CN117571466A - Method for measuring mechanical constitutive relation of welded joint microcell - Google Patents
Method for measuring mechanical constitutive relation of welded joint microcell Download PDFInfo
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- 238000000034 method Methods 0.000 title claims abstract description 58
- 238000012360 testing method Methods 0.000 claims abstract description 67
- 238000007373 indentation Methods 0.000 claims abstract description 44
- 229910000838 Al alloy Inorganic materials 0.000 claims abstract description 31
- 239000000463 material Substances 0.000 claims abstract description 22
- 238000009864 tensile test Methods 0.000 claims abstract description 13
- 238000005482 strain hardening Methods 0.000 claims abstract description 8
- 238000003466 welding Methods 0.000 claims description 40
- KRHYYFGTRYWZRS-UHFFFAOYSA-N Fluorane Chemical compound F KRHYYFGTRYWZRS-UHFFFAOYSA-N 0.000 claims description 12
- VEXZGXHMUGYJMC-UHFFFAOYSA-N Hydrochloric acid Chemical compound Cl VEXZGXHMUGYJMC-UHFFFAOYSA-N 0.000 claims description 12
- 238000004364 calculation method Methods 0.000 claims description 9
- 238000006073 displacement reaction Methods 0.000 claims description 8
- 238000005260 corrosion Methods 0.000 claims description 7
- 230000007797 corrosion Effects 0.000 claims description 7
- GRYLNZFGIOXLOG-UHFFFAOYSA-N Nitric acid Chemical compound O[N+]([O-])=O GRYLNZFGIOXLOG-UHFFFAOYSA-N 0.000 claims description 6
- 239000007788 liquid Substances 0.000 claims description 6
- 238000000691 measurement method Methods 0.000 claims description 6
- 229910017604 nitric acid Inorganic materials 0.000 claims description 6
- 238000003825 pressing Methods 0.000 claims description 6
- 238000012544 monitoring process Methods 0.000 claims description 5
- 244000137852 Petrea volubilis Species 0.000 claims description 4
- 238000005498 polishing Methods 0.000 claims description 4
- 238000005507 spraying Methods 0.000 claims description 4
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims description 4
- 238000009825 accumulation Methods 0.000 claims description 3
- 238000004062 sedimentation Methods 0.000 claims description 3
- 238000010438 heat treatment Methods 0.000 claims description 2
- 238000012545 processing Methods 0.000 claims description 2
- 230000005489 elastic deformation Effects 0.000 abstract description 7
- 238000005259 measurement Methods 0.000 description 8
- 239000010953 base metal Substances 0.000 description 7
- 238000013461 design Methods 0.000 description 7
- 238000004088 simulation Methods 0.000 description 6
- 238000010586 diagram Methods 0.000 description 4
- 239000007769 metal material Substances 0.000 description 3
- 238000010998 test method Methods 0.000 description 3
- XKRFYHLGVUSROY-UHFFFAOYSA-N Argon Chemical compound [Ar] XKRFYHLGVUSROY-UHFFFAOYSA-N 0.000 description 2
- 241000276425 Xiphophorus maculatus Species 0.000 description 2
- 238000012512 characterization method Methods 0.000 description 2
- 238000009826 distribution Methods 0.000 description 2
- 238000011156 evaluation Methods 0.000 description 2
- 239000011259 mixed solution Substances 0.000 description 2
- 230000003014 reinforcing effect Effects 0.000 description 2
- 239000000956 alloy Substances 0.000 description 1
- 229910052786 argon Inorganic materials 0.000 description 1
- 238000012938 design process Methods 0.000 description 1
- 238000001514 detection method Methods 0.000 description 1
- 238000004836 empirical method Methods 0.000 description 1
- 238000007542 hardness measurement Methods 0.000 description 1
- 238000004519 manufacturing process Methods 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 238000005070 sampling Methods 0.000 description 1
- 239000007921 spray Substances 0.000 description 1
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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
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- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
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- G01N1/28—Preparing specimens for investigation including physical details of (bio-)chemical methods covered elsewhere, e.g. G01N33/50, C12Q
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N1/00—Sampling; Preparing specimens for investigation
- G01N1/28—Preparing specimens for investigation including physical details of (bio-)chemical methods covered elsewhere, e.g. G01N33/50, C12Q
- G01N1/32—Polishing; Etching
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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
