Device and method for testing random vibration fatigue of welded round pipe fitting

Abstract

The invention discloses a random vibration fatigue test device and method for welded round pipe fittings. Single-axis and multi-axis random vibration tests are performed on a plurality of test pieces by using the welded round pipe fittings with different punching schemes; the fatigue dangerous part of the test piece has different stress response states by adjusting the counterweight condition and the frequency range and the power spectral density value of the random vibration basic acceleration excitation; when a multi-axis random vibration test is carried out, the assembly position of the counterweight and the counterweight are adjusted, so that a fatigue dangerous part of a test piece structure generates multi-axis random stress response states with different non-proportional degrees under an excitation load. Compared with the prior art, the method has the advantages that single-axis and multi-axis fatigue tests can be carried out on the welded round pipe fitting, the load form is simple, stress response analysis is convenient and easy to understand, and a test basis can be provided for research of a single-axis and multi-axis fatigue life analysis method of an engineering structure, especially a round pipe welding structure under the random vibration load.

Description

Technical Field

[0001] The invention relates to the technical field of fatigue fracture, and in particular to a random vibration fatigue test device and method for welded round pipes. Background Art

[0002] Welded structures are widely used in modern engineering, especially in aerospace, automobile manufacturing, construction and bridge construction, and they are often subjected to complex dynamic loads and vibrations. Since the 20th century, with the development of welding technology and material science, the use of welded round pipe fittings has also increased, evolving from simple structures to welded parts with a variety of complex structures. These welded parts have become the first choice for many high-strength applications due to their superior load-bearing capacity and high structural strength.

[0003] Many welded parts in engineering structures are in service under complex load conditions, and fatigue failure usually occurs at the welds of structural parts due to the influence of random vibration loads. In the early days, fatigue tests on welded parts mainly used static load tests, ignoring the influence of random vibration in actual working conditions. Although this test method can evaluate the basic strength of welded parts to a certain extent, it cannot fully reflect the fatigue damage that may occur in dynamic environments. In addition, with the development of science and technology, vibration fatigue test technology has gradually been proposed, and dynamic load simulation and testing of welded parts are carried out through test devices, which mainly focuses on simplified uniaxial vibration modes and cannot fully represent the multi-directional and multi-frequency random vibration of welded parts in actual working conditions. Since the fatigue research of welded structures under random vibration is still in its infancy, there is little research on structural vibration fatigue tests, especially random vibration fatigue tests of welded structures. Therefore, conducting vibration fatigue tests on welded structures is of great significance for studying the fatigue failure mode and fatigue life analysis methods of different stress states at the welds of welded parts under vibration loads.

[0004] Existing random vibration fatigue test devices mostly use electric vibration tables or pneumatic exciters to perform tests by simulating random vibrations within a specific frequency range. Although these devices can simulate vibration environments to a certain extent, they can usually only perform random vibration tests in a single direction and lack the ability to effectively simulate multi-axis vibrations, which limits the applicability of the test results. This will inevitably lead to inaccurate and unreliable data for fatigue assessment of complex structures.

[0005] In recent years, some scholars have begun to conduct random vibration tests on welded structures. However, the test objects are mostly complex structures or products in actual engineering. Due to the volume and cost of the test objects, only a single small number of tests can be carried out, resulting in inaccurate data and lack of reliability. When conducting design vibration tests on simple welded structures, the test pieces are mostly flat pieces, and there is a lack of random vibration fatigue tests on welded circular pipes that are common in the fields of aerospace and automobile manufacturing. Therefore, there is an urgent need to develop a design method for random vibration fatigue testing equipment for welded circular pipes. This invention can take into account the vibration characteristics of the test piece structure itself, the determination of external excitation loads, the types of random vibration tests, and the analysis of random vibration responses. It has good academic research value and engineering application prospects. Summary of the invention

[0006] In view of the deficiencies and defects involved in the above-mentioned background technology, the purpose of the present invention is to provide a random vibration fatigue test device and method for welded circular pipes, which can perform random vibration fatigue tests on multiple test pieces at the same time, and perform uniaxial and multi-axial random vibration tests on the same welded circular pipes under uniaxial external excitation conditions. In addition, when performing multi-axis random vibration tests, the ratio of the root mean square values ​​of the positive tensile stress and the circumferential shear stress at the weld can be changed by changing the counterweight position and the counterweight situation.

