Similar to the N value described above, the plastic strain ratio R value is also the most important parameter for evaluating the deep impression performance of the metal sheet. Today, Cheng Cheng Xiaobian continued to bring everyone to understand the plastic strain ratio of metal plates.
The slats samples on the tensile testing machine, resulting in 20% stretching, at this time, the edge of the plate width direction, the ratio of the real strain of the thickness direction, It is called plastic strain ratio, also known as the lankford value or R value. It reflects that the metal sheet is resistant or abundant when tier or pressing in a plane. In the actual application of metal materials, especially metal sheets, the strain hardening index (n value) is an important parameter, which can be expressed by the following formula:
Formula: εa- – Real plastic strain in the thickness
εb – Decisiveness in the width direction
During the stretching process, the amount of deformation of the length is easier, more accurate, more accurate than the thickness of the deformation amount than the thickness. Therefore, in the range of the plastic deformation elongation does not exceed the maximum corresponding plastic elongation amount AG, the following formula is obtained by the volume constant principle for calculating the plastic strain ratio Sheet Metal Stamping R value:
[ 123] B is the transverse extensometer instantaneous sample width, B0 is the original width of the sample, L0 is the original spagner, and L is an extension instantaneous length; Let’s take a look at the specific plastic strain ratio Test method:
Tensile test of the sample, test the length and width of the plastic strain level, calculated the plastic strain ratio R value. The sample is specified by the relevant product standards with respect to the sampling direction of the rolling direction and the plasticity of the test R value. As a criterion, the strain level should exceed the yield extension stage, and the plasticity (project) strain is lower than the maximum force.
Second, test equipment
Test should be used to meet at least 1 level accuracy of the tensile testing machine (electronic universal testing machine), and it is preferable that it is preferable to measure the length of the length and transverse extensometer to measure the strain. In addition, it is necessary to prepare a size measuring tool (a cursor caliper and minor or thickness gauge) to measure the width and thickness of the parallel segment of the sample
. Third, the sample requirement
unless otherwise specified, the sample needs to match GB / T228 .1 The sample type in the standard, the thickness of the plate-shaped sample should be the thickness of the original sheet, and the surface of the sample must not be scratched, bumper and other mechanical damage.
Four, the test procedure
1, the environment regulation: the laboratory environment is preferably maintained in the range of 23 ± 5 ° C; 2, measurement sample size
3 The sample is fitted to the test machine and guarantees axial to positive;
4, the sample is tensile test, synchronously record the test curve and the original data; the tensile rate must not exceed the parallel segment strain rate 0.008 / S;
5, if the transverse deformation shown in the figure below, the test is invalid.
6. Data processing
Real plastic strain εb:
The calculation of true plastic strain εa in the thickness direction:
First, the volume is unchanged: So:
The R value can be calculated.
V., in practical applications, often use plastic strain ratio weighted average to measure the plastic deformation capability of materials, the calculation formula is:
0/45/90 is sampleThe direction is taken along the rolling direction, and R0 is sampled in the rolling direction, and R90 is perpendicular to the rolling direction, and R45 is 45 degrees angle in the direction of the sample and the rolling direction.
Cheng Cheng Xiaobian Conclusion: The above is the specific method of using the tensile test machine for metal sheet plastic strain ratio (R value) test, and interest can be further refined to understand the relevant information!