A stress testing device and testing method during high pressure vessel shell forming process

Abstract

The present invention discloses a stress testing device and a testing method during the molding process of a high-pressure container shell, and belongs to the technical field of stress testing during the molding process. The stress testing device during the molding process of a high-pressure container shell includes a fixedly connected mounting plate and a protective plate, wherein the mounting plate is fixed to the tensile side surface of the workpiece, and a plurality of mounting holes are evenly arranged on the mounting plate, wherein strain gauges are installed in the mounting holes, and the strain gauges are pasted on the surface of the workpiece, and slots are arranged on the mounting plate to avoid the strain gauges and the wires, and the projection of the mounting holes on the protective plate is located in the slots. The use of the stress testing device and the testing method during the molding process of a high-pressure container shell described in the present invention can solve the problem that the existing high-pressure container shell cannot perform effective stress testing during the molding process.

Description

Technical Field

[0001] The present invention relates to the technical field of stress testing in a molding process, and in particular to a stress testing device and a testing method in a molding process of a high-pressure container shell. Background Art

[0002] Whether it is to further reveal the mechanism of high-pressure vessel shell forming, conduct process research and technical transformation, or conduct safety assessment and rational use of pressure vessels, it must be based on the accurate grasp of the stress distribution and stress level of the shell. Therefore, the actual stress test and analysis work is an important basic work for shell processing technology research and process method development. During the shell forming process, the deformation is completed in the mold. Whether it is the existing contact or non-contact measurement technology, it is difficult to apply it to stress testing work under this actual pressure processing state. At present, there has been no specific report on the stress test and analysis work of the spherical shell plate and thick-walled container shell forming process at home and abroad.

[0003] The forming process of large-flap high-strength steel spherical tanks and thick-walled high-pressure container shells is to deform the plate point by point. From the beginning to the end of the processing, the plate is always in a state of motion at different positions, and it is a composite motion in the vertical and horizontal directions. The amount of motion and direction at each moment cannot be precisely controlled. At the same time, the plate in the deformation processing part is just in the pressure rolling state of the upper and lower molds. No type of sensor can be set on the surface, and non-contact testing methods cannot be applied. Considering the actual impact on stress and the difficulty of implementation, sensors cannot be embedded in the plate. Therefore, it is difficult to accurately test the stress during the forming process of large-flap high-strength steel spherical tanks and thick-walled high-pressure container shells. Summary of the invention

[0004] The purpose of the present invention is to provide a stress testing device and a testing method during the molding process of a high-pressure container shell, so as to solve the problem that the existing high-pressure container shell cannot be effectively stressed during the molding process.

[0005] To achieve the above-mentioned purpose, the present invention provides a stress testing device for a high-pressure container shell forming process, comprising a fixedly connected mounting plate and a protective plate, the mounting plate being fixed to the tensile side surface of a workpiece, a plurality of mounting holes being evenly arranged on the mounting plate, strain gauges being installed in the mounting holes, the strain gauges being pasted to the surface of the workpiece, slots being arranged on the mounting plate to avoid the strain gauges and the wires, and the projections of the mounting holes on the protective plate being located in the slots.

[0006] Preferably, the distance between adjacent mounting holes is 200 mm-400 mm, and the diameter of the mounting holes is 50 mm-80 mm.

[0007] Preferably, the mounting plate, the protective plate and the workpiece are of equal size, the mounting plate is 3 mm thick, the protective plate is 3 mm thick, and the workpiece is 20 mm-50 mm thick.

[0008] Preferably, the strain gauge comprises a triangular strain gauge or a right-angle strain gauge, and the triangular strain gauge is arranged in a principal stress test area of ​​the workpiece.

[0009] Preferably, the principal stress testing area is a square area determined by the width of the workpiece.

[0010] Preferably, the ultimate strain of the strain gauge is not less than 10000 με.

[0011] Preferably, the slots include transverse slots and longitudinal slots, and the widths of the transverse slots and the longitudinal slots are 50 mm-70 mm.

[0012] The testing method of the stress testing device in the molding process of the high-pressure container shell comprises the following steps:

[0013] S1. Spot weld the mounting plate onto the tensile side surface of the workpiece, and grind and clean the workpiece surface through the mounting hole;

[0014] S2. Place the triangular strain gauge or the right-angle strain gauge in the mounting hole, and fix the triangular strain gauge or the right-angle strain gauge on the surface of the workpiece by gluing;

[0015] S3, the wires of the triangular strain gauge and the right-angle strain gauge are connected to the external strain gauge, the wires are located in the horizontal groove and the vertical groove, and the protection plate and the mounting plate are fixedly connected by spot welding;

[0016] S4, balance and zero the bridge, press the workpiece in the order of pressure relief, measure the strain after point pressure, and store the strain data of the rolling state by the strain gauge; measure the strain again after pressure relief, and store the strain data of the pressure relief state by the strain gauge; after the workpiece is pressed and formed, the strain data is exported;

[0017] S5. Process the data and calculate stress.

