CN112485113A - Method and device for testing material tensile property of small-size sample - Google Patents

Method and device for testing material tensile property of small-size sample Download PDF

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CN112485113A
CN112485113A CN202011285763.7A CN202011285763A CN112485113A CN 112485113 A CN112485113 A CN 112485113A CN 202011285763 A CN202011285763 A CN 202011285763A CN 112485113 A CN112485113 A CN 112485113A
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CN112485113B (en
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张志杰
郑鹏飞
谌继明
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Southwestern Institute of Physics
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N3/00—Investigating strength properties of solid materials by application of mechanical stress
    • G01N3/08—Investigating strength properties of solid materials by application of mechanical stress by applying steady tensile or compressive forces
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N2203/00—Investigating strength properties of solid materials by application of mechanical stress
    • G01N2203/0014—Type of force applied
    • G01N2203/0016—Tensile or compressive
    • G01N2203/0017—Tensile
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N2203/00—Investigating strength properties of solid materials by application of mechanical stress
    • G01N2203/0058—Kind of property studied
    • G01N2203/0069—Fatigue, creep, strain-stress relations or elastic constants
    • G01N2203/0073—Fatigue
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N2203/00—Investigating strength properties of solid materials by application of mechanical stress
    • G01N2203/0058—Kind of property studied
    • G01N2203/0069—Fatigue, creep, strain-stress relations or elastic constants
    • G01N2203/0075—Strain-stress relations or elastic constants
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N2203/00—Investigating strength properties of solid materials by application of mechanical stress
    • G01N2203/02—Details not specific for a particular testing method
    • G01N2203/0202—Control of the test
    • G01N2203/0212—Theories, calculations
    • G01N2203/0216—Finite elements
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N2203/00—Investigating strength properties of solid materials by application of mechanical stress
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    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N2203/00—Investigating strength properties of solid materials by application of mechanical stress
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    • G01N2203/025—Geometry of the test
    • G01N2203/0252—Monoaxial, i.e. the forces being applied along a single axis of the specimen
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    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N2203/00—Investigating strength properties of solid materials by application of mechanical stress
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    • G01N2203/0286—Miniature specimen; Testing on microregions of a specimen
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    • G01—MEASURING; TESTING
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    • G01N2203/00—Investigating strength properties of solid materials by application of mechanical stress
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Abstract

The invention discloses a method for testing the material tensile property of a small-size sample, which comprises the following steps of obtaining a stable load-displacement curve at two clamp ends through a uniaxial tensile loading test of the small-size sample under displacement control; establishing finite element simulation models of the non-equal-straight measurement sections of the two samples; extracting a test curve, and predicting a uniaxial true stress-strain relation which accords with a Hollomon constitutive model according to the load-displacement relation of the sample non-equal-straight measurement section; simultaneously obtaining the elastic modulus E and the tensile strength R of the materialm(ii) a Converting according to the obtained uniaxial true stress-strain relation to obtain an engineering stress-strain curve so as to obtain the yield strength Rp0.2. The invention solves the problem of sample size limitation of the traditional tensile property test method, has reliable basic theoretical support, does not depend on empirical formulas, has simple and convenient test operation, and can accurately obtain the continuous and complete uniaxial stress-strain relationship, yield strength and tensile strength of the material by using small-size samples.

Description

Method and device for testing material tensile property of small-size sample
Technical Field
The invention relates to the technical field of mechanical property testing, in particular to a method and a device for testing the material tensile property of a small-size sample.
Background
The nuclear fusion energy is considered as a brand-new sustainable energy source due to the safety, cleanness and no pollution of the nuclear fusion energy and the inexhaustible nuclear fusion fuel. Before a fusion reactor is built, neutron irradiation examination needs to be carried out on a structural alternative material, the mechanical property of the material after irradiation is tested, the anti-irradiation performance screening is carried out on the structural material, and whether the material meets the use requirement of piling is judged. However, due to the small irradiation space, the high flux volume of IFMIF is only 0.5L, and various samples such as tensile, impact, fatigue, fracture toughness, etc. need to be placed in a limited volume. The Test using conventional tensile standards (ASTM E8-16a. Standard Test Methods for Testing of tensile Materials, annual Book of ASTM standards. West Conshoken, PA: American Society for Testing and Materials; 2016.) results in lower space utilization of the irradiation, and the larger the volume of a single sample, the longer the cooling time after irradiation. Therefore, minimizing the size of the sample while achieving reliable material properties is an effective way to alleviate the above problems. Meanwhile, the small sample has great testing requirements for special fields (such as welding structures and in-service structures in aerospace and nuclear power engineering). Meanwhile, the small sample has great testing requirements for special fields (such as welding structures and in-service structures in aerospace and nuclear power engineering).
