CN111896373B - Test and calculation method for determining equivalent plastic strain forming limit diagram - Google Patents
Test and calculation method for determining equivalent plastic strain forming limit diagram Download PDFInfo
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Abstract
The invention discloses a test and calculation method for measuring an equivalent plastic strain forming limit diagram, which comprises the following steps: measuring the real uniform strain and the real fracture strain of the material; calculating main strain and secondary strain under different simple strain paths; and drawing and correcting an equivalent plastic strain forming limit diagram (EPS-FLD). The invention avoids various defects of the prior art through theoretical innovation, provides a technical solution for the automobile steel in a new situation, integrates the measurement of the material uniform forming limit and the fracture forming limit in a uniaxial tensile DIC test, does not need to additionally increase the test under the condition of not needing to additionally increase the test and reaching a better technical target, and saves precious labor cost and equipment cost, so the invention has important theoretical and engineering practical significance.
Description
Technical Field
The invention relates to a method for measuring a forming limit diagram, in particular to a method for testing and calculating an equivalent plastic strain forming limit diagram of a metal material and correcting the equivalent plastic strain forming limit diagram.
Background
The shaping Limit Diagram (FLD) was proposed in the last 60 th century by Keeler (SAE technical paper 650535) and Goodwin (SAE technical paper 680093). Keeler has proposed that the right half regional analysis that is used for the sheet material to receive the simple strain state region of two tensile deformations, and Goodwin has expanded the analysis that the left half regional simple strain state region that is used for the sheet material to be drawn-pressure deformation on Keeler's basis.
FLD describes the extreme combination of principal (ordinate) and secondary (abscissa) strains near the local necked state under different simple strain paths covering from a purely uniaxial to a purely biaxial stretched state, corresponding to a simple strain path β with a value in the range of-0.5, 1.
Currently, forming limit diagrams have been considered by the industry as effective tools for evaluating the formability of sheet metal, and form mature industry standards, such as GB-T/15825.8-2008 (guide for determination of sheet metal forming performance and test method part 8: forming Limit Diagrams (FLD)), which set up detailed test methods and procedures for determining the FLD of the sheet metal. In brief, firstly, test samples under several simple strain paths are manufactured and tested; secondly, after the test is finished, selecting and measuring the main strain and the secondary strain of the critical grid circle, and marking a measuring point in a forming limit diagram; and finally, fitting according to the distribution state of the measurement points to obtain a Forming Limit Curve (FLC) of the plate, wherein the shape of the FLC is generally V-shaped.
In a standard forming limit diagram, the selection of a critical grid circle for measuring the main strain and the secondary strain is based on whether the critical state of local necking is the judgment standard, and the specific processing method in engineering is as follows: the mesh circle located in the neck region but not broken is taken as a critical mesh circle, or the mesh circle next to the neck or crack is taken as a critical mesh circle, or the mesh circle adjacent to the mesh circle where the neck or crack traverses its middle is taken as a critical mesh circle, and therefore, FLD cannot be used as a criterion for judging material failure in press analysis.
However, in the standard Forming Limit diagram, if the critical grid circle for measuring the main strain and the secondary strain is selected according to whether the critical grid circle is in the critical state of Fracture, the Fracture Forming Limit (FFL for short) of the sheet is obtained by fitting, and if the value range of the simple strain path β is [0,1], according to the volume invariant condition:
ε 1 +ε 2 +ε 3 ＝0 (1)
in the critical state of fracture, the strain in the thickness direction is approximately equal to a constant ε 3 About const, then equation (1) may be changed to:
ε 1 ＝-ε 2 +const. (2)
thus, in the forming limit diagram, FFL approximates a straight line with a slope of "-1".
The FLD provides a technical basis and a practical criterion for conveniently researching the plate forming limit, evaluating the plate forming performance and solving a plurality of problems in the plate forming field, so the FLD is integrated into commercial stamping simulation software and is used as a judgment standard for the plate forming severity.
