CN112307664B - CT sample stress field introducing residual stress and crack propagation analysis method - Google Patents

CT sample stress field introducing residual stress and crack propagation analysis method Download PDF

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CN112307664B
CN112307664B CN202011258222.5A CN202011258222A CN112307664B CN 112307664 B CN112307664 B CN 112307664B CN 202011258222 A CN202011258222 A CN 202011258222A CN 112307664 B CN112307664 B CN 112307664B
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杨夏炜
彭冲
王艳莹
马铁军
张勇
徐雅欣
李文亚
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Northwestern Polytechnical University
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Abstract

The invention relates to a CT sample stress field introducing residual stress and a crack propagation analysis method, wherein ABAQUS finite element analysis software is adopted to establish a CT sample finite element model, a direct value assigning method and a file input numerical method are used for assigning initial stress to a CT sample, and cloud chart integration and a crack propagation finite element technology are used for calculating a stress intensity factor and carrying out finite element simulation analysis on crack propagation on the CT sample. The method fully considers the influence of different stress conditions on the crack propagation trend, obtains a finite element model for accurately calculating the stress intensity factor of the crack tip of the high-temperature alloy CT sample with the introduced residual stress and predicting the crack propagation rule, effectively predicts the influence of the stress on the crack propagation trend, can be widely applied to the field of aerospace, and provides a new idea for the research on the crack propagation behavior by residual stress prediction and pretreatment.

Description

CT sample stress field introducing residual stress and crack propagation analysis method
Technical Field
The invention belongs to a fracture mechanics numerical simulation method, and relates to research on crack tip stress intensity factors and propagation behaviors of aerospace high-temperature alloys under different stresses. In particular to a simulation method of the crack tip stress intensity factor and crack propagation of a high-temperature alloy CT sample introducing residual stress.
Background
The high-temperature alloy is used as an important material of parts such as an aircraft engine turbine, a blade disc, a combustion chamber and the like, and has excellent durability and fatigue performance. The failure modes of the high-temperature alloy are mainly fatigue fracture, stress corrosion and oxidation cracking, namely fracture failure under different conditions, so that the research on the crack propagation behavior of the high-temperature alloy is particularly important. The crack propagation behavior belongs to a very important aspect in the field of fracture mechanics, which belongs to the field of solid mechanics, and mainly studies the behavior of a fracture body bearing stress and strain, and the application of load or residual stress plays an important role. Failure is the biggest problem to be faced by the material in the application process, so that many scholars put the research into the crack initiation and propagation behavior of the material, but in the research of numerical simulation, how to deal with the residual stress is still a big problem. The method comprises the steps of establishing a stress intensity factor calculation model of surface cracks of a spherical shell in deep sea by Zhuyonmei and other people (Zhuyonmei, Yaxiang, Yanlingfeng, Wanxiang, Zhangjian and deep sea spherical shell surface crack stress intensity factors) of mechanical engineering college of Jiangsu science and technology university [ J ] Boneyology, 2020,24(03): 371-.
Disclosure of Invention
The invention solves the technical problems that: the invention relates to a method for analyzing a stress field and crack propagation of a CT sample by introducing residual stress, which solves the technical problems that: the CT sample introduces residual stress and stress field transfer of the elastic material in the continuous analysis step. The influence of different stress conditions on the stress intensity factor of the crack tip and the crack propagation trend is fully considered, a high-temperature alloy CT sample model with/without residual stress is established, a finite element model for accurately calculating the stress intensity factor of the crack tip and the crack propagation of the introduced residual stress is obtained, the influence of the stress on the crack propagation trend is effectively predicted, and a foundation is laid for researching the crack propagation behavior of the high-temperature alloy CT sample by the residual stress.
The technical scheme of the invention is as follows: a method for analyzing stress field and crack propagation of a CT sample introduced with residual stress comprises the following steps:
step 1: characterization scheme for determining residual stress of high-temperature alloy
The residual stress is loaded for the analyzed CT sample by using a Predefined Field Manager function in a Load module of ABAQUS finite element software, and two loading schemes are determined according to different initial conditions of the CT sample to be analyzed: the scheme 1 is suitable for predicting the crack behavior of the CT sample after the pre-loading treatment, and the scheme 2 can be used for the condition beyond the application range of the scheme 1;
scheme 1: applying preload to the CT sample, extracting a generated stress field, and inputting the stress field into the CT sample for analysis;
scheme 2: carrying out direct assignment on the analysis CT sample in a subarea manner under the condition of known stress distribution;
step 2: obtaining the residual stress according to the two schemes in the step 1, and determining the residual state and distribution;
(1) scheme 1: establishing a basic CT sample model, and ensuring that the size and the grid division of the model are completely the same as those of a CT sample analysis model to be established subsequently;
(2) the assignment method of scheme 2: dividing the sample into 3 areas, namely a crack front area, an opening area and a force application area 3 part; directly carrying out stress assignment on 3 areas of the CT sample in ABAQUS finite element analysis software, and inputting four partial stress assignments;
and 3, step 3: the method comprises the steps of establishing a stress intensity factor of a crack tip of a high-temperature alloy CT sample introduced with residual stress and establishing a crack propagation analysis model, wherein the steps are the establishment processes of two analysis CT sample models, and the establishment processes comprise the establishment of a geometric model, the setting of material properties, load and boundary conditions, the loading of a prestress field, the setting of crack conditions and output data, the setting of grid properties, and the submission of operation and data analysis;
and 4, step 4: and comparing the results of the models with and without the residual stress, and analyzing the influence of the residual stress on the stress intensity factor of the crack tip and the crack propagation rule.
