of the specimen under different cycles, and corresponding stress intensity factor range ΔK back into formula (4), we obtain the coefficients k0~k n :

[0061] Where n is determined by the experimenters, it is generally not less than 4.

[0062] The second calibration method:

[0063] A specimen made of engineering component material is subjected to a calibration fatigue test with an increasing number of cycles under the same stress ratio and the same fatigue load range, so as to obtain the number of cycles n+1, the fatigue load range ΔF, and the specimen crack length a corresponding to the number of cycles.

[0064] The stress intensity factor range ΔK for the corresponding number of cycles can be obtained by mathematical analysis, boundary configuration, or finite element method.

[0065] Substituting the obtained n value, fatigue load range ΔF, crack length a of the specimen under different cycles, and corresponding stress intensity factor range ΔK back into formula (4), we obtain the coefficients k0~k n :

[0066] Where n is determined by the experimenters, it is generally not less than 4.

[0067] S7. The critical crack length a of the specimen under different fatigue stress ranges Δσ. f Calculate the corresponding range of specimen stress intensity factor ΔK s This allows us to determine the critical fracture toughness ΔK of engineering component materials under different stress ranges Δσ. fc ; through the critical fracture toughness ΔK of the engineering component material fc The fatigue safety of engineering components under different stress ranges Δσ is evaluated; the critical fracture toughness ΔK of the engineering component material is also assessed. fc The stress range Δσ satisfies the following formula:

[0068]

[0069] Furthermore, the critical fracture toughness ΔK of the engineering component material can be obtained through formula (5). fc The ratio of the stress range Δσ to the fatigue critical crack length a of the engineering component is then obtained. fc ; through the fatigue critical crack length a of the engineering component fc The fatigue safety of engineering components under different stress ranges Δσ is evaluated; the critical fatigue crack length a of the engineering components is determined. fc The calculation formula is:

[0070]

[0071] Where α is the geometric shape factor of the engineering component, which can be obtained by looking up a table.

[0072] The following are specific embodiments of the present invention:

[0073] The engineering component is made of 9Ni alloy, and its room temperature yield strength R p0.2 =609MPa.

[0074] A set (i.e., multiple) of hourglass-shaped specimens with a center diameter D = 6 mm are fabricated from the engineering component material. Each specimen includes two heads and a connecting shaft for connecting the two heads. The hourglass-shaped specimen has a centrally symmetrical structure, and its cross-section is circular at any position. The center diameter of the hourglass-shaped specimen refers to the diameter of the cross-section of the connecting shaft.

[0075] like Figure 1 As shown, this invention provides a method for fatigue safety assessment of engineering components under alternating stress, the method comprising the following steps:

[0076] S1. Multiple hourglass-shaped specimens were subjected to stress ratios R = -1 and different maximum stresses σ. max High-cycle fatigue tests were conducted, and the fatigue failure cycle N of the failed specimens was recorded. f and fatigue stress range Δσ (i.e. Δσ = σ) max -σ min =σ max -Rσ max =2σ max The failed sample was one with fewer than 10 cycles. 7 For specimens where the crack extends to the critical length at the next fatigue failure cycle N, the fatigue failure cycle N is... f The actual number of cycles for the failed sample;

[0077] The high-cycle fatigue test was conducted using a GPS2000 high-frequency vibration fatigue testing machine manufactured by Changchun Testing Machine Factory. When the crack in the specimen extends to the critical crack length, the resonant frequency deviates beyond the set value, causing the fatigue testing machine to automatically stop. At this point, if the number of cycles for the specimen is less than 10... 7 If the test specimen fails, it is considered a failed specimen.

[0078] If the number of cycles for the sample is greater than 10 7 If the fatigue testing machine does not automatically stop at this time, the specimen is considered to be a non-failed specimen; the conditional fatigue limit σ is then obtained. -1 = 460 MPa; Conditional fatigue limit σ -1 For corresponding to 10 7 The critical stress amplitude applied to the specimen during each cycle without causing specimen failure.