Uniaxial stress-strain relationship, elastic modulus E, yield strength R of materialp0.2Tensile strength RmThe method is the basic mechanical property of the material and is very important for mechanical analysis, optimal design and safety evaluation of an engineering structure, so that the method for testing the small tensile sample of the related material is widely researched. As early as 1981, Baja R (Bajaj R, Shogan R P, Deflitch C. tent properties of neutron-irradial ammoniacal PE16[ C]I/ASTM STP 725, West Conshooken, PA: ASTM International, 1981.) in the EBR-2 material irradiation research project, a flat plate-shaped tensile sample (Small Specimen-1, SS-1) is provided, the width of an equal straight section is 1.52mm, the length is 20.32mm, and a sample design and test technical idea is provided for the acquisition tensile property research of a Small-size plate-shaped sample; kohno Y (Kohno Y, Kohyama A, Hamilton M, et al, Specifen size efficiencies on the tensile promoter of JPCA and JFMS [ J]Journal of nuclear Materials,2000,283-287: 10141017), etc. in order to reduce the sample size, a SS-J (Small specific-Japan) sample was proposed, which had an equal length of 1.2mm in width and 5mm in length and which was used to measure the load-displacement of the equal length of the sampleThe curve is used to obtain the tensile property of the material.
The existing small stretching sample testing technology has certain problems: 1. the testing method is lack of an elastoplasticity analysis theory, the testing content is single, and the stability and accuracy of the testing result are not high; 2. the test operation is inconvenient and is not beneficial to the operation in a hot room; 3. the sample size is not small enough, and certain waste exists in the saving of irradiation space.
Chen and Cai power (Chen H, Cai L X. unified elastic model based on strain simulation [ J ]. Applied physical modeling, 2017.52:664 simulation 671.) propose C-C energy equivalent method, that is, the Von Mises equivalence of Representative Volume Element (RVE) and the energy median equivalence in effective deformation domain. According to the functional principle, the external force F does work and is equal to the internal total strain energy, and the relation between the load-displacement and the stress-strain of the unidirectional loading structural element is established:
Figure BDA0002782263090000021
a bridge between the test load-displacement relation of unidirectional loading and the material stress-strain relation is theoretically established.
In the measurement technology, a uniaxial tensile test is completed for a small-size plate-shaped sample, and test conditions and test technology support are provided; a load-displacement semi-analytical prediction model of the geometric dimension of the associated sample and the Hollomon model parameters is given; can be used for predicting the uniaxial tensile property of the material; however, the test method and the test fixture only aim at samples with specific configurations and sizes, and corresponding prediction model parameters are required to be calibrated again for the configuration sizes of other samples; the C-C energy equivalent method provides a basis for theoretical derivation and has a guiding effect on acquisition of uniaxial tensile property.
Disclosure of Invention
Aiming at the technical problems, the invention provides a method and a device for testing the material tensile property of a small-size sample, which solve the problems, the problem of sample size limitation of the traditional tensile property test method is solved, the method has reliable basic theoretical support, does not depend on empirical formulas, is simple and convenient in test operation, and can accurately obtain the continuous and complete uniaxial stress-strain relationship, yield strength and tensile strength of the material by using the small-size sample.
