A method for measuring stress and strain of a dangerous point of a hot end structure and a method for predicting life

Abstract

This invention relates to the field of stress-strain measurement technology for mechanical structures, and discloses a method for measuring stress-strain at critical points and predicting the lifespan of a hot-end structure. The method includes: determining the virtual stress at the critical point of the hot-end structure based on the strain of easily measurable parts of the structure; determining the actual strain at the critical point based on the virtual stress; determining the assumed stress at the critical point based on the actual strain; and determining the actual stress at the critical point based on the assumed stress. This invention improves the accuracy of stress-strain prediction at critical points of hot-end structures and enhances the accuracy of lifespan prediction for hot-end structures through the above solutions.

Description

Technical Field

[0001] This invention relates to the field of stress and strain measurement technology for mechanical structures, and particularly to a method for measuring stress and strain at critical points of hot-end structures and a method for predicting lifespan. Background Technology

[0002] Hot-end structures in service often experience stress concentration and complex operating conditions, making strain measurement at critical points challenging. Accurate measurement of stress and strain at critical points in nonlinear structures is crucial for structural optimization analysis, vibration reduction and isolation design, structural health assessment, and fatigue strength design. Many critical components in in-service engineering projects, including various aero-engines, gas turbines, and hypersonic vehicles, have numerous gaps. These gaps inevitably lead to defects during manufacturing and use, constituting structural critical points. The presence of these critical points can cause stress concentration, increasing the risk of structural failure. Therefore, accurate stress and strain measurement at these critical points is essential. To ensure the safe and reliable operation of structures, fatigue strength analysis of critical points in hot-end structures is necessary to extend their service life, ensure safety, and reduce unnecessary economic losses.

[0003] Currently, methods for measuring stress and strain at critical points in hot-end structures include finite element simulation and strain gauge measurement. However, due to the complex operating conditions and stress concentration experienced by the hot-end structure, none of these methods can accurately measure the stress-strain relationship at critical points in the hot-end structure. Summary of the Invention

[0004] In view of this, the present invention proposes a method for measuring stress-strain at critical points of hot-end structures and a method for predicting lifespan, which solves the technical problem that existing technologies cannot accurately predict the stress-strain relationship at critical points of hot-end structures.

[0005] On one hand, embodiments of the present invention provide a method for measuring the stress and strain at critical points of a hot-end structure, including: Based on the strain of easily measurable parts of the hot-end structure, determine the virtual stress at the critical point of the hot-end structure; Based on the virtual strain and virtual stress at the critical point, the actual strain at the critical point is determined. Based on the actual strain at the critical point, determine the assumed stress at the critical point; Based on the assumed stress at the danger point, the actual stress at the danger point is determined.

[0006] In some implementations, determining the actual strain at the critical point based on the virtual stress at the critical point includes: Based on the virtual strain at the critical point, and using a prediction model of the virtual stress and actual strain at the critical point, the actual strain at the critical point is determined. The expression for the actual strain prediction model is: ; in, Indicates the actual strain at the danger point. Virtual stress representing the danger point, This represents Young's modulus at temperature T. This represents the cyclic hardening coefficient at temperature T. This represents the cyclic hardening index at temperature T.

[0007] In some implementations, the method further includes: The cyclic hardening coefficient is optimized based on the non-proportional hardening factor to obtain the optimized cyclic hardening coefficient. The actual strain prediction model is updated based on the optimized cyclic hardening coefficient to obtain the updated actual strain prediction model.

[0008] In some implementations, the cyclic hardening coefficient is optimized based on a non-proportional hardening factor, resulting in an optimized cyclic hardening coefficient including: Based on fatigue test data of the hot-end structure at different mechanical phase angles, the non-proportional hardening factor is determined. The optimized cyclic hardening coefficient is obtained based on the ratio of the cyclic hardening coefficient to the non-proportional hardening factor.

[0009] In some implementations, determining the actual stress at the critical point based on the assumed stress at the critical point includes: Based on the assumed stress at the critical point, determine the yield strength at the critical point; Based on the yield strength of the critical point, determine the deformation stage of the critical point; Based on the deformation stage of the danger point and the assumed stress of the danger point, the actual stress of the danger point is determined.

[0010] In some implementations, the method further includes: determining the assumed stress increment at the critical point based on the assumed stress at the critical point; Determining the actual stress of the danger point based on the deformation stage of the danger point and the assumed stress of the danger point includes: in response to the deformation stage of the danger point being elastic, determining the assumed stress increment as the actual stress increment of the danger point in the elastic stage; accumulating the actual stress increments in the elastic stage to obtain the actual stress of the danger point; and in response to the deformation stage of the danger point being inelastic, determining the actual stress of the danger point based on the assumed stress of the danger point and the actual strain of the danger point.

[0011] In some implementations, determining the actual stress at the critical point based on the assumed stress and the actual strain at the critical point includes: In response to the fact that the deformation stage at which the critical point is located is an inelastic stage, the actual plastic strain increment at the critical point is determined based on the assumed stress and viscoplastic constitutive model of the critical point. The elastic strain increment of the critical point is determined based on the actual plastic strain increment and the actual strain at the critical point. Based on the elastic strain increment of the critical point, determine the actual stress increment of the critical point in the inelastic stage; The actual stress at the critical point is obtained by summing the actual stress increments of the inelastic stage.

[0012] In some implementations, the method further includes: determining the back stress deviator increment at the danger point based on a back stress deviator increment constitutive model; accumulating the back stress deviator increment to obtain an accumulated back stress deviator; determining the drag stress increment based on a drag stress constitutive model; and accumulating the drag stress increment to obtain an accumulated drag stress. The yield strength of the critical point is determined based on the assumed stress of the critical point, including: determining the yield strength of the critical point based on the assumed stress of the critical point, the accumulated back stress deviation, and the accumulated drag stress.

