CN114322915B - Method and device for measuring forming limit of material - Google Patents
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Abstract
The invention relates to the field of performance detection, in particular to a method and a device for measuring the forming limit of a material, wherein the method comprises the following steps: obtaining a strain history of the specimen in any one strain state by using a strain measurement system, wherein the strain history comprises: strain data of a strain data point on the surface of the sample, which changes along with the strain data point in a strain state, is strain data point of a preset area of the sample when the sample is not deformed, wherein the preset area is an area in a preset radius range by taking a cracking position of the sample as a center; determining a target frame image corresponding to the necking time of the sample based on the strain data; determining the ultimate strain of the sample in any strain state based on the strain data and the target frame image; based on the ultimate strain in various strain states, a forming ultimate curve is obtained, and further, through analysis of the dispersibility of corresponding data, the information of local deformation instability of the material can be obtained, and the accuracy of the ultimate strain is improved.
Description
Technical Field
The invention relates to the field of performance detection, in particular to a method and a device for measuring the forming limit of a material.
Background
The Forming Limit Curves (FLCs) are used to determine the degree of deformation a given material can achieve when subjected to drawing, bulging, or a combination of drawing and bulging.
The forming limit of a material of a certain thickness is influenced by the thermo-mechanical processing of the material, which is limited by the occurrence of local necking or cracking, in relation to the processing history of the material, the forming limit of a sheet metal material being defined as the limit deformation degree that can be reached when the material starts to neck, and the forming limit map of the material being a strip-like region comprising a range of widths, which forming limit map is an ideal form of the forming limit map, being obtained by detecting the limit strains of the material under different linear strain paths.
The method for measuring the forming limit curve mainly comprises a position correlation analysis method and a time correlation analysis method based on section strain data, and a method based on thickness reduction rate analysis.
The position correlation analysis method has higher requirements on the distribution form of the section strain data, and when the distribution form of the section strain is poor or the phenomenon of double peaks and multiple peaks occurs, the limit strain obtained by analysis and calculation of the method is far away from the true limit strain of the material.
The FLC measurement method based on the thickness reduction is difficult to implement at present, the main difficulty is that the control of the test process, the acquisition and the calculation and the analysis of strain data are complex, the key problem is how to define the destabilization moment of the material through the strain change, and the FLC measurement method based on the thickness reduction needs to have accurate limit brief data of the material for supporting, which is also a difficulty.
Therefore, how to improve the accuracy of determining the forming limit of a material is a technical problem to be solved.
Disclosure of Invention
The present invention has been made in view of the above problems, and has as its object to provide a method and apparatus for determining the forming limit of a material which overcomes or at least partially solves the above problems.
In a first aspect, the present invention provides a method of determining the forming limit of a material, comprising:
obtaining a strain history of the specimen in any strain state by using a strain measurement system, wherein the strain history comprises: strain data of the strain data point on the surface of the sample, which changes with the strain data point in the strain state, is strain data point of a preset area of the sample when the sample is not deformed, the preset area is an area in a preset radius range with the cracking position of the sample as the center, and the strain data of the strain data point, which changes with the strain data point in the strain state, is reflected by a frame of image corresponding to each moment;
determining a target frame image corresponding to the time when the necking occurs on the sample based on the strain data;
determining a limit strain of the specimen in any strain state based on the strain data and the target frame image;
the forming limit curve is obtained based on the limit strain at the plurality of strain states.
Further, the strain data includes: the method comprises the steps of determining a target frame image corresponding to the necking time of the sample based on the strain data, wherein the target frame image comprises main strain data, secondary strain data and a main strain data standard deviation corresponding to each frame image, and the method comprises the following steps:
determining a strain path based on the strain data, wherein the strain path is a relation curve of the main strain data and the secondary strain data in the strain data along with the time change;
obtaining a strain path parameter based on interval data which linearly changes on the strain path;
determining a target main strain data standard deviation based on the strain path parameters;
and determining a target image corresponding to the necking time of the sample based on the standard deviation of the target main strain data.
Further, the obtaining the strain path parameter based on the interval data that linearly changes on the strain path includes:
based on the interval section data which is linearly changed on the strain path, obtaining a linear change formula of the interval section data through fitting;
and obtaining the strain path parameter based on the slope of the linear change formula.
