Steel wire rope fatigue failure analysis method under less test sample data

Abstract

The invention discloses a steel wire rope fatigue failure analysis method under less test sample data, relates to the field and is used for solving problems. Comprising the steps of 1, preparing a steel wire test piece and performing steel wire fatigue life test; 2, fitting an S-N curve of the steel wire according to a fatigue life test result by utilizing a least square method; 3, importing the S-N curve obtained in the step 2 into fatigue simulation software FE-SAFE, and setting different load scale factors to perform simulation calculation on the fatigue life of the steel wire rope under various load conditions based on an ABAQUS finite element analysis result; 4, fitting a simulation data S-N curve by using a least square method according to a simulation calculation result; and 5, comparing and verifying the simulation data S-N curve obtained in the step 4 and the S-N curve obtained in the step 2 so as to obtain the fatigue failure rule of the steel wire rope under different load conditions.

Description

Technical Field

[0001] The invention relates to the field of fatigue analysis and evaluation, and in particular to a wire rope fatigue failure analysis method under a small amount of test sample data. Background Art

[0002] The main basis for the study of fatigue failure law and fatigue life of wire rope is fatigue test. According to the fatigue analysis of wire rope, the fatigue life curve (SN curve) of wire material can be fitted, so as to provide material property data for simulation analysis of fatigue life of wire rope, and then the fatigue failure law of wire rope under different load conditions is obtained by combining test and simulation analysis. Based on the obtained fatigue failure law, it provides a better quantitative basis for more targeted determination of replacement cycle of wire rope of each lifting equipment, and provides theoretical and data support for scientifically and rationally determining the overhaul and replacement period of key parts such as wire rope.

[0003] However, due to the complex internal structure of the wire rope, it is impossible to ensure that the surface state, internal contact state, and end consolidation of all test pieces are completely consistent, and the fatigue test results will show a large dispersion. Moreover, due to the limitations of factors such as the loading capacity of the test equipment and the test cost, the fatigue test cannot cover a sufficiently large load range. Therefore, in order to obtain a relatively complete wire rope fatigue life curve (SN curve), fatigue testing must be combined with fatigue simulation analysis. At the same time, in order to ensure the accuracy of the fatigue simulation analysis results, the simulation analysis results need to be compared with the test results and verified. Summary of the invention

[0004] The purpose of the present invention is to provide a wire rope fatigue failure analysis method with little test sample data, which solves the problem that fatigue tests in the prior art cannot obtain a complete wire rope fatigue life curve, thereby obtaining inaccurate fatigue analysis results.

[0005] To achieve the above object, the present invention provides a wire rope fatigue failure analysis method with little test sample data, comprising the following steps:

[0006] Step 1: Prepare the wire rope specimen and conduct the wire fatigue life test;

[0007] Step 2: Use the least square method to fit the SN curve of the wire rope according to the fatigue life test results;

[0008] Step 3: Import the SN curve obtained in step 2 into the fatigue simulation software FE-SAFE, and based on the ABAQUS finite element analysis results, set different load proportional factors to simulate the fatigue life of the wire rope under various load conditions;

[0009] Step 4: According to the simulation calculation results, the simulation data SN curve is fitted using the least squares method;

[0010] Step 5: Compare and verify the simulation data SN curve obtained in step 4 with the SN curve obtained in step 2, so as to obtain the fatigue failure law of the wire rope under different load conditions;

[0011] Step 6: Based on the fatigue failure law obtained, determine the replacement cycle of the lifting equipment wire rope.

[0012] Furthermore, the specific steps of step 1 include:

[0013] Step 11: Prepare the wire rope specimen;

[0014] Step 12: Use an electronic fatigue testing machine to load the steel wire specimen with different frequencies for fatigue testing, and obtain the maximum value S of the alternating stress under different cycle numbers N. max ;

[0015] Step 13: Use the least squares method to fit the SN curve based on the test data.

[0016] Furthermore, the fatigue law obtained in step 5 is:

[0017] In the wire rope pull-up fatigue life test, the fatigue life of the rope strands in contact with each other, that is, near the high stress area in the finite element analysis results, is significantly shorter than that of other parts. The fatigue life of the outer layer of the rope strands is shorter, and the minimum value is located on the side of the wire at the contact point between two adjacent rope strands, while the fatigue life of the inner layer of the rope strands and the PPC rope core in the center of the wire rope interface is longer, reaching more than 107 times, that is, infinite cycle life. The shorter life area is discontinuously distributed along the secondary helix, which is consistent with the distribution law of the extrusion indentation on the actual wire surface;

[0018] In the bending fatigue test of the wire rope, most of the fatigue failure areas appear in the contact area between the wire rope and the pulley. Compared with the parts where the wire rope does not contact the pulley, the overall life of the contact part is reduced and the fatigue damage area is expanded. The strands of the wire rope in contact with the pulley are more likely to break due to fatigue.