[0007] In order to solve the above-mentioned technical problems, the present invention adopts the following technical scheme: a random vibration fatigue testing device for welded round tubes, comprising a perforated welded round tube test piece, a support, a fixture, a counterweight module and a plug; during the test, the support is fixedly connected to the vibration table, one end of the perforated welded round tube test piece is fixed to the support by a fixed end fixture in the fixture, and the counterweight module is fixed to the other end of the perforated welded round tube test piece by the counterweight end fixture; the plug is inserted into the perforated welded round tube test piece.

[0008] The perforated welded round tube test piece is a hollow round tube with openings at both ends; the weld is used as a dividing line, and through holes for installation with a fixed end fixture and a counterweight end fixture are respectively provided at both ends.

[0009] The perforated welded round tube test piece is divided into a uniaxial random vibration test piece and a multiaxial random vibration test piece. The central axes of the clamping end circular hole and the counterweight end circular hole on the side wall of the multiaxial random vibration test piece are perpendicular to each other.

[0010] The fixture includes a fixed end fixture and a counterweight end fixture. Both the fixed end fixture and the counterweight end fixture include two upper and lower rectangular structures, and one side is provided with a concave arc surface that matches the outer cylindrical surface of the punched welded circular tube test piece, and is also provided with a through hole for fixing the punched welded circular tube test piece.

[0011] The plug includes a fixed end plug and a counterweight end plug, which are respectively installed at the fixed end and the counterweight end of the punched welded round tube test piece to prevent the punched welded round tube test piece from being deformed.

[0012] The fixed end plug and the counterweight end plug are bullet-shaped, and have a clearance fit with the inner diameter of the thin-walled round tube test piece. A through hole for positioning and fixing is provided on the side wall of the fixed end plug, and a through hole for positioning and fixing is provided on the side wall of the counterweight end plug.

[0013] A test method for a random vibration fatigue test device for welded round pipes, the specific steps are:

[0014] Step 1, select the test type to be conducted and use the corresponding welded round pipe. When conducting a multi-axis vibration fatigue test, install the counterweight in one of the three through holes at the counterweight end of the round pipe according to the experimental requirements, and adjust the counterweight block;

[0015] Step 2: Pre-test before the experiment;

[0016] Step 2.1, establish a finite element model of the random vibration fatigue test device for welded round pipes, perform structural modal analysis, and set the frequency range of the basic acceleration excitation according to the first-order natural frequency of the structure;

[0017] Step 2.2, set the power spectrum density of the basic excitation acceleration load and perform random vibration analysis of the structure;

[0018] Step 2.3, the acceleration power spectrum density curve obtained by random vibration analysis, if the frequency at the peak of the curve is included in the set frequency range of the basic acceleration excitation, it means that the vibration characteristics of the random vibration fatigue test device system meet the conditions, and execute step 3, otherwise jump to step 2.2;

[0019] Step 3: Input the ideal acceleration power spectrum density curve obtained in step 2 into the test vibration table, make a random vibration fatigue test device for welded round tubes according to the current thin-walled welded round tube test piece type and counterweight conditions, and conduct a random vibration fatigue test. At the same time, the sensor on the vibration table measures the actual output basic excitation acceleration load power spectrum density of the vibration table.

[0020] Step 4: Perform structural random vibration analysis on the model on a computer according to the power spectrum density of the basic excitation acceleration load actually output by the vibration table in the random vibration fatigue test, and obtain the response acceleration power spectrum density curve, stress, strain and other power spectrum density data, and compare them with the data obtained in the actual test.

[0021] Compared with the prior art, the present invention adopts the above technical solution and has the following technical effects:

[0022] 1. It can make welded round pipes be subjected to uniaxial and multi-axial random vibration tests under uniaxial foundation excitation load;

[0023] 2. It can perform random vibration tests on multiple test pieces at the same time, greatly saving test costs and time;

[0024] 3. The multi-axis random vibration load condition can have different non-proportional degrees by changing the type of test piece, changing the position of the counterweight, adjusting the counterweight condition and the excitation load spectrum, and provide test data for the study of multi-axis random vibration fatigue life analysis;

[0025] 4. Reduce the equipment requirements for random vibration fatigue testing of welded structures, and simplify the characterization method and evaluation criteria of external excitation loads;

[0026] 5. Easy to understand and operate, and it is universal for random vibration fatigue test research of round pipes made of different materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 It is a schematic diagram of a uniaxial random vibration scheme of a random vibration fatigue test device for welded round pipes of the present invention;