[0013] In some implementations, determining the back stress deviator increment at the critical point based on the back stress deviator increment constitutive model includes: The back stress deviatoric incremental constitutive model is modified based at least on the non-proportional parameter to obtain the modified back stress deviatoric incremental constitutive model. The non-proportional parameter is determined by the mechanical phase angle. Based on the modified constitutive model of back stress deviator increment, the back stress deviator increment of the critical point is determined.

[0014] On the other hand, embodiments of the present invention also provide a method for predicting the lifespan of a hot-end structure, characterized in that the lifespan of the hot-end structure is predicted based on the actual strain and actual stress at the critical point determined by the critical point stress-strain measurement method of the hot-end structure as described above.

[0015] The present invention has at least the following beneficial effects: This invention provides a method for measuring stress and strain at critical points of a hot-end structure and a method for predicting its lifespan. The method involves determining the virtual stress at critical points of the hot-end structure based on the strain of easily measurable parts of the structure; determining the actual strain at the critical points based on the virtual stress; determining the assumed stress at the critical points based on the actual strain; and determining the actual stress at the critical points based on the assumed stress. This technical solution can accurately determine the actual strain and actual stress at critical points, improving the accuracy of strain and stress measurements at critical points. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other embodiments can be obtained based on these drawings without creative effort.

[0017] Figure 1 A flowchart of a method for measuring the stress and strain at a critical point of a hot-end structure provided in an embodiment of the present invention; Figure 2 A flowchart of another method for measuring the stress and strain at the critical point of a hot-end structure provided in an embodiment of the present invention; Figure 3 This is a flowchart illustrating the correction of the actual strain prediction model in the critical point stress-strain measurement method for a hot-end structure provided in an embodiment of the present invention. Figure 4 A flowchart illustrating the correction of back stress deviation increment in the critical point stress-strain measurement method for a hot-end structure provided in an embodiment of the present invention. Figure 5 This is a schematic diagram of the stress and temperature history of a thin-walled tube in the stress-strain measurement method for the critical point of a hot-end structure provided in an embodiment of the present invention. Figure 6 This is a schematic diagram of the stress and temperature history of the fir tree-shaped structural member in the stress-strain measurement method for the critical point of the hot-end structure provided in the embodiment of the present invention. Figure 7An axial comparison diagram of the stress-strain prediction results of thin-walled tubes obtained by the constitutive model provided in the embodiments of the present invention and the test results obtained by stress-strain tests on high-temperature thin-walled tubes; Figure 8 A torsional comparison diagram of the stress-strain prediction results of thin-walled tubes obtained by the constitutive model provided in the embodiments of the present invention and the test results obtained by stress-strain tests on high-temperature thin-walled tubes. Figure 9 The image shows a comparison between the actual strain at the critical point of a fir tree-shaped structural component obtained by the critical point stress-strain measurement method of the hot-end structure provided in this embodiment of the invention and the simulated strain obtained by finite element analysis simulation of the fir tree-shaped structural component. Figure 10 The image shows a comparison between the actual stress at the critical point of a fir tree-shaped structural component obtained by the critical point stress-strain measurement method of the hot-end structure provided in this embodiment of the invention and the simulated stress obtained by finite element analysis simulation of the fir tree-shaped structural component. Figure 11 A comparison diagram of the predicted life of a fir tree-shaped structural component obtained by the life prediction method of the hot-end structure provided by the present invention and the test life of the fir tree-shaped structural component obtained by life test. Detailed Implementation

[0018] To make the objectives, technical solutions, and advantages of the present invention clearer, the embodiments of the present invention will be further described in detail below with reference to specific examples and the accompanying drawings.

[0019] It should be noted that all uses of "first" and "second" in the embodiments of the present invention are for the purpose of distinguishing two entities or parameters with the same name but different names. It is clear that "first" and "second" are only for the convenience of expression and should not be construed as limiting the embodiments of the present invention. Subsequent embodiments will not explain this in detail.

[0020] The present invention will now be described in detail with reference to the embodiments and accompanying drawings.

[0021] The first aspect of this invention provides a method for measuring the stress and strain at critical points of a hot-end structure, such as... Figure 1 As shown, the method includes steps S10 to S40.

[0022] S10. Determine the virtual stress at the critical point of the hot-end structure based on the strain of the easily measurable parts of the hot-end structure.

[0023] It should be noted that, in this embodiment, the hot end structure refers to the end of the mechanical structural component that bears heat in a high-temperature environment. The easily measurable part refers to the smooth and flat area on the hot end structure. The danger point refers to stress concentration areas, gaps, or other parts of the hot end structure that are prone to structural failure. The specific implementation of this embodiment will be described below.

[0024] In some embodiments, the stress-time history and strain-time history of easily measurable parts can be obtained first through simulation or strain gauge under a set temperature history. Then, the virtual strain-time history (hereinafter referred to as virtual strain history) of the danger point can be obtained through strain concentration factor and strain of easily measurable parts. Based on the virtual strain history of the danger point and Hooke's law, the virtual stress history of the danger point can be determined.

[0025] It should be noted that, in the embodiments of the present invention, the stress-time history, strain-time history, and temperature history of the easily measurable parts include the stress, strain, and temperature of the easily measurable parts at each time point. Based on this, the virtual stress of the danger point at any time point can be obtained, and then the actual strain history, assumed stress history, and other histories of the danger point can be obtained in the subsequent process.

[0026] In structural analysis under variable temperature loading, the strain concentration factor changes due to temperature variations, which is particularly important for stress-strain conversion techniques at critical points in hot-end structures. Therefore, in some embodiments, the strain concentration factor at different temperatures can be obtained through finite element simulation analysis, and then fitted as a temperature-related function. The strain concentration factor varying with temperature is characterized by the strain concentration factors at different temperatures and the fitted temperature-related function. Thus, based on this temperature-varying strain concentration factor, the influence of temperature on the hot-end structure can be fully considered when performing virtual strain prediction, thereby improving the accuracy of the identified virtual strain and virtual stress at critical points.