The invention is realized by the following technical scheme:
a method for testing the tensile property of a material of a small-size sample comprises the following steps:
s1, taking a small-size sample to perform a tensile test, establishing a finite element simulation model of a non-equal-straight measurement section of the small-size sample, and obtaining stable load-displacement curves of two clamp ends clamping two axial ends of the small-size sample through a uniaxial tensile loading test of the small-size sample under displacement control;
s2, extracting a test curve, and predicting a uniaxial true stress-strain relation which accords with a Hollomon constitutive model according to the load-displacement relation of the sample non-equal-straight measurement section; simultaneously obtaining the elastic modulus E and the tensile strength R of the materialm；
S21, performing linear fitting on the elastic section of the load-displacement curve to obtain a slope k; performing power law fitting on the elastic-plastic section to obtain a loading coefficient C and an index m:
Figure BDA0002782263090000022
in the formula (1), F is a test load, and h is displacement;
s22, substituting the parameters k, C and m of the formula (1) into the following formula (2):
Figure BDA0002782263090000031
in the formula (2), E is the elastic modulus of the sample, n is the strain hardening index, K is the strain hardening coefficient, t0、t1、t2、t3、t4Taking the length L of the equal straight section as the finite element model constant of the sample0Is the characteristic length h, and A is the characteristic area;
s23, substituting E, K, n obtained in S22 into a Hollomon model to obtain a uniaxial true stress-strain relation of the material:
Figure BDA0002782263090000032
in formula (3), σTIs true stress,. epsilonTIs true strain, σyNominal yield strength;
s3, converting the uniaxial true stress-strain relation obtained in the step S2 to obtain an engineering stress-strain curve and obtain the yield strength Rp0.2And tensile strength Rm。
Further preferably, in step S3, the obtained true stress-strain relationship is converted into an engineering stress-strain relationship, as shown in formula (4):
Figure BDA0002782263090000033
in the formula (4), epsilonE、σE、εT、σTRespectively engineering strain, engineering stress, true strain and true stress.
Further preferably, the yield strength R is determined by the intersection point of the 0.2% offset line and the engineering stress-strain relation curveP0.2。
More preferably, the tensile strength Rm＝Fmax/A，FmaxFor testing the maximum load, A is the cross-sectional area of the equal straight section of the sample.
Further preferably, the configuration of the small-sized sample is a plate shape or a round bar shape.
Further preferably, the small-sized samples have a size range of: total length H is 14mm, width S of clamping section is 6mm, transition radius R is 1mm, length L of equal straight section 01 mm; for plate-like samples: the equal straight section width b is 1mm, and the thickness t epsilon is 0.5mm and 1 mm; for the round bar sample: the diameter D of the equal straight section is 1 mm.
Further preferably, in step S1, before the small-sized sample is subjected to the tensile test, the surface of the small-sized sample is subjected to a polishing treatment.
A material tensile property testing device of a small-size sample is used for realizing the material tensile property testing method of the small-size sample, and is characterized in that two groups of clamps are symmetrically distributed in a mirror mode, and each group of clamps comprises a bottom plate and a cover plate; one end of the bottom plate in the long axis direction is provided with a mounting groove, and the mounting groove is used for placing a to-be-clamped end of a small-size sample; the cover plate is detachably covered above the mounting groove, and the end to be clamped of the small-size sample is clamped between the mounting groove and the cover plate; the other end of the bottom plate in the long axis direction is used for being arranged between an upper chuck and a lower chuck of the testing machine.
Further preferably, the bottom plate is equipped with the diaphragm at the axial end of keeping away from the mounting groove, and the diaphragm is connected perpendicularly with bottom plate tip and is T type structure.
Further preferably, the device also comprises a positioning plate, wherein the positioning plate is detachably mounted at the axial middle part of the bottom plate or at a position close to the axial middle part, and the axial direction of the positioning plate is vertical to the axial direction of the bottom plate.
The invention has the following advantages and beneficial effects:
1. according to the invention, by designing a sample concept and a test calculation method, the problem of sample size limitation of the traditional uniaxial tensile property test method is solved, an empirical formula is not relied on, and after a small amount of finite elements are used for calibration, the continuous and complete stress-strain relation and strength of the material can be accurately obtained, so that the method is suitable for large-range ductile metal materials;
2. the invention solves the problem that more samples are difficult to place in the irradiation pore space, and improves the utilization rate of the irradiation space;
3. the invention designs the small stretching sample clamp matched with the theoretical method, which is convenient, simple and rapid to operate;
the invention can be applied to the fields of small components, welding joints, pipeline structures, precious materials, in-service structure monitoring and the like. The sample configuration designed by the invention is in a stretching form, the deformation is single stretching deformation, the material tensile strength can be directly and accurately obtained similarly to the traditional stretching, and the method can also be used for obtaining the fatigue property of the material.
