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GB/T 38250-2019 English PDF (GBT38250-2019)

GB/T 38250-2019 English PDF (GBT38250-2019)

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GB/T 38250-2019: Metallic materials -- Verification of the alignment of fatigue testing machines

GB/T 38250-2019
Metalic materials - Verification of the alignment of reliable testing machines ICS 19.060; 77.040.10
N71
National Standards of People's Republic of China
Test of coaxiality of metal material fatigue testing machine
(ISO 23788.2012, IDT)
Published on.2019-10-18
2020-05-01 implementation
State market supervision and administration
China National Standardization Administration issued
Foreword
This standard was drafted in accordance with the rules given in GB/T 1.1-2009. This standard uses the translation method equivalent to ISO 23788.2012 "Metal material fatigue testing machine coaxiality test". The documents of our country that have a consistent correspondence with the international documents referenced in this standard are as follows. --- GB/T 16825.1-2008 Inspection of static single-axis testing machines - Part 1. Tensile and/or Inspection and calibration (ISO 7500-1.2004, IDT).
This standard has made the following editorial changes.
--- Unify the expression of the term "percent bend" in the text, and change "β" in the text to "B"; --- Fixed the symbol error in Figure 3b), c), changed "W" to "w" and "Wg" to "wg". This standard was proposed by the China Machinery Industry Federation.
This standard is under the jurisdiction of the National Testing Machine Standardization Technical Committee (SAC/TC122). This standard was drafted. China National Machinery Testing Equipment Co., Ltd., Shenzhen Wan Testing Equipment Co., Ltd., China Aviation Industry Corporation Beijing Great Wall Metrology and Testing Technology Research Institute, Jinan Xinguang Testing Machine Manufacturing Co., Ltd., Guangzhou University, Chengde Precision Testing Machine Co., Ltd. Division, Shenzhen Hua Test Co., Ltd.
The main drafters of this standard. Liu Jilin, An Jianping, Tian Feng, Wang Jianguo, Xu Zhonggen, Wang Xinhua, Xu Weijia. introduction
The coaxiality of the test machine in this standard refers to the consistency of the fixture geometry (loading) axis. Any deviation from this ideal state will result in Load the chain's angle and/or lateral offset (or different axes) (see Appendix A). Different axes are represented by specimens or coaxiality measuring devices (hereinafter referred to as There is an additional bending stress/strain zone on the "coaxiality sensor"). The bending stress/strain zone is superimposed on the assumed assumed uniformity Stress/strain field. In a pure torsion test, any different axis will result in an additional bending stress/strain condition for biaxial torsion. Different axial axes of the load chain have been shown to significantly affect fatigue test results in axial fatigue test systems (see references [1], [2] and [3]).
The main cause of bending caused by different axes is nothing more than a combination of the following factors. ---The consistency of the fixture center line is poor;
--- The inherent defect of the sample or the coaxiality sensor itself.
Ideally, the bending component produced by the tester will remain the same for all specimens or concentricity sensors. Sample or coaxiality sensor The resulting bending component varies from device to device.
Recent studies (see references [4] and [5]) have shown that no matter how fine the sample or sensor is processed, the inherent bending error Always there. Inherent defects (ie eccentricity and tilt) arise from the geometric asymmetry of the axial centerline of the device and the type of strain gauge selected, installed, Other measurement errors related to performance. The inherent bending error of the device can be significant, sometimes even exceeding the bending error caused by the different axes of the machine. This standard eliminates the error caused by the inherent defects of the coaxiality sensor by the following method. Rotating the coaxiality sensor around its longitudinal axis Turn 180° and subtract its bending component from the measured overall maximum surface bending strain. Therefore, the same material and nominal size are not With the same device, the same coaxiality measurement results should be given; see the example of Figure 10 in Reference [2]. Test of coaxiality of metal material fatigue testing machine
1 Scope
This standard specifies the coaxiality test method for testing machines using strain gauges. This standard applies to dynamic uniaxial tension and/or pressure, pure torsion, composite pull and twist, composite pressure twist and composite tension and compression fatigue of metal materials Labor test machine.
