Welded joint raw plate thickness sample and welded joint toughness weak area determination method

Abstract

The invention provides a welding joint raw plate thickness sample and a welding joint toughness weak area determination method, which are used for determining the toughness weak area of a thick plate welding joint, the sample is provided with a group of gap groups, the gap groups comprise a plurality of gaps, the depths of the gaps are the same, and the gap groups are arranged on a welding seam and an adjacent area thereof. The method can be used for accurately, quickly and economically measuring the weak toughness area of the welded joint through the thick sample of the original plate of the welded joint.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of testing the breaking resistance of metal materials, in particular to a welded joint original plate thickness sample and a method for determining the weak toughness area of a welded joint. BACKGROUND

[0002] Welding is a manufacturing process that connects two or more workpieces to form a welded joint, and plays an extremely important role in modern industry. If the performance of the welded joint is insufficient, it may lead to structural failure, and even cause major accidents. Therefore, by analyzing the performance of the welded joint and finding the weak toughness area of the welded joint, potential dangers can be found in advance, and by taking appropriate preventive measures for the weak area, accidents can be avoided.

[0003] There are multiple angles for the research on the performance of the welded joint, such as fatigue, corrosion resistance, toughness, etc. Among them, toughness refers to the energy absorption capacity of a material before it breaks, which is an important indicator for measuring the crack propagation resistance and breaking performance of a material, and the toughness of the welded joint directly determines the safety of the structure. At present, the research methods for the toughness of the welded joint all use notched samples, such as Charpy impact test, dynamic tear test, plane strain fracture toughness (KIC) test, crack tip opening displacement (CTOD) test, J integral test and original plate thickness wide plate tensile deep notch test, etc. Among them, the Charpy impact test and the dynamic tear test have lower cost, and the weak area of the joint toughness can be accurately found by changing the notch processing position. However, the sample size is limited by standard specifications and equipment conditions, and when testing the thick plate welded joint, the thick plate needs to be thinned, so it is difficult to reflect the true performance level of the original plate thickness welded joint, and the accurate position of the weak area of the entire welded joint cannot be reflected. Although the plane strain fracture toughness (KIC) test, the crack tip opening displacement (CTOD) test, the J integral test and the original plate thickness wide plate tensile deep notch test can conduct original plate thickness test, but in order to determine the weak area of the welded joint through the test itself, a large number of tests are required, which is high in cost.

[0004] The Chinese patent CN112945769A discloses a method for evaluating a weak micro-zone of low-cycle fatigue crack propagation performance of a welded joint. An alternating load is applied to a standard compact tension specimen after processing to preform a fatigue crack. A low-cycle fatigue crack propagation test is performed under a constant stress intensity factor at the fatigue crack tip, and a curve of fatigue crack propagation rate versus fatigue crack length is drawn. The crack length is corresponded to the micro-zone to obtain a correspondence relationship between the crack length and the micro-zone, and a distribution curve of fatigue crack propagation rate of the weld zone, the heat-affected zone and the base material zone in the welded joint is obtained, so as to evaluate the weak micro-zone of low-cycle fatigue crack propagation performance of the welded joint. The evaluation method needs to perform thickness reduction processing on the front and rear surfaces of the standard compact tension specimen, and it is difficult to reflect the real performance level of the original plate thickness welded joint. Meanwhile, the evaluation steps are also relatively complex.

[0005] Therefore, in order to accurately, quickly and economically determine the weak zone of the welded joint, a welded joint original plate thickness specimen and a method for determining the weak zone of the welded joint are needed. SUMMARY

[0006] The present application aims to provide a welded joint original plate thickness specimen and a method for determining the weak zone of the welded joint, which can accurately, quickly and economically determine the weak zone of the welded joint through the welded joint original plate thickness specimen.