Further, the determining the standard deviation of the target main strain data based on the strain path parameter includes:
based on the strain path parameter and a relationship satisfied between the strain path parameter and the standard deviation of the primary strain data:
σ＝αβ 3 +bβ 2 +cβ+d
wherein, beta is a strain path parameter, sigma is a main strain data standard deviation, a, b, c, d are constants, and a target main strain data standard deviation is determined.
Further, the determining, based on the strain data and the target frame image, a limit strain of the specimen in any one strain state includes:
selecting N strain data points with the maximum main strain in the target frame image based on the strain data;
based on the average primary strain and the average secondary strain of the N strain data points, the ultimate strain of the specimen at any one strain state is determined.
Further, the obtaining a forming limit curve based on the limit strain in the plurality of strain states includes:
a shaped limit curve is obtained by connecting the limit strains in at least 5 strain states based on the limit strains in the at least 5 strain states.
Further, the at least 5 strain states include: a unidirectional stretching, a planar strain, an equal bi-directional stretching, a first intermediate state between the unidirectional stretching and the planar strain, and a second intermediate state between the planar strain and the equal bi-directional stretching.
In a second aspect, the present invention also provides an apparatus for determining the forming limit of a material, comprising:
the first obtaining module is used for obtaining the strain history of the sample in any strain state by using the strain measurement system, and the strain history comprises the following steps: strain data of the strain data point on the surface of the sample, which changes with the strain data point in the strain state, is strain data point of a preset area of the sample when the sample is not deformed, the preset area is an area in a preset radius range with the cracking position of the sample as the center, and the strain data of the strain data point, which changes with the strain data point in the strain state, is reflected by a frame of image corresponding to each moment;
the first determining module is used for determining a target frame image corresponding to the necking time of the sample based on the strain data;
a second determining module, configured to determine a limit strain of the specimen in any strain state based on the strain data and the target frame image;
and a second obtaining module for obtaining a forming limit curve based on the limit strain in the plurality of strain states.
In a third aspect, the present invention also provides a computer device comprising a memory, a processor and a computer program stored on the memory and executable on the processor, the processor implementing the above method steps when executing the program.
In a fourth aspect, the present invention also provides a computer readable storage medium having stored thereon a computer program which when executed by a processor performs the above method steps.
One or more technical solutions in the embodiments of the present invention at least have the following technical effects or advantages:
the invention provides a method for determining the forming limit of a material, which comprises the following steps: obtaining a strain history of the specimen in any one strain state by using a strain measurement system, wherein the strain history comprises: strain data of a preset area of the sample when the sample is not deformed, wherein the preset area is an area in a preset radius range with the cracking position of the sample as the center, and the strain data of the sample when the strain data of the sample is changed in a strain state is represented by a frame of image corresponding to each moment; determining a target frame image corresponding to the necking time of the sample based on the strain data; determining the ultimate strain of the sample in any strain state based on the strain data and the target frame image; based on the ultimate strain in various strain states, a forming ultimate curve is obtained, and further, through analysis of the dispersibility of corresponding data, the information of local deformation instability of the material can be obtained, and the accuracy of the ultimate strain is improved.
Drawings
Various other advantages and benefits will become apparent to those of ordinary skill in the art upon reading the following detailed description of the preferred embodiments. The drawings are only for purposes of illustrating the preferred embodiments and are not to be construed as limiting the invention. Also throughout the drawings, like reference numerals are used to designate like parts. In the drawings:
FIG. 1 is a schematic flow chart of the steps of a method for determining a forming limit of a material in an embodiment of the invention;
FIG. 2 is a schematic diagram illustrating the determination of M strain data points in a sample in an embodiment of the present invention;
FIG. 3 is a schematic diagram showing the occurrence of cracks after deformation of a sample in an embodiment of the present invention;
FIG. 4 shows a schematic diagram of the strain path of the sample in an embodiment of the invention;
FIG. 5 is a schematic diagram showing strain path parameters and relationships satisfied between the strain path parameters and the standard deviation of the main strain data in an embodiment of the present invention;
FIGS. 6 and 7 are schematic diagrams of N strain data points before and after deformation in an embodiment of the invention;
FIG. 8 shows a schematic representation of a material forming limit curve in an embodiment of the invention;
FIG. 9 shows a schematic diagram of a device for determining the forming limit of a material in an embodiment of the invention;
fig. 10 shows a schematic diagram of a computer device implementing a method of determining a forming limit of a material in an embodiment of the invention.
