GB/T2423.43-1995 Environmental testing for electrical and electronic products Part 2: Test methods Requirements and guidelines for the installation of components, equipment and other products in dynamic tests such as impact (Ea), collision (Eb), vibration (Fc and Fd) and steady-state acceleration (Ga)
Some standard content:
GB/T 2423. 43--1995
This standard is equivalent to the International Electrotechnical Commission standard IEC68-2-47 "Environmental testing Part 2: Test methods: Installation requirements and guidelines for components, equipment and other products in dynamic tests such as impact (Ea), collision (Eb), vibration (Fc and Fd) and steady-state acceleration (Ga)" 1982 1st edition.
Appendix A of this standard is the appendix of the standard.
This standard is proposed by the Ministry of Electronics Industry of the People's Republic of China. This standard is under the jurisdiction of the National Technical Committee for Environmental Conditions and Environmental Testing for Electrical and Electronic Products. The main drafting unit of this standard: the Fifth Institute of the Ministry of Electronics. The main drafters of this standard: Xu Yongmei and Wang Shurong. 405
GB/T2423.43—1995
IEC Foreword
1) The formal resolutions or agreements on technical issues formulated by the technical committees of the International Electrotechnical Commission, in which all national committees with special concerns on the issue participate, reflect and express the international consensus on the issue as much as possible. 2) These resolutions or agreements are used internationally in the form of recommended standards and are accepted by the national committees in this sense. 3) In order to promote international unification, the International Electrotechnical Commission hopes that all member countries will adopt the contents of the recommended standards of the International Electrotechnical Commission as their national standards when formulating national standards, as long as the specific conditions of the country permit. Any differences between the recommended standards of the International Electrotechnical Commission and the national standards should be clearly pointed out in the national standards as much as possible. This standard was formulated by the 50A Technical Committee (Shock and Vibration Test) of the International Electrotechnical Commission Technical Committee 50 (Environmental Testing).
The decision to start formulating this standard was discussed at the Munich Conference in 1973. The first draft of this standard was discussed at the Hague Conference in 1975, and the discussion led to the formation of Document 50A (Central Office) 141, which was distributed to national committees in January 1977 for voting according to the "six-month method".
The following national committees voted explicitly in favor of this standard: Australia
Hungary
Spainbzxz.net
United Kingdom
Austria
Belgium
Canada
Turkey
Czechoslovakia
South Africa (Republic of)
1 Purpose
National Standard of the People's Republic of China
Environmental testing for electric and electronic products Part 2:test methods
Mounting of components,equipment and other articlesfor dynamic tests including shock(Ea),bump (Eb),vibration (Fc and Fd) and
steady-state acceleration (Ga) (Eb), vibration (Fc and Fd) and steady-state acceleration (Ga)and guidance
GB/T2423.43--1995
idt IEC68-2-47:1982
The purpose of this standard is to specify standard installation methods for components in dynamic tests such as impact (Ea), collision (Eb), vibration (Fc and Fd) and steady-state acceleration (Ga), and to specify installation requirements for equipment and other products subjected to the above dynamic tests. 2 Introduction
This standard specifies installation requirements for components, equipment and other products (hereinafter referred to as samples) in dynamic tests such as impact (Ea), collision (Eb), vibration (Fc and Fd) and steady-state acceleration (Ga), and provides relevant information. In any case, component-type samples should be installed in accordance with the provisions of the relevant specifications. If the relevant specifications do not specify installation details, they may be installed according to several standardized installation methods specified in this standard. Unless otherwise specified in the relevant specification, the equipment type sample should be installed in its normal installation method. Before the test, the sample should first be divided into component type sample or equipment type sample, and then the corresponding test should be carried out. However, if this is not possible, such as packaged samples, this standard is still applicable, and it is for the entire package rather than the sample inside. The general guidance applies not only to the compiler of the specification, but also to the test engineer. 3 Overview
The relevant specification should state whether the influence of gravity is important. If the influence of gravity is important, the sample should be installed so that the direction of gravity is consistent with the direction of gravity in actual use. Otherwise, the sample can be installed arbitrarily. If the following factors are important to the test results. The relevant specification should specify:
a) The temperature limit of the sample during the test (for example, the temperature increase of the vibration table may not be allowed for some samples); b) The maximum value of the interfering magnetic field that can be applied to the sample and (or) the orientation of the sample relative to the magnetic field (for example, close to the electric vibration table). Approved by the State Administration of Technical Supervision on August 29, 1995, and implemented on August 1, 1996
4 Installation of components
GB/T 2423.43—1995
Components shall be installed in accordance with the installation methods specified in the relevant specifications. If the relevant specifications do not specify, but it is clear from the design, such as the installation method from the structure of the sample itself as shown in Figure 1, then this method should be adopted. If the installation method is not clear from the design, the installation method consistent with the principles shown in Figure 2, Figure 3 or Figure 4 should be selected as much as possible. However, it should be considered whether the purpose of the test is to apply dynamic stress to the leads and (or) to the sample itself, or to determine the internal structural strength of the sample. When the test sample is tested with additional connecting leads, the configuration of these leads should be able to make the applied stress and mass the same as when the sample is used in normal conditions.
