Multi-axis creep life prediction method based on notched plate sample

Abstract

The invention discloses a multi-axis creep life prediction method based on a notched plate sample, and relates to the field of life prediction. The method comprises the following steps: acquiring creep parameters; constructing a finite element model; according to the finite element model, determining a stress parameter based on the creep parameter and a set incidence relation; the set incidence relation is obtained by performing linear fitting of section representative stress on the notched round bar sample and the notched flat plate sample by adopting a simulation test method based on an MSRC criterion; wherein if the notched sample is a notched flat plate sample, the notched sample is replaced by a notched round bar sample with the same notched size type as the notched flat plate sample; and determining the creep fracture life according to the stress parameters. The method aims at achieving multi-axis creep life prediction of samples with different notches, and member life evaluation in actual engineering is promoted.

Description

Technical Field

[0001] The present application relates to the field of life prediction, and in particular to a multiaxial creep life prediction method based on a notched flat plate specimen. Background Art

[0002] The Multiaxial Stress Rupture Criterion (MSRC) can be used to accurately predict the creep life of components under multiaxial stress states and is suitable for practical engineering applications. Usually, the determination of MSRC is based on the verification of notched circular rod specimens (Circumferentially-Notched Tension, CNT) using the bone point concept, but some materials are limited and can only be used as notched plate specimens (Notched Plate Tension, NPT). However, according to experimental results, NPT specimens cannot use the same method as CNT specimens to verify MSRC, so NPT specimens cannot predict component life based on MSRC in practical engineering applications, that is, the scope of application of MSRC is limited. Therefore, it is crucial to realize the multiaxial creep life prediction of different notched specimens and promote component life assessment in actual engineering. Summary of the invention

[0003] The purpose of this application is to provide a multiaxial creep life prediction method based on notched flat specimens, which can realize multiaxial creep life prediction of specimens with different notches and promote component life assessment in actual engineering.

[0004] To achieve the above objectives, this application provides the following solutions:

[0005] The present application provides a multiaxial creep life prediction method based on a notched flat specimen, comprising:

[0006] Acquiring creep parameters; the creep parameters include: load and temperature;

[0007] Constructing a finite element model; the finite element model is a physical model constructed based on the creep parameters and the notched specimen; the notched specimen is a notched round bar specimen or a notched flat plate specimen;

[0008] According to the finite element model, based on the creep parameters and the set association relationship, the stress parameter is determined; the set association relationship is obtained by linear fitting of cross-sectional representative stress of the notched round bar specimen and the notched flat plate specimen using a simulation test method based on the MSRC criterion; wherein, if the notched specimen is a notched flat plate specimen, a notched round bar specimen of the same notch size type as the notched flat plate specimen is used instead;

[0009] The creep rupture life is determined according to the stress parameter; the creep rupture life includes: uniaxial creep rupture life and multiaxial creep rupture life.

[0010] Optionally, according to the finite element model, based on the creep parameters and the set association relationship, a direct method or an empirical method is used to determine the stress parameters.

[0011] Optionally, according to the finite element model, based on the creep parameters and the set association relationship, a direct method is used to determine stress parameters, specifically including:

[0012] Based on the creep parameters, a uniaxial creep test is performed using a smooth round bar specimen, and a multiaxial creep test is performed using a notched round bar specimen to obtain test results;

[0013] According to the finite element model, creep simulation is performed based on the creep parameters and the set association relationship to obtain a simulation result;

[0014] Performing normalization processing according to the simulation results and the test results to determine the bone point position;

[0015] Stress components are determined based on the bone point positions, and stress parameters are determined according to the stress components.

[0016] Optionally, an empirical method is used to determine the stress parameters, specifically including:

[0017] Based on the creep parameters, a uniaxial creep test is performed using a smooth round rod specimen to obtain uniaxial test data; the uniaxial test data includes creep strain data;

[0018] constructing a life curve according to the uniaxial test data;

[0019] Performing a derivation process based on the life curve and determining a minimum strain rate; the minimum strain rate is a value with the smallest value selected from the data obtained after the derivation process;

[0020] determining a creep damage tolerance factor based on the minimum strain rate;

[0021] A stress parameter is determined according to the creep damage tolerance factor.