[0028] Figure 2 Schematic diagrams of multi-axis random vibration schemes of three random vibration fatigue test devices for welded round pipes of the present invention; wherein (a) is multi-axis random vibration scheme 1 of the random vibration fatigue test device, (b) is multi-axis random vibration scheme 2 of the random vibration fatigue test device, and (c) is multi-axis random vibration scheme 3 of the random vibration fatigue test device;

[0029] Figure 3 Schematic diagram of the structure of the perforated welded round tube test piece 1, (a) is the schematic diagram of the structure of the uniaxial random vibration test piece Figure 1 (b) is a schematic diagram of the uniaxial random vibration test piece structure Figure 2 , (c) is a schematic diagram of the structure of the multi-axis random vibration test piece Figure 1 , (d) is a schematic diagram of the structure of the multi-axis random vibration test piece Figure 2 ;

[0030] Figure 4 It is a schematic diagram of the three-dimensional structure of the support 2 in the present invention;

[0031] Figure 5 Schematic diagram of the fixture structure, wherein (a) is a schematic diagram of the structure of the fixed end fixture 3-1, and (b) is a schematic diagram of the structure of the counterweight end fixture 3-2;

[0032] Figure 6 Schematic diagram of the plug structure, where (a) is a schematic diagram of the structure of the fixed end plug 5-1, and (b) is a schematic diagram of the structure of the counterweight end plug 5-2;

[0033] Figure 7 It is a schematic diagram of the method for using the plug in the present invention.

[0034] In the figure, 1-punched welded round tube test piece, 2-support, 3-fixture, 4-counterweight module, 5-plug. DETAILED DESCRIPTION

[0035] In order to further explain the technical solution of the present invention in detail below with reference to the accompanying drawings:

[0036] The present invention can be implemented in many different forms and should not be considered to be limited to the embodiments described herein. On the contrary, these embodiments are provided to make this disclosure thorough and complete, and will fully express the scope of the present invention to those skilled in the art. In the accompanying drawings, components are enlarged for clarity.

[0037] A random vibration fatigue test device for welded round tubes comprises a perforated welded round tube test piece 1, a support 2, a fixture 3, a counterweight module 4, and a plug 5; during the test, one end of the perforated welded round tube test piece 1 is fixed to the support 2 by a fixed end fixture 3-1 in the fixture 3, and the counterweight module 4 is fixed to the other end of the perforated welded round tube test piece 1 by a counterweight end fixture 3-2; the plug 5 is inserted into the perforated welded round tube test piece 1.

[0038] like Figure 3 As shown, the perforated welded round tube test piece 1 is divided into a uniaxial random vibration test piece and a multiaxial random vibration test piece, both of which are hollow round tubes with openings at both ends; the uniaxial random vibration test piece is provided with three circular holes with coplanar and parallel central axes on its side wall; the multiaxial random vibration test piece is provided with five circular holes with coplanar and parallel central axes on its side wall, two of which are provided at the clamping end and three at the counterweight end, and the central axes of the circular holes at the clamping end and the circular holes at the counterweight end are perpendicular to each other (the central axis is 90°);

[0039] The support 2 is in an I-shape, and a plurality of through holes for fixing the fixture 3 are provided at the upper end thereof; two through holes for fixing to the vibration table are provided at the lower end of the support 2;

[0040] The clamp 3 includes a fixed end clamp 3-1 and a counterweight end clamp 3-2. The fixed end clamp 3-1 and the counterweight end clamp 3-2 both include two upper and lower rectangular structures, and one side is provided with a concave arc surface that matches the outer cylindrical surface of the punched welded circular tube test piece 1, and is also provided with a through hole for fixing the punched welded circular tube test piece 1; the fixed end clamp 3-1 and the counterweight end clamp 3-2 only differ in size.

[0041] The counterweight module 4 includes a plurality of counterweight blocks of different weights; the counterweight blocks may use a plurality of nuts or washers so as to fix the counterweight blocks on the welded round pipes by bolts.

[0042] The plug 5 includes a fixed end plug 5-1 and a counterweight end plug 5-2, which are respectively installed on the fixed end and the counterweight end of the perforated welded round tube test piece 1 to prevent deformation of the perforated welded round tube test piece 1; the two plugs are bullet-shaped and have a clearance fit with the inner diameter of the thin-walled round tube test piece, and the side wall of the fixed end plug 5-1 is provided with two through holes for positioning and fixing, and the side wall of the counterweight end plug 5-2 is provided with a through hole for positioning and fixing.