- G01N3/02—Details
- G01N3/06—Special adaptations of indicating or recording means
- G01N3/068—Special adaptations of indicating or recording means with optical indicating or recording means
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- 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
- G01N2203/0001—Type of application of the stress
- G01N2203/0003—Steady
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- 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
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- 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
- G01N2203/026—Specifications of the specimen
- G01N2203/0298—Manufacturing or preparing specimens
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- 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
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Abstract
The invention provides a measuring method of micro-area mechanical constitutive relation of a welded joint, which is characterized in that an instrumented indentation test of a micro-area and a tensile test under a digital image correlation method are respectively carried out on an aluminum alloy welded joint sample, stress-strain information of a full plastic deformation stage of the micro-area is obtained through the instrumented indentation test, stress-strain information of an elastic deformation stage and an elastoplastic deformation stage of the micro-area is obtained through the tensile test under the digital image correlation method, the stress-strain information of the elastic deformation stage, the elastoplastic deformation stage and the full plastic deformation stage of the micro-area is fitted and constructed according to a mechanical constitutive relation of strain hardening indexes along with the change of strain, and finally the complete micro-area mechanical constitutive relation is obtained, so that the mechanical deformation behavior of the micro-area of a material can be completely described. The method can solve the problem that the mechanical constitutive relation of the weakest mechanical property area can only be obtained in the mechanical property test process of the material of the non-heat-treatable reinforced aluminum alloy.
Description
Technical Field
The invention relates to the technical field of material mechanical property detection, in particular to a method for measuring a micro-area mechanical constitutive relation of a welded joint.
Background
The aluminum alloy has the advantages of high specific strength, good corrosion resistance, good weldability and the like, and can be widely applied to the fields of ships, aerospace, automobiles and the like. Welding is one of the common methods for forming aluminum alloy members, but a large number of non-heat-treatable reinforced aluminum alloys exist in common 3-series, 5-series, 6-series and other aluminum alloy series, and the aluminum alloys of the type have coarse grains due to heat input of welding, the welding seam and the heat affected zone of a welding joint are usually weakened phases, and the mechanical strength performance is lower than that of a base metal. Therefore, in the process design of the aluminum alloy welding structure, the mechanical properties of the base metal cannot be directly used, and how to characterize the mechanical properties of the local area of the welding joint is the key for carrying out the aluminum alloy structure design. The conventional aluminum alloy welding process evaluation test only carries out an integral tensile test on the welded joint to obtain the tensile strength of the weakest area of the mechanical properties in the welded joint, and the mechanical properties of the rest positions of the joint cannot be represented, so that the structural strength cannot be accurately calculated when the strength is complemented by adopting methods such as high welding surplus or reinforcing ribs, and the like, thereby generally adopting a design with higher safety redundancy, improving the production cost and increasing the weight of the component. The yield strength is also a key index in structural design, the whole joint stretching method in welding process evaluation is used, the yield strength is measured under the influence of the position of the extensometer and the gauge length of the extensometer, and the measured minimum dimension length is more than 5 mm. It is difficult to accurately characterize the yield strength of the localized area of the joint.