However, in the process of implementing the present invention, the inventors of the present application found through research that: the traditional FLD criterion has technical defects on a test method:
firstly, the deformation degree of the critical grid circle is judged according to the main strain and the secondary strain measured under different simple strain paths, so that the same deformation level is difficult to guarantee, and the FLC curve does not accord with the theoretical prediction result in form.
Secondly, the main strain and the secondary strain under the condition of large deformation measured by the test are measured under a specific size, the ratio of the main strain and the secondary strain is not necessarily equal to the corresponding beta under the test condition, the accuracy of the value depends on the size of the grid seriously, and generally speaking, the ratio of the main strain to the secondary strain can only strictly correspond to the beta value when the size of the grid is equal to 1.0 mm.
Third, it is required to perform complicated tests, and the test results are affected by many factors, such as a test tool, a material thickness of a sample, an n value, and the like.
Furthermore, with the large number of applications of Advanced High Strength Steels (AHSS), the conventional FLD has been repeatedly shown to be unpredictable in AHSS press forming (SAE Technical Paper 2014-01-0985), especially with respect to the edge cracking and local failure problems common to AHSS, and the conventional FLD criteria are completely ineffective.
Therefore, the conventional FLD is questioned and is continuously improved and developed due to various shortcomings of the prior art in the testing method and engineering application. The invention supplements and perfects the traditional FLD, and the theoretical basis is as follows:
for the critical mesh circle, according to the volume invariant condition, there are:
ε 1 +ε 2 +ε 3 ＝0 (3)
wherein epsilon 1 、ε 2 And ε 3 The main strains in three directions are respectively, and the r value is defined as follows:
then e 2 And ε 3 Using epsilon 1 The r values are expressed as follows:
equivalent strain in a uniaxially stretched state
Is represented as follows:
when formulas (5) and (6) are substituted into formula (7), the following are provided:
by using
And r represents ε 1 、ε 2 And epsilon 3 The following were used:
the strain state (. Epsilon.) of the critical mesh circle according to the formulas (9), (10) and (11) 1 、ε 2 And epsilon 3 ) Is constant as follows:
its physical meaning represents: the material yield surface or the subsequent yield surface characterized on the basis of the strain state is characterized in that the strain strength or the equivalent strain is a constant value which is only dependent on the deformation degree of the critical grid circle and is independent of the strain path or the strain state, and the material yield surface or the subsequent yield surface is characterized by the radius of (12)
A standard spherical surface of (2). According to the formulas (3), (7) and (12), the characterization material adopts an isotropic hardening model.
For engineering application, the three-dimensional yield surface represented by formula (12) can be reduced to two-dimensional expression, and formula (3) is substituted into formula (7), so that the following expression is provided:
its physical meaning represents: by principal strain ε 1 As ordinate, secondary strain ε 2 On the abscissa, the shape of the material yield surface or the subsequent yield surface is a standard ellipse, and the expressions (9) and (10) are substituted into the expression (13), and the expression (13) is also satisfied.
According to the formulas (9) and (10), r value in the formula represents the value range of simple strain state,
indicating a specific degree of deformation, the primary strain and the secondary strain of other simple strain paths having the same deformation level can be calculated by measuring the equivalent strain of any simple strain path, and therefore, the forming limit diagram FLD of the material can be theoretically drawn. For example, from a uniaxial extension test, the equivalent uniform strain based on the uniform necking limit of the specimen is determined>
For press forming, the value of r is generally in the range of [ -0.5,1]Thus, drawingCreating a uniform forming limit curve which is a portion of an ellipse, whereby the uniform forming limit curve is convex, likewise if the equivalent breaking strain is determined from a uniaxial tensile test>
A fracture forming limit curve can be drawn.
Disclosure of Invention
1. Technical problem to be solved by the invention
Aiming at the defects in the prior art, the technical problems to be solved by the invention are as follows: in uniaxial tensile testing, the equivalent uniform strain of a material was determined
And equivalent breaking strain->
Based on the isotropic hardening model of the material, the equivalent plastic strain of the material under the uniform forming limit and the fracture forming limit is independent of the stress strain state of the critical grid circle, and is based on the ^ or the ^ under uniaxial stretching>
And &>
The real principal strain epsilon under any simple strain state under the same deformation degree, such as uniform forming limit or fracture forming limit can be calculated theoretically major And true secondary strain ε minor Therefore, an Equivalent Plastic Strain Forming Limit Diagram (EPS-FLD for short) can be drawn without the existing FLD measuring method, and the defects in the prior art are directly avoided.