Detailed Description
Exemplary embodiments of the present disclosure will be described in more detail below with reference to the accompanying drawings. While exemplary embodiments of the present disclosure are shown in the drawings, it should be understood that the present disclosure may be embodied in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the disclosure to those skilled in the art.
Example 1
An embodiment of the present invention provides a method for determining a forming limit of a material, as shown in fig. 1, including:
s101, obtaining the strain history of the sample in any strain state by using a strain measurement system, wherein the strain history comprises the following steps: strain data of a preset area of the sample when the sample is not deformed is strain data of the strain data points of the surface of the sample, wherein the preset area is an area in a preset radius range with the crack position of the sample as the center, and the strain data of the strain data points changing with the strain data points in the strain state is represented by a frame of image corresponding to each moment.
S102, determining a target frame image corresponding to the necking time of the sample based on strain data;
s103, determining limit strain of the sample in any strain state based on the strain data and the target frame image;
and S104, obtaining a forming limit curve based on the limit strain in various strain states.
In a specific embodiment, in S101, the strain history of the sample surface is recorded using a strain measurement system, which may be, for example, a DIC system based on continuous image analysis.
For example, a total of 23 samples of a material for forming limit determination include 8 shapes numbered 1# to 8# with 3 samples for each shape, with 2 samples for the last shape 8 #.
And acquiring an image corresponding to one sample from undeformed to the last frame of image before the sample cracks in a plane strain state of the sample by adopting a strain measurement system. Analyzing the last image before the sample is cracked, determining the position of the sample cracking in a main strain distribution cloud image, taking the position as the center, and selecting data points with radius within R range from an original undeformed image, namely strain data points, wherein M strain data points within the R range comprise a sample deformation instability region and a surrounding region without deformation instability, as shown in figure 2. Preferably, the M data points are 150-250, and 200 data points are selected in the invention. As shown in fig. 3, a schematic diagram showing the occurrence of cracks after the deformation of the sample is shown.
And recording strain data of the M strain data points, wherein the strain data comprises main strain data and secondary strain data, and a standard deviation of the main strain data corresponding to each frame of image.
Taking the main strain statistics of the selected area of the sample 1# -1 at different moments as an example, the main strain statistics are shown by the following table in the plane strain state:
strain data for strain data points of the sample surface are obtained at either strain state of the sample.
Next, S102 is performed to determine a target frame image corresponding to the time when the necking occurs in the sample based on the strain data.
Specifically, a strain path is determined based on the strain data, wherein the strain path is a relation curve of main strain data and secondary strain data in the strain data, and the relation curve changes with time;
obtaining a strain path parameter based on interval data which linearly changes on the strain path;
determining a target main strain data standard deviation based on the strain path parameters;
and determining a target image corresponding to the necking time of the sample based on the standard deviation of the target strain data.
As shown in FIG. 4, the strain path diagram of the sample 1# -1, wherein the linear variation section is a main strain range of 0.1478-0.3695.
Obtaining strain path parameters based on interval data of linear change on the strain path, wherein the method specifically comprises the following steps:
based on the interval section data which is linearly changed on the strain path, obtaining a linear change formula of the interval section data through fitting; the strain path parameters are obtained based on the slope of the linear variation formula.
Specifically, by fitting the data with the sections 0.1478-0.3695, a linear change formula of the interval data is obtained, and after fitting, the linear change formula is y= -1.8115x+0.0181, R 2 =0.9997, thereby obtaining a strain path parameter
After the strain path parameters are obtained, a target main strain data standard deviation is determined based on the strain path parameters.
