First, purpose of the experiment
1. Be further familiar with the operation of electronic universal experimental machine and the basic operation process of tensile experiment;
2. Through the tensile test of rubber materials, understand the mechanical properties of polymer materials during stretching, observe the deformation characteristics of rubber during stretching, and determine the elastic modulus E and strength limit σb of rubber materials. Elongation δ and section shrinkage.
Second, experimental principle
When stretching rubber specimens, the experimental machine can automatically draw the tensile stress-strain curve of rubber. The initial stage of the experiment will show a curve, which is caused by the sliding of the sample head in the fixture and the gap of the experimental machine. In the analysis, the straight line segment in the graph should be extended to intersect the abscissa at point 0 as the origin of its coordinates. The stretching of rubber has only the elastic stage. The stretching curve can intuitively and accurately reflect the deformation characteristics of rubber during stretching and the relationship between stress and deformation.
When the rubber is stretched, it basically satisfies Hooke's law, and it is roughly a straight line on the stress-strain curve. Therefore, the slope of this straight line can be used to express the elastic modulus E. In order to more accurately calculate the value of the elastic cross, Mattab can be used to fit the data within the proportional limit to obtain the slope of the fitted straight line, which is the value of the elastic modulus.
Third, precautions for Selection of Tensile Testing Machine
Due to the large deformation of rubber during stretching, especially for latex products, the elongation may be as high as more than 1000%, so before the rubber sample breaks, it is necessary to ensure that the gripper has sufficient stroke.
High precision and high frequency data acquisition
Tensile rubber does not require a large force, and the tensile force measurement range does not need to be large, so the accuracy of the force value is required; it is generally required to be able to obtain a force value with an accuracy of more than two decimal places; in addition, due to testing the tensile properties of rubber Several tensile values in the stretching process are required, and the tensile test cannot be repeated, so the real-time and accurate recording of the tensile value of each test section.
Device for accurately describing stress-strain curves
There is a close correlation between the tensile value and the gauge distance in the tensile specimen. For example, the constant tensile stress of the specimen needs to measure the force value of the specimen stretching to a given elongation, while the constant stress needs to measure the gauge distance of the specimen stretching to a given stress. After the test is completed, the accurate stress-strain curve can reproduce the test process and clearly reflect the value of each test section, which is convenient for calculating the items required by the test.
Accurate gauge measuring and recording device
The measurement of sample gauge distance is an important data for calculating rubber elongation, so the strain of the sample must be accurately measured and recorded immediately.
Contact Person: Miss. Silivia Zhang