This standard specifies the test method for the impact toughness of fatigue crack specimens of welded joints, that is, the ECO test method for welded joints. JB/T 7717-1995 ECO test method for welded joints JB/T7717-1995 Standard download decompression password: www.bzxz.net

Mechanical Industry Standard of the People's Republic of China
ECO Test Method for Welded Joints
1 Subject Content and Scope of Application
JB/T 7717—95
This standard specifies the test method for impact toughness of fatigue crack specimens of welded joints, that is, the ECO test method for welded joints. This standard is applicable to the determination of the impact toughness of fatigue crack specimens of fusion welded joints (weld metal and parent material) of metal materials under atmospheric conditions. The determination of the ECO value of general steel can refer to this standard method. 2 Reference standards
Metal Charpy (V-notch) impact test method GB 21061
GB2649
Metallic Charpy (V-notch) impact test method GB2650Metallic impact test method for welded joints
GB4159Metallic low-temperature Charpy impact test methodMethod for crack opening displacement (COD) of welded jointsJB4291
3 Definitions and symbols
3.1 Impact absorption Ak
The energy absorbed by a welded joint specimen of a certain shape and size when it breaks under an impact load. The unit is joule (J). Note: The conversion between kilogram force (kgf)·meter (m) and joule (J) can be calculated as 1kgf·m=9.8J. 3.2 Impact toughness value ak
The quotient obtained by dividing the impact absorption energy by the cross-sectional area below the notch of the specimen. The unit is joule/cm2 (J/cm2). 3.3 Impact toughness value of the specimen with fatigue crack ECO The impact toughness v when the theoretical value of the fatigue crack is zero. The unit is joule/cm2 (J/cm2). It is represented by the symbol Ek. 3.4 Crack tip opening displacement COD
The opening displacement of the original crack tip when the specimen is subjected to an opening type (type I) load. The unit is mm. It is represented by the symbol?. 3.5 Symbols
--specimen thickness, mm;
thickness of the test plate of the structure or simulated structure, mm; w
width of the specimen, mm
a:--length of the prefabricated crack (excluding the notch) at the fracture point of the specimen, mm; a--average value of the measured length of the prefabricated crack (excluding the notch) at the fracture of the specimen, mm; S
loading span of three-point bending, mm;
length of the specimen, mm
t;--depth of the measuring point of the V-shaped cane, mm; Frmnx
maximum load applied by the prefabricated fatigue crack, NFmin
--Minimum load applied to prefabricate fatigue crack, N;--Ultimate load of specimen, N;
Approved by the Ministry of Machinery Industry of the People's Republic of China on June 20, 1995 and implemented on January 1, 1996
i--Natural number series;
--Number of specimens;
Cv--Charpy (V-notch) test;
--Dynamic fracture toughness, MPa m;
.--Yield strength, N/mm*(N/m2);
JB/T 7717-95
Krr--Fracture toughness under plane strain conditions, MPa m,;--Crack initiation COD, mm;wwW.bzxz.Net
J,--Initiation J integral, N/mm.
4 Test specimens
4.1 Sampling method
4.1.1 The preparation and cutting of test specimens shall comply with the provisions of GB2649. 4.1.2 The selection of the cutout position of the test specimen in the weld joint area shall comply with the provisions of GB2650. 4.2 Test specimens and preparation
4.2.1 This standard stipulates that the test specimen with a V-notch of 10mm×10mm×55mm is the standard basic test specimen. The test specimen drawing, test specimen dimensions and deviations shall comply with the provisions of GB2650. 4.2.2 This standard stipulates that the test specimen with a wire cutting notch of 10mm×5mm×55mm is the reference test specimen. The test specimen drawing and deviations shall comply with the provisions of JB4291.
4.2.3 When the test purpose is to evaluate ECO or to compare ECO with Cv, 4.2.1 should be followed; when the test purpose is to compare COD (or K1d), 4.2.2 can be followed. 5 Test equipment
5.1 Impact testing machine
The pendulum impact testing machine should ensure the rigidity and stability during the test, and the specific parameters should comply with the provisions of GB2106. 5.2 Fatigue testing machine
In principle, any type of fatigue testing machine can be used, but it must be equipped with a device for observing cracks, and its observation error should comply with the provisions of JB4291. In order to analyze the test results, the testing machine should also have a device for recording the number of cycles. 5.3 Tool microscope
In order to measure the length of the fracture crack, a tool microscope with an accuracy higher than 0.005mm is required. 6 Test
6.1 Fatigue crack prefabrication
6.1.1 The selection of fatigue crack prefabrication load is estimated according to formula (1), and appropriate experimental exploration is carried out, with the ligament not being the original toilet. B
(Wa)3a>F>0. 728 =
6.1.2 In principle, three-point bending should be used to prefabricate fatigue cracks. The span of the three-point bending should be: S=4W
6.1.3 Other load forms can also be used to fatigue. If other load forms are used to fatigue, appropriate explanations must be made in the report. The test data is for reference.
6.1.4 The loading frequency is ≤200Hz to avoid heating of the metal. 6.2 Impact test
The impact test shall comply with the provisions of GB2106, and the low-temperature impact test shall comply with the provisions of GB4159. 6.3 Determination of a
6.3.1a is calculated as:
Where: n—a; the number of measurements, n≥5. JB/T 7717--95
B/4B/4
Figure 1ai position diagram
Impact breaking zone
Epidemic zone
Sugar mouth zone
6.3.2 If the outer corridor of the sample is used as the reference for measurement, α: three measured total lengths are equal to ti. At this time, t: should be the measured value. 6.4 Number of samples
6.4.1 The number of test samples depends on the required reliability and special requirements for joint performance. 6.4.2 More than 4 valid samples must be available to obtain one ECO data. (3)
6.4.3 The so-called effective specimen refers to the specimen whose average value of the crack measurement length satisfies formula (4), and the angle between the crack extension plane and the symmetry center plane cannot exceed 5°.
[ai+1-a,1≥0.25
6.4.4 a is 1~3mm.
Data processing Determination of ECO value)
7.1 Selection of data coordinates
Select the rectangular coordinate system with av as the vertical axis and crack length as the horizontal axis. 7.2 Determination of Ek value
Take the center of gravity of the test points (ai, akv) The calculation method of the center of gravity is shown in Appendix A (Supplement) and point (8, 0) Draw a line and intersect the a axis at one point, then the intersection of this line and the av axis is defined as Ek. aua
Data processing diagram
JB/T7717-95
The purpose of fracture inspection is to determine the exact position and validity of the specimen in the weld joint area. 8 Report
8.1 The mechanical properties of the weld joint must be stated in the report, and the mechanical properties should at least include the α value. 8.2 The process conditions of the steel and weld joint must be stated in the report. 8.3 Where possible, it is hoped that the fracture toughness K1 of the steel and weld joint will be indicated. 8.4 The fatigue pre-cracking load, test frequency, and number of cycles must be stated in the report. 8.5 The results obtained from the reference specimen are expressed in Ek. 336
Where: m-
Number of specimens.
Additional instructions:
JB/T 7717—95
Center of gravity calculation method
(Supplement)
This standard was proposed by the National Welding Standardization Technical Committee of the Ministry of Machinery Industry. This standard is drafted by Harbin Welding Research Institute of the Ministry of Machinery Industry. The main drafters of this standard are Zhang Baochang, Jiao Wei and Wang Shaoqing.
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