The method specifically comprises the following steps:
based on the strain path parameters and the relationship satisfied between the strain path parameters and the standard deviation of the main strain data:
σ＝αβ 3 +bβ 2 +cβ+d
wherein, beta is a strain path parameter, sigma is a main strain data standard deviation, a, b, c, d are constants, and a target main strain data standard deviation is determined. The relation is specifically shown in fig. 5.
And obtaining a target main strain data standard deviation sigma= 11.587 at a strain path parameter beta= -0.552, and obtaining a graph frame with a 34 th sequence number corresponding to the data closest to the target main strain data standard deviation through searching the upper table, namely according to the strain data obtained in S101.
After the target frame image is determined, the ultimate strain of the specimen in either strain state is determined based on the target frame image and the strain data.
Specifically, on the target frame image, based on the strain data, N strain data points with the largest main strain are selected, N may be 3-5 points, and 4 points are selected in the present invention, as shown in fig. 6 and 7, which are N strain data points before and after deformation.
Next, the ultimate strain of the specimen at either strain state is determined based on the average primary strain and the average secondary strain of the N strain data points.
Averaging the principal strain values of the 4 strain data points to obtain an average principal strain; the sub-strain values of the 4 strain data points are averaged to obtain an average sub-strain. The ultimate strain of the specimen in the strain state of the plane stress is (average principal strain, average secondary strain).
And respectively obtaining corresponding strain path parameters, corresponding standard deviations of main strain data and corresponding limit strains according to the samples 1# to 1-8# to 2, wherein the standard deviations are shown in the following table:
| sample preparation | 1/β | β | σ(β) | Ultimate secondary strain | Ultimate principal strain |
| 1#-1 | -1.812 | -0.552 | 11.588 | -0.269 | 0.530 |
| 1#-2 | -2.022 | -0.495 | 10.062 | -0.239 | 0.528 |
| 1#-3 | -1.826 | -0.548 | 11.464 | -0.245 | 0.530 |
| 2#-1 | -2.137 | -0.468 | 9.407 | -0.233 | 0.560 |
| 2#-2 | -2.087 | -0.479 | 9.677 | -0.232 | 0.562 |
| 2#-3 | -2.190 | -0.457 | 9.136 | -0.233 | 0.590 |
| 3#-1 | -3.061 | -0.327 | 6.435 | -0.129 | 0.477 |
| 3#-2 | -2.899 | -0.345 | 6.771 | -0.138 | 0.505 |
| 3#-3 | -2.971 | -0.337 | 6.617 | -0.124 | 0.450 |
| 4#-1 | -8.263 | -0.121 | 3.477 | -0.026 | 0.377 |
| 4#-2 | -8.560 | -0.117 | 3.431 | -0.022 | 0.342 |
| 4#-3 | -8.831 | -0.113 | 3.393 | -0.026 | 0.379 |
| 5#-1 | 38.313 | 0.026 | 2.200 | 0.024 | 0.299 |
| 5#-2 | 47.655 | 0.021 | 2.235 | 0.023 | 0.299 |
| 5#-3 | 38.988 | 0.026 | 2.203 | 0.021 | 0.334 |
| 6#-1 | 6.713 | 0.149 | 1.575 | 0.058 | 0.327 |
| 6#-2 | 8.113 | 0.123 | 1.676 | 0.053 | 0.328 |
| 6#-3 | 8.097 | 0.123 | 1.675 | 0.054 | 0.315 |
| 7#-1 | 1.761 | 0.568 | 1.499 | 0.198 | 0.388 |
| 7#-2 | 1.874 | 0.534 | 1.427 | 0.218 | 0.428 |
| 7#-3 | 1.880 | 0.532 | 1.424 | 0.207 | 0.409 |
| 8#-1 | 1.165 | 0.859 | 2.271 | 0.383 | 0.461 |
| 8#-2 | 1.047 | 0.955 | 2.491 | 0.407 | 0.463 |
Wherein, different sample shapes correspond to different strain states, and 2-3 samples with the same sample shape correspond to the same strain state.
Finally, S104 is performed to obtain a forming limit curve based on the limit strain in the plurality of strain states.
Specifically, a forming limit curve is obtained by connecting the limit strain states of at least 5 strain states based on the limit strain in the at least 5 strain states. A forming limit curve as shown in fig. 8 was obtained.