[0022] Optionally, determining the creep rupture life according to the stress parameter specifically includes:

[0023] Determine the uniaxial creep rupture life based on the applied uniaxial tensile stress;

[0024] Calculating representative stress according to the stress parameter;

[0025] Determine the multiaxial creep rupture life based on representative stresses;

[0026] The calculation formula of the representative stress is:

[0027] σ rep-1 =ασ I +(1-α)σ eq ;

[0028] Among them, σ rep-1 is the representative stress; α is the stress parameter; σ I is the principal stress; eq is the equivalent stress. Optionally, the calculation formula of the creep rupture life is:

[0029] t u =C(T)σ -v ;

[0030]

[0031] Among them, t u is the uniaxial creep rupture life; C(T) is the temperature-dependent coefficient; σ is the applied uniaxial tensile stress; v is the creep rupture exponent; t nu is the multiaxial creep rupture life.

[0032] According to the specific embodiments provided in this application, this application discloses the following technical effects:

[0033] The present application provides a multi-axial creep life prediction method based on a notched flat plate specimen. By using a simulation test method based on the MSRC criterion, a linear fitting of the cross-sectional representative stress of a notched round bar specimen and a notched flat plate specimen is performed to obtain a set correlation relationship; then the stress parameters are determined based on the constructed finite element model, and the creep rupture life is determined. The present application is no longer limited to the MSRC verification of notched round bar specimens using the bone point concept, but some materials are limited to the dilemma of only being able to make notched flat plate specimens, so that different notched specimens can achieve multi-axial creep life prediction, thereby promoting the life assessment of components in actual engineering. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0035] Figure 1 This is a flow chart of the multiaxial creep life prediction method based on notched flat specimens;

[0036] Figure 2 It is a schematic diagram of the linear regression curve;

[0037] Figure 3 It is a schematic diagram of the curve based on creep strain data and total life of creep strain;

[0038] Figure 4 For Figure 3 Schematic diagram of the curve after the derivative processing of each data of the middle curve;

[0039] Figure 5 Schematic diagram of creep damage at each stage;

[0040] Figure 6 The detailed dimension drawing of the standard notched ring specimen;

[0041] Figure 7 It is the detailed dimension drawing of the circular notched ring specimen;

[0042] Figure 8 Schematic diagram of a 1 / 8 section of the SNPT specimen used for 3D finite element modeling;

[0043] Fig. 9 Schematic diagram of a 1 / 8 section of CNPT specimen used for 3D finite element modeling;

[0044] Fig.10 Schematic diagram of a quarter section of the SCNT specimen used for two-dimensional axisymmetric finite element modeling;

[0045] Fig.11 Schematic diagram of a quarter of a CCNT specimen used for 2D axisymmetric finite element modeling;

[0046] Fig.12 This is a schematic diagram of the maximum principal stress comparison of the standard notched grid;

[0047] Fig.13 It is a schematic diagram of the bone point position corresponding to the central section of the standard notched specimen;

[0048] Fig.14 This is a schematic diagram of the bone point position corresponding to the cross section at 1 / 4 of the thickness of the standard notched specimen;

[0049] Fig.15 Schematic diagram of the bone point position corresponding to the free surface (unconstrained) of the standard notched specimen;

[0050] Fig.16 It is a schematic diagram of the bone point position of the standard notched specimen;

[0051] Fig.17 It is a schematic diagram of the bone point position corresponding to the central section of the circular notch specimen;

[0052] Fig.18 It is a schematic diagram of the bone point position corresponding to the cross section at 1 / 4 of the thickness of the circular notch specimen;

[0053] Fig.19 Schematic diagram of the bone point position corresponding to the free surface (unconstrained) of the circular notch specimen;