[0019] Therefore, the present invention adopts the above-mentioned wire rope fatigue failure analysis method with less test sample data, which has the following beneficial effects:

[0020] First, the present invention obtains the SN curve equation through FE-SAFE and compares it through experiments, which solves the problem that the fatigue failure law is studied by fatigue test alone, which has a long cycle, high cost and great dispersion of test data;

[0021] Secondly, the present invention shows through experimental comparison that the curve equation has a high degree of consistency with the actual fatigue failure law of the wire rope, thereby providing effective data guarantee for accurately predicting the fatigue life of the wire rope.

[0022] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 These are the results of steel wire fatigue tests when the loading frequency is 10 Hz.

[0024] Figure 2 For S max =0.9S b The wire length variation curve.

[0025] Figure 3 For S max =0.8S b The wire length variation curve.

[0026] Figure 4 For S max =0.7S b The wire length variation curve.

[0027] Figure 5 For S max =0.6S b The wire length variation curve.

[0028] Figure 6 For S max =0.5S b The wire length variation curve.

[0029] Figure 7 (a)-(b) are S max =0.9S b , the overall morphology and port morphology of the fractured part of the steel wire specimen when N=14652.

[0030] Figure 8 (a)-(b) are S max =0.5S b , the overall morphology and port morphology of the fractured part of the steel wire specimen when N=54973.

[0031] Fig. 9 (a)-(b) are S max =0.5S b , the overall morphology and end morphology of the fractured part of the steel wire specimen when N=13116.

[0032] Fig.10 This is the tensile creep curve of metal.

[0033] Fig.11 The relationship between creep law and stress.

[0034] Fig.12 (a)-(b) are the residual stresses caused by plastic bending of the steel wire; Fig.12 (a) is the residual tensile stress on the inner surface of the bending part, Fig.12 (b) is the tensile stress caused by external load.

[0035] Fig.13 The contact stress distribution on the wire surface.

[0036] Fig.14 It is a steel wire section with an oblique fracture.

[0037] Fig.15 The cross section of the steel wire has a straight fracture.

[0038] Fig.16 (a)-(b) are the fracture images of the oblique fracture (magnification 100) and the crack extension zone image (magnification 500), respectively.

[0039] Fig.17 (a)-(b) are the fracture images of the straight fracture (magnification 100) and the crack extension zone images (magnification 500), respectively.

[0040] Fig.18 Comparison of fatigue test results at loading frequencies of 15 Hz and 10 Hz.

[0041] Fig.19 is the fitted SN curve in the double logarithmic coordinate system.

[0042] Fig. 20 is the fitted SN curve.

[0043] Fig.21 This is the specimen dimension drawing.

[0044] Fig. 22 The appearance of the test piece.

[0045] Fig.23 This is the overall appearance of specimen No. 1 after failure.

[0046] Fig.24 This is the local appearance of specimen No. 1 after failure.

[0047] Fig.25 This is a local enlarged view of the damaged failure area of ​​specimen No. 1.

[0048] Fig.26 This is the overall appearance of specimen No. 2 after failure.

[0049] Fig. 27This is the local appearance of specimen No. 2 after failure.

[0050] Fig.28 This is a local enlarged view of the damaged failure area of ​​specimen No. 2.

[0051] Fig.29 This is a local enlarged view of the damaged failure area of ​​specimen No. 5.

[0052] Fig.30 is the axial deformation displacement curve of the wire rope (S max =7.45kN, N=555749).

[0053] Fig.31 is the axial deformation displacement curve of the wire rope (S max =5kN, N=10 6 ).

[0054] Fig.32 is the fatigue life distribution of wire rope (1.25t load).

[0055] Fig.33 Fatigue life distribution on two adjacent rope strands (1.25t load).

[0056] Fig.34 is the fatigue life distribution of the wire rope cross section (1.25t load).

[0057] Fig.35 Fatigue life distribution of steel wire at the contact point of adjacent rope strands.

