This standard specifies the test method for the tensile strength and elongation after fracture of wire used for rivet contacts. This standard is applicable to various wires used for rivet contacts processed by various methods, and also to other wires used for contacts. JB/T 7780.4-1995 Mechanical and physical properties test of wire used for rivet contacts JB/T7780.4-1995 Standard download decompression password: www.bzxz.net

Mechanical Industry Standard of the People's Republic of China
Test methods for mechanical and physical properties of wire for rivet contacts Tensile test methods for wire for rivet contactsbZxz.net
Subject content and scope of application
This standard specifies the test methods for tensile strength and elongation after fracture of wire for rivet contacts. JB/T 7780. 4-1995
This standard is applicable to various types of wire for rivet contacts processed by various methods, and also to other wires for contacts. 2 Principle
The principle of tensile test is to use tensile force to stretch the specimen until it breaks to determine the mechanical properties. 3 Symbols, names and units
The symbols, names and units are listed in Table 1.
4 Specimen
Original diameter of the parallel length of the specimen
Vertical length of the specimen
Original gauge length of the specimen
Gauge length after breaking of the specimen
Original gauge length of the cut gauge length
Gauge length after breaking of the cut gauge length
Original cross-sectional area of ​​the parallel length of the specimenMaximum force during the breaking of the specimen
Tensile strength
Elongation after breaking of the specimen with a fixed gauge length of 100mm
Mass of the cut gauge length
Density of the wire
4.1 The specimen shall be cut directly from any part of the wire that has passed the appearance inspection without machining. If the relevant standards or the agreement between the two parties have other provisions on the sampling location, it shall be implemented in accordance with the provisions.
4.2 The surface of the specimen shall be free of knife marks, grinding marks or mechanical damage, cracks, burrs and metallurgical defects visible to the naked eye. 4.3 The specimen should be as straight as possible. The specimen can be straightened by hand or by lightly hammering it on a wooden board with a wooden hammer. The mechanical properties of the specimen shall not be significantly affected.
4.4 The tensile specimen shall be a fixed-gauge specimen. Its shape is shown in Figure 1. The original gauge length of the specimen is L. = 100mm, and the parallel length Le is 150mm. If the relevant standards or agreements have other provisions, they shall be implemented in accordance with them. Approved by the Ministry of Machinery Industry on October 9, 1995
Implemented on January 1, 1996
5 Test equipment and test conditions
JB/T 7780.4--1995
Figure 1 Schematic diagram of fixed-gauge specimen and gauge length
5.1 The testing machine shall be equipped with a speed control indicator. Unless otherwise specified, the separation rate of the two chucks of the testing machine under the tensile force shall not exceed 0.5 L./min.
5.2 The testing machine or clamping device shall allow the specimen to be freely positioned and axially stressed in the tensile direction. 5.3 The chuck of the testing machine shall be able to clamp the specimen (clamp L. at both ends) without slipping or loosening during the test. 5.4 The test shall be carried out at room temperature of 10~~35℃. 6 Measurement of specimen dimensions and calibration of original gauge length 6.1 The measuring tool for measuring the original diameter of the specimen shall have a dry scale with an accuracy of 0.01mm. 6.2 The cross-sectional diameter shall be measured once at both ends of the gauge length and in the two mutually perpendicular directions in the middle, and the arithmetic mean shall be taken, and the minimum value of the cross-sectional area measured at the three locations shall be selected.
The cross-sectional area is calculated according to formula (1):
S. - yuan d./4
6.3 The original gauge length is marked with quick-drying ink or colored paint. Mark 15 equal parts of equal distance in the parallel length (see Figure 1). 6.4 The original gauge length should be accurate to 0.5% of the nominal gauge length. 7 Test steps
7.1 Before the test, clamp the two ends of the specimen on the testing machine, and the test should be parallel to the direction of force application. 7.2 Apply tensile force to the specimen continuously and evenly at the specified position extension speed until the specimen breaks. 8 Measurement of tensile strength
Pull the specimen to break and read the maximum force F from the force measuring dial. The tensile strength is calculated according to formula (2): =Fb/S.