2. Technical scheme of the invention
In order to achieve the object of the technical problem to be solved by the present invention, the present invention provides a test and calculation method for determining an equivalent plastic strain forming limit diagram, comprising the steps of:
step one, manufacturing a uniaxial tension test sample of a tested material, performing a uniaxial tension test, and measuring the real uniform strain of the tested material
And true break strain->
/>
Said true uniform strain
The method comprises the following steps: in the uniform necking deformation stage, the initial length, width and height of the sample are respectively l 0 ·w 0 ·h 0 The finite body A of (a) is uniformly deformed all the time until the end of uniform necking of the sample is judged, wherein l 0 Is an initial gauge length, w 0 Is the initial width of the specimen, h 0 For the specimen thickness, the limiting body A retains the true uniform strain->
Calculated using the formula:
wherein l u Is the initial gauge length l 0 The deformed length at the end of uniform necking;
said true strain at break
The method comprises the following steps: in the local necking deformation stage, in the fracture center area of the sample, the initial length, width and height are always respectively l 0 '·l 0 '·h 0 The finite body always keeps uniform deformation until the material is judged to be invalid, and the maximum initial gauge length meeting the condition is taken as l max The limiting body B maintains the true break strain ∑ with the limit deformed uniformly>
Calculated using the formula:
wherein l f Is the maximum initial gauge length l of the finite body B max The length of deformation at the moment of fracture;
said true uniform strain
Is also equal to the equivalent uniform strain->
Said true break strain->
Is also equal to the equivalent breaking strain->
Step two, respectively calculating the real principal strain epsilon under different simple strain paths according to the following two formulas major And true secondary strain ε minor ：
Wherein beta is the true secondary strain epsilon minor With true principal strain epsilon major A specific value of the ratio represents a specific simple strain path state, and the value ranges are [ - ∞, + ∞ [ - ] +∞ [ ]]，
The equivalent plastic strain is independent of the strain state;
or, respectively calculating the real principal strain epsilon under different simple strain paths according to the following two formulas major And true secondary strain ε minor ：
Wherein r is a plastic strain ratio, and a specific value thereof represents a specific simple strain path state in the range of [ - ∞, + ∞ [ - ]]，
The equivalent plastic strain is independent of the strain state.
Step three, using the real principal strain epsilon major As ordinate, true secondary strain ε minor Drawing an equivalent plastic strain forming limit curve if the equivalent plastic strain is taken as an abscissa
Is equal to true uniform strain->
The drawn curve is called as a uniform forming limit curve; if the equivalent plastic strain is taken>
Is equal to the true break strain->
The drawn curve is called a fracture forming limit curve; the two curves are both in the shape of an ellipse, and the two curves are drawn in the same picture to obtain the pictureTo the equivalent plastic strain forming limit diagram of the tested material.
Further, the test and calculation method for determining the equivalent plastic strain forming limit diagram is characterized in that: in step one, the true uniform strain
Is the initial gauge length l 0 The diameter is 10mm, and a finite element A on a test sample is always in the maximum true strain under uniform necking deformation; said true break strain->
Means that the maximum initial gauge length of the finite body B is l max 1.0mm, the length, width and height of the material are 1.0 mm.1.0 mm.h 0 Is always at the maximum true strain under uniform neck-in deformation.
Further, the test and calculation method for determining the equivalent plastic strain forming limit diagram is characterized in that: in the third step, the simple strain path state covered by the forming limit diagram is taken, the range of the simple strain path state is gradually changed from the pure biaxial stretching state to the pure uniaxial stretching state, if the formulas (3) and (4) are adopted in the second step, the value range corresponding to beta is [1, -0.5], if the formulas (5) and (6) are adopted in the second step, the value range corresponding to r is [ -0.5,1], and the equivalent plastic strain forming limit diagram of the tested material with the same simple strain path range as the traditional forming limit diagram is obtained.