[0054] Fig. 20 It is a schematic diagram of the bone point position of the circular notch specimen;

[0055] Fig.21 To select multi-axial representative stress diagrams based on uniaxial data;

[0056] Fig. 22 This is the representative stress comparison diagram of the standard notch calculation corresponding to the direct method;

[0057] Fig.23 This is the representative stress comparison diagram of the circular notch calculated by the direct method;

[0058] Fig.24 This is a schematic diagram of the dispersion band of the standard notch predicted life and the test life corresponding to the direct method;

[0059] Fig.25 This is a schematic diagram of the scatter band of the circular notch predicted life and the experimental life corresponding to the direct method;

[0060] Fig.26 This is the representative stress comparison diagram of the standard notch calculation corresponding to the empirical method;

[0061] Fig. 27 This is the representative stress comparison diagram of the circular notch calculation corresponding to the empirical method;

[0062] Fig.28 This is a schematic diagram of the dispersion band of the standard notch predicted life and the test life corresponding to the empirical method;

[0063] Fig.29 This is a schematic diagram of the circular notch predicted life and test life dispersion band corresponding to the empirical method;

[0064] Fig.30 It is a schematic diagram of the stress parameter prediction results determined based on the empirical method;

[0065] Fig.31 Schematic diagram of stress parameter prediction results determined based on the direct method. DETAILED DESCRIPTION

[0066] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0067] In order to make the above-mentioned objects, features and advantages of the present application more obvious and easy to understand, the present application is further described in detail below with reference to the accompanying drawings and specific implementation methods.

[0068] like Figure 1 As shown, the embodiment of the present application provides a multiaxial creep life prediction method based on a notched flat plate specimen, and the notched flat plate specimen life prediction method includes:

[0069] Step 100: Obtain creep parameters. Creep parameters include: load and temperature.

[0070] Step 200: construct a finite element model. The finite element model is a physical model constructed based on creep parameters and a notched specimen. The notched specimen is a notched round bar specimen or a notched flat plate specimen.

[0071] Step 300: Determine stress parameters based on the finite element model, creep parameters and set association relationships. The set association relationships are obtained by using a simulation test method based on the MSRC criteria to perform linear fitting of cross-sectional representative stresses on notched round bar specimens and notched flat plate specimens; if the notched specimen is a notched flat plate specimen, a notched round bar specimen with the same notch size type as the notched flat plate specimen is used instead.

[0072] Step 400: Determine the creep rupture life according to the stress parameter. The creep rupture life includes: uniaxial creep rupture life and multiaxial creep rupture life.

[0073] In one embodiment, the stress parameters are determined by a direct method or an empirical method based on the finite element model, creep parameters and set association relationships.

[0074] Specifically, according to the finite element model, based on the creep parameters and the set association relationship, the stress parameters are determined by the direct method, including:

[0075] Based on the creep parameters, uniaxial creep tests were carried out using smooth round bar specimens, and multiaxial creep tests were carried out using notched round bar specimens, and the test results were obtained.

[0076] According to the finite element model, creep simulation is performed based on creep parameters and set association relationships to obtain simulation results.

[0077] Normalization is performed based on the simulation results and the test results to determine the locations of the bone points.

[0078] Stress components are determined based on the locations of the bone points, and stress parameters are determined based on the stress components.

[0079] As an optional implementation, the stress parameters are determined by an empirical method, specifically including:

[0080] Based on the creep parameters, a uniaxial creep test is carried out using a smooth round bar specimen to obtain uniaxial test data; the uniaxial test data includes creep strain data.

[0081] A life curve is constructed based on the uniaxial test data; a derivative is performed based on the life curve, and the minimum strain rate is determined; the minimum strain rate is the value with the smallest value selected from the data obtained after the derivative process; the creep damage tolerance factor is determined based on the minimum strain rate; and the stress parameter is determined based on the creep damage tolerance factor.