In any case, the component should be fixed in a rigid test fixture or directly fastened to the mounting surface of the test bench. 5 Installation of equipment and other products
The sample shall be mechanically fastened to the mounting surface of the test bench directly or with the aid of a rigid test fixture, or mounted as specified in the relevant specification.
When the normal mounting structure of the equipment can be utilized, the relevant specification shall state whether this normal mounting structure should be utilized. The use of any additional brackets and straps shall be avoided. Any connection to the sample, such as cables, conduits, etc., shall be such that the stress or mass applied is the same as the stress to which the sample is subjected when it is in its working position. To achieve this, the cables, conduits, etc. must be fixed to the fixture. Samples used with shock absorbers shall normally be tested with the shock absorbers. If it is difficult to test with suitable shock absorbers, the sample shall be removed from the shock absorber and tested at different test severity levels as specified in the relevant specification. The relevant specification may require additional testing of samples with external shock absorbers removed or locked to determine whether the sample has achieved the minimum acceptable structural strength. In this case, the severity level used shall be given in the relevant specification. 6 Contents to be given in relevant specifications
When the relevant specifications adopt this test, the following contents should be given: a) influence of gravity (Chapter 3);
b) maximum or minimum temperature (Chapter 3); c) maximum interfering magnetic field (Chapter 3);
d) installation of components (Chapter 4);
e) installation of equipment (Chapter 5).
Installation method
GB/T2423.43—1995
Components with obvious mounting methods, such as diodes, electrolytic capacitors, rectifiers, switches, connectors, relays, transformers, high-power transistors Figure 1 Installation example of components with obvious mounting methods 109
Installation method
6mmtimm
2mm ±0. 5 mm
GB/T2423.43-1995
Crystal tubes, integrated circuits, relays and other components whose distance to the fire tool is limited by design
Resistors, capacitors
Resistors, capacitors, inductors, poles wgtw
Resistors, capacitors, inductors, diodes, transistors Note: It is important that the relevant specifications should specify whether the component should be in contact with the mounting surface.
Example of mounting components using only component leads
Mounting method
GB/T2423.43-1995
Tubular components with fragile shells, such as high-power resistors, transistors, diodes
Integrated circuits
Figure 3 Example of mounting components using only the component itself12
Mounting method
GB/T2423.43-1995
Capacitors and relays that must be additionally fixed (such as additional brackets) due to the quality of the components and the severity of the testTransistors mounted on heat sinks
Transformers, coils
Relays
Figure 4 Example of mounting components using the component itself and leadsA1 Components
GB/T2423.43--1995
Appendix A
(Appendix to the standard)
Guidelines
When the purpose of the test is to determine the adaptability of the component to its working environment, the relevant specifications should ensure that the component is installed in a manner that simulates actual use. Particular emphasis should be placed on the fact that components above a certain mass require support during the test as in actual use and this should be specified in the relevant standards. It is important that the mounting method complies with the manufacturer's requirements. If the manufacturer does not make such a requirement, the details given in Figures 1 to 4 may be used.