[0018] Preferably, S5 is specifically:

[0019] S51, analyze the strain to obtain the strain field matrix ε of each measuring point in the rolling state represented by the principal strain Z and the stress relief strain field matrix ε of each measuring point in the stress relief state expressed by the principal strain Q ;

[0020] S52, calculate the strain recovery after unloading and obtain the regression strain matrix ε ZQ =ε Z -ε Q ;

[0021] S53. Calculate the residual stress σ expressed as principal stress using the elastic-plastic linear hardening model R .

[0022] Preferably, in S53, the residual stress σ R There are three cases for the calculation:

[0023] 1) The strain in the rolling state does not reach or is equal to the elastic limit strain, and the residual stress σ R Equal to the product of residual strain and elastic modulus Eσ R =ε ZQ ×E;

[0024] 2) The strain in the rolling state exceeds the elastic limit strain, and the strain difference between the rolling state and the unloading state is less than the elastic strain limit, and the residual stress σ R Equal to the product of residual strain and elastic modulus Eσ R =ε ZQ ×E;

[0025] 3) The strain in the rolling state exceeds the elastic limit strain, and the strain difference between the rolling state and the unloading state is greater than the elastic strain limit, and the residual stress σ R is the product of the difference between the elastic limit strain and the residual strain and the plastic stage modulus E' R =(ε e -ε ZQ )×E'.

[0026] The advantages and positive effects of the stress testing device and testing method in the high-pressure container shell molding process of the present invention are:

[0027] 1. The mounting plate of the present invention is fixed to the tensile side of the workpiece by spot welding. Macroscopically, there is surface contact between the lower die and the workpiece. The mounting plate and the protective plate are equivalent to adding a uniform interlayer between the lower die and the workpiece, which does not change the load and constraint conditions of the workpiece pressure processing at all, and thus will not have a significant impact on the stress field of the workpiece.

[0028] 2. The strain gauge is located between the mounting plate and the protective plate. The mounting plate and the protective plate are used to protect the strain gauge and the wire to ensure safe and stable data output.

[0029] 3. The present invention can realize the strain measurement of the workpiece during the stamping process and calculate the residual stress, provide reference data for the selection of stamping process parameters and the determination of the process scheme, ensure the yield rate of the shell stamping process, and understand the safety margin of the high-pressure container.

[0030] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 It is a schematic structural diagram of a stress testing device according to an embodiment of the present invention;

[0032] Figure 2 This is a schematic diagram of the structure of the mounting plate of the stress testing device according to an embodiment of the present invention;

[0033] Figure 3 A schematic diagram of the structure of a protective plate of a stress testing device according to an embodiment of the present invention;

[0034] Figure 4 It is a schematic diagram of the installation distribution structure of the strain gauge of the stress testing device according to an embodiment of the present invention;

[0035] Reference numerals

[0036] 1. Mounting plate; 2. Protective plate; 3. Mounting hole; 4. Horizontal groove; 5. Vertical groove; 6. Workpiece; 7. Triangular strain gauge; 8. Right-angle strain gauge. DETAILED DESCRIPTION

[0037] In the description of the present invention, it should be noted that the terms "upper", "lower", "inside", "outside", etc. indicate positions or positional relationships based on the positions or positional relationships shown in the accompanying drawings, or the positions or positional relationships in which the invented product is usually placed when in use. They are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present invention. In the description of the present invention, it should also be noted that, unless otherwise clearly specified and limited, the terms "setting", "installation", and "connection" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be an indirect connection through an intermediate medium, or it can be a connection between the two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0038] The embodiments of the present invention are described in detail below in conjunction with the accompanying drawings.

[0039] like Figure 1 , Figure 2 , Figure 3 , Figure 4 As shown. A stress testing device for a high-pressure container shell molding process comprises a mounting plate 1 and a protective plate 2 which are fixedly connected. The mounting plate 1, the protective plate 2 and the workpiece 6 are of equal size, and the thickness of the mounting plate 1 is 3 mm. The thickness of the protective plate 2 is 3 mm. The thickness of the workpiece 6 is 20 mm-50 mm. The elongation of the mounting plate 1 and the protective plate 2 is greater than the elongation of the workpiece 6. The mounting plate 1 and the protective plate 2 are fixedly connected together by spot welding. The mounting plate 1 and the protective plate 2 are located between the workpiece 6 and the lower die.