[0082] In one embodiment, determining the creep rupture life according to the stress parameter specifically includes:

[0083] The uniaxial creep rupture life is determined based on the applied uniaxial tensile stress; the representative stress is calculated based on the stress parameter; the multiaxial creep rupture life is determined based on the representative stress; wherein the calculation formula for the representative stress is:

[0084] σ rep =ασ I +(1-α)σ eq ;

[0085] Among them, σ rep-1 is the representative stress; α is the stress parameter; σ I is the principal stress; eq is the equivalent stress.

[0086] The calculation formula for creep rupture life is:

[0087] t u =C(T)σ -v ;

[0088]

[0089] Among them, t u is the uniaxial creep rupture life; C(T) is the temperature-dependent coefficient; σ is the applied uniaxial tensile stress; v is the creep rupture exponent; t nu is the multiaxial creep rupture life.

[0090] In practical applications, the present application invents a method to verify the creep rupture criterion (MSRC) instead of the notched flat specimen, that is, to verify the MSRC using a notched round bar specimen with the same notch size as the notched flat specimen. The verification method used is as follows:

[0091] 1. Direct method:

[0092] 1.Use smooth round bar specimens to carry out uniaxial creep tests, and notched round bar specimens (CNT) to carry out multiaxial creep tests. Obtain the life of uniaxial and multiaxial creep tests under certain load and temperature conditions.

[0093] 2. Establish a finite element model consistent with the test specimen, carry out finite element simulation under the same load and temperature conditions, and prove the independence of the mesh by setting different mesh densities and comparing the results, thus proving the effectiveness of finite element modeling.

[0094] 3. After determining the validity of the finite element modeling, by changing the creep parameters in the simulation, a total of 5 groups were adjusted and the corresponding simulation results were obtained. A path was established on the notch plane of the model, and the Mises stress, i.e., equivalent stress, from the root of the notch to the center of the notch was output. After normalization, the 5 groups of data would have a unique intersection, which is the bone point position (bone point definition: refers to a specific position at the root of the notch of the material, where the stress state remains unchanged during the creep process, has nothing to do with time, and is not related to the elasticity, plasticity or creep properties of the material, nor is it affected by the stress state. It is only related to the notch geometry and shape, and one notch type corresponds to a unique bone point. The stress components at the bone point are called bone point stresses, and these stress components can be used to characterize the characteristics of the notch specimen in terms of overall creep behavior).

[0095] 4. After determining the position of the bone point, output the stress components at the bone point, and calculate the α value in SHL MSRC based on the stress at the bone point, that is, the stress parameter.

[0096]

[0097] σ rep is the representative stress at the bone point (obtained through test data).

[0098] 5. Substitute the calculated α into formula (2) to calculate the representative stress, and fit it with the representative stress obtained from the test data. If the two fit well and show a good linear relationship, it is preliminarily considered that the material meets the MSRC criteria.

[0099] σ rep-1 =ασ I +(1-α)σ eq (2)

[0100] 6. According to the calculated σ rep-1 , life prediction is carried out, and the predicted value is compared with the test value. If the two are close and within a certain error range, it is considered that the predicted life of components of the same material based on the position of the bone point is effective, and it is further demonstrated that the material meets the MSRC criteria.

[0101] Uniaxial life creep formula:

[0102] t u =C(T)σ -v (3)

[0103] C(T) is a temperature-dependent coefficient that reflects the effect of temperature on creep life; σ is the uniaxial tensile stress applied in the test; ν is the creep rupture exponent, which is a material constant (data from uniaxial creep tests).

[0104] like Figure 2 As shown, plotting log(t u ) as the horizontal coordinate and log(σ) as the vertical coordinate, a linear regression analysis was performed and the slope of the best fitting line was -1 / v.

[0105] Based on the uniaxial data, the v value is obtained and then substituted into formula (3) to obtain the C(T) value, which can be applied to formula (4). According to the obtained σ rep-1 , the multiaxial creep rupture life can be predicted.