The mounting method for some components with special shapes, such as discs, balls, bulbs and components requiring special fixing devices, is not shown in the figure. The relevant specifications must give detailed information on the mounting method for these components. If a sample design has several mounting methods, all methods should be considered. It is recommended to use a new component for each test. Regardless of which method is specified or selected, it is important that the component is rigidly fastened to the test fixture or the mounting surface of the test bench. This can be achieved by suitable clamping, welding, embedding or gluing of the component body or the component leads. Fixing the component to a printed circuit board of standard size does not usually give sufficient rigidity and it is impossible to achieve the test requirements with this method. In addition, reproducibility will probably be reduced. However, the use of small printed circuit boards can meet the test requirements as long as its dynamic characteristics are taken into account. When designing fixtures for high impact acceleration tests or high frequency vibration tests, care should be taken that no resonance exists within the frequency range specified in the test. In addition: the transmission speed of sound in the fixture material must be taken into account. The path should be kept as short as possible as much as possible to less than 1/4 wavelength. Special considerations must be given to fixtures for large components or for testing several components at the same time, and the general principles for fixtures for equipment also apply (see Chapter A3). If the component must be subjected to a lead strength test after the test, its leads must not be bent during the test and must not be displaced relative to the component body. However, if this situation cannot be avoided, the relevant specifications should stipulate that different components must be used for each test. It should be noted that when performing internal strength tests, the mounting method is rarely used in working environments. However, the basic requirement of internal strength tests is that dynamic stresses are transmitted to the internal structure of the sample. In order to meet this requirement, both the sample itself and the leads of the sample must be fixed during the test.
A2 Equipment and other products
It is important that equipment and other products be mounted in a typical mounting arrangement in the environment in which they will be used. For example, samples that are usually mounted with panels should be mounted with panels during testing. If the original mounting structure is available and is actually used, it is recommended to use it because it is more representative of the working conditions of the equipment. However, it must be remembered that the fixing points involved in the relevant tests are those of the mounting structure, not those of the sample.
If the original mounting structure is not applicable, or in special cases, such a mounting structure is available and it is known that this mounting structure has no effect on the characteristics of the equipment, therefore, a fixture designed to meet the test requirements should still be used. Samples intended for use with shock absorbers must sometimes be tested without the shock absorbers if they are installed in a common system with other samples or if the dynamic characteristics of the shock absorbers vary greatly (for example, with temperature). Therefore, the test severity level will need to be modified. In addition to the steady-state acceleration test, the new level should be determined by the envelope of the transfer characteristic curve of the shock absorber on each axis. If it is known that the test severity level varies with the direction of applied stress, this should also be taken into account. If no transfer characteristic curve is available, a new test severity level needs to be selected artificially, but it is best determined after discussion between the supplier and the buyer. In the case of sinusoidal vibration tests (GB/T2423.10--1995, IEC68-2-6, 1982, Environmental testing for electrical and electronic products Part 2: Test method Test Fc and guidance: Vibration (sinusoidal)), some common transfer characteristic curves are given in Appendix A, Section A5.1 of this standard.