The at least 5 strain states include a unidirectional stretching, a planar strain, an equal bi-directional stretching, and a first intermediate strain state between the unidirectional stretching and the planar strain, and a second intermediate strain state between the planar strain and the equal bi-directional stretching.
One or more technical solutions in the embodiments of the present invention at least have the following technical effects or advantages:
the invention provides a method for determining the forming limit of a material, which comprises the following steps: obtaining a strain history of the specimen in any one strain state by using a strain measurement system, wherein the strain history comprises: strain data of a preset area of the sample when the sample is not deformed, wherein the preset area is an area in a preset radius range with the cracking position of the sample as the center, and the strain data of the sample when the strain data of the sample is changed in a strain state is represented by a frame of image corresponding to each moment; determining a target frame image corresponding to the necking time of the sample based on the strain data; determining the ultimate strain of the sample in any strain state based on the strain data and the target frame image; based on the ultimate strain in various strain states, a forming ultimate curve is obtained, and further, through analysis of the dispersibility of corresponding data, the information of local deformation instability of the material can be obtained, and the accuracy of the ultimate strain is improved.
Example two
Based on the same inventive concept, the present invention also provides a device for determining a forming limit of a material, as shown in fig. 9, comprising:
the first obtaining module 901 is configured to obtain a strain history of the sample in any strain state by using a strain measurement system, where the strain history includes: strain data of the strain data point on the surface of the sample, which changes with the strain data point in the strain state, is strain data point of a preset area of the sample when the sample is not deformed, the preset area is an area in a preset radius range with the cracking position of the sample as the center, and the strain data of the strain data point, which changes with the strain data point in the strain state, is reflected by a frame of image corresponding to each moment;
a first determining module 902, configured to determine, based on the strain data, a target frame image corresponding to a time when necking occurs in the sample;
a second determining module 903, configured to determine a limit strain of the sample in any strain state based on the strain data and the target frame image;
a second obtaining module 904 is configured to obtain a forming limit curve based on limit strain at a plurality of strain states.
In an alternative embodiment, the first determining module 902 includes:
the first determining subunit is used for determining a strain path based on the strain data, wherein the strain path is a relation curve of main strain data and secondary strain data in the strain data, and the relation curve changes with time;
the first obtaining subunit is used for obtaining a strain path parameter based on interval section data which linearly changes on the strain path;
a second determining subunit, configured to determine a target main strain data standard deviation based on the strain path parameter;
and the third determination subunit is used for determining a target image corresponding to the necking time of the sample based on the target main strain data standard deviation.
In an alternative embodiment, the first obtaining subunit is configured to:
based on the interval section data which is linearly changed on the strain path, obtaining a linear change formula of the interval section data through fitting;
and obtaining the strain path parameter based on the slope of the linear change formula.
A second determination subunit configured to:
based on the strain path parameter and a relationship satisfied between the strain path parameter and the standard deviation of the primary strain data:
σ＝aβ 3 +bβ 2 +cβ+d
wherein, beta is a strain path parameter, sigma is a main strain data standard deviation, a, b, c, d are constants, and a target main strain data standard deviation is determined.
In an alternative embodiment, the second determining unit is configured to:
selecting N strain data points with the maximum main strain in the target frame image based on the strain data;
based on the average primary strain and the average secondary strain of the N strain data points, the ultimate strain of the specimen at any one strain state is determined.
In an alternative embodiment, the second obtaining module is configured to:
a shaped limit curve is obtained by connecting the limit strains in at least 5 strain states based on the limit strains in the at least 5 strain states.
In an alternative embodiment, the at least 5 strain states include: a unidirectional stretching, a planar strain, an equal bi-directional stretching, a first intermediate state between the unidirectional stretching and the planar strain, and a second intermediate state between the planar strain and the equal bi-directional stretching.
Example III
Based on the same inventive concept, an embodiment of the present invention provides a computer device, as shown in fig. 10, including a memory 1004, a processor 1002, and a computer program stored in the memory 1004 and executable on the processor 1002, where the processor 1002 executes the program to implement the steps of the method for determining a forming limit of a material described above.