[0058] Fig.36 (a)-(j) are the comparisons of fatigue life of wire ropes under load sizes of 0.5t, 1t, 1.2t, 1.25t, 2t, 3t, 5t, 7t, 9t and 11t respectively.

[0059] Fig.37 It is the SN curve of wire rope.

[0060] Fig.38 It is the overall fatigue life distribution of wire rope and pulley.

[0061] Fig.39 Life distribution diagram of the contact area between wire rope and pulley.

[0062] Fig.40 Fatigue life distribution over the cross section of a wire rope. DETAILED DESCRIPTION

[0063] In the description of the present invention, it is also necessary to explain that, unless otherwise clearly specified and limited, these embodiments are only used to illustrate the present invention and are not used to limit the scope of the present invention. In addition, it should be understood that after reading the content taught by the present invention, those skilled in the art make various changes or modifications to the present invention, and these equivalent forms also fall within the scope limited by the claims attached to the application.

[0064] 1. Traditional steel wire fatigue life test

[0065] The test was conducted in accordance with GBT 3075-2008 "Method for controlling axial force in fatigue test of metal materials". The test environment temperature was room temperature and the test equipment used was an Instron E10000 electronic fatigue testing machine. The test specimen was a 0.7mm diameter steel wire with a length of 200mm extracted from the surface of the strands of a 6×36WS+PPC steel wire rope. The steel wire material was No. 60 steel with a nominal tensile strength of 1770MPa. During the test, the steel wire specimen was fixed on the testing machine by a special steel wire clamp. The gauge length was 60mm. The clamping part of the clamp was designed with a special curved surface to avoid stress concentration at the clamping and fixing part of the specimen.

[0066] The nominal tensile strength of the steel wire is 1770MPa, the cross-sectional area is 0.38mm2, and the corresponding nominal breaking force is 681N. The maximum value S of the alternating load in the axial tensile fatigue test of the steel wire max Breaking force S b The minimum value of alternating load S is set as 90% of the value of min Determined by stress ratio R = 0.4, that is, S min =0.4S max Each group of load tests 5 to 10 specimens. During the test, it was found that the steel wire specimen in a spiral bending state showed greater elasticity. When the frequency test was performed at 15 Hz, when S max Less than 0.7S b When S max Less than 0.5S b The test machine cannot track the load value and number of specimens in the test.

[0067] Table 1 Load values ​​and number of specimens for steel wire fatigue test

[0068]

[0069] The steel wire fatigue test results when the loading frequency is 10Hz, such as Figure 1 As shown in the figure, it can be seen that as the load decreases, the fatigue life tends to increase gradually, but at S max Less than 0.7S b(476N), the fatigue life has an inflection point; in addition, S max Equal to 0.5S b The fatigue life test results at (340N) show a large dispersion.

[0070] Figure 2 to Figure 6 The maximum value S of the alternating load is shown. max According to the breaking force S b The curve of the change of the steel wire length during the cyclic loading process of the steel wire specimen when S is taken at different ratios. It can be seen that when S max >0.7S b When S is , the length change of the steel wire specimen is basically the same, which is similar to the three-stage change of metal tensile creep, and the elongation at break increases with the increase of stress. max <0.7S b When the load is tensile, the length variation of the steel wire shows diversity, which indicates that the failure of the steel wire is not only caused by the tensile load.

[0071] In S max =0.9S b Under the load condition of , the morphology of the fracture part of the steel wire specimen with fatigue life of 14652 is as follows: Figure 7 It can be seen that under this load condition, the steel wire is basically straightened, and the steel wire is mainly subjected to tensile fatigue load during the fatigue process. The fracture is a typical tensile fracture + tearing morphology. The tensile fracture comes from the tensile load, and the tearing fracture comes from the lateral force caused by the elasticity of the steel wire.

[0072] In S max =0.5S b Under the load condition of , the morphology of the fracture site of the steel wire specimen with fatigue life of 54973 is as follows: Figure 8 As shown in the figure, it can be seen that the steel wire specimen was not completely straightened under this load condition. The fracture site of the specimen is located in the relatively straight section of the steel wire, and the fracture morphology is tensile fracture + tearing morphology, which is consistent with Figure 7 Shown max =0.9s b The fracture morphology of the load conditions is similar. The long life is due to the small stress.

[0073] In S max =0.5S b Under the load condition of , the morphology of the fracture part of the steel wire specimen with fatigue life of 13116 is as follows: Fig. 9 As shown in the figure, the fracture site of the specimen is located in the bending section and presents a straight port morphology, indicating that this part may have suffered bending fatigue damage in addition to tensile fatigue, so the fatigue life is lower than the fatigue life under pure tensile load.