Further, the test and calculation method for determining the equivalent plastic strain forming limit diagram is characterized in that: measuring the plastic strain ratio r of the material under the gauge length of 1.0mm 1.0 The value of r is ranged from [ -0.5,1]Updated to [ -0.5,r 1.0 ]The corresponding equivalent plastic strain forming limit diagram is updated accordingly.
Further, the test and calculation method for determining the equivalent plastic strain forming limit diagram is characterized in that: measuring the edge damage coefficient eta of the material in a uniaxial tension state, and on a local equivalent plastic strain forming limit diagram, combining two forming limit curvesUpper true secondary strain epsilon minor The abscissa value of is less than
The equivalent plastic strain forming limit diagram after further correction is obtained by deleting the data, and the edge damage coefficient eta is calculated according to the following formula:
wherein true strain at break
And (3) measuring by a uniaxial tension test in the step one, and measuring the hole expansion rate lambda by a material hole expansion test.
Further, the test and calculation method for determining the equivalent plastic strain forming limit diagram is characterized in that: in the first step, uniaxial tensile test is carried out at different strain rates, and then an equivalent plastic strain forming limit diagram at each strain rate is obtained.
3. The invention has the advantages of
The invention provides a test and calculation method for measuring an equivalent plastic strain forming limit diagram, which avoids the defects of the prior art, and compared with the prior technical scheme, the test and calculation method has the following beneficial effects:
firstly, the existing FLD has the defects that FLC is concave in theory and convex in practice, and is not strict in method, and the main strain and secondary strain measurement is not verified by the condition of unchanged volume, and the defects of the traditional FLD in theory and method cause various problems in practical engineering application and cannot meet the technical requirement of lightweight automobile steel in a new situation, so the EPS-FLD avoids various defects of the prior art through theoretical innovation, and provides a technical solution for the automobile steel in the new situation.
Secondly, because the prior FLD needs to be manufactured into measuring samples under different simple strain paths and measured by adopting special test equipment, the FLD for measuring the material wastes time and labor, and the method integrates the measurement of the uniform forming limit and the fracture forming limit of the material into a uniaxial tensile test, does not need to additionally increase the test, can realize more accurate technical target and saves precious labor cost and equipment cost.
In conclusion, by implementing the method, important material forming parameters can be obtained at extremely low cost, so the method has important theoretical and engineering practical significance and very wide application prospect.
Drawings
The present invention will be described in further detail with reference to the accompanying drawings.
FIG. 1 is a schematic flow chart of the present embodiment;
FIG. 2 is a uniform forming limit curve for material DP 780;
FIG. 3 is a complete uniform forming limit curve for material DP 780;
FIG. 4 is a fracture shaping limit curve for material DP 780;
FIG. 5 is a complete fracture shaping limit curve for material DP 780;
FIG. 6 is a complete equivalent plastic strain forming limit diagram for material DP 780;
FIG. 7 is a graph of equivalent plastic strain forming limits for material DP 780;
FIG. 8 is a simple strain path region of uniform and deformed deformation of material DP 780;
FIG. 9 is a diagram of equivalent plastic strain forming limits after correction, taking into account the effect of plastic strain ratio;
FIG. 10 is a corrected equivalent plastic strain forming limit diagram taking into account the effect of the edge damage factor;
fig. 11 is an equivalent plastic strain forming limit diagram after correction in consideration of the influence of the plastic strain ratio and the edge damage coefficient.
Detailed Description
The technical solution of the present invention will be clearly and completely described below with reference to the accompanying drawings.