The existing methods capable of carrying out micro-region mechanical property characterization of the metal material include a microhardness method, a digital image correlation method and an instrumented indentation method. The microhardness method is a semi-quantitative empirical method, and accurate test results are difficult to ensure by carrying out microzone hardness measurement on the sectional structure of the welded joint and combining metallographic structure conditions of corresponding regions and deducing tensile mechanical property results from hardness results of different regions. The digital image correlation rule is to spray a speckle mark on the surface of a tensile sample, and record the change of the mark in the tensile process value to obtain the integral strain condition of the joint. However, for the non-heat-treatable reinforced aluminum alloy, the complete stress-strain constitutive relation can be obtained only in the area with the weakest mechanical property, and for other areas, only partial constitutive relation can be obtained, so that the yield strength can be accurately represented, but the tensile strength of the micro-area cannot be represented. For an instrumented indentation method, an indentation load-depth curve is obtained by indentation the micro-area surface of the measured material by a micro-pressure head, and a mechanical constitutive relation of the measured material is constructed by fitting the load-depth curve, so that corresponding mechanical performance parameters are obtained. The instrumented indentation method considers that the stress-strain information of the material obtained by the indentation load-depth curve is in the complete plastic deformation stage of the material, and the yield strength of the material is in the elastoplastic deformation stage, so that the instrumented indentation method has the problem of poor precision in the representation of the yield strength of the micro-region, and the deviation can reach more than 15%.
In summary, the existing test method cannot realize accurate measurement of the micro-area mechanical constitutive relation of the non-heat-treatable reinforced aluminum alloy welded joint.
Disclosure of Invention
In view of the above, the invention aims to provide a method for measuring the micro-area mechanical constitutive relation of a non-heat-treatable reinforced aluminum alloy welded joint. The method solves the problem that the measurement method in the prior art can not realize the accurate measurement of the micro-area mechanical constitutive relation of the non-heat-treatable reinforced aluminum alloy welded joint.
In order to achieve the above purpose, the technical scheme of the invention is realized as follows:
a measuring method of the mechanical constitutive relation of a micro-area of a welded joint, wherein the welded joint is an aluminum alloy welded joint which can not be subjected to heat treatment, comprises the following steps:
s1, processing an aluminum alloy welding test plate into a standard plate-shaped tensile sample;
s2, respectively marking the sections of the welding lines on two sides of the sample as a section A and a section B, wherein the section A is subjected to corrosion treatment to enable a welding line area to be visible to naked eyes, the section B is not treated, and the micro-area position of the sample is determined according to the center of the welding line;
s3, carrying out an instrumented ball indentation test on an A section of the micro-zone position according to the micro-zone position of the sample in the step S2, and obtaining a load-depth curve;
s4, spraying speckle marks required by a digital image related test on the section B of the sample, and then carrying out a tensile test under digital image related monitoring on a tensile tester;
s5, calculating true stress-true strain information of the complete plastic deformation stage obtained by the instrumented ball press-in test in the step S3;
s6, calculating stress-strain information of an elastic stage and an elastoplastic stage obtained by the digital image related test in the step S4;
and S7, fitting according to the results obtained in the steps 5 and 6 to obtain the stress-strain mechanical constitutive relation of the complete micro-region position.
The method provided by the invention can be used for obtaining the complete micro-region mechanical constitutive relation, and can be used for completely describing the mechanical deformation behavior of the material micro-region, so that the problem that the non-heat-treatable reinforced aluminum alloy can only obtain the mechanical constitutive relation of the region with the weakest mechanical property in the material mechanical property test process is solved.
Further, in step S5, the method further includes the steps of:
s51, calculating true strain epsilon p ：
Wherein R is the radius of the ball press head, and a is the true contact radius of the ball press mark.
S52, calculating true stress sigma t ：
Where F is the applied load,for the actual indentation contact depth, ψ is a plastic constraint factor, ψ=3.0-n, n is the strain hardening index of the measured material, and an initial n value can be obtained according to the curvature ratio of the loading curve.