[0043] like Figure 1 , Figure 2 As shown, the random vibration fatigue test device for welded round pipes includes a perforated welded round pipe test piece 1, a support 2, a fixture 3, a counterweight block module 4 and a plug 5, wherein the geometric dimensions of the perforated welded round pipe test piece 1, the geometric dimensions of the fixture 3 and the assembly position of the counterweight block are adjustable design variables. In the multi-axis design vibration test, the diameter and wall thickness of the round pipe will affect the multi-axis non-proportional degree of the stress response of the fatigue risk part of the structure.

[0044] like Figure 3 As shown, the perforated welded round tube test piece 1 is a test piece obtained by punching a hole in a direction perpendicular to the axis of the round tube and welding it. It is made of materials whose random vibration fatigue performance of the welded structure is to be studied and evaluated, and is the main part of the test piece in the random vibration fatigue test of the welded structure. Compared with welded test pieces of other shapes, the round tube has a symmetrical geometric shape, which makes it easy to analyze and calculate the various stresses on the dangerous parts when subjected to force and vibration.

[0045] The support 2 and the fixed end fixture are the fixed parts of the random vibration fatigue test device for welded round pipes. Figure 5 As shown in (a), one side of the fixed end fixture 3-1 is cut to fit the outer surface shape of the welded round tube test machine, and two through holes are processed along the axis on the long and wide surfaces. The holes on the side of the punched welded round tube cylinder are connected to a pair of holes in the fixed end fixture 3-1 by bolts. In order to ensure the durability of the counterweight end fixture 3-2, it is recommended to use stainless steel for processing. Figure 4As shown, the support 2 is an I-shaped punched part, and the two through holes on the plane side of the fixed end fixture 3-1 are fixedly connected with the two through holes on the upper surface of the support 2 by bolts, and the holes on the lower end surface of the support 2 distributed at both ends of the support beam are fixedly connected with the threaded holes on the vibration table by bolts, so as to load the basic acceleration random vibration excitation generated by the vibration table onto the welded round tube test piece. In order to ensure that the support 2 has sufficient strength and rigidity, and considering the storage performance, it is recommended to use stainless steel for manufacturing and processing. The welded round tube is divided into two parts with the weld as the boundary, and one end with two through holes is called the fixed end, and the other end is called the counterweight end; most of the fixed end of the welded round tube is covered by the fixture 3, and the distance from the edge of the fixture 3 to the weld is small. When conducting the test, the parts subject to greater stress are the weld and the extremely small areas on both sides of the weld, and the strength of the weld is lower than the strength of the accessory base material, so fatigue failure will occur at the weld.

[0046] The counterweight end fixture 3-2 and the counterweight block module 4 together constitute the counterweight part of the random vibration fatigue test device for welded round pipes. Figure 5 As shown in (b), the counterweight end fixture 3-2 is made by cutting and punching a rectangular parent material, one end of which is cut to fit the outer surface shape of the welded round tube testing machine, and the hole on the side of the welded round tube is connected to a pair of holes of the counterweight end fixture 3-2 by bolts; in order to ensure the durability of the counterweight end fixture 3-2, it is recommended to use stainless steel for processing. The counterweight block can be composed of standard nuts and washers, and the position and mass of the counterweight can be changed by changing the number of nuts and washers.

[0047] Random vibration fatigue test scheme for welded round pipes Figure 1 , Figure 2 As shown, four test pieces can be fixed on a support 2 at the same time, that is, four test pieces can be tested at the same time. This scheme can describe the fatigue life dispersion under the same random vibration load condition; the direction of the external random vibration load is the vertical direction, and the stress response of the fatigue-hazardous parts of the structure can be changed by changing the counterweight mass and the power spectral density function of the external vibration load, thereby making the time for fatigue failure of the test piece under the vibration load different.

[0048] Figure 1 This is a uniaxial random vibration fatigue test scheme for welded circular pipes. In order to avoid interference between the counterweights of different test pieces during vibration, the counterweights are designed to be matched at the top and bottom. The counterweights at the top or bottom will not affect the consistency of the load-bearing conditions at the weld, that is, from the perspective of force analysis, the statistical characteristics of the stress state of the welded circular pipe when the counterweights are at the top or bottom are consistent. At this time, the stress response of the dangerous part of the weld is provided by a principal stress.