[0074] From the above analysis, we can see that in S max >0.7S b Under high stress conditions, the wire rope specimens were basically straightened, and the fracture mainly manifested as tensile fatigue failure, and the dispersion of fatigue life test data was small. max <0.7S b Under low stress conditions, the steel wire specimen cannot be completely straightened. Due to the secondary helix shape of the steel wire, the fracture occurs sometimes in the straighter section and sometimes in the arc section with a smaller radius of curvature. The effects of tensile stress and bending stress on fatigue failure vary in cross sections at different locations. The fracture failure is manifested as a composite effect of tensile fatigue and bending fatigue, so the dispersion of fatigue life test data is relatively large.

[0075] It can be seen that the data obtained from the traditional steel wire fatigue life test has a large dispersion, and the SN curve obtained (see Figure 1 ) is not complete, that is, a complete SN curve cannot be obtained through fatigue test alone.

[0076] 2. Analysis of steel wire fatigue fracture failure mechanism

[0077] In order to solve the problem that the above-mentioned traditional fatigue test cannot obtain a complete SN curve, the present invention first analyzes the steel wire fatigue fracture failure mechanism as follows:

[0078] (1) Steel wire deformation law

[0079] From the above test results, it can be seen that when S max >0.7S b When the steel wire is basically straightened, it is mainly subjected to cyclic tensile load. The length of the steel wire gradually increases before breaking, and the change curve is similar to Fig.10 The three-stage variation law of metal tensile creep is shown in the figure. The strain at t = 0 is the strain generated after loading, including elastic strain and plastic strain. Under the condition of constant load, as time goes by, the strain ε gradually increases. The strain change rate in the initial stage is Gradually decreasing, the second stage Keep it constant, in the third stage The duration of the second stage is directly related to the stress. The smaller the stress, the longer the duration of this stage. Fig.11 As shown in the figure, this law can be quickly verified by the test results of different loads mentioned above. Usually, carbon steel shows more significant creep behavior at around 300℃~350℃. Although the test did not reach the temperature range of significant creep, the repeated tensile deformation of the steel wire will cause the temperature of the metal material to rise. The test data shows that the heating phenomenon during the fatigue test has a certain impact on the material properties.

[0080] (2) Macroscopic morphology of steel wire fracture

[0081] During the wire rope manufacturing process, various factors will cause discontinuous high stress areas on the wire surface, thus affecting the fatigue performance of the wire.

[0082] First, the steel wire is pre-bent before being twisted into a steel wire rope, which causes tensile and compressive plastic deformation on the inner and outer sides of the bending part of the steel wire. After unloading, due to the recovery of elastic deformation, residual compressive and tensile stresses will be generated on the inner and outer sides of the bending part, such as Fig.12 When subjected to tensile load again, the residual tensile stress on the inner surface of the bending part will be superimposed on the tensile stress generated by the external load, making the stress level at this part higher than that at other parts.

[0083] Secondly, the finite element simulation results of the wire rope show that after the steel wires are twisted into a wire rope, the steel wires in the shape of secondary helices squeeze and contact each other, forming a discontinuous high stress area, especially the surface steel wires, such as Fig.13 This feature is verified by checking the surface of the outer wire of the strand removed from the wire rope, where there are visible discontinuous indentations distributed along the helical line.

[0084] Since the processing residual stress, extrusion contact indentation and surface roughness on the steel wire surface will lead to stress concentration, the possibility of microcracks on the steel wire surface under cyclic tensile load is greater than that inside the steel wire material. The initiation and expansion of surface microcracks are the result of cyclic slip, so the microcracks occur in the direction of maximum shear stress. Under uniaxial loading conditions, the direction of the microcracks is approximately 45° to the load direction. Under cyclic loads, after the microcracks expand to a length range of the order of 10μm, they gradually deviate from the original direction and tend to the plane perpendicular to the loading direction (i.e., the maximum tensile stress plane) and form a main crack. As the crack continues to expand, the remaining bearing area of ​​the steel wire gradually decreases. In addition, the stress concentration effect at the crack tip causes the stress in the unbroken part of the steel wire to increase rapidly and causes plastic yield of the steel wire material. Since the fracture accompanied by obvious plastic deformation is related to the maximum shear stress, it presents the following Fig.14 The fracture is 45° from the axis. Due to the complexity of the distribution of high stress areas on the wire surface, micro cracks may start from two opposite directions or more directions at the same time and extend to the center, so it may also appear as Fig.15 The straight fracture shown.