The further technical scheme of the invention is as follows: the stress subareas of the scheme 2 are divided and assigned according to the actual stress cloud pictures.
The further technical scheme of the invention is as follows: according to the selected grid type, four-node linear plane stress quadrilateral units are adopted at the edge positions of the CT sample, an hourglass control and reduction integral CPS4R are adopted, CPS4 is adopted at the middle position, a refined grid is adopted in the middle area of the sample, and the edge positions are subjected to coarsening treatment.
The further technical scheme of the invention is as follows: in step 3 of patent claim 2, the displacement of the two holes in the X direction and the rotation in the X-Y plane are limited, and the convergence of the simulation process is improved.
The further technical scheme of the invention is as follows: regarding part (1) of step 2: the CT specimen model was built in part module: selecting a two-dimensional model for the CT model, selecting a deformable body as the geometric attribute of the model, and carrying out region division on the model in a part module of ABAQUS software; establishing two models, wherein one model is used for drawing a straight line at the center of the CT sample by utilizing a partition function to serve as a crack and is used for evaluating the stress intensity factor analysis CT model and is defined as a model 1, and the other model is not used for drawing the crack and is used for evaluating the crack propagation analysis CT sample and is defined as a model 2;
setting material properties in the material model: the pre-loading CT sample model needs to be provided with elastic properties (Young modulus and Poisson ratio) and plastic properties;
assembling a model in an assembly module, and setting the model as an independent attribute;
setting boundary conditions and loads in a Load module: the method is freely set according to the expected preloading mode, the loading mode of applying pressure load is adopted, wherein the pressure load acts on the top end of the CT sample, the bottom end of the sample is provided with a completely fixed constraint condition, and the load is in the form of the amplitude of a table;
create analysis step in step module and set output option: selecting a statics general analysis step, and checking S, U, PHILSM, PSILSM, SDEG and STATUS XFEM in field output; ALLAE, ALLCD, ALLFD, ALLIE, ALLPD of the history output;
setting crack attributes in an interaction module: model 1 requires setting the pre-crack as team in the Special;
setting grid attributes and dividing grids in the mesh module;
submitting the operation in the jobmodule and carrying out analysis post-processing;
the odb file output at this step provides initial stress values for subsequent steps in analyzing the CT model.
The further technical scheme of the invention is as follows: regarding part (2) of step 2: the required input values are four partial stresses of S11, S22, S33 and S12, wherein S11 is positive stress in the X-axis direction, S22 is positive stress in the Y-axis direction, S33 is positive stress in the Z-axis direction, and S12 is shearing force in the Y-axis direction on a YZ plane.
The further technical scheme of the invention is as follows: the step 3: establishing model setting parameters:
setting Material properties in a Material module: the applied force optical parameters include only the elastic parameters;
and setting an output option in the step module: increasing history output options, selecting a crack option, and checking the output of stress intensity factors, and selecting 5 cloud picture numbers;
setting crack attributes in an interaction module: selecting and creating a crack in the special function column, selecting a Contour integral as a crack type, and selecting the position and the direction of the tip of the crack in the CT model;
and setting Load and boundary conditions in a Load module: setting the coupling relation between the inner surfaces of two holes of the CT sample and the center of the hole, and respectively applying a concentrated force to the two center points, wherein the upper hole is a concentrated force in the upward direction (Y direction), and the lower hole is a concentrated force in the downward direction; introducing the residual stress described in step 1 using a Predefined Field Manager function; quoting the odb file of the pre-loading model in the method 1 in the step 2 in a Predefined Field Manager function, and selecting an analysis step and an increment step where a pre-stress model area and a required stress are required to be loaded, or directly assigning values to an analysis sample according to the method 2;
crack propagation analysis CT specimen model:
establishing a prefabricated crack in the part module: besides establishing a CT sample main body model, the model also needs to establish a straight line as an initial crack by selecting a two-dimensional deformable body and a shell part;
setting material properties in material: elastic properties and damage property parameters need to be set, and the damage property parameters include: maximum principal stress damage, damage evolution and damage stability parameters;
assembling the model in an assembly module: assembling a crack and analyzing a CT sample model, wherein the crack and the CT sample are both dependent attributes;
setting crack attributes in an interaction module: creating cracks in the special function column, and checking XFEM as the crack type to allow the cracks to expand;
the Load module is arranged as the stress intensity factor analysis CT sample model;
dividing grids in a mesh module: and refining the grid around the crack so that the crack traverses the grid.