[0027] S20. Based on the virtual stress at the critical point, determine the actual strain at the critical point.

[0028] In some embodiments, an actual strain prediction model can be constructed based on the elastoplastic constitutive relationship between strain and stress. This actual strain prediction model is used to obtain the actual strain at the critical point. Then, the virtual stress at the critical point is substituted into the actual strain prediction model to obtain the actual strain at the critical point.

[0029] In some embodiments, the actual strain history of the critical point can also be obtained based on the virtual stress history of the critical point and the actual strain prediction model.

[0030] The embodiments of the present invention construct an actual strain prediction model based on the elastoplastic constitutive relationship between strain and stress, which can accurately express the relationship between virtual stress and actual strain, thereby accurately predicting the actual strain of the danger point based on the virtual stress of the danger point.

[0031] S30. Determine the assumed stress at the critical point based on the actual strain at the critical point.

[0032] In some embodiments, the assumed stress at the critical point can be obtained based on the actual strain at the critical point and the generalized Hooke's law.

[0033] In some embodiments, the hypothetical stress history of the danger point can be obtained based on the actual strain history of the danger and the generalized Hooke's law.

[0034] S40. Based on the assumed stress at the critical point, determine the actual stress at the critical point.

[0035] In some embodiments, the yield strength of the critical point can be determined based on the assumed stress of the critical point, thereby determining whether the deformation stage of the critical point is elastic or inelastic based on the yield strength of the critical point, and then determining the actual stress of the critical point accordingly.

[0036] In some embodiments, the yield strength of the critical point at any time can be determined based on the assumed stress history of the critical point. Based on the yield strength of the critical point, it can be determined whether the deformation stage of the critical point is elastic or inelastic, and then the actual stress of the critical point can be determined in a targeted manner.

[0037] In some embodiments, regardless of whether the deformation stage at which the danger point is located is elastic or inelastic, the assumed stress history based on the danger point can be first processed into the form of assumed stress increments. For example, according to a set time increment, the assumed stress history of the danger point in this embodiment is divided into several intervals, and the change in stress / strain at the end point of each interval compared to the starting point is called the stress / strain increment.

[0038] When the deformation stage of the danger point is the elastic stage, the assumed stress increment is determined as the actual stress increment of the danger point in the elastic stage, and the actual stress increment of the elastic stage is accumulated to obtain the actual stress of the danger point.

[0039] When the deformation stage of the critical point is in the inelastic stage, the actual plastic strain increment of the critical point can be determined first based on the assumed stress and other stress-strain parameters (such as back stress, inelastic strain, etc.). Then, based on the actual plastic strain increment and the actual strain of the critical point, the elastic strain increment of the critical point can be determined. Based on the elastic strain increment of the critical point, the actual stress increment of the critical point in the inelastic stage can be determined. Finally, the actual stress increments of the inelastic stage are accumulated to obtain the actual stress of the critical point.

[0040] This embodiment uses a technical solution to determine the virtual stress at the critical point of the hot-end structure based on the strain of easily measurable parts of the hot-end structure; to determine the actual strain at the critical point based on the virtual stress; to determine the assumed stress at the critical point based on the actual strain; and to determine the actual stress at the critical point based on the assumed stress. This solution can accurately determine the actual strain and actual stress at the critical point, thus improving the accuracy of strain and stress measurement at the critical point.

[0041] In some embodiments of the present invention, such as Figure 2 As shown, the virtual strain and virtual stress at the critical point can be determined based on steps S200~S203.

[0042] S200: Obtain the stress history, strain history, and temperature history of easily measurable parts.

[0043] By using simulation or strain gauges (attached to easily measurable parts of the hot-end structure to measure strain), the stress-strain history of easily measurable parts and the temperature of critical points can be obtained. The stress-strain history, including the stress at each time point in the easily measurable parts. and strain The expression is: ,

[0044] Among them, in the matrix For easily measurable axial stress components, Torsional stress components in easily measurable parts ( ), The axial strain components are for easily measurable parts. Torsional strain components of easily measurable parts ( ), The transverse strain components are for easily measurable parts. The vertical strain components are for easily measurable parts.

[0045] In some specific embodiments, the hot-end structure can be a thin-walled tube. Multiaxial thermomechanical nonlinear finite element analysis data of this thin-walled tube can be obtained through finite element simulation. The stress-time history and temperature-time history applied to the thin-walled tube are shown below. Figure 5 As shown.

[0046] In some specific embodiments, the hot-end structure can be a fir tree-shaped structure. Multiaxial thermomechanical nonlinear finite element analysis data of this fir tree-shaped structure can be obtained through finite element simulation. The stress-time history and temperature-time history loaded onto the fir tree-shaped structure are shown below. Figure 6 As shown.

[0047] In some specific embodiments, the material of the hot-end structure can be a high-temperature alloy, such as GH4169 (precipitation-strengthened nickel-based superalloy). For example, the hot-end structure can be a thin-walled tube made of GH4169 material, a fir-tree structure made of GH4169 material, etc.

[0048] S201, Calculate the strain concentration factor .

[0049] In structural analysis under variable temperature loading, the strain concentration factor changes due to temperature variations, which is particularly important for stress-strain conversion techniques at critical points in thermal structures. Therefore, finite element simulation analysis is first used to obtain the strain concentration factor at different temperatures, and then these factors are fitted as functions related to temperature to characterize the effect of temperature changes. The strain concentration factor in different directions is then analyzed. The expression is as follows:

[0050] in, It can be expressed as a function of temperature T. represents the strain concentration factor at room temperature in different directions. Wherein, The axial strain concentration factor. The transverse strain concentration factor. This is the torsional strain concentration factor.

[0051] S202. Obtain the virtual strain history of the danger point based on the strain concentration factor and the strain history of the easily measurable parts.

[0052] S203. Based on the virtual strain at the critical point and Hooke's law, determine the virtual stress history at the critical point.