Drawings
The accompanying drawings, which are included to provide a further understanding of the embodiments of the invention and are incorporated in and constitute a part of this application, illustrate embodiment(s) of the invention and together with the description serve to explain the principles of the invention. In the drawings:
FIG. 1 is a schematic representation of a sample configuration employed in an embodiment of the present invention; wherein FIG. 1(a) shows a plate-like sample, and FIG. 1(b) shows a rod-like sample;
FIG. 2 is a finite element analysis model of a plate sample according to an embodiment of the present invention;
FIG. 3 is a Hollomon constitutive model curve of the present invention;
FIG. 4 is a CLF-1 steel plate sample load-displacement curve in the embodiment of the present invention;
FIG. 5 is a stress-strain curve of a CLF-1 steel plate-like sample in an embodiment of the present invention; wherein fig. 5(a) shows a uniaxial true stress-strain curve, and fig. 5(b) shows an engineering stress-strain curve;
fig. 6 is a small sample test fixture provided in the present invention.
Reference numbers and corresponding part names in the drawings: 1-bottom plate, 2-cover plate, 3-positioning plate, 4-sample, 5-loading line, 6-clamping section I, 7-measuring section and 8-clamping section II.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is further described in detail below with reference to examples and accompanying drawings, and the exemplary embodiments and descriptions thereof are only used for explaining the present invention and are not meant to limit the present invention.
Example 1
The embodiment provides a method for testing the uniaxial stress-strain relationship and strength of a metal material obtained by a small-size sample, which comprises the following steps:
step 1, processing a metal material into a plate-shaped sample or a round bar sample with a specific size according to a test requirement, and manually polishing the sample by using sand paper with a particle size of more than 800 meshes; as shown in fig. 1, two sample configuration sizes are provided for alternative use, including a sample non-equal straight measuring section and a clamp holding section. FIG. 2 shows a finite element analysis model diagram of a small-sized plate-shaped sample non-equal straight measurement section. After the initial machining of the sample, it is considered appropriate to manually finish the surface of the sample with a piece of sandpaper of 800 mesh or more through a plurality of test trials.
And 2, mounting the polished small tensile sample in the step 1 to a test fixture, and fixing the small tensile sample to an upper chuck and a lower chuck of a testing machine on the basis of ensuring the coaxiality and fastening connection.
Step 3, acquiring a stable load-displacement curve between the upper clamp and the lower clamp through a uniaxial tensile loading test of the small sample under displacement control;
the sample is axially stretched and loaded by a testing machine, and the loading rate is moderate (0.005mm & s)-1Left and right), synchronously acquiring real-time load and displacement between the chucks, and stretching the sample until the sample is broken.
Step 4, extracting a test curve, and predicting a uniaxial true stress-strain relation which accords with a Hollomon constitutive model according to the load-displacement relation of the sample non-equal-straight measurement section; the specific operation is as follows:
step 4-1, performing linear fitting on the elastic section of the load-displacement curve to obtain a slope k; performing power law fitting on the elastic-plastic section to obtain a loading coefficient C and an index m:
Figure BDA0002782263090000051
in the formula (1), F is external load, and h is displacement;
step 4-2, substituting the parameters k, C and m of formula (1) into the following formula (2):
Figure BDA0002782263090000052
in the formula (2), E is the elastic modulus of the sample, n is the strain hardening index, K is the strain hardening coefficient, t0、t1、t2、t3、t4Taking the length L of the equal straight section as the finite element model constant of the sample0Is the characteristic length h, and A is the characteristic area;
the design sample configuration size of the present embodiment is shown in fig. 1, wherein the U end is a fixed end, and the P end is a displacement loadAnd (4) an end. For the Sheet-like (ST) sample, a ═ tb, t is the sample thickness, b is the sample constant straight width; for Round Bar (Round-Bar, RB) samples, A ═ 1/4 π D ^2And D is the diameter of the equal straight section of the sample. The Hollomon constitutive model parameters E, K, n of the material can be obtained through the formula (2); and substituting the parameter E, K, n into the Hollomon constitutive model to obtain the uniaxial true stress-strain relation and the elastic modulus E.