Effects of the invention
The invention has the technical effects that: the CT sample model adopted by the invention is commonly used for calculating the stress intensity factor and the fatigue life of the crack and researching the crack propagation rule, but no document related to the influence of residual stress on the crack behavior in the CT sample is found. The invention provides two introduction methods of residual stress of a CT sample. The method can be widely applied to the field of aerospace, and provides a new idea for predicting residual stress and researching crack propagation behavior by pretreatment.
Because the continuous integral and XFAM technology is only suitable for linear elastic mechanics, continuous analysis steps cannot accurately transmit stress in a model applying the technology, and therefore, the goal of calculating the stress intensity factor under the residual stress cannot be achieved by independently applying one model. In the scheme 1 of the invention, 2 models are established, the common points of the models are a step module and a mesh module, one model is used for obtaining the stress distribution of the high-temperature alloy CT sample under the elastoplasticity preloading condition, and then residual stress is introduced into the other model, so that the problem can be avoided; in many dynamic thermal coupling processes, stress distribution is often not very uniform, the law is not obvious, and the method in scheme 2 can introduce residual stress into a model more flexibly to realize crack analysis of a CT sample in an analysis stress state.
The invention fully considers the influence of different stress conditions on the stress intensity factor of the tip of the crack and the crack propagation trend, establishes a high-temperature alloy CT sample model without residual stress, provides two methods for assigning values of the residual stress, obtains a finite element model for accurately calculating the stress intensity factor of the tip of the crack and the crack propagation, effectively predicts the influence of the stress on the crack propagation trend, and lays a foundation for researching the residual stress on the crack propagation behavior of the high-temperature alloy CT sample;
the method adopts two methods to endow the high-temperature alloy CT sample with residual stress, and the two methods are compared to play a mutual verification role.
Drawings
FIG. 1 is a schematic representation of a superalloy CT specimen in millimeters
FIG. 2 is a schematic diagram of the force applied to analyze a CT sample
FIG. 3 is a schematic diagram of the stress of a high-temperature alloy pre-loaded CT sample in scheme 1;
FIG. 4 is a schematic view of the region partition of the CT sample in embodiment 2. The crack tip is located in the region, the crack front region and the force application position region
FIG. 5 is a graph showing the effect of residual stress on the stress intensity factor at the crack tip as determined in example 1, scheme 1
FIG. 6 is a graph of the effect of the residual stress sought for example 1, option 2, on the crack tip stress intensity factor.
FIG. 7 shows the results of crack propagation in the absence of residual stress.
FIG. 8 is the effect of residual stress on crack propagation behavior determined in example 2, scheme 1, wherein the same row is applied with the same preload in absolute terms, and the tensile load on the leftAnd the right side is a pressing load; from top to bottom, the preload values are 1E respectively 7 Pa、5E 7 Pa、1E 8 Pa and 5E 8 Pa。
FIG. 9 is a graph of the effect of residual stress on crack propagation behavior as determined in case 2 of example 2, wherein the approximate absolute values of stresses in the same row are the same, tensile stress on the left and compressive stress on the right; the values of the approximate stress at the tip of the crack are respectively 5E from top to bottom 7 Pa、2E 8 Pa、8E 8 Pa and 1E 9 Pa。
FIG. 10 is a schematic diagram of two embodiments
Detailed Description
Referring to fig. 1 to 10, the technical scheme of the invention is as follows: a simulation method for the stress intensity factor and the crack propagation of a high-temperature alloy CT sample crack tip introducing residual stress is characterized in that the simulation method is carried out in finite element simulation software according to the following steps:
step 1: characterization scheme for determining residual stress of high-temperature alloy
The CT sample is one of the detection means of the material performance, which is commonly used for researching the properties of the material, such as fracture toughness, crack propagation possibility and the like, the cloud chart integration technology relied on by the invention for calculating the stress concentration factor and the propagation finite element technology applied in the crack propagation process are both based on linear elastic mechanics, the plastic deformation behavior of the CT sample is not considered in the calculation process, the cloud chart can not be accurately inherited to the next analysis step after the pre-load which does not lead the sample to reach the damage standard is unloaded, therefore, the method for determining the residual stress introduced by the high-temperature alloy CT sample in the invention is as follows: the residual stress was loaded for the CT sample under analysis using the Predefined Field Manager function in the Load module of the ABAQUS finite element software, two loading schemes were determined depending on the initial conditions of the CT sample to be analyzed: while protocol 1 is applicable to the prediction of crack behavior after pre-loading of CT specimens, protocol 2 may be applicable outside the scope of protocol 1.