[0040] The mounting plate 1 is fixed on the working tensile side by spot welding. Macroscopically, there is surface contact between the lower die and the workpiece 6. The mounting plate 1 and the protective plate 2 are equivalent to adding a uniform interlayer between the lower die and the workpiece 6, which does not change the load and constraint conditions of the pressure processing of the workpiece 6 at all, and therefore will not have a significant impact on the stress field of the workpiece 6.

[0041] The mounting plate 1 is fixed to the tensile side surface of the workpiece 6 by spot welding. A plurality of mounting holes 3 are evenly arranged on the mounting plate 1. The distance between adjacent mounting holes 3 is 200mm-400mm, preferably 300mm. The lateral spacing of the mounting holes 3 is equal to the longitudinal spacing. The aperture of the mounting hole 3 is 50mm-80mm, preferably 60mm. The aperture of the mounting hole 3 meets the installation requirements of the strain gauge and can meet the needs of grinding and cleaning the surface of the workpiece 6, which is convenient for the installation of the strain gauge.

[0042] A strain gauge is installed in the mounting hole 3, and the strain gauge is fixed to the surface of the workpiece 6 by glue. The strain gauge is used to measure the strain on the tensile side surface of the workpiece 6. The strain gauge includes a triangular strain gauge 7 and a right-angle strain gauge 8. The triangular strain gauge 7 is arranged in the main stress test area of ​​the workpiece 6. The main stress test area is a square area determined by the width of the workpiece 6, and the main stress test area is located at the end of the workpiece 6. It is convenient to compare and analyze the edge strain of the workpiece 6 with the center strain of the workpiece 6. The limit strain of the strain gauge is not less than 10000με, which meets the strain gauge's need to measure the strain of the workpiece 6 during the forming process.

[0043] For the spherical high-pressure container shell, the workpiece 6 needs to be gradually rolled after multiple pressure reliefs to finally stamp the entire plate into a spherical surface with a single curvature. The curvature of each part in the intermediate process is changing, so the stress state at any point and at any time cannot be estimated in advance. The use of isosceles triangle strain rosettes at the measuring point can fully reflect the stress distribution and changes in the point pressure deformation process.

[0044] The mounting plate 1 is provided with slots for avoiding strain gauges and wires, and the projection of the mounting hole 3 on the protective plate 2 is located in the slots. The slots include transverse slots 4 and longitudinal slots 5, and the width of the transverse slots 4 and longitudinal slots 5 is 50mm-70mm, preferably 60mm. The transverse slots 4 and longitudinal slots 5 are located between adjacent strain gauges to meet the needs of wire routing. The mounting plate 1 and the protective plate 2 protect the strain gauges and wires to avoid damage to the wires and strain gauges during the mold pressing process, and ensure the normal and smooth transmission of data.

[0045] The feasibility analysis of the stress testing device of the present invention is as follows:

[0046] Since the thickness dimension of workpiece 6 is much smaller than other two-dimensional dimensions, the ratio of the maximum deflection during and after plastic processing to the thickness dimension of the plate is also less than 5, so it can be regarded as a flexible plate. Therefore, during the forming process, it mainly bears bending internal forces, and has certain in-plane tensile and shear internal forces.

[0047] Stress testing can only be performed on the surface of the plate, and the measured stress is actually the reflection of the comprehensive effect of various internal forces on the surface. According to the analysis of elastic-plastic theory, whether in the processing or in the use process, the maximum tensile stress on the high-pressure container shell that bears the internal pressure will always appear on the outer surface of the shell (excluding other non-spherical structures attached to it and stress concentration caused by process factors), so arranging the test points on the outer surface is not only feasible but also of practical significance.

[0048] From the perspective of failure criterion theory, internal pressure vessels generally use the third strength criterion (Tresca criterion) as the failure criterion.

[0049] That is, σ≤σ 1 -σ 3

[0050] The actual thin-walled shell is generally in a plane stress state, that is, the stress along the thickness direction is approximately 0, that is, σ 3 =σ r =0

[0051] The actual Tresca failure criterion then becomes:

[0052] σ≤σ 1 -σ 3 =σ 1 =σ max

[0053] It also shows that for the stress analysis of spherical tanks, it is appropriate to test the maximum stress on the outer surface.