[0053] In steps S202 and S203, the strain is based on the easily measurable location. The strain history is analyzed, and the virtual strain history at the critical point is calculated considering the strain concentration factor. The formulas for calculating the virtual strain at the critical point in three different directions are as follows:

[0054] in, For easily measurable axial strain. For easily measurable torsional strain, The axial strain concentration factor. The transverse strain concentration factor. This is the torsional strain concentration factor.

[0055] Virtual stress at dangerous points The expression is:

[0056] in, The virtual axial stress component at the critical point. The virtual torsional stress component at the danger point ( ), This represents the virtual transverse stress component at the danger point.

[0057] Substituting the obtained virtual strain history of the danger point into the generalized Hooke's law yields the virtual stress history of the danger point. :

[0058]

[0059]

[0060] in, Let be the Young's modulus at temperature T. Poisson's ratio at temperature T Let T be the shear modulus at temperature T.

[0061] This embodiment uses the above-described scheme to predict virtual strain based on the strain concentration factor that changes with temperature, fully considering the impact of temperature changes on the hot-end structure, thereby improving the accuracy of the virtual strain and virtual stress at the identified danger points.

[0062] In some embodiments of the present invention, such as Figure 2 As shown, the actual stress at the critical point can be determined based on step S204.

[0063] S204. Based on the virtual stress history and actual strain prediction model of the danger point, determine the actual strain history of the danger point.

[0064] The expression for the actual strain prediction model is as follows: ; in, Indicates the actual strain at the danger point. Virtual stress representing the danger point, This represents Young's modulus at temperature T. This represents the cyclic hardening coefficient at temperature T. This represents the cyclic hardening index at temperature T.

[0065] In this embodiment, the Nerbur rule and the Ramberg-Osgood equation can be combined to establish an actual strain prediction model that can represent the relationship between virtual stress and actual strain at the critical point, thereby obtaining the actual strain at the critical point.

[0066] Specifically, under multiaxial thermomechanical cyclic loading, the relationship between actual stress and virtual stress is shown by Nerbur's rule:

[0067] in, The actual stress at the critical location. The actual strain at the dangerous location. This refers to the virtual stress at the dangerous location. This refers to the virtual strain at the dangerous location.

[0068] The actual strain history at the notch needs to be obtained using the Ramberg-Osgood equation, the expression of which is as follows:

[0069] in, Let be the Young's modulus at temperature T. The cyclic hardening coefficient at temperature T. The cyclic hardening index is the temperature T.

[0070] Based on steps S201-S203, the virtual stress and virtual strain at the critical point have been obtained. By combining Nerbur's rule with the Ramberg-Osgood equation, a relationship can be established between the actual strain and virtual stress at the critical point, resulting in a prediction model for the actual strain at the critical point, which can then be used to calculate the actual strain at the critical point. The expression for the actual strain prediction model is as follows:

[0071] After substituting the obtained virtual stress at the critical point into the above formula, the actual strain at the corresponding critical point can be obtained by using the bisection method.

[0072] This embodiment establishes an actual strain prediction model that can represent the relationship between the actual strain and the virtual stress at the critical point through the above scheme. Thus, the actual strain at the critical point can be accurately calculated based on the virtual stress at the critical point, thereby improving the accuracy of the actual strain calculation at the critical point.

[0073] In some embodiments of the present invention, such as Figure 3 As shown, the method provided by the present invention can also update the actual strain prediction model based on the following steps, so as to be based on the updated actual strain prediction model.

[0074] S310. Based on fatigue test data of the hot-end structure under different mechanical phase angles, determine the non-proportional hardening factor.

[0075] S320. Based on the ratio of the cyclic hardening coefficient and the non-proportional hardening factor, the optimized cyclic hardening coefficient is obtained.

[0076] S330. The actual strain prediction model is updated based on the optimized cyclic hardening coefficient to obtain the updated actual strain prediction model.

[0077] Under multi-axis cyclic loading, non-proportional cyclic hardening occurs due to the presence of the mechanical phase angle. Therefore, in this embodiment, a non-proportional hardening factor that varies with the mechanical phase angle is proposed. Non-proportional hardening factor The expression is:

[0078] in, Indicates the mechanical phase angle. and The constant is obtained by fitting the stress amplitude and plastic stress amplitude from multiaxial thermomechanical fatigue test data under different mechanical phase angles.

[0079] Based on this non-proportional hardening factor, the cyclic strength coefficient can be optimized to obtain the optimized cyclic hardening coefficient. This optimized cyclic hardening coefficient can accurately reflect the non-proportional cyclic hardening phenomenon that occurs in the hot end structure under multiaxial cyclic loading, thereby correcting the actual strain prediction model and further improving the accuracy of the actual strain calculation at the critical point.

[0080] In this embodiment, the optimized cyclic hardening coefficient The expression is as follows:

[0081] Based on the optimized cyclic hardening coefficient Replace the cyclic hardening coefficient in the actual strain prediction model This allows for the updating of actual strain prediction models.

[0082] The updated actual strain prediction model obtained through the above scheme in this embodiment can accurately reflect the non-proportional cyclic hardening phenomenon that occurs in the hot end structure under multi-axis cyclic loading, thereby further improving the accuracy of actual strain calculation at dangerous points.

[0083] In this embodiment of the invention, the actual strain data of the critical point obtained by the above steps can be brought into the constitutive model to calculate the actual stress history of the critical part.

[0084] In some embodiments, such as Figure 2 As shown, the assumed stress history of the critical point can be determined based on the actual strain history of the critical point, and the actual stress of the critical point can be determined based on steps S205~S209.

[0085] S205. Based on the assumed stress history of the critical point, determine the assumed stress increment of the critical point, and based on the actual strain history of the critical point, determine the actual strain increment of the critical point.