Examples
In this embodiment, a DP780/1.4mm material is used, a model of a tensile testing machine adopted is Zwick/Roell Z050, and a DIC testing system is an ARAMIS system of GOM corporation in germany, and a method for testing and calculating an equivalent plastic strain forming limit diagram of the material according to the present invention is described in detail, as shown in fig. 1, and the method comprises the following steps:
step one, measuring the True Uniform Strain (True Uniform Strain) of the tested material according to the method described in 'a test and calculation method for measuring the True stress-Strain curve of the material, application number 201910801077.1')
And True Fracture Strain (True Fracture Strain)>
Uniaxial tensile tests were performed at a quasi-static tensile rate.
Said true uniform strain
The method comprises the following steps: in the stage of uniform necking deformation under the uniaxial stretching strain state, the limiters A with initial length, width and height of 10mm & lt 12mm & gt & lt 1.4mm are kept uniformly deformed all the time until the end of uniform necking of the sample is judged, and the initial gauge length l is used 0 =10mm calculated maximum true strain. Initial gauge length l as measured by DIC techniques 0 Deformed length l at the end of uniform necking u =12.254mm, the true uniform strain is calculated by substituting the following equation>
Said true strain at break
The method comprises the following steps: localized under uniaxial tensile strainIn the necking deformation stage, in the central area of the sample fracture, the finite body B always keeps uniform deformation until the judgment of material failure, and the maximum initial gauge length l of the finite body B meeting the condition max The maximum true strain calculated when =1.0mm, the initial length, width and height of the limiter B are 1.0mm · 1.0mm · 1.4mm, respectively. Maximum initial gage length l as measured by DIC techniques max Length of deformation at break f =1.537mm, calculated using the formula:
said true uniform strain
Is also equal to the equivalent uniform strain->
Said true break strain->
Is also equal to the equivalent breaking strain->
Step two, respectively calculating the real principal strain epsilon under different simple strain paths according to the following two formulas major And true secondary strain ε minor ：
Wherein r is the plastic strain ratio and has a value range of [ - ∞, + ∞ [ - ]]A particular pick value representing a particular simple strain path state,
the equivalent plastic strain is independent of the strain state.
If equivalent plastic strain
Respectively fetch true uniform strain>
And true strain at break
r is in the range of [ - ∞, + ∞ [ - ]]True principal Strain (Major True Strain) ε calculated according to expressions (5) and (6) major And True secondary Strain (Minor True Strain) ε minor As shown in table 1.
Step three, using the real principal strain epsilon major As ordinate, true secondary strain ε minor On the abscissa, an equivalent plastic strain forming limit diagram (EPS-FLD) is plotted according to the calculation results of Table 1.
If taking equivalent plastic strain
Is equal to true uniform strain->
The plotted curve is referred to as the uniform forming limit curve, as shown in FIG. 2; the true principal strain ε at the limit of uniform deformation in Table 1 major And true secondary strain ε minor Multiplying the two data by-1, keeping the corresponding relation of the two constant to obtain new calculation data, and drawing a complete uniform forming limit curve according to the table 1 and the new calculation data, wherein the shape of the curve is an ellipse as shown in fig. 3.
If taking equivalent plastic strain
Is equal to the true break strain->
The plotted curve is referred to as the fracture forming limit curve, as shown in FIG. 4; TABLE 1 true principal strain ε at the limit of interrupted fissile major And true secondary strain ε minor Multiplying the two data by-1, keeping the corresponding relationship between the two data unchanged to obtain new calculation data, and drawing a complete fracture forming limit curve according to the table 1 and the new calculation data, wherein the shape of the curve is an ellipse as shown in fig. 5.
TABLE 1 true Primary and true Secondary Strain at different simple Strain regimes
Drawing the equivalent plastic strain forming limit curves of the two curves with the shapes of standard ellipses in fig. 3 and 5 in the same graph, obtaining the equivalent plastic strain forming limit graph of the tested material, as shown in fig. 6, which is essentially: a two-dimensional main strain plane which is degraded or reduced in dimension from an initial yield surface and a subsequent yield surface of a three-dimensional main strain space (spherical space) based on an isotropic hardening model; the essence of the r value is a parameter that characterizes a simple strain path.