GB/T 2423.43—1995
For steady-state acceleration tests, it should be noted that in some cases, if the sample is tested with a shock absorber, there may be a safety problem, so the use of brackets and straps is inevitable. A3 Test fixtures
The installation and positioning of the sample are always inseparable from the fixture. Therefore, the design of the fixture must focus on issues that may hinder the achievement of the test requirements and may affect reproducibility. However, this guide does not propose a solution to this problem, because such solutions can often be found in the technical literature. The basic purpose of the test fixture is to faithfully transfer the stresses generated by the test bench to the test specimen and to ensure that the requirements of the specification are met at the fixing points of the specimen. The design of the test fixture is determined by the main parameters such as the geometry and mass of the specimen, the severity of the test required, and the capacity of the test bench. The latter two parameters depend on the test to be performed. A3.1 Shock and Impact Tests The total mass allowed by the test bench and the maximum test severity are usually specified by the manufacturer. For a given mass of specimen, if the capacity of the test bench is significantly greater than the capacity required for the test, the design of the test fixture is usually easy. This is because the fixture can be designed to be heavier and simpler. Considering the effects of rigidity and size is still an important issue in the design of shock and impact test fixtures (Clause A3.4). A3.2 Vibration Tests The main factor limiting the total mass of the specimen and its fixture in the design of vibration test fixtures is the thrust of the vibration table. The force of the shaker is usually specified by the manufacturer. The most important characteristics in the test severity standard are the test frequency range and the displacement and/or acceleration values specified. However, high force and wide frequency band are usually incompatible in the performance of the shaker. Therefore, it is not possible to use the largest shaker possible, as is the case with shock and impact tests. Therefore, the fixtures required for vibration tests are more complex than those required for other tests. More experience will be required to achieve satisfactory results. Also remember that when the fixture and specimen are fixed to the shaker, the cheek response may be affected. Some parameters to consider in the design of the vibration fixture are given in Sections A3.4 and A3.5. A3.3 Steady-State Acceleration Tests
For steady-state acceleration tests, the fixture design is the simplest, because the steady-state acceleration is applied to the specimen step by step, and the dynamic characteristics of the fixture and specimen are negligible. Therefore, the fixture only needs to be rigid enough to withstand the static loads involved and to allow easy adjustment of the specimen orientation. However, it should be remembered that the maximum capacity of the steady-state acceleration test machine is specified by the manufacturer. It should be noted that at very high acceleration values, especially above 10,000 m/s2, the test element will have many difficulties. A3.4 Material Selection
When designing a test fixture, the material selection is mainly based on the quality and rigidity of the fixture. Each of the above tests has to consider several issues related to mass limitations. Rigidity is only important when the dynamic characteristics of the fixture need to be considered, and there are strict restrictions in the fixture design.
The rigidity of a material is a physical property of the material, and the rigidity of various plastics and metals is very different. For any given material, the rigidity will vary with its size and support method (such as a rigidly fixed single beam or dual beams). And to some extent, it also varies with its manufacturing method. Some materials have a high rigidity-to-mass ratio, that is, when the same mass of material is used, it can be made into a rigid fixture, which is the most ideal material. Another material property is damping, which is also a manifestation of the internal properties of the material. For example, the internal damping of aluminum is about 4 times that of steel. Damping mainly has some influence on the performance of the vibration fixture. The main purpose of the test fixture design is to make it resonance-free within the frequency range specified in the test. If this cannot be achieved, the fidelity of the vibration transmission from the test bench to the sample will be affected. The extent of the effect is directly related to damping. It should be remembered that the damping of most common metals, although it varies from material to material, has a relatively small effect on the overall performance of the fixture. Therefore, it only needs to be considered and utilized in certain circumstances. For impact tests requiring a fast rise time, or for vibration tests requiring a high upper frequency limit, another characteristic that must be considered is the speed of sound propagation in the selected material. GB/T2423.43-1995
The distance along the propagation path between any fixed point and the vibration table table should be as small as possible in the fixture material. For the calculation of the wavelength, the vibration mode associated with the lowest speed of sound, usually the transverse mode, must be considered: For example, for an aluminum test fixture with an upper frequency of 2000 Hz, the speed of sound in aluminum is: Longitudinal wave
Ui = 6 300 m/s
V2 = 3 200 m/s
Therefore, the wavelength to be considered is:
= 3 200
f-2000
The maximum length of the propagation path is L-^/4 = 1.6m/4 = 0.4mThe test fixture should not be made entirely of the same material. When damping is to be increased for various reasons (such as electrical or thermal insulation), it may be necessary to use a combination of metal and plastic, or even metal and ceramic. A3.5 Fabrication methods
There are many methods for fabricating fixtures, including threading, riveting, welding, casting, and gluing. The choice of these methods depends on whether the test requirements can be met and the materials used. The test fixture should be as simple as possible, for example a solid block is usually best. It should be noted that the rigidity of the structure of the threaded connection is not as good as other connection methods. This factor becomes more important when it comes to large and/or high-frequency test specimens. All contact surfaces should be flat to ensure good mechanical contact. In addition, the maximum number of mounting holes on the test bench mounting surface should be used depending on the size of the fixture.
