Recently, we have received a lot of inquiries from friends in the metal industry, who have a strong interest and demand in the equipment, sample preparation, test content and result expression of metal bending mechanics test. Metal bending mechanical properties testing has always been a key link in the field of metal engineering, which not only provides important data support for material design and manufacturing, but also is directly related to the safety and performance of products in practical applications.
In order to meet everyone's needs, this article will provide you with a comprehensive and in-depth test guide for the relevant content of metal bending mechanical properties test. From the selection of test equipment to the preparation of the sample, to the specific content of the test and the presentation of the results, we will analyze them in detail one by one to help you better understand and apply the relevant knowledge of metal bending mechanical properties test.
First, the principle of the test.
The bending force is applied to the circular or rectangular cross-sectional interview specimen by three-point bending or four-point bending, generally until fracture, and its bending mechanical properties are determined.
Second, the test standard.
Refer to the standard YB T 5349-2006 "Test Method for Mechanical Properties of Metal Bending".
3. Test equipment.
1. Universal testing machine.
The accuracy of the testing machine is level 1 or better.
The testing machine should be calibrated regularly according to JJG 139, JJG 157 or JJG 475 verification procedures.
2. Three-point bending test device.
3. Four-point bending test device.
4. Three-point bending test device for thin plate specimens.
5. Four-point bending test device for thin plate test.
6. a deflectometer.
7. a safety shield.
Fourth, the content of the test and the results of the display.
1. Test conditions.
1) The test should be carried out at room temperature 10-35. For the test with strict temperature requirements, the test temperature should be 23 5
2) During the test, the rate of bending stress increase should be controlled within the range of 3 30MPa s and a certain value that is as constant as possible.
3) During the bending test, the bending force should be applied slowly.
2. Preparation of samples.
1) Specimen shape and size.
Circular cross-sectional and rectangular cross-sectional interviews are used. The shape, size, tolerance and surface requirements of the sample shall be in accordance with the provisions of the relevant standards or agreements.
2) Cutting of sample blanks and preparation of samples.
A. The direction and position of billet cutting should be implemented in accordance with the relevant standards or GB2975 regulations. The method of cutting the sample blank and machining the specimen should not change the bending mechanical properties of the material.
b. If there is no provision in the relevant standards or agreements, the dimensional tolerance and shape tolerance of the machined sample shall be specified in Table 4. The shape tolerance is the difference between the maximum and minimum values of the dimensions of the same cross-section within the span.
c. Whether the casting specimen needs to be machined or not should be specified by the relevant standards or agreements. If machining is required, its surface roughness r. The value should be no greater than 32 m,d, the surface roughness r of the four adjacent sides of the hard metal specimen should not be greater than 04μm。The four long edges should be chamfered at an angle of 45°, and the chamfer width should not exceed 05mm。The chamfer grinding machine is machined in the same direction as the specimen length.
e. The two wide surfaces of the sheet specimen should retain the original surface, and the machining surface roughness of the two narrow surfaces should be r. The value is generally not greater than 63μm。The burrs on the edges of the specimen should be removed.
f. The machined surface roughness r of other types of specimens within their length range. The value should be no greater than 08 m, unless otherwise specified in the relevant standards or protocols.
e. The specimen should be straight. Sheet specimens cut from coils are allowed to bend slightly, but the ratio of radius of curvature to thickness should be greater than 500. Straightening or leveling of the specimen is not permitted.
3) Number of specimens.
a. Sheet samples: at least 6 samples are tested, and 3 samples are tested on the arch side up and down during the test. Circular and rectangular cross-sectional test samples: Generally, 3 samples need to be tested at each test point.
4) Specimen size measurement.
a. The diameter of the circular cross-sectional interview specimen should be measured in two mutually perpendicular directions at both ends of the span and in the middle. To calculate the flexural modulus of elasticity, the arithmetic mean of the three diameter measurements is taken; To calculate the bending stress, the arithmetic mean of the diameter measurement at the middle is taken.
b. The height and width of the rectangular cross-sectional interview specimen should be measured at both ends and in the middle of the span. To calculate the flexural modulus of elasticity, the arithmetic mean of the three height measurements and the arithmetic mean of the three width measurements are taken. To calculate the bending stress, the height and width measured in the middle are taken. For sheet specimens, specimens with a height measurement of more than 2% of their average value should not be used for testing.
2. Test content.
1) Determination of flexural elastic modulus.
a. Manual recording method.