Further, in step S52, the actual indentation contact depthThe calculation formula of (2) is as follows:
where h is the maximum contact depth at loading, s is the curvature of the tangent of the unloading curve at load P, h pile Indicating the variation of the contact depth of the indentation caused by accumulation or sedimentation; h is a pile And h p The relation of (2) is expressed as:
further, in step S51, the true contact radius a of the ball indentation is calculated as follows:
further, in step S7, the stress-strain mechanical constitutive relationship is as follows:
wherein σ is true stress, ε is true strain, B is a strength coefficient, N is a characteristic hardening exponent, and C1 and C2 are constants.
6. The measurement method according to claim 1, wherein in step S1, the micro-zone position includes a welding center micro-zone point, a micro-zone point one, a micro-zone point two, and a micro-zone point three.
Further, in the step S1, the original thickness of the sample is more than or equal to 2mm, and 1000-mesh sand paper is adopted for polishing at the section of the welding seam of the sample to remove the oxide layer on the surface.
Further, in step S2, the treatment liquid used for the corrosion treatment of the section a is a mixed liquid of hydrofluoric acid, hydrochloric acid, nitric acid and water, and the volume ratio of the treatment liquid to the mixed liquid is 2:3:5:190, wherein the concentration of hydrofluoric acid is 1.15g/m, the concentration of hydrochloric acid is 1.19g/mL, and the concentration of nitric acid is 1.40g/mL.
Further, in the step S3, a carbide ball head with the diameter of 0.5-1.0 mm is adopted for pressing, displacement control is adopted for pressing test, 10-15 times of loading and unloading cycles are carried out, the maximum pressing depth of the ring is 0.12-0.16 mm, and the unloading rate of each loading and unloading cycle is not lower than 40% of the current maximum load.
Further, in step S4, the test is controlled by using the displacement of the cross beam, and the test speed is 2mm/min until the sample breaks.
Compared with the prior art, the measuring method for the micro-area mechanical constitutive relation of the welding joint has the following advantages:
1) According to the invention, an instrumented indentation test of a micro-area and a tensile test under a digital image correlation method are respectively carried out on the same non-heat-treatable reinforced aluminum alloy welded joint sample, stress-strain information of a full plastic deformation stage of the micro-area is obtained through the instrumented indentation test, stress-strain information of an elastic deformation stage and an elastoplastic deformation stage is obtained through the tensile test under the digital image correlation method, the stress-strain information of the elastic deformation stage, the elastoplastic deformation stage and the full plastic deformation stage of the micro-area is fitted and constructed according to a mechanical constitutive relation of strain hardening indexes along with strain, and finally, the complete mechanical constitutive relation of the micro-area is obtained, so that the mechanical deformation behavior of the micro-area of a material can be completely described. The method can solve the problem that the non-heat-treatable reinforced aluminum alloy can only obtain the mechanical constitutive relation of the weakest area of the mechanical property in the process of testing the mechanical property of the material;
2) The method can test the accurate representation of the micro-area mechanical property and mechanical constitutive relation of the aluminum alloy welded joint, and the representation result can be applied to finite element simulation in the aluminum alloy structure design process, so that the mechanical behavior of the aluminum alloy structure under load can be accurately simulated, the current situation of the existing high-safety redundancy design is changed, the residual height of the aluminum alloy welded structure or the size of a reinforcing rib is effectively reduced, the material and process cost is reduced, and the equipment is light; the method has wide application prospect in the fields of aluminum alloy welding structure design and mechanical property characterization in the fields of ships, aerospace, automobiles and the like.
Drawings
FIG. 1 is a schematic illustration of a cross-sectional test of sample A according to the present invention;
FIG. 2 is a schematic illustration of a cross-sectional test of sample B according to the present invention;
FIG. 3 is a schematic diagram of a micro-area mechanical property test position of a welded joint sample according to an embodiment 5083-5383 of the invention;
FIG. 4 is a graph of load and depth for different micro-zone locations instrumented with micro-zones of a weld joint sample according to embodiments 5083-5383 of the present invention;
FIG. 5 is a diagram showing the strain distribution obtained by the digital image correlation method for welded joint samples according to examples 5083-5383 of the present invention;
FIG. 6 is a graph showing the constitutive relation of microcell mechanics obtained by digital image correlation and instrumented indentation of samples of welded joints according to examples 5083 (left) -5383 (right) of the present invention;
FIG. 7 is a schematic diagram of a weld joint area simulated by Abaqus software according to an embodiment of the present invention;
FIG. 8 is a graph comparing a test measured stress-strain curve with a finite element simulation measured stress-strain curve according to an embodiment of the present invention.