It is advantageous to design a fixture that can be used many times with different specimens. If threaded holes are used and the material is prone to excessive wear, it is recommended to use steel threaded sleeves embedded in the material to increase wear resistance. However, it should be noted that their assembly must be satisfactory and no damage should occur. In addition, if threads are used, the threaded connection should also have high tensile strength. When fixing the specimen to the fixture, it is important that the fixture and specimen do not deform. If deformation occurs, it is likely that the fixture is not rigid enough and will prevent the required test severity from being applied to the various fixing points of the specimen. As far as practicable, all threaded connections should be tightened to their maximum permissible torque. If damping is important, it should be noted that the internal damping of threaded or riveted connections is greater than that of welded connections. A4 Balance
Balance problems are usually only a problem in vibration and steady-state acceleration tests, but they must also be considered for shock and impact tests. A4.1 Vibration
In the case of vibration, when the fixture is mounted with the sample, it must be ensured that the center of gravity of the fixture (which should be as low as possible) is in principle maintained on the center of gravity through the entire vibration table moving unit and perpendicular to the surface of the moving unit. In some cases, it is impossible to ensure that the center of gravity of the fixture and the sample after the sample is mounted is on the thrust axis of the vibration table. Due to the length of the propagation path and the shaking, deformations and standing wave patterns will be generated, all of which limit the usable frequency range and the requirements for the test at the sample fixing point. Therefore, counterweighting techniques must be used, but this technique should be avoided as much as possible unless necessary. Due to the increase in frequency, the sample (and perhaps the fixture) may resonate. If this happens, a relative displacement of the dynamic center of gravity will be caused by continuous movement. If counterweight technology is used at this time, this displacement will be aggravated. Therefore, a situation has been created for which there is currently no practical solution to this problem. Therefore, this effect is usually allowed. If this is not the case, this effect can be reduced by using a higher-power vibration table, provided that the requirements of the test specification are still met. It is common to use a slide table connected to the vibration table, especially when the sample is very sensitive to gravity. If this is not done, the design of the fixture is very complicated. Even so, problems similar to those described above will still be encountered. A4.2 Steady-state acceleration
For steady-state acceleration tests, a centrifuge is usually used. In order to prevent damage to the supporting parts of the test bench, the sample and the fixture must be kept statically and dynamically balanced relative to the test bench. The permissible degree of imbalance is usually specified by the manufacturer. 115
A5 Accelerometer location
GB/T2423.43-1995
The design of the test fixture should allow the accelerometer to be connected at the location required by the relevant test. There are many methods of connection, which are usually recommended by the manufacturer of the accelerometer, including threaded connection, special adhesive bonding, etc. In vibration tests, it is sometimes possible to install several additional accelerometers, so that the dynamic characteristics of the fixture can be checked. A6 Performance check of test fixture
Before conducting vibration tests, it is useful to check whether the test requirements at specified points are met when the fixture is installed or not installed with a sample with dynamic representative characteristics or with a real sample. In the latter case (referring to the installation of real samples), it is more appropriate to check at a lower amplitude than at the specified amplitude. This check is also appropriate for other dynamic tests included in this standard. A7 Large and complex samples
It is difficult to define the terms "large" or "complex" samples. A fixture designed for a particular piece of equipment may be too large for a test room that normally tests only components. This is not a situation considered in this part of the standard. "Large" refers to the specimen plus fixture, which is usually difficult to handle in the equipment test room and requires solutions that exceed the current state of the art because of its mass and size, complex connections, or the specified frequency range. When a "large" or "complex" fixture is required, it will inevitably be found that it is difficult to fully meet the test requirements by ordinary means because the resonant characteristics of the fixture and specimen have not been understood. After investigating other techniques, which may include the use of multiple synchronized shakers, it will be necessary to refer to the test requirements to determine what measures must be taken. In this case, the test procedure usually requires attention to the various parameter values achieved and the need for agreement between the supplier and the buyer. 165 Fabrication Methods
There are many ways to fabricate fixtures, including threading, riveting, welding, casting, and gluing. The choice of these methods depends on whether the test requirements can be met and the materials used. The test fixture should be as simple as possible, for example a solid block is usually best. It should be noted that the rigidity of the structure of the threaded connection is not as good as other connection methods. This factor becomes more important when it comes to large and/or high-frequency test samples. All contact surfaces should be flat to ensure good mechanical contact. In addition, the maximum number of mounting holes on the test bench mounting surface should be used depending on the size of the fixture.