The methods outlined in this standard are general and can be applied to static testers and non-metallic materials. 2 Normative references
The following documents are indispensable for the application of this document. For dated references, only dated versions apply to this article. Pieces. For undated references, the latest edition (including all amendments) applies to this document. Testing of static uniaxial testing machines for metal materials - Part 1 . Tensile and/or Inspection and calibration
3 Terms and definitions
The following terms and definitions apply to this document.
3.1
Coaxial alignment
Consistency of the forcing axis of the load chain assembly (including the sample). Note. Failure to meet this consistency results in additional bending moments on the specimen. 3.2
Coaxiality sensor alignmentcel
Strain gauge measuring device for coaxial machine inspection of precision machining test machine. 3.3
Coaxial gauge alignmentgauge
A precision machined mechanism consisting of a pair of split rods and a through stop gauge for fixture compliance inspection. 3.4
Average axial strain averageaxialstrain
Εo
The average longitudinal axis strain measured by a set of strain gauges distributed in the same cross section on the surface of the concentricity sensor. Note. The average axial strain represents the strain at the geometric center of the section. 3.5
Loading chain loadtrain
All parts between the two, including the beam and the drive.
Note. The loading chain includes the sample.
3.6
Bending strain bendingstrain
Εb
The difference between the local strain measured by the strain gauge and the average axial strain. Note. Bending strain is a vector characterized by size, direction, and discrete points of action. It usually varies with the position of the surface of the coaxiality sensor. 3.7
Testing machine coaxiality machinealignment
The degree of consistency of the fixture axis characterized by the maximum bending strain component εb, max, mc. Note. Different axes of the machine appear to have lateral offset and/or angular tilt for the forcing axis of the upper and lower clamps. 3.8
Test machine orientation machineaspect
Front, rear, left and right sides of the test machine.
3.9
Maximum bending strain maximumbendingstrain
Εb,max
The vector with the largest bending strain amplitude in a given cross section. Note. The maximum bending strain vector is characterized by size, direction, and discrete points of action. 3.10
Percentage percentagebending
The maximum bending strain is multiplied by 100 and divided by the average axial strain. 3.11
Measuring plane measurementplane
The cross section of the transverse axis of a set of strain gauges on the concentricity sensor. 3.12
Measuring orientation measurementorientation
The position of the coaxiality sensor relative to its longitudinal axis (0°, 90°, 180°, and 270°). The measurement orientation defines the strain gauge 1 or the coaxiality sensor A permanent mark on the surface relative to the position in front of the machine. Note. The front of the machine is the R-direction.
3.13
Parallel length paralellength
Lp
The length of the parallel portion of the necking section of the coaxiality sensor. 3.14
Proportional limit proportionallimit
The material is able to maintain the maximum stress of elasticity, ie without any stress-strain ratio deviation. 3.15
R-direction R-direction
A fixed reference direction relative to the test machine frame.
Note. Usually refers to the front center of the test machine.
3.16
Strain gauge axial spacing straingaugeaxialseparation
Lg
The coaxiality sensor measures the axial distance between the planes up and down. 3.17
Strain gauge lateral spacing straingaugetransverseseparation
Wg
The lateral distance between the center of the strain gauge on the wide face of the thin rectangular coaxiality sensor. 4 symbol
The following symbols apply to this document.
A1~A4. Upper strain gauge group.
B1~B4. Lower strain gauge group.
d. the minimum diameter of the cylindrical coaxiality sensor; the inner diameter of the coaxial gauge. D. diameter of the clamping end of the cylindrical coaxiality sensor.
e. eccentric or lateral offset.
Lp. Parallel length.
Lg. axial spacing of the strain gauges.
Lz. The total length of the coaxiality sensor, coaxial gauge or specimen. r. the parallel length of the coaxiality sensor or sample and the fillet radius of the clamp end. t. thickness of the neck section of the rectangular coaxiality sensor.
w. width of the neck section of the rectangular coaxiality sensor.
W. The width of the clamping end of the rectangular coaxiality sensor.
Wg. The lateral spacing of the strain gauges.
B. percentage of bending.
Bac. Percentage of bending caused by inherent defects in the coaxiality sensor. Bmc. Percentage of bending caused by different axes of the test machine. Εo. average axial strain.
Ε1, ε2, etc.. readings of the respective strain gauges (ie, local strain). Εb. bending strain (combined value).