[0079] S2, Fatigue failure cycles N of the failed specimen f The first fitting parameter P and the first fitting exponent q are obtained by performing a power function fit on the corresponding fatigue stress range Δσ, and the fitted curve is output (e.g., ...). Figure 2 As shown), the fatigue failure cycle N of the specimen was obtained. f The first fitted relationship with the fatigue stress range Δσ is: N f =P(Δσ) q (1);

[0080] S3. After marking the crack leading edge of each failed specimen using the heat-dyeing method or the secondary fatigue method, each failed specimen is broken to obtain the critical crack length 'a' of the corresponding failed specimen. f ;

[0081] S4. Fatigue stress range Δσ and fatigue failure cycles N for each failed specimen. f and the critical crack length a of the sample f By performing a fitting operation, the second fitting parameter A and the second fitting exponent m are obtained, and the fatigue stress range Δσ and fatigue failure cycles N are obtained. f and the critical crack length a of the sample f The second fitting formula: a f =N f A(Δσ) m (2);

[0082] S5. Substitute formula (1) into formula (2) to obtain the critical crack length a of the sample. f The relationship between the stress range Δσ and the fatigue stress range is: a f =AP(Δσ) m+q (3);

[0083] S6. Perform five fatigue tests on the hourglass-shaped specimen with a fixed stress ratio and a fixed load range at five different cycle numbers. Record the number of different cycle numbers (n+1=5), the fatigue load range ΔF, and the specimen crack length a at the corresponding cycle number. Then, use the finite element method to obtain the stress intensity factor range ΔK of the crack at the corresponding cycle number. Then, substitute the experimentally obtained parameter values ​​n=4, fatigue load range ΔF, specimen crack length a at the corresponding cycle number, and stress intensity factor range ΔK obtained by the finite element method into the relationship between stress intensity factor range ΔK and crack length a, and calculate the coefficients k0=0.0461, k1=-0.2416, k2=1.5233, k3=-3.386, k4=3.1884, and then obtain the final relationship between specimen stress intensity factor range ΔK and specimen crack length a.

[0084]

[0085] S7. The critical crack length a of the specimen under different fatigue stress ranges Δσ. f The corresponding range of stress intensity factor ΔK at the crack tip of the specimen is calculated. This range of stress intensity factor ΔK at the crack tip is the critical fracture toughness ΔK of the engineering component material under the corresponding fatigue stress range Δσ. fc In other words, by substituting formula (3) into formula (4), the critical fracture toughness ΔK of the engineering component material under different fatigue stress ranges Δσ can be obtained. fc This is used as a criterion for crack instability to assess the fatigue safety of engineering components under different fatigue stress ranges Δσ.

[0086] Critical fracture toughness ΔK of engineering component materials under different fatigue stress ranges Δσ fc The formula is:

[0087]

[0088] It is understandable that the maximum stress value σ varies under different fatigue stress ranges Δσ. max The range of values ​​must satisfy: σ'≤σ max ≤σ”, where σ”≤609MPa; σ’≤460MPa, in this embodiment σ max The preferred value range satisfies: 400MPa≤σ max Since the fatigue stress range Δσ is ≤600MPa, the preferred range of values ​​is 800MPa≤Δσ≤1200MPa.

[0089] Furthermore, the critical fracture toughness ΔK of the engineering component material is obtained through formula (5). fcThe ratio of the stress range Δσ to the fatigue critical crack length a of the engineering component is then obtained. fc By determining whether the cracks in engineering components under different stress ranges Δσ extend to the fatigue critical crack length a under the corresponding stress range Δσ. fc This enables fatigue safety assessment of engineering components under different stress ranges Δσ.

[0090] The critical fatigue crack length a of engineering components fc The calculation formula is:

[0091]

[0092] Where α is the geometric shape factor of the engineering component, which can be obtained from a table, and its value is generally 1.12.

[0093] The fatigue critical crack length a of the engineering component is plotted using formula (6). fc The relationship curve between the ratio of fatigue critical fracture toughness and stress range, as shown in the figure. Figure 3 As shown.

[0094] In summary, this invention, by fully considering the influence of alternating stress on the fatigue critical fracture toughness of engineering component materials, obtains the fatigue critical fracture toughness of engineering component materials under different fatigue stress ranges. This conforms to the actual fracture characteristics of engineering component materials under different fatigue conditions, effectively ensuring the accuracy of fatigue safety assessment of engineering components.

[0095] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the invention. Any person skilled in the art can modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by those skilled in the art without departing from the spirit and technical concept disclosed in the present invention should still be covered by the claims of the present invention.