Where in FIG. 10, a bus architecture (represented by bus 1000), the bus 1000 may comprise any number of interconnected buses and bridges, with the bus 1000 linking together various circuits, including one or more processors, represented by the processor 1002, and memory, represented by the memory 1004. Bus 1000 may also link together various other circuits such as peripheral devices, voltage regulators, power management circuits, etc., as are well known in the art and, therefore, will not be described further herein. The bus interface 1006 provides an interface between the bus 1000 and the receiver 1001 and transmitter 1003. The receiver 1001 and the transmitter 1003 may be the same element, i.e. a transceiver, providing a means for communicating with various other apparatus over a transmission medium. The processor 1002 is responsible for managing the bus 1000 and general processing, while the memory 1004 may be used to store data used by the processor 1002 in performing operations.
Example IV
Based on the same inventive concept, a fourth embodiment of the present invention provides a computer-readable storage medium having stored thereon a computer program which, when executed by a processor, implements the steps of the above-described method of determining a forming limit of a material.
The algorithms and displays presented herein are not inherently related to any particular computer, virtual system, or other apparatus. Various general-purpose systems may also be used with the teachings herein. The required structure for a construction of such a system is apparent from the description above. In addition, the present invention is not directed to any particular programming language. It will be appreciated that the teachings of the present invention described herein may be implemented in a variety of programming languages, and the above description of specific languages is provided for disclosure of enablement and best mode of the present invention.
In the description provided herein, numerous specific details are set forth. However, it is understood that embodiments of the invention may be practiced without these specific details. In some instances, well-known methods, structures and techniques have not been shown in detail in order not to obscure an understanding of this description.
Similarly, it should be appreciated that in the foregoing description of exemplary embodiments of the invention, various features of the invention are sometimes grouped together in a single embodiment, figure, or description thereof for the purpose of streamlining the disclosure and aiding in the understanding of one or more of the various inventive aspects. However, the disclosed method should not be construed as reflecting the intention that: i.e., the claimed invention requires more features than are expressly recited in each claim. Rather, as the following claims reflect, inventive aspects lie in less than all features of a single foregoing disclosed embodiment. Thus, the claims following the detailed description are hereby expressly incorporated into this detailed description, with each claim standing on its own as a separate embodiment of this invention.
Those skilled in the art will appreciate that the modules in the apparatus of the embodiments may be adaptively changed and disposed in one or more apparatuses different from the embodiments. The modules or units or components of the embodiments may be combined into one module or unit or component and, furthermore, they may be divided into a plurality of sub-modules or sub-units or sub-components. Any combination of all features disclosed in this specification (including any accompanying claims, abstract and drawings), and all of the processes or units of any method or apparatus so disclosed, may be used in combination, except insofar as at least some of such features and/or processes or units are mutually exclusive. Each feature disclosed in this specification (including any accompanying claims, abstract and drawings), may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise.
Furthermore, those skilled in the art will appreciate that while some embodiments herein include some features but not others included in other embodiments, combinations of features of different embodiments are meant to be within the scope of the invention and form different embodiments. For example, in the following claims, any of the claimed embodiments can be used in any combination.
Various component embodiments of the invention may be implemented in hardware, or in software modules running on one or more processors, or in a combination thereof. Those skilled in the art will appreciate that a microprocessor or Digital Signal Processor (DSP) may be used in practice to implement some or all of the functions of some or all of the components in a material forming limit determination apparatus, computer device, according to embodiments of the present invention. The present invention can also be implemented as an apparatus or device program (e.g., a computer program and a computer program product) for performing a portion or all of the methods described herein. Such a program embodying the present invention may be stored on a computer readable medium, or may have the form of one or more signals. Such signals may be downloaded from an internet website, provided on a carrier signal, or provided in any other form.
It should be noted that the above-mentioned embodiments illustrate rather than limit the invention, and that those skilled in the art will be able to design alternative embodiments without departing from the scope of the appended claims. In the claims, any reference signs placed between parentheses shall not be construed as limiting the claim. The word "comprising" does not exclude the presence of elements or steps not listed in a claim. The word "a" or "an" preceding an element does not exclude the presence of a plurality of such elements. The invention may be implemented by means of hardware comprising several distinct elements, and by means of a suitably programmed computer. In the unit claims enumerating several means, several of these means may be embodied by one and the same item of hardware. The use of the words first, second, third, etc. do not denote any order. These words may be interpreted as names.