Εb, ac. the bending strain component caused by the inherent defect of the coaxiality sensor. Εb, mc. the bending strain component caused by the different axes of the test machine. Εb, max. maximum bending strain (combined value).
Εb, max, ac. The maximum bending strain component caused by the inherent defect of the coaxiality sensor. Εb, max, mc. the maximum bending strain component caused by the different axes of the test machine. γ. inclined (oblique) angle.
Θac. εb, max, ac relative to the position angle of the strain gauge 1 (or a permanent mark on the surface of the coaxiality sensor) (top view, clockwise direction). Θmc. εb, max, mc relative to the front of the test machine (R-direction) position angle (top view, clockwise direction). 5 Measurement requirements
5.1 Testing machine
The test system shall include a force measurement system consisting of a force sensor (load sensor), a conditioning (data acquisition) and an indicator unit. The system shall comply with the requirements of ISO 7500-1.
Note. The 1.1 level test machine requires that the indication error within the force value verification range does not exceed ±1%. It is important that the fixture be able to rotate the coaxiality sensor 180° about its longitudinal axis and also ensure that the coaxiality sensor is repeatedly positioned. The minimum axis change is minimal when clamping and clamping (see Appendix B). It is recommended that (not necessary) a part of the test machine loading chain be equipped with lateral and angular offset adjustments. Also recommended. a) reduce the number of components of the clamping device to reduce the number of mechanical interfaces; b) maximally increase the lateral stiffness of the fatigue tester in tests involving alternating tensile and compressive loads to reduce any so-called The effect of alternating bending on fatigue test results (see reference [1]). Note 2. Refer to Appendix C for the test method of lateral stiffness of the test machine. 5.2 Coaxiality sensor
The coaxiality sensor used in the measurement has a slight influence on the coaxiality measurement (see Figure 13 of Ref. [2]); The lower the stiffness of the device, the higher the sensitivity of the test machine coaxiality test. A good coaxiality sensor should also be stable enough for continuous use. Long time (ie years). Care should be taken to ensure that these two requirements are fully met. In theory, a suitable coaxiality sensor material should have.
a) a sufficiently large line elastic range;
b) high organizational stability;
c) no significant residual stress to ensure dimensional stability;
d) Good oxidation resistance.
Fully tempered steel (such as alloy steel with Rp0.2 of approximately 1000 MPa) is an ideal material for coaxiality sensor fabrication (see references) [3] and [4]). High-strength aluminum alloys (such as 7075-T6) are also suitable candidates. 5.3 Design and manufacture
5.3.1 Design
The total length of the coaxiality sensor should be the same as the fatigue specimen (but the gauge length and cross-sectional area are not necessarily the same). It should be used with fatigue specimens Load the fixture in the same way to avoid the use of special adapters. For cylindrical sensors, the diameter d should not exceed 10 mm or fatigue The diameter of the sample, whichever is greater. The recommended standard diameters are 5mm, 7.5mm and 10mm. Table 1, Table 2 and Table 3 give the recommended standard ratios. Use a section smaller than the size shown in the table, perhaps limited by the appropriate strain The acquisition of the film. Figure 1 and Figure 2 show the requirements for the concentricity, straightness and parallelism of the basic shape of the coaxiality sensor (ie affecting the coaxiality). Surface machining tolerances).
Other geometric shapes and side profile shapes are permitted, subject to the main requirements of this standard. However, significant size changes It hinders a meaningful comparison with the measurement of the recommended standard sensor. Recommended other geometry and clamping end design see reference Literature [4].
5.3.2 Dimensions of circular section coaxiality sensor
The dimensions of the circular section coaxiality sensor are shown in Table 1 and Figure 1. Table 1 Nominal dimensions of circular cross-section coaxiality sensor
5.3.3 Dimensions of thick rectangular section coaxiality sensor
The dimensions of the thick rectangular section coaxiality sensor are shown in Table 2 and Figure 2. Table 2 Nominal dimensions of thick rectangular section coaxiality sensor 5.3.4 Dimensions of thin rectangular section coaxiality sensor
The dimensions of the thin rectangular section coaxiality sensor are shown in Table 3 and Figure 2. Table 3 Nominal dimensions of thin rectangular section coaxiality sensor 5.4 Machining
During finishing, the cutting and filling should be small and reduced, so that the metallographic structure and properties of the sensor material are not affected, and Causes excessive residual stress. In order to effectively bond the strain gauge, the optimum surface roughness Ra of the coaxiality sensor should be 0.8μm~ Within the range of 1.6 μm.
