A method for preparing weld samples for slow strain rate tensile testing

Abstract

This invention provides a method for preparing weld samples for slow strain rate tensile testing, comprising the following steps: Step S1: Plate welding; welding the substrate of the material to be tested using a roll welding method; Step S2: Blank cutting; cutting a strip-shaped blank containing the weld from the welded test plate of the material to be tested using a wire cutting method, wherein the length direction of the blank is perpendicular to the length direction of the weld; Step S3: Weld positioning and excess height removal: removing the excess height on the weld surface, making the surface of the weld area flush with the surfaces of the base materials on both sides, forming a flat plane, and obtaining a tensile sample; Step S4: Sample end connection: fixing and connecting the sample to a macroscopic clamping end adapted to a slow strain rate tensile testing machine to form the final test sample. This invention uses a roll welding process to minimize the residual stress caused by traditional machining, ensuring the accuracy of the slow strain rate tensile test for testing the sensitivity of the material surface / near-surface structure.

Description

Technical Field

[0001] This invention belongs to the field of material performance testing technology, specifically relating to a method for preparing weld samples for slow strain rate tensile tests, and particularly a method for preparing micro-samples that can accurately evaluate the mechanical properties of the weld area. Background Technology

[0002] Slow strain rate tensile testing is an important method for evaluating the environmental sensitivity (such as stress corrosion cracking susceptibility) of materials, especially metallic materials, under stress. For welded structures, the weld zone, due to its complex metallurgical process and microstructure, is often the weakest link in the entire structure. Therefore, accurately obtaining the mechanical property parameters of the weld metal under slow strain rates (such as yield strength, tensile strength, elongation, and fracture toughness) is crucial for optimizing welding processes, assessing structural safety, and predicting lifespan.

[0003] However, existing methods for preparing weld tensile specimens have significant shortcomings. Traditional methods do not distinguish whether the test area simultaneously includes the weld and the base metal, typically directly cutting tensile specimens containing the weld, heat-affected zone, and base metal from the weld plate. The tensile results of such specimens reflect the combined properties of the weld region and the base metal, rather than the true mechanical behavior of the weld metal itself. Furthermore, traditional machining methods, when preparing small-sized specimens, easily introduce work hardening or residual stress layers into the sample surface. This introduces significant experimental errors for slow strain rate tensile tests, which are highly sensitive to surface conditions, affecting the assessment of the material's sensitivity to its actual environment. Therefore, there is an urgent need for a specimen preparation method that can accurately separate and test the mechanical properties of the weld metal itself. Summary of the Invention

[0004] Therefore, the present invention provides a method for preparing weld samples for slow strain rate tensile tests, comprising the following steps:

[0005] Step S1: Plate welding; The substrate of the material to be tested is welded using a roll bonding method;

[0006] Step S2: Blank cutting; From the welding test plate of the material to be tested, a strip blank containing the weld is cut by wire cutting, wherein the length direction of the blank is perpendicular to the length direction of the weld;

[0007] Step S3: Weld positioning and excess height removal: Specifically, mechanical grinding is used to remove the excess height on the weld surface, making the weld area surface flush with the base material surfaces on both sides, forming a flat observation and processing plane to obtain the tensile sample;

[0008] Step S4: Sample end connection: The sample is fixedly connected to the macroscopic clamping end adapted to the slow strain rate tensile testing machine to form the final test sample.

[0009] Preferably, in step S1: the welding parameters are 6.5KA and 0.27MPa;

[0010] In step S3: the gauge length of the tensile sample is 6 mm wide, 15 mm long, and 1 mm thick, and the total length of the tensile sample is 96 mm.

[0011] Preferably, in step S4, a centering clamp is used to ensure that the axial direction of the micro-stretched sample coincides with the stretching axis of the macro-clamping end, with an eccentricity of less than 5 μm.

[0012] Preferably, the material of the macroscopic clamping end is a metal material with a coefficient of thermal expansion similar to that of the welding base material, in order to reduce the additional stress exerted on the sample by ambient temperature fluctuations.

[0013] Preferably, the centering fixture includes a drive motor, a rotating plate, a first crank, a second crank, a first sliding plate, and a second sliding plate. The output end of the drive motor is connected to the middle of the rotating plate. The first crank and the second crank are respectively hinged to the two ends of the rotating plate. The first crank is hinged to the middle of the first sliding plate, and the second crank is hinged to the middle of the second sliding plate. The other side of the first sliding plate has a first centering plate, and the other side of the second sliding plate has a second centering plate.