Reference numerals illustrate:
1-instrumented indenter head, 2-sample A section, 3-micro-area test position, 31-welding area, 311-first micro-area point, 32-5083 heat affected zone, 321-second micro-area point, 33-5383 heat affected zone, 331-third micro-area point, 34-5083 base material area, 341-fourth micro-area point, 35-5383 base material area, 351-fifth micro-area point, 4-sample weld joint, 5-tensile tester chuck, 6-speckle mark, 7-sample B section, 8-digital image related equipment.
Detailed Description
In order that the above objects, features and advantages of the invention will be readily understood, a more particular description of the invention will be rendered by reference to specific embodiments thereof which are illustrated in the appended drawings.
A measuring method of micro-area mechanics constitutive relation of a non-heat-treatable reinforced aluminum alloy welded joint adopts the following design ideas: preparing a transverse sample on a welded test plate or structure to be tested, determining the absolute position of the center of a welding line on the section of the sample by dimension measurement on the section of the welding line on one side of the sample, and then determining the relative position of a micro-area to be measured and the center of the welding line. And carrying out an instrumented continuous ball indentation test on the micro-region to be tested to obtain a load-depth curve, fitting stress-strain point information of the complete plastic deformation stage, and then carrying out a tensile test under digital image related monitoring on the other side of the sample to obtain an incomplete stress-strain curve of the same micro-region. And finally, inputting stress-strain information of a complete plastic deformation stage obtained by an instrumented continuous ball indentation test and stress-strain information of an elastic deformation stage and an elastoplastic deformation stage obtained by a digital image correlation method according to the functional relation of the constitutive model, and carrying out fitting calculation to obtain the integral parameters of the constitutive mechanical model of the micro-region of the corresponding welded joint.
The specific implementation steps are as follows:
(1) An aluminum alloy welding test plate is subjected to a metal material tensile test according to GB/T228.1 part 1: the room temperature test method is characterized in that the standard platy tensile sample is processed according to the requirements, the original thickness of the sample is more than or equal to 2mm, 1000-mesh sand paper is adopted for polishing at the section of a welding seam of the sample, and an oxide layer on the surface is removed.
(2) The weld joint area on one side of the sample was subjected to corrosion treatment with a volume mixed solution of hydrofluoric acid (ρ1.15 g/mL), hydrochloric acid (ρ1.19 g/mL), nitric acid (ρ1.40 g/mL) and water in a volume of (2+3+5+190), and the corroded section was designated as section A and the other side as section B. The thickness of the sample and the width of the weld center were measured using a vernier caliper to determine the absolute position of the weld center on the sample, denoted as P0, then the relative position of the test position with respect to the weld center P0 was determined according to the micro-zone position to be tested, denoted as Pi (i=1, 2,3 … …), for example, the intersection position of the weld center axis with the weld line was denoted as P1 and P2, the heat affected zone position 3mm outside the intersection position of the weld center axis with the weld line was denoted as P3 and P4, and the base material position 8mm outside the intersection position of the weld center axis with the weld line was denoted as P5 and P6.
(3) And carrying out an instrumented ball indentation test on the section A of the sample, wherein the indentation test is recommended to be carried out by adopting a carbide ball head with the diameter of 0.5-1.0 mm, the indentation test is carried out by adopting displacement control, and carrying out loading and unloading cycles for 10-15 times, wherein the maximum indentation depth of the ring is 0.12-0.16 mm, and the unloading rate of each loading and unloading cycle is not lower than 40% of the current maximum load. And (3) performing an instrumented indentation test on the sample position selected in the step (2), wherein the center of the pressure head and the selected micro-area point are positioned on the same axis during the test, and recording a load-depth curve during the test.