9 Measurement of elongation after fracture
9.1 After the specimen is broken, the broken parts are tightly connected at the fracture point, and the axes are as close as possible to a straight line. If a gap is formed at the break, the gap should be included in the gauge length of the specimen after it is broken. Select the original gauge length L for measurement. The fracture length Li of =100mm is made as close as possible to the center of the measuring length. 9.2 Measurement of the post-break gauge length L1
The minimum scale value of the measuring tool for measuring the post-break gauge length shall not be greater than 0.1 mm. 9.2.1 Direct measurement method: If the distance from the break to the nearest end point of the gauge length is greater than 1/3L., directly measure the distance between the two end points of the gauge length. 9.2.2 Shift method: If the distance from the break to the nearest end point of the gauge length is less than or equal to 1/3L., measure L1 as follows: Take a number from the break 0 on the long section that is substantially equal to the number of grids of the short section, and obtain point B. Then take a number that is equal to half of the remaining number of grids of the long section (even number, Figure 2(a)), and obtain point C. 84
JB/T 7780.4—1995
Or take a number of grids (odd number, Figure 2(b)) that is subtracted by 1 and half that is added by 1, respectively, and obtain points C and C1. After displacement, L1 is: AB+2BC and AB+BC+BC1.
9.2.3 Elongation after fracture is calculated according to formula (3): 9.3 Measurement of elongation after fracture by mass method
9.3.1 Principle
L(actual)
L(after displacement)
Li(actual)
L(after displacement)
Figure 2 Schematic diagram of displacement method
According to the principle that the mass before and after stretching remains unchanged, the original actual length L of the cut section is, Lm/SD
The elongation calculation formula is:
9.3.2 Measurement steps
(4))
-(1/L+1/L)×100
9.3.2.1 The cross-sectional area of ​​the specimen shall be determined according to 6.2. 9.3.2.2 Density of the sample is measured in accordance with JB/T7780.1-1995. 9.3.2.3 Measurement of the gauge length L after the gauge length segment is cut off According to 9.1.1, cut the original gauge length L-100.mm, and use sandpaper to smooth the cut ends. Tightly connect the two cut sections, and measure their length L with a caliper with an accuracy of 0.02mm. 9.3.2.4 Measure the mass m of the L section with a balance with an accuracy of 0.1mg. Calculate L according to formula (4). 9.3.2.5 Elongation after fracture is calculated according to formula (5). 9.4 The sample is pulled apart at the position described by the displacement method. 9.4.1 If the elongation after fracture obtained by the direct measurement method reaches the minimum value specified in the relevant standard or agreement, the displacement method may not be used. 9.4.2 In arbitration test, if the elongation after fracture measured by direct measurement method and displacement method is less than the minimum value specified in the relevant standard or agreement by a rounded value, the mass method must be used.
JB/T 7780. 4--1995
In arbitration test, if the elongation after fracture measured by displacement method and mass method does not reach the minimum value specified in the relevant standard or agreement, it shall be considered as no 9.4.3
Rounding of numerical value
Numerical value shall be rounded according to the provisions of Table 2.
Test item
11 Test result processing
Numerical range
>200～1000
11.1 If the specimen breaks outside the gauge length, resulting in unqualified performance, the test result shall be invalid. The test shall be repeated. Rounded to
0.5 (mass method 0.05)
1 (mass method 0.1)
11.2 If the sample shows metallurgical defects visible to the naked eye after the test (such as delamination, bubbles, inclusions, shrinkage holes, etc.), it should be noted in the test records and reports.
Additional Notes:
This standard was proposed and managed by the Guilin Electric Science Research Institute of the Ministry of Machinery Industry. This standard was drafted by the Guilin Electric Science Research Institute. The main drafter of this standard is Jiang Hansong
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