[0106]

[0107] 2. Empirical method:

[0108] According to the uniaxial test data of the smooth round bar specimen (a curve can be drawn for each uniaxial data under each load, and each curve is calculated separately), the t r The graph with the creep strain data ε as the horizontal axis and the creep strain data ε as the vertical axis is shown in Figure 3 .

[0109] After derivation, we can get the minimum strain rate See Figure 4 .according to Substitute the corresponding t1 into Figure 3 , get ε min , along ε min Draw a tangent line that intersects the y-axis at ε p ,See Figure 5 .

[0110]

[0111] t r is the total creep strain life.

[0112] ε f =ε p +ε sec +ε ter (6)

[0113] ε f is the total creep, ε p is the first stage creep, ε sec is the second stage creep, ε ter This is the third stage of creep.

[0114] 1. After calculating the creep damage at each stage, substitute it into formula (7) to calculate the creep damage tolerance factor λ. A λ can be calculated for each set of uniaxial data, and the average value can be taken.

[0115]

[0116] 2. Substitute the calculated λ value into the simple empirical relationship for estimating α, see formula (8), and calculate the corresponding α value.

[0117] α=e 0.337-0.538λ (8)

[0118] After the α value is calculated, the subsequent verification step MSRC is the same as steps 5 and 6 of the direct method.

[0119] The material used in this application is a Ti-6Al-2Cr-2Mo titanium alloy plate specimen. The elastic modulus E and yield stress σ of the material y The creep material constants are taken from the test with aging time t = 20h, n = 6.8, A = 0.138 × 10 -23 [1. / MPa] -n h -1 , v = 5.79, C = 1.08 × 10 -20 [1. / MPa] -n h -1 Two different notch types of notched flat specimens were used, namely standard notched ring specimens and circular notched ring specimens. Figure 6 and Figure 7 .

[0120] Regarding the test process, on a Chevenard type creep-testing machine, the temperature was set to 402°C, and the uniaxial specimens were set to carry out uniaxial creep tests at four stress levels of 500MPa, 550MPa, 600MPa and 650MPa, and the notched specimens were set to carry out creep tests at five stress levels of 600MPa, 700MPa, 800MPa, 900MPa and 950MPa. The uniaxial and multiaxial creep test data of Ti-6Al-2Cr-2Mo titanium alloy at 402°C are shown in Table 1.

[0121] Table 1 Uniaxial and multiaxial creep test data of Ti-6Al-2Cr-2Mo titanium alloy at 402℃

[0122]

[0123] Finite element simulation: modeling validation.

[0124] The finite element model established according to the specimen size used in the test is as follows: Figures 8 to 11 As shown, there are a total of 4 sample models, namely the standard notch plate SNPT sample and the circular notch plate CNPT sample consistent with the experiment, as well as the (standard notch round rod) SCNT sample and (circular notch round rod) CCNT sample with the same notch size type as the two.

[0125] Considering the symmetry of the NPT specimen in the XZ plane, YZ plane and thickness direction, only 1 / 8 of the specimen was modeled in three dimensions. Pressure was used to apply load on the top plane of the specimen, and symmetric boundary conditions were used on the XY, XZ, and YZ symmetry planes of the model. In order to reduce the amount of calculation, the transition mesh technology was used, and the obtained transition mesh was highlighted with red squares. In order to ensure the effectiveness of the finite element result modeling, the mesh independence verification was carried out, such as Fig.12 As shown in the figure, taking the standard notch as an example, different sections are selected at different thicknesses of the specimen, and the maximum principal stresses when the grid sizes are 200 and 300 are output respectively. It can be seen that the maximum principal stresses of the two sizes completely coincide, and the grid independence is proved.