[0086] In this embodiment of the invention, the actual strain at each time point in the actual strain history of the danger point can be determined according to the above scheme. Based on this, in this embodiment of the invention, the entire process to be calculated can be divided into multiple intervals according to the set time increment. The change in stress / strain at the end point of each interval compared to the starting point is called the increment. Based on this, in step S205, the actual strain history of the danger point can be processed into the form of increments, and the hypothetical stress history of the danger point can be processed into the form of hypothetical stress increments for subsequent calculations. The size of the time step can be set according to actual needs, and can be 1s, 2s, 3s, 10s, 20s, 30s, 1min, 2min, 10min, or 20min, etc., without specific limitation here.

[0087] S206. Determine the yield strength of the critical point based on the assumed stress at the critical point.

[0088] S207. Based on the yield strength of the critical point, determine whether the critical point is in the elastic stage.

[0089] In steps S206 and S207, the yield strength of the critical point can be determined based on the assumed stress, back stress, and drag stress at the critical point. More specifically, the stage at which the critical point of the hot-end structure is located in each interval—whether it is in an elastic or inelastic stage—can be determined by yield criterion calculation. The expression for the yield criterion is: ; in, f Indicates yield strength. Indicates stress, Indicates back stress. express von Mises equivalent stress, Indicates drag stress, This represents the initial yield stress.

[0090] It should be noted that in the yield criterion expression of this embodiment, the back stress... The back stress and drag stress are calculated at the end of the previous interval (i.e., at the beginning of the current interval). This is the drag stress calculated at the end of the previous interval, assuming the stress is the assumed stress at the beginning of the current interval.

[0091] if f＜0 If the stress is in the elastic stage, then the actual stress at the danger point is also in the elastic stage, and step S208 is executed.

[0092] if f≥0 If the stress is inelastic, then the actual stress at the danger point is also inelastic, and steps S209~S211 are executed.

[0093] S208. The assumed stress increment is determined as the actual stress increment at the critical point in the elastic stage; the actual stress increment in the elastic stage is accumulated to obtain the actual stress at the critical point.

[0094] Assuming stress increment Directly assign the actual stress increment to the critical point ,Right now:

[0095] Subsequently, the actual stress increment at the danger point was calculated. By performing cumulative calculations, the actual stress at the critical point can be obtained. .

[0096] S209. Based on the assumed stress and actual stress increment of the critical point, determine the actual stress increment of the critical point in the inelastic stage; accumulate the actual stress increments in the inelastic stage to obtain the actual stress of the critical point.

[0097] Specifically, the actual plastic strain increment at the critical point can be determined based on the assumed stress and viscoplastic constitutive model; the elastic strain increment at the critical point can be determined based on the actual plastic strain increment and the actual strain increment at the critical point; the actual stress increment at the critical point in the inelastic stage can be determined based on the elastic strain increment at the critical point; and the actual stress at the critical point can be obtained by accumulating the actual stress increments in the inelastic stage.

[0098] In some specific embodiments, the actual plastic strain rate at the critical point can be calculated first using the following viscoplastic constitutive model, the expression of which is as follows:

[0099] in, Indicates inelastic strain rate. To accumulate inelastic strain rate, This is the stress tensor (initially 0). For back stress tensor; This is the stress deviator; This is the back stress deviator.

[0100] The above viscoplastic constitutive model can also be expressed in incremental form, that is,

[0101] in, This represents the actual increase in plastic strain. Indicates the increment of inelastic strain. This is the stress tensor calculated at the end of the previous interval (the initial interval is 0). This is the back stress tensor calculated at the end of the previous interval; For corresponding Stress deviance; For corresponding Back stress deviation.

[0102] Among them, the cumulative inelastic strain increment The expression is:

[0103] in, and These represent parameters describing the viscoplastic behavior of a material. For time increments; The cumulative inelastic strain increment The cumulative inelastic strain is obtained by cumulative calculation. .

[0104] Subsequently, it can be seen that the actual strain increment at the critical point is compared with the actual plastic strain increment at the critical point. Subtracting the two yields the elastic strain increment at the critical point. .

[0105] Subsequently, based on the generalized Hooke's law and the elastic strain increment at the critical point... Find the actual stress increment at the critical point. .

[0106] The actual stress increment at the critical point By accumulating the stresses, the actual stress at the critical point can be obtained. The actual stress at the critical point at the end of the previous interval is taken as the actual stress at the critical point at the beginning of the current interval, and the increment of the actual stress at the critical point calculated for the current interval is used. Add the actual stress at the danger point at the beginning of the current interval to obtain the actual stress at the danger point at the end of the current interval.

[0107] S210. Based on the drag stress constitutive model, determine the drag stress increment; accumulate the drag stress increment to obtain the accumulated drag stress.

[0108] The drag stress constitutive model is as follows:

[0109] in, Indicates the increase in drag stress. Q Indicates drag stress R The stable value, b represents the drag stress. R Reaching a stable value Q The speed.

[0110] Based on the above drag stress constitutive model, the drag stress increment can be calculated. .

[0111] For drag stress increment The drag stress is obtained by performing cumulative calculations. R The drag stress at the end of the previous interval is used as the drag stress at the beginning of the current interval, and the drag stress increment calculated for the current interval is used. Add the drag stress at the beginning of the current interval to obtain the drag stress at the end of the current interval.

[0112] S211. Based on the constitutive model of back stress deviator increment, determine the back stress deviator increment at the critical point; accumulate the back stress deviator increment to obtain the accumulated back stress deviator.

[0113] In this embodiment, the constitutive model for the back stress deviator increment is:

[0114]

[0115] Where m represents the number of stages. Indicates the first Back stress eccentricity of the stage Indicates the first The increase in back stress eccentricity during the stage Indicates the first Stable value of stage back stress eccentricity Indicates the first The rate at which the stage back stress eccentricity reaches a stable value This indicates the inelastic strain increment.

[0116] Based on the aforementioned constitutive model of back stress deviatoric increment, the back stress deviatoric increment can be calculated.