(4) And (3) spraying a speckle mark required by a digital image related test on the section B of the sample, and then carrying out a tensile test under digital image related monitoring on a tensile tester, wherein the test adopts beam displacement control, and the test speed is 2mm/min until the sample breaks.
(5) The true stress-true strain information of the complete plastic deformation phase obtained by the instrumented indentation test is calculated. True plastic strain ε p Calculated using equation (1), the expression is as follows:
wherein R is the radius of the ball press head, and a is the true contact radius of the ball press mark.
True stress sigma t Calculated using equation (2), the expression is as follows:
where F is the applied load,for the actual indentation contact depth, ψ is a plastic constraint factor, ψ=3.0-n, n is the strain hardening index of the measured material, and an initial n value can be obtained according to the curvature ratio of the loading curve. Actual indentation contact depth +.>Calculated using equation (3), the expression is as follows:
where h is the maximum contact depth at loading, s is the curvature of the tangent of the unloading curve at load P, h pile Indicating the variation of the contact depth of the indentation caused by accumulation or sedimentation phenomenon, h pile Calculated using equation (4), the expression is as follows:
the true contact radius a of the ball indentation is calculated according to equation (5) as follows:
thus, the true stress and true strain information of the complete plastic deformation stage corresponding to each loading and unloading cycle can be calculated.
(6) Stress-strain information of the elastic phase and the elastoplastic phase obtained by the digital image correlation method is calculated. In the calculation software of the digital image, the central position of a required calculation area is determined according to the absolute position of the center of the welding seam and the relative position of an instrumented indentation test point, and the stress-strain information of the area is calculated by selecting the length of 2 times of the maximum indentation depth according to the indentation depth and the stretching direction.
(7) And (5) constitutive relation calculation. Step (6) obtains the tensile mechanical stress-strain relation of the selected area, the stress-strain relation of other areas except the fracture position of the welding line is incomplete, but all constitutive information of elastic deformation and elastoplastic deformation stages is covered, the incomplete stress-strain information obtained in step (6) and the stress-strain information point of the complete plastic deformation stage obtained in step (5) are subjected to least square fitting according to the mechanical constitutive relation of the strain hardening index along with the change of strain shown in formula (6), numerical values of B, N, C and C2 are fitted, and finally the complete stress-strain mechanical constitutive relation of the area is obtained, wherein the relational expression is shown in formula (6).
Wherein sigma is true stress, epsilon is true strain, B is a strength coefficient, N is a characteristic hardening exponent, and C1 and C2 are constants.
The measuring method of the micro-area mechanical constitutive relation of the welded joint can be applied to micro-area mechanical property tests of welded joints made of various aluminum alloy materials. The procedure and results of the micro-area constitutive relation measurement are shown below using a 5083-5383MIG weld joint material as an example, and the results are verified.
Test materials: the 5083-5383 welding joint with the thickness of 10mm is prepared by MIG. The welding material is ER5183 with the diameter of 1.2mm, the welding current is 170A, and the argon flow is 20-25L/min.
Test temperature: 23-25 ℃, and the relative humidity of the environment: 40 to 50 percent
The test process comprises the following steps:
(1) An aluminum alloy welding test plate is subjected to a metal material tensile test according to GB/T228.1 part 1: the room temperature test method is characterized in that the standard platy tensile sample is processed according to the requirements, 1000-mesh sand paper is adopted for polishing at the sections of welding seams at two sides of the sample, and the surface oxide layer is removed.