[0049] Figure 2This is a multi-axial random vibration fatigue test scheme for welded round pipes. At this time, the main stresses of the stress response of the dangerous parts of the weld are the hoop shear stress and the positive tensile stress. By changing the position and weight of the counterweight, the ratio of the root mean square values ​​of the above two stresses in the dangerous parts of the weld can be changed, thereby providing a variety of data support for multi-axial fatigue life analysis. Figure 2 From (a) to (c), as the position of the counterweight changes, the ratio of the RMS value of the normal tensile stress to the hoop shear stress decreases one by one.

[0050] The use of the plug 5 is as follows Figure 7 As shown, thin-walled round tubes are prone to deformation when clamped. The plug 5 can provide internal support to help maintain the shape of the tube and prevent deformation caused by excessive clamping force during installation and testing. The plug can enhance the rigidity of the clamping point and provide a more uniform clamping force, thereby improving the clamping stability and enabling the excitation load to be better transmitted to the round tube. Figure 6 As shown, the two types of plugs are bullet-shaped, with an internal threaded hole at the bottom of the plug. The plug is extended to the corresponding position of the round tube by a bolt that meets the model. The hole on the cylindrical side of the plug and the hole on the side of the round tube are positioned and fixed by bolts. The bolts simultaneously serve as a fixing counterweight and a positioning pin.

[0051] The present invention also discloses a test method of a random vibration fatigue test device for welded round pipes, comprising the following steps:

[0052] Step 1, select the test type (single axis or multi-axis) and use the corresponding welded round pipe. When conducting a multi-axis vibration fatigue test, install the counterweight in one of the three through holes at the counterweight end of the round pipe according to the experimental requirements and adjust the counterweight.

[0053] Step 2: Pre-test before the experiment;

[0054] Step 2.1, establish a finite element model of the random vibration fatigue test device for welded round pipes, perform structural modal analysis, and set the frequency range of the basic acceleration excitation according to the first-order natural frequency of the structure;

[0055] Step 2.2, set the power spectrum density of the basic excitation acceleration load and perform random vibration analysis of the structure;

[0056] Step 2.3, the acceleration power spectrum density curve obtained by random vibration analysis, if the frequency at the peak of the curve is included in the set frequency range of the basic acceleration excitation, it means that the vibration characteristics of the random vibration fatigue test device system meet the conditions, and execute step 3, otherwise jump to step 2.2;

[0057] Step 3: Input the ideal acceleration power spectrum density curve obtained in step 2 into the test vibration table, make a random vibration fatigue test device for welded round tubes according to the current thin-walled welded round tube test piece type and counterweight conditions, and conduct a random vibration fatigue test. At the same time, the sensor on the vibration table measures the actual output basic excitation acceleration load power spectrum density of the vibration table.

[0058] Step 4: Perform structural random vibration analysis on the model on a computer according to the power spectrum density of the basic excitation acceleration load actually output by the vibration table in the random vibration fatigue test. The obtained response acceleration power spectrum density curve, stress, strain and other power spectrum density data are compared with the data obtained in the actual test. If the error is small, the fatigue life prediction can be calculated based on the finite element model; if the error is large, adjust the finite element model until it meets expectations.

[0059] This test device invention can correct the finite element dynamic analysis model by comparing the test measurement results of the acceleration response and the finite element analysis results, ensuring the calculation accuracy of the dynamic response analysis results as the input conditions of the fatigue life analysis module. The vibration fatigue life analysis of welded structures includes two modules, structural dynamic response analysis and vibration fatigue life analysis. The accuracy of the structural dynamic response analysis results is a prerequisite for ensuring the reliability of the vibration fatigue life analysis results. The correction of the finite element dynamic model of the structure provides conditions for studying the fatigue life analysis model of welded structures under random vibration loads.

[0060] The invention of the test device can carry out uniaxial and multiaxial random vibration tests on welded round tube test pieces under the action of uniaxial basic excitation acceleration load. This beneficial effect reduces the requirements for test equipment when carrying out random vibration fatigue tests of different load types on parts of the same material, and achieves the purpose of using one vibration table to carry out multiple random vibration fatigue tests.

[0061] When conducting a multi-axis random vibration test on a welded round pipe, the experimental device of the invention can adjust the multi-axis non-proportional degree of stress response at a dangerous part of the test piece by changing the position of the counterweight, adjust the vibration characteristics of the test device system by changing the counterweight situation, and adjust the vibration mode of the structure excited by changing the frequency range and power spectrum density value of the basic excitation load, thereby being able to comprehensively consider the influence of various stress response states on fatigue life.