Scheme 1: a preload is applied to the CT specimen, the resulting stress field is extracted, and the stress field is input to the CT specimen for analysis. The method involves creating a model of the same CT sample as the CT sample being analyzed, loading it, and extracting the output file data.
Scheme 2: the CT sample to be analyzed is directly assigned in a subarea mode under the condition of known stress distribution. This step is built on a pre-loaded CT model, a crack propagation analysis CT model, and a stress intensity factor calculation CT model.
And 2, step: acquisition of residual stress
The method is established on the characterization scheme in the step 1, mainly comprises the steps of establishing the pre-loaded CT sample model in the scheme 1 and specific assignment parameters and assignment conditions of the direct assignment method in the scheme 2, determining the state and distribution of the residual stress, and laying a cushion for the crack stress intensity factor and crack propagation calculation of the high-temperature alloy CT sample with the residual stress introduced in the subsequent step 3.
Scheme 1 the establishment of the pre-loaded CT sample model mainly comprises the following steps: this step requires the creation of a basic CT sample model, called a pre-loaded model, which ensures that the size and grid partitioning of the model is exactly the same as the subsequent analytical CT sample model to be built. The method comprises the steps of establishing a CT sample model, setting material properties, loads and boundary conditions, loading a prestress field, setting crack conditions and output data, setting grid properties, submitting operation and analyzing data in ABAQUS finite element analysis software, wherein the setting is based on the step 2.
The CT specimen model was built in part module: the CT model selects a two-dimensional model, selects a deformable body as the geometric attribute of the model, and performs region division on the model in a part module of ABAQUS software so as to obtain more uniform grids. And establishing two models according to different cracks used by a subsequent analysis CT sample model, wherein one model is used for drawing a straight line at the center of the CT sample by utilizing a partition function to serve as a crack for the assignment of the stress intensity factor analysis CT model and is defined as a model 1, and the other model is not used for drawing the crack and is used for the assignment of the crack propagation analysis CT sample and is defined as a model 2. In the present invention, the sizes of the CT samples are all set to be 20mm, 40mm and W 1 50mm, 11mm, 5mm, 25mm and 3mm for crack length;
setting material properties in a material model: the pre-loaded CT sample model needs to be provided with elastic properties (Young modulus and Poisson ratio) and plastic properties, the parameters used by the method are that the Young modulus is 215GPa, and the Poisson ratio is 0.29, so as to represent the high-temperature alloy;
assembling a model on an assembly module, and setting the model as an independent attribute;
setting boundary conditions and loads in a Load module: the method is freely set according to the expected preloading mode, the loading mode of applying pressure load is adopted, wherein the pressure load acts on the top end of the CT sample, the bottom end of the sample is provided with a completely fixed constraint condition, and the load is in the form of the amplitude of a table;
create analysis step in step module and set output option: selecting a statics general analysis step, and checking S, U, PHILSM, PSILSM, SDEG and STATUS XFEM in field output; ALLAE, ALLCD, ALLFD, ALLIE, ALLPD of the history output;
setting crack attributes in an interaction module: model 1 requires setting the pre-crack as team in the Special;
setting grid attributes and dividing grids in a mesh module: in the invention, the edge position of the CT sample adopts a four-node linear plane stress quadrilateral unit, the hourglass control and the reduction integral CPS4R are adopted, the CPS4 is adopted at the middle position, and the reduction integral is closed to improve the calculation accuracy. The global size is set to be 2.5m, the grid size of the central position (the first region and the second region in the attached figure 4) of the pre-loaded CT sample of the stress intensity factor is set to be 0.25mm, and 9940 grids are arranged globally; the grid size of the center position of the pre-loaded CT specimen for crack propagation was set to 0.33mm for a total of 6038 grids.
And submitting the job in the jobmodule and performing analysis post-processing.
The odb file output at this step provides initial stress values for subsequent steps in analyzing the CT model.
The assignment method of the method 2 comprises the following steps:
the method firstly needs to directly perform partition processing on an analysis CT sample model according to the distribution of a stress cloud picture, and the sample is simply divided into 3 areas which are respectively a crack front area, an opening area and a force application area 3. Stress assignment is directly carried out on 3 areas of a CT sample in a Load module Predefined Field Manager function of ABAQUS finite element analysis software, and the required input values are mainly four partial stresses S11, S22, S33 and S12 (wherein S11 is positive stress in an X-axis direction, S22 is positive stress in a Y-axis direction, S33 is positive stress in a Z-axis direction, and S12 is shearing force in the Y-axis direction on a YZ plane), wherein the value of S33 is 0Pa according to the requirement of ABAQUS 2017.