[0117] Subsequently, the back stress deviation increment The cumulative back stress deviator is obtained by performing an accumulation calculation. The specific method for accumulating the back stress deviator is similar to the method for accumulating drag stress and the method for accumulating actual stress; therefore, the method for accumulating the back stress deviator will not be elaborated here. The accumulated back stress deviator... It can be used as the back stress deviator in the viscoplastic constitutive model to determine the actual plastic strain increment at the critical point based on the assumed stress at the critical point and the viscoplastic constitutive model.

[0118] Subsequently, the calculated parameters are updated, such as the actual stress at the critical point. Back stress deviation Drag stress R The parameters are set up, and the updated values ​​of each parameter are recorded.

[0119] S212: Determine if there is still data available for calculating the stress and strain at the critical point.

[0120] If there is still data, it means the calculation is not complete, and steps S206 to S211 are recalculated.

[0121] If no further data is received, the calculation is complete.

[0122] This invention, through steps S200 to S212, achieves the measurement of stress and strain at critical points in a hot-end structure. It predicts virtual strain based on a strain concentration factor that varies with temperature, fully considering the impact of temperature changes on the hot-end structure, thereby improving the accuracy of the identified virtual strain and virtual stress at critical points. By establishing a real strain prediction model that represents the relationship between the actual strain and virtual stress at critical points, the actual strain at critical points can be accurately calculated based on the virtual stress, thus improving the accuracy of the actual strain calculation. Based on a drag stress constitutive model, the drag stress increment is determined; the drag stress increments are accumulated to obtain the accumulated drag stress, based on the back stress... An incremental constitutive model of force deviatoric stress is used to determine the incremental back stress deviatoric stress at the critical point. These incremental back stress deviatoric stresses are then accumulated to obtain the accumulated back stress deviatoric stress. Based on the assumed stress at the critical point, the accumulated back stress deviatoric stress, and the accumulated drag stress, the yield strength at the critical point is determined. Thus, based on the assumed stress, back stress, and drag stress at the critical point, the yield strength can be accurately determined. Based on this yield strength, the deformation stage at the critical point can be accurately determined. Furthermore, based on the determined deformation stage, combined with the assumed stress, actual strain, and viscoplastic constitutive model at the critical point, the actual stress at the critical point in both the elastic and inelastic stages can be calculated, thereby improving the accuracy of the actual stress calculation at the critical point.

[0123] To comprehensively verify the accuracy and reliability of the stress-strain prediction method for the critical point of the hot-end structure proposed in this invention, in some specific embodiments, the stress and strain of the thin-walled tube can be predicted based on steps S201 to S212 to obtain the stress-strain prediction results. A constant-amplitude high-temperature multiaxial thermodynamic experiment is performed on the thin-walled tube, and the stress-strain test results are obtained. The obtained stress-strain prediction results and the stress-strain test results are compared, and the comparison results are as follows: Figure 7 and Figure 8 As shown, by analyzing Figure 7 and Figure 8 Analysis shows that the viscoplastic constitutive model proposed in this invention can well characterize the stress-strain history of materials.

[0124] In some specific embodiments, the stress and strain at the critical points of the fir tree-shaped structural member can also be predicted based on steps S201 to S212 to obtain the actual strain and actual stress at the critical points. Finite element nonlinear simulation is then performed on the critical points of the fir tree-shaped structural member to obtain the simulated strain and simulated stress at the critical points. The actual strain and actual stress at the critical points of the fir tree-shaped structural member obtained through the stress and strain prediction scheme described in this invention are compared with the simulated strain and simulated stress obtained from the finite element nonlinear simulation. The comparison results are as follows: Figure 9 and Figure 10 As shown, by analyzing Figure 9 and Figure 10 Analysis shows that the critical point stress-strain prediction method proposed in this invention has good consistency with the results of nonlinear finite element simulation. This indicates that the critical point stress-strain prediction method proposed in this invention is feasible and reliable when performing critical point stress-strain conversion of hot-end components.

[0125] In some embodiments of the present invention, the constitutive model of back stress deviator increment can be modified to calculate the back stress deviator increment based on the modified constitutive model, thereby improving the accuracy of the back stress deviator increment and the accuracy of the actual stress at the critical point in the inelastic state.

[0126] like Figure 4 As shown, the method provided by the present invention can also modify the constitutive model of back stress deviator based on steps S410 and S420.

[0127] S410. Based at least on the non-proportional parameter, the back stress deviatoric incremental constitutive model is modified to obtain the modified back stress deviatoric incremental constitutive model. The non-proportional parameter is determined by the mechanical phase angle.

[0128] S420. Based on the modified constitutive model of back stress deviator increment, determine the back stress deviator increment at the critical point.

[0129] To account for the effects of cyclic softening and non-proportional additional hardening on the cyclic mechanical behavior of materials, this invention introduces a non-proportional parameter and a softening coefficient to correct the back stress deviator. Specifically, the back stress deviator increment constitutive model is modified based on the non-proportional parameter and the softening coefficient to obtain the modified back stress deviator increment constitutive model. The expression of the modified back stress deviator increment constitutive model is as follows:

[0130] in, Indicates the first The back stress skewness increased after the stage correction. For non-proportional parameters, The softening coefficient is... The number of cycles. The dynamic recovery coefficient is given by m, which represents the number of stages. Indicates the first Back stress eccentricity of the stage Indicates the first Stable value of stage back stress eccentricity Indicates the first The rate at which the stage back stress eccentricity reaches a stable value This indicates the inelastic strain increment.

[0131] Among them, non-proportional parameters The expression is:

[0132] in, This represents the mechanical phase angle between the axial and torsional directions.

[0133] Among them, the softening coefficient The dynamic restitution coefficient was obtained from the peak stress curve of the experiment. It was obtained by fitting stress-strain data from uniaxial thermomechanical fatigue tests.

[0134] Based on the same inventive concept, according to another aspect of the present invention, embodiments of the present invention also provide a life prediction method for a hot-end structure. The life prediction method for a hot-end structure includes predicting the life of the hot-end structure based on the actual strain and actual stress at the critical point determined by the critical point stress-strain measurement method of the hot-end structure as described above.