In Table 1, only the value range of r is [ -0.5,1]Corresponding true principal strain epsilon major And true secondary strain ε minor The data, draw homogeneous shaping limit curve and fracture shaping limit curve in the same picture, get the equivalent plastic strain shaping limit picture that applies in engineering, the result is as shown in fig. 7, its physical meaning is that the range of the simple strain path state changes from pure biaxial stretching state to pure uniaxial stretching state step by step, it is identical with the simple strain path range that the traditional shaping limit picture represents, can be used for the parameter input of shaping limit picture of the punching forming emulation material DP 780.
In fig. 7, a sector area surrounded by the simple strain path r =1, the Uniform shaping limit curve (Uniform _ EPS-FLC), and the simple strain path r = -0.5, such as Zone-1 in fig. 8, indicates that the material in the area with the strain state is safe, and at the same time, indicates that the part is in a global or overall Uniform deformation state. If the Uniform forming limit curve (uniformity _ EPS-FLC) is shifted outward to indicate that the forming width is larger, the larger Zone-1 indicates that the same deformation can be distributed or spread to a larger area and the strain state distribution range is larger, and therefore, a more complicated part can be formed, i.e., the Uniform forming ability is stronger.
In fig. 7, a sector area surrounded by the simple strain path r =1, the Fracture forming limit curve (Fracture _ EPS-FLC), the simple strain path r = -0.5 and the Uniform forming limit curve (Uniform _ EPS-FLC), such as Zone-2 in fig. 8, indicates that there is a risk of different degrees of the material in this area in the strain state, and at the same time, indicates that the part is in the local deformation state — the increased deformation is assumed by the local area on the part, and the greater the increased deformation, the greater the risk of cracking. If the Fracture forming limit curve (Fracture _ EPS-FLC) moves outwards to indicate that the forming depth is larger, the larger Zone-2 indicates that deformation only occurs in the strain state range of a local area, and the larger area indicates that the local forming capability is better.
According to the method described in 'a test and calculation method for measuring the plastic strain ratio of a metal material, application number 201910801202.9', the plastic strain ratio r of a material DP780 at a gauge length of 1.0mm is measured 1.0 =0.78, the value of r is ranged from [ -0.5,1]Updated to [ -0.5,0.78]Then the corresponding equivalent plastic strain forming limit diagram as shown in fig. 7 is updated accordingly, and as a result, as shown in fig. 9, the data of the shaded portion in the diagram will be deleted from the forming limit diagram (e.g., zone-3 area in fig. 9).
True strain at break of material DP780
The hole expansion ratio λ =23 measured by the hole expansion test, and the edge damage coefficient η of the material DP780 in the uniaxial tension state were calculated as follows:
then press
Calculated true secondary strain with damage epsilon minor ＝-0.104。
On the equivalent plastic strain forming limit diagram shown in fig. 7, the data of the abscissa value of the two forming limit curves being smaller than the true secondary strain-0.104 is deleted to obtain the corrected equivalent plastic strain forming limit diagram, and as a result, as shown in fig. 10, the data of the shaded portion (Zone-4 area in fig. 10) in the diagram is deleted from the forming limit diagram.
On the equivalent plastic strain forming limit diagram shown in fig. 9, the data that the horizontal coordinate value of the two forming limit curves is smaller than the true secondary strain-0.104 is deleted to obtain the corrected equivalent plastic strain forming limit diagram, and as a result, as shown in fig. 11, the data of the shaded part (such as Zone-5 area in fig. 11) in the diagram is deleted from the forming limit diagram, the corrected forming limit diagram is only used for the free edge area with edge damage on the part, and the non-free edge area is still adapted to the uncorrected forming limit diagram.
The above embodiments are only exemplary embodiments of the present invention, and are not intended to limit the present invention, and the scope of the present invention is defined by the claims. Various modifications and equivalents may be made by those skilled in the art within the scope of the invention as defined by the appended claims.
