The effect of stretching rate on strength

The effect of stretching rate on strength

The tensile test is carried out on the material testing machine. The testing machine has mechanical, hydraulic, electro-hydraulic or electronic servo type. The sample type can be a full cross-section of the material, or it can be processed into a round or rectangular standard sample. Some physical samples such as steel bars and wires generally do not need to be processed and keep their full cross-sections for testing. When preparing the sample, avoid the influence of cold and hot processing on the material structure, and ensure a certain degree of smoothness. The effect of the tensile rate on the strength of the tensile testing machine is very important, and it is necessary to know the tensile test clearly. During the test, the testing machine uniformly stretches the sample at a specified rate, and the testing machine can automatically draw a tensile curve. For low-carbon steel and other materials with good plasticity, when the sample is stretched to the yield point, the force measurement pointer will obviously jitter, and the upper and lower yield points (and) can be distinguished. In the calculation, the δ and ψ can be calculated by combining the specimens after the test is broken, and measuring the elongation and reduction of the section. Start the testing machine, load slowly and evenly, and carefully observe the rotation of the force measuring pointer and the drawing of the drawing device. Pay attention to capture the yield load value and record it to calculate the yield point stress value σS. Pay attention to the slip phenomenon in the yield stage. After the yield stage, the loading speed can be faster. When the maximum value is about to be reached, pay attention to the phenomenon of 'neck contraction'. Stop immediately after the test piece is broken, and record the maximum load value. The effects of tensile rate on strength are as follows: 　1. Tensile strength: As the test speed increases, the tensile strength increases, but after reaching a certain stage, it tends to stabilize. Electronic universal testing machine rubber tensile testing machine.　2. Yield strength: When the test speed is slow, the difference between the yield strength and the tensile strength is relatively large; the faster the test speed, the difference between the yield strength and the tensile strength gradually decreases.　　3. Elongation after breaking: The increase of stretching speed reduces the elongation after breaking, and the decrease of elongation after breaking after a certain stage tends to be slow. (In addition, the tensile strength and elongation after fracture with large plasticity are more sensitive to the tensile speed, while the tensile strength and elongation after fracture with small plasticity are relatively less sensitive to the tensile speed. The result is obtained by the tensile test. The data can determine the material's elastic limit, elongation, elastic modulus, proportional limit, area reduction, tensile strength, yield point, yield strength and other tensile performance indicators.

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