[0135] According to the embodiments of the present invention, the lifespan of the hot-end structure can be accurately predicted by accurately predicting the actual strain and actual stress at the critical point, thereby improving the accuracy of lifespan prediction.

[0136] The life prediction method for hot-end structures proposed in this invention can accurately obtain the stress-strain history of critical points through a critical point stress-strain prediction scheme, laying the foundation for the accuracy of life prediction of actual structural components under high-temperature conditions and the accurate life extension of various equipment.

[0137] In some embodiments, the lifespan of a hot-end structure can be predicted based on fatigue damage, creep damage, and creep-fatigue interaction damage at critical points.

[0138] In this embodiment, the process of determining fatigue loss is as follows: First, the critical surface of the danger point is determined by finding the plane with the maximum normal strain amplitude as the critical surface of pure mechanical fatigue damage. At the same time, the normal strain amplitude value between the two maximum shear strain amplitude reversal points on the critical surface is also determined. Then, its pure fatigue damage was calculated using a tensile unified multiaxial fatigue damage model:

[0139]

[0140] in, For each cycle of pure fatigue damage, For pure fatigue life, The material fatigue constant at the critical point. This is the elastic modulus of the material at room temperature. This represents the maximum normal strain amplitude.

[0141] In this embodiment, the process of determining creep damage is as follows: The axial stress-time history and temperature-time history of the critical point within a cycle are obtained. Using a subdivision method, the cycle is divided into an appropriate number of intervals; the more intervals divided, the higher the calculation accuracy. Then, the creep stress in each interval is determined. When the axial stress value in an interval is positive, the Mises equivalent stress of the tensile and torsional stresses in that interval is used as the creep stress. When the axial stress value in an interval is negative, the creep stress in that interval is set to 0. The specific expression for calculating the creep stress at the critical point is as follows:

[0142] in, The creep stress at the danger point, Let be the axial stress at the critical point in interval i. Let be the shear stress at the critical point on interval i.

[0143] The formula for calculating creep damage is as follows:

[0144] in, Indicates the first Creep fracture time under partial temperature and equivalent creep stress; Indicates the first The duration of a portion.

[0145] Among them, creep fracture time The stress fracture can be obtained using the Manson-Succop (MS) stress fracture equation, the expression of which is as follows:

[0146] in, , It is the first Partial temperature; , It is the first Partial equivalent creep stress; is a material constant.

[0147] Then, the creep damage in each interval is calculated according to the creep endurance equation of the material, and then the creep damage in a cycle is accumulated. .

[0148] In this embodiment, the process of determining creep-fatigue interactive damage is as follows: First, the equivalent temperature of the cycle is determined by taking the highest and lowest temperatures of the high-temperature portion (>500℃) of a cycle and averaging them as the equivalent temperature of that cycle. Second, the creep-fatigue interaction coefficient is determined. The creep-fatigue interaction coefficient is determined by fitting high-temperature uniaxial fatigue data to obtain the creep-fatigue interaction coefficient at a specific temperature. Then, coefficients at different temperatures are fitted separately to characterize the effect of temperature on the creep-fatigue interaction coefficient. The creep-fatigue interaction coefficient is mainly determined by the following expression:

[0149]

[0150] in, This indicates creep-fatigue interactive damage. Indicates fatigue damage. This indicates creep damage, where T represents temperature. a and b The fitting constant for the material at the danger point is obtained by regression from experimental data. The value varies for different materials and is only related to the high-temperature mechanical properties of the material itself.

[0151] In this embodiment, the specific process of predicting the life of the hot end structure based on the fatigue damage, creep damage, and creep-fatigue interactive damage at the danger point is as follows: the creep damage, fatigue loss, and creep-fatigue interactive damage are accumulated to obtain the total loss, and the life value is obtained by taking the reciprocal of the total damage.

[0152]

[0153]

[0154] in, Total damage, To predict lifespan.

[0155] Figure 11 This is a comparison chart showing the predicted life of a fir tree-shaped structural component obtained by using the life prediction method for hot-end structures provided by the present invention, and the test life of the fir tree-shaped structural component obtained through life testing. Figure 11 It can be seen that the error between the predicted life of the fir tree-shaped structural component obtained by the life prediction method of the hot end structure provided by the present invention and the test life of the fir tree-shaped structural component obtained by the life test is mostly within 2 times the band, and a few are within 3 times the band.

[0156] The embodiments of the present invention, through the above-described scheme, can accurately and reliably predict the lifespan of hot-end structures, solving the problem that stress and strain measurement at critical points is very difficult in high-temperature environments. This has significant engineering implications for structural health assessment, structural optimization design, and accurate lifespan prediction of hot-end components.

[0157] The method for measuring the stress and strain at critical points of a hot-end structure described in this invention can be executed by an electronic device. Specifically, the electronic device includes a processor and a memory, the memory storing a computer program that can run on the processor, and the processor executing the program performs the steps of the method described above.

[0158] The memory, as a non-volatile storage medium, can be used to store non-volatile software programs, non-volatile computer-executable programs, and modules, such as the program instructions / modules corresponding to the methods described in the embodiments of this application. The processor executes various functional applications and data processing of the device by running the non-volatile software programs, instructions, and modules stored in the memory, thereby implementing the methods described in the above embodiments.

[0159] The memory may include a program storage area and a data storage area, wherein the program storage area may store the operating system and applications required for at least one function; the data storage area may store data created based on the use of the device, etc. Furthermore, the memory may include high-speed random access memory and may also include non-volatile memory, such as at least one disk storage device, flash memory device, or other non-volatile solid-state storage device. In some embodiments, the memory may optionally include memory remotely located relative to the processor, which can be connected to the local module via a network. Examples of such networks include, but are not limited to, the Internet, corporate intranets, local area networks, mobile communication networks, and combinations thereof.