As shown in fig. 2, 3, and 4, the X direction is a horizontal direction, the Y direction is a vertical direction, and the Z direction is a model thickness direction. The X-Y plane is the plane where the provided schematic exists, restricting X-Y direction rotation, i.e. inhibiting rotation of the model. S11 represents a positive stress in the X direction, S22 represents a positive stress in the Y direction, S12 represents a slitting stress in the X, Y direction in S21, and S33 represents a positive stress in the Z direction, and the numerical value in the present invention is 0.
And 3, step 3: establishment of residual stress-induced high-temperature alloy CT sample crack tip stress intensity factor and crack propagation analysis model
The step is divided into two establishing processes of analyzing a CT sample model, and the establishing processes mainly comprise establishing a geometric model, setting material properties, load and boundary conditions, loading a prestress field, setting crack conditions and output data, setting grid properties, submitting operation and analyzing data, wherein the setting is based on the step 3. The specific setting is similar to the establishment of the preloading model in the step 2, and the difference is as follows:
stress intensity factor analysis CT model:
setting Material properties in a Material module: the applied force optical parameters include only the elastic parameters;
and setting an output option in a step module: increasing a course output option, selecting a crack option, and checking the output of a stress intensity factor, wherein 5 is selected for the number of the cloud pictures;
setting crack attributes in an interaction module: selecting and creating a crack in the special function column, selecting a Contour integral as a crack type, and selecting the position and the direction of the tip of the crack in the CT model;
and setting Load and boundary conditions in a Load module: setting the coupling relation between the inner surfaces of two holes of the CT sample and the center of the hole, and respectively applying a concentrated force to the two center points, wherein the upper hole is a concentrated force in the upward direction (Y direction), and the lower hole is a concentrated force in the downward direction; referring to the actual experimental condition and the convergence of the model, limiting the displacement of the two holes in the X direction and the rotation in the X-Y plane, and introducing the residual stress in the step 1 by using a Predefined Field Manager function; and (3) introducing the odb file of the pre-loading model in the method 1 in the step (2) in a Predefined Field Manager function, selecting an area needing to load the pre-stress model and an analysis step and an increment step where stress is needed, or directly assigning values to the analysis sample according to the method (2).
Crack propagation analysis CT specimen model:
establishing a prefabricated crack in the part module: besides establishing a CT sample main body model, the model also needs to establish a straight line as an initial crack by selecting a two-dimensional deformable body and a shell part;
setting material properties in material: elastic properties and damage property parameters need to be set, and the damage property parameters include: maximum principal stress damage, damage evolution and damage stability parameters;
assembling the model in an assembly module: assembling a crack and analyzing a CT sample model, wherein the crack and the CT sample are both non-independent attributes;
setting crack attributes in an interaction module: creating a crack in the special function bar, and checking XEFM as the crack type to allow the crack to expand;
the Load module is arranged as the stress intensity factor analysis CT sample model;
dividing grids in a mesh module: the grid around the crack is refined, so that the crack traverses the grid, and the calculation accuracy can be improved by setting.
After the two models are established, the job is submitted in the jobmodule, the data is processed and analyzed, the pre-loaded load and direction (or stress value) are changed, a group of CT sample models without residual stress is made, and the job is submitted. And comparing the results of the models with and without the residual stress, and analyzing the influence of the residual stress on the stress intensity factor of the crack tip and the crack propagation rule.
Example 1
The method for simulating the influence of the residual stress on the stress intensity factor of the high-temperature alloy CT sample comprises the following steps:
(1) establishing a geometric model of the high-temperature alloy stress intensity factor analysis CT sample, which specifically comprises the following steps:
the geometric model is built in a part module, and the sizes of CT samples are all set to be 20mm, 40mm and W 1 The length of the crack is set to be 3mm by dividing the model, wherein the length of the crack is 50mm, F is 11mm, D is 5mm, H is 25mm, the shape and the size of the CT sample are shown in the attached figure 1, and the unit is millimeter;
defining material property parameters in a property module, and selecting elastic property, wherein the Young modulus is 215GPa, and the Poisson ratio is 0.29;
assembling a model on an assembly module, and setting the model as an independent model;
establishing a static force general analysis step in a step module, and setting the time as 1 s; the increment is set to be automatic, the initial increment is set to be 0.01, and the minimum increment is set to be 1E -9 Setting the maximum increment step to be 1, and keeping the other settings to be default; selecting S, U, PHILSM, PSILSM, SDEG and STATUSXFEM in the field output; ALLAE, ALLCD, ALLFD, ALLIE, ALLPD of the history output; establishing a course output, setting an output area as a crack, checking and outputting a stress intensity factor, and setting the number of the cloud pictures as 5;
setting crack attributes in an interaction module: selecting and creating a crack in the special function column, checking a Contour integer as a crack type, selecting a crack tip position in the CT model, wherein the crack direction is (0,1,0), and designating the crack position as a team; setting the coupling relation between the inner surfaces of the two holes of the CT sample and the center of the hole;
setting load and boundary conditions at a load module, wherein the loading condition is as shown in the attached figure 2: applying a concentrated force to the two central points respectively with a value of 3E 6 And N is added. Limiting the displacement of the two holes in the X direction and the rotation in the X-Y plane;
the mesh module is provided with mesh attributes and is divided into meshes, the edge position of the CT sample adopts a four-node linear plane stress quadrilateral unit, a hourglass control and a reduction integral CPS4R are adopted, the middle position adopts a CPS4, and the reduction integral is closed to improve the calculation accuracy. The overall size is set to be 2.5mm, the grid size of the central position of the CT sample is set to be 0.25mm, and 9940 grids are arranged in total;
and submitting operation in the jobmodule to obtain a stress intensity factor under the condition of no residual stress.