Note. The surface roughness Ra of the fatigue specimen is usually in the range of 0.2 μm to 0.4 μm. 5.5 Inspection before strain gauge installation
Before attaching the strain gauge, carefully check the coaxiality sensor (using an instrument such as an optical projector or comparator) to confirm all key gauges. Inch and related geometric tolerances to ensure that it meets all geometric requirements. After the strain gauge is pasted, it is impossible to test the coaxial transmission with these methods. The sensor is gone.
5.6 strain gauge
A batch of 8 strain gauges (4 components in two groups) should be numbered and positioned as shown in Figure 3 (see references [4] and [5]). Pair of cylinders The coaxiality sensor [see Figure 3a)], the strain gauges should be equally spaced 90° apart along the circumference of the coaxiality sensor. Figure 3b) shows the distribution structure Suitable for rectangular coaxiality sensors with a width-to-thickness ratio w/t< 3. For coaxiality sensors with a larger aspect ratio (≥3), the strain gauges can be backed up The backs are mounted in pairs at equidistant positions from the centerline of the coaxiality sensor, as shown in Figure 3c). The strain gauges should all match, that is, from the same system The same batch of products produced by the manufacturer. The recommended effective length is approximately 0.1 Lp or less. The coaxiality measurement parameters (determinants) of this standard are determined by the ratio of the measured strains. Therefore, they are not suitable for temperature changes. ring. It is recommended to use a temperature-compensated strain gauge matched to the coaxiality sensor material, especially to accurately measure the absolute axial average. Time changes, such as modulus measurements, are also required.
According to the requirements of Figure 3, Table 4 shows the mounting position of the strain gauge on the surface of the coaxiality sensor. Table 4 Installation position of the strain gauge
It should be noted that the strain gauges are selected according to the manufacturer's recommendations. Also ensure that the strain gauges are pasted in accordance with the manufacturer's recommended procedure. Strain gauges should be installed At the specified position, the deviation does not exceed 0.1 mm or 0.01 times the diameter or width of the coaxiality sensor, whichever is greater. Its measuring axis should be the same The longitudinal axis of the shaft sensor is aligned with a deviation of less than 2°. After installation, the appropriate instrument, such as angular optics, should be used before adding the protective layer. Check the alignment of the strain gauges with the circular marking of the projector or low magnification microscope. Strain measurement and data acquisition systems (without coaxiality sensors) should be calibrated accordingly. Used to calibrate strain measurement and data acquisition The system's shunt resistors and/or any other equipment should be traceable to the relevant national standards. Strain measurement and data acquisition systems (including the same The strain measurement uncertainty of the axial sensor should be within ±5με or within ±1.0% of the reading, whichever is greater. The three strain gauge type sensors (hereinafter referred to as "three-piece type sensors") are listed in Appendix D. 5.7 System Check
5.7.1 To ensure proper functioning of the coaxiality measuring system, the following checks should be performed. 5.7.2 As part of the coaxiality sensor commissioning process, the following checks should be performed at least once. Connect the coaxiality sensor to the test On the machine, a small force is applied to it so that the coaxiality sensor produces a corresponding nominal value εo, which is in the range of 100με~1000με Inside, compare the average axial strain of the upper and lower strain gauge sets. If their consistency is not within 5με, the coaxiality sensor should be replaced. Note. The nominal value εo of the coaxiality sensor is determined by the average of all strain gauges. 5.7.3 As part of the testing machine loading chain or fixture commissioning process, the following checks shall be performed at least once. Appendix B specifies the weight of the sample Accuracy evaluation of complex clamping.
5.7.4 The following checks should be performed in each coaxiality test procedure. Determining the secant or modulus of elasticity of the coaxiality sensor material (eg, When the average value εo of all strain gauges is approximately equal to 1000 με). Between the two tests and the entire life cycle of the coaxiality sensor Within this value, the value should be stable and the deviation is within ± 3% of the average (or known value). Otherwise, the cause should be identified and appropriate measure...

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