It is advantageous to design a fixture that can be used many times with different samples. If threaded holes are used and the material is prone to excessive wear, it is recommended to use steel threaded sleeves embedded in the material to increase wear resistance. However, it should be noted that their assembly must meet the requirements and cannot be damaged. In addition, if threads are used, the threaded connection should also have high tensile strength. When fixing the sample to the fixture, it is important that the fixture and the sample do not deform. If deformation occurs, it is likely that the fixture is not rigid enough and will prevent the required test severity from being applied to the fixing points of the specimen. For practical purposes, all threaded connections should be tightened to the maximum torque they allow. If damping is important, it should be noted that the internal damping of threaded or riveted connections is greater than that of welds. A4 Balance
Balance problems are usually only a problem in vibration and steady-state acceleration tests, but they must also be considered for shock and impact tests. A4.1 Vibration
In the case of vibration, when the fixture is mounted with the specimen, it must be ensured that the center of gravity of the fixture (which should be as low as possible) is in principle maintained on the center of gravity through the entire vibration table motion unit and perpendicular to the surface of the motion unit. In some cases, it is impossible to ensure that the center of gravity of the fixture and the specimen after the specimen is mounted is on the thrust axis of the vibration table. Due to the length of the propagation path and the shaking, deformations and standing wave patterns will occur, all of which limit the usable frequency range and the requirements for the test to be achieved at the specimen fixing point. Therefore, the use of counterweights is necessary, but this should be avoided as far as possible. Due to the increased frequency, the specimen (and perhaps the fixture) may resonate. If this happens, a relative displacement of the dynamic center of gravity will occur due to the continuous movement. If counterweights are used, this displacement will be aggravated. This results in a situation where there is currently no practical solution to this problem. Therefore, this effect is usually allowed. If this is not the case, it can be reduced by using a more powerful shaker, provided that the requirements of the test specification are still met. It is common to use a sliding table connected to the shaker, especially when the specimen is sensitive to gravity. If this is not done, the design of the fixture is complicated. However, problems similar to those described above may still be encountered. A4.2 Steady-state acceleration
For steady-state acceleration tests, a centrifuge is usually used. In order to prevent damage to the supporting parts of the test bench, the specimen and the fixture are kept statically and dynamically balanced relative to the test bench. The permissible imbalance is usually specified by the manufacturer. 115
A5 Accelerometer location
GB/T2423.43-1995
The design of the test fixture should allow the accelerometer to be connected at the location required by the relevant test. There are many methods of connection, which are usually recommended by the manufacturer of the accelerometer, including threaded connection, special adhesive bonding, etc. In vibration tests, it is sometimes possible to install several additional accelerometers, so that the dynamic characteristics of the fixture can be checked. A6 Performance check of test fixture
Before conducting vibration tests, it is useful to check whether the test requirements at specified points are met when the fixture is installed or not installed with a sample with dynamic representative characteristics or with a real sample. In the latter case (referring to the installation of real samples), it is more appropriate to check at a lower amplitude than at the specified amplitude. This check is also appropriate for other dynamic tests included in this standard. A7 Large and complex samples
It is difficult to define the terms "large" or "complex" samples. A fixture designed for a particular piece of equipment may be too large for a test room that normally tests only components. This is not a situation considered in this part of the standard. "Large" refers to the specimen plus fixture, which is usually difficult to handle in the equipment test room and requires solutions that exceed the current state of the art because of its mass and size, complex connections, or the specified frequency range. When a "large" or "complex" fixture is required, it will inevitably be found that it is difficult to fully meet the test requirements by ordinary means because the resonant characteristics of the fixture and specimen have not been understood. After investigating other techniques, which may include the use of multiple synchronized shakers, it will be necessary to refer to the test requirements to determine what measures must be taken. In this case, the test procedure usually requires attention to the various parameter values to be achieved and the need for agreement between the supplier and the buyer. 165 Fabrication Methods
There are many ways to fabricate fixtures, including threading, riveting, welding, casting, and gluing. The choice of these methods depends on whether the test requirements can be met and the materials used. The test fixture should be as simple as possible, for example a solid block is usually best. It should be noted that the rigidity of the structure of the threaded connection is not as good as other connection methods. This factor becomes more important when it comes to large and/or high-frequency test samples. All contact surfaces should be flat to ensure good mechanical contact. In addition, the maximum number of mounting holes on the test bench mounting surface should be used depending on the size of the fixture.