(2) Endowing the analysis CT model with residual stress by adopting two modes: a pre-load method and a direct-valued method. Scheme 1, preloading method:
the scheme needs to establish a model similar to that in the step 1, and the specific steps are as follows:
establishing a geometric model of the CT sample in a part module, and performing the same step (1);
endowing material properties for the CT sample in a property module, wherein the parameters needing to be set comprise elastic properties and plastic properties, the elastic properties are the same as those in the step (1), and the plastic properties are set according to an attached table 1;
assembling a model on an assembly module;
establishing an analysis step in a step module, and performing the step (1);
when the Load module specifies the loading mode, the loading condition is as shown in fig. 3: the preload CT model adopts a pressure loading mode, specifically, a pressure load is applied to the top, and the bottom is completely constrained. The pressure setting is divided into pressure and tension, the absolute values are 1E respectively 7 Pa，5E 7 Pa，1E 8 Pa，5E 8 Pa；
Appointing the grid attribute and dividing the grid in the mesh module, the same step (1)
Creating and submitting operation in the jobmodule to obtain the odb file
And (3) in the load module of the model established in the step (1), using a Predefined Field Manager function to refer to the odb file obtained in the step (2), selecting an input stress option, checking the input file, selecting the obtained odb file and the analysis step and increment step for introducing the stress. And (2) establishing and submitting the model in the step (1) to operation to obtain data of the stress intensity factor.
Scheme 2, direct assignment method
Directly utilizing the Predefined Field Manager function of the model load module established in the step (1) to directly input the stress in a partitioning manner, the method is simply divided into three regions (when the method is applied, partitioning is carried out according to the stress Field of a mother model for taking out a CT sample model), wherein 1 is a crack tip region, 2 is a crack front edge region, and 3-position force application position regions are divided as shown in the attached figure 4. Wherein, the region 1 is the region where the crack tip is located, and the numerical settings are shown in table 1; region 2 is the region where the crack front is located, and has a fixed value, where S11 is 2E 7 Pa，S22＝1E 8 Pa，S33＝0Pa，S12＝-5E 7 Pa; region 3 is a force application region, and the numerical value is fixed, and is set to S11-3E 5 Pa，S22＝2E 6 Pa，S33＝0Pa，S12＝-1E 6 Pa。
And (3) submitting a job and analyzing by a jobmodule of the model created in the step (1).
The results of this example are shown in figures 5 and 6 and show that: for a high-temperature alloy CT sample, the stress intensity factor of the crack tip can be obviously changed by the loading of the residual stress, the residual stress is tensile stress, the stress intensity factor is reduced to some extent, and the stress intensity factor is increased to some extent when the residual stress is compressive stress. The greater the deviation in the stress intensity factor as the value of the residual stress increases. The CT sample model adopted by the invention has the stress intensity factor calculated under the condition of no residual stress
Figure BDA0002773728670000131
And the analytical solution of the stress intensity factor of the model with the same parameters is
Figure BDA0002773728670000132
The error is about 0.048%, and the accuracy of the simulation result of the example can be proved, so that the method plays a role in promoting the research and development of stress intensity factor calculation in the subsequent residual stress state.
Example 2
The method for simulating the influence of the residual stress on the crack propagation behavior of the high-temperature alloy CT sample comprises the following steps of:
(1) establishing a high-temperature alloy crack propagation analysis CT sample model, which specifically comprises the following steps:
the geometric model is built in the part module, the basic size of the CT sample is the same as that of the example 1, the difference is that the geometric model is required to be built independently for cracks in the example, a two-dimensional deformable body is selected, a straight line is selected, and the length is 3 mm.