[0014] Preferably, the system further includes a frame, with the drive motor disposed on one side of the back of the frame and the first centering plate and the second centering plate disposed on one side of the front of the frame.

[0015] Preferably, the frame has a slide rail, and the first sliding plate and the second sliding plate cooperate with the slide rail to slide.

[0016] Preferably, the system further includes a guide structure, which includes a guide roller assembly. The side of the frame is connected to and fixed with the roller assembly frame of the guide rollers via a connecting piece. The first centering plate and the second centering plate are located outside the guide roller assembly.

[0017] The beneficial effects of this invention are as follows:

[0018] 1. Reduce processing damage and improve experimental accuracy: The use of roll welding process minimizes residual stress caused by traditional machining, ensuring the accuracy of slow strain rate tensile tests for testing the sensitivity of material surface / near-surface structure.

[0019] 2. Achieving accurate measurement of the intrinsic properties of weld: This invention, through precision positioning and micromachining technology, completely confines the gauge length of the tensile sample within the weld metal, effectively eliminating interference from the base material and the heat-affected zone, thus enabling the evaluation of the true constitutive mechanical properties of the weld metal under slow strain rates.

[0020] 3. Provide data support for critical structure evaluation: The accurate data obtained by this invention can be directly used for finite element simulation, life prediction and safety assessment of welded structures, which has important application value for key fields such as aerospace, nuclear power and petrochemicals. Attached Figure Description

[0021] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0022] Figure 1 This is a schematic diagram of the structure of the tensile sample prepared by the present invention;

[0023] Figure 2 This is a stress-strain curve and mechanical property parameter test diagram of pure weld metal according to an embodiment of the present invention;

[0024] Figure 3 This is a schematic diagram of the back structure of the centering fixture according to an embodiment of the present invention;

[0025] Figure 4 This is a front structural diagram of the centering fixture according to an embodiment of the present invention;

[0026] Figure 5 This is a schematic diagram of the inclined observation structure of the centering fixture according to an embodiment of the present invention;

[0027] Figure 6 This is a schematic diagram of the centering fixture according to an embodiment of the present invention, omitting the component structure.

[0028] Explanation of reference numerals in the attached figures:

[0029] 1: Base material; 2: Weld seam; 3: Side edges; 5: Blank; 11: Centering fixture; 12: Drive motor; 13: Rotating plate; 14: First crank; 15: Second crank; 16: First sliding plate; 17: Second sliding plate; 18: First centering plate; 19: Second centering plate; 20: Frame; 21: Slide rail; 22: Guide structure; 23: Guide roller group; 24: Connecting piece; 25: Roller group frame. Detailed Implementation

[0030] The technical solution of the present invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0031] Example 1:

[0032] This embodiment uses the weld seam of a 304L austenitic stainless steel welded plate as the test object, and the preparation steps are as follows:

[0033] S1 Plate Welding: Take a 1mm thick stainless steel welding test plate 1 and use a roll welding machine to roll weld a single steel plate. The parameters are selected as 6.5KA and 0.27MPa.

[0034] S2 blank cutting: Take a 1mm thick 304L austenitic stainless steel welding test plate 1 from the above-mentioned welded sample, which includes the base material on both sides 1 and the central weld 2. For example... Figure 1 As shown, wire electrical discharge machining (EDM) is used to cut a blank 5 with a length of 96mm (L), a width of 24mm (W), and a height of 1mm, perpendicular to the weld length direction. This ensures that weld 2 is located in the middle of the blank 5. This step uses wire EDM to cut a strip of blank from a complete welding test plate. Compared to other existing processing methods, wire EDM has no mechanical impact, high cutting precision, and can effectively avoid extrusion deformation and cracking damage to weld 2 and the surrounding base material 1 during the cutting process, preserving the original mechanical properties of the welded area.

[0035] S3 Weld Positioning and Residual Height Removal: The surface of blank 5 is ground and polished. Mechanical grinding is used to precisely remove the residual height of the weld surface until the weld surface is completely flush with the surfaces of the base materials on both sides, forming a flat processing reference surface. Through grinding, excess welding residual height on the surface of weld 2 is removed, ultimately ensuring that the surface height of the weld area is flush with the surfaces of the base materials 1 on both sides. This process creates a flat, smooth, and uniformly stressed observation and processing plane, eliminating the stress concentration hazards caused by weld residual height, and producing a standard tensile sample with satisfactory surface flatness and uniform overall structure. S4 Connection to Clamping End: Install the prepared sample onto the macroscopic clamping end of the slow strain rate tensile testing machine, at a 1×10... -6 s -1 The sample is stretched at a strain rate until it breaks. Figure 2 As shown, by recording load-displacement data, the stress-strain curve and mechanical property parameters of pure weld metal can be obtained. Figure 2 The key data results obtained from slow strain rate tensile testing of samples prepared using the method of this invention are presented intuitively, which is the core basis for evaluating the mechanical properties of weld metal.