It is advantageous to design a fixture that can be used many times with different samples. If threaded holes are used and the material is prone to excessive wear, it is recommended to use steel threaded sleeves embedded in the material to increase wear resistance. However, it should be noted that their assembly must meet the requirements and cannot be damaged. In addition, if threads are used, the threaded connection should also have high tensile strength. When fixing the sample to the fixture, it is important that the fixture and the sample do not deform. If deformation occurs, it is likely that the fixture is not rigid enough and will prevent the required test severity from being applied to the fixing points of the specimen. For practical purposes, all threaded connections should be tightened to the maximum torque they allow. If damping is important, it should be noted that the internal damping of threaded or riveted connections is greater than that of welds. A4 Balance
Balance problems are usually only a problem in vibration and steady-state acceleration tests, but they must also be considered for shock and impact tests. A4.1 Vibration
In the case of vibration, when the fixture is mounted with the specimen, it must be ensured that the center of gravity of the fixture (which should be as low as possible) is in principle maintained on the center of gravity through the entire vibration table motion unit and perpendicular to the surface of the motion unit. In some cases, it is impossible to ensure that the center of gravity of the fixture and the specimen after the specimen is mounted is on the thrust axis of the vibration table. Due to the length of the propagation path and the shaking, deformations and standing wave patterns will occur, all of which limit the usable frequency range and the requirements for the test to be achieved at the specimen fixing point. Therefore, the use of counterweights is necessary, but this should be avoided as far as possible. Due to the increased frequency, the specimen (and perhaps the fixture) may resonate. If this happens, a relative displacement of the dynamic center of gravity will occur due to the continuous movement. If counterweights are used, this displacement will be aggravated. This results in a situation where there is currently no practical solution to this problem. Therefore, this effect is usually allowed. If this is not the case, it can be reduced by using a more powerful shaker, provided that the requirements of the test specification are still met. It is common to use a sliding table connected to the shaker, especially when the specimen is sensitive to gravity. If this is not done, the design of the fixture is complicated. However, problems similar to those described above may still be encountered. A4.2 Steady-state acceleration
For steady-state acceleration tests, a centrifuge is usually used. In order to prevent damage to the supporting parts of the test bench, the specimen and the fixture are kept statically and dynamically balanced relative to the test bench. The permissible imbalance is usually specified by the manufacturer. 115
A5 Accelerometer location
GB/T2423.43-1995
The design of the test fixture should allow the accelerometer to be connected at the location required by the relevant test. There are many methods of connection, which are usually recommended by the manufacturer of the accelerometer, including threaded connection, special adhesive bonding, etc. In vibration tests, it is sometimes possible to install several additional accelerometers, so that the dynamic characteristics of the fixture can be checked. A6 Performance check of test fixture
Before conducting vibration tests, it is useful to check whether the test requirements at specified points are met when the fixture is installed or not installed with a sample with dynamic representative characteristics or with a real sample. In the latter case (referring to the installation of real samples), it is more appropriate to check at a lower amplitude than at the specified amplitude. This check is also appropriate for other dynamic tests included in this standard. A7 Large and complex samples
It is difficult to define the terms "large" or "complex" samples. A fixture designed for a particular piece of equipment may be too large for a test room that normally tests only components. This is not a situation considered in this part of the standard. "Large" refers to the specimen plus fixture, which is usually difficult to handle in the equipment test room and requires solutions that exceed the current state of the art because of its mass and size, complex connections, or the specified frequency range. When a "large" or "complex" fixture is required, it will inevitably be found that it is difficult to fully meet the test requirements by ordinary means because the resonant characteristics of the fixture and specimen have not been understood. After investigating other techniques, which may include the use of multiple synchronized shakers, it will be necessary to refer to the test requirements to determine what measures must be taken. In this case, the test procedure usually requires attention to the various parameter values achieved and the need for agreement between the supplier and the buyer. 1643-1995