The property parameters of the material are defined in the property module, and comprise elastic property and damage parameter, and the elastic property is the same as that of example 1. The maximum principal stress damage (Maxps damage) is selected from the damage criteria and is set to 1.202E 9 The damage evolution rule is set as judging damage according to energy, linearly softening, and selecting power law mode, wherein the fracture energy in three directions is 136887J/m 3 The damage-stable viscosity coefficient was set to 5E -5 ；
Assembling a CT model and a crack model together in an assembly module, wherein the CT model and the crack model are set to be independent;
establishing an analysis step in a step module, and the same as the example 1;
setting crack attributes in an interaction module, selecting XFEM as a crack type, allowing crack to expand, and selecting a crack existing area and a crack tip;
setting load and boundary conditions in the load module, and selecting the value of the concentration force 5E 6 N, the remainder as in example 1;
the mesh attribute and the division mesh are set in the mesh module, the mesh size of the central region (r) and region (ii) of fig. 4) of the CT sample is set to 0.33mm, and 6038 meshes are counted in the rest of the example 1.
And submitting operation in the jobmodule to obtain the stress intensity factor without residual stress.
(2) Endowing the analysis CT model with residual stress by adopting two modes: a pre-load method and a direct-valued method. Scheme 1, preloading method:
the scheme needs to establish a model similar to that in the step 1, and the specific steps are as follows:
establishing a geometric model of the CT sample in a part module, and performing the step (1) in the same way as the example;
the remaining correlation settings were set in the same manner as those in step (2) of example 1
Scheme 2, direct assignment method
All settings were the same as those relating to step (2) of example 1.
The results of this example are shown in fig. 7, 8 and 9, and it can be seen that the crack propagation path, stress field distribution and stress values are clearly different under different conditions. The results show that: for the superalloy CT specimen, the loading of residual stress significantly alters the stress field at the crack tip, thereby affecting crack propagation. When the same amount of compressive and tensile stress is applied, the crack deflects in the opposite direction compared to the propagation path of the crack in the absence of residual stress. The degree of deviation of the crack propagation path gradually increases as the residual stress increases. Under the condition that the residual stress is obviously smaller than the damage stress, the residual tensile stress can promote the crack to be expanded to a certain degree, and the residual compressive stress can play a role in hindering the crack to be expanded, so that the conclusion can be obtained that the mechanical property of the material is improved to a certain degree by the residual compressive stress.
When the CT sample is used for researching the crack resistance of the material, the residual stress is almost impossible to avoid, and the influence of the residual stress must be considered to obtain a more accurate result, so that the method has important guiding significance.
The above are only some examples of the present invention, but the scope of the present invention should not be limited thereby; therefore, all the equivalent changes and modifications made according to the claims of the present invention should be covered by the scope of the present invention.
TABLE 1 Plastic Property parameters of selected superalloys
TABLE 1 plasticity parameters of the superalloys
Figure BDA0002773728670000151
Table 2 shows stress values used in the direct evaluation method of scheme 2, in which all values have negative values when applying compressive stress and all values have positive values when applying tensile stress, and S33 has 0 value according to the plane stress requirement of ABAQUS 2017.
TABLE 2 stress values used in scheme 2 direct assignment method
Figure BDA0002773728670000161

Claims (7)

1. A CT sample stress field introducing residual stress and crack propagation analysis method is characterized in that the simulation method is carried out in finite element simulation software ABAQUS according to the following steps:
step 1: characterization scheme for determining residual stress of high-temperature alloy
The residual stress was loaded for the CT sample under analysis using the Predefined Field Manager function in the Load module of the ABAQUS finite element software, two loading schemes were determined depending on the initial conditions of the CT sample to be analyzed: the scheme 1 is suitable for predicting the crack behavior of the CT sample after the pre-loading treatment, and the scheme 2 can be used for the condition outside the applicable range of the scheme 1;
scheme 1: applying preload to the CT sample, extracting a stress field generated, and inputting the stress field into the CT sample to be analyzed;
scheme 2: carrying out direct assignment on the analysis CT sample in a subarea manner under the condition of known stress distribution;
step 2: obtaining the residual stress, and determining the residual state and distribution according to the two schemes in the step 1;
(1) scheme 1: establishing a basic CT sample model, and ensuring that the size and the grid division of the model are completely the same as those of a CT sample analysis model to be established subsequently;
(2) the assignment method of scheme 2: dividing the sample into 3 areas, namely a crack front area, an opening area and a force application area 3 part; directly carrying out stress assignment on 3 areas of the CT sample in ABAQUS finite element analysis software, and inputting four partial stress assignments;
and step 3: the method comprises the steps of establishing a high-temperature alloy CT sample crack tip stress intensity factor and a crack propagation analysis model by introducing residual stress, wherein the steps are two establishment processes of analyzing the CT sample model, and the establishment processes comprise the establishment of a geometric model, the setting of material properties, load and boundary conditions, the loading of a prestress field, the setting of crack conditions and output data, the setting of grid properties, and the submission of operation and data analysis;
and 4, step 4: and comparing the results of the models with and without residual stress, and analyzing the influence of the residual stress on the stress intensity factor of the crack tip and the crack propagation rule.