[0160] Finally, it should be noted that those skilled in the art will understand that all or part of the processes in the above embodiments can be implemented by a computer program instructing related hardware. The program can be stored in a computer-readable storage medium, and when executed, it can include the processes of the embodiments of the above methods. The storage medium for the program can be a magnetic disk, optical disk, read-only memory (ROM), or random access memory (RAM), etc. The above computer program embodiments can achieve the same or similar effects as any of the corresponding foregoing method embodiments.

[0161] The above are exemplary embodiments disclosed in this invention. However, it should be noted that various changes and modifications can be made without departing from the scope of the embodiments of this invention as defined by the claims. The functions, steps, and / or actions of the methods according to the disclosed embodiments described herein do not need to be performed in any particular order. The sequence numbers of the disclosed embodiments of this invention are for descriptive purposes only and do not represent the superiority or inferiority of the embodiments. Furthermore, although the elements disclosed in the embodiments of this invention may be described or claimed individually, they may be understood as multiple unless explicitly limited to a singular number.

[0162] It should be understood that, as used herein, the singular form “a” is intended to include the plural form as well, unless the context clearly supports an exception. It should also be understood that, as used herein, “and / or” refers to any and all possible combinations of one or more of the associated listed items.

[0163] Those skilled in the art should understand that the discussion of any of the above embodiments is merely exemplary and is not intended to imply that the scope of the invention (including the claims) is limited to these examples. Within the framework of the invention, technical features of the above embodiments or different embodiments can be combined, and many other variations of different aspects of the invention exist, which are not provided in the details for the sake of brevity. Therefore, any omissions, modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the invention should be included within the protection scope of the invention.

Claims

1. A method for measuring the stress and strain at critical points of a hot-end structure, characterized in that, include: Based on the strain of easily measurable parts of the hot-end structure, determine the virtual stress at the critical point of the hot-end structure; Based on the virtual stress at the critical point, determine the actual strain at the critical point; Based on the actual strain at the critical point, determine the assumed stress at the critical point; Based on the assumed stress at the danger point, the actual stress at the danger point is determined.

2. The method according to claim 1, characterized in that, Determining the actual strain at the critical point based on the virtual stress at the critical point includes: Based on the virtual stress and actual strain prediction model of the critical point, the actual strain of the critical point is determined, wherein the expression of the actual strain prediction model is: ； in, Indicates the actual strain at the danger point. Virtual stress representing the danger point, This represents Young's modulus at temperature T. This represents the cyclic hardening coefficient at temperature T. This represents the cyclic hardening index at temperature T.

3. The method according to claim 2, characterized in that, Also includes: The cyclic hardening coefficient is optimized based on the non-proportional hardening factor to obtain the optimized cyclic hardening coefficient. The actual strain prediction model is updated based on the optimized cyclic hardening coefficient to obtain the updated actual strain prediction model.

4. The method according to claim 3, characterized in that, The cyclic hardening coefficient was optimized based on a non-proportional hardening factor, resulting in the following optimized cyclic hardening coefficients: Based on fatigue test data of the hot-end structure at different mechanical phase angles, the non-proportional hardening factor is determined. The optimized cyclic hardening coefficient is obtained based on the ratio of the cyclic hardening coefficient to the non-proportional hardening factor.

5. The method according to claim 1, characterized in that, Determining the actual stress at the critical point based on the assumed stress includes: Based on the assumed stress at the critical point, determine the yield strength at the critical point; Based on the yield strength of the critical point, determine the deformation stage of the critical point; Based on the deformation stage of the danger point and the assumed stress of the danger point, the actual stress of the danger point is determined.

6. The method according to claim 5, characterized in that, Also includes: Based on the assumed stress at the critical point, determine the assumed stress increment at the critical point; Determining the actual stress of the danger point based on the deformation stage of the danger point and the assumed stress of the danger point includes: in response to the deformation stage of the danger point being elastic, determining the assumed stress increment as the actual stress increment of the danger point in the elastic stage; accumulating the actual stress increments in the elastic stage to obtain the actual stress of the danger point; and in response to the deformation stage of the danger point being inelastic, determining the actual stress of the danger point based on the assumed stress of the danger point and the actual strain of the danger point.

7. The method according to claim 6, characterized in that, Determining the actual stress at the critical point based on the assumed stress and the actual strain at the critical point includes: Based on the assumed stress and viscoplastic constitutive model of the critical point, the actual plastic strain increment of the critical point is determined; The elastic strain increment of the critical point is determined based on the actual plastic strain increment and the actual strain at the critical point. Based on the elastic strain increment of the critical point, determine the actual stress increment of the critical point in the inelastic stage; The actual stress at the critical point is obtained by summing the actual stress increments of the inelastic stage.

8. The method according to claim 5, characterized in that, Also includes: Based on the constitutive model of back stress deviator increment, the back stress deviator increment of the critical point is determined; The back stress deviator increments are accumulated to obtain the accumulated back stress deviator; the drag stress increment is determined based on the drag stress constitutive model. The drag stress increments are accumulated to obtain the accumulated drag stress; The yield strength of the critical point is determined based on the assumed stress of the critical point, including: determining the yield strength of the critical point based on the assumed stress of the critical point, the accumulated back stress deviation, and the accumulated drag stress.

9. The method according to claim 8, characterized in that, Based on the constitutive model of back stress deviator increment, the back stress deviator increment at the critical point is determined as follows: The back stress deviatoric incremental constitutive model is modified based at least on the non-proportional parameter to obtain the modified back stress deviatoric incremental constitutive model. The non-proportional parameter is determined by the mechanical phase angle. Based on the modified constitutive model of back stress deviator increment, the back stress deviator increment of the critical point is determined.

10. A method for predicting the lifetime of a hot-end structure, characterized in that, Based on the actual strain and actual stress at the critical point determined by the critical point stress-strain measurement method of the hot-end structure as described in any one of claims 1 to 9, the lifespan of the hot-end structure is predicted.

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