(2) The weld joint area on one side of the sample was subjected to corrosion treatment with a volume mixed solution of hydrofluoric acid (ρ1.15 g/mL), hydrochloric acid (ρ1.19 g/mL), nitric acid (ρ1.40 g/mL) and water in a volume of (2+3+5+190), and the corroded section was designated as section A. The thickness of the sample and the width of the center of the weld are measured by using a vernier caliper to determine the absolute position of the center of the weld, and the welding areas 31, 5083 heat affected zones 32, 5383 heat affected zones 33, 5083 base metal areas 34, 5383 base metal areas 35 are respectively selected from the central axes of the sections of the welding joints of the sample, wherein the welding areas 31 are provided with first micro-area points 311, the 5083 heat affected zones 32 are provided with second micro-area points 321, 5383 heat affected zones 33 are provided with third micro-area points 331, the 5083 base metal areas 34 are provided with fourth micro-area points 341, the 5383 base metal areas 35 are provided with fifth micro-area points 351,5 as micro-area mechanical property test positions, as shown in fig. 3, the distances between the second micro-area points and the third micro-area points are the same, the distances between the fourth micro-area points and the fifth micro-area points are the same, the 5 micro-area points are on the same straight line, and the straight line is parallel to the long side of the welding joint.
(3) An instrumented ball indentation test is carried out at 5 micro-area points on the section A of the sample, an indentation is carried out by adopting a carbide ball head with the diameter of 1.0mm, the indentation test is carried out by adopting displacement control, 15 loading and unloading cycles are carried out, the maximum indentation depth of a ring is 0.12, the unloading rate of each loading and unloading cycle is 40% of the current maximum load, and a load-depth curve in the test process is recorded, as shown in figure 4.
(4) And (3) spraying a speckle mark required by a digital image related test on the section B of the sample, and then carrying out a tensile test under digital image related monitoring on an INSTRON 5985250kN tensile tester, wherein the test adopts beam displacement control, the test speed is 2mm/min until the sample breaks, and the obtained strain distribution diagram is shown in figure 5.
(5) The true stress-true strain information of the complete plastic deformation phase obtained by the instrumented indentation test is calculated.
(6) Stress-strain information of the elastic phase and the elastoplastic phase obtained by the digital image correlation method is calculated. In the calculation software of the digital image, the center position of a required calculation area is determined according to the absolute position of the center of the welding line and the relative position of an instrumented indentation test point, and the stress-strain relation of the area is calculated according to the indentation depth and the length of 2mm in the stretching direction.
(7) And (5) constitutive relation calculation. The values of B, N, C and C2 are fitted by least square method to the mechanical constitutive relation of strain hardening index with strain change according to the stress-strain information of elastic deformation stage, elastoplastic deformation stage and complete plastic deformation stage of microdomains, as shown in Table 1. The strain-strain curve is plotted according to the calculated constitutive relationship as shown in fig. 6.
TABLE 1 constitutive relation calculation results
(8) And (5) verifying results. Finite element simulation is carried out on the constitutive relation result obtained by the method and is compared with the actual measurement test result to verify. In order to obtain more subdivided performance units in finite element simulation, sampling and distributing more densely-distributed micro-area mechanics constitutive relation tests on the same welding plate, taking three areas at the center of a welding line, taking two areas at two sides of a heat affected zone respectively, and taking two areas at two sides of a base metal respectively. The constitutive results obtained are input into the Abaqus software as shown in fig. 7. The tensile test sample process is simulated, according to the assumption that the volume is unchanged in the tensile process, the tensile strength is considered to be achieved when the true strain is equal to the strain hardening index, the result of the calculation of the tensile strength and the yield strength is shown in table 2, the simulated test curve and the actual test curve are shown in fig. 8, the deviation between the mechanical property result of finite element simulation carried out by the constitutive relation obtained by the method and the test result of actual measurement mechanical property test is 3%, and the method has high accuracy in measuring the constitutive relation of the micro-area mechanical property of the non-heat-treatable reinforced aluminum alloy welded joint.