Claims

1. A method for fatigue safety assessment of engineering components under alternating stress, characterized in that, The method includes the following steps: S1. Conduct high-cycle fatigue tests on multiple specimens made of engineering component materials under the same stress ratio but different fatigue stress ranges, and record the fatigue failure cycle N of the failed specimens. f and fatigue stress range Δσ; the failed specimen has less than 10 cycles. 7 For specimens where the crack extends to the critical length at the next fatigue failure cycle N, the fatigue failure cycle N is... f The actual number of cycles for the failed specimen; the specimen is a specimen with a circular cross-section; S2, By analyzing the fatigue failure cycles N of each failed specimen. f The fatigue stress range Δσ is fitted with a power function to obtain the number of fatigue failure cycles N of the specimen. f The first fitting formula with the fatigue stress range Δσ: N f =P(Δσ) q Where P is the first fitting parameter and q is the first fitting exponent; S3. After marking the crack lead edge of each failed specimen, pull each failed specimen apart to obtain the critical crack length 'a' of the corresponding failed specimen. f ; S4. By analyzing the fatigue stress range Δσ and fatigue failure cycles N of each failed specimen... f and the critical crack length a of the sample f By performing fitting, the fatigue stress range Δσ and the number of fatigue failure cycles N can be obtained. f and the critical crack length a of the sample f The second fitting formula: a f =N f A(Δσ) m Where A is the second fitting parameter; m is the second fitting index; S5. Obtain the critical crack length a of the sample using the first and second fitting formulas. f The relationship between the stress range Δσ and the fatigue stress range is: a f =AP(Δσ) m+q ; S6. Calibrate the coefficients in the relationship between the stress intensity factor range ΔK and the crack length a to determine the final relationship between the stress intensity factor range ΔK and the crack length a of the specimen: Where ΔF is the range of fatigue loads borne by the specimen; D is the diameter of the cross-section at the center of the sample; S0 is the original cross-sectional area at the center of the sample, derived from the formula... Sure; The geometric factor coefficient of the sample; k0~k n The coefficients obtained from calibration; n+1 is the number of different cycles in the calibration test, and n is usually 4; S7. The critical crack length a of the specimen under different fatigue stress ranges Δσ. f The corresponding stress intensity factor range ΔK of the specimen is calculated, and then the critical fracture toughness ΔK of the engineering component material under different stress ranges Δσ is determined. fc ; through the critical fracture toughness ΔK of the engineering component material fc The fatigue safety of engineering components under different stress ranges Δσ is evaluated; the critical fracture toughness ΔK of the material of the engineering components is also assessed. fc The stress range Δσ satisfies the following formula:

2. The fatigue safety assessment method for engineering components under alternating stress according to claim 1, characterized in that, Obtain the critical fracture toughness ΔK of the engineering component material fc The ratio of the stress range Δσ to the fatigue critical crack length a of the engineering component is then obtained. fc ; through the fatigue critical crack length a of the engineering component fc The fatigue safety of engineering components under different stress ranges Δσ is evaluated; the critical fatigue crack length a of the engineering components is determined. fc The calculation formula is: Where α is the geometric shape factor of the engineering component, which can be obtained by looking up a table.

3. The fatigue safety assessment method for engineering components under alternating stress according to claim 2, characterized in that, step The calibration process for S6 includes the following steps: S61. Conduct fatigue tests on n+1 specimens made of engineering component materials under different cycles, the same stress ratio, and the same fatigue load range, and record the number of specimens n+1, the fatigue load range ΔF, and the crack length a of the specimen corresponding to the number of cycles. S62. Obtain the stress intensity factor range ΔK for the corresponding number of cycles; S63. Using the obtained fatigue load range ΔF, the crack length a of the specimen under different cycles, and the corresponding stress intensity factor range ΔK, calculate the coefficients k0~k in the relationship between the stress intensity factor range ΔK and the crack length a of the specimen. n .

4. The fatigue safety assessment method for engineering components under alternating stress according to claim 3, characterized in that, Replace step S61 with: Perform a calibration fatigue test on a specimen made of engineering component material with the same stress ratio and the same fatigue load range, with the number of cycles increasing sequentially, to obtain the number of different cycle numbers n+1, the fatigue load range ΔF, and the specimen crack length a corresponding to the number of cycles.

5. A fatigue safety assessment method for engineering components under alternating stress according to claim 3 or 4, characterized in that, The stress intensity factor range ΔK corresponding to the number of cycles can be obtained by mathematical analysis, boundary configuration, or finite element method.

6. The fatigue safety assessment method for engineering components under alternating stress according to claim 1, characterized in that, The crack leading edge of the failed specimen in step S3 is marked using either the heat coloring method or the secondary fatigue method.

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