Claims (6)
1. A test and calculation method for determining an equivalent plastic strain forming limit diagram comprises the following steps:
step one, manufacturing a uniaxial tension test sample of a tested material, performing a uniaxial tension test, and measuring the real uniform strain of the tested material
And true strain at break
The true uniformity should beBecome
The method comprises the following steps: in the uniform necking deformation stage, the initial length, width and height of the sample are respectively l 0 ·w 0 ·h 0 The finite body A of (a) is uniformly deformed all the time until the end of uniform necking of the sample is judged, wherein l 0 Is an initial gauge length, w 0 Is the initial width of the specimen, h 0 For the thickness of the sample, the finite element A maintains a true uniform strain of ultimate uniform deformation
Calculated using the formula:
wherein l u Is the initial gauge length l 0 The deformed length at the end of uniform necking;
said true strain at break
The method comprises the following steps: in the local necking deformation stage, l 'is always present in the sample fracture center region' 0 ·l' 0 ·h 0 The finite body always keeps uniform deformation until the material is judged to be invalid, and the maximum initial gauge length meeting the condition is taken as l max Of the finite body B to maintain true fracture strain of ultimate uniform deformation
Calculated using the formula:
wherein l f Is the maximum initial gauge length l of the finite body B max Length of deformation at moment of fracture；
Said true uniform strain
Is also equal to the equivalent uniform strain
Said true strain at break
Is also equal to the equivalent fracture strain
Step two, respectively calculating the real principal strain epsilon under different simple strain paths according to the following two formulas major And true secondary strain ε minor ：
Wherein beta is the true secondary strain epsilon minor With true principal strain epsilon major A specific value of the ratio represents a specific simple strain path state, and the value ranges are [ - ∞, + ∞ [ - ] +∞ [ ]]，
The equivalent plastic strain is independent of the strain state;
or, respectively calculating the real principal strain epsilon under different simple strain paths according to the following two formulas major And true secondary strain ε minor ：
Wherein r is a plastic strain ratio, and a specific value represents a specific simple strain path state in a range of [ - ∞, + ∞ ]]，
The equivalent plastic strain is independent of the strain state;
step three, using the real principal strain epsilon major As ordinate, true secondary strain ε minor Drawing an equivalent plastic strain forming limit curve for the abscissa, and if the equivalent plastic strain is taken
Equal to true uniform strain
The drawn curve is called as a uniform forming limit curve; if taking equivalent plastic strain
Equal to true strain at break
The drawn curve is called a fracture forming limit curve; the two curves are both in an ellipse shape, and the two curves are drawn in the same picture to obtain an equivalent plastic strain forming limit diagram of the measured material.
2. A test and calculation method for determining an equivalent plastic strain forming limit diagram according to claim 1, characterized in that: in step one, the true uniform strain
Is the initial gauge length l 0 The thickness is 10mm, and a finite body A on a sample is always in the maximum true strain under uniform necking deformation; said true strain at break
Means that the maximum initial gauge length of the finite body B is l max 1.0mm, the length, width and height of the material are 1.0 mm.1.0 mm.h 0 Is always at the maximum true strain under uniform neck-in deformation.
3. A test and calculation method for determining an equivalent plastic strain forming limit diagram according to claim 2, characterized in that: in the third step, the simple strain path state covered by the forming limit diagram is taken, the range of the simple strain path state is gradually changed from the pure biaxial stretching state to the pure uniaxial stretching state, if the formulas (3) and (4) are adopted in the second step, the value range corresponding to beta is [1, -0.5], if the formulas (5) and (6) are adopted in the second step, the value range corresponding to r is [ -0.5,1], and the equivalent plastic strain forming limit diagram of the tested material with the same simple strain path range as the traditional forming limit diagram is obtained.
4. A test and calculation method for determining an equivalent plastic strain forming limit diagram according to claim 3, characterized in that: measuring the plastic strain ratio r of the material under the gauge length of 1.0mm 1.0 The value of r is ranged from [ -0.5,1]Updated to [ -0.5,r 1.0 ]The corresponding equivalent plastic strain forming limit diagram is updated accordingly.