Claims (9)
1. A method of determining a forming limit of a material, comprising:
obtaining a strain history of the specimen in any strain state by using a strain measurement system, wherein the strain history comprises: strain data of a strain data point of the sample surface changing with the strain state, wherein the strain data point is a strain data point of a preset area of the sample when the sample is not deformed, and the strain data comprises: the strain data points are changed along with the strain data points in the strain state and are represented by a frame of image corresponding to each moment;
determining a strain path based on the strain data, wherein the strain path is a relation curve of the main strain data and the secondary strain data in the strain data along with the time change;
obtaining a strain path parameter based on interval data which linearly changes on the strain path;
determining a target main strain data standard deviation based on the strain path parameters;
determining a target frame image corresponding to the necking time of the sample based on the standard deviation of the target main strain data;
determining a limit strain of the specimen in any strain state based on the strain data and the target frame image;
the forming limit curve is obtained based on the limit strain at the plurality of strain states.
2. The method according to claim 1, wherein the obtaining the strain path parameter based on the interval data linearly varying on the strain path includes:
based on the interval section data which is linearly changed on the strain path, obtaining a linear change formula of the interval section data through fitting;
and obtaining the strain path parameter based on the slope of the linear change formula.
3. The method of determining of claim 1, wherein determining a target primary strain data standard deviation based on the strain path parameters comprises:
based on the strain path parameter and a relationship satisfied between the strain path parameter and the standard deviation of the primary strain data:
σ＝aβ 3 +bβ 2 +cβ+d
wherein, beta is a strain path parameter, sigma is a main strain data standard deviation, a, b, c, d are constants, and a target main strain data standard deviation is determined.
4. The method of measuring according to claim 1, wherein determining a limit strain of the specimen in any one of the strain states based on the strain data and the target frame image includes:
selecting N strain data points with the maximum main strain in the target frame image based on the strain data;
based on the average primary strain and the average secondary strain of the N strain data points, the ultimate strain of the specimen at any one strain state is determined.
5. The method of measuring according to claim 1, wherein the obtaining a forming limit curve based on the limit strain in the plurality of strain states includes:
a shaped limit curve is obtained by connecting the limit strains in at least 5 strain states based on the limit strains in the at least 5 strain states.
6. The assay of claim 5, wherein the at least 5 strain states comprise: a unidirectional stretching, a planar strain, an equal bi-directional stretching, a first intermediate state between the unidirectional stretching and the planar strain, and a second intermediate state between the planar strain and the equal bi-directional stretching.
7. A device for determining a forming limit of a material, comprising:
the first obtaining module is used for obtaining the strain history of the sample in any strain state by using the strain measurement system, and the strain history comprises the following steps: strain data of a strain data point of the sample surface changing with the strain state, wherein the strain data point is a strain data point of a preset area of the sample when the sample is not deformed, and the strain data comprises: the strain data points are changed along with the strain data points in the strain state and are represented by a frame of image corresponding to each moment;
the path determining module is used for determining a strain path based on the strain data, wherein the strain path is a relation curve of the main strain data and the secondary strain data in the strain data, and the relation curve changes with time;
the parameter determining module is used for obtaining the parameter of the strain path based on the interval data which linearly changes on the strain path;
the standard deviation determining module is used for determining a target main strain data standard deviation based on the strain path parameters;
the target image determining module is used for determining a target frame image corresponding to the necking time of the sample based on the standard deviation of the target main strain data;
a second determining module, configured to determine a limit strain of the specimen in any strain state based on the strain data and the target frame image;
and a second obtaining module for obtaining a forming limit curve based on the limit strain in the plurality of strain states.
8. A computer device comprising a memory, a processor and a computer program stored on the memory and executable on the processor, wherein the processor implements the method of any of claims 1-6 when the program is executed.
9. A computer readable storage medium, on which a computer program is stored, characterized in that the program, when being executed by a processor, implements the method according to any of claims 1-6.
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