Plate samples or round bar samples can be selected according to test conditions and requirements, and the configuration related parameters of the two samples are shown in table 1:
TABLE 1 parameter List
Figure BDA0002782263090000061
For other similar configuration sizes, only t needs to be recalibrated0、t1、t2、t3、t4This method can be used by setting the material elastic modulus E to 200GPa (which may be any constant value of 60GPa to 250 GPa) and the nominal yield strength σ using ANSYS softwareyThe strain hardening index n is converted into 5 values of 0.1, 0.15, 0.2, 0.25 and 0.3 in sequence, and the 5 values are respectively calculated to obtain 5 load-displacement curves, and the parameter t can be calibrated by combining the formulas (1) and (2) and knowing E, K, n0、t1、t2、t3、t4。
Step 5, converting the uniaxial true stress-strain relation obtained in the step 4 to obtain an engineering stress-strain curve and obtain yield strength Rp0.2And tensile strength Rm。
Converting the obtained true stress-strain relationship into an engineering stress-strain relationship:
Figure BDA0002782263090000062
in the formula (3), epsilonE、σE、εT、σTRespectively engineering strain,Engineering stress, true strain, true stress.
Further, determining the yield strength R through the intersection point of the 0.2% offset line and the engineering stress-strain relation curveP0.2。
Further, tensile strength Rm＝Fmax/A，FmaxFor testing the maximum load, A is the cross-sectional area of the equal straight section of the sample.
Example 2
This embodiment provides a device for testing the uniaxial stress-strain relationship and strength of a small-sized sample obtained metal material, and is used in the method for testing the uniaxial stress-strain relationship and strength of a small-sized sample obtained metal material provided in embodiment 1. The fixture comprises two groups of clamps which are distributed in a mirror symmetry manner, wherein each group of clamps comprises a bottom plate 1 and a cover plate 2; one end of the bottom plate 1 in the long axis direction is provided with a mounting groove, and the mounting groove is used for placing a to-be-clamped end of a small-size sample; the cover plate 2 is detachably covered above the mounting groove, the end to be clamped of the small-size sample is clamped between the mounting groove and the cover plate 2, the detachable mounting structure can be connected by threads, the cover plate 2 is provided with a through hole, a threaded hole is formed in the surface of one end part (near the mounting groove) of the bottom plate 1, and a bolt penetrates through the through hole and then is screwed into the threaded hole for fixation; the other end of the bottom plate 1 in the long axis direction is used for being installed between an upper chuck and a lower chuck of the testing machine. The bottom plate 1 is equipped with the diaphragm at the axial end of keeping away from the mounting groove, and the diaphragm is connected perpendicularly with 1 tip of bottom plate and is T type structure. The positioning plate 3 is detachably arranged at the axial middle part or the position close to the axial middle part of the bottom plate 1, and the axial direction of the positioning plate 3 is vertical to the axial direction of the bottom plate 1; the detachable mounting structure of the positioning plate 3 and the bottom plate 1 can adopt threaded connection, a through hole is formed in the positioning plate 3, a threaded hole is formed in the bottom plate 1, and the positioning plate 3 can be detachably fixed on the bottom plate 1 by screwing the bolt into the threaded hole after penetrating through the through hole.
The using method comprises the following steps: the polished tensile small sample of example 1 was mounted on the apparatus as shown in fig. 6, and fixed to the upper and lower chucks of the testing machine on the basis of ensuring the coaxiality and the fastening connection; as shown in fig. 6, there are two sets of clamps with identical structures and mirror symmetry, and the whole clamp has 6 parts (i.e. two bases 1, two cover plates 2 and two positioning plates 3). The clamping section of the small-size sample 4 is placed in the mounting groove of the clamp bottom plate 1, the small-size sample 4 is preliminarily fixed by using the bolt on the cover plate 2, and the other to-be-clamped end of the small-size sample 4 performs the same operation. Finally, the clamp is placed in the upper and lower plate clamps of the testing machine, and the clamp and the chuck of the testing machine are ensured to be coaxial through the positioning plate 3; if the depth of the clamp of the testing machine plate is small, the positioning plate 3 can be removed, the T-shaped design at the end part of the clamp bottom plate 1 can ensure that the small sample clamp and the loading shaft of the testing machine have good coaxiality, 2N-5N tensile load is applied after the clamp of the testing machine plate is clamped, and then the bolt on the cover plate 2 is screwed down to complete sample installation.