The deflectometer is mounted in the measuring position, the specimen is symmetrically placed on the flexure test device, and the equivalent of PBO is applied to the specimeno1 (or Specify the residual bending stress rbo.)o1) pre-bending force fo below 10%, and record this force and the deflection at the midpoint of the span, and then apply a bending force to the specimen continuously until it corresponds to pboO1 (or rbo.)o1). The increment of the bending force and the increment of the corresponding deflection are recorded. The flexural modulus of elasticity is calculated as follows:
Three-point flexural modulus of elasticity calculation formula:
Formula for calculating the modulus of elasticity of four-point bending:
b. ** Law.
The deflectometer is mounted in the measuring position, and the distance between the end of the deflectometer span and the nearest support point or force application point should not be less than the height or diameter of the specimen. The specimen is symmetrically placed on the flexure test device, and the bending force is continuously applied to the specimen, while the flexural force-deflection curve is continuously recorded by the automatic method until the corresponding PBO is exceededO1 (or rbo.)o1). When recording, it is recommended that the ratio of the force axis and the magnification of the deflection axis be selected, and the angle between the curve elastic straight line segment and the force axis should not be less than 40 °, and the height of the elastic straight line segment should exceed 3 5 of the force axis range. On the recorded graph, the best elastic straight segment is determined with the help of the straight edge of the ruler. Read the bending force increment and the corresponding deflection increment for the straight segment. Calculate the modulus of elasticity as follows:
Three-point flexural modulus of elasticity calculation formula:
Four-point bending calculation formula:
2) Stipulate the determination of non-proportional bending stress.
A deflectometer is installed and the specimen is placed symmetrically on the flexure test device. The bending force is continuously applied to the specimen, and the bending force-deflection curve is continuously recorded using the automatic method. When recording, the stress represented by the axis of force per millimeter should not be greater than 15MPa, and it is advisable to make the measured F pb on the curve more than 1 2 of the range of the axis of force. The deflection magnification should be selected so that the length of the OC segment on the graph in Figure 6 is not less than 15mm. On the recorded graph, the oc segment corresponding to the specified non-proportional bending strain is intercepted from the intersection point o of the elastic straight line segment and the deflection axis. The parallel line Ca intersection curve of the elastic straight line segment through point C is at point A, and the force corresponding to point A is the measured non-proportional bending force FPB, and the calculation formula of non-proportional bending stress is specified
Rectangular cross-sectional interview sample calculation formula:
3) Determine the residual bending stress.
The specimen is placed symmetrically on the flexure test device and the expected PBO is applied to it10% pre-bending force of O1 f. , measure the deflection of the midpoint of the span, and record the reading of the deflection meter as the zero point at this time. The residual deflection is measured by applying a bending force to the specimen continuously or in stages and discharging it to the pre-bending force. The force is applied and discharged repeatedly until the measured residual deflection reaches or slightly exceeds the deflection corresponding to the specified residual bending strain.
Residual bending force calculation formula:
Formula for calculating the residual bending stress specified in the three-point bending test:
Formula for calculating the residual bending stress specified in the four-point bending test:
4) Determination of flexural strength.
The specimen is placed symmetrically on the flexure test device, and a bending force is continuously applied to the specimen until the specimen breaks. The maximum bending force is read from the testing machine force dial or from the recorded bending force-deflection curve.
Three-point flexure test calculation formula:
Four-point bending test calculation formula:
5) Determination of deflection at break.
The specimen is symmetrically placed on the bending test device, and the bending force is continuously applied to the specimen until the specimen breaks, and the deflection of the specimen at the moment of fracture is measured, which is the deflection at break, and the unit is mm.
The determination of deflection at break can generally be carried out in the same test as the determination of flexural strength. The deflection of the fracture can be determined by using the displacement of the beam of the testing machine, but the influence of factors such as the flexibility of the testing machine should be corrected.
6) Determination of bending fracture energy.
The specimen is symmetrically placed on the flexure test device, the bending force is continuously applied to the specimen, the deflection of the specimen at the midpoint of the span is measured, and the bending force-deflection curve is continuously recorded by the automatic method until the specimen breaks.
On the recorded graph, the area s under the flexural force-deflection curve are determined by an area meter or other method to an accuracy of 2%.
Bending Breaking Energy Calculation Formula:
The above is the content of the introduction of the metal bending mechanical properties test, I hope it can help you! If you still want to know more about the test methods, test reports, test standards, metal bending performance test standards and scope of application, universal testing machine operating procedures and other questions, you are welcome to send us private messages and messages, Kezhun measurement and control technical team will answer for you for free!