[0126] Therefore, the minimum mesh size of the SNPT specimen near the notch root tip is set to 175μm, and the minimum mesh size of the CNPT specimen near the notch root tip is set to 300μm. The commercial ABAQUS code is used for analysis using a three-dimensional eight-node hexahedral volume integral unit (C3D8R). Axisymmetric two-dimensional modeling is used for 1 / 4 of the CNT specimen. Pressure is applied as a load on the top of the model, and symmetric boundary conditions are used on the XZ symmetry plane. The minimum mesh size of the CCNT specimen near the notch root tip is 209μm, and the minimum mesh size of the SCNT specimen near the notch root tip is 300μm. The commercial ABAQUS code is used for analysis using a four-node bilinear axisymmetric quadrilateral and a simplified integration unit (CAX4R).

[0127] Determine the location of the bone point:

[0128] Due to the circumferential characteristics of the notch, the stress state of the CNT sample remains consistent on all cross sections, which is determined by their geometric symmetry. On the other hand, since the NPT sample has a plate-like structure, its stress state changes at different cross-sectional thicknesses, resulting in uneven stress distribution. Therefore, this application selects three cross sections at different thicknesses of the sample, the sample thickness is B, the cross section thickness is selected as z, surface 1 is the cross section at the center of the sample, z / B=0.5; surface 2 is the cross section at 1 / 4 of the sample thickness, z / B=0.25; surface 3 is the free surface of the sample (unconstrained), z / B=0.

[0129] Change the creep parameters of the material, see Table 2.

[0130] Table 2 Five groups of creep parameters for determining bone points

[0131]

[0132] According to the parameters in Table 2, simulations were carried out respectively. According to the simulation results, the paths from the notch center to the notch root were established along three different cross sections for the flat specimens (SNPT and CNPT), and the paths from the notch center to the notch root were output for the round bar specimens (SCNT and CCNT), and the bone point position was found, such as Figure 13-Figure 20 shown.

[0133] according to Figure 13-Figure 20 It can be seen that the positions of the bone points selected according to different cross sections on the flat specimen are different, which does not conform to the basic definition of the bone point (the bone point is only related to the geometric size of the notch and has nothing to do with the stress state). The flat specimen cannot determine the unique bone point.

[0134] According to the obtained bone point positions, the stresses at the bone point positions are output in the finite element analysis and normalized. The obtained parameters are shown in Table 3.

[0135] Table 3 Normalized stress table of each specimen at the bone point

[0136]

[0137] σ eq is the Mises equivalent stress, σ m is the mean stress of the principal stress, σ m =σ I +σ II +σ III ; σ I is the maximum principal stress; σ II is the second principal stress; III is the third principal stress; σ net Net cross-sectional stress for notch size.

[0138] Calculate the representative stress:

[0139] Draw a graph based on the uniaxial test data, such as Fig.21 As shown, based on the multiaxial test life, Fig.21 Select the corresponding representative stress σ rep .

[0140] The representative stress of each specimen under different loads based on multiaxial life can be seen in Table 4.

[0141] Table 4 Normalized representative stress table

[0142]

[0143]

[0144] The test life of SCNT refers to the test life of SNPT, so the σ of SCNT rep / σ net Same as SNPT. Same as CCNT.

[0145] Substitute the data in Table 3 and Table 4 and calculate α according to formula (1). The specific values ​​are shown in Fig. 22 and Fig.23 According to the calculated α value, substitute it into formula (2) to calculate the representative stress. Fig. 22 and Fig.23 Because the uniaxial data is limited, the data fitting is only for the life range between 300h-2000h.

[0146] according to Fig. 22 and Fig.23 It can be seen that the prediction effects of the representative stress of each cross section of SCNT and SNPT are consistent, and CCNT and CNPT are also consistent, which shows that the method of using round rod specimens of the same notch size type to replace flat specimens of the corresponding notch size type is feasible, because the prediction effects of the two are consistent.

[0147] At the same time, according to Fig. 22 and Fig.23 It can be seen that the multiaxial representative stress prediction value of the material has a good linear fitting effect with the uniaxial representative stress test value, and has a strong linear correlation. It can be considered that the material meets the MSRC criteria.

[0148] Life expectancy prediction:

[0149] The multiaxial life of the material is predicted and evaluated based on the calculated representative stress, and the verification results are further demonstrated.