2. The method for analyzing the stress field and the crack propagation of the CT sample introduced with the residual stress as claimed in claim 1, wherein: the stress partition of the scheme 2 is divided and assigned according to the actual stress cloud chart.
3. The method for analyzing the stress field and the crack propagation of the CT sample introduced with the residual stress as claimed in claim 1, wherein: according to the selected grid type, four-node linear plane stress quadrilateral units are adopted at the edge positions of the CT sample, an hourglass control and reduction integral CPS4R are adopted, CPS4 is adopted at the middle position, a refined grid is adopted in the middle area of the sample, and the edge positions are subjected to coarsening treatment.
4. The method for analyzing the stress field and the crack propagation of the CT sample introduced with the residual stress as claimed in claim 1, wherein: in step 3 of patent claim 2, the displacement of the two holes in the X direction and the rotation in the X-Y plane are limited, and the convergence of the simulation process is improved.
5. The method for analyzing the stress field and the crack propagation of the CT sample introduced with the residual stress as claimed in claim 1, wherein: regarding part (1) of step 2: the CT specimen model was built in part module: selecting a two-dimensional model for the CT model, selecting a deformable body as the geometric attribute of the model, and carrying out region division on the model in a part module of ABAQUS software; establishing two models, wherein one model is used for drawing a straight line at the center of a CT sample by utilizing a partition function to serve as a crack and is used for evaluating a stress intensity factor analysis CT model and is defined as a model 1, and the other model is not used for drawing the crack and is used for evaluating a crack propagation analysis CT sample and is defined as a model 2;
setting material properties in the material model: the pre-loading CT sample model needs to be provided with elastic properties (Young modulus and Poisson ratio) and plastic properties;
assembling a model in an assembly module, and setting the model as an independent attribute;
setting boundary conditions and loads in a Load module: the method is freely arranged according to the expected preloading mode, a loading mode of applying pressure load is adopted, wherein the pressure load acts on the top end of the CT sample, the bottom end of the sample is provided with a completely fixed constraint condition, and the load is in an amplitude form of a table;
create analysis step in step module and set output option: selecting a statics general analysis step, and selecting S, U, PHILSM, PSILSM, SDEG and STATUSXFEM in field output; ALLAE, ALLCD, ALLFD, ALLIE, ALLPD of the history output;
setting crack attributes in an interaction module: model 1 requires setting the pre-crack as team in the Special;
setting grid attributes and dividing grids in the mesh module;
submitting operation in the jobmodule and performing analysis post-processing;
the odb file output at this step provides initial stress values for subsequent steps in analyzing the CT model.
6. The method for analyzing the stress field and the crack propagation of the CT sample introduced with the residual stress as claimed in claim 1, wherein: regarding part (2) of step 2: the required input values are four partial stresses of S11, S22, S33 and S12, wherein S11 is positive stress in the X-axis direction, S22 is positive stress in the Y-axis direction, S33 is positive stress in the Z-axis direction, and S12 is shearing force in the Y-axis direction on a YZ plane.
7. The method for analyzing the stress field and the crack propagation of the CT sample introduced with the residual stress as claimed in claim 1, wherein: the step 3: establishing model setting parameters:
setting Material properties in a Material module: the applied force mechanical parameters include only the elastic parameter;
and setting an output option in a step module: increasing history output options, selecting a crack option, and checking the output of stress intensity factors, and selecting 5 cloud picture numbers;
setting crack attributes in an interaction module: selecting and creating a crack in the special function column, selecting a Contour integral as a crack type, and selecting the position and the direction of the tip of the crack in the CT model;
and setting Load and boundary conditions in a Load module: setting the coupling relation between the inner surfaces of two holes of the CT sample and the center of the hole, and respectively applying a concentrated force to the two center points, wherein the upper hole is a concentrated force in the upward direction (Y direction), and the lower hole is a concentrated force in the downward direction; introducing the residual stress described in step 1 using a Predefined Field Manager function; quoting the odb file of the pre-loading model in the method 1 in the step 2 in a Predefined Field Manager function, and selecting an analysis step and an increment step where a pre-stress model area and a required stress are required to be loaded, or directly assigning values to an analysis sample according to the method 2;
crack propagation analysis CT specimen model:
establishing a prefabricated crack in the part module: besides establishing a CT sample main body model, the model also needs to establish a straight line as an initial crack by selecting a two-dimensional deformable body and a shell part;
setting material properties in material: elastic properties and damage property parameters need to be set, and the damage property parameters include: maximum principal stress damage, damage evolution and damage stability parameters;
assembling the model in an assembly module: assembling a crack and analyzing a CT sample model, wherein the crack and the CT sample are both dependent attributes;
setting crack attributes in an interaction module: creating a crack in the special function bar, and checking XEFM as the crack type to allow the crack to expand;
the Load module is arranged as the stress intensity factor analysis CT sample model;
dividing grids in a mesh module: and refining the grid around the crack so that the crack traverses the grid.
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