Test fixtures shall be designed to allow accelerometers to be attached at the locations required for the test concerned. The methods of attachment vary and are usually recommended by the manufacturer of the accelerometer and include threaded connections, special adhesives, etc. During vibration tests, it is sometimes possible to allow the installation of several additional accelerometers so that the dynamic characteristics of the fixture can be checked. A6 Performance Check of Test Fixtures
Before carrying out vibration tests, it is useful to check whether the test requirements are met at specified points when the fixture is mounted with or without a specimen having dynamic representative characteristics or with a real specimen. In the latter case (with a real specimen), it is more appropriate to check at a lower amplitude than at the specified amplitude. Such checks are also appropriate for other dynamic tests covered by this standard. A7 Large and Complex Specimens
It is difficult to define the terms "large" or "complex" specimens. A fixture designed for a certain equipment may be too large for a laboratory that normally tests only components. This is not considered in this part of the standard. "Large" refers to the sample plus fixture, which is usually difficult to handle in the equipment test room. And because of its mass and volume, complex connections, or the required frequency range, the solution required exceeds the current state of the art. When a "large" or "complex" fixture is required, it will inevitably be found that it is difficult to fully meet the test requirements with ordinary methods because the resonance characteristics of the fixture and sample have not yet been mastered. After studying other techniques, which may include the use of multiple synchronized vibration tables, it is finally necessary to refer to the test requirements to determine what measures must be taken. In this case, the test procedure usually requires attention to the various parameter values achieved and the need to obtain a unanimous agreement between the supplier and the buyer. 1643-1995
Test fixtures shall be designed to allow accelerometers to be attached at the locations required for the test concerned. The methods of attachment vary and are usually recommended by the manufacturer of the accelerometer and include threaded connections, special adhesives, etc. During vibration tests, it is sometimes possible to allow the installation of several additional accelerometers so that the dynamic characteristics of the fixture can be checked. A6 Performance Check of Test Fixtures
Before carrying out vibration tests, it is useful to check whether the test requirements are met at specified points when the fixture is mounted with or without a specimen having dynamic representative characteristics or with a real specimen. In the latter case (with a real specimen), it is more appropriate to check at a lower amplitude than at the specified amplitude. Such checks are also appropriate for other dynamic tests covered by this standard. A7 Large and Complex Specimens
It is difficult to define the terms "large" or "complex" specimens. A fixture designed for a certain equipment may be too large for a laboratory that normally tests only components. This is not considered in this part of the standard. "Large" refers to the sample plus fixture, which is usually difficult to handle in the equipment test room. And because of its mass and volume, complex connections, or the required frequency range, the solution required exceeds the current state of the art. When a "large" or "complex" fixture is required, it will inevitably be found that it is difficult to fully meet the test requirements with ordinary methods because the resonance characteristics of the fixture and sample have not yet been mastered. After studying other techniques, which may include the use of multiple synchronized vibration tables, it is finally necessary to refer to the test requirements to determine what measures must be taken. In this case, the test procedure usually requires attention to the various parameter values achieved and the need to obtain a unanimous agreement between the supplier and the buyer. 16
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