[0054] The material for processing the shell of a high-pressure vessel is a structural material with good plastic processing properties, with an elongation of about 20% and obvious tensile strengthening. According to the plasticity theory, a simplified linear strengthening elastic-plastic model can be used to describe the stress-strain relationship of this type of material, namely:

[0055] |ε|≤ε s σ=E·ε

[0056] |ε|>ε s When σdε>0 (loading)σ=[σ s+ E'(|ε|-ε s )]signε

[0057] When σdε<0 (unloading) dσ=Edε

[0058] Wherein: E is the elastic modulus of the material; E' is the modulus of the material in the strengthening stage; signε is the sign, when ε>0, signε=1, when ε<0, signε=-1.

[0059] According to the estimation of shell deformation during the processing, the total elastic-plastic deformation of the shell after final forming is within 1%. The appropriate strain testing method is selected to accurately measure the total strain field and reasonably distinguish the elastic-plastic strain components. Then, according to the plasticity theory, the above model can be used to perform stress analysis and calculation during the forming process.

[0060] The testing method of the stress testing device in the molding process of the high-pressure container shell comprises the following steps:

[0061] S1. Spot weld the mounting plate 1 on the tensile side surface of the workpiece, that is, the mounting plate 1 is located between the workpiece 6 and the lower die. Grind and clean the surface of the workpiece 6 through the mounting hole 3 to facilitate the fixation of the strain gauge on the workpiece 6.

[0062] S2. Place the triangular strain gauge 7 or the right-angle strain gauge 8 in the mounting hole 3, and fix the triangular strain gauge 7 or the right-angle strain gauge 8 on the surface of the workpiece 6 by gluing.

[0063] The wires of S3, triangular strain gauge 7 and right-angle strain gauge 8 are connected to the external strain gauge, which is an existing structure and is used for storing and outputting strain data. The wires are located in the transverse groove 4 and the longitudinal groove 5, and the protective plate 2 and the mounting plate 1 are fixedly connected by spot welding.

[0064] S4, balance and zero the bridge, press the workpiece 6 in the order of pressure relief, measure the strain after point pressure, and store the strain data of the rolling state. Strain measurement is performed again after pressure relief, and the strain gauge stores the strain data of the pressure relief state. Then the strain measurement is performed during the next point pressure, and each measurement is performed while retaining the previous test results, so as to track the strain changes and distribution during the entire stamping process. After the workpiece 6 is pressed and formed, the strain data is exported.

[0065] S5. Process the data and calculate stress.

[0066] S5 is as follows:

[0067] S51, the strain is analyzed by the existing analysis method to obtain the strain field matrix ε of each measuring point in the rolling state represented by the principal strain Z and the stress relief strain field matrix ε of each measuring point in the stress relief state expressed by the principal strain Q .

[0068] S52, calculate the strain recovery after unloading and obtain the regression strain matrix ε ZQ =εZ -ε Q .

[0069] S53. Calculate the residual stress σ expressed as principal stress using the elastic-plastic linear hardening model R .

[0070] Residual stress σ R There are three cases for the calculation:

[0071] 1) The strain in the rolling state does not reach or is equal to the elastic limit strain, and the residual stress σ R Equal to the product of residual strain and elastic modulus Eσ R =ε ZQ ×E. In the absence of constraints, the strain should be completely restored after unloading, that is, the unloading strain value is 0, otherwise it means that there is some kind of constraint that keeps it in a tensile state, that is, there is residual tensile stress. This situation may occur in the outer peripheral area of ​​the rolling tire.

[0072] 2) The strain in the rolling state exceeds the elastic limit strain, and the strain difference between the rolling state and the unloading state is less than the elastic strain limit, and the residual stress σ R Equal to the product of residual strain and elastic modulus Eσ R =ε ZQ × E. This may occur in the inner and outer areas of the pressed tire.

[0073] 3) The strain in the rolling state exceeds the elastic limit strain, and the strain difference between the rolling state and the unloading state is greater than the elastic strain limit, and the residual stress σ R is the product of the difference between the elastic limit strain and the residual strain and the plastic stage modulus E' R =(ε e -ε ZQ ) × E'. This may occur in the inner center area of ​​the rolling tire.

[0074] The calculated residual stress helps the staff understand the maximum stress level that can be generated inside the workpiece 6 during the stamping process, provides reference data for the selection of stamping process parameters and the determination of process plans, and ensures the yield rate of the shell stamping process. At the same time, it can also let them know the residual stress of the shell after stamping and understand the safety margin of the high-pressure container.