Example 3
In this embodiment, the method provided in embodiment 1 and the test fixture provided in embodiment 2 are used for testing, and the test method is summarized as follows:
small-sized plate samples and round bar samples are taken as examples. As shown in fig. 1, the sample is divided into a non-equal measuring section and a clamping section. As shown in FIG. 2, two kinds of finite element simulation models of the non-equal-straight measurement section of the sample are established, one end of the finite element simulation model is fixedly hinged, and the other end of the finite element simulation model is subjected to axial tension loading. A Hollomon constitutive model (shown in figure 3) is used as a material constitutive relation simulation, the model comprises an elastic modulus E, a strain hardening index n and a strain hardening coefficient K, and the three parameters are changed to calculate various working conditions, so that load-displacement curves of different hypothetical materials are obtained, and the calibration of constants in a formula is completed.
Uniaxial tensile test under displacement control was carried out using a plate-like sample of CLF-1(Chinese Low activation Steel) steel, the radius of the transition arc R being 1mm, the thickness t being 0.5mm, and the length L of the equal straight section01mm, 1mm in width b and 6mm in non-equal straight measuring section L; and (3) carrying out uniaxial tension test on the 3 parallel samples, collecting the relative displacement h of the clamps at the two ends, and acquiring a continuous and stable load-displacement test curve shown in figure 5.
Fitting the straight line segment of the curve by using a linear function, fitting the elastic-plastic curve segment by using a power law function to obtain a slope k, a loading coefficient C and an index m, and combining a formula to obtain a Hollomon constitutive modelSubstituting E, K, n into a Hollomon model to obtain a uniaxial true stress-strain relation prediction result of the material according to parameters of an elastic modulus E, a strain hardening coefficient K and a strain hardening index n; by the formula Rm＝FmaxCalculating to obtain tensile strength Rm(ii) a Simultaneously, carrying out uniaxial tensile test on a CLF-1 steel Standard Round Bar (SRB) sample to obtain a CLF-1 steel uniaxial true stress-strain relation; as shown in fig. 5(a), the uniaxial true stress-strain curves of 3 parallel samples (referring to 3 plate-shaped small samples of the same configuration and size) substantially coincide with the results of the standard round bar; as shown in fig. 5(b), the obtained true stress-strain relationship is converted into an engineering stress-strain relationship, thereby obtaining the yield strength Rp0.2. In the practical engineering use, the sample size can be adjusted, and only simple finite element calculation needs to be carried out again to calibrate the parameters of the prediction model. The CLF-1 steel test prediction results are shown in Table 2.
TABLE 2 prediction results List
Figure BDA0002782263090000081
The invention designs small-size plate-shaped and round rod tensile samples and a special tool clamp, can perform small-sample uniaxial tensile test, can predict a uniaxial true stress-strain curve corresponding to a material according to a load-displacement curve of a non-equal-straight measurement section, and can obtain a yield strength R of a common engineering parameterp0.2And tensile strength Rm(ii) a The invention solves the problem of sample size limitation, has reliable basic theoretical support, does not depend on empirical formulas, and can obtain continuous and complete stress-strain relationship. The method has great engineering application value for obtaining the uniaxial tensile property of the material in the key fields of small-sized components, welding joints, pipeline structures, precious materials, in-service structure monitoring and the like.
The above-mentioned embodiments are intended to illustrate the objects, technical solutions and advantages of the present invention in further detail, and it should be understood that the above-mentioned embodiments are merely exemplary embodiments of the present invention, and are not intended to limit the scope of the present invention, and any modifications, equivalent substitutions, improvements and the like made within the spirit and principle of the present invention should be included in the scope of the present invention.