[0062] It will be understood by those skilled in the art that, unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as those generally understood by those skilled in the art in the art to which the present invention belongs. It should also be understood that terms such as those defined in common dictionaries should be understood to have meanings consistent with the meanings in the context of the prior art, and will not be interpreted with idealized or overly formal meanings unless defined as herein.

[0063] The specific implementation methods described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific implementation method of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A random vibration fatigue test device for welded round pipes, characterized in that: A perforated welded round tube test piece (1), a support (2), a fixture (3), a counterweight module (4), and a plug (5); during the test, the support (2) is fixedly connected to the vibration table, one end of the perforated welded round tube test piece (1) is fixed to the support (2) via a fixed end fixture (3-1) in the fixture (3), and the counterweight module (4) is fixed to the other end of the perforated welded round tube test piece (1) via a counterweight end fixture (3-2); and the plug (5) is inserted into the perforated welded round tube test piece (1).

2. The random vibration fatigue testing device for welded round pipes according to claim 1 is characterized in that: The perforated welded circular tube test piece (1) is a hollow circular tube with openings at both ends; the weld is used as a dividing line, and through holes for installation with a fixed end fixture (3-1) and a counterweight end fixture (3-2) are respectively arranged at both ends.

3. The random vibration fatigue testing device for welded round pipes according to claim 2 is characterized in that: The perforated welded round tube test piece (1) is divided into a uniaxial random vibration test piece and a multiaxial random vibration test piece. The central axes of the clamping end circular hole and the counterweight end circular hole on the side wall of the multiaxial random vibration test piece are perpendicular to each other.

4. The random vibration fatigue testing device for welded round pipes according to claim 1 is characterized in that: The fixture (3) comprises a fixed end fixture (3-1) and a counterweight end fixture (3-2), each of which comprises two upper and lower rectangular parallelepiped structures, and one side of the fixture is provided with a concave arc surface that matches the outer cylindrical surface of the punched welded round tube test piece (1), and a through hole for fixing the punched welded round tube test piece (1).

5. The random vibration fatigue testing device for welded round pipes according to claim 1 is characterized in that: The plug (5) comprises a fixed end plug (5-1) and a counterweight end plug (5-2), which are respectively installed at the fixed end and the counterweight end of the punched welded round tube test piece (1) to prevent deformation of the punched welded round tube test piece (1).

6. The random vibration fatigue testing device for welded round pipes according to claim 4 is characterized in that: The fixed end plug (5-1) and the counterweight end plug (5-2) are bullet-shaped and are clearance-matched with the inner diameter of the thin-walled round tube test piece. A through hole for positioning and fixing is provided on the side wall of the fixed end plug (5-1), and a through hole for positioning and fixing is provided on the side wall of the counterweight end plug (5-2).

7. A test method for a random vibration fatigue test device for welded round pipes, characterized in that: The specific steps are: Step 1, select the test type to be conducted and use the corresponding welded round pipe. When conducting a multi-axis vibration fatigue test, install the counterweight in one of the three through holes at the counterweight end of the round pipe according to the experimental requirements, and adjust the counterweight block; Step 2: Pre-test before the experiment; Step 2.1, establish a finite element model of the random vibration fatigue test device for welded round pipes, perform structural modal analysis, and set the frequency range of the basic acceleration excitation according to the first-order natural frequency of the structure; Step 2.2, set the power spectrum density of the basic excitation acceleration load and perform random vibration analysis of the structure; Step 2.3, the acceleration power spectrum density curve obtained by random vibration analysis, if the frequency at the peak of the curve is included in the set frequency range of the basic acceleration excitation, it means that the vibration characteristics of the random vibration fatigue test device system meet the conditions, and execute step 3, otherwise jump to step 2.2; Step 3, input the ideal acceleration power spectrum density curve obtained in step 2 into the test vibration table, make a random vibration fatigue test device for welded round tubes according to the current thin-walled welded round tube test piece type and counterweight conditions, and conduct a random vibration fatigue test. At the same time, the sensor on the vibration table measures the actual output basic excitation acceleration load power spectrum density of the vibration table; Step 4: Perform structural random vibration analysis on the model on a computer according to the power spectrum density of the basic excitation acceleration load actually output by the vibration table in the random vibration fatigue test, and obtain the response acceleration power spectrum density curve, stress, strain and other power spectrum density data, and compare them with the data obtained in the actual test.

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