[0085] (3) SEM morphology of steel wire fracture

[0086] Fig.16(a) shows an electron microscope scanning photo with an oblique fracture. It can be found that the entire cross section is divided into two parts by an arc, the left side is the fatigue crack extension zone, and the right side is the instantaneous fracture zone. The process of tensile fatigue fracture of steel wire is that fatigue crack sources will be generated in places where there are defects on the surface of the steel wire, such as steel wire indentation and rust. Under the repeated action of alternating loads, plastic deformation occurs due to stress concentration, and the cracks continue to expand until the steel wire can no longer withstand the load and breaks instantly to form an instantaneous fracture zone. Since the maximum load on the steel wire is shear stress, which is at a 45-degree angle to the plane, the instantaneous fracture zone of the steel wire is generally at an inclined angle to the plane. Fig.16 (a) The fatigue instantaneous fracture area on the right is a brittle fracture and is relatively smooth. Since the steel wire is always under tension but not pressure, the crack extension area is not smoothed. Fig.16 (b) shows the crack propagation zone, where many dimples formed by the load and some secondary cracks can be found, but the crack band is not obvious. Fig.17 The figure shows the SEM morphology of a flat fracture. It can be found that the surface has obvious texture features. The area on the left side of the fracture is the fatigue source, and the bright area on the right side is the instantaneous fracture area. Due to the small force, the area of ​​the instantaneous fracture area is small.

[0087] (4) SN curve of steel wire specimen

[0088] The above-mentioned traditional fatigue life test was carried out on the steel wire specimens using two cyclic loading frequencies of 15 Hz and 10 Hz. In the test with a loading frequency of 15 Hz, when S max <0.7S b When the spiral steel wire specimen is not completely straightened, it shows a smaller elastic coefficient similar to that of a spiral spring, making it impossible for the actuator of the fatigue testing machine to achieve frequency tracking; in the test with a loading frequency of 10 Hz, S max <0.7S b When the spiral steel wire specimen is not completely straightened, fatigue fracture is manifested as the coupling of tensile fatigue and bending fatigue. Due to the complex shape of the secondary spiral line of the steel wire specimen, the coupling of tensile fatigue and bending fatigue at different parts is not completely consistent. The randomness of the fracture failure position leads to a large dispersion of the test results. Therefore, the main factor that can reflect the fatigue life law of the steel wire specimen is S max >0.7S b Test data under loading conditions.

[0089] Fig.18 The figure shows the comparison of fatigue test results of steel wire specimens under two different loading frequencies of 15Hz and 10Hz. It can be seen that under the same load conditions, the fatigue life of 15Hz is slightly lower than that of 10Hz, but the trend of fatigue life of the two being affected by load is basically the same.

[0090] Since the fatigue life curve (SN curve) changes between the number of cycles N and the maximum alternating stress S max In the double logarithmic coordinate system, it is approximately an inclined straight line. Therefore, in this coordinate system, the least squares method can be used to fit the SN curve according to the test data, so that the fatigue life under different load conditions can be approximately estimated.

[0091] Let x = logN, y = logS max , the SN curve equation in the double logarithmic coordinate system is fitted using the least squares method:

[0092]

[0093] in,

[0094]

[0095] The linear equation of the SN curve at a load frequency of 15 Hz fitted by the test data in the double logarithmic coordinate system is:

[0096] y=2.7337-0.2399(x-4.3571) (5)

[0097] The linear equation of the SN curve at a load frequency of 10 Hz fitted by the test data in the double logarithmic coordinate system is:

[0098] y=2.7337-0.2587(x-4.3852) (6)

[0099] The fitted straight line in the double logarithmic coordinate system is as follows Fig.19 shown.

[0100] According to equations (5) and (6), the number of cycles can be calculated to be 10 3 ~10 6 The corresponding S in the range max Coordinate values, thus obtaining the SN curve, such as Fig. 20 shown.

[0101] 3. Wire rope fatigue life test

[0102] After the above fatigue life test on the steel wire is carried out, in order to verify and analyze the life data of the entire steel wire rope after the cable knot is added to the steel wire rope, the following fatigue life test is carried out on the steel wire rope.