[0150] Plotting the uniaxial life, we get v = 5.79, and substituting it into formula (3), we get C(T) = 1.33e+19.

[0151] t u =C(T)σ -v (3)

[0152] Substitute the calculated parameters into formula (4), calculate the life according to the representative stress, and establish a dispersion band with the test life. Fig.24 and Fig.25 .

[0153] Depend on Fig.24 and Fig.25It can be seen that the life prediction results of CNT samples and NPT samples of the same notch size type are almost the same, which further confirms the feasibility of the innovation of this application (using CNT samples of the same notch size type instead of NPT samples to verify MSRC and carry out subsequent life prediction work). At the same time, it can be seen that the life prediction effect of this material is within the 2-fold dispersion band compared with the actual test effect in the life range of 300-2000h, which further proves that the material mentioned above is suitable for the MSRC criteria.

[0154] The values ​​obtained based on the uniaxial test data are shown in Table 5.

[0155] Table 5 Single-axis data calculated based on empirical method

[0156] σ <![CDATA[ε · min ]]> <![CDATA[t r ]]> <![CDATA[ε min ]]> <![CDATA[ε sec ]]> <![CDATA[ε f ]]> <![CDATA[ε ter ]]> λ 700 6.93E-04 455.479 0.315647 0.77 2.71667 1.631023 3.118212 650 3.56E-04 816.781 0.290692 0.649 2.4333 1.493608 3.301399 600 5.06E-04 1000 0.5057 0.437 1.65 0.7073 2.618535 550 3.37E-04 1600 0.53936 0.126 1.28024 0.61488 5.88

[0157] The mean value of λ is 3.729, and substituting it into formula (8) to calculate α is 0.188.

[0158] α=e 0.337-0.538λ (8)

[0159] Substitute the data in Table 3 and Table 4, and α calculated by the empirical formula, into formula (2) to calculate the representative stress. Fig.26 and Fig. 27 Because the uniaxial data is limited, the data fitting is only for the life range between 300h-2000h.

[0160] according to Fig.26 and Fig. 27 It can be seen that based on the empirical formula, the prediction effect of the CNT sample is good, while the prediction effect of the NPT sample is poor. That is, when verifying whether the material is applicable to the MSRC criteria, the NPT sample is not applicable to the empirical method, but the CNT sample is applicable and the effect is better. Therefore, using CNT samples of the same notch size type to replace NPT samples to verify MSRC is not only feasible, but also has more methods that can be adopted and has stronger applicability.

[0161] At the same time, according to Fig.26 and Fig. 27 It can be seen that the multiaxial representative stress prediction value of the material has a good linear fitting effect with the uniaxial representative stress test value, and has a strong linear correlation. It can be considered that the material meets the MSRC criteria.

[0162] The multiaxial life of the material is predicted and evaluated based on the calculated representative stress, and the verification results are further demonstrated.

[0163] Plotting the uniaxial life, we get v = 5.79, and substituting it into formula (3), we get C(T) = 1.33e+19.

[0164] t u =C(T)σ -v (3)

[0165] Substitute the calculated parameters into formula (4), calculate the life according to the representative stress, and establish a dispersion band with the test life. Fig.28 and Fig.29 .

[0166] Depend on Fig.28 and Fig.29 It can be obtained that when the material has a lifespan of 300-2000h, when the empirical method is used for prediction, the life prediction effect of the CNT sample is almost within the 2-fold dispersion band compared with the actual test effect, which further proves that the material is suitable for the MSRC criterion as mentioned above; but the predicted values ​​of the NPT sample are almost all at the edge of the dispersion band, which is consistent with the conclusion that the NPT sample is not suitable for the empirical method as mentioned above, and also indirectly proves the necessity of using CNT samples instead of NPT samples to verify MSRC.

[0167] The α value predicted by equation (8) is similar to the α value of the bone point stress of the annular notch specimen calculated by the direct method. The comparison of the two prediction results is shown in Fig.30 and Fig.31 .