[0007] To achieve the above-mentioned purpose, the present application provides a welded joint original plate thickness specimen and a method for determining the weak zone of the welded joint. The technical scheme of the present application is as follows:

[0008] A welded joint original plate thickness specimen is used to determine the weak zone of the welded joint of a thick plate. A group of notches is arranged on the specimen, and the group of notches comprises a plurality of notches with the same notch depth. The group of notches is arranged in the weld and the adjacent area thereof.

[0009] Further, the notch width is less than 0.2mm, and the interval between the notches is 1-3mm.

[0010] Further, the thickness of the specimen is the same as that of the original plate.

[0011] Further, the range of the group of notches is from the center of the weld to the base material.

[0012] A method for determining the weak zone of the welded joint uses the above-mentioned welded joint original plate thickness specimen to determine the weak zone of the welded joint, comprising the following steps:

[0013] S1, preparing the specimen;

[0014] S2, determining the loading mode and the loading position;

[0015] S3, performing the loading test;

[0016] S4, determining the weak area of the joint.

[0017] Further, in S2, the loading mode is four-point bending loading.

[0018] Further, in S2, the method for determining the loading position is: by adjusting the distance between the lower support points and the position of the sample, ensuring that the group of notches is located in the central position between the upper loading points; the group of notches is located near the side of the lower support point, so that the opening direction of the group of notches is consistent with the force direction.

[0019] Further, in S3, the "force-time" curve is collected in real time, the curve change is observed, the force value is found to suddenly decrease, and the test is immediately stopped.

[0020] Further, in S3, the test is repeated at least 5 times.

[0021] Further, in S4, the cracking position of the sample is checked, and the weak area of the welded joint is determined by the cracking position.

[0022] Compared with the prior art, the welded joint original plate thickness sample and the welded joint toughness weak area determination method have the following advantages:

[0023] 1. The present application provides a welded joint original plate thickness sample, the thickness of the sample is the same as that of the original plate, which can reflect the true performance level of the welded joint original plate thickness and the accurate position of the weak area of the entire welded joint.

[0024] 2. The present application provides a welded joint toughness weak area determination method, which gives the steps and result determination method. The test method of the present application has the advantages of simple test, low cost, high test efficiency and high test precision. BRIEF DESCRIPTION OF DRAWINGS

[0025] Figure 1 The figure is a schematic diagram of the welded joint original plate thickness sample and the loading mode according to embodiment 1 of the present application.

[0026] Figure 2 The figure is a schematic diagram of the force-time curve according to embodiment 1 of the present application.

[0027] Figure 3 The figure is a test result photo of the present application.

[0028] Explanation of reference signs:

[0029] 1, base material; 2, weld; 3, wire cutting notch; 4, crack initiation point. DETAILED DESCRIPTION

[0030] In order to make the objects, technical solutions and advantages of the present application clearer, the following further describes the present application with reference to the accompanying drawings and embodiments. It should be understood that the described embodiments are part of the embodiments of the present application, rather than all the embodiments. The specific embodiments described herein are only used to explain the present application, and are not used to limit the present application. It should be noted that the embodiments in the present application and the features in the embodiments can be combined with each other without conflict.

[0031] A kind of original plate thickness sample of welded joint, for determining the toughness weak area of thick plate welded joint. A group of notches are provided on the sample, the notch group includes multiple notches, the notch depth is the same, and the notch group is arranged in the weld and its adjacent area. The stress state of the notch tip is made to be a plane strain state by prenotching, so that the tip is more prone to cracking. In the plane strain state, the strain of the material in the thickness direction is close to zero, and the stress is mainly concentrated in the plane, which is beneficial to the stable analysis of crack propagation. The notch group is arranged in the weld and its adjacent area to specifically analyze the crack in the welded joint area. The notch group is arranged in the weld and its adjacent area, which can cover the failure caused by the stress change of the continuous transition area from the weld center to the heat affected zone to the base material, so that the conditions of multiple areas are presented in one test. When the same stress (bending moment) is applied to each notch, the tip of the weakest notch will first appear a crack. Therefore, the tester can determine where the toughness weak area of the welded joint is by judging the position of the crack. Compared with the common single-notch different-area examination mode, the present application is simpler and more efficient.