[0036] By analyzing this stress-strain curve, several key mechanical property parameters of the weld metal can be accurately obtained, including: yield strength: the stress value at which the material begins to undergo significant plastic deformation; tensile strength: the maximum stress value that the material can withstand before fracture; and elongation: the degree of permanent deformation that occurs after fracture, reflecting its plasticity. These parameters are core data for evaluating the mechanical behavior of weld metal, conducting safety assessments of welded structures, and predicting their lifespan.

[0037] In the preferred embodiment:

[0038] In step S1: the substrate (referring to the raw material metal plate used to manufacture the test sample) has a size of 30cm*30cm, and the welding parameters are 6.5KA and 0.27MPa;

[0039] In step S3: The tensile sample has a gauge length H with a width of 6 mm, a gauge length d of 15 mm, a thickness of 1 mm, and a total length L of 96 mm. The gauge length is a horizontal extension. The overall shape of the tensile sample is a narrower, horizontally extending gauge length in the middle, followed by an arc-shaped transition extension, and finally a wider fixed clamping end on the outer side. This dumbbell-shaped structure, with a narrower gauge length in the middle and an arc-shaped transition to a wider clamping end, ensures the accuracy and effectiveness of the test. It ensures that fracture occurs within the gauge length, making it the area with the smallest cross-sectional area of ​​the sample, where it will bear the greatest stress first and most concentratedly during the tensile process. The arc-shaped transition extension avoids stress concentration and prevents premature fracture. Simultaneously, the wider clamping end design ensures that it maintains shape stability during plastic deformation in the gauge length, guaranteeing that the clamping end does not deform.

[0040] In a preferred embodiment: In step S4, the centering clamp 11 is used to ensure that the axial direction of the micro-stretching sample coincides with the tensile axis of the macro-clamping end, and the eccentricity is less than 5 μm. That is, when the prepared micro-stretching sample is installed on the testing machine, the offset between the central axis of the sample and the tensile axis of the testing machine (i.e., the difference in axiality) is controlled within 5 micrometers (0.005 millimeters).

[0041] As a preferred embodiment of this solution, such as Figures 3 to 6 As shown, an additional centering clamp 11 is added during the assembly process in this step to assist in positioning and clamping. Through the precise centering and guiding effect of the centering clamp 11, it is strictly ensured that the central axis of the micro-tensile sample is completely coincident with the tensile axis of the macro-clamping end, and the sample clamping eccentricity is strictly controlled to be less than 5μm. This eliminates the problems of additional bending moment and stress eccentricity caused by clamping eccentricity, and improves the test accuracy and data reliability of slow strain rate tensile test.

[0042] In a preferred embodiment: the macroscopic clamping end is made of a metal with a coefficient of thermal expansion similar to that of the base metal being welded, to reduce the additional stress exerted on the sample by ambient temperature fluctuations. In this preferred embodiment, the macroscopic clamping end is made of a metal with a coefficient of thermal expansion similar to that of the base metal being welded. Because the clamping end and the base metal have a high degree of matching in thermal expansion characteristics, the thermal stress caused by ambient temperature fluctuations during the test can be minimized, avoiding additional stress on the sample due to temperature changes, eliminating temperature interference factors, and ensuring that the test results only reflect the stress corrosion and tensile mechanical properties of the weld and the base metal itself, further improving the accuracy of the test. After clamping, a final test sample is obtained that can be directly used for mechanical property testing.

[0043] Example 2:

[0044] In this embodiment, the centering fixture 11 includes a drive motor 12, a rotating plate 13, a first crank 14, a second crank 15, a first sliding plate 16, and a second sliding plate 17. The output end of the drive motor 12 is connected to the middle of the rotating plate 13. The two ends of the rotating plate 13 are respectively hinged to the first crank 14 and the second crank 15. The first crank 14 is hinged to the middle of the first sliding plate 16, and the second crank 15 is hinged to the middle of the second sliding plate 17. The other side of the first sliding plate 16 has a first centering plate 18, and the other side of the second sliding plate 17 has a second centering plate 19. Figure 5 As can be seen, the first sliding plate 16 and the first centering plate 18 form a frame structure, and the guide roller group 23 is located in the middle. Correspondingly, the second sliding plate 17 and the second centering plate 19 form a frame structure.