TABLE 2 comparison of finite element simulation results with actual measurement results using the inventive measurement constitutive relations
Although the present invention is disclosed above, the present invention is not limited thereto. Various changes and modifications may be made by one skilled in the art without departing from the spirit and scope of the invention, and the scope of the invention should be assessed accordingly to that of the appended claims.
Claims (10)
1. The method for measuring the mechanical constitutive relation of the micro-area of the welded joint is characterized in that the welded joint is an aluminum alloy welded joint which can not be subjected to heat treatment, and comprises the following steps:
s1, processing an aluminum alloy welding test plate into a standard plate-shaped tensile sample;
s2, respectively marking the sections of the welding lines on two sides of the sample as a section A and a section B, wherein the section A is subjected to corrosion treatment to enable a welding line area to be visible to naked eyes, the section B is not treated, and the micro-area position of the sample is determined according to the center of the welding line;
s3, carrying out an instrumented ball indentation test on an A section of the micro-zone position according to the micro-zone position of the sample in the step S2, and obtaining a load-depth curve;
s4, spraying speckle marks required by a digital image related test on the section B of the sample, and then carrying out a tensile test under digital image related monitoring on a tensile tester;
s5, calculating true stress-true strain information of the complete plastic deformation stage obtained in the instrumented ball press-in test in the step S3;
s6, calculating stress-strain information of an elastic stage and an elastoplastic stage obtained by the digital image related test in the step S4;
and S7, fitting according to the results obtained in the steps 5 and 6 to obtain the stress-strain mechanical constitutive relation of the complete micro-region position.
2. The measurement method according to claim 1, characterized in that in step S5, further comprising the steps of:
s51, calculating true strain epsilon p ：
Wherein R is the radius of the ball press head, and a is the true contact radius of the ball press mark.
S52, calculating true stress sigma t ：
Where F is the applied load,for the actual indentation contact depth, ψ is the plastic constraint factor, ψ=3.0-n, n is the strain hardening index of the measured material.
3. The measurement method according to claim 2, wherein in step S52, the actual indentation contact depthThe calculation formula of (2) is as follows:
where h is the maximum contact depth at loading, s is the curvature of the tangent of the unloading curve at load P, h pile Indicating the variation of the contact depth of the indentation caused by accumulation or sedimentation; h is a pile And h p The relation of (2) is expressed as:
4. a measuring method according to claim 3, characterized in that in step S51 the true contact radius a of the ball indentation is calculated as follows:
5. the method according to claim 1, wherein in step S7, the stress-strain mechanical constitutive relation is as follows:
wherein σ is true stress, ε is true strain, B is a strength coefficient, N is a characteristic hardening exponent, and C1 and C2 are constants.
6. The measurement method according to claim 1, wherein in step S1, the micro-zone position includes a welding center micro-zone point, a micro-zone point one, a micro-zone point two, and a micro-zone point three.
7. The method according to claim 1, wherein in step S1, the original thickness of the sample is not less than 2mm, and 1000 mesh sand paper is used for polishing the section of the weld joint of the sample to remove the oxide layer on the surface.
8. The measurement method according to claim 1, wherein in step S2, the treatment liquid used for the corrosion treatment of the a section is a mixed liquid of hydrofluoric acid, hydrochloric acid, nitric acid and water, and the volume ratio is 2:3:5:190, wherein the concentration of hydrofluoric acid is 1.15g/m, the concentration of hydrochloric acid is 1.19g/mL, and the concentration of nitric acid is 1.40g/mL.
9. The method according to claim 1, wherein in the step S3, a carbide ball head with a diameter of 0.5mm to 1.0mm is used for pressing, the pressing test is performed by displacement control for 10 to 15 times of loading and unloading cycles, the maximum pressing depth of the ring is 0.12 to 0.16mm, and the unloading rate of each loading and unloading cycle is not lower than 40% of the current maximum load.
10. The method according to claim 1, wherein in step S4, the test is performed using beam displacement control at a test speed of 2mm/min until the sample breaks.
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