[0075] Therefore, the stress testing device and method during the molding process of the high-pressure container shell of the present invention can solve the problem that the existing high-pressure container shell cannot be effectively stressed during the molding process.

[0076] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that they can still modify or replace the technical solution of the present invention with equivalents, and these modifications or equivalent replacements cannot cause the modified technical solution to deviate from the spirit and scope of the technical solution of the present invention.

Claims

1. A stress testing device for a high pressure vessel shell during molding, characterized in that: It includes a fixedly connected mounting plate and a protective plate. The mounting plate is fixed on the tensile side surface of the workpiece. A number of mounting holes are evenly arranged on the mounting plate. Strain gauges are installed in the mounting holes. The strain gauges are pasted on the surface of the workpiece. The mounting plate is provided with slots for avoiding the strain gauges and wires. The projection of the mounting holes on the protective plate is located in the slots.

2. A stress testing device for a high pressure vessel shell during molding according to claim 1, characterized in that: The distance between adjacent mounting holes is 200mm-400mm, and the diameter of the mounting holes is 50mm-80mm.

3. A stress testing device for a high pressure vessel shell during molding according to claim 1, characterized in that: The sizes of the mounting plate, the protective plate and the workpiece are equal, the thickness of the mounting plate is 3mm, the thickness of the protective plate is 3mm, and the thickness of the workpiece is 20mm-50mm.

4. A stress testing device for a high pressure vessel shell during molding according to claim 1, characterized in that: The strain gauge comprises a triangular strain gauge or a right-angle strain gauge, and the triangular strain gauge is arranged in the main stress test area of ​​the workpiece.

5. A stress testing device for a high pressure vessel shell during molding according to claim 4, characterized in that: The main stress test area is a square area determined by the width of the workpiece.

6. A stress testing device for a high pressure vessel shell during molding according to claim 1, characterized in that: The ultimate strain of the strain gauge is not less than 10000με.

7. The stress testing device during the molding process of a high-pressure container shell according to claim 1, characterized in that: The slots include transverse slots and longitudinal slots, and the widths of the transverse slots and the longitudinal slots are 50 mm to 70 mm.

8. A testing method for a stress testing device during the molding process of a high pressure vessel shell according to any one of claims 1 to 7, characterized in that: The following steps are involved: S1. Spot weld the mounting plate onto the tensile side surface of the workpiece, and grind and clean the workpiece surface through the mounting hole; S2. Place the triangular strain gauge or the right-angle strain gauge in the mounting hole, and fix the triangular strain gauge or the right-angle strain gauge on the surface of the workpiece by gluing; S3, the wires of the triangular strain gauge and the right-angle strain gauge are connected to the external strain gauge, the wires are located in the horizontal groove and the vertical groove, and the protection plate and the mounting plate are fixedly connected by spot welding; S4, balance and zero the bridge, press the workpiece in the order of pressure relief, measure the strain after point pressure, and store the strain data of the rolling state by the strain gauge; measure the strain again after pressure relief, and store the strain data of the pressure relief state by the strain gauge; after the workpiece is pressed and formed, the strain data is exported; S5. Process the data and calculate stress.

9. The testing method of a stress testing device during the molding process of a high-pressure container shell according to claim 8, characterized in that: The S5 is specifically: S51, analyze the strain to obtain the strain field matrix ε of each measuring point in the rolling state represented by the principal strain Z and the stress relief strain field matrix ε of each measuring point in the stress relief state expressed by the principal strain Q ; S52, calculate the strain recovery after unloading and obtain the regression strain matrix ε ZQ =ε Z -ε Q ; S53. Calculate the residual stress σ expressed as principal stress using the elastic-plastic linear hardening model R .

10. The testing method of a stress testing device during the molding process of a high-pressure container shell according to claim 9, characterized in that: In the S53, the residual stress σ R There are three cases for the calculation: 1) The strain in the rolling state does not reach or is equal to the elastic limit strain, and the residual stress σ R Equal to the product of residual strain and elastic modulus Eσ R =ε ZQ ×E; 2) The strain in the rolling state exceeds the elastic limit strain, and the strain difference between the rolling state and the unloading state is less than the elastic strain limit, and the residual stress σ R Equal to the product of residual strain and elastic modulus Eσ R =ε ZQ ×E; 3) The strain in the rolling state exceeds the elastic limit strain, and the strain difference between the rolling state and the unloading state is greater than the elastic strain limit, and the residual stress σ R is the product of the difference between the elastic limit strain and the residual strain and the plastic stage modulus E' R =(ε e -ε ZQ )×E'.

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