[0168] The prediction results of the α values ​​obtained by the two methods are similar, which proves the effectiveness of the empirical method. This application can use CNT specimens with the same notch size as the NPT specimen to verify MSRC, so as to expand the scope of application of MSRC and better promote the life assessment of components in actual engineering.

[0169] The technical features of the above embodiments may be combined arbitrarily. To make the description concise, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0170] This article uses specific examples to illustrate the principles and implementation methods of this application. The description of the above embodiments is only used to help understand the method and core ideas of this application. At the same time, for those skilled in the art, according to the ideas of this application, there will be changes in the specific implementation methods and application scope. In summary, the content of this specification should not be understood as limiting this application.

Claims

1. A multiaxial creep life prediction method based on notched flat specimens, characterized in that: The multiaxial creep life prediction method based on notched flat plate specimens includes: Acquiring creep parameters; the creep parameters include: load and temperature; Constructing a finite element model; the finite element model is a physical model constructed based on the creep parameters and the notched specimen; the notched specimen is a notched round bar specimen or a notched flat plate specimen; According to the finite element model, based on the creep parameters and the set association relationship, the stress parameter is determined; the set association relationship is obtained by linear fitting of cross-sectional representative stress of the notched round bar specimen and the notched flat plate specimen using a simulation test method based on the MSRC criterion; wherein, if the notched specimen is a notched flat plate specimen, a notched round bar specimen of the same notch size type as the notched flat plate specimen is used instead; The creep rupture life is determined according to the stress parameter; the creep rupture life includes: uniaxial creep rupture life and multiaxial creep rupture life.

2. The multiaxial creep life prediction method based on notched flat specimen according to claim 1 is characterized in that: According to the finite element model, based on the creep parameters and the set association relationship, the stress parameters are determined by a direct method or an empirical method.

3. The multiaxial creep life prediction method based on notched flat specimen according to claim 2 is characterized in that: According to the finite element model, based on the creep parameters and the set association relationship, a direct method is used to determine stress parameters, specifically including: Based on the creep parameters, a uniaxial creep test is performed using a smooth round bar specimen, and a multiaxial creep test is performed using a notched round bar specimen to obtain test results; According to the finite element model, creep simulation is performed based on the creep parameters and the set association relationship to obtain a simulation result; Performing normalization processing according to the simulation results and the test results to determine the bone point position; Stress components are determined based on the bone point positions, and stress parameters are determined according to the stress components.

4. The multiaxial creep life prediction method based on notched flat specimen according to claim 2 is characterized in that: The stress parameters are determined by empirical methods, including: Based on the creep parameters, a uniaxial creep test is performed using a smooth round rod specimen to obtain uniaxial test data; the uniaxial test data includes creep strain data; constructing a life curve according to the uniaxial test data; Performing a derivation process based on the life curve and determining a minimum strain rate; the minimum strain rate is a value with the smallest value selected from the data obtained after the derivation process; determining a creep damage tolerance factor based on the minimum strain rate; A stress parameter is determined according to the creep damage tolerance factor.

5. The multiaxial creep life prediction method based on notched flat specimen according to claim 1 is characterized in that: Determining the creep rupture life according to the stress parameters specifically includes: Determine the uniaxial creep rupture life based on the applied uniaxial tensile stress; Calculating representative stress according to the stress parameter; Determine the multiaxial creep rupture life based on representative stresses; The calculation formula of the representative stress is: s rep-1 =as I +(1-a)s eq ; Among them, σ rep-1 is the representative stress; α is the stress parameter; σ I is the principal stress; eq is the equivalent stress.

6. The multiaxial creep life prediction method based on notched flat specimen according to claim 5 is characterized in that: The calculation formula of the creep rupture life is: t u =C(T)σ -v ; Among them, t u is the uniaxial creep rupture life; C(T) is the temperature-dependent coefficient; σ is the applied uniaxial tensile stress; v is the creep rupture exponent; t nu is the multiaxial creep rupture life.

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