This standard specifies the four-point bending fatigue test method for welded joints. This standard is applicable to fatigue tests for finding fatigue weak links in the joint area of ​​welded structures and fatigue life assessment. Steel structures can also refer to it. JB/T 7716-1995 Four-point bending fatigue test method for welded joints JB/T7716-1995 Standard download decompression password: www.bzxz.net

Mechanical Industry Standard of the People's Republic of China
Fatigue test method for four-point bending of welded joints
1 Subject content and scope of application
This standard specifies the fatigue test method for four-point bending of welded joints. JB/T 7716-95
This standard is applicable to fatigue tests for finding fatigue weak links in the joint area of ​​welded structures and fatigue life assessment. Steel structures can also be used as a reference.
2 Reference standards
GB/T13816 Pulsating tensile fatigue test method for welded joints GB/T15111 Shear tensile fatigue test method for spot welded joints 3 Terms and definitions
3.1 Four-point bending
It refers to a load-bearing mode in which the support is a simply supported support to achieve bidirectional pressure. See Figure 1. The median perpendicular line between the loader and the specimen
Fr-F+-F
Figure 1 Schematic diagram of four-point bending loading
3.2 Loading force of four-point bending loading type
The loading force of four-point bending loading type refers to F in Figure 1, and F,=F,=F. 3.3 Median perpendicular line between the loader and the specimen
The median perpendicular line of the loader refers to the perpendicular line from the center of the distance between the two points of force (C, D) of the loader to the specimen; the median perpendicular line of the specimen refers to the perpendicular line from the center of the distance between the support points (A, B) of the specimen to the specimen. 3.4 Four-point bending stress
Four-point bending stress refers to the bending stress between the points of force (C, D) of the loader. 3.5S (stress)-N number of cycles) curve
The curve drawn with four-point bending stress as the vertical axis and the number of stress cycles as the horizontal axis is usually called SN curve. 3.6 Conditional fatigue limit
refers to the maximum value of the four-point bending stress that can withstand a certain number of cycles. Approved by the Ministry of Machinery Industry of the People's Republic of China on June 20, 1995 and sold on January 1, 1996
4 Preparation of test pieces and test specimens
4.1 Preparation of test pieces
JB/T 7716-95
4.1.1 The test piece can be directly cut from the welded structure or steel structure. When cutting the test piece, sufficient machining allowance for machining the test piece should be left. 4.1.2 If the test piece cannot be cut from the real structure, a simulated test plate can be welded. The welding process and welding materials of the simulated test plate should be consistent with the real structure.
4.2 Test specimen
4.2.1 The test specimen is processed from the cut test piece, see Figure 2. The thickness of the test specimen in Figure 2 is determined by referring to the thickness of the test piece plate and the tonnage of the testing machine. W-2B, L24W,
Circular surface*
Figure 2 Test specimen
4.2.2 The center of the weld should coincide with the mid-vertical line of the specimen. 4.2.3 The cut marks of machining should follow the direction of force. 5 Testing machine
5.1 Various types of testing machines that can realize the four-point bending force type are allowed to be used. 5.2 The distance between the two force points of the loader should be greater than the outer petal size of the weld, and the distance between each force point and the outer edge of the adjacent weld should not be less than 5mm.
5.3 If the testing machine used does not have a four-point bending loading device, it is allowed to make it by yourself, but the strength and degree of the loading device must be guaranteed.
Before the test, the testing machine should be calibrated, and the dynamic load oscilloscope fluctuation should be less than or equal to 3%. 6 Test method
6.1 During the test, the specimen should not be loose during the test, and the applied stress should be quickly adjusted to the test stress. 6.2 During the test, the test stress is not allowed to be greater than the test stress. The test stress error is ±2%. 6.3 The test process should not be interrupted.
6.4 Except for special requirements. The frequency of a test should be a fixed value. 6.:5 The loader and the perpendicular midline of the specimen should coincide. 7
Data processing method
7.1 The number of cycles N
can be read from the counter of the testing machine. If a self-made counter is used, the error range of the count must be given, and the error value must be included in the error of the fatigue limit and conditional fatigue limit finally determined by the test. 7.2 Four-point bending stress S
The four-point bending stress is calculated by a typical material mechanics formula. The specimen size parameter in the calculation is the average value of the three numbers between the points of application.
7.3 Drawing of SN curve
JB/T 7716—95
7.3.1 The SN curve is drawn using double logarithmic coordinates, with stress on the vertical axis. 7.3.2 To draw a complete SN curve, at least five stress levels must be selected, and each level must have no less than three valid test points. 7.3.3 In the SN double logarithmic coordinate diagram, the line connecting the mean values ​​of the test points at each level of stress is the SN curve. 7.4 Determination of conditional fatigue limit
7.4.1 The condition of conditional fatigue limit, that is, the number of cycles can be 1×10°, 5×10°, 2×10°1×10 (or special requirements in the structure). 7.4.2 The conditional fatigue limit can be determined by one of the following methods according to the conditions: a.
It can be found in the SN curve according to the required conditions. It can be determined according to the "approximation method" in GB/T13816. It can be determined according to the conditional fatigue limit\ in GB/T15111. If this method is used, it is necessary to convert the F (force)-N (number of cycles) in the reference standard into the corresponding SN relationship and then determine it. 8 Report
The report format is in accordance with Appendix A (reference).
Test name:
Standard grade
Tensile strength: N/mm2
Yield strength: N/mm*
Elongation:
Testing machine, load, stress
Type:
Capacity:
Frequency:
Others:
Load F
Stress S
Fracture Number of cycles:
Remarks:
SN curve
Additional instructions:
Test overflow:
Others:
JB/T7716—95
Appendix A
Test report format
(reference)
Specimen number
Maximum load:
Minimum load:||tt| |Maximum stress:
Minimum stress:
Full amplitude (AS):
This standard is proposed by the National Technical Committee for Welding Standardization
Test date:
Welding method:
Welding material type:
Groove type:
Welding current:bzxz.net
Welding speed:
Preheating temperature:
Surface treatment:
Hardness of welding zone:
Others:
mm/min
Specimen section size and weld bead appearance
Thickness B
Fracture condition when double fracture:
Width W
Fatigue limit (or conditional fatigue limit)
This standard is drafted by Harbin Welding Research Institute of the Ministry of Machinery Industry. The main drafters of this standard are Zhang Baochang, Wang Shaoqing and Jiao Wei. 332
Tester:
Welding position:
Diameter, brand:
Welding voltage:
Wire running method:
Post-heating temperature:
Surface processing:
Appearance shape of weld bead
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