[0045] It also includes a frame 20, on the back side of which the drive motor 12 is disposed, and on the front side of which the first centering plate 18 and the second centering plate 19 are disposed. To clearly show the relevant structure, only a part of the structure of the frame 20 is shown in the figure. It may also have other connecting parts or support parts to form a stable support and fixing frame structure.

[0046] The frame 20 has a slide rail 21, and the first sliding plate 16 and the second sliding plate 17 both cooperate with the slide rail 21. Specifically, they cooperate with the slide rail 21 through the connecting part 161 to slide.

[0047] It also includes a guide structure 22, which includes a guide roller group 23. The side of the frame 20 is connected and fixed to the roller group frame 25 of the guide roller group 23 by a connecting piece 24. The first centering plate 18 and the second centering plate 19 are located outside the guide roller group 23.

[0048] As a preferred embodiment of this solution, a dedicated centering fixture 11 is added during the assembly process to assist in positioning and clamping. Relying on the mechanical precision centering function of this dedicated fixture, the sample is clamped without eccentricity, strictly ensuring that the central axis of the micro-tensile sample is completely coincident with the tensile axis of the macro-clamping end, and precisely controlling the sample clamping eccentricity within 5μm. This completely eliminates the problems of additional bending moment and stress eccentricity caused by clamping eccentricity, and improves the test accuracy and data reliability of slow strain rate tensile tests. Among them, the centering fixture 11 is a bidirectional centering and positioning fixture, and its specific structure includes a drive motor 12, a rotating plate 13, a first crank 14, a second crank 15, a first sliding plate 16, and a second sliding plate 17. The entire positioning mechanism is integrated and assembled on the frame 20. The output end of the drive motor 12 is fixedly connected to the middle of the rotating plate 13, which can drive the rotating plate 13 to rotate around the center at a fixed angle. The two ends of the rotating plate 13 are respectively hinged to the first crank 14 and the second crank 15. The end of the first crank 14 is hinged to the middle of the first sliding plate 16, and the end of the second crank 15 is hinged to the middle of the second sliding plate 17, thus forming a transmission structure that can convert the rotational motion of the rotating plate 13 into the synchronous opposing linear sliding motion of the two sets of sliding plates. The outer end of the first sliding plate 16 is fixedly provided with a first centering plate 18, and the outer end of the second sliding plate 17 is fixedly provided with a second centering plate 19. The two centering plates are the reference surfaces for direct contact positioning of the sample.

[0049] In practical use, the base material 1 from the aforementioned embodiment is placed between the first centering plate 18 and the second centering plate 19. The first centering plate 18 and the second centering plate 19 then clamp and fix the base material in the center position. During this process, the first centering plate 18 and the second centering plate 19 contact the two side edges of the base material 1 and then move towards the center to align it. During this process, one end of the base material 1 can be held manually, and when contact occurs between the first centering plate 18 and the second centering plate 19, the operator passively moves the base material 1 until it is firmly clamped and fixed by the first centering plate 18 and the second centering plate 19. This completes the centering process. Subsequently, the upper and lower ends of the base material 1 are clamped and fixed by the macro-clamping end of the slow strain rate tensile testing machine. Then, the first centering plate 18 and the second centering plate 19 are released to re-align. Finally, tensile force is applied by the macro-clamping end of the slow strain rate tensile testing machine to complete the gap test.

[0050] In this embodiment, before sample clamping, the centering fixture 11 is used to automatically center and pre-clamp the tensile sample (base material 1). The specific centering operation process is as follows: First, the centering fixture 11 is controlled to keep the first centering plate 18 and the second centering plate 19 in an open state. The operator initially places the prepared tensile sample (base material 1) in the center position between the first centering plate 18 and the second centering plate 19. Then, the fixture is driven to move, so that the first centering plate 18 and the second centering plate 19 move towards each other in opposite directions and close and clamp.