5. A test and calculation method for determining an equivalent plastic strain forming limit diagram according to claim 4, characterized in that: measuring the edge damage coefficient eta of the material in a uniaxial tension state, and on a local equivalent plastic strain forming limit diagram, determining the real secondary strain epsilon on two forming limit curves minor The abscissa value of is less than
The equivalent plastic strain forming limit diagram after further correction is obtained by deleting the data, and the edge damage coefficient eta is calculated according to the following formula:
wherein true strain at break
And (3) measuring by a uniaxial tension test in the step one, and measuring the hole expansion rate lambda by a material hole expansion test.
6. A test and calculation method for determining an equivalent plastic strain forming limit diagram according to claim 1, 2 or 5, characterized in that: in the first step, uniaxial tensile test is carried out at different strain rates, and then an equivalent plastic strain forming limit diagram at each strain rate is obtained.
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Citations (8)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN101379381A (en) * | 2006-02-01 | 2009-03-04 | 新日本制铁株式会社 | Breaking prediction method |
| CN101599094A (en) * | 2009-06-26 | 2009-12-09 | 东北大学 | A kind of model method of setting up forming limit diagram of transformation induced plasticity steel plate |
| CN101598720A (en) * | 2009-06-26 | 2009-12-09 | 东北大学 | A kind of experimental technique of setting up forming limit diagram of transformation induced plasticity steel plate |
| CN109870362A (en) * | 2019-03-04 | 2019-06-11 | 燕山大学 | A kind of the fracture forming limit diagram method for building up and system of high strength alumin ium alloy plate |
| CN110411837A (en) * | 2019-08-28 | 2019-11-05 | 武汉上善仿真科技有限责任公司 | A kind of test and calculation method measuring material gauge length effect curve |
| CN110411836A (en) * | 2019-08-28 | 2019-11-05 | 武汉上善仿真科技有限责任公司 | A kind of test and calculation method measuring metal material plastic strain ratio |
| CN110501224A (en) * | 2019-08-28 | 2019-11-26 | 肖锋 | A kind of test and calculation method measuring material true stress―strain curve |
| CN111292813A (en) * | 2020-01-17 | 2020-06-16 | 中国石油天然气集团有限公司 | Method for drawing fracture forming limit diagram of anisotropic material based on fracture criterion and use method thereof |
-
2020
- 2020-06-30 CN CN202010618096.3A patent/CN111896373B/en active Active
Patent Citations (8)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN101379381A (en) * | 2006-02-01 | 2009-03-04 | 新日本制铁株式会社 | Breaking prediction method |
| CN101599094A (en) * | 2009-06-26 | 2009-12-09 | 东北大学 | A kind of model method of setting up forming limit diagram of transformation induced plasticity steel plate |
| CN101598720A (en) * | 2009-06-26 | 2009-12-09 | 东北大学 | A kind of experimental technique of setting up forming limit diagram of transformation induced plasticity steel plate |
| CN109870362A (en) * | 2019-03-04 | 2019-06-11 | 燕山大学 | A kind of the fracture forming limit diagram method for building up and system of high strength alumin ium alloy plate |
| CN110411837A (en) * | 2019-08-28 | 2019-11-05 | 武汉上善仿真科技有限责任公司 | A kind of test and calculation method measuring material gauge length effect curve |
| CN110411836A (en) * | 2019-08-28 | 2019-11-05 | 武汉上善仿真科技有限责任公司 | A kind of test and calculation method measuring metal material plastic strain ratio |
| CN110501224A (en) * | 2019-08-28 | 2019-11-26 | 肖锋 | A kind of test and calculation method measuring material true stress―strain curve |
| CN111292813A (en) * | 2020-01-17 | 2020-06-16 | 中国石油天然气集团有限公司 | Method for drawing fracture forming limit diagram of anisotropic material based on fracture criterion and use method thereof |
Non-Patent Citations (2)
| Title |
|---|
| 复合变形路径下的板材冲压成形极限应变(Ⅱ)――冲压成形极限应变的计算与试验;曹宏深;《机械工程学报》;20090115(第01期);全文 * |
| 金属板材成形性能的力学分析;魏毅静等;《宝钢技术》;20141231;全文 * |
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