[0103] (1) Specimen preparation

[0104] The test specimen uses a steel wire rope of the same specification as the hoisting mechanism of the LHBT 5t bridge crane, which is a 6×36WS+PPC right-hand cross-lay galvanized steel wire rope produced by Jiangsu Langshan Wire Rope Co., Ltd. with a nominal diameter of 12mm and a nominal tensile strength of 1770MPa.

[0105] In order to facilitate the connection with the fatigue testing machine, the connection parts are made of SOA-03 open cable joints cast by Babbitt alloy at both ends of the tested wire rope. This rope end processing method can minimize the strength loss of the wire rope connection part and avoid excessive stress concentration. The net length of the wire rope part of the test piece is 420mm, the diameter of the open cable joint connection pin is 26mm, and the distance between the connection pins at both ends is 651mm. The overall dimensions of the test piece are as follows Fig.21 As shown, the appearance is Fig. 22 shown.

[0106] (2) Test methods

[0107] The test method refers to GBT 3075-2008 "Axial force control method for fatigue test of metallic materials", the test environment temperature is room temperature, and the test equipment uses a hydraulic servo fatigue testing machine.

[0108] The load frequency of the fatigue test is 10 Hz, and the alternating load amplitude is S a According to the maximum rated lifting capacity of LHBT 5t bridge crane, the lifting mechanism four-fold pulley block single rope carries 1.25t load, which is taken as 1.25t, 1t, 0.75t and 0.5t respectively. The minimum value of alternating load S min The load values ​​of the fatigue test are all taken as 0.1kN. The load values ​​of the fatigue test are shown in Table 2. During the test, two specimens are tested for each load group. When the wire rope specimen breaks, the test is stopped and the number of cycles is recorded. If the number of cycles reaches 10 6 If there is still no wire breakage, stop the test.

[0109] Table 2 Load values ​​and number of specimens for wire rope fatigue test

[0110] <![CDATA[Load amplitude S a Corresponding load-bearing weight (t)]]> 1.25 1.00 0.75 0.50 <![CDATA[Load amplitude S a (kN)]]> 12.25 9.80 7.35 4.90 <![CDATA[Maximum load S max (kN)]]> 12.35 9.90 7.45 5.00 <![CDATA[Minimum load S min (kN)]]> 0.1 0.1 0.1 0.1 Test piece number 1、2 3、4 5、6 7、8

[0111] Fatigue wire breakage occurred in specimens No. 1 and No. 2 with a load amplitude of 12.25 kN, and specimen No. 5 with a load amplitude of 7.37 kN. The fatigue life test results are shown in Table 3.

[0112] Table 3 Wire rope fatigue life test results

[0113]

[0114] The fatigue life of specimen No. 1 is N=80218 times, and the entire strand breaks at the root of the wire rope. The broken part has obvious color change caused by local overheating, and the internal PPC rope core also melts and breaks, indicating that the wire rope generates local high temperature due to repeated deformation of high stress areas and mutual friction between steel wires during cyclic stretching. Fig.23 and Fig.24They are the overall appearance and local conditions of specimen No. 1 after failure.

[0115] Fig.25 This is a local enlarged picture of the damaged and failed part of specimen No. 1. It can be seen that the morphology of the broken part of the steel wire is similar to the fracture of the previous single steel wire fatigue test, with both broken + torn fractures and straight fractures.

[0116] The fatigue life of specimen No. 2 is N = 179032 times. Part of the wire rope was found to be broken at the root. Fig.26 and Fig. 27 They are the overall appearance and local conditions of specimen No. 2 after failure.

[0117] Fig.28 The figure shows a local enlarged image of the damaged and failed part of specimen No. 2. It can be seen that the fractured part of the steel wire is mainly a straight fracture, which is somewhat different from the fracture morphology of the steel wire at the damaged and failed part of specimen No. 1.

[0118] The fatigue life of specimen No. 5 with a load amplitude of 7.37 kN is N = 555749 times. Part of the wire rope was found to be broken at the root of the wire rope. The local enlarged picture of the failure site is shown in the figure below. Fig.29 shown.

[0119] From the local enlarged image of the failure site of the above specimen, it can be seen that there is no obvious wear near the wire fracture, indicating that the surface wear of the steel wire inside the wire rope is not obvious under the action of cyclic tensile load.

[0120] The axial deformation law of the wire rope specimen with fatigue wire breakage during cyclic loading is similar to that of the wire fatigue fracture process, and also presents the following Fig.30 The three-stage variation curve shown is similar to the metal tensile creep, indicating that the deformation law of the wire rope under cyclic load is consistent with that of a single steel wire.