Claims (10)

1. A method for testing the material tensile property of a small-size sample is characterized by comprising the following steps:
s1, taking a small-size sample to perform a tensile test, establishing a finite element simulation model of a non-equal-straight measurement section of the small-size sample, and obtaining stable load-displacement curves of two clamp ends clamping two axial ends of the small-size sample through a uniaxial tensile loading test of the small-size sample under displacement control;
s2, extracting a test curve, and predicting a uniaxial true stress-strain relation which accords with a Hollomon constitutive model according to the load-displacement relation of the sample non-equal-straight measurement section; simultaneously obtaining the elastic modulus E and the tensile strength R of the materialm；
S21, performing linear fitting on the elastic section of the load-displacement curve to obtain a slope k; performing power law fitting on the elastic-plastic section to obtain a loading coefficient C and an index m:
Figure FDA0002782263080000011
in the formula (1), F is a test load, and h is displacement;
s22, substituting the parameters k, C and m of the formula (1) into the following formula (2):
Figure FDA0002782263080000012
in the formula (2), E is the elastic modulus of the sample, n is the strain hardening index, K is the strain hardening coefficient, t0、t1、t2、t3、t4Taking the length L of the equal straight section as the finite element model constant of the sample0Is the characteristic length h, and A is the characteristic area;
s23, substituting E, K, n obtained in S22 into a Hollomon model to obtain a uniaxial true stress-strain relation of the material:
Figure FDA0002782263080000013
in formula (3), σTIs true stress,. epsilonTIs true strain, σyNominal yield strength;
s3, converting the uniaxial true stress-strain relation obtained in the step S2 to obtain an engineering stress-strain curve and obtain the yield strength Rp0.2And tensile strength Rm。
2. The method for testing the material tensile property of the small-sized sample according to claim 1, wherein in step S3, the obtained true stress-strain relationship is converted into an engineering stress-strain relationship, as shown in formula (4):
Figure FDA0002782263080000014
in the formula (4), epsilonE、σE、εT、σTRespectively engineering strain, engineering stress, true strain and true stress.
3. The method for testing the material tensile property of the small-sized sample according to claim 2, wherein the yield strength R is determined by the intersection point of a 0.2% offset line and an engineering stress-strain relation curveP0.2。
4. The method for testing the tensile property of a material of a small-sized sample according to claim 1, wherein the tensile strength R ism＝Fmax/A，FmaxFor testing the maximum load, A is the cross-sectional area of the equal straight section of the sample.
5. The method for testing the material tensile property of the small-sized sample according to claim 1, wherein the small-sized sample has a plate shape or a round rod shape.
6. The method for testing the material tensile property of the small-sized sample according to claim 1 or 5, wherein the small-sized sample has a size range of: total length H is 14mm, width S of clamping section is 6mm, transition radius R is 1mm, length L of equal straight section01 mm; for plate-like samples: the equal straight section width b is 1mm, and the thickness t epsilon is 0.5mm and 1 mm; for the round bar sample: the diameter D of the equal straight section is 1 mm.
7. The method for testing the material tensile property of the small-sized sample according to claim 1, wherein in step S1, the surface of the small-sized sample is polished before the tensile test of the small-sized sample.
8. A material tensile property testing device for small-sized samples, which is used for realizing the material tensile property testing method for the small-sized samples as claimed in any one of claims 1 to 7, and is characterized in that two groups of clamps are distributed in a mirror symmetry mode, and each group of clamps comprises a bottom plate (1) and a cover plate (2); one end of the bottom plate (1) in the long axis direction is provided with a mounting groove, and the mounting groove is used for placing a to-be-clamped end of a small-size sample; the cover plate (2) is detachably covered above the mounting groove, and the end to be clamped of the small-size sample is clamped between the mounting groove and the cover plate (2); the other end of the bottom plate (1) in the long axis direction is used for being installed between an upper chuck and a lower chuck of the testing machine.
9. The device for testing the material tensile property of the small-sized sample according to claim 8, wherein the bottom plate (1) is provided with a transverse plate at the axial end far away from the mounting groove, and the transverse plate is vertically connected with the end part of the bottom plate (1) to form a T-shaped structure.
10. The device for testing the material tensile property of the small-sized sample according to claim 1, further comprising a positioning plate (3), wherein the positioning plate (3) is detachably mounted at the axial middle part or a position close to the axial middle part of the bottom plate (1), and the axial direction of the positioning plate (3) is perpendicular to the axial direction of the bottom plate (1).
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