[0032] The depth of each notch of the notch group is the same, which facilitates the comparison of the fracture toughness of different areas.

[0033] Preferably, the range of the notch group is from the weld center to the base material. So that multiple notches can correspond to different areas of the welded joint respectively: weld, heat affected zone and base material, and then take into account the examination of different areas.

[0034] The sample is an original plate thickness welded joint sample, i.e. the thickness of the sample is the same as the original plate. The original plate thickness welded joint sample is used to truly reflect the overall performance of the welded joint and close to the engineering practice.

[0035] A wire cutting is used to process a notch group with a width less than 0.2 mm, and the spacing between the notches is 1-3 mm. The notch width is small to simulate the initial state of the crack or defect. The spacing is moderate to avoid stress field interference between the notches.

[0036] Whether to remove the weld reinforcement is determined according to the structure type, stress state, detection standard and use environment.

[0037] For example, the thickness of the sample is the same as the original plate, and the sample is an original plate thickness welded joint sample. Figure 1The figure shows that t is the original plate thickness. Preferably, the sample size and notch setting relationship is as shown in Table 1.

[0038] Table 1 Sample size and notch setting

[0039]

[0040] A method for determining the weak area of a welded joint, comprising the following steps:

[0041] S1, preparing a sample.

[0042] A welded joint sample is made of the same material as the original plate. The thickness of the welded joint sample is the same as the original plate. The sample is processed according to the size set in Table 1, and the number of samples is at least 5.

[0043] S2, determining the loading mode and loading position.

[0044] The loading mode is four-point bending loading, so that the notch tip bears the same bending moment. The support rollers are supported at the lower ends of the sample, and the pressure heads are symmetrically arranged above the middle of the sample. The distance between the two support points (support rollers) at the ends of the sample is the support span, and the distance between the two loading points (pressure heads) is the loading span. Preferably, the loading span is 1 / 3~1 / 2 of the support span.

[0045] By adjusting the distance between the lower support points (support rollers) and the position of the sample, it is ensured that the group of notches is located at the central position between the upper loading points (pressure heads). The group of notches is located near the lower support points (support rollers) on one side, so that the opening direction of the group of notches is consistent with the force direction. Preferably, the support span is 8t, and the loading span is 4t. Preferably, the lower support points and the upper loading points are symmetrically arranged about the center of the weld.

[0046] The loading schematic diagram of the test is shown in Figure 1 , wherein P is the loading force. The loading speed can be set according to the capacity of the testing machine and the requirements of the test.

[0047] S3, loading test.

[0048] During the loading process, the force sensor is used to collect the "force-time" curve in real time, the curve change is observed, and when the force value suddenly decreases, it is found that the pre-made notch cracks, and the test is immediately stopped. In order to ensure the accuracy of the test results, the number of tests is at least 5 times.

[0049] S4, determining the weak area of the joint.

[0050] The cracking position of the sample is checked, and the weak area of the welded joint is determined by the cracking position.

[0051] Example 1

[0052] The embodiment provides a method for determining a weak area of a welded joint, and comprises the following steps.

[0053] S1, preparing a sample.

[0054] FH40 steel with a thickness of 20 mm is selected, K-type bevels are used for welding, and the sample is processed according to Table 1, and the number of samples is 5. The length of the sample is 200 mm, the height is 40 mm, the notch depth is 15 mm, the number of notches is 21, and the notch spacing distance is 1 mm. The actual size of the sample is shown in Table 2.

[0055] Table 2 Actual sample size

[0056]

[0057] S2, determining the loading mode and loading position.