[0121] When the load is small, the wire rope specimen is cycled for 10 6 If fatigue wire breakage does not occur for the first time, the axial deformation of the wire rope does not increase significantly after the initial deformation stage. Fig.31 shown.

[0122] 4. Simulation analysis of wire rope tensile fatigue life

[0123] (1) Simulation parameter setting

[0124] The fatigue life simulation of the wire rope is completed using the fatigue simulation software FE-SAFE based on the ABAQUS finite element analysis results.

[0125] Setting the surface smoothness factor K in FE-SAFE tis 1, the elastic modulus of the steel wire material is 210 GPa, and the tensile strength is 1770 MPa. The multiple SN curves under different load frequencies obtained by formula (1) are imported into FE-SAFE, and then ABAQUS is used to perform finite element analysis at different steel wire rope loads (0.5 t, 1.0 t, etc.). The finite element analysis results are then imported into FE-SAFE, and different load proportional factors are set to simulate and calculate the fatigue life of the steel wire rope under various load conditions. The calculation is performed using Miner's law.

[0126] (2) Analysis of fatigue life calculation results under rated load

[0127] The maximum rated lifting capacity of LHBT 5t bridge crane is 5t, and the maximum load of a single wire rope branch of its four-fold pulley block is 1.25t. Taking the fatigue life analysis results under this load condition as an example, the fatigue life distribution characteristics of different parts in the internal structure of the wire rope are explained.

[0128] Fig.32 The figure shows the fatigue life cloud diagram of the wire rope under the load of 1.25t. The minimum value of fatigue life in this figure is located at both ends of the model, which is mainly due to the stress concentration caused by the boundary constraint. Excluding the parts affected by the boundary effect at both ends, it can be found that the parts with smaller fatigue life are mainly located near the contact area between the rope strands.

[0129] From the simulation results, separate Fig.33 The two adjacent rope strands shown in the figure show that the fatigue life of the rope strands at the contact point between the rope strands, that is, near the high stress area in the finite element analysis results, is significantly shorter than that of other parts.

[0130] Fig.34 The figure shows the fatigue life distribution of the cross section at the axial 1 / 2 length of the wire rope model. This part is least affected by the boundary effect. It can be seen that the fatigue life of the outer layer of the rope strand is small, and the minimum value is located on the side of the wire at the contact point between the two adjacent rope strands. The fatigue life of the inner layer of the rope strand and the PPC rope core in the center of the wire rope interface is large, which can reach 10 7 More than times, that is, infinite cycle life.

[0131] Fig.35 The figure shows the fatigue life distribution of the steel wire with the smallest fatigue life, that is, the surface steel wire at the contact point between adjacent rope strands. It can be seen that the area with shorter life is discontinuously distributed along the secondary spiral line, which is consistent with the actual distribution law of extrusion indentation on the surface of the steel wire.

[0132] (3) Comparison of fatigue life calculation results under different load conditions

[0133] In order to demonstrate the effect of wire rope fatigue life simulation analysis using SN curve as input, the fatigue life calculation results are compared under different load conditions.

[0134] The fatigue life comparison of the cross section of the wire rope under different load conditions of 0.5t to 11t is as follows Fig.36 (a)-(j) As shown in Figure 1, it can be seen that as the load gradually increases, the fatigue life of the wire rope cross section approaches 10 7 The area of ​​sub-infinite life gradually decreases, and when the load reaches 1.1t, a more obvious finite life area appears on the cross section of the wire rope.

[0135] The minimum value of fatigue life is extracted from the calculation results of fatigue life of wire rope cross section under different load conditions, and the corresponding relationship between wire rope load and fatigue life is obtained as shown in Table 4.

[0136] Table 4 Correspondence between wire rope load and fatigue life

[0137]

[0138]

[0139] Since the load of the fatigue life simulation calculation result is not continuous, and the fatigue life simulation software cannot directly give the function equation of the SN curve, in order to facilitate the calculation of the remaining life of the wire rope failure prediction, let x = log N, y = log S max , the SN curve equation in the double logarithmic coordinate system is fitted using the least squares method:

[0140] y=1.417-0.1802(x-2.8563) (7)

[0141] Fig.37 The figure shows the comparison of wire rope fatigue test data, FE-SAFE simulation data, and SN curve fitted by simulation data. It can be seen that the simulation data curve and the fitting curve are not much different, especially in the common load range below 12.25kN corresponding to the rated load of the crane, the test data, simulation data and fitting curve have a high degree of consistency.