[0051] As the two centering plates gradually approach each other, the first centering plate 18 and the second centering plate 19 respectively contact the left and right edges 3 of the base material 1. At this time, the operator can hold the upper or lower end of the base material 1 to assist in supporting the sample without forcibly positioning it. As the two centering plates continue to move inward to center, they will automatically push and correct the left and right position of the base material 1, causing the base material 1 to passively adjust its displacement. Finally, the base material 1 is completely straightened and centered, and is symmetrically and firmly clamped by the two centering plates. This accurately completes the automatic centering and pre-fixation of the base material 1, ensuring that the central axis of the base material 1 is completely coincident with the tensile axis of the testing machine.

[0052] With the fixtures aligned and the sample fixed in a centered position, the slow strain rate tensile testing machine is started. The machine's macro-clamping ends are used to clamp and fix the upper and lower ends of the base material 1, achieving reliable assembly between the sample and the testing machine. After the upper and lower clamping ends of the testing machine are fully locked and securely clamp the sample, the alignment fixture 11 is controlled to move in the reverse direction, causing the first centering plate 18 and the second centering plate 19 to open and release to both sides, releasing the lateral clamping limit on the sample. This allows the sample to remain in a free-force state, with only the upper and lower ends suspended and clamped by the macro-clamping ends of the testing machine, avoiding contact constraints from the fixtures that could affect the tensile test results.

[0053] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A method for preparing weld samples for slow strain rate tensile testing, characterized in that, Includes the following steps: Step S1: Plate welding; The substrate of the material to be tested is welded using a roll bonding method; Step S2: Blank cutting; From the welding test plate of the material to be tested, a strip blank containing the weld is cut by wire cutting, wherein the length direction of the blank is perpendicular to the length direction of the weld; Step S3: Weld positioning and excess height removal: Specifically, mechanical grinding is used to remove the excess height on the weld surface, making the weld area surface flush with the base material surfaces on both sides, forming a flat observation and processing plane to obtain the tensile sample; Step S4: Sample end connection: The sample is fixedly connected to the macroscopic clamping end adapted to the slow strain rate tensile testing machine to form the final test sample.

2. The method for preparing weld samples for slow strain rate tensile testing according to claim 1, characterized in that, In step S1: the welding parameters are 6.5KA and 0.27MPa.

3. The method for preparing weld samples for slow strain rate tensile testing according to claim 1, characterized in that, In step S3: the gauge length of the tensile sample is 6 mm wide, 15 mm long, and 1 mm thick, and the total length of the tensile sample is 96 mm.

4. The method for preparing weld samples for slow strain rate tensile testing according to claim 1, characterized in that, The overall shape of the tensile sample is a narrow, horizontally extending gauge length in the middle, followed by an arc-shaped transition extension, and finally a wider fixing clamping end on the outer side.

5. The method for preparing weld samples for slow strain rate tensile testing according to claim 1, characterized in that, In step S4, a centering clamp is used to ensure that the axial direction of the micro-stretched sample coincides with the stretching axis of the macro-clamping end, with an eccentricity of less than 5 μm.

6. The method for preparing weld samples for slow strain rate tensile testing according to claim 1, characterized in that, The material of the macroscopic clamping end is a metal material with a coefficient of thermal expansion similar to that of the welding base material, in order to reduce the additional stress exerted on the sample by ambient temperature fluctuations.

7. The method for preparing weld samples for slow strain rate tensile testing according to claim 1, characterized in that, The centering fixture includes a drive motor, a rotating plate, a first crank, a second crank, a first sliding plate, and a second sliding plate. The output end of the drive motor is connected to the middle of the rotating plate. The first crank and the second crank are respectively hinged to the two ends of the rotating plate. The first crank is hinged to the middle of the first sliding plate, and the second crank is hinged to the middle of the second sliding plate. The other side of the first sliding plate has a first centering plate, and the other side of the second sliding plate has a second centering plate.

8. The method for preparing weld samples for slow strain rate tensile testing according to claim 1, characterized in that, It also includes a frame, with the drive motor disposed on one side of the back of the frame, and the first centering plate and the second centering plate disposed on one side of the front of the frame.

9. The method for preparing weld samples for slow strain rate tensile testing according to claim 1, characterized in that, The frame has a slide rail, and the first sliding plate and the second sliding plate cooperate with the slide rail to slide.

10. The method for preparing weld samples for slow strain rate tensile testing according to claim 1, characterized in that, It also includes a guide structure, which includes a guide roller assembly. The side of the frame is connected to and fixed with the roller assembly frame of the guide rollers via a connecting piece. The first centering plate and the second centering plate are located outside the guide roller assembly.

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