[0058] The sample is installed on the testing machine, the support rollers are supported below the two ends of the sample, and the pressure head is symmetrically arranged above the middle part of the sample. By adjusting the distance between the support rollers and the sample position, it is ensured that the notch group is located in the middle position between the support rollers and the pressure head. The notch group is located near the support roller, so that the opening direction of the notch group is consistent with the force direction. The support span is 160 mm, and the loading span is 80 mm.

[0059] S3, loading test.

[0060] The test is carried out by setting the loading rate to 2 mm / s, and the force value change is observed in real time. It is found that the force value suddenly decreases, as shown in Figure 2 , immediately stop loading, and take down the sample. The sudden decrease in force value indicates that the sample has cracked, and the change point is the cracking point 4.

[0061] Under the same conditions, the same test is repeated on 5 samples.

[0062] S4, determining the weak area of the joint.

[0063] The position of the sample notch cracking is observed, and the results are shown in Table 3.

[0064] Table 3 Notch cracking position of the sample of the original plate thickness welded joint

[0065]

[0066] In order to verify the effectiveness of the method, the Charpy impact test of the welded joint is carried out according to the standard GB / T229-2020 “Metallic materials Charpy pendulum impact test method”, and the test results are shown in Table 4.

[0067] Table 4 Charpy impact test results

[0068]

[0069] The test results of table 3 and table 4 both show that the toughness weak area of the 20mm thick FH40 steel welded joint is located in the center of the weld, the conclusions are consistent, and the correctness and feasibility of the present application are further verified. At the same time, the present application achieves the effect of nine times of charpy impact test through five times of test, which not only improves the test efficiency, but also reduces the loss of test materials.

[0070] The present application designs a kind of original plate thick welded joint notch sample from the angle of determining the weak area of the use performance of original plate thick welded joint, clearly defines the form and specific size of the sample, gives the loading mode and the judging method of test result effectiveness. The test method proposed in the present application has the advantages of simple test, low cost, high test efficiency and high test precision.

[0071] Although the present application is disclosed as above, the present application is not limited thereto. Any person skilled in the art can make various changes and modifications without departing from the spirit and scope of the present application, therefore the protection scope of the present application should be subject to the range defined by the claims.

Claims

1. A sample of the original plate thickness of a welded joint, characterized in that, The specimen is used to determine the weak toughness area of ​​the welded joint of thick plate. The specimen is provided with a group of notches, which contains multiple notches of the same depth. The notch group is located in the weld and its adjacent area.

2. The sample according to claim 1, characterized in that, The notch width is less than 0.2mm, and the notches are spaced 1~3mm apart.

3. The sample according to claim 1, characterized in that, The thickness of the sample is the same as that of the original plate.

4. The sample according to claim 1, characterized in that, The range of the notch group extends from the weld center to the base material.

5. A method for determining the toughness weakness zone of a welded joint, characterized in that, The toughness of the weak zone of the welded joint was determined using a sample of the original plate thickness as described in any one of claims 1-4. Includes the following steps: S1, Sample preparation; S2, determine the loading method and loading location; S3, conduct the loading test; S4, determine the weak area of ​​the joint.

6. The determination method according to claim 4, characterized in that, In S2, the loading method is four-point bending loading.

7. The determination method according to claim 6, characterized in that, In S2, the loading position is determined by adjusting the distance between the lower support points and the position of the sample to ensure that the notch group is located in the center between the upper loading points; the notch group is located on the side close to the lower support point so that the opening direction of the notch group is consistent with the direction of the applied force.

8. The determination method according to claim 4, characterized in that, In step S3, the force-time curve is collected in real time, and the changes in the curve are observed. If the force value suddenly drops, the test is stopped immediately.

9. The determination method according to claim 4, characterized in that, In S3, the number of tests is at least 5.

10. The determination method according to claim 4, characterized in that, In step S4, the location of cracks in the sample is checked, and the weak area of ​​the welded joint is determined by the location of the cracks.

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