[0142] 5. Simulation analysis of wire rope bending fatigue life

[0143] The finite element analysis using ABAQUS software includes two parts: bending fatigue life simulation and tensile fatigue life simulation, as follows:

[0144] (1) Simulation parameter setting

[0145] The simulation parameter settings of wire rope tensile fatigue are the same as those of the steel wire rope. The finite element results of the steel wire rope bending around the pulley in Abaqus are imported into Fe-safe. The load is 1.25t, and the Miner law is used to calculate the fatigue life of the steel wire rope under rated load conditions.

[0146] (2) Analysis of calculation results of wire rope bending fatigue life

[0147] Fig.38 This is the overall life distribution cloud diagram of the wire rope and the pulley. It can be seen that the fatigue life times of most areas of the wire rope have reached 10 7 More than times, no fatigue damage occurred. Limited life areas appeared in some stress concentration areas. The two end surfaces of the wire rope have a short local life due to the constraint effect and have no reference value. After removing the invalid areas at both ends of the wire rope, the fatigue life of the contact area between the wire rope and the pulley and the contact area between the wires is short, and the minimum fatigue life is 59567 times. The National Metal Products Quality Supervision and Inspection Center was commissioned to conduct a bending fatigue test of the wire rope under a load of 1.25t, and the result was 27090 times, which is basically consistent with the simulation results and is on the same order of magnitude. Fig.39 It can be seen that most of the fatigue failure areas appear at the contact point between the wire rope and the pulley. Fig.39 The area where the wire rope is not in contact with the pulley has a reduced overall lifespan and a larger fatigue damage area. Fig.40 It can be seen that fatigue damage did not occur in most areas of the middle cross-section of the wire rope, but fatigue damage occurred in the area where the rope strands contacted each other, and the fatigue failure area in the lower half of the wire rope cross-section was larger than that in the upper half, indicating that the several rope strands in contact with the pulley are more prone to fatigue breakage.

[0148] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that they can still modify or replace the technical solution of the present invention with equivalents, and these modifications or equivalent replacements cannot cause the modified technical solution to deviate from the spirit and scope of the technical solution of the present invention.

Claims

1. A wire rope fatigue failure analysis method with little test sample data, characterized in that: The following steps are involved: Step 1: Prepare the wire rope specimen and conduct the wire fatigue life test; Step 2: Use the least square method to fit the SN curve of the wire rope according to the fatigue life test results; Step 3: Import the SN curve obtained in step 2 into the fatigue simulation software FE-SAFE, and based on the ABAQUS finite element analysis results, set different load proportional factors to simulate the fatigue life of the wire rope under various load conditions; Step 4: According to the simulation calculation results, the simulation data SN curve is fitted using the least squares method; Step 5: Compare and verify the simulation data SN curve obtained in step 4 with the SN curve obtained in step 2, so as to obtain the fatigue failure law of the wire rope under different load conditions; Step 6: Based on the fatigue failure law obtained, determine the replacement cycle of the lifting equipment wire rope.

2. The complex system risk assessment method based on relevant evidence reasoning rules according to claim 1 is characterized in that: The specific steps of step 1 include: Step 11: Prepare the wire rope specimen; Step 12: Use an electronic fatigue testing machine to load the steel wire specimen with different frequencies for fatigue testing, and obtain the maximum value S of the alternating stress under different cycle numbers N. max ; Step 13: Use the least squares method to fit the SN curve based on the test data.

3. The complex system risk assessment method based on relevant evidence reasoning rules according to claim 1 is characterized in that: Step 5: The fatigue law is: In the wire rope pull-up fatigue life test, the fatigue life of the rope strands in contact with each other, that is, near the high stress area in the finite element analysis results, is significantly shorter than that of other parts. The fatigue life of the outer layer of the rope strands is shorter, and the minimum value is located on the side of the wire at the contact point between two adjacent rope strands, while the fatigue life of the inner layer of the rope strands and the PPC rope core in the center of the wire rope interface is longer, reaching more than 107 times, that is, infinite cycle life. The shorter life area is discontinuously distributed along the secondary helix, which is consistent with the distribution law of the extrusion indentation on the actual wire surface; In the bending fatigue test of the wire rope, most of the fatigue failure areas appear in the contact area between the wire rope and the pulley. Compared with the parts where the wire rope does not contact the pulley, the overall life of the contact part is reduced and the fatigue damage area is expanded. The strands of the wire rope in contact with the pulley are more likely to break due to fatigue.

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